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Volume 17, Number 12,
Issue of June 15, 1997
pp. 4527-4535
Copyright ©1997 Society for Neuroscience
Brain-Derived Neurotrophic Factor Mediates the Activity-Dependent
Regulation of Inhibition in Neocortical Cultures
Lana C. Rutherford,
Andrew DeWan,
Holly M. Lauer, and
Gina
G. Turrigiano
Department of Biology and Volen Center for Complex Systems,
Brandeis University, Waltham, Massachusetts 02254
 ABSTRACT
- INTRODUCTION
- MATERIALS AND METHODS
- RESULTS
- DISCUSSION
- FOOTNOTES
- REFERENCES
ABSTRACT 
The excitability of cortical circuits is modulated by interneurons
that release the inhibitory neurotransmitter GABA. In primate and
rodent visual cortex, activity deprivation leads to a decrease in the
expression of GABA. This suggests that activity is able to adjust the
strength of cortical inhibition, but this has not been demonstrated
directly. In addition, the nature of the signal linking activity to
GABA expression has not been determined. Activity is known to regulate
the expression of the neurotrophin brain-derived neurotrophic factor
(BDNF), and BDNF has been shown to influence the phenotype of GABAergic
interneurons. We use a culture system from postnatal rat visual cortex
to test the hypothesis that activity is regulating the strength of
cortical inhibition through the regulation of BDNF. Cultures were
double-labeled against GABA and the neuronal marker MAP2, and the
percentage of neurons that were GABA-positive was determined. Blocking
spontaneous activity in these cultures reversibly decreased the number
of GABA-positive neurons without affecting neuronal survival.
Voltage-clamp analysis of inhibitory currents demonstrated that
activity blockade also decreased GABA-mediated inhibition onto
pyramidal neurons and raised pyramidal neuron firing rates. All of
these effects were prevented by incubation with BDNF during activity
blockade, but not by neurotrophin 3 or nerve growth factor.
Additionally, blockade of neurotrophin signaling mimicked the effects
of activity blockade on GABA expression. These data suggest that
activity regulates cortical inhibition through a BDNF-dependent
mechanism and that this neurotrophin plays an important role in the
control of cortical excitability.
Key words:
BDNF;
visual cortex;
dissociated culture;
activity-dependent;
inhibition;
GABA;
interneurons
INTRODUCTION
Maintaining the correct balance of excitation and
inhibition is crucial for the proper functioning of cortical circuits
(Kriegstein et al., 1987; Chagnac-Amitai et al., 1989 ), suggesting that
this balance should be tightly regulated both during development and in
adulthood. The excitability of cortical circuits is modulated by
interneurons that release the inhibitory neurotransmitter GABA. In
primate and rodent visual cortex, expression of GABA is influenced by
visual input; dark-rearing or TTX injection into one eye decreases the
number of GABA-immunopositive neurons in primary visual cortex (Hendry
and Jones, 1986; Benevento et al., 1995). This suggests that activity
is able to adjust the strength of cortical inhibition, but this has not
been demonstrated directly.
What is the signal linking activity to the regulation of cortical GABA
expression? An interesting candidate for this signal is the
neurotrophin brain-derived neurotrophic factor (BDNF). The
neurotrophins are a class of factors, including BDNF, nerve growth
factor (NGF), and neurotrophin 3 (NT3), that support the survival and
differentiation of a variety of peripheral and central neurons (for
review, see Lindsay et al., 1994). BDNF expression in postnatal cortex
is tightly regulated by neuronal activity. Seizure induction in
vivo or depolarization by high potassium in culture increase
cortical BDNF expression (Isackson et al., 1991; Ghosh et al., 1994).
There is a sharp increase in BDNF expression in visual cortex after eye
opening (Maisonpierre et al., 1990), and dark-rearing decreases BDNF
expression in rat visual cortex both during development and in
adulthood (Castrén et al., 1992). A role for BDNF has now been
suggested in a number of cortical processes (Ghosh et al., 1994;
Cabelli et al., 1995; McAllister et al., 1995, 1996). BDNF can increase
the GABA content and level of GAD activity in GABAergic neostriatal
neurons in culture (Mizuno et al., 1994; Ventimiglia et al., 1995),
influence peptide expression in hippocampal interneurons (Marty et al.,
1996a,b), and increase GABA uptake and soma size in embryonic cortical
interneurons (Widmer and Hefti, 1994). These studies suggest that BDNF
can influence transmitter expression in several populations of central
interneurons.
These observations raise the possibility that activity regulates
inhibition in visual cortical circuits through the regulation of BDNF.
We use a postnatal culture system from rat visual cortex, containing
both excitatory pyramidal neurons and inhibitory interneurons, to test
this hypothesis. We show that blockade of spontaneous activity
reversibly decreases the number of neurons that are immunopositive for
GABA. This decrease in GABA expression is correlated with a decrease in
inhibition between interneurons and pyramidal neurons and an increase
in pyramidal neuron firing rates. These effects of activity blockade
can be prevented by BDNF, but not by NGF or NT3, and blockade of
neurotrophin receptor signaling with K252a mimics the effects of
activity blockade. These data suggest that activity continuously
adjusts cortical inhibition and pyramidal neuron firing rates by
regulating the production of BDNF.
MATERIALS AND METHODS
Cell cultures
Cultures from postnatal rat visual cortex were prepared using a
modification of the technique of Huettner and Baughman (1986, 1988).
Rat pups between postnatal days 4 and 6 were anesthetized using
isofluorane and decapitated. The brain was removed, and a portion of
occipital cortex corresponding to visual cortex was removed and placed
into sterile artificial cerebral spinal fluid (ACSF) containing (in
mM): 126 NaCl, 3 KCl, 2 CaCl2, 2 MgSO4, 1 NaHPO4, and 25 NaHCO3,
equilibrated with 5% CO2/95% O2). The tissue
was minced and the ACSF was withdrawn, and enzyme solution composed of
25 U/ml papain, 1 mM L-cystein, and 0.5 mM EDTA (Worthington Biochemical, Freehold, NJ) in Earle's
balanced salt solution (EBSS, Life Technologies, Gaithersburg, MD) was
added and the tissue was incubated for 1.5 hr in a 5% CO2
incubator at 37°C. The tissue was rinsed in a weak trypsin inhibitor
solution (1 mg/ml ovomucoid and 1 mg/ml BSA in sterile EBSS) and gently
triturated, and a strong inhibitor solution (10 mg/ml ovomucoid and 10 mg/ml BSA in sterile EBSS) was added and the suspension centrifuged at
low speed for 5 min. The supernatant was withdrawn, and the pellet was
resuspended in 5 ml of growth medium (see below) and plated at a
density of ~100,000 cells/cm2 onto glass-bottom 35 mm
culture dishes previously coated with rat tail collagen. Growth medium
consisted of MEM (Life Technologies) with 5% fetal bovine serum, 1%
N2 supplement (Life Technologies), 30 mM dextrose, 200 mM L-glutamine, and 50 U/ml
penicillin/streptomycin, with a final osmolarity between 310 and 320 mOsM. Cultures were incubated in a 5% CO2 incubator at
37°C until use. Cultures were fed every 3-4 d by replacing 1 ml of
medium with fresh medium. After 3-5 d in vitro, when
non-neuronal cells became confluent, cell proliferation was inhibited
by adding 10 µM 1-gamma-D-arabinofuranosyl cytosine.
Electrophysiology
Current-clamp recordings. For electrophysiological
recordings, cultures were moved to the stage of an inverted Nikon
Diphot microscope and superfused continuously with ACSF + 20 mM dextrose at room temperature, with an osmolarity of
305-310 mOsM. The ACSF was bubbled continuously with 5%
CO2/95% O2. The preparation was grounded with
a silver/silver chloride ground wire connected to the headstage of an
Axoclamp 2B. Whole-cell recordings were obtained using patch pipettes
(3-5 M resistances) filled with intracellular solution consisting
of (in mM): 130 KMeSO4, 10 KCl, 10 K-HEPES, 2 MgSO4, 0.5 EGTA, and 3 ATP; final osmolarity was adjusted
to 290-295 mOsM with sucrose. Seal resistances were 3-6 G, and
series resistances were 5-15 M and were left uncompensated. The
amplifier was controlled, and data were acquired using the Pulse
Control software (J. Herrington, K. Newton, and R. Bookman, University of Miami) running on a PowerMac 7100 interfaced with the amplifier using an ITC 16 board (Instrutech, Great Neck, NY). Neurons with resting potentials of less than  50 mV, input resistances of <700 M, or recordings with series resistances >20 M were discarded. For recording purposes, bipolar interneurons were identified
morphologically, based on a distinctive oval shape to the soma with two
prominent dendrites emerging from the long axes (see Fig.
2D).
Fig. 2.
GABA immunoreactivity in cortical cultures.
A, MAP2-positive neurons from cortical cultures after
7 d in vitro, viewed with fluorescein filters.
B, Same field of view as in A, using
rhodamine filters to show GABA-positive neurons. C,
GABA-positive multipolar neuron. D, GABA-positive
bipolar neuron. Scale bars: A, B, 10 µm; C, D, 25 µm.
[View Larger Version of this Image (77K GIF file)]
Voltage-clamp recordings. Synaptic currents were recorded as
described above, except that the amplifier used was an Axopatch 1B in
voltage-clamp mode, and the internal solution contained 130 mM CeMeSO4 in place of KMeSO4 to
block potassium currents, 10 mM EGTA, and 10 mM
QX-314 to block generation of action potentials. This allowed neurons
to be voltage-clamped to 0 mV (the reversal potential of the excitatory
currents) so that large, outward GABA-mediated currents could be
recorded in isolation. Each neuron was voltage-clamped to 70 mV and
then stepped up to 0 mV for 30 sec recording periods interspersed with
30 sec rest periods at 70 mV. Four minutes of data was obtained and
averaged for each neuron. For each recording, series resistance and
input resistance were continuously monitored, and if these values
changes by >15%, the data were discarded, as were recordings with
series resistances of >20 M.
Immunohistochemistry
Cultures were processed for indirect immunofluorescence against
GABA and the neuronal marker MAP2. Cultures were fixed for 10 min using
a 4% paraformaldehyde, 5% sucrose solution in 0.2 M
phosphate buffer. Cultures were washed three times in PBS (137 mM NaCl, 3 mM KCl, in 0.2 M
phosphate buffer). They were then blocked and permeabilized in 10%
goat serum and 0.1% Triton X-100 in PBS for 20 min. The cultures were
then incubated overnight in primary antibody in 10% goat serum in PBS
(PBS-G). Cultures were rinsed three times with PBS and washed for 1 hr
in PBS-G. The cultures were incubated in the secondary antibodies in
PBS-G for 1 hr at room temperature, then washed for 2 hr in PBS,
serially dehydrated in ethanol, and rinsed two times in xylene. They
were mounted in DPX (Electron Microscopy Sciences, Fort Washington, PA)
and coverslipped and allowed to dry before examination.
To double-label cultures against both GABA and MAP2, cultures were
incubated concurrently in a rabbit anti-GABA polyclonal antiserum
(Sigma, 1:800) and a mouse monoclonal anti-MAP2 antibody (Sigma,
1:500). Secondary antibodies were a rhodamine-conjugated goat
anti-rabbit and a fluorescein-conjugated goat anti-mouse (Boehringer-Mannheim, Indianapolis, IN, both used at concentrations of
1:50). Preabsorption of the anti-GABA antiserum for 4 hr with 10 4 M GABA completely abolished staining, whereas
staining was unaffected by preabsorption with 104 M
glutamate. No staining was observed when the primary antibodies were
omitted from the protocol. Cultures were photographed using a laser
scanning Bio-Rad MRC 600 Confocal microscope (Hercules, CA) equipped
with rhodamine and fluorescein optics.
Cell counts and physiological data analysis
Cultures were examined and counted using a Nikon Diphot inverted
microscope equipped with fluorescence optics. Cell counts were
accomplished by counting the number of immunostained neurons in
consecutive fields of view in two independent strips through the center
of each dish. Results for the two strips were then averaged. Each field
of view was counted first for the total number of MAP2-positive neurons
using fluorescein filters and then for the total number of
GABA-positive neurons using rhodamine filters. For each dish, the
number of GABA-positive neurons/strip was divided by the total number
of neurons/strip to give the percent of GABA-positive neurons for each
dish. Only dishes in which there were >100 neurons/strip were
included, although results for less dense cultures were not significantly different. Among the dishes with >100 neurons/strip, neuronal densities did not vary significantly among conditions and
averaged 62 ± 12 neurons/mm2. All numbers are
expressed as the mean ± SEM for the number of cultures (for cell
counts) or the number of neurons (for physiological recordings)
indicated. Each manipulation was tested on cultures from at least two
different platings. For each experiment, controls from sister cultures
were run in parallel. To analyze spike frequency data, the number of
spontaneous action potentials generated in a 4 min period was measured,
and this number was then expressed as spikes/min. To accurately measure
resting potentials and input resistances, these values were measured
with synaptic transmission blocked with the AMPA receptor antagonist
CNQX (50 µM) and the GABAA receptor
antagonist bicuculline (10 µM). To analyze synaptic current data, the total area under the outward current transients was
integrated for each 30 sec sweep of data. This value was averaged over
eight such 30 sec sweeps to give a measure of the outward current per
unit time for each neuron.
For wash experiments, cultures were treated with TTX for 2 d, and
the TTX was then washed out through seven exchanges of 1 ml of medium
with fresh control medium. Control cultures were washed identically to
experimental cultures and fixed and processed in parallel. A stock
solution of TTX (Sigma) was made in sterile H2O and kept at
4°C; 2 µl was added to each treated culture for a final
concentration of 0.1 µM. TTX was refreshed after 24 hr. For some control cultures, vehicle was added at the same concentration and had no effect on GABA staining. Human recombinant BDNF, NGF, and
NT3 were obtained from the following sources: BDNF, from Promega, Hercules, CA; NGF, from Upstate Biotechnology (Lake Placid, NY); and
NT3, from Amgen (Thousand Oaks, CA). Aliquots of stock solutions of
BDNF, NGF, and NT3 in 1 mg/ml BSA were kept at 80°C until use, then
thawed and added to the cultures at the indicated concentration. Neurotrophins were not refreshed on subsequent days. K252a was added at
concentrations of 10, 50, or 200 nM and was refreshed after 24 hr.
RESULTS
Activity blockade reduces the percentage of GABA-positive neurons
in cortical cultures
Cortical cultures were plated between postnatal days 4 and 6 and
were maintained in culture for 1-2 weeks before experimentation. During this time, the neurons adhered to the substrate, extended processes, and formed synaptic connections. Whole-cell recordings showed that by 5 d in vitro, spontaneous synaptic
potentials could be detected (Fig. 1A,
arrow), which periodically brought the neurons over
threshold for firing action potentials. This activity was completely
blocked by the sodium channel antagonist TTX (0.1 µM) (Fig. 1B).
Fig. 1.
Spontaneous activity of cortical neurons in
culture. A, Control, A whole-cell
recording from a cortical pyramidal neuron after 5 d in
vitro. Depolarizing synaptic potentials (arrow)
could be detected, which periodically brought the neuron over threshold to fire overshooting action potentials. B, This activity
was completely abolished by addition of 0.1 µM TTX to the
perfusate.
[View Larger Version of this Image (16K GIF file)]
We wished to know whether the number of GABA-positive neurons in
these cultures is influenced by spontaneous activity. The percentage of
neurons in culture that were GABA-positive was determined by
double-labeling cultures against both the neuronal marker MAP2 and GABA
(Fig. 2A,B). All
GABA-positive neurons were MAP2-positive. The GABA-positive neurons had
a variety of morphologies, including bipolar and multipolar, associated
with GABAergic interneurons in vivo (Fig.
2C,D). In control cultures, 29.6 ± 1.0% of
the neurons were found to be GABA-positive (n = 26).
This percentage is within the range reported for visual cortex of
primate, rat, and cat (Gabbott and Somogyi, 1986; Hendry and Jones,
1986; Benevento et al., 1995) and in dissociated cortical cultures
(Alho et al., 1988; Gotz and Boltz, 1994). Between 7 and 14 d
in vitro, there was no significant effect of time in culture
on the percentage of GABA-positive neurons; therefore, data from these
ages were combined.
Treatment of cultures for 2 d with TTX reduced the percentage of
GABA-positive neurons to 19.2 ± 0.9%. This represents a decrease to 64.9 ± 3.0% of control values (Fig.
3A, TTX) (n = 14, TTX significantly different from control, Student's t
test, p < 0.01). This effect is similar in magnitude
to the effect of visual deprivation on the number of GABA-positive
neurons in rat and primate visual cortex (a reduction to ~70% of
control values) (Hendry and Jones, 1986; Benevento et al., 1995). There
was no effect of TTX treatment on neuronal survival (Table
1). Measurement of input resistances and resting
membrane potentials of bipolar interneurons (a subset of interneurons
that can be readily morphologically identified) revealed no effect of
TTX treatment on these parameters (Table 2). Control
experiments showed that TTX completely blocked spike generation for the
duration of the treatment (data not shown).
Fig. 3.
The effects of activity blockade and neurotrophins
on the percentage of GABA-positive neurons in cortical cultures.
A, Cultures were treated with 0.1 µM TTX,
either alone (TTX) or in the presence of 25 ng/ml
BDNF (TTX + BDNF), 50 ng/ml NGF (TTX + NGF), or 25 ng/ml NT3 (TTX + NT3) for
2 d; *significantly different from control, p < 0.01. B, The effects of different doses of BDNF on
the ability of TTX to reduce the percentage of GABA-positive neurons
were determined. TTX (0.1 µM) was applied in the presence
of the indicated concentration of BDNF for 2 d and the percentage
of GABA-positive neurons determined. For each condition in
A and B, the ratio of GABA-positive to
GABA-negative neurons was determined, and these values are expressed as
a percent of the values obtained for control cultures (control = 100%, dashed line).
[View Larger Version of this Image (22K GIF file)]
Table 1.
Effects of culture conditions on neuronal
survival
| Condition |
Neuronal density (% control) |
|
| TTX
(14) |
102 ± 13 |
| TTX + BDNF (11) |
127 ± 16 |
| TTX + NGF
(6) |
130 ± 13 |
| BDNF (9) |
98 ± 14 |
| K252a (9) |
102
± 8 |
| TTX + WASH (6) |
97 ± 16 |
| TTX + WASH + BDNF (3) |
96
± 6 |
|
|
Neuronal density in cultures grown for 2 d under the different
experimental conditions. Drug dosages are as reported in Results. Values are mean ± SEM for the number of cultures indicated in parentheses.
|
|
BDNF prevents the activity-dependent reduction in the number of
GABA-positive neurons
BDNF levels in visual cortex can be rapidly modulated by activity
(Castrén et al., 1992) and can regulate the phenotype of GABAergic interneurons in hippocampus, mesencephalon, striatum, and
cortex (Hyman et al., 1994; Mizuno et al., 1994; Marty et al.,
1996a,b). This suggests that visual input may regulate cortical GABA
expression through the activity-dependent regulation of BDNF. If the
reduction in the number of GABA-positive neurons in our visual cortical
cultures produced by activity blockade is the consequence of reduced
endogenous production of BDNF, then exogenous BDNF should prevent this
reduction. We tested this possibility by applying TTX for 2 d in
the presence of 25 ng/ml BDNF. Under these conditions, there was no
reduction in the percentage of GABA-positive neurons over control
values (Fig. 3A, TTX + BDNF) (n = 8). TTX + BDNF was significantly different from
TTX alone (p < 0.01, Student's t
test) and was not different from control. BDNF significantly reduced
the effects of TTX on GABA levels at concentrations as low as 1 ng/ml
(the lowest concentration tested) and was saturating at concentrations
between 5 and 10 ng/ml (Fig. 3B). Interestingly, when BDNF
(25 ng/ml) was applied for 2 d in the presence of spontaneous
activity, there was no effect on the percentage of GABA-positive
neurons (Fig. 3A, BDNF) (n = 9).
Like BDNF, NT3 is expressed in visual cortex during prenatal and early
postnatal development, but levels peak at approximately P0 and then
decrease steadily, whereas BDNF levels increase steadily during the
first three postnatal weeks (Maisonpierre et al., 1990; Schoups et al.,
1995). NGF and its receptor TrkA are present only at very low levels in
cortex (Maisonpierre et al., 1990; Allendoerfer et al., 1994; Schoups
et al., 1995). Neither NGF nor NT3 was effective at preventing the
reduction in GABA produced by TTX. Incubation for 2 d with TTX and
50 ng/ml NGF reduced the percentage of GABA-positive neurons to
68.2 ± 3.4% of control values (Fig. 3A, TTX + NGF) (n = 6). Incubation with TTX and 25 ng/ml NT3 produced a similar reduction, to 71.6 ± 1.6% of
control values (Fig. 3A, TTX + NT3) (n = 5). These treatments were not significantly
different from TTX alone. None of these manipulations significantly
influenced neuronal survival (Table 1).
Blockade of neurotrophin receptor signaling reduces the number of
GABA-positive neurons
The above data suggest that activity blockade is reducing the
percentage of GABA-positive neurons in culture by reducing the production of BDNF. This raised the question of whether blocking the
action of endogenous neurotrophins might influence the expression of
GABA in these cortical cultures. The neurotrophins act through the Trk
tyrosine kinase receptors TrkA (NGF), TrkB (BDNF), and TrkC (NT3) (for
review, see Heumann, 1994). This family of receptors is blocked by the
compound K252a, which prevents autophosphorylation of the tyrosine
kinase domain of the receptors. At concentrations of 200 nM
or less, K252a is a specific inhibitor of Trk receptors and blocks
TrkA, TrkB, and TrkC with approximately equal efficacy, but leaving
other tyrosine kinase signaling pathways, as well as protein kinase C
pathways, intact (Kiozumi et al., 1988; Berg et al., 1992; Nye et al.,
1992; Tapley et al., 1992).
To test whether endogenous neurotrophin signaling influences GABA
expression, cultures were incubated for 2 d with various concentrations of K252a. Concentrations of K252a as low as 10 nM produced a decrease in the percentage of GABA-positive
neurons (n = 3), and at concentrations of 50 nM and above, K252a significantly reduced the percentage of
GABA-positive neurons to 65.3 ± 1.8 and 62.1 ± 3.4% of
control, respectively (Fig. 4). The reduction produced
by 50 nM (n = 3) and 200 nM
(n = 9) K252a was comparable with that produced by
blockade of activity with TTX (see Fig. 3A). In the presence
of 200 nM K252a, BDNF did not prevent the TTX-induced
reduction in the percentage of GABA-positive neurons (Fig. 4, TTX + BDNF + K252a) (n = 3), indicating that K252a was effectively blocking Trk receptor signaling at this concentration. K252a treatment had no influence on neuronal survival at any of the
concentrations tested (Table 1). These data suggest that endogenous
neurotrophin signaling through Trk receptors is regulating GABA
expression in cortical interneurons. These data do not allow us to
distinguish between signaling through the different Trk receptors, but
given that neither NT3 nor NGF has any effect on GABA expression in
this system, the most likely possibility is that this effect is
mediated by endogenous release of BDNF.
Fig. 4.
The effects of Trk receptor blockade on the
percentage of GABA-positive neurons. K252a, a blocker of Trk receptor
signaling, was applied for 2 d at the indicated concentration
(10, 50, or 200 nM) and
the percentage of GABA-positive neurons determined. The effect of BDNF
(25 ng/ml) and TTX (0.1 µM) in the presence of K252a (200 nM) for 2 d was also determined
(TTX+BDNF+K252a). Numbers are expressed as a percentage of
the value obtained for control cultures (control = 100%,
dashed line); *significantly different from control,
p < 0.05; **significantly different from control,
p < 0.001.
[View Larger Version of this Image (20K GIF file)]
The activity-dependent reduction in the number of GABA-positive
neurons is reversible
Studies on the role of visual input and neuronal activity on GABA
expression in visual cortex have suggested that decreased activity acts
to lower GABA levels in surviving neurons, rather than to decrease
interneuronal survival (Hendry and Jones, 1986; Benson et al., 1991).
These studies have suggested a model in which activity can continuously
modulate the amount of GABA produced by cortical interneurons. This
model predicts that the activity-dependent reduction in the number of
GABA-positive neurons in visual cortex should be reversible on
reinstatement of activity, but this has not been tested.
To address this issue, activity was blocked for 2 d with TTX, then
TTX was washed out and the cultures incubated for two additional days
in normal medium. Control cultures were washed similarly and fixed and
processed in parallel. Control experiments indicated that 2 d
after TTX washout, spike generation was normal (data not shown). GABA
levels were partially restored 2 d after TTX washout, to 82.7 ± 3.0% of control values (Fig. 5) (n = 6, wash significantly different from TTX alone, p < 0.05, Student's t test). When BDNF (25 ng/ml) was added
immediately after TTX washout, GABA levels were completely restored to
control levels after 2 d (106.0 ± 8.7% of control,
n = 3) (Fig. 5). These data indicate that the reduction
in the percentage of GABA-positive neurons produced by activity
blockade is fully reversible and that the degree of reversal can be
influenced by exogenous BDNF.
Fig. 5.
The activity-dependent reduction in the percentage
of GABA-positive neurons is reversible. Cultures were treated with TTX (0.1 µM) for 2 d. Cultures were then fixed,
processed, and counted immediately (TTX); washed
for 2 d before fixation (TTX/WASH); or
washed and BDNF (25 ng/ml) added for 2 d before fixation. Numbers are expressed as a percentage of the value obtained for control cultures (control = 100%, dashed line);
*significantly different from control, p < 0.05;
**significantly different from control, p < 0.01.
[View Larger Version of this Image (18K GIF file)]
Activity blockade reduces inhibition onto cortical
pyramidal neurons
Although decreased activity is known to decrease the number of
GABA-immunopositive neurons in visual cortex (Hendry and Jones, 1986;
Benevento et al., 1995), it is unclear whether this translates into a
functional reduction in inhibition. To address this issue, we asked
whether chronic TTX treatment decreases the magnitude or frequency of
spontaneous inhibitory currents received by pyramidal neurons. Cultures
were treated for 2 d with TTX, and the TTX was then washed out for
at least 30 min before recording. The blockade of spiking by TTX was
fully reversible (see below). To measure IPSCs in isolation, pyramidal
neurons were voltage-clamped at 0 mV (where glutamate-mediated currents
reverse), allowing us to record large outward IPSCs that could be
blocked by bicuculline (data not shown). Pretreatment with TTX for
2 d dramatically reduced the frequency of these spontaneous IPSCs
to ~20% of control levels (Fig.
6A,B)
(n = 8 neurons in each condition). To measure the total
amount of inhibitory current per unit time under the different conditions, the area under the outward current transients was integrated over 30 sec time periods, and these values were averaged over 4 min of data for each neuron. Pretreatment with TTX produced a
reduction in total inhibitory current to ~36% of control values (Fig. 6A,C). Both this reduction in
magnitude and the reduction in frequency of inhibitory currents were
blocked by co-application of 25 ng/ml BDNF (Fig. 6) (n = 8 neurons). There were no significant differences in series
resistance among recordings under the different conditions
(control = 8.1 ± 0.5 M; TTX = 7.3 ± 0.6 M;
and TTX + BDNF = 7.9 ± 1.6 M).
Fig. 6.
Activity blockade reduces inhibition onto
pyramidal neurons. A, Representative voltage-clamp
recordings of spontaneous IPSCs from pyramidal neurons grown in control
medium (CONTROL) in medium supplemented with 0.1 µM TTX for 2 d (TTX) or in
medium supplemented with TTX and BDNF (25 ng/ml) for 2 d.
B, Frequency of spontaneous IPSCs from pyramidal neurons
grown under the conditions indicated in A
(n = 8 neurons in each condition).
C, Total inhibitory current integrated over time, from
the same population as in B; *significantly different
from control (Student's t test, p < 0.04); **p < 0.01.
[View Larger Version of this Image (26K GIF file)]
Activity blockade increases pyramidal neuron firing rates
Electrophysiological recordings from visual cortex of dark-reared
rats show an increase in spontaneous activity relative to control
animals that correlate with decreases in the number of GABA-positive
neurons (Benevento et al., 1995). We asked whether the reduction in
inhibition onto pyramidal neurons produced by activity blockade in our
cortical cultures was correlated with an increase in pyramidal neuron
firing rates. Whole-cell recordings were obtained from pyramidal
neurons from control cultures or from cultures treated for 2 d
with TTX after at least 0.5 hr washout of the TTX. TTX treatment was
found to increase pyramidal neuron firing rates by more than an order
of magnitude, from 1.6 ± 0.3 spikes/min (n = 29)
to 16.5 ± 3.5 spikes/min (Fig. 7)
(n = 23). Co-incubation with TTX and BDNF (25 ng/ml),
which prevents the reduction in inhibition, also prevents the increase
in pyramidal neuron firing rates (spike frequency was 1.4 ± 0.5, n = 13). In contrast, NT3 and NGF, which do not prevent
the reduction in the number of GABA-positive neurons, also do not
prevent the increase in pyramidal neuron firing rates (Fig. 7)
(n = 14 and 11, respectively). No differences were
found in input resistances or resting membrane potentials from neurons
grown under the different experimental conditions (Table 2). These data
indicate that activity can regulate pyramidal neuron firing rates and
suggest that one mechanism of this regulation is the BDNF-dependent
modulation of inhibition.
Fig. 7.
Activity blockade increases pyramidal neuron
firing rates. A, Representative current-clamp recordings
of spontaneous firing from pyramidal neurons grown in control medium
(CONTROL), in medium supplemented with 0.1 µM TTX for 2 d (TTX), or in
medium supplemented with TTX and BDNF (25 ng/ml) for 2 d
(TTX + BDNF). B, Average spike frequency of
pyramidal neurons grown for 2 d under the conditions described in
A or in TTX + 50 ng/ml NGF (TTX + NGF) or TTX + 25 ng/ml NT3 (TTX + NT3);
*significantly different from TTX (Student's t test,
p < 0.01).
[View Larger Version of this Image (20K GIF file)]
DISCUSSION
Sensory deprivation leads to a decrease in the number of
GABA-immunopositive neurons in both somatosensory and visual cortex (Hendry and Jones, 1986; Warren et al., 1989; Kossut et al., 1991; Benevento et al., 1995). This decrease in GABA immunoreactivity appears
to be a general response of cortical circuits to a reduction in
excitatory drive and suggests that activity levels can regulate the
strength of cortical inhibition in both developing and adult animals.
In this study, we use an in vitro model system to ask whether activity-dependent changes in GABA expression lead to a
functional change in cortical inhibition and to address the mechanism
by which this process occurs.
We show that the number of GABA-positive neurons can be decreased in
postnatal cortical cultures by blockade of spontaneous activity and
that this reduction can be reversed on reinstatement of activity. The
magnitude of this effect, an approximate 30% reduction in the number
of GABA-positive neurons, is similar to that observed in intact visual
cortex after blockade of visual input (Hendry and Jones, 1986;
Benevento et al., 1995). Further, we show that the decrease in GABA
immunoreactivity can be blocked by BDNF, but not NGF or NT3, and can be
mimicked by blockade of Trk receptor signaling with K252a. Finally, we
show that the reduction in GABA is correlated with a decrease in the
amount and frequency of inhibitory currents onto cortical pyramidal
neurons and an increase in pyramidal neuron firing rates. These data
suggest that activity continuously adjusts cortical excitability
through the BDNF-dependent regulation of inhibition.
All of the effects of activity blockade on our cortical cultures,
including the reductions in the number of GABA-immunopositive neurons,
the reduction in inhibition, and the increase in pyramidal neuron
firing rates, were blocked by co-application of exogenous BDNF. This
suggests that activity blockade is exerting these effects through a
reduction in endogenous BDNF production. A similar model has been
proposed for the activity-dependent regulation of peptide expression in
hippocampal interneurons (Marty et al., 1996a). Interestingly, BDNF had
no significant effect on any of the parameters measured when activity
was intact. BDNF alone did produce a small increase in the frequency of
inhibitory currents over control values, but these effects were not
statistically significant (Fig. 6), and BDNF alone had no effect on the
number of GABA-immunopositive neurons (Fig. 3) or on pyramidal neuron
firing rates. The failure of exogenous BDNF to significantly influence
these parameters with activity intact suggests that under control
conditions, endogenous production of BDNF is close to saturating. If
so, then exogenous BDNF would only have an effect under conditions in
which endogenous production was reduced, such as activity blockade.
Although cortical neuronal cultures are known to express BDNF in an
activity-dependent manner, the concentration of this neurotrophin in
cortical cultures is unknown (Ghosh et al., 1994).
The effects of BDNF reported here are expressed in the absence of
neuronal activity. This is in contrast to several other reported
effects of BDNF on cortical neurons, including effects on survival and
on dendritic growth (Ghosh et al., 1994; McAllister et al., 1996),
although BDNF has been shown to regulate peptide expression in
hippocampal interneurons in the absence of spiking activity (Marty et
al., 1996b). This suggests that there are heterogeneous mechanisms by
which BDNF influences different cortical neuronal properties, some of
which require conjoint activity in target neurons and some of which do
not. The data reported here show that BDNF regulates inhibition onto
cortical pyramidal neurons in the absence of spike generation and
spike-mediated synaptic activity. One of the likely functions of this
activity-dependent regulation of inhibition is to globally reduce
inhibition when activity levels fall too low. To participate in this
process, BDNF must be capable of regulating inhibition during periods
of absent or very low activity.
BDNF can promote survival of several populations of cultured central
neurons, including retinal ganglion cells (Myer-Franke et al., 1995)
and largely pure embryonic cortical neurons (Ghosh et al., 1994), as
well as some populations of sensory and autonomic neurons (Buj-Bello et
al., 1995). In our postnatal cortical cultures, we observed no effect
of BDNF on survival over a 2 d period. Additionally, blockade of
Trk receptors with K252a for 2 d produced no decrease in neuronal
survival. K252a was able to completely block the effects of exogenous
BDNF, indicating that it was effectively blocking Trk receptors. K252a
is effective at reducing neurotrophin-mediated survival in other
systems (Doherty et al., 1989). The failure of K252a to reduce survival
in our cultures suggests that under the culture conditions used, in
which cortical neurons were co-cultured with cortical astrocytes,
survival of postnatal cortical neurons is independent of Trk
receptor-mediated signaling pathways. There is evidence that multiple
survival signals converge on some populations of central neurons so
that dependence on any one factor is not absolute (Myer-Franke et al.,
1995).
Several observations suggest that activity blockade is reducing GABA
expression within surviving interneurons below our ability to detect
rather than reducing interneuronal survival. First, total neuronal
survival was not compromised by activity blockade or by any of the
manipulations performed in this study. Second, the decrease in
GABA-positive neurons was completely reversible. This suggests that a
surviving pool of interneurons can be reinduced to express GABA after
reinstatement of activity. The alternative possibility is that reversal
of activity blockade is inducing a new population of GABAergic neurons
to differentiate from a population of neuronal precursor cells present
in culture. This is unlikely because cultured embryonic cortical
neurons are already postmitotic (Ghosh et al., 1994), and our postnatal
cultures are made subsequent to the period of cortical neuronal
birth.
The reduction in the number of GABA-positive neurons produced by
activity blockade is correlated with a reduction in functional inhibition onto pyramidal neurons. Both the frequency and the magnitude
of spontaneous IPSCs were dramatically reduced. An interesting question
is whether the change in IPSC frequency is accompanied by a change in
the number of synaptic contacts between inhibitory interneurons and
pyramidal neurons. Blockade of activity with TTX has been reported to
reduce inhibitory synaptogenesis onto cerebellar Purkinje neurons in
organotypic cultures (Seil and Drake-Baumann, 1994). An intriguing
possibility is that transmitter expression, inhibitory synaptic
strength, and the number of synaptic contacts in our cortical cultures
are regulated in tandem by ongoing electrical activity.
The decreased inhibition produced by activity blockade is correlated
with a dramatic increase in pyramidal neuron firing rates. Consistent
with this, electrophysiological recordings from visual cortex of
dark-reared rats show an increase in spontaneous activity relative to
control animals that correlate with a decrease in the number of
GABA-positive neurons (Benevento et al., 1995). In addition, chronic
treatments that block spontaneous activity, such as TTX, have been
reported to produce hyperexcitability in cortical cultures when washed
out, as would be expected for manipulations that reduced inhibition
(Ramakers et al., 1990). Activity is known to regulate a number of
properties of neurons and circuits, including the expression of
conductances that influence intrinsic excitability (Turrigiano et al.,
1994, 1995). Although the reduction in inhibition reported here is
likely to contribute substantially to the increase in pyramidal neuron
firing rates, other factors are also likely to contribute. In addition
to reducing inhibition, activity blockade increases the amplitude of
miniature excitatory synaptic currents onto pyramidal neurons,
suggesting that inhibition and excitation are reciprocally regulated by
activity (Turrigiano et al., 1996). Interestingly, BDNF is able to
completely prevent the effects of activity blockade on pyramidal neuron
firing rates, suggesting that any factors contributing to this change
in firing rate are being conjointly regulated by BDNF.
The data we have presented suggest that activity is continuously
modulating the amount of inhibition in cortical circuits and that this
results in an adjustment in pyramidal neuron firing rates. Our data
suggest that this activity-dependent regulation of circuit excitability
is mediated through the activity-dependent regulation of BDNF. This in
turn suggests that an important function for this neurotrophin is in
the control of cortical excitability.
FOOTNOTES
Received Jan. 17, 1997; revised March 26, 1997; accepted March 28, 1997.
This work was supported by National Science Foundation Grant
IBN-9421233, the Whitehall Foundation, National Institutes of Health
Grant K02 NS-01893, and the Sloan Center for Theoretical Neurobiology.
We thank Amgen, Incorporated, (Thousand Oaks, CA) for providing us with
NT3. We thank Susan Birren and Sacha Nelson for useful discussions and
for their critical reading of this manuscript.
Correspondence should be addressed to Dr. Gina G. Turrigiano,
Department of Biology, Brandeis University, Waltham, MA
02254.
REFERENCES
-
Alho H,
Ferrarese C,
Vicini S,
Vaccarino F
(1988)
Subsets of GABAergic neurons in dissociated cell cultures of neonatal rat cerebral cortex show co-localization with specific modulator peptides.
Brain Res
467:193-204[Medline].
-
Allendoerfer KL,
Cabelli RJ,
Escandon E,
Kaplan DR,
Nikolics E,
Shatz CJ
(1994)
Regulation of neurotrophin receptors during the maturation of the mammalian visual system.
J Neurosci
14:1795-1811[Abstract].
-
Benevento LA,
Bakkum BW,
Cohen RS
(1995)
Gamma-aminobutyric acid and somatostatin immunoreactivity in the visual cortex of normal and dark-reared rats.
Brain Res
689:172-182[Web of Science][Medline].
-
Benson DL,
Isackson PJ,
Gall CM,
Jones EG
(1991)
Differential effects of monocular deprivation on glutamic acid decarboxylase and type II calcium-calmodulin-dependent protein kinase gene expression in the adult monkey visual cortex.
J Neurosci
11:31-47[Abstract].
-
Berg M,
Sternberg D,
Parada L,
Choa M
(1992)
K252a inhibits nerve growth factor-induced Trk proto-oncogene tyrosine phosphorylation and kinase activity.
J Biol Chem
267:13-16[Abstract/Free Full Text].
-
Buj-Bello A,
Buchman VL,
Horton A,
Rosenthal A,
Davies AM
(1995)
GDNF is an age-specific survival factor for sensory and autonomic neurons.
Neuron
15:821-828[Web of Science][Medline].
-
Cabelli RJ,
Hohn A,
Shatz CJ
(1995)
Inhibition of ocular dominance column formation by infusion of NT-4/5 or BDNF.
Science
267:1662-1666[Abstract/Free Full Text].
-
Castrén E,
Zafra F,
Thoenen H,
Lindholm D
(1992)
Light regulates expression of brain-derived neurotrophic factor mRNA in rat visual cortex.
Proc Natl Acad Sci USA
89:9444-9448[Abstract/Free Full Text].
-
Chagnac-Amitai Y,
Conners BW
(1989)
Synchronized excitation and inhibition driven by intrinsically bursting neurons in neocortex.
J Neurophysiol
62:1149-1162[Abstract/Free Full Text].
-
Doherty P,
Walsh FS
(1989)
K252a specifically inhibits the survival and morphological differentiation of NGF-dependent neurons in primary cultures of human dorsal root ganglion.
Neurosci Lett
96:1-6[Web of Science][Medline].
-
Gabbott PL,
Somogyi P
(1986)
Quantitative distribution of GABA-immunoreactive neurons in the visual cortex of the cat.
Exp Brain Res
61:323-331[Web of Science][Medline].
-
Ghosh A,
Carnahan J,
Greenberg ME
(1994)
Requirement for BDNF in activity-dependent survival of cortical neurons.
Science
263:1618-1623[Abstract/Free Full Text].
-
Gotz M,
Bolz J
(1994)
Differentiation of transmitter phenotypes in rat cerebral cortex.
Eur J Neurosci
6:18-32[Web of Science][Medline].
-
Hendry SHC,
Jones EG
(1986)
Reduction in number of immunostained GABAergic neurones in deprived-eye dominance columns of monkey area 17.
Nature
320:750-753[Medline].
-
Heumann R
(1994)
Neurotrophin signalling.
Curr Opin Neurobiol
4:668-679[Medline].
-
Huettner JE,
Baughman RW
(1986)
Primary cultures of identified neurons from the visual cortex of postnatal rats.
J Neurosci
6:3044-3060[Abstract].
-
Huettner JE,
Baughman RW
(1988)
The pharmacology of synapses formed by identified corticocollicular neurons in primary cultures of rat visual cortex.
J Neurosci
8:160-175[Abstract].
-
Hyman C,
Juhasz M,
Jackson C,
Wright P,
Ip NY,
Lindsay RM
(1994)
Overlapping and distinct actions of the neurotrophins BDNF, NT-3, and NT-4/5 on cultured dopaminergic and GABAergic neurons of the ventral mesancephalon.
J Neurosci
14:335-347[Abstract].
-
Isackson PJ,
Huntsman MM,
Murray KD,
Gall CM
(1991)
BDNF mRNA expression is increased in adult rat forebrain after limbic seizures: temporal patterns of induction distinct from NGF.
Neuron
6:937-948[Web of Science][Medline].
-
Koizumi S,
Contreras ML,
Matsuda Y,
Hama T,
Lazarovici P,
Curoff G
(1988)
K-252a: a specific inhibitor or the action of nerve growth factor on PC12 cells.
J Neurosci
8:715-721[Abstract].
-
Kossut M,
Stewart MG,
Siucinska E,
Bourne RC,
Gabbott PLA
(1991)
Loss of gama-aminobytyric acid (GABA). Immunoreactivity from mouse first somatosensory (SI) cortex following neonatal, but not adult, denervation.
Brain Res
538:165-170[Web of Science][Medline].
-
Kreigstein AR,
Suppes T,
Prince DA
(1987)
Cellular and synaptic physiology and epileptogenesis of developing rat neocortical neurons in vitro.
Dev Brain Res
34:161-171.
-
Lindsay RM,
Wiegand SJ,
Altar CA,
Sistefano PS
(1994)
Neurotrophic factors: from molecule to man.
Trends Neurosci
17:182-190[Web of Science][Medline].
-
Maisonpierre PC,
Belluscio L,
Friedman B,
Alderson RF,
Wiegand SJ,
Furth ME,
Lindsay RM,
Yancopoulos GD
(1990)
NT-3, BDNF, and NGF in the developing rat nervous system: parallel as well as reciprocal patterns of expression.
Neuron
5:501-509[Web of Science][Medline].
-
Marty S,
Berninger B,
Carroll P,
Thoenen H
(1996a)
GABAergic stimulation regulates the phenotype of hippocampal interneurons through the regulation of brain-derived neurotrophic factor.
Neuron
16:565-570[Web of Science][Medline].
-
Marty S,
Carroll P,
Cellerino A,
Castrén E,
Staiger V,
Thoenen H,
Lindholm D
(1996b)
Brain-derived neurotrophic factor promotes the differentiation of various hippocampal nonpyramidal neurons, including Cajal-Retzius cells, in organotypic slice cultures.
J Neurosci
16:675-687[Abstract/Free Full Text].
-
McAllister AK,
Lo DC,
Katz LC
(1995)
Neurotrophins regulate dendritic growth in developing visual cortex.
Neuron
15:791-803[Web of Science][Medline].
-
McAllister AK,
Katz LC,
Lo DC
(1996)
Neurotrophin regulation of cortical dendritic growth requires activity.
Neuron
17:1057-1064[Web of Science][Medline].
-
Mizuno K,
Carhahan J,
Nawa H
(1994)
Brain-derived neurotrophic factor promotes differentiation of striatal GABAergic neurons.
Dev Biol
165:243-256[Web of Science][Medline].
-
Myer-Franke A,
Kaplan MR,
Pfrieger FW,
Barres BA
(1995)
Characterization of the signaling interactions that promote the survival and growth of developing retinal ganglion cells in culture.
Neuron
15:805-819[Web of Science][Medline].
-
Nye S,
Squinto S,
Glass D,
Stitt T,
Hantzopoulos G
(1992)
K252a and staurosporine selectively block autophosphorylation of neurotrophin receptors and neurotrophin-mediated responses.
Mol Biol Cell
3:677-686[Abstract].
-
Ramakers GJA,
Corner MA,
Habets AM
(1990)
Development in the absence of spontaneous bioelectric activity results in increased stereotyped burst firing in cultures of dissociated cerebral cortex.
Exp Brain Res
79:157-166[Web of Science][Medline].
-
Schoups AA,
Elliott RC,
Friedman WJ,
Black IB
(1995)
NGF and BDNF are differentially modulated by visual experience in the developing geniculocortical pathway.
Brain Res
86:326-334.
-
Seil FJ,
Drake-Baumann R
(1994)
Reduced cortical inhibitory synaptic in organotypic cerebellar cultures developing in the absence of neuronal activity.
J Comp Neurol
342:366-377[Web of Science][Medline].
-
Tapley P,
Lamballe F,
Barbacid M
(1992)
K252a is a selective inhibitory of the tyrosine protein kinase activity of the Trk family of oncogenes and neurotrophin receptors.
Oncogene
7:371-381[Web of Science][Medline].
-
Turrigiano GG,
Abbott LF,
Marder E
(1994)
Activity-dependent changes in the intrinsic properties of cultured neurons.
Science
264:974-976[Abstract/Free Full Text].
-
Turrigiano GG,
Le Masson G,
Marder E
(1995)
Selective regulation of current densities underlies spontaneous changes in the activity of cultured neurons.
J Neurosci
15:3640-6552[Abstract].
-
Turrigiano GG,
Leslie KR,
Desai N,
Nelson SB
(1996)
Activity-dependent regulation of quantal amplitude in visual cortical cultures.
Soc Neurosci Abstr
22:275.
-
Ventimiglia R,
Mather PE,
Jones BE,
Lindsay RM
(1995)
The neurotrophins BDNF, NT-3, and NT-4/5 promote survival and morphological and biochemical differentiation of striatal neurons in vitro.
Eur J Neurosci
7:213-222[Web of Science][Medline].
-
Warren R,
Trembray N,
Dykes RW
(1989)
Quantitative study of glutamic acid decarboxylase-immunoreactive neurons and cytochrome oxidase activity in normal and partially deafferented rat hindlimb somatosensory cortex.
J Comp Neurol
288:583-592[Web of Science][Medline].
-
Widmer HR,
Hefti F
(1994)
Stimulation of GABAergic neuron differentiation by NT-4/5 in cultures of rat cerebral cortex.
Dev Brain Res
80:279-284[Medline].
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|
|
I. Colin-Le Brun, N. Ferrand, O. Caillard, P. Tosetti, Y. Ben-Ari, and J.-L. Gaiarsa
Spontaneous synaptic activity is required for the formation of functional GABAergic synapses in the developing rat hippocampus
J. Physiol.,
August 15, 2004;
559(1):
129 - 139.
[Abstract]
[Full Text]
[PDF]
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S. B. Elmariah, M. A. Crumling, T. D. Parsons, and R. J. Balice-Gordon
Postsynaptic TrkB-Mediated Signaling Modulates Excitatory and Inhibitory Neurotransmitter Receptor Clustering at Hippocampal Synapses
J. Neurosci.,
March 10, 2004;
24(10):
2380 - 2393.
[Abstract]
[Full Text]
[PDF]
|
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K. Kohara, A. Kitamura, N. Adachi, M. Nishida, C. Itami, S. Nakamura, and T. Tsumoto
Inhibitory But Not Excitatory Cortical Neurons Require Presynaptic Brain-Derived Neurotrophic Factor for Dendritic Development, as Revealed by Chimera Cell Culture
J. Neurosci.,
July 9, 2003;
23(14):
6123 - 6131.
[Abstract]
[Full Text]
[PDF]
|
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X. Jin, H. Hu, P. H. Mathers, and A. Agmon
Brain-Derived Neurotrophic Factor Mediates Activity-Dependent Dendritic Growth in Nonpyramidal Neocortical Interneurons in Developing Organotypic Cultures
J. Neurosci.,
July 2, 2003;
23(13):
5662 - 5673.
[Abstract]
[Full Text]
[PDF]
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M. Neal, J. Cunningham, I. Lever, S. Pezet, and M. Malcangio
Mechanism by which Brain-Derived Neurotrophic Factor Increases Dopamine Release from the Rabbit Retina
Invest. Ophthalmol. Vis. Sci.,
February 1, 2003;
44(2):
791 - 798.
[Abstract]
[Full Text]
[PDF]
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H. Nadeau and H. A. Lester
NRSF Causes cAMP-Sensitive Suppression of Sodium Current in Cultured Hippocampal Neurons
J Neurophysiol,
July 1, 2002;
88(1):
409 - 421.
[Abstract]
[Full Text]
[PDF]
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V. Kilman, M. C. W. van Rossum, and G. G. Turrigiano
Activity Deprivation Reduces Miniature IPSC Amplitude by Decreasing the Number of Postsynaptic GABAA Receptors Clustered at Neocortical Synapses
J. Neurosci.,
February 15, 2002;
22(4):
1328 - 1337.
[Abstract]
[Full Text]
[PDF]
|
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|
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O. Rahimi and S. L. Juliano
Transplants of NGF-Secreting Fibroblasts Restore Stimulus-Evoked Activity in Barrel Cortex of Basal-Forebrain-Lesioned Rats
J Neurophysiol,
October 1, 2001;
86(4):
2081 - 2096.
[Abstract]
[Full Text]
[PDF]
|
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J. Shi, S. M. Aamodt, M. Townsend, and M. Constantine-Paton
Developmental Depression of Glutamate Neurotransmission by Chronic Low-Level Activation of NMDA Receptors
J. Neurosci.,
August 15, 2001;
21(16):
6233 - 6244.
[Abstract]
[Full Text]
[PDF]
|
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G. S. Pollock, E. Vernon, M. E. Forbes, Q. Yan, Y.-T. Ma, T. Hsieh, R. Robichon, D. O. Frost, and J. E. Johnson
Effects of Early Visual Experience and Diurnal Rhythms on BDNF mRNA and Protein Levels in the Visual System, Hippocampus, and Cerebellum
J. Neurosci.,
June 1, 2001;
21(11):
3923 - 3931.
[Abstract]
[Full Text]
[PDF]
|
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D. C. Gillespie, M. C. Crair, and M. P. Stryker
Neurotrophin-4/5 Alters Responses and Blocks the Effect of Monocular Deprivation in Cat Visual Cortex during the Critical Period
J. Neurosci.,
December 15, 2000;
20(24):
9174 - 9186.
[Abstract]
[Full Text]
[PDF]
|
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S. Marty, R. Wehrle, and C. Sotelo
Neuronal Activity and Brain-Derived Neurotrophic Factor Regulate the Density of Inhibitory Synapses in Organotypic Slice Cultures of Postnatal Hippocampus
J. Neurosci.,
November 1, 2000;
20(21):
8087 - 8095.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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T. W. Troyer and A. J. Doupe
An Associational Model of Birdsong Sensorimotor Learning I. Efference Copy and the Learning of Song Syllables
J Neurophysiol,
September 1, 2000;
84(3):
1204 - 1223.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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F. J. Seil and R. Drake-Baumann
TrkB Receptor Ligands Promote Activity-Dependent Inhibitory Synaptogenesis
J. Neurosci.,
July 15, 2000;
20(14):
5367 - 5373.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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M. M. Bolton, A. J. Pittman, and D. C. Lo
Brain-Derived Neurotrophic Factor Differentially Regulates Excitatory and Inhibitory Synaptic Transmission in Hippocampal Cultures
J. Neurosci.,
May 1, 2000;
20(9):
3221 - 3232.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
C. Lodovichi, N. Berardi, T. Pizzorusso, and L. Maffei
Effects of Neurotrophins on Cortical Plasticity: Same or Different?
J. Neurosci.,
March 15, 2000;
20(6):
2155 - 2165.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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S. M. Aamodt, J. Shi, M. T. Colonnese, W. Veras, and M. Constantine-Paton
Chronic NMDA Exposure Accelerates Development of GABAergic Inhibition in the Superior Colliculus
J Neurophysiol,
March 1, 2000;
83(3):
1580 - 1591.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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A. Balkowiec, D. L. Kunze, and D. M. Katz
Brain-Derived Neurotrophic Factor Acutely Inhibits AMPA-Mediated Currents in Developing Sensory Relay Neurons
J. Neurosci.,
March 1, 2000;
20(5):
1904 - 1911.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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A. Nitta, M. Ito, H. Fukumitsu, M. Ohmiya, H. Ito, A. Sometani, H. Nomoto, Y. Furukawa, and S. Furukawa
4-Methylcatechol Increases Brain-Derived Neurotrophic Factor Content and mRNA Expression in Cultured Brain Cells and in Rat Brain In Vivo
J. Pharmacol. Exp. Ther.,
December 1, 1999;
291(3):
1276 - 1283.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
A. K. McAllister
Subplate neurons: A missing link among neurotrophins, activity, and ocular dominance plasticity?
PNAS,
November 23, 1999;
96(24):
13600 - 13602.
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. S. Lein, E. M. Finney, P. S. McQuillen, and C. J. Shatz
Subplate neuron ablation alters neurotrophin expression and ocular dominance column formation
PNAS,
November 9, 1999;
96(23):
13491 - 13495.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
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J. M. Kittelberger and R. Mooney
Lesions of an Avian Forebrain Nucleus That Disrupt Song Development Alter Synaptic Connectivity and Transmission in the Vocal Premotor Pathway
J. Neurosci.,
November 1, 1999;
19(21):
9385 - 9398.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. Kryl, T. Yacoubian, A. Haapasalo, E. Castren, D. Lo, and P. A. Barker
Subcellular Localization of Full-Length and Truncated Trk Receptor Isoforms in Polarized Neurons and Epithelial Cells
J. Neurosci.,
July 15, 1999;
19(14):
5823 - 5833.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. A. Crozier, I. B. Black, and M. R. Plummer
Blockade of NR2B-Containing NMDA Receptors Prevents BDNF Enhancement of Glutamatergic Transmission in Hippocampal Neurons
Learn. Mem.,
May 1, 1999;
6(3):
257 - 266.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
S. Bao, L. Chen, X. Qiao, and R. F. Thompson
Transgenic Brain-Derived Neurotrophic Factor Modulates a Developing Cerebellar Inhibitory Synapse
Learn. Mem.,
May 1, 1999;
6(3):
276 - 283.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
N. S. Desai, L. C. Rutherford, and G. G. Turrigiano
BDNF Regulates the Intrinsic Excitability of Cortical Neurons
Learn. Mem.,
May 1, 1999;
6(3):
284 - 291.
[Abstract]
[Full Text]
|
|
|
|
|
|
|
T. Kushikata, J. Fang, and J. M. Krueger
Brain-derived neurotrophic factor enhances spontaneous sleep in rats and rabbits
Am J Physiol Regulatory Integrative Comp Physiol,
May 1, 1999;
276(5):
R1334 - R1338.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y.-X. Li, Y. Zhang, H. A. Lester, E. M. Schuman, and N. Davidson
Enhancement of Neurotransmitter Release Induced by Brain-Derived Neurotrophic Factor in Cultured Hippocampal Neurons
J. Neurosci.,
December 15, 1998;
18(24):
10231 - 10240.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Kokaia, F. Asztely, K. Olofsdotter, C. B. Sindreu, D. M. Kullmann, and O. Lindvall
Endogenous Neurotrophin-3 Regulates Short-Term Plasticity at Lateral Perforant Path-Granule Cell Synapses
J. Neurosci.,
November 1, 1998;
18(21):
8730 - 8739.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
D. D. Murphy, N. B. Cole, and M. Segal
Brain-derived neurotrophic factor mediates estradiol-induced dendritic spine formation in hippocampal neurons
PNAS,
September 15, 1998;
95(19):
11412 - 11417.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. L. Dantzker and E. M. Callaway
The Development of Local, Layer-Specific Visual Cortical Axons in the Absence of Extrinsic Influences and Intrinsic Activity
J. Neurosci.,
June 1, 1998;
18(11):
4145 - 4154.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. T. Lockhart, G. G. Turrigiano, and S. J. Birren
Nerve Growth Factor Modulates Synaptic Transmission between Sympathetic Neurons and Cardiac Myocytes
J. Neurosci.,
December 15, 1997;
17(24):
9573 - 9582.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
J. L. Hanover, Z. J. Huang, S. Tonegawa, and M. P. Stryker
Brain-Derived Neurotrophic Factor Overexpression Induces Precocious Critical Period in Mouse Visual Cortex
J. Neurosci.,
November 15, 1999;
19(22):
RC40 - RC40.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
K. R. Leslie, S. B. Nelson, and G. G. Turrigiano
Postsynaptic Depolarization Scales Quantal Amplitude in Cortical Pyramidal Neurons
J. Neurosci.,
October 1, 2001;
21(19):
RC170 - RC170.
[Abstract]
[Full Text]
[PDF]
|
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