Repeated Stress Induces Dendritic Spine
Loss in the Rat Medial Prefrontal Cortex
Jason J. Radley1,2, Anne B. Rocher1, Melinda Miller1,3,
William G.M. Janssen1, Conor Liston3, Patrick R. Hof1,2,
Bruce S. McEwen2,3and John H. Morrison1,2
1Department of Neuroscience, Mount Sinai School of
Medicine, New York, NY 10029, USA,2NIMH Center
for Fear and Anxiety, New York, NY, 10003, USA and
3Laboratory of Neuroendocrinology, Rockefeller
University, New York, NY 10021, USA
The prefrontal cortex (PFC) plays an important role in higher
cognitive processes, and in the regulation of stress-induced
hypothalamic--pituitary--adrenal (HPA) activity. Here we examined
the effect of repeated restraint stress on dendritic spine number in
the medial PFC. Rats were perfused after receiving 21 days of daily
restraint stress, and intracellular iontophoretic injections of Lucifer
Yellow were carried out in layer II/III pyramidal neurons in the
anterior cingulate and prelimbic cortices. We found that stress
results in a significant (16%) decrease in apical dendritic spine
density in medial PFC pyramidal neurons, and confirmed a previous
observation that total apical dendritic length is reduced by 20% in
the same neurons. We estimate that nearly one-third of all
axospinous synapses on apical dendrites of pyramidal neurons in
medial PFC are lost following repeated stress. A decrease in medial
PFC dendritic spines may not only be indicative of a decrease in the
total population of axospinous synapses, but may impair these
neurons’ capacity for biochemical compartmentalization and plas-
ticity in which dendritic spines play a major role. Dendritic atrophy
and spine loss may be important cellular features of stress-related
psychiatric disorders where the PFC is functionally impaired.
Keywords: axospinous synapse, cell loading, dendritic spine,
post-traumatic stress disorder, prefrontal, stress
There is a clinically well established relationship between
stressful life events and mental illnesses (Sapolsky, 1996; Heim
et al., 1997). Following exposure to a stressor, hypothalamic--
pituitary--adrenal (HPA) activity affects brain function to pro-
duce adaptive responses for the organism (McEwen, 1998).
However, in instances where behavioral stress is extreme or
manner. Whereas such research has focused on the hippocam-
pus both as a regulator of the response to stress and as a target
of its effects (Jacobson and Sapolsky, 1991; McEwen, 2001),
recent evidence suggests that the PFC also plays a role in these
The medial PFC plays an important role in the integration of
cognitive and emotionally relevant information, and has been
implicated in the modulation of attention through functional
imaging studies in humans (Bush et al., 1998, 2000; MacDonald
et al., 2000; Kerns et al., 2004). The medial PFC also contains
high levels of glucocorticoid receptors (Ahima and Harlan,
1991; Sanchez et al., 2000), and regulates HPA activity under
behaviorally stressful conditions (Diorio et al., 1993). Collec-
tively, these functions underscore the role for the medial PFC
in the evaluation of contextually relevant stimuli in shaping
responses to salient environmental events during stressful
is associated with post-traumatic stress disorder (PTSD; Rauch
et al., 2003) and depression (Drevets et al., 1997). Moreover,
medial PFC lesions result in the disinhibition of some affective
behaviors and attentional impairments in rodent and primate
models (Morgan and LeDoux, 1995; Dias et al., 1996; Birrell and
Brown, 2000). Despite this recent convergence of evidence
concerning the medial PFC and stress-related mental illnesses,
little is known of its cellular morphologic changes.
In a previous report, rats subjected to repeated restraint
stress revealed a 20% decrease in total apical dendritic length of
layer II/III pyramidal neurons of the medial PFC (Radley et al.,
2004). In the present study we investigated the effect of stress
on dendritic spine density in the medial PFC, and correlated
changes in spine density with dendritic length to estimate the
overall change in axospinous synaptic input into this region. To
this end, we performed intracellular iontophoretic injections of
Lucifer Yellow in layer II/III pyramidal neurons in the medial
PFC following 21 days of repeated restraint stress, and estimated
spine densities on deconvolved image stacks, acquired on
a confocal laser scanning microscope, of systematic--randomly
chosen dendritic segments at progressive radial distances from
the neuronal soma.
Materials and Methods
Male Sprague--Dawley rats (Charles River, Wilmington, MA), weighing
250--280 g at the onset of the experiment, were housed in groups of
2--3 per cage. Animals had unlimited access to food and water except
during restraint sessions. Control rats (n = 8) were housed in
a separate room from stressed rats (n = 8), and were maintained on
a 12 h light/dark schedule (lights on from 07:00 to 19:00 h). All rats
were handled for 7 days prior to the beginning of restraint. Rats were
restrained for 6 h daily (10:00--16:00 h) for 21 days with wire mesh
restrainers and then returned to their home cages throughout the
restraining period. To ensure that the analysis was done blind, each
animal was coded by an independent observer prior to the perfusion,
and the code was not broken until the analysis was completed. On day
22, rats were given a euthanizing dose of 30% chloral hydrate and
transcardially perfused with cold 1% paraformaldehyde in phosphate-
buffered saline (PBS; pH 7.4), followed by fixation with cold 4%
paraformaldehyde with 0.125% glutaraldehyde in PBS. Brains were
dissected and postfixed for 2 h in the same fixative. All procedures
were conducted in accordance with the National Institutes of Health
Guide for the Care and Use of Laboratory Animals and were approved
by the Rockefeller University and Mount Sinai School of Medicine
Institutional Animal Care and Use Committees.
Coronal sections (250 lm thick) were mounted on nitrocellulose
filter paper and immersed in PBS. The lamination patterns of the medial
PFC subregions anterior cingulate cortex and prelimbic area (ACC and
PL, respectively) were identified by briefly exposing sections to a
fluorescent nucleic acid stain (4,6-diamidino-2-phenylindole; Sigma,
St Louis, MO). Neurons in layer II/III were loaded with intracellular
injections of 5% Lucifer Yellow (Molecular Probes, Eugene, OR) under
a DC current of 1--6 nA for 10 min. Sections were coverslipped with
Published by Oxford University Press 2005.
Cerebral Cortex March 2006;16:313--320
Advance Access publication May 18, 2005
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PermaFluor and reconstructed in 3-D at 3400 using a Zeiss Axiophot 2
microscope and Neurolucida software (MicroBrightField, Williston, VT).
Entry into the analysis required that neurons: (i) lie within layer II/III
and within the boundary of ACC and PL; (ii) exhibit complete filling of
the dendritic tree, evidenced by well-defined endings; and (iii) display
intact primary,secondaryand tertiary branches. The boundariesfor ACC
and PL were carefully delineated in order to avoid inadvertently
including filled neurons that were dorsal and ventral to the regions of
interest. ACC was differentiated from the more dorsolateral frontal area
2 (Fr2) by its more tightly laminated and dense layer II/III and a less
laminated and thin layer V (see Krettek and Price, 1977; Paxinos and
Watson, 1986). Since this distinction was not always evident to the
experimenter during cell filling, neurons near the dorsal boundary of
ACC and Fr2 were often excluded from the analysis. At the ventral
aspect, the boundary of the PL and infralimbic (IL) cortices was more
readily distinguished by the transition from a well-defined layer II/III
in PL to a lack of any such clear lamination pattern exhibited in IL.
Neurons that ended up in the analysis typically had perikarya that were
located 10--60 lm below the surface of the section, and had an apical
dendritic field that projected parallel, or ventral to, the top of the
The method for sampling dendritic branches for spine density (i.e.,
spines per lm dendritic length) was designed to minimize any possible
bias. The selection of a particular branch for optical imaging had to
satisfy the following criteria: (i) the entire segment had to fall within
a depth of 50 lm, owing to the vertical limit of the laser scanning
microscope’s imaging capacity; (ii) they had to be either parallel or at
acute angles to the coronal surface of the section; and (iii) they did not
show overlap with other branches that would obscure visualization of
spines. For apical dendrites, segments were selected with a systematic
random design at 50, 100, 150 and 200 lm from the soma for digital
reconstruction. A fifth category of segments of large diameter (corre-
sponding to diametersof >3 lm) were sampled at radialdistancesof100
and 150 lm, since initial observations revealedthat these main dendrites
had a substantially higher number of spines per unit length than each of
the other branch types analyzed. In some instances, sites were sampled
redundantly. For basal dendrites, segments were randomly selected at
50 and 100 lm for digital reconstruction. Samples were collected at
150 lm wherever possible; however, there was not enough material to
justify any statistical comparison. In total, ~500 reconstructed dendritic
segments (320 apical, 180 basal) were analyzed (9 segments/neuron,
5 neurons/animal, n = 8/group).
Dendritic segment and spine reconstructions were performed using
a Zeiss 410 confocal laser scanning microscope using a 488 nm
excitation wavelength, at a magnification of 31000 and a zoom of 35.
After gain and offset settings were optimized, segments were digitally
reconstructed at 0.1 lm increments, throughout the entire z-axis of the
branch. The digitized optical stacks were then deconvolved with
AutoDeblur (AutoQuant, Troy, NY) and analyzed using Neurolucida
software. The analysis for spine number and length was carried out by
controlling manually the plane of focus for z-step increments and
marking spines as they appeared. After the total spine numbers for each
branch were recorded, the length of the branch was traced, and
dendriticlength and spine numbers were obtained using NeuroExplorer
software (MicroBrightField). Values for each branch segment were
expressed as spine number/lm. Under the present analysis, the average
dendritic segment was ~30 lm in length.
Dendritic arbor measurements have been previously described in
greater detail (Radley et al., 2004) and were expressed here only in
terms of total dendritic length. Analyses for basal dendrites were done
for each individual dendrite, instead of summing them together for
analysis on a cell-by-cell basis, due to truncation of at least 1--2 primary
branches that occurred with nearly every neuron examined. For spine
densities, individual site and total averages were obtained for each
neuron, and then by averaging the number of neurons within each
animal. Group averages were obtained fromcell averages (~9 segments /
neuron, n = 5 neurons/animal) within each animal. Statistical testing was
performed usinga two-tailed t test (significance level a = 0.05)wherever
appropriate. The grouped data for radial distances were compared using
repeated ANOVA with post-hoc, pairwise comparisons (Bonferroni).
Values were represented as the mean ± SEM.
After 21 days of repeated restraint stress, rats from both groups
were indistinguishable from each other; they appeared well-
groomed and healthy. Given the numerous reports that have
demonstrated that this repeated restraint stress model produces
significant increases in plasma corticosterone and modest
increases in adrenal weights compared with unstressed rats
(Watanabe et al., 1992; Magarin ˜ os and McEwen, 1995), these
assays were not performed in the present study. However, as
also previously demonstrated (Watanabe et al., 1992) stressed
rats (360± 9 g) weighed ~15% less than the controls (412± 7 g)
at the end of 21 days of restraint (P = 0.004). This difference was
characterized by a slower weight gain during the first 7 days of
restraint compared to control animals, followed by an equiva-
lent rate of gain over the remaining duration of the 3 week
Since one of the distinguishing cytoarchitectural features of
II/III, pyramidal neurons that were loaded in this region were
readily identified from neurons inadvertently loaded in Fr2 or IL
(see plate 9 in Paxinos and Watson, 1986). A few loaded neurons
in Fr2 tended to have a more ‘classical’ pyramidal neuron shape
with a long-shaft apical dendrite extending parallel to the
coronal plane (these cells were not included in the analysis),
whereas apical dendrites of ACC and PL neurons exhibited
greater morphological diversity (Figs 1 and 2). The longest shaft
apical dendrite observed was 100 lm; the shortest was ~5 lm,
and the rest varied continuously within this range. Medial PFC
apical dendrites tended to project at angles that were not
necessarily parallel tothecoronalplane ororthogonaltothe pial
surface (Figs 1 and 2). This was observed in several neurons
examined within single animals, ruling out the possibility that
subtle variations in sectioning through the coronal plane could
account for suchdifferences. Nonetheless, apical dendrites in all
neurons examined extended through layer I, and the total
dendritic lengths and branch numbers were observed to be
comparable within each animal. The variability of total branch
5 and 10% (see below), regardless of whether they were long- or
short-shaft primary apical dendrites. Therefore, it seemed
appropriate to perform one analysis for all pyramidal neurons
according to apical dendritic morphology.
Similar to recent findings from our group (Radley etal., 2004),
we found a 20% decrease in overall apical dendritic length
(Stress, 1839 ± 91 lm; Control, 2325 ± 131 lm; P = 0.025)
following 21 days of restraint stress. Since these effects were
uniformly present in both the ACC and PL, no further attempts
were made to consider them as separate entities in the
quantitative analysis. No effect was observed in basal dendrites
(Stress, 468 ± 39 lm; Control, 499 ± 52 lm; P = 0.6).
Dendritic spines were sparse at the proximal aspect of the
trunk of primary apical and basal dendritic arbors, becoming
more evident within 20--70 lm of the soma. Within 20--70 lm,
spines became more evident, and this varied according to the
dendritic morphology, over the continuum of short- to long-
shaft apical dendrites. For this reason, dendritic segments that
were sampled at radial distances of 50 lm were small diameter
second or third order branches, which bifurcated from the
primary trunk and coursed back toward the vicinity of the soma.
By 100 lm from the soma, spine densities were maximally
elevated on large diameter dendritic segments, and seemed to
Stress Induces Spine Loss in Rat Medial PFC
Radley et al.
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decrease at larger radial distances from the soma. No correlation
was observed between spine density and ascending branch
order (data not shown).
Most striking was the overall high density of spines (Figs 2
and 3), averaging 3.0--3.8 spines/lm on both apical and basal
dendrites. On large diameter primary dendrites that were
animals, the overall spine density was significantly less in basal
(3.0 ± 0.1 spines/lm) compared to apical (3.7 ± 0.2 spines/lm)
dendrites (P = 0.021). Spine density on apical dendritic arbors
seemed to vary relative to the distance of the dendritic arbor
from the soma, and not in terms of ascending branch order. This
observation is consistent with previous reports suggesting that
spine density in apical dendrites of neocortical pyramidal
neurons peaks around 70--100 lm from the soma, and decreases
thereafter (Peters and Jones, 1984).
Twenty-one days of repeated daily restraint stress produced
an overall (16%) decrease in the apical dendritic spine density
[Stress, 3.1 ± 0.1 spines/lm; Control, 3.7 ± 0.2 spines/lm;
F(1,12) = 6.0, P = 0.03; Fig. 4A], an overall effect for radial
micrometer distance from soma [F(4,48) = 23.1, P < 0.0001],
and no interaction between density and distance [F(4,48) = 1.6,
P = 0.18]. When separate analyses were carried out for each
site (Fig. 4B), chronic stress produced a significant decrease in
spine density at 200 lm from somata (Stress, 2.6 ± 0.1 spines/
lm; Control, 3.0 ± 0.1 spines/lm; P < 0.001) and on large
diameter dendrites (Stress, 3.9 ± 0.3 spines/lm; Control, 4.8 ± 0.2
spines/lm; P = 0.046). Moreover, large diameter dendrites
were significantly more spiny (P < 0.01) than segments at
other radial micrometer distances from soma. No regional
differences were observed in spine densities between the
ACC and PL pyramidal neurons. Basal dendritic spine density
was unaffected following repeated restraint stress (Fig. 4C,D).
The main finding of this study is a significant overall reduction in
apical dendritic spine density in pyramidal neurons of the
medial PFC after exposure to repeated restraint stress. This
effect was most pronounced at distances of 200 lm from somata
and on large diameter dendrites. We also confirmed that
chronic stress produces a 20% decrease in total apical dendritic
length and branch number. When these two observations are
taken together, we estimate that repeated stress produces
a 33% reduction in the total number of axospinous synapses
on apical dendrites of pyramidal neurons in the medial PFC.
Finally, we did not observe any change in basal dendritic length
or spine density, suggesting that the effect of repeated stress in
the medial PFC is highly selective.
Figure 1. 3-D reconstructed neurons in rat medial PFC. Representative layer II/III pyramidal neurons from the medial PFC of control (A) and restraint stress animals (B). Apical
dendrites extend to the right side of the diagram, toward the pial surface (not shown).
Cerebral Cortex March 2006, V 16 N 3 315
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One issue surrounding the cell loading technique in lightly
fixed tissue is whether dendrites and spines may fail to fill in
stressed animals due to technical reasons. There is a conver-
gence of evidence utilizing multiple techniques that chronic
stress induces morphological and functional changes in cortico-
limbic structures (Watanabe et al., 1992; Vyas et al., 2002, 2003;
McEwen and Chattarji, 2004; Radley et al., 2004), and one other
group has shown using a different technique that repeated
restraint stress results in apical dendritic retraction of medial
PFC neurons (Cook and Wellman, 2004). In our data collection,
we did not encounter any problems in the cell filling procedure
that suggested more difficulty filling neurons from stressed
animals, and observed clear endings of dendrites that were
characterized by their tapering to a well-defined tip. Finally,
Lucifer Yellow is a dye of low molecular weight, making it
a suitable choice for the filling of spines and dendrites for
confocal microscopic analysis.
The overall high spine density observed in the medial PFC in
both control and stressed animals provides further evidence
that cell loading is appropriate for the examination of dendritic
morphology and spine density. Our estimates of 3.0--3.8 spines/
lm on medial PFC pyramidal neurons is in the range of
axospinous synapse density derived from 3-D reconstructions
in electron microscopic studies in other cortical brain regions
(Harris et al., 1992; Megı´as et al., 2001), and substantially higher
than spine density estimates in the medial PFC using the Golgi
technique (Seib and Wellman, 2003; Silva-Gomez et al., 2003).
The disparity in our results from the latter two studies is
attributable to differences in methodological and analytic
approaches for estimating spine densities. Our analyses of spine
density were performed on high resolution 3-D deconvolved
datasets and thus included all spines rather than only those
orthogonal and lateral to the dendritic shaft, and involved the
systematic sampling of nine sites per neuron, computing
densities from segments that were ~30 lm in length. Finally,
high spine densities in medial PFC have been reported
elsewhere, and may represent a specialized anatomical feature
of these neurons. In the rhesus monkey, the PFC has a spine
density comparable to our observations in the rodent, at ~3
spines/lm, and PFC spine densities are also much higher than
in other neocortical regions (Elston et al., 2001).
One of the interesting aspects of the pyramidal cell
population examined was that their quantitative features
seemed to be conserved regardless of their morphologic
diversity. For example, the random inclusion of 40 different
neurons per experimental group, comprising long- and short-
shaft apical dendrites, resulted in small overall variations in
total apical dendritic lengths and branch endings (see Radley
et al., 2004). One possible explanation for these similarities is
that the location of all of the neurons examined was between
250--300 lm from the pial surface, in the more superficial
aspect of layer II/III. Since medial PFC pyramidal neurons in
layers II/III and V extend to layer I, layer V and deep layer
II/III neurons might be expected to have larger dendritic
arbors than neurons located more superficially in layer II. The
distance of a pyramidal neuron from the pial surface may be
a more important predictor of its quantitative features, at least
for apical dendrites, such as total branch number and length.
Another interesting aspect of this dendritic analysis is that the
total apical dendritic lengths were nearly double what has
Figure 2. Digital reconstruction of Lucifer Yellow-filled neurons in medial PFC. This layer II/III pyramidal neuron was loaded on the ACC/PL border from a control rat, and
imaged on a Zeiss 410 confocal laser-scanning microscope at 3 160. In order to depict the entire neuron in one field, the image was merged from five separate confocal
digital stacks (z-step 5 0.1lm) that were deconvolved using AutoQuant and aligned in the x--y--z planes using the VIAS software (Rodriguez et al., 2003). Concentric circles
were drawn to select dendritic segments at radial increments of 50 lm relative to the soma for the spine density analysis. The apical dendrite is indicated by an arrow. The
arrowheads point to the axon.
Stress Induces Spine Loss in Rat Medial PFC
Radley et al.
by guest on June 7, 2013
been previously reported (Radley et al., 2004). This difference
results from adopting a more stringent set of criteria for the
inclusion of apical dendritic arbors in the present analysis.
Whereas, in the previous study, apical dendritic arbors were
included that occasionally had truncated tertiary branches,
arbors were only included in this analysis if they had complete
secondary and tertiary branches.
Another aspect of these results is whether stress-induced
changes in dendritic spine density correlate with a net change
in overall excitatory synapses. Because 95% of all cortical
excitatory synapses are made onto pyramidal neurons, with
each spine head receiving one excitatory terminal (Spacek and
Hartmann, 1983; Harris and Stevens, 1989; Peters et al., 1991),
changes in spine number may therefore represent an index of
total excitatory input. One alternative is that although re-
peated stress might decrease the number of axospinous
synapses, it may be compensated for by an increase in
excitatory dendritic shaft synapses. While we cannot rule
out this possibility, it is noteworthy that electron microscopy
studies have shown that repeated restraint and repeated
variable stress both result in a decrease in the density of
excitatory synapses in hippocampal pyramidal neurons (Sousa
et al., 2000; Sandi et al., 2003). The similarity in effects of
stress on hippocampus and medial PFC supports the interpre-
tation that excitatory synapse loss, through the retraction of
apical dendrites and decrease in spine number, may be
a compensatory reaction to elevated excitatory amino acid
levels in the medial PFC. In this regard, it has been demon-
strated that repeated stress is associated with a sustained
increase in glutamate neurotransmission in the medial PFC
(Moghaddam, 2002). Moreover, dendritic spine loss has been
demonstrated to result from excitatoxic injury (Jiang et al.,
Dendritic spines play a role in the sequestration of Ca2+,
because the spine neck prevents its exchange between the
spine head and dendrite (Nimchinsky et al., 2002). This barrier
to Ca2+exchange, along with the compartmentalization of
molecules associated with postsynaptic density and spine
apparatus, is important for the regulation of synaptic transmission.
Ca2+sequestration by spines also may be neuroprotective,
preventing excitotoxicity to the dendrite and neuron by
restricting excessive influxes of Ca2+within the synaptic region
(Segal, 1995). In the present context, repeated stress may
result in morphologic changes in dendritic spines in the medial
PFC that would render them more resistant to excitotoxity
from excessive Ca2+influx and a reduction in spine number
Figure 3. Digital reconstructions of dendritic segments. Examples of randomly selected dendritic segments are shown in control (A) and stressed (B) rats. Numbers shown for
each segment represent spines/lm for each branch analyzed. Scale bar 5 10 lm.
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would also help to ameliorate excitotoxic effects from pro-
longed glutamate release. In this regard, it is worth noting
that changes in dendritic spine morphology and number are
associated with a number of neurological disorders (Fiala et al.,
2002; Nimchinsky et al., 2002)
A decrease in axospinous synaptic input to the medial PFC by
33% may have a significant impact on the functional properties
of this region. A magnitude of this effect is comparable to age-
related alterations in spine number of the PFC (Duan et al.,
2003), and estrogen depletion (Tang et al., 2004). However, it
should be noted that the stress-induced decrease in dendritic
spine number may not necessarily result in a permanent or
irreversible loss of synapses. For example, dendritic atrophy that
occurs in hippocampal neurons following repeated stress is
reversible (Conrad et al., 1999), and dendritic spine density in
CA1 fluctuates across the estrous cycle (Woolley et al., 1990).
One potential neuroantomical substrate relevant to PTSD is
the medial PFC-amygdala circuit (Newport and Nemeroff,
2000). Ultrastructural evidence reveals that the basolateral
amygdala makes synapses onto dendritic spines of layer II/III
pyramidal neurons in the medial PFC (Bacon et al., 1996).
Accordingly, the medial PFC may inhibit amygdala output
through its connections onto GABAergic intercalated cells at
the border of the lateral and central nucleus (McDonald et al.,
1996; Quirk et al., 2003). Experimental lesions of the PFC result
in enhancement of amygdala-dependent behaviors, such as
emotionality and fear conditioning (Morgan and LeDoux,
1995; Dias et al., 1996). That repeated stress also results in
enhanced fear conditioning (Conrad et al., 1999) suggests that
stress’ effects on the medial PFC may a key contributor to
the disinhibition of information flow through the amygdala.
Functional neuroimaging studies reveal augmented amygdala
responses and diminished medial prefrontal cortex responses
during the symptomatic state in PTSD (Shin et al., 2004; 2005),
and also that PTSD patients show a reduction in medial PFC
volume (Rauch et al., 2003; Yamasue et al., 2003). The possibility
that these stress-induced alterations in brain plasticity may be
ameliorated may have significant consequences for the treat-
ment of stress-related mental illness. Future studies are needed
in order to investigate the extent to which these morphologic
changes are reversible, the relationship between these synaptic
changes and their interconnections with the extended amyg-
dala, and their relationship to amygdala-dependent forms of
We thank Dr Paul E. Sawchenko for helpful comments and suggestions,
and Athena Wang for technical assistance. Dr. Susan L. Wearne provided
access to the VIAS software. This work was supported by NIH grant
Address correspondence to Jason J. Radley, Laboratory of Neuronal
Structure and Function, Salk Institute for Biological Studies, PO Box
85800, San Diego, CA 92310, USA. Email: email@example.com or john.
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Figure 4. Spine density changes in medial PFC following repeated stress. Spine density histograms for apical (A, B) and basal (C, D) dendrites. Twenty-one days of repeated
restraint stress resulted in a significant decrease in overall spine density on apical (A), but not on basal (C) dendrites (*, P\0.05). In (B), dendritic spine density averages are
depicted for each individual site sampled on apical dendritic arbors, reveal decreases at radial distance 200 lm and on large diameter dendrites. (D) Averages for individual sites
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