The Journal of Neuroscience, August 6, 2003, 23(18):7012-7020
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Patterned Vision Causes CRE-Mediated Gene Expression in the Visual Cortex through PKA and ERK
Laura Cancedda,2 *
Elena Putignano,2 *
Soren Impey,3
Lamberto Maffei,1,2
Gian Michele Ratto,1 and
Tommaso Pizzorusso1,2
1Institute of Neuroscience of Consiglio Nazionale
delle Ricerche, 56100 Pisa, Italy, 2Scuola Normale
Superiore, 56100 Pisa, Italy, and 3Vollum Institute,
Oregon Health Sciences University, Portland, Oregon 97201-3098
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Abstract
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Normal visual experience during postnatal development is necessary for the
maturation of visual cortical circuits and acts through molecular mechanisms
that are still poorly understood. Recently, it has been shown that ERK
(extracellular signal-regulated kinase) 1/2, protein kinase A (PKA), and CREB
(cAMP response element-binding protein) are crucial factors for
experience-dependent development of the visual cortex, but very little is
known about the role of visual experience in their activation. Here, we show
that visual stimulation after a brief period of dark rearing caused a
transient ERK activation in the visual cortex. Visually induced ERK activation
occurred primarily in excitatory neurons of layers II-III and VI and was
prevented by binocular lid suture. ERK phosphorylation was strongly reduced by
cortical infusion with the cAMP-PKA inhibitor Rp-8-Cl-cAMPS, thus establishing
a link between PKA and ERK activation.
To analyze the downstream consequences of ERK and PKA signaling, we studied
the action of visual stimulation on transcription of genes controlled by CREB
in transgenic mice carrying the LacZ reporter gene under the control
of the CRE (cAMP response element) promoter. Visual stimulation triggered a
prolonged episode of CRE-mediated gene expression in the visual cortex that
was suppressed by infusion with the ERK inhibitor U0126. Cortical
administration of Rp-8-Cl-cAMPS attenuated the experience-dependent activation
of CRE-mediated gene transcription. These results show that ERK
phosphorylation in visual cortical neurons represents a molecular readout of
patterned visual stimuli and that visual activation of ERK involves the
cAMP-PKA system. Finally, because CRE-mediated gene expression was totally
dependent on ERK activation, we suggest that PKA action on CRE-mediated gene
expression is mediated by ERK.
Key words: visual cortex; ERK; CREB; PKA; plasticity; visual stimulation
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Introduction
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The visual system reaches its mature form during a critical period of early
postnatal development, in which electrical activity elicited by vision of
spatial patterns has an essential role in sculpting cortical circuitry. The
role of visual experience is highlighted by the effects of the suture of the
eyelids of one eye (monocular deprivation). In this condition, vision of
patterned stimuli through the sutured eye is impaired. As a consequence,
cortical cells that are normally driven by both eyes become responsive almost
exclusively to the nondeprived eye (Wiesel
and Hubel, 1965
). Notwithstanding 40 years of study of
experience-dependent plasticity of the visual cortex, little is known about
the intracellular mechanisms that convert patterned vision into modification
of cortical circuits. Although recent experiments have demonstrated the
implication in these processes of the three signaling molecules, ERK
(extracellular signal-regulated kinase), protein kinase A (PKA), and CREB
(cAMP response element-binding protein), the lack of knowledge on the
signaling pathways, activated by patterned visual experience in cortical
neurons, precludes the unification of the information in a comprehensive
scheme that designs the cause-effect relationship between visually induced
electrical activity, PKA, ERK, and CRE (cAMP response element)-mediated gene
expression. Several studies have analyzed the interactions between these
factors primarily in the in vitro system; however, the transferal of
notions on signaling gathered in vitro to the behaving animal is not
straightforward. Indeed, activity-dependent signaling is affected critically
by the cellular context, characteristics of the in vitro model, and
method of stimulation. For example, the picture of the relationship between
PKA and CRE-mediated gene expression that emerges from in vitro
studies is very variegated. PKA can act on CREB independently of ERK
(Dash et al., 1991
), or it can
converge on ERK in a positive (Impey et
al., 1998
; Roberson et al.,
1999
) or negative (Grewal et
al., 1999
) way, allowing different partially incompatible
pathways. To unravel the links between these factors in vivo, we
analyzed ERK phosphorylation and CRE-mediated gene expression after patterned
visual stimulation in animals treated with ERK and PKA inhibitors. We found
that ERK phosphorylation in visual cortical neurons represents a molecular
readout of patterned visual stimuli that is necessary for the subsequent
activation of CRE-mediated gene expression. PKA inhibition affected
CRE-mediated gene expression but also reduced experience-dependent ERK
activation, suggesting that its action on CRE-mediated gene expression is
mediated by ERK.
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Materials and Methods
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Animals were used in accordance with protocols approved by the Italian
Minister for Scientific Research. Control animals were exposed to a 12 hr
light/dark cycle, with the light phase beginning at 6:00 A.M. All animals were
killed at the same time of the day, between 8:00 and 9:00 A.M. Manipulations
during dark rearing were performed in complete darkness using infrared
viewers.
Animal treatment. A group of animals was implanted with osmotic
minipumps (0.5 µl/hr; ALZET 1007D; Alzet, Palo Alto, CA) connected to a
cannula (gauge 30; model 1007D; Alzet) via PVC tubing at a location 4 mm
anterior and 3 mm lateral to
for mice, and 5 mm anterior and 4 mm
lateral for rats. Minipumps were filled with U0126 (250 µM;
Promega, Madison, WI), Rp-8-Cl-cAMPS (20 mM; Biolog), or DMSO
(1%).
Immunohistochemistry. A total of 33 Long-Evans Hooded rats and 16
C57BL6/J mice were used to study ERK activation. We used animals inside the
critical period ranging from postnatal day (P) 23-P27. Transcardial perfusion
was executed with ice-cold 4% paraformaldehyde in 0.1 M TBS and 1
mM sodium orthovanadate, pH 7.4 (TBSV). Brains were quickly removed
and cryoprotected in 30% sucrose overnight and then 35 µm coronal sections
were cut on cryostat and processed for phosphorylated ERK (pERK)
immunohistochemistry. Free-floating sections were subjected to a 1 hr block
(TBSV containing 10% BSA and 0.3% Triton X-100) followed by incubation with
pERK antibody (1:1000; Sigma, St. Louis, MO) (in TBSV containing 5% BSA and
0.1% Triton X-100). The reaction was completed with biotinylated secondary
antibody (1:200; Vector Laboratories, Burlingame, CA) followed by
Extravidin-Cy3 (1: 1000; Sigma). For double immunostaining, GFAP (1:500; Dako,
Carpinteria, CA), neuronal-specific nuclear protein (1:500; Chemicon,
Temecula, CA), and GAD 67 (1:500; Chemicon) were added after the end of pERK
immunohistochemistry. The reactions were then completed with Alexa
488-conjugated (1:400 for GFAP and NeuN; Molecular Probes, Eugene, OR) or
fluorescein-conjugated secondary antibodies (1:300 for GAD 67; Jackson
ImmunoResearch, West Grove, PA). Slices were coded, and confocal images
(Olympus FV-300; Olympus Optical, Melville, NY) of at least six representative
fields for each animal were acquired blind. All sections were acquired in
random order in a single session to minimize fluctuation in laser output and
degradation of fluorescence. Images were analyzed through custom-made software
to count positive neurons and measure their fluorescence intensity. The code
was broken only at the end of the analysis process.
X-gal histochemistry. We used 82 CRE-LacZ transgenic mice
(Impey et al., 1996
) as
detailed in Table 1. Colony
founders were bred with wild-type C57BL6/J mice. The transgene was maintained
in heterozygous mice. Genotyping was performed by PCR. Animals were
decapitated, and the brains were rapidly dissected and then submerged in
ice-cold fixative (3% paraformaldehyde, 0.1 M phosphate buffer) for
4 hr on ice. X-gal histochemistry was described previously
(Barth et al., 2000
).
Afterward, slices were stained with neutral red to visualize the cortical
layers. Acquisition of at least five different fields for each animal was
performed at the confocal microscope operating in transmitted light mode using
the red line (647 nm) of an Ar-Kr laser to maximize the contrast of the blue
cells against the red background.
pERK activation in cultured neurons. Cultures were prepared from
rat visual cortex (P1) as described previously
(Pizzorusso et al., 2000
).
After pharmacological treatment, cells were fixed in ice-cold 4%
paraformaldehyde in 0.1 M TBSV and treated for pERK histochemistry
as described above.
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Results
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Experience-dependent activation of ERK and CRE-mediated gene expression in
the visual cortex was measured at different times from the onset of an episode
of visually driven activity. Such a visual stimulation was provided by
exposing the animals to a normal visual environment after a brief period of
complete darkness.
Visual experience causes transient ERK phosphorylation in
vivo
Rats and mice that were within the critical period for ocular dominance
plasticity (P23-P27) were placed in darkness for 3 d. A group of control
animals was anesthetized while still in complete darkness and immediately
perfused. Three other experimental groups were perfused after exposure to
normal visual environment for 5, 15, and 40 min. Immunohistochemistry with an
antibody that binds specifically to pERK was performed on slices from all
experimental groups (Fig. 1).
Visual stimulation caused a strong increase of the pERK signal in the visual
cortex (Fig. 1A), as
shown in representative fields of the superficial layers of the binocular
visual cortex (Fig.
1B). pERK induction was expressed by both an augmented
fluorescence and an increase in the number of positive cells. Quantification
of data for each experimental group is shown in
Figure 1C. In all
experiments, image acquisition and data analysis were performed by an operator
who was blind to the treatment. Visual stimulation induced a rapid increase of
the number of pERK positive cells that was clearly discernible after 5 min of
visual activity and peaked at 15 min [percentage, with respect to the
dark-reared (Dr) control group kept in darkness: 190 ± 21% rat, 5 min;
215 ± 16% rat, 15 min; 228 ± 18% mouse, 15 min). This activation
was transient because 40 min after the beginning of visual stimulation, the
amount of pERK positive profiles returned to the baseline level held by the Dr
group (92 ± 25% rats; 70 ± 20% mice). No significant difference
in the temporal evolution of ERK activation was observed between rats and mice
(Fig. 1C).

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Figure 1. Visual experience induced ERK phosphorylation in the visual cortex after a
3 d period of obscurity during the critical period. A, pERK
immunofluorescence of a transverse section of a mouse brain approximately -3
mm from bregma, 15 min after return to light. Positive cells were concentrated
in the primary (Oc1) and secondary (Oc2) visual cortices. B, Fields
of layers II-III in rats exposed to light for the specified time. C,
pERK-positive cells were counted in fields (0.49 mm2) centered on
the binocular cortex. Open symbols show the average count for each animal and
the average ± SEM for each experimental group. Two-way ANOVA showed no
effect of the species (p = 0.234) and a significant effect of the
time (p < 0.001). The density of pERK-positive cells was
significantly different from Dr at 5 and 15 min (p < 0.05) but not
at 40 min (p > 0.05; Tukey tests). The horizontal bar with an
asterisk indicates that the groups are statistically different, and the open
circle indicates statistical identity. D, Left, Double immunostaining
for pERK (red) and the neuronal marker NeuN (green). In layers II-III, 25% of
the neuronal population was pERK positive after 15 min of visual activity.
Right, pERK-positive neurons had a characteristic pyramidal morphology.
E, Immunostaining for pERK and GAD67 (green) shows that the vast
majority of pERK-positive neurons was excitatory, as quantified in the pie
diagram (three animals). F, Double immunostaining for NeuN and pERK
shows that pERK-positive neurons were distributed primarily in the superficial
layers of the cortex. Counting has been performed on a single optical section
at the confocal microscope, dividing the cortex in bins of 100 µm thick.
Averages of counting on two slices were obtained from three separate rats.
Identical results have been obtained in mice. Scale bars: A, 1 mm;
B, 100 µm; D, 20 µm; E, 40 µm.
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To characterize the populations of pERK-positive cells, we performed double
immunostaining of cortical slices from the group exposed to light for 15 min.
Immunostaining for pERK and astrocytic marker GFAP showed no colocalization
between these antigens (data not shown). The neuronal nature of pERK-positive
cells was confirmed by double immunostaining with the neuronal marker NeuN and
by a clear pyramidal morphology (Fig.
1D). Immunostaining for pERK and GAD 67 revealed that, in
layers II-III, only 6% of the GAD 67-positive profiles are also positive to
pERK (18 of 297) (Fig.
1E). The remaining pERK-positive cells (396) did not
colocalize with GAD 67 and were therefore excitatory. In most cells, the pERK
staining was rather uniformly distributed in the cytoplasm, nucleus, and
proximal segment of primary dendrites (Fig.
1D). However, occasionally, cells with a low nuclear
staining were observed (Fig.
1E), but their number did not correlate with the
treatment and varied from animal to animal, possibly reflecting differences in
the preparation of the tissue for immunohistochemistry.
Neurons that were positive for pERK were unevenly distributed across the
cortical layers. Sections of the primary visual cortex were processed for pERK
and NeuN immunoreactivity, and cells positive for the two stainings were
counted in 100 µm thick bins along the cortical thickness
(Fig. 1F). The
fraction of pERK-positive cells, with respect to the total number of neurons,
peaked in layers II-III, in which
25% of the total neuronal population
was pERK positive, and peaked in layer VI. In contrast, the fraction of
pERK-positive neurons was much lower in layers IV and V
(Fig. 1F).
Anesthesia is a condition that is known to impair many forms of plasticity;
for example, repeated administrations of anesthetic prevent the effect of
monocular deprivation (Rauschecker and
Hahn, 1987
). Because ERK acts as an encoder of visually driven
activity, it is interesting to study the link between visual stimulation and
ERK activation under anesthesia. Urethane anesthesia prevented ERK induction
by light exposure (Fig.
2A). The dose used (1.2 gm/kg) is common for
anesthetizing rodents during physiological recordings and does not suppress
visually driven activity in the cortex. This inhibition is not caused by a
direct effect of the anesthetic on the ERK pathway because urethane,
administered to cultured visual cortical neurons at a concentration (10
mM) similar to the plasma level attained during surgical anesthesia
(Hara and Harris, 2002
), did
not interfere with ERK activation caused by KCl-driven depolarization for 3
min (Fig. 2B,C). These
data demonstrate that ERK is rapidly and transiently activated by patterned
visual experience in neurons of the rodent visual cortex.

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Figure 2. ERK phosphorylation induced by visual activity required wakefulness.
A, Fifteen rats were kept in darkness for 3 d and then nine animals
received an intraperitoneal injection of urethane (n = 5) or saline
before being returned to light for 15 min. The remaining six rats were kept in
darkness and acted as controls. Anesthetized animals had a level of pERK
phosphorylation comparable with the Dr controls (dotted line), whereas
saline-injected animals had normal activation (one-way ANOVA; p <
0.01; post hoc Tukey test; light plus urethane vs Dr, p >
0.05, and vs light, p < 0.05). B, An anesthetic
concentration of urethane did not directly inhibit ERK phosphorylation.
Cultured neurons from the visual cortex were processed for pERK immunostaining
after a pulse of 90 mM KCl in the presence of 10 mM
urethane and under control conditions. Each symbol represents the average
counting obtained from several fields acquired on each coverslip, and filled
symbols indicate mean ± SEM. One-way ANOVA (p < 0.05)
followed by post hoc Student-Newman-Keuls test shows that KCl and KCl
plus urethane did not differ between each other (p > 0.05) and
were statistically different from saline or urethane (p < 0.05).
Urethane, per se, did not affect pERK levels (p > 0.05).
C, Fields showing pERK immunostaining in the indicated conditions.
Scale bar, 50 µm.
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Visual experience induces CRE-mediated gene expression through ERK
activation
Next, we investigated whether ERK activation, induced by visual
stimulation, was followed by CRE-mediated gene expression by using transgenic
mice carrying the LacZ reporter gene under the control of a minimal
promoter driven by five copies of the CRE promoter
(Impey et al., 1996
).
Involvement of ERK in downstream gene transcription was assessed by using
U0126, a selective inhibitor of the ERK kinase MEK (MAP kinase kinase). This
inhibitor, which fully blocks ERK activation after presentation of a variety
of stimuli (Roberson et al.,
1999
; Pizzorusso et al.,
2000
), was infused by osmotic minipumps to the cortex. U0126
infusion prevents the effects of monocular deprivation without altering either
spontaneous or visually driven electrical activity of cortical neurons
(Di Cristo et al., 2001
).
-galactosidase, the product of the LacZ gene, can be assayed
by a histochemical reaction that produces a blue precipitate in cells in which
CRE-mediated gene expression occurred. Because of the heterogeneous expression
of LacZ in animals derived from the same founder
(Impey et al., 1996
;
Pham et al., 1999
;
Barth et al., 2000
), not all
genotyped mice were included in the analysis. We examined brain sections cut
from the occipital pole up to the parietal cortex of each genotyped
CRE-LacZ mouse, and it was assigned to the LacZ-expressing
group if we could detect at least one clearly stained neuron in these
sections. The animals with these characteristics corresponded to
44% of
the total number of processed animals
(Table 1). Mice within the
critical period (P23-P26) were divided in five experimental groups and treated
as follows: the control group was kept in a normal light/dark cycle; a second
group was killed at the end of a 3 d period of dark rearing without any
exposure to light; the third group was dark reared for a similar duration and
then exposed to a normal visual environment for 12 hr; and the fourth and
fifth groups of mice were implanted with an osmotic minipump, delivering
either U0126 (250 µM) or the vehicle solution (1% DMSO). After 3
d of dark rearing, these mice were exposed to light for 12 hr.
Visual stimulation activated CRE-mediated gene expression, as demonstrated
by mere visual inspection of the processed brains
(Fig. 3A). The visual
cortex of the group that returned to light appeared blue against a clear
background. Infusion of U0126 to one hemisphere completely prevented the
expression of LacZ in the treated hemisphere but not in the
contralateral cortex. Figure
3B shows examples of X-gal staining from the different
experimental groups.

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Figure 3. Visual experience after a 3 d period of darkness caused CRE-mediated gene
expression to be dependent on ERK activation. A, Brains that reacted
for X-gal histochemistry show that the visual cortex was densely populated
with positive neurons. Treatment with the ERK kinase inhibitor U0126
completely suppressed CRE-mediated gene expression in the treated but not in
the control hemisphere. B, Fields from superficial layers of the
visual cortex in the indicated conditions. C, Quantification of the
density of positive cells (1 mm2 fields). Dr has significantly less
positive cells than mice kept in a normal visual environment (Nor) (t
test; p < 0.01). Exposure to light significantly increased the
number of positive cells, an effect completely prevented by U0126 but not by
its vehicle (one-way ANOVA; p < 0.01; post hoc Tukey
test; p < 0.05). The Dr plus light (Dr+L) group was composed of
eight mice plus an additional 12 cortices from the control side of the
minipump experiments. D, Two and 12 hr of visual experience equally
activated CRE-mediated gene expression (one-way ANOVA; p < 0.01;
post hoc Tukey test; p < 0.01). E, Thirty
minutes of visual experience followed by 90 min of darkness was sufficient to
trigger CRE-mediated gene expression to a level not significantly different
from visual stimulation for the same period of time (t test;
p = 0.64). Gene expression was not maintained in the absence of
visual experience, because if the 30 min stimulation was followed by 11.5 hr
of darkness, the number of X-gal-positive cells was strongly decreased
(t test; p < 0.01). F, Distribution of
X-gal-positive cells throughout the cortical depth. Scale bars, 50 µm.
Asterisks and circles indicate groups that are statistically different or
identical, respectively. Open symbols indicate data from a single animal;
filled symbols are the averages.
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The density of cells with
-gal activity in the visual cortex of each
animal in the five experimental groups is shown in
Figure 3C. Dark
rearing induced a significant reduction in the number of stained cells,
compared with the control group that was kept in a normal light/dark cycle.
Twelve hours of visual experience after 3 d of darkness caused a marked
induction of LacZ expression, as indicated by a more than threefold
increase in the density of X-gal-positive cells. The induction of CRE-mediated
transcription by visual experience was blocked in cortices infused with U0126.
Normal induction was observed in cortices treated with vehicle.
Recent experiments observe a high density of LacZ-positive cells
in the visual cortex contralateral to the nondeprived eye of monocularly
deprived CRE-LacZ mice (Pham et
al., 1999
). By comparing the number of positive cells in
monocularly deprived mice treated with U0126 in the cortex contralateral to
the nondeprived eye with that of monocularly deprived control mice, we found
that ERK inhibition strongly affected LacZ expression also after
monocular deprivation (U0126, 9.9 ± 2.3 cells per field; control, 113.5
± 36.8 cells per field; t test; p < 0.05). These
data demonstrate that visual experience induces CRE-mediated gene expression
in visual cortical neurons by activating intracellular signaling pathways that
require ERK phosphorylation.
Kinetics of CRE-mediated gene expression
Because the peak of ERK phosphorylation occurred between 5 and 40 min after
the return of Dr animals to normal visual environment, we asked whether we
could detect any sign of CRE-mediated gene expression at a shorter time than
12 hr. A group of Dr mice was killed 2 hr after returning to light. At this
time, the density of X-gal-positive cells was not significantly different from
the density observed after 12 hr of exposure to light. Because the turnover of
-gal is
8 hr (Pham et al.,
1999
), we can infer that in the presence of normal vision,
CRE-mediated gene expression is maintained for at least several hours
(Fig. 3D).
Furthermore, because pERK peaks within 30 min from induction, we wondered
whether exposure to normal visual environment for this duration would be
sufficient to drive gene expression. Two groups of Dr mice received the
following treatments. The first group was returned to light for 30 min and
then returned to complete darkness for an additional 90 min period
(Fig. 3E, 30').
This additional period of dark rearing restricted visual experience to the
time when ERK activation peaked and allowed a subsequent lag period for
-gal synthesis. The second experimental group was treated equally but
was returned to darkness for 11 hr and 30 min
(Fig. 3E, 30'-12
hr) before being killed.
The brief episode of light exposure evoked a level of CRE-mediated gene
expression that, 2 hr after the beginning of treatment (30 min of light plus
90 min of darkness), was identical to the level caused by continuous exposure
to light for the same time. This indicates that 30 min of visual experience
was sufficient to induce CRE-mediated gene expression, which, given the
kinetics of ERK activation, is consistent with a causal role for ERK in
experience-dependent CRE-mediated gene expression. However, the maintenance of
LacZ expression was impaired by the return to darkness. Indeed, after
11.5 hr of obscurity, the density of positive cells returned almost to the Dr
level. Another spatio-temporal aspect of visual experience-dependent gene
expression is reflected by the distribution of positive cells across the
thickness of the visual cortex (Fig.
3F). Measures of cell density (in 100 µm thick bins)
in the function of cortical depth show that 2 hr after return to light, the
distribution of X-gal-positive cells is maximum toward the surface of the
cortex, whereas 10 hr later, more cells are recruited in the deeper cortical
layers. These experiments showed that a 30 min exposure to normal visual
environment is sufficient to activate CRE-mediated gene expression, and that
continuous exposure to normal environment is required for prolonged
expression.
Light-induced ERK activation and CRE-mediated gene expression require
patterned visual stimulation
The effects of visual deprivations are thought to be attributable to the
lack of patterned visual stimulation through the deprived eye(s). The loss of
cortical response to the deprived eye that is typically caused by unilateral
suture of the eyelids is also present when one eye is deprived of patterned
visual stimuli by unilateral blur (Christen
and Mower, 1987
; Movshon et
al., 1987
). At the cellular level, the lack of patterned visual
stimulation likely results in depriving cortical neurons of the high-frequency
trains of action potentials relevant for plasticity. We asked whether the
different patterns of visual stimulation that occur in normal animals and
animals with binocular lid suture can have a molecular readout, in terms of
ERK phosphorylation and CRE-mediated gene expression.
A group of rats received a bilateral eyelid suture before the beginning of
the 3 d period of dark rearing and were exposed to light for 15 min before
being killed. As shown in Figure
4A, binocular deprivation prevented ERK activation by
visual experience. Consistently, 12 hr after the end of dark rearing, X-gal
staining in binocularly deprived CRE-LacZ mice was more than threefold lower
than in nondeprived animals exposed to light for the same period of time
(Fig. 4B).

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Figure 4. Pattern vision was required for ERK phosphorylation and CRE-mediated gene
expression. A, Three rats in the critical period were deprived of
pattern vision by binocular deprivation (BD). After 3 d in darkness, they were
returned to light for 15 min. Two additional rats were returned to light with
open eyelids, and four rats remained in darkness and acted as controls.
PERK-positive cell counting is expressed as a fraction of control. BD
completely suppressed pERK activation after returning to light (Kruskal-Wallis
one-way ANOVA on ranks, p = 0.004; post hoc Dunn's method BD
vs light, p < 0.05, and vs Dr, p > 0.05). B,
A similar protocol of BD and dark rearing was applied to the CRE-LacZ mice
(see Table 1). Cell densities
are shown normalized to the density of control mice that were kept in a normal
light/dark cycle. BD drastically reduced the gene expression 12 hr after
returning to light (one-way ANOVA, p < 0.001; post hoc
Tukey test, BD vs light, p < 0.05, vs Dr and norm, p >
0.05).
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cAMP signaling is required for CRE-mediated gene expression
Inhibition of cAMP signaling by Rp-8-Cl-cAMPS blocks ocular dominance
plasticity induced by monocular deprivation
(Beaver et al., 2001
). In
vitro experiments have shown that PKA can act on CRE-mediated gene
expression through the ERK pathway (Impey
et al., 1998
); we asked whether a similar dependency might be
present in the visual cortex in vivo. A group of CRE-LacZ mice was
implanted with osmotic minipumps containing the cAMP inhibitory analog
Rp-8-Cl-cAMPS (20 mM) before the beginning of the darkness period.
Minipumps filled with the vehicle were used as controls. Animals were
processed after 12 hr of exposure to normal visual environment. We found that
inhibition of cAMP signaling strongly reduced the induction of CRE-mediated
gene expression by visual experience (Fig.
5A). The cAMP pathway also contributed to the visually
induced activation of ERK. Figure
5B shows that cortices implanted with osmotic minipumps
containing Rp-8-Cl-cAMPS showed only 43% of the visually dependent ERK
activation present in cortices treated with vehicle. The inhibition of the
cAMP-PKA pathway did not appear to cause a block of pERK translocation into
the nucleus, because we did not observe any increase in the percentage of
cells with low pERK nuclear staining compared with control (control, 10.3
± 0.9%; Rp-8-Cl-cAMPS, 10.2 ± 2.6%). We conclude that cAMP-PKA
is involved in the signaling process that mediates the action of visual
experience on ERK activation and CRE-mediated gene expression.

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Figure 5. Inhibition of cAMP signaling reduced visually driven CRE-mediated gene
expression and ERK phosphorylation. A, CRE-LacZ mice were implanted
with osmotic minipumps that delivered either vehicle or Rp-8-Cl-cAMPS to the
visual cortex. After 3 d in darkness, the animals were returned to light for
12 hr before being killed and histochemistry. The density of X-gal-positive
cells in Rp-8-Cl-cAMPS-treated cortices was reduced with respect to the
untreated cortex of the same animal (paired t test; p <
0.05) but was increased with respect to Dr (t test; p <
0.05). Vehicle treatment was ineffective (paired t test; p
> 0.05). B, Ratio of pERK-positive cells in the treated vs
untreated cortex of eight rats implanted with osmotic minipumps as above.
After 3 d in darkness, the animals were returned to light for 15 min before
being killed. The density of pERK-positive neurons was clearly reduced by the
infusion of Rp-8-Cl-cAMPS (paired t test; untreated cortex vs treated
cortex of the same animal; p < 0.05), although it was increased
with respect to Dr rats (t test; p < 0.05). The treatment
with vehicle did not affect ERK activation (paired t test; p
> 0.05). Open symbols indicate data from each animal; filled symbols are
the group averages.
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Discussion
|
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In this study, we demonstrate that ERK, cAMP-PKA, and CREB are part of a
single experience-dependent transduction pathway, thus unifying into a single
interpretative framework (Fig.
6), recent results that have demonstrated the necessity of these
factors for ocular dominance plasticity
(Beaver et al., 2001
;
Di Cristo et al., 2001
;
Mower et al., 2002
).
Specifically, activation of the ERK pathway is obligatory for upregulation of
CRE-modulated transcription, because it was completely blocked by infusion
with the inhibitor U0126. ERK activation and CRE-mediated gene expression are
downstream of cAMP signaling, because infusion with the cAMP inhibitory analog
Rp-8-Cl-cAMPS attenuated both processes.
Specificity of visually induced ERK activation
Signaling through the ERK pathway is critical for synaptic plasticity
(Sweatt, 2001
), and it is
essential for the shift of ocular dominance that occurs in the visual cortex
after monocular deprivation (Di Cristo et
al., 2001
). In vitro experiments indicate that the ERK
pathway acts as a sensor, translating electrical activity into varying degrees
of ERK phosphorylation (English and
Sweatt, 1996
; Fields et al.,
1997
; Winder et al.,
1999
) through signaling that is regulated by activity-dependent
modulation of the levels of Ca2+ influx and cAMP
(Bading and Greenberg, 1991
;
Fiore et al., 1993
; Impey et
al., 1998
,
1999
). Similar mechanisms
might also be operating in the brain of the behaving animal, but the
relationship between physiological stimulation and ERK activation has been
little investigated in vivo. We show that visually driven electrical
activity brought about by exposure to normal visual environment after a brief
period of darkness powerfully activated ERK in the visual cortex. ERK
activation displayed remarkable spatial and temporal characteristics.
Specifically, ERK activation was transient, peaking at 15 min after light
exposure and returning to baseline within 40 min, and it was maximal in layers
II-III. Layer V cells and inhibitory interneurons, regardless of their
cortical depth, were poorly responsive. A simple explanation of the spatially
segregated activation of ERK might be the result of low levels of expression
of ERK in the neuronal populations that were pERK negative. This
interpretation seems unlikely, because a wide array of stimuli, including
infusion with BDNF (Han and Holtzman,
2000
), ischemia (Kitagawa et
al., 1999
), and epileptic seizure
(Berkeley et al., 2002
) induces
widespread ERK activation in the cortex. A more attractive interpretation is
that the levels of visually induced ERK phosphorylation are determined by the
responsiveness of each neuronal class to visual stimulation. Indeed, the cells
displaying the strongest visually induced ERK activation, such as layer II-III
pyramids, are also the cells known to respond to visual stimuli with the
highest spike rates (Gray and McCormick,
1996
; Brumberg et al.,
2000
). In contrast, the large pyramidal cells of layer V and
inhibitory interneurons respond to visual stimuli with a lowspiking frequency
(Mason and Larkman, 1990
;
Azouz et al., 1997
) and showed
minimal ERK activation.
The importance of the pattern of incoming electrical activity for ERK
induction is highlighted by the lack of ERK activation in animals exposed to
light with bilateral eyelid suture, a condition in which visually driven
electrical activity lacks the high-frequency spiking that is characteristic of
pattern vision. This finding emphasizes the ability of ERK to respond
specifically to the patterns of electrical activity that are essential for
synapse stabilization during development. The presence of such a specificity
of activation is also suggested by the lack of visually driven ERK activation
in anesthetized rats. Indeed, anesthesia is known to prevent ocular dominance
plasticity (Rauschecker and Hahn,
1987
). Thus, ERK is likely to act as an early mediator of the
action of visual experience on synaptic plasticity, primarily in neurons
located in layers II-III, the layers in which experience-dependent cortical
reorganization is initiated in a number of models of cortical plasticity
(Buonomano and Merzenich, 1998
;
Feldman, 2000
;
Trachtenberg et al., 2000
;
Trachtenberg and Stryker,
2001
).
Visual experience uses the cAMP-PKA system and ERK to regulate
CRE-mediated gene expression
CREB is a calcium-activated transcription factor that regulates the
expression of genes bearing a CRE promoter
(Lonze and Ginty, 2002
). CREB
regulation of gene expression is important for plasticity in various brain
structures (Silva et al.,
1998
). In particular, the introduction of a dominant negative form
of CREB into visual cortical neurons blocks the effects of monocular
deprivation (Mower et al.,
2002
), suggesting that the plastic rearrangements induced by
monocular deprivation requires CREB action. Indeed, Pham et al.
(1999
) showed that
CRE-mediated gene expression is activated in the visual cortex of monocularly
deprived CRE-LacZ mice. However, monocular deprivation does not allow
distinguishing between the direct regulation of CRE-mediated transcription by
visual experience and the activation of CRE-mediated gene expression
associated with the plasticity mechanisms elicited by the competitive
interactions between the two eyes. We showed that visual experience sustained
a basal level of CRE-mediated gene expression, and that 30 min of light
exposure after Dr was sufficient to cause a dramatic episode of CRE-mediated
gene expression that returned to control levels within several hours. As
previously shown for ERK, visual stimulation through the sutured eyelids was
not sufficient to activate CRE-mediated gene expression, underscoring the
importance of patterned visual stimuli for activation of CRE-mediated
transcription.
What are the cellular events that mediate the effects of visual experience
on CRE-mediated gene expression? Studies on cultured neurons have shown that
activation of CREB-mediated transcription by electrical activity relies on the
activation of signaling pathways involving ERK, cAMP-PKA, and CaMKs
(calmodulin-dependent protein kinase)
(West et al., 2001
;
Deisseroth and Tsien, 2002
). A
major finding of this study is that physiological visual stimulation of
cortical neurons in vivo requires ERK for initiation of CRE-mediated
gene expression. Intriguingly, CRE-mediated transcription initially appears in
superficial cortical layers, the same layers in which ERK is activated, but
subsequently also becomes evident in the deep layers. It is conceivable that
the initial episode of ERK phosphorylation might trigger the production and
release of other molecular mediators such as neurotrophins that, in
conjunction with visually driven activity, could be responsible for spreading
and maintaining CRE-mediated gene expression.
Inhibition of cAMP signaling by the analog Rp-8-Cl-cAMPS strongly reduced
visually induced ERK phosphorylation. Increased levels of cAMP can cause ERK
phosphorylation (Martin et al.,
1997
) by two different molecular pathways
(Grewal et al., 1999
). First,
cAMP activates PKA that, in turn, activates the G-protein Rap1
(Vossler et al., 1997
;
York et al., 1998
). Second,
cAMP activates, independently of PKA, the Ras activator CNras-GEF
(Pham et al., 2000
) and the
Rap1 activator Epac/cAMP-GEF (de Rooij et
al., 1998
; Kawasaki et al.,
1998
) with consequent activation of ERK
(Grewal et al., 2000
;
Iida et al., 2001
). Although
PKA is certainly blocked by Rp-8-Cl-cAMPS, nothing is known about the action
of this compound on molecules belonging to the PKA independent pathways. Even
if the use of Rp-8-Cl-cAMPS does not allow a clear discrimination between
these mechanisms, our data demonstrate that the cAMP-PKA system acts upstream
of ERK to transduce visually driven activity.
Our data show that the infusion with Rp-8-Cl-cAMPS strongly attenuated
CRE-mediated gene expression triggered by visual experience, demonstrating
that the integrity of both the ERK and PKA pathways is required for proper
long-lasting activation of CREB-dependent gene expression. The most economical
interpretation of these data is that cAMP-PKA acts only upstream of ERK. In
keeping with this possibility, previous studies showed that the PKA-dependent
activation of ERK mediates the depolarization-induced initiation of the
CRE-mediated gene expression in neuronal cultures
(Impey et al., 1998
). However,
because the requirement for ERK activation could occur at a level downstream
of CREB (Grewal et al., 2000
),
it cannot be excluded that PKA cooperates with ERK-dependent mechanisms at the
level of the transcriptional complex of CRE-bearing genes to regulate gene
expression.
Recent results demonstrate that the mutation of the autophosphorylation
site of
CaMKII causes impairments in ocular dominance plasticity
(Taha et al., 2002
). Because
CaMKII contributes to ERK regulation
(Chen et al., 1998
;
Kim et al., 2003
), it is
conceivable that its actions on ocular dominance plasticity might occur
through ERK. In summary, our results indicate that ERK integrates the action
of various signaling pathways (dependent and independent on PKA) activated by
patterned visual stimuli and funnels this information to the transcription
complex that regulates the expression of genes bearing a CRE promoter.
 |
Footnotes
|
|---|
Received Apr. 2, 2003;
revised May. 12, 2003;
accepted May. 16, 2003.
This work was supported by Ministero dell'Istruzione,
dell'Università e della Ricerca COFIN 2001 and 2002, Consiglio
Nazionale delle Ricerche Project SP-5, Progetto Strategico Neuroscienze
Consiglio Nazionale delle Ricerche, and Fondo per gli Investimenti della
Ricerca Projects RBNE019J7C_004 and RBNE01RZH4_002.
Correspondence should be addressed to Gian Michele Ratto, Institute of
Neuroscience of Consiglio Nazionale delle Ricerche, Via Moruzzi 1, 56100 Pisa,
Italy. E-mail:
gimmi{at}in.pi.cnr.it.
Copyright © 2003 Society for Neuroscience
0270-6474/03/237012-09$15.00/0
* L.C. and E.P. contributed equally to this work. 
 |
References
|
|---|
Azouz R, Gray CM, Nowak LG, McCormick DA (1997)
Physiological properties of inhibitory interneurons in cat striate cortex.
Cereb Cortex 7:
534-545.[Abstract/Free Full Text]
Bading H, Greenberg ME (1991) Stimulation of protein
tyrosine phosphorylation by NMDA receptor activation. Science
253: 912-914.[Abstract/Free Full Text]
Barth AL, McKenna M, Glazewski S, Hill P, Impey S, Storm D, Fox K
(2000) Upregulation of cAMP response element-mediated gene
expression during experience-dependent plasticity in adult neocortex. J
Neurosci 20:
4206-4216.[Abstract/Free Full Text]
Beaver CJ, Ji Q, Fischer QS, Daw NW (2001) Cyclic
AMP-dependent protein kinase mediates ocular dominance shifts in cat visual
cortex. Nat Neurosci 4:
159-163.[Web of Science][Medline]
Berkeley JL, Decker MJ, Levey AI (2002) The role of
muscarinic acetylcholine receptor-mediated activation of extracellular
signal-regulated kinase 1/2 in pilocarpine-induced seizures. J
Neurochem 82:
192-201.[Medline]
Brumberg JC, Nowak LG, McCormick DA (2000) Ionic
mechanisms underlying repetitive high-frequency burst firing in supragranular
cortical neurons. J Neurosci 20:
4829-4843.[Abstract/Free Full Text]
Buonomano DV, Merzenich MM (1998) Cortical plasticity:
from synapses to maps. Annu Rev Neurosci
21: 149-186.[Web of Science][Medline]
Chen HJ, Rojas-Soto M, Oguni A, Kennedy MB (1998) A
synaptic Ras-GTPase activating protein (p135 SynGAP) inhibited by CaM kinase
II. Neuron 20:
895-904.[Web of Science][Medline]
Christen WG, Mower GD (1987) Effects of monocular
occlusion and diffusion on visual system development in the cat. Brain
Res 415:
233-241.[Web of Science][Medline]
Dash PK, Karl KA, Colicos MA, Prywes R, Kandel ER
(1991) cAMP response element-binding protein is activated by
Ca2+/calmodulin- as well as cAMP-dependent protein kinase.
Proc Natl Acad Sci USA 88:
5061-5065.[Abstract/Free Full Text]
de Rooij J, Zwartkruis FJ, Verheijen MH, Cool RH, Nijman SM,
Wittinghofer A, Bos JL (1998) Epac is a Rap1
guanine-nucleotide-exchange factor directly activated by cyclic AMP.
Nature 396:
474-477.[Medline]
Deisseroth K, Tsien RW (2002) Dynamic
multiphosphorylation passwords for activity-dependent gene expression.
Neuron 34:
179-182.[Web of Science][Medline]
Di Cristo G, Berardi N, Cancedda L, Pizzorusso T, Putignano E,
Ratto GM, Maffei L (2001) Requirement of ERK activation for
visual cortical plasticity. Science 292:
2337-2340.[Abstract/Free Full Text]
English JD, Sweatt JD (1996) Activation of p42
mitogen-activated protein kinase in hippocampal long term potentiation.
J Biol Chem 271:
24329-24332.[Abstract/Free Full Text]
Feldman DE (2000) Timing-based LTP and LTD at vertical
inputs to layer II/III pyramidal cells in rat barrel cortex.
Neuron 27:
45-56.[Web of Science][Medline]
Fields RD, Eshete F, Stevens B, Itoh K (1997) Action
potential-dependent regulation of gene expression: temporal specificity in
Ca2+, cAMP-responsive element binding proteins, and
mitogen-activated protein kinase signaling. J Neurosci
17: 7252-7266.[Abstract/Free Full Text]
Fiore RS, Murphy TH, Sanghera JS, Pelech SL, Baraban JM
(1993) Activation of p42 mitogen-activated protein kinase by
glutamate receptor stimulation in rat primary cortical cultures. J
Neurochem 61:
1626-1633.[Web of Science][Medline]
Ginty DD, Bonni A, Greenberg ME (1994) Nerve growth
factor activates a Ras-dependent protein kinase that stimulates c-fos
transcription via phosphorylation of CREB. Cell
77: 713-725.[Web of Science][Medline]
Gray CM, McCormick DA (1996) Chattering cells:
superficial pyramidal neurons contributing to the generation of synchronous
oscillations in the visual cortex. Science
274: 109-113.[Abstract/Free Full Text]
Grewal SS, York RD, Stork PJ (1999)
Extracellular-signal-regulated kinase signalling in neurons. Curr Opin
Neurobiol 9:
544-553.[Web of Science][Medline]
Grewal SS, Fass DM, Yao H, Ellig CL, Goodman RH, Stork PJ
(2000) Calcium and cAMP signals differentially regulate
cAMP-responsive element-binding protein function via a Rap1-extracellular
signal-regulated kinase pathway. J Biol Chem
275: 34433-34441.[Abstract/Free Full Text]
Han BH, Holtzman DM (2000) BDNF protects the neonatal
brain from hypoxic-ischemic injury in vivo via the ERK pathway. J
Neurosci 20:
5775-5781.[Abstract/Free Full Text]
Hara K, Harris RA (2002) The anesthetic mechanism of
urethane: the effects on neurotransmitter-gated ion channels. Anesth
Analg 94:
313-318.[Abstract/Free Full Text]
Iida N, Namikawa K, Kiyama H, Ueno H, Nakamura S, Hattori S
(2001) Requirement of Ras for the activation of mitogen-activated
protein kinase by calcium influx, cAMP, and neurotrophin in hippocampal
neurons. J Neurosci 21:
6459-6466.[Abstract/Free Full Text]
Impey S, Mark M, Villacres EC, Poser S, Chavkin C, Storm DR
(1996) Induction of CRE-mediated gene expression by stimuli that
generate long-lasting LTP in area CA1 of the hippocampus.
Neuron 16:
973-982.[Web of Science][Medline]
Impey S, Obrietan K, Wong ST, Poser S, Yano S, Wayman G, Deloulme
JC, Chan G, Storm DR (1998) Cross talk between ERK and PKA is
required for Ca2+ stimulation of CREB-dependent transcription and
ERK nuclear translocation. Neuron 21:
869-883.[Web of Science][Medline]
Impey S, Obrietan K, Storm DR (1999) Making new
connections: role of ERK/MAP kinase signaling in neuronal plasticity.
Neuron 23:
11-14.[Web of Science][Medline]
Kawasaki H, Springett GM, Mochizuki N, Toki S, Nakaya M, Matsuda M,
Housman DE, Graybiel AM (1998) A family of cAMP-binding proteins
that directly activate Rap1. Science
282: 2275-2279.[Abstract/Free Full Text]
Kim JH, Lee HK, Takamiya K, Huganir RL (2003) The role
of synaptic GTPase-activating protein in neuronal development and synaptic
plasticity. J Neurosci 23:
1119-1124.[Abstract/Free Full Text]
Kitagawa H, Warita H, Sasaki C, Zhang WR, Sakai K, Shiro Y,
Mitsumoto Y, Mori T, Abe K (1999) Immunoreactive Akt, PI3-K and
ERK protein kinase expression in ischemic rat brain. Neurosci
Lett 274:
45-48.[Web of Science][Medline]
Lonze BE, Ginty DD (2002) Function and regulation of
CREB family transcription factors in the nervous system. Neuron
35: 605-623.[Web of Science][Medline]
Martin KC, Michael D, Rose JC, Barad M, Casadio A, Zhu H, Kandel ER
(1997) MAP kinase translocates into the nucleus of the
presynaptic cell and is required for long-term facilitation in
Aplysia. Neuron 18:
899-912.[Web of Science][Medline]
Mason A, Larkman A (1990) Correlations between
morphology and electrophysiology of pyramidal neurons in slices of rat visual
cortex. II. Electrophysiology. J Neurosci
10: 1415-1428.[Abstract]
Movshon JA, Eggers HM, Gizzi MS, Hendrickson AE, Kiorpes L, Boothe
RG (1987) Effects of early unilateral blur on the macaque's
visual system. III. Physiological observations. J Neurosci
7: 1340-1351.[Abstract]
Mower AF, Liao DS, Nestler EJ, Neve RL, Ramoa AS
(2002) cAMP/Ca2+ response element-binding protein
function is essential for ocular dominance plasticity. J
Neurosci 22:
2237-2245.[Abstract/Free Full Text]
Pham N, Cheglakov I, Koch CA, de Hoog CL, Moran MF, Rotin D
(2000) The guanine nucleotide exchange factor CNrasGEF activates
ras in response to cAMP and cGMP. Curr Biol
10: 555-558.[Web of Science][Medline]
Pham TA, Impey S, Storm DR, Stryker MP (1999)
CRE-mediated gene transcription in neocortical neuronal plasticity during the
developmental critical period. Neuron
22: 63-72.[Web of Science][Medline]
Pizzorusso T, Ratto GM, Putignano E, Maffei L (2000)
Brain-derived neurotrophic factor causes cAMP response element-binding protein
phosphorylation in absence of calcium increases in slices and cultured neurons
from rat visual cortex. J Neurosci 20:
2809-2816.[Abstract/Free Full Text]
Rauschecker JP, Hahn S (1987) Ketamine-xylazine
anaesthesia blocks consolidation of ocular dominance changes in kitten visual
cortex. Nature 326:
183-185.[Medline]
Roberson ED, English JD, Adams JP, Selcher JC, Kondratick C, Sweatt
JD (1999) The mitogen-activated protein kinase cascade couples
PKA and PKC to cAMP response element binding protein phosphorylation in area
CA1 of hippocampus. J Neurosci 19:
4337-4348.[Abstract/Free Full Text]
Silva AJ, Kogan JH, Frankland PW, Kida S (1998) CREB
and memory. Annu Rev Neurosci 21:
127-148.[Web of Science][Medline]
Sweatt JD (2001) The neuronal MAP kinase cascade: a
biochemical signal integration system subserving synaptic plasticity and
memory. J Neurochem 76:
1-10.[Web of Science][Medline]
Taha S, Hanover JL, Silva AJ, Stryker MP (2002)
Autophosphorylation of alphaCaMKII is required for ocular dominance
plasticity. Neuron 36:
483-491.[Web of Science][Medline]
Trachtenberg JT, Stryker MP (2001) Rapid anatomical
plasticity of horizontal connections in the developing visual cortex. J
Neurosci 21:
3476-3482.[Abstract/Free Full Text]
Trachtenberg JT, Trepel C, Stryker MP (2000) Rapid
extragranular plasticity in the absence of thalamocortical plasticity in the
developing primary visual cortex. Science
287: 2029-2032.[Abstract/Free Full Text]
Vossler MR, Yao H, York RD, Pan MG, Rim CS, Stork PJ
(1997) cAMP activates MAP kinase and Elk-1 through a B-Raf- and
Rap1-dependent pathway. Cell 89:
73-82.[Web of Science][Medline]
West AE, Chen WG, Dalva MB, Dolmetsch RE, Kornhauser JM, Shaywitz
AJ, Takasu MA, Tao X, Greenberg ME (2001) Calcium regulation of
neuronal gene expression. Proc Natl Acad Sci USA
98: 11024-11031.[Abstract/Free Full Text]
Wiesel TN, Hubel DH (1965) Comparison of the effects
of unilateral and bilateral eye closure on cortical unit responses in kittens.
J Neurophysiol 28:
1029-1040.[Free Full Text]
Winder DG, Martin KC, Muzzio IA, Rohrer D, Chruscinski A, Kobilka
B, Kandel ER (1999) ERK plays a regulatory role in induction of
LTP by theta frequency stimulation and its modulation by beta-adrenergic
receptors. Neuron 24:
715-726.[Web of Science][Medline]
York RD, Yao H, Dillon T, Ellig CL, Eckert SP, McCleskey EW, Stork
PJ (1998) Rap1 mediates sustained MAP kinase activation induced
by nerve growth factor. Nature 392:
622-626.[Medline]
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