 |
 Previous Article | Next Article 
The Journal of Neuroscience, January 1, 1998, 18(1):512-520
Postnatal Development of Phase-Locked High-Fidelity Synaptic
Transmission in the Medial Nucleus of the Trapezoid Body of the
Rat
Nao
Chuhma and
Harunori
Ohmori
Department of Physiology, Faculty of Medicine, Kyoto University,
Kyoto 606-01, Japan
 |
ABSTRACT |
Synaptic transmission in the medial nucleus of the trapezoid body
of rats was analyzed in postnatal days 4-13 (P4-P13) by applying the
whole-cell patch-recording technique to brain slices. In P4-P6
animals, evoked EPSCs fluctuated extensively in amplitude and occurred
in marked asynchrony, followed by spontaneous EPSCs. With development
of animals, the evoked EPSCs increased in amplitude, and the rise time
became faster. In addition, the synaptic transmission became
phase-locked. The coefficient of variation (CV) of EPSC amplitude
decreased with development (0.32 ± 0.03 for P4-P5 and 0.05 ± 0.01 for P9-P11). The amplitude of miniature EPSCs did not change
throughout the postnatal days investigated ( 30.2 ± 0.3 pA at
70 mV). The CV was dependent on extracellular
Ca2+ concentration
([Ca2+]o) and was reduced with
the increase of [Ca2+]o, and
this [Ca2+]o dependence was shifted
toward lower [Ca2+]o with development.
Direct patch recording of the presynaptic terminals demonstrated an
increase in Ca2+ currents during these postnatal
days. The phase-locked high-fidelity transmission in this synapse is
achieved with development likely through the increase of
Ca2+ currents and Ca2+
sensitivity of transmitter release mechanisms in the presynaptic terminal.
Key words:
MNTB; development; synapse; EPSC; coefficient of
variation; presynaptic Ca2+ currents; calyx of
Held
| |
INTRODUCTION |
The medial nucleus of the trapezoid
body (MNTB) is a relay nucleus in the auditory system. The principal
neuron of MNTB receives a glutamatergic input from a globular bushy
cell in the contralateral anteroventral cochlear nucleus (AVCN) (Wu and
Kelly, 1992 ; Suneja et al., 1995) and sends an inhibitory projection
fiber to neurons in the ipsilateral lateral superior olive (LSO)
nucleus (Morest, 1968). The MNTB likely contributes to the binaural
sound localization, and the synapse formed onto it has a large
calyx-shaped presynaptic terminal (calyx of Held) (Held, 1893). In
mature animals the synapse is characterized by the phase-locked, highly
reliable (high-fidelity) transmission (Goldberg and Brown, 1968; Aitkin
1986; for review, see Koyano and Ohmori, 1996).
The presynaptic terminal in MNTB was identified morphologically at the
day of birth [postnatal day 0 (P0)] as thin, filamentous terminal
processes around the principal neuron. During postnatal development
terminal swellings with radiating filopodia-like processes emerged at
around P5, followed by their extensive transformation into digit-like
structures surrounding the principal neuron. The mature calyx of Held
was observed at around P14-P16 (Kandler and Friauf, 1993; Kil et al.,
1995). Because both the presynaptic terminal and postsynaptic neuron
are electrophysiologically accessible, the properties of both
presynaptic terminals and postsynaptic responses have been investigated
extensively (Barnes-Davies and Forsythe, 1995; Borst et al., 1995;
Takahashi et al., 1996). However, the development of synaptic
transmission has not been investigated previously, and the underlying
mechanisms leading to the phase-locked high-fidelity nature of this
synaptic transmission remain unclear.
We have applied the whole-cell patch-recording technique to this
synapse in P4-P13 rats and have investigated the development of
synaptic transmission. The extremely reliable, phase-locked synaptic
transmission was established during early postnatal development and
accompanied an increase in presynaptic Ca2+ currents
and an increase in Ca2+ sensitivity of synaptic
transmission.
| |
MATERIALS AND METHODS |
Preparation of brain slices. Wistar rats aged P4-P13
were deeply anesthetized with ether. After decapitation, the brainstem was removed together with the cerebellum. This block of brain was
cooled in ice-cold 35 mM glucose saline (35GS; in
mM: 130 NaCl, 4.5 KCl, 2 CaCl2, 5 PIPES-Na, and 35 glucose, pH 7.4) saturated with 100% O2
and then mounted in a 3% agarose gel (Low Gelling Temperature;
Nakalai, Kyoto, Japan) prepared with the 35GS. Transverse brain slices
(150-300 µm sections) containing MNTB were cut with a vibratome
(DTK-2000; Dosaka, Kyoto, Japan). Slices were preincubated in
Ca2+-free, high-Mg2+ artificial
CSF (Mg-ACSF; in mM: 125 NaCl, 2.5 KCl, 26 NaHCO3, 1.25 NaH2PO4,
5 MgCl2, and 35 glucose, pH 7.4) saturated with 95%
O2-5% CO2 at 35°C for at least 1 hr. After
preincubation, slices were maintained in a 100 mM glucose
ACSF (100-glucose ASCF; in mM: 75 NaCl, 2.5 KCl, 26 NaHCO3, 1.25 NaH2PO4,
2 CaCl2, 1 MgCl2, and 100 glucose, pH 7.4) saturated with 95% O2-5%
CO2 at room temperature (20-25°C). Before recording, the
slices were treated with dispase II (3.3 mg/ml; Boehringer Mannheim,
Mannheim, Germany) or DNase I (0.1 mg/ml; Sigma, St. Louis, MO) in
100-glucose ACSF for 10-15 min at room temperature. This enzyme
treatment facilitated formation of gigaohm seals. We did not observe
any differences in membrane excitability, including peak amplitude or
time course of EPSCs, after enzyme treatment.
Recordings of EPSC and EPSP. A slice was mounted in the
recording chamber on the stage of an upright fluorescence microscope equipped with Nomarski optics (BX50WI; Olympus, Tokyo, Japan). The
chamber was continuously circulated with standard ACSF (in mM: 125 NaCl, 2.5 KCl, 26 NaHCO3, 1.25 NaH2PO4, 2 CaCl2, 1 MgCl2, and 17 glucose, pH 7.4). The MNTB neurons
were monitored through a CCD camera (C2400-07ER; Hamamatsu Photonics,
Hamamatsu, Japan) and were contrast-enhanced using an image processor
(Argus-10; Hamamatsu Photonics). Whole-cell recordings were made with
an Axopatch 200A amplifier (Axon Instruments, Foster City, CA) or with
an EPC-7 amplifier (List). Patch pipettes were fabricated from
thin-walled borocilicate glass capillaries and were coated with Sylgard
(Dow Corning Asia). Pipette resistances were ~3-5 M . The
composition of pipette solution was as follows (in mM): 140 K-gluconate, 11 KCl, 0.5 EGTA, 10 HEPES, and 5.5 KOH, pH 7.3. To block
Na+ currents, a local anesthetic, QX314 (5 mM; Alamone labs, Jerusalem, Israel), was added to the
pipette solution. The liquid junction potential (approximately 10 mV)
was corrected. Neurons were voltage-clamped at 70 mV. Presynaptic
nerve fibers were electrically stimulated by a bipolar tungsten
electrode placed on the trapezoid body halfway between the midline and
the MNTB. A single pulse (3-21 V, 100 µsec duration) was applied
every 5 sec. The stimulus voltage required to induce postsynaptic
responses was higher in P4-P5 preparations (>15 V) than in more
mature preparations (3-8 V). The approximate distance between the
location of the stimulating electrode and the medial edge of MNTB was
200 µm in P4 and 240 µm in P12 preparations. The medial to lateral
diameter of MNTB was 430 µm at P4 and 660 µm at P12. Because of its
winding projection, the exact length of the afferent fiber between the
stimulus electrode and the calyx could not be determined accurately.
All experiments were performed at room temperature (20-25°C).
MNTB neurons are reported to receive both glycinergic and
glutamatergic inputs, and both NMDA and non-NMDA receptors are
expressed at the early postnatal days (Forsythe and Barnes-Davies,
1993). The glycinergic input was blocked by adding 20 µM
strychnine (Sigma); NMDA receptors were blocked by 50 µM D-2-amino-5-phosphonovalerate (APV;
Tocris).
We have accepted the recorded EPSCs only when the following two
conditions were satisfied. (1) The evoked EPSC showed all-or-none responses to changes in stimulus intensity. This criterion was to
ensure that the EPSC was generated from a single presynaptic terminal.
There was no change in this all-or-none response property of evoked
EPSC during the period P4-P11. (2) The evoked EPSC had the maximum
peak amplitude >300 pA at 70 mV. This criterion was to maintain a
sufficient signal-to-noise ratio. Series resistance was 24-36 M and
was compensated by 40-70% in most experiments. The extent of series
resistance compensation affected the amplitude and time course of
EPSCs. In a few experiments, especially in younger animals, series
resistance compensation was not made, because of the extra noise
induced. Series resistance was compensated by >70% in all experiments
in which the rise time of EPSCs was measured. The presence of series
resistance compensation did not affect the extent of fluctuation of the
peak amplitude of EPSCs (n = 4 cells; paired
t test, p < 0.005).
Voltage commands were generated by a programmable stimulator (OI-8;
Shosin EM, Okazaki, Japan). Data were low-pass-filtered at 5 kHz with
four-pole Bessel characteristics, analog-to-digital (A/D) sampled at
40-500 µsec intervals with 12 bit resolution, and stored in a
personal computer (PC-9801 FA; NEC, Tokyo, Japan).
Recording of presynaptic Ca2+ current and
action potentials. Whole-cell recordings from the calyces of Held
were made by a patch pipette with electrode resistance of 5-10 M
(see Fig. 1A). The pipette solution contained (in
mM): 136 Cs-glucuronate, 14 CsCl, 10 HEPES-Cs, 5 EGTA, 5 Mg-ATP, and 5 creatine phosphate, and pH was adjusted to 7.3. Lucifer
yellow (1 mg/ml) was added to the pipette solution, and the recording
from calyx terminal was confirmed by fluorescence imaging at the end of
each experiment. Presynaptic Ca2+ currents were
recorded in either 2 mM CaCl2, 1 mM MgCl2 or 0.75 mM
CaCl2, 2 mM MgCl2 medium.
Both contained 1 µM TTX to block Na+
currents and 1 mM 4-aminopyridine and 20 mM
tetraethylammonium chloride by replacing equimolar NaCl in the standard
ACSF to block K+ currents. Ca2+
currents were recorded in response to step pulses of 20-100 msec duration applied at 5 sec intervals to voltages between 100 and +40
mV from the holding potential of 80 mV. Rundown of
Ca2+ currents was accelerated by an increased rate
of repetition of step depolarizations. Series resistance was 12-35
M and was compensated by 70-85%. Data were low-pass-filtered at 5 kHz with four-pole Bessel characteristics and were A/D sampled at
100-300 µsec. In some recordings, a pulse-divided-by-four protocol
was used to subtract leakage currents. However, most recordings were
made from presynaptic terminals of minimum leakage conductance without leak subtraction.
In experiments involving recording from both presynaptic terminals and
postsynaptic neurons, the presynaptic terminal was current-clamped, and
action potentials were generated by current injection through a
recording patch electrode. The patch electrode was filled with a
K+-based internal medium: 120 K+-glucuronate-based medium for tip filling and 120 K+-glutamate-based medium for the back fill. Both
solutions further contained (in mM): 20 KCl, 0.2 EGTA, 5 Mg-ATP, and 5 creatine phosphate and were adjusted to pH 7.4 by 10 mM HEPES-K+. Without back filling with
K+-glutamate, we could not induce EPSCs in the
postsynaptic neuron. The postsynaptic neuron was voltage-clamped as
described above.
Data analysis. All data were analyzed by commercially
available software (Axograph; Axon Instruments). Rise time of the EPSCs was defined as the time between 20 and 80% of the peak amplitude. The
amplitude fluctuation of EPSCs was analyzed from >50 consecutively recorded traces. Statistical calculations were made in subgroups of 10 consecutive EPSC records to eliminate additional variation from the
trend. Then a grand average was made and used as the statistic of an
individual experiment. The statistical nature of the amplitude
fluctuation of EPSCs was analyzed in two ways: as the coefficient of
variation (CV) and as the ratio of variance to mean
( 2/µ). The CV is defined as the ratio of the SD to the
mean. If we assume binomial statistics, both CV and
2/µ will be expressed as follows:
|
(1)
|
|
(2)
|
where N is the number of transmitter release sites in
a presynaptic terminal, p is the release probability, and
q is the mean miniature EPSC (mEPSC) amplitude. The binomial
statistic assumes that (1) p is constant in response to each
electrical stimulation and among release sites, and (2) q is
constant. These assumptions will be discussed later.
mEPSCs were observed in young animals (P4-P7), particularly after
evoked EPSCs, and sizes of these mEPSCs were measured. To avoid
contamination with evoked EPSCs of small size, mEPSCs were measured
only from the late phase of the traces, which had apparent preceding
evoked EPSCs. In animals older than P9, mEPSCs were induced by adding
10 mM BaCl2 and 1 µM TTX to the
external solution together with APV (50 µM), strychnine
(20 µM), and bicuculline (20 µM). In these
older animals, mEPSCs were rarely observed even after evoked EPSCs.
The mean amplitude of mEPSCs (q) was calculated by averaging
the amplitudes of recorded mEPSCs from groups of events that had a
single peak in the amplitude histogram. Most of the amplitude histograms of mEPSCs had a single peak, and the distribution was slightly skewed toward larger amplitudes (see Fig.
8B). Some of the amplitude histograms of
Ba2+-induced mEPSCs had more than two peaks and were
not included in this calculation to avoid contamination of multiquantal
events.
Data are given as mean ± SE (number of cells), unless otherwise
noted.
| |
RESULTS |
Formation of the calyx of Held
The formation of calyces of Held is initiated by terminal swelling
at around P5, and the adult-like morphology is seen by P14 in rat
(Kandler and Friauf, 1993). We have confirmed the morphological development of the synapse by injection of Lucifer yellow into the
presynaptic terminal through the patch electrode (Fig.
1B,C). On P5, the
presynaptic terminal did not encircle the postsynaptic neuron but
showed marked swellings and had many filopodia-like structures (Fig.
1B). The presynaptic terminal became thicker with
maturation and covered the large surface area of the postsynaptic neuron by P10, exhibiting the shape of a mature calyx (Fig.
1A,C).
View larger version (60K):
[in this window]
[in a new window]
|
Figure 1.
Nomarski and fluorescence images of calyces of
Held. A, Nomarski image of the calyx in a P10
preparation. The calyx (small arrowheads) and the
presynaptic fiber (large arrowhead) are shown. An
arrow indicates a patch electrode. B, C,
Fluorescence images of calyces. Calyces were stained with Lucifer
yellow injected through the patch pipette. B, A calyx in
a P5 preparation. Arrowheads indicate the presynaptic
fiber in B and C. C, A
calyx in a P10 preparation.
|
|
Achievement of high-fidelity synaptic transmission
We recorded evoked EPSPs and action potentials from MNTB neurons
at P4-P11 (Fig. 2). When the projection
fiber from AVCN was electrically stimulated, the principal neuron of
MNTB generated action potentials from EPSPs under current-clamp
conditions. On P4, the EPSP rose slowly and generated a single action
potential. The timing of action potential generation fluctuated over 5 msec (Fig. 2Aa). With postnatal development, the
timing of action potential generation showed less fluctuation. By P10,
action potentials fired at almost a fixed interval after electrical
stimulation (Fig. 2Ab).
View larger version (16K):
[in this window]
[in a new window]
|
Figure 2.
Postnatal development of synaptic transmission.
EPSPs and EPSCs were recorded from postsynaptic MNTB neurons with patch
electrodes. APV was not added to the external solution in this
experiment. A, EPSPs and action potentials in P4 and P10
neurons. Membrane potential was maintained at 70 mV in both neurons
by injecting small currents through the patch pipette.
a, EPSPs and action potentials from a P4 neuron (8 records were superimposed); b, from a P10 neuron (10 records were superimposed). Note a marked contrast in action potential
generation from evoked EPSPs between P4 and P10. B,
EPSCs in P4 and P9 neurons. The membrane was voltage-clamped at 70mV.
a, EPSCs in P4 neuron. Ten traces were superimposed. Note small mEPSC-like current responses (*) in late portion of traces.
b, EPSCs in P9 neuron. Ten traces were superimposed.
C, Postnatal changes in the amplitude of evoked EPSCs.
Each point was calculated from more than four cells. The
large SE at P10 was attributable to a single cell among six cells with
exceptionally large EPSC of 3.5 nA.
|
|
The principal neuron of MNTB is an interneuron in the pathway to the
LSO and needs phase-locked transmission to discriminate small time
differences between binaural inputs (Wu and Kelly, 1991; Banks and
Smith, 1992). Therefore, the neuron should generate action potentials
with minimum timing fluctuations after receiving synaptic input. Figure
2A shows that this feature of action potential generation is completed during the early postnatal days of development. The phase-locked nature of MNTB action potential generation could be
achieved by several factors, including increased excitability of both
the presynaptic terminal and the postsynaptic neuron and changes in
synaptic transmission onto the MNTB neuron. Developmental changes in
synaptic transmission are also suggested by the extensive morphological
transformation of the presynaptic terminal (Fig. 1).
EPSCs were compared at P4 and P9 under voltage-clamp conditions in
Figure 2B. The sizes of evoked EPSCs at P4 were
small, and EPSCs showed extensive fluctuations both in amplitude and in
timing (Fig. 2Ba). After the induction of the main
EPSCs, small mEPSC-like current transients (*) were frequently observed
during P4-P7. Because these mEPSC-like current transients were not
observed preceding the evoked EPSCs, these current transients could be an asynchronous part of the evoked synaptic responses. We will refer to
these events as mEPSCs hereafter. At P9 EPSCs were larger in amplitude
and showed less timing fluctuation (Fig. 2Bb). Mean amplitudes of evoked EPSCs were calculated by measuring the peak of
each trace, and averages are plotted against postnatal day in Figure
2C. The mean amplitude of evoked EPSCs became larger with
development and reached a plateau level about P8. The increase of mean
evoked EPSC amplitude (Fig. 2C), together with the reduction of both the amplitude fluctuation and the peak time fluctuation (Fig.
2B), seems essential to development of high-fidelity
synaptic transmission at this synapse (Fig. 2A).
Synchronization of EPSCs with development
The time course of EPSC rise and decay was accelerated with
development. When P4 evoked EPSCs were ensemble-averaged by aligning the stimulus artifact, both the rise time and the total time course were much slower than those of P9 evoked EPSC (Fig.
3Ba,Bd,Ca). The rise time of
evoked EPSCs was ~1 msec (0.96 ± 0.03 msec; 12 cells) at P4-P5
and 0.37 ± 0.01 msec at P9-P11 (seven cells). The falling phase
of a P4 EPSC was also slower than that of a P9 EPSC. There is extensive
fluctuation in the timing of evoked individual EPSCs in P4 (Fig.
3Aa), whereas the timing was fixed in P9 (Fig.
3Ab).
View larger version (26K):
[in this window]
[in a new window]
|
Figure 3.
Comparison of the time course of EPSCs between P4
and P9. A, Evoked EPSCs were superimposed for P4
(a, 69 traces), and P9 (b, 45 traces)
neurons recorded at 70 mV. Note the marked fluctuation in EPSCs in
timing and in amplitude at P4 and less fluctuation at P9. The stimulus
artifact was retouched in all traces. B, Evoked EPSCs
and mEPSCs were extracted and rearranged by alignment with the stimulus
artifact (a), with the time to reach 50% of the
peak (b) for evoked EPSCs, and for mEPSCs
(c). Traces in a and
b are the same set of records but time-shifted in
b. Ensemble averages of traces including four traces
shown in a-c are illustrated in d
(average of 24 traces), e (24 traces), and
f (20 traces). C, Ensemble averaged
traces (P4) in B, d-f, are superimposed on the ensemble
average of A, b (P9), after amplitude scaling. In
a, two ensemble-averaged traces are aligned to the
stimulus artifact, and the time to reach the 50% of the peak is shown
in b and c.
|
|
When P4 evoked EPSCs were ensemble-averaged by aligning the time of
50% peak amplitude (Fig. 3Bb,Be), the rising phase was almost superimposing on the rising phase of P9 evoked EPSCs (Fig. 3Cb). The falling phase was still delayed to the falling
phase of P9 evoked EPSC.
When mEPSCs were extracted from the traces in Figure 3Aa
(Fig. 3Bc) and were ensemble-averaged by aligning the time
to reach 50% of the peak amplitude (Fig. 3Bf), the
time course of this ensemble-averaged mEPSC was almost completely
superimposing after amplitude scaling on the time course of the P9
evoked EPSC (Fig. 3Cc). Similar results were obtained in
three other P4 evoked EPSCs and mEPSCs. The slow rise and fall of
averaged P4 evoked EPSCs are thus likely attributable to the
asynchronous release of transmitter quanta after electrical stimulation
of the presynaptic fiber. The postnatal development of synaptic
transmission, therefore, includes both the synchronization of
neurotransmitter release (Fig. 3) and the increase in the quantity of
neurotransmitter released (Fig. 2C).
Timing fluctuations of evoked EPSCs could be attributable to the
timing fluctuations of presynaptic invasion of action potentials
The timing fluctuation of EPSC onset during early postnatal days
might reflect fluctuation of action potential invasion into the
presynaptic terminal after electrical stimulation. Figure 4A illustrates several
traces from an experiment performed on a P6 synapse in which both
presynaptic action potentials and postsynaptic EPSCs were recorded
simultaneously. Presynaptic action potentials were generated by current
injection. The time of the action potential peak fluctuated over a 3 msec interval, and the time of the EPSC peak showed similar
fluctuation. However, when paired records were aligned on the rising
phases of action potentials at 50% of the peak amplitude, the EPSC
rising phase was fixed (Fig. 4B). The time to reach
50% of action potential peak and that of EPSC peak amplitude were
measured from 61 pairs of these traces and are plotted in Figure
4C. These two parameters fluctuated over 8.5 msec but showed
a significant correlation (r = 0.99; 61 record pairs).
The x-intersection of the linear regression line indicates that action potentials preceded EPSCs by 1.04 msec. This difference varied from 0.83 to 2.1 msec in six other synapses measured in P6-P13;
however, it remained fixed in each synapse (r = 0.97 ± 0.04; n = 6 cells).
View larger version (15K):
[in this window]
[in a new window]
|
Figure 4.
Presynaptic action potentials and EPSCs.
A, Presynaptic action potentials and EPSCs were
simultaneously recorded from a P6 synapse. Consecutively recorded five
pairs of traces are superimposed to show fluctuation in onset time.
Action potentials were generated by current injection from the resting
potential of 72 to 69 mV, and EPSCs were recorded at 60 mV.
B, Action potentials were aligned to the rising phase
(time to reach 50% of the peak from the resting potential); the paired
EPSCs are time-displaced to the same extent. The onset of EPSCs became
fixed. C, The time to reach 50% of the action potential
peak, and to reach 50% of the EPSC peak, measured from the onset of
current injection to the presynaptic terminal, are plotted. Correlation
coefficient was 0.99. The dotted line is a least square
fit to the distribution and was y = 0.96x 1.007.
|
|
Multiple generation of action potentials in the presynaptic terminal
after a single current injection of a short duration was not observed
in any of the seven paired recordings and another 21 recordings of
preterminal action potentials.
Amplitude fluctuation of EPSCs
The EPSC amplitude is determined by the number of released
transmitter packets and by the corresponding elementary current generated in the postsynaptic membrane (the size of mEPSC) (see Katz,
1966). The number of released packets, or neurotransmitter quanta, is a
function of both the number of occupied release sites (N) and the release probability
(p). These two presynaptic parameters will determine
the CV of the amplitude fluctuation (see Materials and Methods; Fig.
5, inset) (Korn and Faber,
1991). Figure 5 shows the CV as a function of postnatal age. On P4, the
CV was large (0.32 ± 0.03, eight cells); it decreased with
postnatal development and reached a constant value after P9 (0.05 ± 0.01, 11 cells of P9-P11). In these evaluations, CVs were
calculated from the peak amplitude of EPSCs. When we calculated CVs by
time, integrating the entire postsynaptic current induced by a single
presynaptic stimulus, these CVs showed a strong correlation with the
CVs calculated from the peak amplitudes of EPSCs (r = 0.96; 37 cells from P4-P11) and also decreased with development.
View larger version (9K):
[in this window]
[in a new window]
|
Figure 5.
Decrease in the EPSC amplitude fluctuation with
postnatal development. CV of EPSC amplitude is plotted against
postnatal age. CV was calculated from >50 consecutively recorded EPSC
traces in each experiment. Each point was calculated
from two to eight cells; P5 and P7 were from two cells.
Inset, Formulation of CV in binomial statistics. CV
decreased with increasing age, and the decrease was saturated at
P9.
|
|
Ca2+ dependence of amplitude fluctuation
The neurotransmitter release probability or the amplitude of
postsynaptic electrical responses is dependent on the extracellular Ca2+ concentration
([Ca2+]o) (del Castillo and
Katz 1954; Dodge and Rahamimoff 1967). Figure 6A shows evoked EPSCs
from both P4 and P9, recorded in 2 mM
[Ca2+]o (standard ACSF) and 5 mM [Ca2+]o. As shown
already in Figure 2, the amplitudes of P4 EPSCs fluctuated extensively
in 2 mM [Ca2+]o,
whereas P9 EPSCs showed less fluctuation (Fig. 6Aa).
In 5 mM [Ca2+]o,
the amplitude fluctuations of P4 EPSCs became less obvious (Fig.
6Ab, top traces) and was similar to that of P9 EPSCs
in 2 mM [Ca2+]o. The
amplitude fluctuations of P9 EPSCs were similarly reduced by increase
of [Ca2+]o, but to a lesser
extent than P4 EPSCs (Fig. 6Ab, bottom traces).
View larger version (12K):
[in this window]
[in a new window]
|
Figure 6.
[Ca2+]o
dependence of EPSC amplitude fluctuations. A, EPSCs
recorded in 2 mM [Ca2+]o
(standard ACSF; a) and in 5 mM
[Ca2+]o (b) in
P4 and P9 neurons. Four to six traces are superimposed in each panel.
B, Fluctuation in EPSC amplitude was calculated as CV
and was evaluated as a function of
[Ca2+]o in two groups of animals,
either immature ( , P4-P6) or mature ( , P9-P11). CV is plotted
against [Ca2+]o on semilogarithmic
coordinates. All points are from measurements of two to
nine cells; 10 mM [Ca2+]o
was from two cells.
|
|
The effects of [Ca2+]o on the
amplitude fluctuation of EPSCs were investigated systematically in
0.5-10 mM [Ca2+]o. CVs of
evoked EPSCs were calculated in two groups of animals: an immature
group (P4-P6) and a mature group (P9-P11). In the immature group, the
CV decreased extensively by increase of
[Ca2+]o to between 1 and 5 mM, and the decrease was almost saturated by 5 mM and higher [Ca2+]o
(Fig. 6B, ). In the mature group, the CV was
decreased between 0.5 and 2 mM
[Ca2+]o, and the decrease was
saturated at 2 mM and higher
[Ca2+]o (Fig. 6B, ). The dependence
of CV on [Ca2+]o apparently shifted
toward lower [Ca2+]o with development,
and this may indicate increased Ca2+ sensitivity of
the transmitter release mechanism in mature presynaptic terminals.
Ca2+ current in the presynaptic terminal
Several factors may contribute to the observed increase of
Ca2+ sensitivity of the CV in the mature synapses,
and the quantity of Ca2+ influx into the presynaptic
terminal may be the one important factor. Figure
7A shows
Ca2+ currents recorded from presynaptic terminals at
P6 and P10; their I-V relationships are shown in
Figure 7B ( for P6-Ca2+ currents; for P10). The maximum amplitude of presynaptic Ca2+
current was observed at 25 to 10 mV in 2 mM
[Ca2+]o, irrespective of animal
age (20.0 ± 2.2 mV for P5-P6, six cells; 17.9 ± 2.8 mV
for P7, seven cells; 20.8 ± 3.5 mV for P10-P11, six cells;
ANOVA, p = 0.95). With the progress of postnatal development, the maximum amplitude of presynaptic
Ca2+ currents increased (Fig. 7C):
0.86 ± 0.06 nA for P5-P6 (six cells), 1.05 ± 0.10 nA
for P7 (seven cells), and 1.75 ± 0.15 nA for P10-P11 (six
cells). This increase of presynaptic Ca2+ currents
is consistent with the increased
[Ca2+]o sensitivity of the CV of EPSC
amplitude fluctuations with development.
View larger version (18K):
[in this window]
[in a new window]
|
Figure 7.
Presynaptic Ca2+ current.
A, a, Ca2+ current recorded from a P6
presynaptic terminal. The holding potential was 80 mV, and
Ca2+ current was induced by step depolarizations;
traces illustrated were recorded at 20, 15, 5, 5, 15, and 25 mV.
A, b, Ca2+ current recorded from a
P10 presynaptic terminal. The holding potential was 80 mV, and the
traces illustrated were recorded at 15, 10, 0, 10, 20, and 30 mV.
B, I-V relationships of presynaptic Ca2+ currents of a P6 neuron () and a P10 neuron
(). C, Mean maximum amplitude of presynaptic
Ca2+ current plotted against postnatal age. Animals
were placed into three groups: immature (P5-P6), intermediate (P7),
and mature (P10-P11). Horizontal bars at each
point indicate the range of postnatal days included at
that point, and error bars indicate SE. Each point was
the average of six or seven cells.
|
|
Because the complex morphology of presynaptic terminals may affect the
quality of space clamp, the absolute value of Ca2+
currents may be underestimated. However, in recordings with small series resistance and with proper compensation, we should have overcome
most problems arising from this complex structure (see Llano et al.,
1991). We have tested the validity of the postnatal increase of
Ca2+ currents in two ways. (1) When we recorded
Ca2+ currents with
[Ca2+]o reduced to 0.75 mM
(with 2 mM
[Mg2+]o), the mean maximum
Ca2+ current amplitude was 270 ± 19 pA at P6
(three cells), 476 ± 25 pA at P8 (three cells), and 633 ± 49 pA at P10-P11 (three cells). These values are close to the
expectation from the Ca2+ current averages in Figure
7C and from the ratio of
[Ca2+]o of 0.75 and 2 mM.
(2) When series resistance compensation (70-85%) was turned off
intentionally, the amplitude of maximum Ca2+ current
became smaller by 32 ± 34% (16 cells). The reduction was
independent of postnatal age (ANOVA, p = 0.38): 56 ± 44% (four cells) from P5-P6, 13 ± 9% (five cells) from P7,
and 32 ± 35% (seven cells) from P10-P11. These reductions of
Ca2+ current amplitude partly reflect the rundown of
presynaptic Ca2+ channels; the
Ca2+ currents obtained with the series resistance
compensation tuned to the initial level were still smaller by 16 ± 20% (eight cells) than those recorded previously without
compensation. Despite the difficulty of obtaining perfect recordings,
because of the complex morphology of the presynaptic terminal, these
data suggest that the presynaptic Ca2+ currents are
increasing during this postnatal period.
Miniature EPSC
Figure 8A shows
traces of spontaneous EPSCs (mEPSCs) recorded at P4 and P9. Although
mEPSCs were rarely observed in this synapse after maturation, mEPSCs
were frequently observed immediately after the evoked EPSCs in P4-P7
neurons (Figs. 2Ba, 3Aa,B). Several traces
of these mEPSCs are presented in Figure 8Aa. In older
synapses of P8-P13 neurons, mEPSCs were induced by extracellular
application of Ba2+ (10 mM) (Fig.
8Ab). In some neurons at P7-P8, mEPSCs could be recorded both after evoked EPSCs and by extracellular application of
Ba2+. The amplitude did not differ significantly
between these two sets of mEPSCs (t test, p = 0.50): 29.3 ± 1.6 pA after evoked EPSCs (17 cells) and
31.2 ± 2.4 pA by Ba2+ induction (17 cells).
View larger version (20K):
[in this window]
[in a new window]
|
Figure 8.
Amplitudes of mEPSCs. A, mEPSCs
recorded in P4 (a) and P9
(b) neurons. a, mEPSCs were
extracted from traces after evoked EPSCs. b, mEPSCs
generated in external solution enriched with 10 mM
Ba2+ and 1 µM TTX (high
Ba2+-ACSF). B, Amplitude histograms
of absolute value of mEPSCs in a P4 neuron (left) and a
P9 neuron (right). The mean mEPSC of the P4 histogram
was 26.5 pA and was 23.6 pA for the P9 histogram. C,
Mean absolute amplitudes of mEPSCs plotted against postnatal day. Each
point is the average of more than three cells, except for P12 and P13 (1 cell). Mean of P12 and P13 is plotted as a single
point with a horizontal bar.
|
|
Amplitude histograms of mEPSCs with a clear single peak are shown in
Figure 8B for P4 (left) and P9
(right) neurons. These histograms were constructed from data
that included the traces illustrated in Figure 8A.
Most of the mEPSC amplitude histograms had a single peak and showed a
distribution skewed toward the larger amplitudes. In a few cases,
histograms had several peaks, particularly when mEPSCs were induced by
Ba2+ (see Materials and Methods). The mean absolute
value of mEPSC q was calculated at each synapse and is
plotted against ages of animals in Figure 8C; q
was almost constant throughout (30.2 ± 0.3 pA). The time constant
of mEPSC decay was not significantly changed during P4-P13 (ANOVA,
p = 0.38): 2.2 ± 0.1 msec in P4-P5 (n = 4 cells), 2.1 ± 0.1 msec in P7-P8
(n = 4 cells), and 2.3 ± 0.1 msec in P9-P13
(n = 5 cells).
| |
DISCUSSION |
Achievement of high-fidelity synaptic transmission
with development
We have recorded EPSCs in the large calyx-shaped synapse formed
onto the principal neuron of MNTB in animals aged P4-P13 and have
investigated developmental changes of synaptic transmission. The
amplitude of evoked EPSCs increased with development (Fig. 2C). In younger animals evoked EPSCs fluctuated extensively
both in their timing of occurrence and in their amplitude (Fig.
2B) and showed less fluctuation with development
(Figs. 2, 3, 5). Development of the characteristic phase-locked,
high-fidelity synaptic transmissions was completed at around P9.
We have evaluated the extent of EPSC amplitude fluctuation by
calculating the CV. Postnatal development was accompanied by decrease
of the CV and increased Ca2+ sensitivity (Figs. 5,
6). These changes are likely attributable to increase in
Ca2+ currents in the presynaptic terminal (Fig. 7)
and may include increase in the Ca2+ sensitivity of
transmitter release mechanisms downstream of Ca2+
influx. We have not particularly investigated development of the
postsynaptic apparatus. However, the postsynaptic non-NMDA receptors
seem to be already in the mature form at the period we investigated
(P4-P13), at least qualitatively, because both q and the
time course of mEPSC decay were not changed significantly in these
periods (Fig. 8).
Maturation of synaptic transmission was completed on P8-P9 (Figs.
2C, 5). This conclusion is similar to the observation made at synapses between MNTB and LSO by Kandler and Friauf (1995). They
reported that the contralateral synaptic input to LSO through the MNTB
principal neuron depolarized the LSO neuron in the early developmental
stage and then turned to hyperpolarize the LSO neuron after P8. These
postsynaptic potentials were glycinergic, and this developmental change
of reversal potential was proposed to be attributable to a decrease of
[Cl ]i. Therefore, the synapses in
the pathway from the contralateral AVCN, through MNTB to LSO, undergo
substantial development and become mature at around P8-P9.
Increase in release probability p with development of
the MNTB synapse
The CV is a function of both the number of release sites
(N) and the release probability
(p). From the measurement of the CV alone, we have no
way to determine which of these two parameters increased
developmentally. If we assume binomial statistics, the ratio of the
EPSC variance to the mean (2/µ) will be
the product of mean mEPSC amplitude (q) and the probability (1 p), the probability of not releasing a
neurotransmitter when the presynaptic fiber is stimulated (see Eq. 2 in
Materials and Methods; Fig. 9A,
inset). 2/µ has a dimension of current
(A). Figure 9A shows the postnatal change
of 2/µ. 2/µ was 0.021 ± 0.003 nA on P4 (eight cells) and decreased with postnatal development. The
decrease saturated after P9 (0.004 ± 0.001 nA, 11 cells of
P9-P11). Because the size of q was constant during this
period of postnatal development (Fig. 8C), this decrease of
2/µ indicates an increase of p.
View larger version (13K):
[in this window]
[in a new window]
|
Figure 9.
Variance/mean of EPSCs (2/µ) as a
function of postnatal day and [Ca2+]o.
A, 2/µ was calculated from the same set
of records as Figure 5 and averaged for each postnatal day.
Inset, Formulation of 2/µ in binomial
statistics. B, [Ca2+]o
dependence of EPSC amplitude fluctuations. 2/µ was
measured from the same set of records shown in Figure 6 for immature
(, P4-P6) and mature (, P9-P11). 2/µ is
plotted against [Ca2+]o on
semilogarithmic coordinates.
|
|
Using the mean value of q, we could calculate p
to be 0.34 on P4 and 0.87 on P9-P11. Borst and Sakmann (1996) reported
a quantal size of 43 pA at 80 mV. If we adopted their estimate of
q after correcting the difference of holding potential (70
mV in our experiments), the estimates of p would become
larger at younger ages: 0.49 on P4 and 0.87 on P9-P11.
In calculations of p from 2/µ, we adopted
simple binomial statistics assuming a uniform release probability. In
cultured hippocampal synapses, terminals of high and low release
probabilities were reported in the autapses onto a single hippocampal
neuron measured by the different rate of suppression of current through
NMDA receptor channels by
(5R,10S)-(+)-5-methyl-10,11-dihydro-5H-dibenzo[a,d]cyclo-hepten-5,10-imine hydrogen maleate (MK801) (Rosenmund et al., 1993) and as the different extent of uptake of fluorescence dye N-(3-triethylammonium
propyl)-4-(4-(dibutylamino)styryl) pyridinium dibromide in addition to
using MK801 (Murthy et al., 1997). We do not have evidence indicating
differences in release probabilities between sites of transmitter
release within the calyx of Held. Because transmitter release sites in
the calyx of Held are in a single terminal structure and probably
adjacent to each other, there may not be large differences of release
probability among nearby sites.
The number of release sites N was estimated statistically
from the CV, and N did not differ significantly among
different ages of animals; N varied from 54 to 99. N was calculated from the mean EPSCs amplitude
(µ = Npq) by adopting the release probability (p) and the size of mEPSC (q) or from the
CV after evaluating p; evaluation of p needs
estimation of q. Therefore, evaluation of N could
have greater errors than estimation of p or q.
Borst and Sakmann (1996) estimated the quantal content (Np)
of this synapse in mature animals (P8-P10) and reported 151-210
depending on the method of calculation.
Mature calyces of MNTB synapse have a high probability or a high
capability for transmitter release. This feature is appropriate for
phase-locked high-fidelity transmission in this auditory relay nucleus.
In contrast, in the CA3 CA1 unitary synapse of the hippocampus, release probability was demonstrated to decrease with postnatal development, and at this synapse LTP emerged only when the release probability was reduced either by postnatal development or by reduced
[Ca2+]o (Bolshakov and Siegelbaum,
1995). This synapse property would be necessary in mature hippocampus,
which appears to be involved in spatial learning (Silva et al.,
1992).
Synchronization of the transmitter release
The morphology of calyx changed drastically during the postnatal
days we investigated (Fig. 1). During this postnatal period, the
filamentous and radiating filopodia-like processes of presynaptic terminal disappeared, and terminal swellings appeared that ultimately encapsulated the postsynaptic principal neuron of the MNTB. The mature
calyx structure would favor phase-locked transmission in the MNTB.
Moreover, the phase-locked transmission of this synapse was likely
achieved by a synchronized release of neurotransmitters (Fig. 3).
Synchronized release should be favored by reduced fluctuation in the
time of action potential invasion of the presynaptic terminal after
electrical stimulation of the afferent (Fig. 4). This could likely be
accomplished by an increase of presynaptic Na+
currents and also K+ currents. However, the
observations made were by whole-cell recording from presynaptic
terminals, and the recording itself might have modified the
excitability of a small structure such as a presynaptic terminal.
Therefore, the reduced fluctuation of action potential invasion time
could not be the sole factor to synchronize the EPSC with development.
We should not eliminate possibilities of changes of other presynaptic
regulatory factors of transmitter release. Particularly, increase of
Ca2+ sensitivity of transmitter release would
facilitate synchronization (Fig. 6). When release probability
p was reduced, Isaacson and Walmsley (1995) observed a large
fluctuation in EPSC amplitude and timing of occurrence at the synapses
between auditory nerve fibers and AVCN neurons (end bulb of Held); in
these experiments Ca2+ influx to the presynaptic
terminal was reduced by extracellular application of
Cd2+ (100 µM).
Ca2+ sensitivity of the CV became higher with
development (Fig. 6), and similar results were obtained when we
calculated 2/µ from the same set of records (Fig.
9B). We have not measured the size of mEPSCs at different
[Ca2+]o. However, because mEPSCs
(31.2 ± 2.4 pA) induced by 10 mM Ba2+ were not different from those (29.3 ± 1.6 pA) that occurred spontaneously after evoked EPSCs in the standard
2 mM Ca2+ extracellular medium,
q was probably not affected by the 0.5-10 mM
[Ca2+]o we have used in experiments of
Figures 6 and 9B. Therefore, the Ca2+
sensitivity of release probability p seems to increase
developmentally. This suggests that presynaptic terminals become more
efficient in increasing [Ca2+]i with
development, which in turn increases the Ca2+
sensitivity of the transmitter release mechanisms. The amplitudes of
presynaptic Ca2+ currents were increased with
development (Fig. 7). In the chick ciliary ganglion, clusters of
Ca2+ channels were demonstrated in the membrane
facing to the synaptic cleft (Haydon et al., 1994). Greater
accumulation of Ca2+ channels in the active zones
with development would facilitate release of neurotransmitter.
Asynchronous late release of neurotransmitter was observed in pairs of
cultured superior cervical ganglion neurons after injection, into the
presynaptic partner, a recombinant N type Ca2+
channel containing a site interacting with syntaxin and
synaptosome-associated protein of 25 kDa. The intracellular presence of
this fusion protein is expected to disrupt the interaction of N-type
Ca2+ channels with syntaxin and to inhibit synaptic
transmission (Mochida et al., 1996). Ca2+ sensors
with distinct affinity for Ca2+ are reported in
hippocampal neurons, and they appear to mediate late release of
neurotransmitters when Sr2+ replaced
Ca2+ in the extracellular medium (Goda and Stevens,
1994). The increased synchronization of transmitter release with
development observed in the present study might indicate addition or
replacement of proteins in the synaptic terminal that enhance
Ca2+ sensitivity of the neurotransmitter release
cascade. The basic mechanisms of membrane fusion and transmitter
release triggered by Ca2+ influx appear completed at
early phases of development, because the time course of the P4 mEPSC
superimposed on the P9 evoked EPSC where neurotransmitter was released
with a high degree of synchronization (Fig. 3Cc). This
further suggests that the postsynaptic receptors (in particular the
non-NMDA glutamate receptors) are already present in the mature form at
P4 in the principal neuron of the MNTB.
| |
FOOTNOTES |
Received Aug. 21, 1997; revised Oct. 14, 1997; accepted Oct 17, 1997.
This work was supported by grants-in-aid from the Ministry of
Education. N.C. is a research fellow of the Japan Society for the
Promotion of Sciences. We acknowledge Dr. M. E. Barish for valuable comments and contributions to improving this manuscript and
Dr. T. Hirano, Dr. Y. Kang, and Dr. K. Koyano for reading this
manuscript. Dr. M. Takada is appreciated for helpful discussions and
suggestions. We also thank Mr. M. Fukao for excellent technical assistance.
Correspondence should be addressed to Harunori Ohmori at the above
address.
| |
REFERENCES |
-
Aitkin L
(1986)
Neural coding of sound location.
In: The auditory midbrain, pp 145-183. Clifton, NJ: Humana.
-
Banks IM,
Smith PH
(1992)
Intracellular recordings from neurobiotin-labeled cells in brain slices of the rat medial nucleus of the trapezoid body.
J Neurosci
12:2819-2837[Abstract].
-
Barnes-Davies M,
Forsythe ID
(1995)
Pre- and postsynaptic glutamate receptors at a giant excitatory synapse in rat auditory brain stem slices.
J Physiol (Lond)
488:387-406[Abstract/Free Full Text].
-
Bolshakov VY,
Siegelbaum SA
(1995)
Regulation of hippocampal transmitter release during development and long-term potentiation.
Science
269:1730-1734[Abstract/Free Full Text].
-
Borst JGG,
Sakmann B
(1996)
Calcium influx and transmitter release in a fast CNS synapse.
Nature
383:431-434[Medline].
-
Borst JGG,
Helmchen F,
Sakmann B
(1995)
Pre- and postsynaptic whole-cell recordings in the medial nucleus of the trapezoid body of the rat.
J Physiol (Lond)
489:825-840[Abstract/Free Full Text].
-
del Castillo J,
Katz B
(1954)
Quantal components of the end-plate potential.
J Physiol (Lond)
124:560-573.
-
Dodge FA,
Rahamimoff R
(1967)
Co-operative action of calcium ions in transmitter release at the neuromuscular junction.
J Physiol (Lond)
193:419-432[Abstract/Free Full Text].
-
Forsythe ID,
Barnes-Davies M
(1993)
The binaural auditory pathway: excitatory amino acid receptors mediate dual timecourse excitatory postsynaptic currents in the rat medial nucleus of the trapezoid body.
Proc R Soc Lond [Biol]
251:151-157[Medline].
-
Goda Y,
Stevens CF
(1994)
Two components of transmitter release at a central synapse.
Proc Natl Acad Sci USA
91:12942-12946[Abstract/Free Full Text].
-
Goldberg JM,
Brown PB
(1968)
Functional organization of the dog superior olivary complex: an anatomical and electrophysiological study.
J Neurophysiol
31:639-656[Free Full Text].
-
Haydon PG,
Henderson E,
Stanley EF
(1994)
Localization of individual calcium channels at the release face of a presynaptic nerve terminal.
Neuron
13:1275-1280[Web of Science][Medline].
-
Held H (1893) Die centrale Gehörleitung. Arch Anat
Physiol Anat Abteil 201-248.
-
Isaacson JS,
Walmsley B
(1995)
Counting quanta: direct measurements of transmitter release at a central synapse.
Neuron
15:875-884[Web of Science][Medline].
-
Kandler K,
Friauf E
(1993)
Pre- and postnatal development of efferent connections of the cochlear nucleus in the rat.
J Comp Neurol
328:161-184[Web of Science][Medline].
-
Kandler K,
Friauf E
(1995)
Development of glycinergic and glutamatergic synaptic transmission in the auditory brainstem of perinatal rats.
J Neurosci
15:6890-6904[Abstract/Free Full Text].
-
Katz B
(1966)
In: Nerve, muscle and synapse. New York: McGraw Hill.
-
Kil J,
Kageyama GH,
Semple MM,
Kitzes LM
(1995)
Development of ventral cochlear nucleus projections to the superior olivary complex in gerbil.
J Comp Neurol
353:317-340[Web of Science][Medline].
-
Korn H,
Faber S
(1991)
Quantal analysis and synaptic efficacy in the CNS.
Trends Neurosci
14:439-445[Web of Science][Medline].
-
Koyano K,
Ohmori H
(1996)
Cellular approach to auditory signal transmission.
Jpn J Physiol
46:289-310[Web of Science][Medline].
-
Llano I,
Marty A,
Armstrong CM,
Konnerth A
(1991)
Synaptic- and agonist-induced excitatory currents of Purkinje cells in rat cerebellar slices.
J Physiol (Lond)
434:183-213[Abstract/Free Full Text].
-
Mochida S,
Sheng Z-H,
Baker C,
Kobayashi H,
Catterall WA
(1996)
Inhibition of neurotransmission by peptides containing the synaptic protein interaction site of N-type Ca2+ channels.
Neuron
17:781-788[Web of Science][Medline].
-
Morest DK
(1968)
The collateral system of the medial nucleus of the trapezoid body of the cat, its neuronal architecture and relation to the olivo-cochlear bundle.
Brain Res
9:288-311[Medline].
-
Murthy VN,
Sejnowski TJ,
Stevens CF
(1997)
Heterogeneous release properties of visualized individual hippocampal synapses.
Neuron
18:599-612[Web of Science][Medline].
-
Rosenmund C,
Clements JD,
Westbrook GL
(1993)
Nonuniform probability of glutamate release at a hippocampal synapse.
Science
262:754-757[Abstract/Free Full Text].
-
Silva AJ,
Paylor R,
Wehner JM,
Tonegawa S
(1992)
Impaired spatial learning in
 -calcium-calmodulin kinase II mutant mice.
Science
257:206-211[Abstract/Free Full Text]. -
Suneja SK,
Benson CG,
Gross J,
Potashner SJ
(1995)
Evidence for glutamatergic projections from the cochlear nucleus to the superior olive and the ventral nucleus of the lateral lemniscus.
J Neurochem
64:161-171[Web of Science][Medline].
-
Takahashi T,
Forsythe ID,
Tsujimoto T,
Barnes-Davies M,
Onodera K
(1996)
Presynaptic calcium current modulation by a metabotropic glutamate receptor.
Science
274:594-597[Abstract/Free Full Text].
-
Wu SH,
Kelly JB
(1991)
Physiological properties of neurons in the mouse superior olive: membrane characteristics and postnatal responses studied in vitro.
J Neurophysiol
65:230-246[Abstract/Free Full Text].
-
Wu SH,
Kelly JB
(1992)
Synaptic pharmacology of the superior olivary complex studied in mouse brain slice.
J Neurosci
12:3084-3097[Abstract].
Copyright © 1998 Society for Neuroscience 0270-6474/98/181512-09$05.00/0
This article has been cited by other articles:
|
|
|
|
 
R. A. Ingram, M. Fitzgerald, and M. L. Baccei
Developmental Changes in the Fidelity and Short-Term Plasticity of GABAergic Synapses in the Neonatal Rat Dorsal Horn
J Neurophysiol,
June 1, 2008;
99(6):
3144 - 3150.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. Rodriguez-Contreras, J. S. S. van Hoeve, R. L. P. Habets, H. Locher, and J. G. G. Borst
Dynamic development of the calyx of Held synapse
PNAS,
April 8, 2008;
105(14):
5603 - 5608.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
F. V. Chirila, K. C. Rowland, J. M. Thompson, and G. A. Spirou
Development of gerbil medial superior olive: integration of temporally delayed excitation and inhibition at physiological temperature
J. Physiol.,
October 1, 2007;
584(1):
167 - 190.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. Youssoufian, S. Oleskevich, and B. Walmsley
Development of a Robust Central Auditory Synapse in Congenital Deafness
J Neurophysiol,
November 1, 2005;
94(5):
3168 - 3180.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. K Magnusson, C. Kapfer, B. Grothe, and U. Koch
Maturation of glycinergic inhibition in the gerbil medial superior olive after hearing onset
J. Physiol.,
October 15, 2005;
568(2):
497 - 512.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Taschenberger, V. Scheuss, and E. Neher
Release kinetics, quantal parameters and their modulation during short-term depression at a developing synapse in the rat CNS
J. Physiol.,
October 15, 2005;
568(2):
513 - 537.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. Renden, H. Taschenberger, N. Puente, D. A. Rusakov, R. Duvoisin, L.-Y. Wang, K. P. Lehre, and H. von Gersdorff
Glutamate Transporter Studies Reveal the Pruning of Metabotropic Glutamate Receptors and Absence of AMPA Receptor Desensitization at Mature Calyx of Held Synapses
J. Neurosci.,
September 14, 2005;
25(37):
8482 - 8497.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Korogod, X. Lou, and R. Schneggenburger
Presynaptic Ca2+ Requirements and Developmental Regulation of Posttetanic Potentiation at the Calyx of Held
J. Neurosci.,
May 25, 2005;
25(21):
5127 - 5137.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S Oleskevich, M Youssoufian, and B Walmsley
Presynaptic plasticity at two giant auditory synapses in normal and deaf mice
J. Physiol.,
November 1, 2004;
560(3):
709 - 719.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
I. Joshi, S. Shokralla, P. Titis, and L.-Y. Wang
The Role of AMPA Receptor Gating in the Development of High-Fidelity Neurotransmission at the Calyx of Held Synapse
J. Neurosci.,
January 7, 2004;
24(1):
183 - 196.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Kuba, R. Yamada, and H. Ohmori
Evaluation of the limiting acuity of coincidence detection in nucleus laminaris of the chicken
J. Physiol.,
October 15, 2003;
552(2):
611 - 620.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
T. Yamashita, T. Ishikawa, and T. Takahashi
Developmental Increase in Vesicular Glutamate Content Does Not Cause Saturation of AMPA Receptors at the Calyx of Held Synapse
J. Neurosci.,
May 1, 2003;
23(9):
3633 - 3638.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
R. M. Leao and H. Von Gersdorff
Noradrenaline Increases High-Frequency Firing at the Calyx of Held Synapse During Development by Inhibiting Glutamate Release
J Neurophysiol,
May 1, 2002;
87(5):
2297 - 2306.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
I. Joshi and L.-Y. Wang
Developmental profiles of glutamate receptors and synaptic transmission at a single synapse in the mouse auditory brainstem
J. Physiol.,
May 1, 2002;
540(3):
861 - 873.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Kuba, K. Koyano, and H. Ohmori
Development of membrane conductance improves coincidence detection in the nucleus laminaris of the chicken
J. Physiol.,
April 15, 2002;
540(2):
529 - 542.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
V. Scheuss, R. Schneggenburger, and E. Neher
Separation of Presynaptic and Postsynaptic Contributions to Depression by Covariance Analysis of Successive EPSCs at the Calyx of Held Synapse
J. Neurosci.,
February 1, 2002;
22(3):
728 - 739.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Chuhma and H. Ohmori
Role of Ca2+ in the Synchronization of Transmitter Release at Calyceal Synapses in the Auditory System of Rat
J Neurophysiol,
January 1, 2002;
87(1):
222 - 228.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
E. Neher and T. Sakaba
Estimating Transmitter Release Rates from Postsynaptic Current Fluctuations
J. Neurosci.,
December 15, 2001;
21(24):
9638 - 9654.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Brenowitz and L. O. Trussell
Maturation of Synaptic Transmission at End-Bulb Synapses of the Cochlear Nucleus
J. Neurosci.,
December 1, 2001;
21(23):
9487 - 9498.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
A. C. Meyer, E. Neher, and R. Schneggenburger
Estimation of Quantal Size and Number of Functional Active Zones at the Calyx of Held Synapse by Nonstationary EPSC Variance Analysis
J. Neurosci.,
October 15, 2001;
21(20):
7889 - 7900.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
Y. Sahara and T. Takahashi
Quantal components of the excitatory postsynaptic currents at a rat central auditory synapse
J. Physiol.,
October 1, 2001;
536(1):
189 - 197.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Iwasaki and T. Takahashi
Developmental regulation of transmitter release at the calyx of Held in rat auditory brainstem
J. Physiol.,
August 1, 2001;
534(3):
861 - 871.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
N. Chuhma, K. Koyano, and H. Ohmori
Synchronisation ofneurotransmitter release during postnatal development in a calyceal presynaptic terminal of rat
J. Physiol.,
January 1, 2001;
530(1):
93 - 104.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Taschenberger and H. von Gersdorff
Fine-Tuning an Auditory Synapse for Speed and Fidelity: Developmental Changes in Presynaptic Waveform, EPSC Kinetics, and Synaptic Plasticity
J. Neurosci.,
December 15, 2000;
20(24):
9162 - 9173.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Iwasaki, A. Momiyama, O. D. Uchitel, and T. Takahashi
Developmental Changes in Calcium Channel Types Mediating Central Synaptic Transmission
J. Neurosci.,
January 1, 2000;
20(1):
59 - 65.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
M. C Bellingham, R. Lim, and B. Walmsley
Developmental changes in EPSC quantal size and quantal content at a central glutamatergic synapse in rat
J. Physiol.,
September 15, 1998;
511(3):
861 - 869.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
S. Iwasaki and T. Takahashi
Developmental changes in calcium channel types mediating synaptic transmission in rat auditory brainstem
J. Physiol.,
June 1, 1998;
509(2):
419 - 423.
[Abstract]
[Full Text]
[PDF]
|
|
|
|
|
|
|
H. Kuba, K. Koyano, and H. Ohmori
Development of membrane conductance improves coincidence detection in the nucleus laminaris of the chicken
J. Physiol.,
March 1, 2002;
(2002)
200101336.
[Abstract]
[PDF]
|
|
|
|
|
|
|
I. Joshi and L.-Y. Wang
Developmental profiles of glutamate receptors and synaptic transmission at a single synapse in the mouse auditory brainstem
J. Physiol.,
March 15, 2002;
(2002)
2001013506.
[Abstract]
[PDF]
|
|
|
|
Top
Abstract
Introduction
