Activity-stress induces atrophy of apical dendrites of hippocampal pyramidal neurons in male rats

Aspects of Area Deprivation Index in Relation to Hippocampal Volume Among Children

Importance

Area deprivation index (ADI) has been shown to be associated with reduced hippocampal volume (HV) among youths. The social environment may interact with the association between ADI and HV.

Objective

To investigate which aspects of ADI are uniquely associated with bilateral HV and whether school and family environments have moderating interactions in associations between ADI and HV.

Design, Setting, and Participants

This cross-sectional study used data from the Adolescent Brain and Cognitive Development (ABCD) study. Participants aged 9 and 10 years were recruited from 21 sites in the US between September 2016 and August 2018. Data analysis was performed between March 2023 and April 2024.

Exposures

ADI aspects were derived from participant primary home addresses provided by parents or guardians.

Main Outcomes and Measures

HV was automatically segmented from structural brain images ascertained from magnetic resonance imaging. Multiple generalized linear mixed modeling tested associations between 9 indices of ADI and bilateral HV, with family groups and recruitment sites as random effects. After stepwise backward selection, models were adjusted for individual-level covariates, including age, sex, race and ethnicity, parental education, household income, and estimated intracranial volume.

Results

This study included 10 114 participants aged 9 and 10 years (median [IQR] age, 9.92 [9.33-10.48] years; 5294 male [52.3%]; 200 Asian [2.0%], 1411 Black [14.0%], and 6655 White [65.8%]; 1959 Hispanic [19.4%]). After stepwise backward selection and adjusting for covariates, only the percentage of neighborhood-level single-parent households was associated with right HV (adjusted β per 1-SD increase in single-parent households, -0.03; 95% CI, -0.06 to -0.01; P = .01). School environment interacted with neighborhood-level single-parent households in its association with right HV (adjusted β per 1-SD increase in score, 0.02; 95% CI, 0.01 to 0.03; P = .003), such that there was an inverse association only among those at a school with the mean environment score (adjusted β per 1% increase in single-parent households, -0.03; 95% CI, -0.05 to -0.01; P = .02) and worse (-1 SD score) school environment score (adjusted β per 1% increase in single-parent households, -0.05; 95% CI, -0.09 to -0.01; P < .001) but not among those at better (+1 SD score) school environments.

Conclusions and Relevance

In this study, an increased percentage of neighborhood-level single-parent households was associated with reduced right HV among children in schools with the mean or worse but not better environment score. These findings suggest that longitudinal research concerning the association of neighborhood-level characteristics and school environments with hippocampal development may be warranted to better understand complex interactions between various social factors and child neurodevelopment and mental health outcomes.

Unpredictable chronic mild stress shows neuronal remodeling in multipolar projection neurons of hippocampal complex in postnatal chicks

The hippocampal complex of birds is a narrow-curved strip of tissue that plays a crucial role in learning, memory, spatial navigation, and emotional and sexual behavior. This study was conducted to evaluate the effect of unpredictable chronic mild stress in multipolar neurons of 3-, 5-, 7-, and 9-week-old chick's hippocampal complex. This study revealed that chronic stress results in neuronal remodeling by causing alterations in dendritic field, axonal length, secondary branching, corrected spine number, and dendritic branching at 25, 50, 75, and 100 µm. Due to stress, the overall dendritic length was significantly retracted in 3-week-old chick, whereas no significant difference was observed in 5- and 7-week-old chick, but again it was significantly retracted in 9-week-old chick along with the axonal length. So, this study indicates that during initial days of stress exposure, the dendritic field shows retraction, but when the stress continues up to a certain level, the neurons undergo structural modifications so that chicks adapt and survive in stressful conditions. The repeated exposure to chronic stress for longer duration leads to the neuronal structural disruption by retraction in the dendritic length as well as axonal length. Another characteristic which leads to structural alterations is the dendritic spines which significantly decreased in all age groups of stressed chicks and eventually leads to less synaptic connections, disturbance in physiology, and neurology, which affects the learning, memory, and coping ability of an individual.

Gestational protein restriction alters early amygdala neurochemistry in male offspring

BACKGROUND

Gestational protein intake restriction-induced long-lasting harmful outcomes in the offspring's organs and systems. However, few studies have focused on this event's impact on the brain's structures and neurochemical compounds.

AIM

The present study investigated the effects on the amygdala neurochemical composition and neuronal structure in gestational protein-restricted male rats' offspring.

METHODS

Dams were maintained on isocaloric standard rodent laboratory chow with regular protein [NP, 17%] or low protein content [LP, 6%]. Total cells were quantified using the Isotropic fractionator method, Neuronal 3D reconstruction, and dendritic tree analysis using the Golgi-Cox technique. Western blot and high-performance liquid chromatography performed neurochemical studies.

RESULTS

The gestational low-protein feeding offspring showed a significant decrease in birth weight up to day 14, associated with unaltered brain weight in youth or adult progenies. The amygdala cell numbers were unchanged, and the dendrites length and dendritic ramifications 3D analysis in LP compared to age-matched NP progeny. However, the current study shows reduced amygdala content of norepinephrine, epinephrine, and dopamine in LP progeny. These offspring observed a significant reduction in the amygdala glucocorticoid (GR) and mineralocorticoid (MR) receptor protein levels. Also corticotrophin-releasing factor (CRF) amygdala protein content was reduced in 7 and 14-day-old LP rats.

CONCLUSION

The observed amygdala neurochemical changes may represent adaptation during embryonic development in response to elevated fetal exposure to maternal corticosteroid levels. In this way, gestational malnutrition stress can alter the amygdala's neurochemical content and may contribute to known behavioral changes induced by gestational protein restriction.

Altered dendritic morphology in dorsolateral prefrontal cortex of nonhuman primates prenatally exposed to maternal immune activation

Women who contract a viral or bacterial infection during pregnancy have an increased risk of giving birth to a child with a neurodevelopmental or psychiatric disorder. The effects of maternal infection are likely mediated by the maternal immune response, as preclinical animal models have confirmed that maternal immune activation (MIA) leads to long lasting changes in offspring brain and behavior development. The present study sought to determine the impact of MIA-exposure during the first or second trimester on neuronal morphology in dorsolateral prefrontal cortex (DLPFC) and hippocampus from brain tissue obtained from MIA-exposed and control male rhesus monkey (Macaca mulatta) during late adolescence. MIA-exposed offspring display increased neuronal dendritic branching in pyramidal cells in DLPFC infra- and supragranular layers relative to controls, with no significant differences observed between offspring exposed to maternal infection in the first and second trimester. In addition, the diameter of apical dendrites in DLPFC infragranular layer is significantly decreased in MIA-exposed offspring relative to controls, irrespective of trimester exposure. In contrast, alterations in hippocampal neuronal morphology of MIA-exposed offspring were not evident. These findings demonstrate that a maternal immune challenge during pregnancy has long-term consequences for primate offspring dendritic structure, selectively in a brain region vital for socioemotional and cognitive development.

The Duration of Stress Determines Sex Specificities in the Vulnerability to Depression and in the Morphologic Remodeling of Neurons and Microglia

Stress exposure has been shown to induce a variety of molecular and functional alterations associated with anxiety and depression. Some studies suggest that microglia, the immune cells of the brain, play a significant role in determining neuronal and behavioral responses to chronic stress and also contribute to the development of stress-related psychopathologies. However, little is known about the impact of the duration of stress exposure upon microglia and neurons morphology, particularly considering sex differences. This issue deserves particular investigation, considering that the process of morphologic remodeling of neurons and microglia is usually accompanied by functional changes with behavioral expression. Here, we examine the effects of short and long unpredictable chronic mild stress (uCMS) protocols on behavior, evaluating in parallel microglia and neurons morphology in the dorsal hippocampus (dHIP) and in the nucleus accumbens (NAc), two brain regions involved in the etiology of depression. We report that long-term uCMS induced more behavioral alterations in males, which present anxiety and depression-like phenotypes (anhedonia and helplessness behavior), while females only display anxiety-like behavior. After short-term uCMS, both sexes presented anxiety-like behavior. Microglia cells undergo a process of morphologic adaptation to short-term uCMS, dependent on sex, in the NAc: we observed a hypertrophy in males and an atrophy in females, transient effects that do not persist after long-term uCMS. In the dHIP, the morphologic adaptation of microglia is only observed in females (hypertrophy) and after the protocol of long uCMS. Interestingly, males are more vulnerable to neuronal morphological alterations in a region-specific manner: dendritic atrophy in granule neurons of the dHIP and hypertrophy in the medium spiny neurons of the NAc, both after short- or long-term uCMS. The morphology of neurons in these brain regions were not affected in females. These findings raise the possibility that, by differentially affecting neurons and microglia in dHIP and NAc, chronic stress may contribute for differences in the clinical presentation of stress-related disorders under the control of sex-specific mechanisms.

Rodent models of stress and dendritic plasticity – Implications for psychopathology

Stress, as commonplace as it is, is a major environmental risk factor for psychopathology. While this association intuitively, anecdotally, and empirically makes sense, we are still very early in the process of understanding what the neurobiological manifestations of this risk truly are. Seminal work from the past few decades has established structural plasticity in the brain as a potential key mechanism. In this review we discuss evidence linking particularly chronic stress exposure in rodent models to plasticity at the dendrites, like remodeling of dendritic branches and spines, in a range of brain regions. A number of candidate mechanisms that seek to explain how stress influences neuroanatomy at this level have been proposed, utilizing in vivo, ex vivo and in vitro methods. However, a large gap still remains in our knowledge of how such dynamic structural changes ultimately relate to downstream effects such as altered affective and cognitive states relevant for psychopathology. We propose that future work expand our understanding of plasticity of specific stress-related brain circuits and cell-types. We also note that the vast majority of the work has been conducted solely on male rodents. The next big strides in our understanding of the neurobiology of psychopathology will require the inclusion of female subjects, as several studies have suggested both sex divergent and convergent features. By understanding plasticity, we can harness it. The growth of this body of knowledge will inform our efforts to improve the therapeutic options for stress-related psychopathology.

Synaptamide Improves Cognitive Functions and Neuronal Plasticity in Neuropathic Pain

Neuropathic pain arises from damage or dysfunction of the peripheral or central nervous system and manifests itself in a wide variety of sensory symptoms and cognitive disorders. Many studies demonstrate the role of neuropathic pain-induced neuroinflammation in behavioral disorders. For effective neuropathic pain treatment, an integrative approach is required, which simultaneously affects several links of pathogenesis. One promising candidate for this role is synaptamide (N-docosahexaenoylethanolamine), which is an endogenous metabolite of docosahexaenoic acid. In this study, we investigated the activity of synaptamide on mice behavior and hippocampal plasticity in neuropathic pain induced by spared nerve injury (SNI). We found a beneficial effect of synaptamide on the thermal allodynia and mechanical hyperalgesia dynamics. Synaptamide prevented working and long-term memory impairment. These results are probably based on the supportive effect of synaptamide on SNI-impaired hippocampal plasticity. Nerve ligation caused microglia activation predominantly in the contralateral hippocampus, while synaptamide inhibited this effect. The treatment reversed dendritic tree degeneration, dendritic spines density reduction on CA1-pyramidal neurons, neurogenesis deterioration, and hippocampal long-term potentiation (LTP) impairment. In addition, synaptamide inhibits changes in the glutamatergic receptor expression. Thus, synaptamide has a beneficial effect on hippocampal functioning, including synaptic plasticity and hippocampus-dependent cognitive processes in neuropathic pain.

Sex and chronic stress alter delta opioid receptor distribution within rat hippocampal CA1 pyramidal cells following behavioral challenges

Following oxycodone (Oxy) conditioned place preference (CPP), delta opioid receptors (DORs) differentially redistribute in hippocampal CA3 pyramidal cells in female and male rats in a manner that would promote plasticity and opioid-associative learning processes. However, following chronic immobilization stress (CIS), males do not acquire Oxy-CPP and the trafficking of DORs in CA3 pyramidal neurons is attenuated. Here, we examined the subcellular distribution of DORs in CA1 pyramidal cells using electron microscopy in these same cohorts.

CPP

Saline (Sal)-females compared to Sal-males have more cytoplasmic and total DORs in dendrites and more DOR-labeled spines. Following Oxy-CPP, DORs redistribute from near-plasmalemma pools in dendrites to spines in males.

CIS

Control females compared to control males have more near-plasmalemmal dendritic DORs. Following CIS, dendritic DORs are elevated in the cytoplasm in females and near-plasmalemma in males.

CIS plus CPP

CIS Sal-females compared to CIS Sal-males have more DORs on the plasmalemma of dendrites and in spines. After Oxy, the distribution of DORs does not change in either females or males.

Conclusion

Following Oxy-CPP, DORs within CA1 pyramidal cells remain positioned in naïve female rats to enhance sensitivity to DOR agonists and traffic to dendritic spines in naïve males where they can promote plasticity processes. Following CIS plus behavioral enrichment, DORs are redistributed within CA1 pyramidal cells in females in a manner that could enhance sensitivity to DOR agonists. Conversely, CIS plus behavioral enrichment does not alter DORs in CA1 pyramidal cells in males, which may contribute to their diminished capacity to acquire Oxy-CPP.

Hippocampal LASP1 ameliorates chronic stress-mediated behavioral responses in a mouse model of unpredictable chronic mild stress

Substantial evidence has revealed that abnormalities in synaptic plasticity play important roles during the process of depression. LASP1 (LIM and SH3 domain protein 1), a member of actin-binding proteins, has been shown to be associated with the regulation of synaptic plasticity. However, the role of LASP1 in the regulation of mood is still unclear. Here, using an unpredictable chronic mild stress (UCMS) paradigm, we found that the mRNA and protein levels of LASP1 were decreased in the hippocampus of stressed mice and that UCMS-induced down-regulation of LASP1 was abolished by chronic administration of fluoxetine. Adenosine-associated virus-mediated hippocampal LASP1 overexpression alleviated the UCMS-induced behavioral results of forced swimming test and sucrose preference test in stressed mice. It also restored the dendritic spine density, elevated the levels of AKT (a serine/threonine protein kinase), phosphorylated-AKT, insulin-like growth factor 2, and postsynaptic density protein 95. These findings suggest that LASP1 alleviates UCMS-provoked behavioral defects, which may be mediated by an enhanced dendritic spine density and more activated AKT-dependent LASP1 signaling, pointing to the antidepressant role of LASP1.

The Relationship Between Cumulative Exogenous Corticosteroid Exposure and Volumes of Hippocampal Subfields and Surrounding Structures

PURPOSE/BACKGROUND

Glucocorticoids are a class of hormones that include naturally occurring cortisol and corticosterone, as well as prescription drugs commonly used to manage inflammatory, autoimmune, and allergic conditions. Adverse effects, including neuropsychiatric symptoms, are common. The hippocampus appears to be especially sensitive to the effects of glucocorticoids. However, to our knowledge, no studies to date have examined hippocampal subfields in humans receiving glucocorticoids. We examined patients on chronic glucocorticoid regimens to determine relationships between dose and duration of treatment, and hippocampal subfields, and related regions volumes.

METHODS/PROCEDURES

The study included adult men and women receiving at least 5 mg daily of prednisone equivalents for at least 6 months. Volumes of brain regions were measured via magnetic resonance imaging. A multivariate general linear model was used for analysis, with brain volumes as dependent variables and age, sex, and cumulative corticosteroid exposure, as predictors.

FINDINGS/RESULTS

The study population consisted of 81 adult outpatients (43 male) on corticosteroids (mean dose, 7.88 mg; mean duration, 76.75 months). Cumulative glucocorticoid exposure was negatively associated with left and right hippocampal dentate gyrus/CA3 volume. In subsequent subgroup analysis, this association held true for the age group older than the median age of 46 years but not for the younger age group.

IMPLICATIONS/CONCLUSIONS

This finding is consistent with previous studies showing detrimental effects of elevated glucocorticoids on the hippocampus but further suggests that the dentate gyrus and CA3 regions are particularly vulnerable to those effects, which is consistent with animal models of chronic stress but has not been previously demonstrated in humans.

Stochastic Modeling of Radiation-induced Dendritic Damage on in silico Mouse Hippocampal Neurons

Cognitive dysfunction associated with radiotherapy for cancer treatment has been correlated to several factors, one of which is changes to the dendritic morphology of neuronal cells. Alterations in dendritic geometry and branching patterns are often accompanied by deficits that impact learning and memory. The purpose of this study is to develop a novel predictive model of neuronal dendritic damages caused by exposure to low linear energy transfer (LET) radiation, such as X-rays, γ-rays and high-energy protons. We established in silico representations of mouse hippocampal dentate granule cell layer (GCL) and CA1 pyramidal neurons, which are frequently examined in radiation-induced cognitive decrements. The in silico representations are used in a stochastic model that describes time dependent dendritic damage induced by exposure to low LET radiation. Changes in morphometric parameters, such as total dendritic length, number of branch points and branch number, including the Sholl analysis for single neurons are described by the model. Our model based predictions for different patterns of morphological changes based on energy deposition in dendritic segments (EDDS) will serve as a useful basis to compare specific patterns of morphological alterations caused by EDDS mechanisms.

Chronic corticosterone administration reduces dendritic complexity in mature, but not young granule cells in the rat dentate gyrus

Background: Our previous work has shown that exposure to the stress hormone corticosterone (40 mg/kg CORT) for two weeks induces dendritic atrophy of pyramidal neurons in the hippocampal CA3 region and behavioral deficits. However, it is unclear whether this treatment also affects the dentate gyrus (DG), a subregion of the hippocampus comprising a heterogeneous population of young and mature neurons.

Objective: We examined the effect of CORT treatment on the dendritic complexity of mature and young granule cells in the DG.

Methods: We utilized a Golgi staining method to investigate the dendritic morphology and spine density of young neurons in the inner granular cell layer (GCL) and mature neurons in the outer GCL in response to CORT application. The expressions of glucocorticoid receptors during neuronal maturation were examined using Western blot analysis in a primary hippocampal neuronal culture.

Results: Sholl analysis revealed that CORT treatment decreased the number of intersections and shortened the dendritic length in mature, but not young, granule cells. However, the spine density of mature and young neurons was not affected. Western blot analysis showed a progressive increase in the protein levels of glucocorticoid receptors (GRs) in the cultured primary hippocampal neurons during neuronal maturation.

Conclusion: These data suggest that mature neurons are likely more vulnerable to chronic exposure to CORT; this may be due to their higher expression of GRs when compared to younger DG neurons.

Synaptic Plasticity, Metaplasticity and Depression

The development of a persistent depressive affective state has for some time been thought to result from persistent alterations in neurotransmitter-mediated synaptic transmission. While the identity of those transmitters has changed over the years, the literature has lacked mechanistic connections between the neurophysiological mechanisms they regulate, and how these mechanisms alter neuronal function, and, hence, affective homeostasis. This review will examine recent work that suggests that both long-term activity-dependent changes in synaptic strength (“plasticity”), and shifting set points for the ease of induction of future long-term changes (“metaplasticity”), may be critical to establishing and reversing a depressive behavioral state. Activity-dependent long-term synaptic plasticity involves both strengthening and weakening of synaptic connections associated with a dizzying array of neurochemical alterations that include synaptic insertion and removal of a number of subtypes of AMPA, NMDA and metabotropic glutamate receptors, changes in presynaptic glutamate release, and structural changes in dendritic spines. Cellular mechanisms of metaplasticity are far less well understood. Here, we will review the growing evidence that long-term synaptic changes in glutamatergic transmission, in brain regions that regulate mood, are key determinants of affective homeostasis and therapeutic targets with immense potential for drug development.

Exercise increases mTOR signaling in brain regions involved in cognition and emotional behavior

Exercise can enhance learning and memory and produce resistance against stress-related psychiatric disorders such as depression and anxiety. In rats, these beneficial effects of exercise occur regardless of exercise controllability: both voluntary and forced wheel running produce stress-protective effects. The mechanisms underlying these beneficial effects of exercise remain unknown. The mammalian target of rapamycin (mTOR) is a translation regulator important for cell growth, proliferation, and survival. mTOR has been implicated in enhancing learning and memory as well as antidepressant effects. Moreover, mTOR is sensitive to exercise signals such as metabolic factors. The effects of exercise on mTOR signaling, however, remain unknown. The goal of the present study was to test the hypothesis that exercise, regardless of controllability, increases levels of phosphorylated mTOR (p-mTOR) in brain regions important for learning and emotional behavior. Rats were exposed to 6 weeks of either sedentary (locked wheel), voluntary, or forced wheel running conditions. At 6 weeks, rats were sacrificed during peak running and levels of p-mTOR were measured using immunohistochemistry. Overall, both voluntary and forced exercise increased p-mTOR-positive neurons in the medial prefrontal cortex, striatum, hippocampus, hypothalamus, and amygdala compared to locked wheel controls. Exercise, regardless of controllability, also increased numbers of p-mTOR-positive glia in the striatum, hippocampus, and amygdala. For both neurons and glia, the largest increase in p-mTOR positive cells was observed after voluntary running, with forced exercise causing a more modest increase. Interestingly, voluntary exercise preferentially increased p-mTOR in astrocytes (GFAP+), while forced running increased p-mTOR in microglia (CD11+) in the inferior dentate gyrus. Results suggest that mTOR signaling is sensitive to exercise, but subtle differences exist depending on exercise controllability. Increases in mTOR signaling could contribute to the beneficial effects of exercise on cognitive function and mental health.

Chronic stress and hippocampal dendritic complexity: Methodological and functional considerations

The current understanding of how chronic stress impacts hippocampal dendritic arbor complexity and the subsequent relationship to hippocampal-dependent spatial memory is reviewed. A surge in reports investigating hippocampal dendritic morphology is occurring, but with wide variations in methodological detail being reported. Consequently, this review systematically outlines the basic neuroanatomy of relevant hippocampal features to help clarify how chronic stress or glucocorticoids impact hippocampal dendritic complexity and how these changes occur in parallel with spatial cognition. Chronic stress often leads to hippocampal CA3 apical dendritic retraction first with other hippocampal regions (CA3 basal dendrites, CA1, dentate gyrus, DG) showing dendritic retraction when chronic stress is sufficiently robust or long lasting. The stress-induced reduction in hippocampal CA3 apical dendritic arbor complexity often coincides with impaired hippocampal function, such as spatial learning and memory. Yet, when chronic stress ends and a post-stress recovery period ensues, the atrophied dendritic arbors and poor spatial abilities often improve. However, this process differs from a simple reversal of chronic stress-induced deficits. Recent reports suggest that this return to baseline-like functioning is uniquely different from non-stressed controls, emphasizing the need for further studies to enhance our understanding of how a history of stress subsequently alters an organism's spatial abilities. To provide a consistent framework for future studies, this review concludes with an outline for a quick and easy reference on points to consider when planning chronic stress studies with the goal of measuring hippocampal dendritic complexity and spatial ability.

The influence of stress and gonadal hormones on neuronal structure and function

This article is part of a Special Issue "SBN 2014". The brain is highly plastic, allowing us to adapt and respond to environmental and physiological challenges and experiences. In this review, we discuss the relationships among alterations in dendritic arborization, spine morphology, and behavior due to stress exposure, endogenous hormone fluctuation, or exogenous hormonal manipulation. Very few studies investigate structure-function associations directly in the same cohort of animals, and there are notable inconsistencies in evidence of structure-function relationships in the prefrontal cortex and hippocampus. Moreover, little work has been done to probe the causal relationship between dendritic morphology and neuronal excitability, leaving only speculation about the adaptive versus maladaptive nature of experience-dependent dendritic remodeling. We propose that future studies combine electrophysiology with a circuit-level approach to better understand how dendritic structure contributes to neuronal functional properties and behavioral outcomes.

Behavioral problems after early life stress: contributions of the hippocampus and amygdala

BACKGROUND

Early life stress (ELS) can compromise development, with higher amounts of adversity linked to behavioral problems. To understand this linkage, a growing body of research has examined two brain regions involved with socioemotional functioning-amygdala and hippocampus. Yet empirical studies have reported increases, decreases, and no differences within human and nonhuman animal samples exposed to different forms of ELS. This divergence in findings may stem from methodological factors, nonlinear effects of ELS, or both.

METHODS

We completed rigorous hand-tracing of the amygdala and hippocampus in three samples of children who experienced different forms of ELS (i.e., physical abuse, early neglect, or low socioeconomic status). Interviews were also conducted with children and their parents or guardians to collect data about cumulative life stress. The same data were also collected in a fourth sample of comparison children who had not experienced any of these forms of ELS.

RESULTS

Smaller amygdala volumes were found for children exposed to these different forms of ELS. Smaller hippocampal volumes were also noted for children who were physically abused or from low socioeconomic status households. Smaller amygdala and hippocampal volumes were also associated with greater cumulative stress exposure and behavioral problems. Hippocampal volumes partially mediated the relationship between ELS and greater behavioral problems.

CONCLUSIONS

This study suggests ELS may shape the development of brain areas involved with emotion processing and regulation in similar ways. Differences in the amygdala and hippocampus may be a shared diathesis for later negative outcomes related to ELS.

Estrogens are neuroprotective factors for hypertensive encephalopathy

Estrogens are neuroprotective factors for brain diseases, including hypertensive encephalopathy. In particular, the hippocampus is highly damaged by high blood pressure, with several hippocampus functions being altered in humans and animal models of hypertension. Working with a genetic model of primary hypertension, the spontaneously hypertensive rat (SHR), we have shown that SHR present decreased dentate gyrus neurogenesis, astrogliosis, low expression of brain derived neurotrophic factor (BDNF), decreased number of neurons in the hilus of the dentate gyrus, increased basal levels of the estrogen-synthesizing enzyme aromatase, and atrophic dendritic arbor with low spine density in the CA1 region compared to normotensive Wistar Kyoto (WKY) ratsl. Changes also occur in the hypothalamus of SHR, with increased expression of the hypertensinogenic peptide arginine vasopressin (AVP) and its V1b receptor. Following chronic estradiol treatment, SHR show decreased blood pressure, enhanced hippocampus neurogenesis, decreased the reactive astrogliosis, increased BDNF mRNA and protein expression in the dentate gyrus, increased neuronal number in the hilus of the dentate gyrus, further increased the hyperexpression of aromatase and replaced spine number with remodeling of the dendritic arbor of the CA1 region. We have detected by qPCR the estradiol receptors ERα and ERβ in hippocampus from both SHR and WKY rats, suggesting direct effects of estradiol on brain cells. We hypothesize that a combination of exogenously given estrogens plus those locally synthesized by estradiol-stimulated aromatase may better alleviate the hippocampal and hypothalamic encephalopathy of SHR. This article is part of a Special Issue entitled "Sex steroids and brain disorders".

Dendritic atrophy constricts functional maps in resonance and impedance properties of hippocampal model neurons

A gradient in the density of hyperpolarization-activated cyclic-nucleotide gated (HCN) channels is necessary for the emergence of several functional maps within hippocampal pyramidal neurons. Here, we systematically analyzed the impact of dendritic atrophy on nine such functional maps, related to input resistance and local/transfer impedance properties, using conductance-based models of hippocampal pyramidal neurons. We introduced progressive dendritic atrophy in a CA1 pyramidal neuron reconstruction through a pruning algorithm, measured all functional maps in each pruned reconstruction, and arrived at functional forms for the dependence of underlying measurements on dendritic length. We found that, across frequencies, atrophied neurons responded with higher efficiency to incoming inputs, and the transfer of signals across the dendritic tree was more effective in an atrophied reconstruction. Importantly, despite the presence of identical HCN-channel density gradients, spatial gradients in input resistance, local/transfer resonance frequencies and impedance profiles were significantly constricted in reconstructions with dendritic atrophy, where these physiological measurements across dendritic locations converged to similar values. These results revealed that, in atrophied dendritic structures, the presence of an ion channel density gradient alone was insufficient to sustain homologous functional maps along the same neuronal topograph. We assessed the biophysical basis for these conclusions and found that this atrophy-induced constriction of functional maps was mediated by an enhanced spatial spread of the influence of an HCN-channel cluster in atrophied trees. These results demonstrated that the influence fields of ion channel conductances need to be localized for channel gradients to express themselves as homologous functional maps, suggesting that ion channel gradients are necessary but not sufficient for the emergence of functional maps within single neurons.

The effects of chronic restraint on the morphology of ventral CA1 neurons in female Long Evans rats

Women are more likely than men to develop psychopathology as a result of stress, but there is little research regarding the effects of a stressful condition and its treatment in female non-human animals, perhaps because of inherent hormonal activity. Recent studies have demonstrated that there are structural and functional differences between the dorsal and ventral hippocampus, but the effects of stress on the morphology of CA1 and CA3 neurons have been studied primarily in the dorsal hippocampus. This study assessed the effects of stress induced by restricted movement on the morphology of ventral hippocampal CA1 neurons in male and female rats. Male and female Long Evans (LE) rats were subjected to restraint stress for 6 h every day for 25 days. One group of rats was used to study the dendritic morphology of CA1 ventral hippocampal neurons using the Golgi-Cox stain. A second group of rats was used to analyze learning and memory using the Morris water maze. Stressed female rats exhibited a decrease in the density of basilar dendritic spines, an increase in the number of apical dendritic intersections and deficits in spatial memory. There were no apparent effects of stress on male rats. Our data support previous findings of a dimorphic response to chronic stress and indicate that the ventral hippocampus is not particularly susceptible to the effects of stress.

The Effects of Maternal Deprivation on the Hippocampal Structure in Adult Rats

Objectives:

To examine the ultrastructural effects of maternal deprivation during developmental periods of limbi-chypothalamo-pituitary-adrenal system on hippocampal dendritic structures in adult rats.

Methods:

The experiments were carried out with male and female wistar rats in our department. The rats were mated and, after birth, the pups were divided into four groups. The first group (control group) pups remained undisturbed with their dam until postweaning day 22. Maternal deprived groups were separated from their dams for 24 hours at postnatal day 4, 9 and 18. The subjects were provided with food and water ad libitum until 3-months-of-age. At the third month, the rats were transcardially perfused, samples were taken from CA1 and CA3 regions of the hippocampus. Tissues were prepared for electron microscopy.

Results:

When the data were analyzed, there were no differences between male and female rats in both ultrastructure and semiquantitative analysis of axodendritic synapses. The ultrastructure of Group 1 was seen as normal while in the second Group some neurons nuclear envelope made deep invagination into the nucleus. Additionally, axodendritic synapses were found normal. In Group 3, micrographs and axodendritic synapses were showed normal structure. However, in Group 4 in some neurons invaginations were seen similar to Group 2. Axodendritic synapses were found to be normal.

Conclusion:

These experiments establish that MD in rats produces slight ultrastructural changes and decreases the number of synapses in CA1 and CA3 subregions of the hippocampus.

Effects of exercise intensity on spatial memory performance and hippocampal synaptic plasticity in transient brain ischemic rats

Memory impairment is commonly noted in stroke survivors, and can lead to delay of functional recovery. Exercise has been proved to improve memory in adult healthy subjects. Such beneficial effects are often suggested to relate to hippocampal synaptic plasticity, which is important for memory processing. Previous evidence showed that in normal rats, low intensity exercise can improve synaptic plasticity better than high intensity exercise. However, the effects of exercise intensities on hippocampal synaptic plasticity and spatial memory after brain ischemia remain unclear. In this study, we investigated such effects in brain ischemic rats. The middle cerebral artery occlusion (MCAO) procedure was used to induce brain ischemia. After the MCAO procedure, rats were randomly assigned to sedentary (Sed), low-intensity exercise (Low-Ex), or high-intensity exercise (High-Ex) group. Treadmill training began from the second day post MCAO procedure, 30 min/day for 14 consecutive days for the exercise groups. The Low-Ex group was trained at the speed of 8 m/min, while the High-Ex group at the speed of 20 m/min. The spatial memory, hippocampal brain-derived neurotrophic factor (BDNF), synapsin-I, postsynaptic density protein 95 (PSD-95), and dendritic structures were examined to document the effects. Serum corticosterone level was also quantified as stress marker. Our results showed the Low-Ex group, but not the High-Ex group, demonstrated better spatial memory performance than the Sed group. Dendritic complexity and the levels of BDNF and PSD-95 increased significantly only in the Low-Ex group as compared with the Sed group in bilateral hippocampus. Notably, increased level of corticosterone was found in the High-Ex group, implicating higher stress response. In conclusion, after brain ischemia, low intensity exercise may result in better synaptic plasticity and spatial memory performance than high intensity exercise; therefore, the intensity is suggested to be considered during exercise training.

Estradiol increases dendritic length and spine density in CA1 neurons of the hippocampus of spontaneously hypertensive rats: a Golgi impregnation study

Increased neuronal vulnerability has been described in the brain of spontaneously hypertensive rats (SHR), models of primary hypertension. Previous data indicate that estradiol treatment corrects several dysfunctions of the hippocampus and hypothalamus of SHR. Considering this evidence we analyzed the dendritic arborization and spine density of the CA1 subfield in SHR and Wistar-Kyoto (WKY) normotensive rats with and without estradiol treatment. Five month old male SHR and WKY rats received single estradiol or cholesterol pellets (sham treatment) for 2 weeks. A substantial rise of circulating estradiol (>25 fold) and testicular atrophy was present in all estradiol-receiving rats. In both SHR and WKY rats, estradiol decreased blood pressure by ~20 mm Hg; however, a moderate hypertension persisted in SHR (164 mm Hg). Using a modified Golgi impregnation technique, apical and basal dendrites of the CA1 subfield were subjected to Sholl analysis. Spine density was also statistically analyzed. Apical dendritic length was significantly lower in SHR compared to WKY rats (p<0.01), whereas estradiol treatment increased dendritic length in the SHR group only (SHR vs SHR+estradiol; p<0.01). Apical dendritic length plotted against the shell distances 20-100, 120-200 and 220-300 μm, revealed that changes were more pronounced in the range 120-200 μm between SHR vs. WKY rats (p<0.05) and SHR vs. SHR+estradiol (p<0.05). Instead, basal dendrites were not significantly modified by hypertension or steroid treatment. Spine density of apical dendrites was lower in SHR than WKY (p<0.05) and was up-regulated in the SHR+estradiol group compared to the SHR group (p<0.001). Similar changes were obtained for basal dendritic spines. These data suggest that changes of neuronal processes in SHR are plastic events restorable by estradiol treatment. In conjunction with previous results, the present data reveal new targets of estradiol neuroprotection in the brain of hypertensive rats.

Gestational protein restriction induces CA3 dendritic atrophy in dorsal hippocampal neurons but does not alter learning and memory performance in adult offspring

Studies have demonstrated that nutrient deficiency during pregnancy or in early postnatal life results in structural abnormalities in the offspring hippocampus and in cognitive impairment. In an attempt to analyze whether gestational protein restriction might induce learning and memory impairments associated with structural changes in the hippocampus, we carried out a detailed morphometric analysis of the hippocampus of male adult rats together with the behavioral characterization of these animals in the Morris water maze (MWM). Our results demonstrate that gestational protein restriction leads to a decrease in total basal dendritic length and in the number of intersections of CA3 pyramidal neurons whereas the cytoarchitecture of CA1 and dentate gyrus remained unchanged. Despite presenting significant structural rearrangements, we did not observe impairments in the MWM test. Considering the clear dissociation between the behavioral profile and the hippocampus neuronal changes, the functional significance of dendritic remodeling in fetal processing remains undisclosed.

Diffusion-weighted MRI and quantitative biophysical modeling of hippocampal neurite loss in chronic stress

Chronic stress has detrimental effects on physiology, learning and memory and is involved in the development of anxiety and depressive disorders. Besides changes in synaptic formation and neurogenesis, chronic stress also induces dendritic remodeling in the hippocampus, amygdala and the prefrontal cortex. Investigations of dendritic remodeling during development and treatment of stress are currently limited by the invasive nature of histological and stereological methods. Here we show that high field diffusion-weighted MRI combined with quantitative biophysical modeling of the hippocampal dendritic loss in 21 day restraint stressed rats highly correlates with former histological findings. Our study strongly indicates that diffusion-weighted MRI is sensitive to regional dendritic loss and thus a promising candidate for non-invasive studies of dendritic plasticity in chronic stress and stress-related disorders.

Alterations of sex-typical microanatomy: prenatal stress modifies the structure of medial preoptic area neurons in rats

Prenatal stress disrupts normal sexual differentiation and behavior with concomitant alterations in brain development; however, its effects on the cytoarchitecture of neurons in the sexually dimorphic medial preoptic area (mPOA) of the hypothalamus is not known. Morphometric analysis of the mPOA of adult rats showed sex differences as neurons from control females had significantly greater numbers of basal dendritic branches and cumulative basal dendritic length as compared to control male neurons. Prenatal stress significantly altered these sexual dimorphisms, as prenatally stressed (P-S) males had increased measures of cell body area, perimeter, cumulative basal dendritic length, and branch point numbers as compared to control males. Prenatal stress also altered the cytoarchitecture in the female mPOA neurons as P-S female neurons had significantly greater measures for primary dendritic branch number and a trend towards significance for several additional measures as compared to control females. Therefore, there are significant effects of both sex and prenatal stress on neuronal architecture in the mPOA that may help to explain the well-documented alterations in reproductive behaviors observed in P-S animals.

Impact of glucocorticoids on brain function: relevance for mood disorders

Exposure to stressful situations activates two hormonal systems that help the organism to adapt. On the one hand stress hormones achieve adaptation by affecting peripheral organs, on the other hand by altering brain function such that appropriate behavioral strategies are selected for optimal performance at the short term, while relevant information is stored for reference in the future. In this chapter we describe how cellular effects induced by stress hormones--in particular by glucocorticoids--may contribute to the behavioral outcome after a single stressor. In addition to situations of acute stress, chronic uncontrollable and unpredictable stress also exerts profound effects on structure and function of limbic neurons. The impact of chronic stress is not a mere cumulative effect of what is seen after acute stress exposure. Dendritic trees are expanded in some regions but reduced in others. In general, cells are exposed to a higher calcium load upon depolarization, but show attenuated responses to serotonin. Synaptic strengthening is largely impaired. In this viewpoint we speculate how cellular effects after chronic stress may be maladaptive and could contribute to the development of psychopathology in genetically vulnerable individuals.

Depression: a repair response to stress-induced neuronal microdamage that can grade into a chronic neuroinflammatory condition?

Depression is a major contributor to the global burden of disease and disability, yet it is poorly understood. Here we review data supporting a novel theoretical model for the biology of depression. In this model, a stressful life event leads to microdamage in the brain. This damage triggers an injury repair response consisting of a neuroinflammatory phase to clear cellular debris and a spontaneous tissue regeneration phase involving neurotrophins and neurogenesis. During healing, released inflammatory mediators trigger sickness behavior and psychological pain via mechanisms similar to those that produce physical pain during wound healing. The depression remits if the neuronal injury repair process resolves successfully. Importantly, however, the acute psychological pain and neuroinflammation often transition to chronicity and develop into pathological depressive states. This hypothesis for depression explains substantially more data than alternative models, including why emerging data show that analgesic, anti-inflammatory, pro-neurogenic and pro-neurotrophic treatments have antidepressant effects. Thus, an acute depressive episode can be conceptualized as a normally self-limiting but highly error-prone process of recuperation from stress-triggered neuronal microdamage.

Chronic stress-induced hippocampal dendritic retraction requires CA3 NMDA receptors

Chronic stress induces dendritic retraction in the hippocampal CA3 subregion, but the mechanisms responsible for this retraction and its impact on neural circuitry are not well understood. To determine the role of NMDA (N-methyl-d-aspartic acid) receptor (NMDAR)-mediated signaling in this process, we compared the effects of chronic immobilization stress (CIS) on hippocampal dendritic morphology, hypothalamic-pituitary-adrenal (HPA) axis activation, and anxiety-related and hippocampus-dependent behaviors, in transgenic male mice in which the NMDAR had been selectively deleted in CA3 pyramidal cells and in non-mutant littermates. We found that CIS exposure for 10 consecutive days in non-mutant mice effectively induces HPA axis activation and dendritic retraction of CA3 short-shaft pyramidal neurons, but not CA3 long-shaft pyramidal neurons, suggesting a differential cellular stress response in this region. Dendritic reorganization of short-shaft neurons occurred throughout the longitudinal axis of the hippocampus and, in particular, in the ventral pole of this structure. We also observed a robust retraction of dendrites in dorsal CA1 pyramidal neurons in the non-mutant C57BL/6 mouse strain. Strikingly, chronic stress-induced dendritic retraction was not evident in any of the neurons in either CA3 or CA1 in the mutant mice that had a functional lack of NMDARs restricted to CA3 pyramidal neurons. Interestingly, the prevention of dendritic retraction in the mutant mice had a minimal effect on HPA axis activation and behavioral alterations that were induced by chronic stress. These data support a role for NMDAR-dependent glutamatergic signaling in CA3 in the cell-type specific induction of dendritic retraction in two hippocampal subregions following chronic stress.

Beneficial Effects of Tianeptine on Hippocampus-Dependent Long-Term Memory and Stress-Induced Alterations of Brain Structure and Function

Tianeptine is a well-described antidepressant which has been shown to prevent stress from producing deleterious effects on brain structure and function. Preclinical studies have shown that tianeptine blocks stress-induced alterations of neuronal morphology and synaptic plasticity. Moreover, tianeptine prevents stress from impairing learning and memory, and, importantly, demonstrates memory-enhancing properties in the absence of stress. Recent research has indicated that tianeptine works by normalizing glutamatergic neurotransmission, a mechanism of action that may underlie its effectiveness as an antidepressant. These findings emphasize the value in focusing on the mechanisms of action of tianeptine, and specifically, the glutamatergic system, in the development of novel pharmacotherapeutic strategies in the treatment of depression.

Stress, sex, and neural adaptation to a changing environment: mechanisms of neuronal remodeling

The adult brain is much more resilient and adaptable than previously believed, and adaptive structural plasticity involves growth and shrinkage of dendritic trees, turnover of synapses, and limited amounts of neurogenesis in the forebrain, especially the dentate gyrus of the hippocampal formation. Stress and sex hormones help to mediate adaptive structural plasticity, which has been extensively investigated in the hippocampus and to a lesser extent in the prefrontal cortex and amygdala, all brain regions that are involved in cognitive and emotional functions. Stress and sex hormones exert their effects on brain structural remodeling through both classical genomic as well as non-genomic mechanisms, and they do so in collaboration with neurotransmitters and other intra- and extracellular mediators. This review will illustrate the actions of estrogen on synapse formation in the hippocampus and the process of stress-induced remodeling of dendrites and synapses in the hippocampus, amygdala, and prefrontal cortex. The influence of early developmental epigenetic events, such as early life stress and brain sexual differentiation, is noted along with the interactions between sex hormones and the effects of stress on the brain. Because hormones influence brain structure and function and because hormone secretion is governed by the brain, applied molecular neuroscience techniques can begin to reveal the role of hormones in brain-related disorders and the treatment of these diseases. A better understanding of hormone-brain interactions should promote more flexible approaches to the treatment of psychiatric disorders, as well as their prevention through both behavioral and pharmaceutical interventions.

Blockade of insulin-like growth factor-I has complex effects on structural plasticity in the hippocampus

Physical exercise enhances adult neurogenesis in the hippocampus. Running induces the uptake of blood insulin-like growth factor-I (IGF-I) into the brain. A causal link between these two phenomena has been reported; running-induced increases in adult neurogenesis can be blocked by peripheral infusion of anti-IGF-I. Running also alters other aspects of hippocampal structure, including dendritic spine density. It remains unclear, however, whether these effects are also mediated through an IGF-I mechanism. To examine this possibility, we blocked peripheral IGF-I and examined adult neurogenesis and dendritic spine density in treadmill running mice. Two weeks of running resulted in an increase in cell proliferation in the dentate gyrus (DG) as well as an increase in dendritic spine density on DG granule cells and basal dendrites of CA1 pyramidal neurons, while having no effect on apical or basal dendritic spine density of CA3 pyramidal neurons. IGF-I blockade reduced cell proliferation in both sedentary and running mice, but by contrast, this treatment had no effect on granule cell or CA3 pyramidal cell dendritic spine density in sedentary or running mice. However, IGF-I antibody treatment seemed to prevent the running-induced increase in spine density on basal dendrites of CA1 pyramidal cells. These results suggest that IGF-I exerts a complex influence over hippocampal structure and that its effects are not restricted to those induced by running.

Chronic stress effects on hippocampal structure and synaptic function: relevance for depression and normalization by anti-glucocorticoid treatment

Exposure of an organism to environmental challenges activates two hormonal systems that help the organism to adapt. As part of this adaptational process, brain processes are changed such that appropriate behavioral strategies are selected that allow optimal performance at the short term, while relevant information is stored for the future. Over the past years it has become evident that chronic uncontrollable and unpredictable stress also exerts profound effects on structure and function of limbic neurons, but the impact of chronic stress is not a mere accumulation of repeated episodes of acute stress exposure. Dendritic trees are reduced in some regions but expanded in others, and cells are generally exposed to a higher calcium load upon depolarization. Synaptic strengthening is largely impaired. Neurotransmitter responses are also changed, e.g., responses to serotonin. We here discuss: (a) the main cellular effects after chronic stress with emphasis on the hippocampus, (b) how such effects could contribute to the development of psychopathology in genetically vulnerable individuals, and (c) their normalization by brief treatment with anti-glucocorticoids.

Correlated memory defects and hippocampal dendritic spine loss after acute stress involve corticotropin-releasing hormone signaling

Stress affects the hippocampus, a brain region crucial for memory. In rodents, acute stress may reduce density of dendritic spines, the location of postsynaptic elements of excitatory synapses, and impair long-term potentiation and memory. Steroid stress hormones and neurotransmitters have been implicated in the underlying mechanisms, but the role of corticotropin-releasing hormone (CRH), a hypothalamic hormone also released during stress within hippocampus, has not been elucidated. In addition, the causal relationship of spine loss and memory defects after acute stress is unclear. We used transgenic mice that expressed YFP in hippocampal neurons and found that a 5-h stress resulted in profound loss of learning and memory. This deficit was associated with selective disruption of long-term potentiation and of dendritic spine integrity in commissural/associational pathways of hippocampal area CA3. The degree of memory deficit in individual mice correlated significantly with the reduced density of area CA3 apical dendritic spines in the same mice. Moreover, administration of the CRH receptor type 1 (CRFR(1)) blocker NBI 30775 directly into the brain prevented the stress-induced spine loss and restored the stress-impaired cognitive functions. We conclude that acute, hours-long stress impairs learning and memory via mechanisms that disrupt the integrity of hippocampal dendritic spines. In addition, establishing the contribution of hippocampal CRH-CRFR(1) signaling to these processes highlights the complexity of the orchestrated mechanisms by which stress impacts hippocampal structure and function.

A critical review of chronic stress effects on spatial learning and memory

The purpose of this review is to evaluate the effects of chronic stress on hippocampal-dependent function, based primarily upon studies using young, adult male rodents and spatial navigation tasks. Despite this restriction, variability amongst the findings was evident and how or even whether chronic stress influenced spatial ability depended upon the type of task, the dependent variable measured and how the task was implemented, the type and duration of the stressors, housing conditions of the animals that include accessibility to food and cage mates, and duration from the end of the stress to the start of behavioral assessment. Nonetheless, patterns emerged as follows: For spatial memory, chronic stress impairs spatial reference memory and has transient effects on spatial working memory. For spatial learning, however, chronic stress effects appear to be task-specific: chronic stress impairs spatial learning on appetitively motivated tasks, such as the radial arm maze or holeboard, tasks that evoke relatively mild to low arousal components from fear. But under testing conditions that evoke moderate to strong arousal components from fear, such as during radial arm water maze testing, chronic stress appears to have minimal impairing effects or may even facilitate spatial learning. Chronic stress clearly impacts nearly every brain region and thus, how chronic stress alters hippocampal spatial ability likely depends upon the engagement of other brain structures during behavioral training and testing.

Tianeptine: an antidepressant with memory-protective properties

The development of effective pharmacotherapy for major depression is important because it is such a widespread and debilitating mental disorder. Here, we have reviewed preclinical and clinical studies on tianeptine, an atypical antidepressant which ameliorates the adverse effects of stress on brain and memory. In animal studies, tianeptine has been shown to prevent stress-induced morphological sequelae in the hippocampus and amygdala, as well as to prevent stress from impairing synaptic plasticity in the prefrontal cortex and hippocampus. Tianeptine also has memory-protective characteristics, as it blocks the adverse effects of stress on hippocampus-dependent learning and memory. We have further extended the findings on stress, memory and tianeptine here with two novel observations: 1) stress impairs spatial memory in adrenalectomized (ADX), thereby corticosterone-depleted, rats; and 2) the stress-induced impairment of memory in ADX rats is blocked by tianeptine. These findings are consistent with previous research which indicates that tianeptine produces anti-stress and memory-protective properties without altering the response of the hypothalamic-pituitary-adrenal axis to stress. We conclude with a discussion of findings which indicate that tianeptine accomplishes its anti-stress effects by normalizing stress-induced increases in glutamate in the hippocampus and amygdala. This finding is potentially relevant to recent research which indicates that abnormalities in glutamatergic neurotransmission are involved in the pathogenesis of depression. Ultimately, tianeptine’s prevention of depression-induced sequelae in the brain is likely to be a primary factor in its effectiveness as a pharmacological treatment for depression.

Neurobiological constituents of active, passive, and variable coping strategies in rats: integration of regional brain neuropeptide Y levels and cardiovascular responses

Effective coping strategies build resilience against stress-induced pathology. In the current study, young male rats were categorized as active, passive, or variable copers by observing their responses to being gently restrained on their backs (i.e., the back-test). The rats were subsequently exposed to chronic unpredictable stress, which included several ethologically relevant stressors such as predator odors and calls, for approximately three weeks. During this time, the variable copers, defined as rats that demonstrated a variable as opposed to a rigid response to stress, exhibited more seemingly adaptive responsiveness in three successive forced swim tests than the more consistently responding passive and active copers. This behavioral flexibility was accompanied by increased neuropeptide Y-immunoreactivity in the bed nucleus of the stria terminalis (BNST) and the amygdala and increased fos-immunoreactivity in the BNST. Additionally, the alterations in fecal corticosteroid levels and cardiovascular measures (systolic blood pressure and tail blood volume) between baseline and stress conditions differed according to coping strategy. Factor analysis indicates that variable copers were characterized by a distinct cardiovascular and neural response to the stress exposure. These results suggest that this animal coping model may be useful in discerning the adaptive nature of particular response strategies in the face of environmental exigencies.