Activity-stress increases density of GFAP-immunoreactive astrocytes in the rat hippocampus

The stress of losing sleep: Sex-specific neurobiological outcomes

Sleep is a vital and evolutionarily conserved process, critical to daily functioning and homeostatic balance. Losing sleep is inherently stressful and leads to numerous detrimental physiological outcomes. Despite sleep disturbances affecting everyone, women and female rodents are often excluded or underrepresented in clinical and pre-clinical studies. Advancing our understanding of the role of biological sex in the responses to sleep loss stands to greatly improve our ability to understand and treat health consequences of insufficient sleep. As such, this review discusses sex differences in response to sleep deprivation, with a focus on the sympathetic nervous system stress response and activation of the hypothalamic-pituitary-adrenal (HPA) axis. We review sex differences in several stress-related consequences of sleep loss, including inflammation, learning and memory deficits, and mood related changes. Focusing on women's health, we discuss the effects of sleep deprivation during the peripartum period. In closing, we present neurobiological mechanisms, including the contribution of sex hormones, orexins, circadian timing systems, and astrocytic neuromodulation, that may underlie potential sex differences in sleep deprivation responses.

Chronic Early-Life Social Isolation Enhances Spatial Memory in Male and Female Rats

Social adversity during childhood and adolescence can alter brain development in ways that may increase the likelihood of many prominent mental illnesses. To determine the underlying mechanisms, several animal models have been developed, such as Chronic Early-Life Social Isolation (CELSI), which sees rats isolated for several weeks after weaning. Although such a paradigm does cause many consistent changes in adult behaviour, one area where uncertainty exists concerns its effect upon hippocampal-dependent learning and memory. To help sort out how CELSI affects spatial learning and memory, male and female siblings from 15 Sprague-Dawley rat litters were stratified by sex and then randomly assigned to either group-housing (3 animals/cage), or social isolation (1 animal/cage) for 7 weeks. Spatial learning and memory were then tested over 5 days using the Morris water maze. Next, the animals were euthanised, and stress-sensitive biometrics, including serum corticosterone levels, were collected. Lastly, to determine whether CELSI affected neural cell density, the expression of key neuronal and glial proteins (such as PSD-95 and GFAP, respectively) was assessed in isolated hippocampal tissue using immunoblotting. Notably, both male and female rats that had experienced post-weaning social isolation displayed stronger spatial learning and memory abilities than their group-housed counterparts. As well, socially isolated male rats exhibited a clear increase in expression of PSD-95. However, housing condition did not seem to affect either stress-sensitive biometrics, or hippocampal GFAP expression. Our results support the possibility that CELSI may enhance some aspects of hippocampal-dependent behaviour in a fashion similar among male and female rats.

IL-1 Mediates Chronic Stress-Induced Hyperalgesia Accompanied by Microglia and Astroglia Morphological Changes in Pain-Related Brain Regions in Mice

Chronic stress causes several pain conditions including fibromyalgia. Its pathophysiological mechanisms are unknown, and the therapy is unresolved. Since the involvement of interleukin-1 (IL-1) has been described in stress and inflammatory pain but no data are available regarding stress-induced pain, we studied its role in a chronic restraint stress (CRS) mouse model. Female and male C57Bl/6J wild-type (WT) and IL-1αβ-deficient (knock-out: IL-1 KO) mice were exposed to 6 h of immobilization/day for 4 weeks. Mechanonociception, cold tolerance, behavioral alterations, relative thymus/adrenal gland weights, microglia ionized calcium-binding adaptor molecule 1 (IBA1) and astrocyte glial fibrillary acidic protein (GFAP) integrated density, number and morphological transformation in pain-related brain regions were determined. CRS induced 15–20% mechanical hyperalgesia after 2 weeks in WT mice in both sexes, which was significantly reduced in female but not in male IL-1 KOs. Increased IBA1+ integrated density in the central nucleus of amygdala, primary somatosensory cortex hind limb representation part, hippocampus cornu ammonis area 3 (CA3) and periaqueductal gray matter (PAG) was present, accompanied by a cell number increase in IBA1+ microglia in stressed female WTs but not in IL-1 KOs. CRS induced morphological changes of GFAP+ astrocytes in WT but not in KO mice. Stress evoked cold hypersensitivity in the stressed animals. Anxiety and depression-like behaviors, thymus and adrenal gland weight changes were detectable in all groups after 2 but not 4 weeks of CRS due to adaptation. Thus, IL-1 mediates chronic stress-induced hyperalgesia in female mice, without other major behavioral alterations, suggesting the analgesic potentials of IL-1 in blocking drugs in stress-related pain syndromes.

The Molecular Relationship between Stress and Insomnia

The bi-directional relationship between sleep and stress has been actively researched as sleep disturbances and stress have become increasingly common in society. Interestingly, the brain and underlying neural circuits important for sleep regulation may respond uniquely to stress that leads to post-traumatic stress disorder (PTSD) and stress that does not. In stress that does not lead to PTSD, the hypothalamic-pituitary-adrenal axis (HPA) pathway is activated normally that results in sympathetic nervous system activation that allows the brain and body to return to baseline functioning. However, exposure to stress that leads to PTSD, causes enhanced negative feedback of this same pathway and results in long-term physiological and psychological changes. In this review, how stress regulates glucocorticoid signaling pathways in brain glial cells called astrocytes, and then mediates stress-induced insomnia are examined. Astrocytes are critical sleep regulatory cells and their connections to sleep and stress due to disturbed glucocorticoid signaling provide a novel mechanism to explain how stress leads to insomnia. This review will examine the interactions of stress neurobiology, astrocytes, sleep, and glucocorticoid signaling pathways and will examine the how stress that leads to PTSD and stress that does not impacts sleep-regulatory processes.

Electroacupuncture improves repeated social defeat stress-elicited social avoidance and anxiety-like behaviors by reducing Lipocalin-2 in the hippocampus

Background

Post-traumatic stress disorder (PTSD) is a trauma-related disorder that is associated with pro-inflammatory activation and neurobiological impairments in the brain and leads to a series of affective-like behaviors. Electroacupuncture (EA) has been proposed as a clinically useful therapy for several brain diseases. However, the potential role of EA treatment in PTSD and its molecular and cellular mechanisms has rarely been investigated.

Methods

We used an established preclinical social defeat stress mouse model to study whether EA treatment modulates PTSD-like symptoms and understand its underlying mechanisms. To this end, male C57BL/6 mice were subjected to repeated social defeat stress (RSDS) for 6 consecutive days to induce symptoms of PTSD and treated with EA at Baihui (GV 20) and Dazhui (GV 14) acupoints.

Results

The stimulation of EA, but not needle insertion at Baihui (GV 20) and Dazhui (GV 14) acupoints effectively improved PTSD-like behaviors such as, social avoidance and anxiety-like behaviors. However, EA stimulation at the bilateral Tianzong (SI11) acupoints did not affect the PTSD-like behaviors obtained by RSDS. EA stimulation also markedly inhibited astrocyte activation in both the dorsal and ventral hippocampi of RSDS-treated mice. Using next-generation sequencing analysis, our results showed that EA stimulation attenuated RSDS-enhanced lipocalin 2 expression in the hippocampus. Importantly, using double-staining immunofluorescence, we observed that the increased lipocalin 2 expression in astrocytes by RSDS was also reduced by EA stimulation. In addition, intracerebroventricular injection of mouse recombinant lipocalin 2 protein in the lateral ventricles provoked social avoidance, anxiety-like behaviors, and the activation of astrocytes in the hippocampus. Interestingly, the overexpression of lipocalin 2 in the brain also altered the expression of stress-related genes, including monoamine oxidase A, monoamine oxidase B, mineralocorticoid receptor, and glucocorticoid receptor in the hippocampus.

Conclusions

This study suggests that the treatment of EA at Baihui (GV 20) and Dazhui (GV 14) acupoints improves RSDS-induced social avoidance, anxiety-like behaviors, astrocyte activation, and lipocalin 2 expression. Furthermore, our findings also indicate that lipocalin 2 expression in the brain may be an important biomarker for the development of PTSD-related symptoms.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13041-021-00860-0.

Maternal separation induces retinal and peripheral blood mononuclear cell alterations across the lifespan of female rats

Early life stress alters the function and feedback regulation of the hypothalamic-pituitaryadrenal (HPA) axis, and can contribute to neuroinflammation and neurodegeneration by modifying peripheral blood mononuclear cell (PBMC) activity. The retina, as part of the nervous system, is sensitive to immune changes induced by stress. However, the consequences of stress experienced at an early age on retinal development have not yet been elucidated. Here we aimed to evaluate the impact of maternal separation (MatSep) across three stages of the lifespan (adolescent, adult, and aged) on the retina, as well as on progression through the cell cycle and mitochondrial activity in PBMCs from female Wistar rats. Newborn pups were separated from their mother from postnatal day (PND) 2 until PND 14 for 3 h/day. Retinal analysis from the MatSep groups showed architectural alterations such as a diminished thickness of retinal layers, as well as increased expression of proinflammatory markers DJ-1, Iba-1, and CD45 and the gliotic marker GFAP. Additionally, MatSep disrupted the cell cycle and caused long-term increases in mitochondrial activity in PBMCs from adolescent and adult rats. Changes in the cell cycle profile of the PBMCs from aged MatSep rats were undetected. However, these PBMCs exhibited increased sensitivity to H₂O₂-induced oxidative stress in vitro. Therefore, these results suggest that early life stress can have long-term effects on retinal structure and function, possibly elicited by neonatal immune preconditioning.

Zinc Deficiency During Pregnancy Leads to Altered Microbiome and Elevated Inflammatory Markers in Mice

Zinc is an essential trace metal for bacteria of the intestinal flora. Approximately 20% of dietary zinc – intake is used by intestinal bacteria. The microbiome has recently been described as an important factor for healthy brain function via so-called gut-brain interactions. Similarly, zinc deficiency has been associated with neurological problems such as depression, mental lethargy and cognitive impairments in humans and animal models. However, the underlying pathomechanisms are currently not well understood and a link between zinc deficiency and altered microbiota composition has not been studied. Especially during pregnancy, women may be prone to low zinc status. Thus, here, we investigate whether zinc deficiency alters gut-brain interaction in pregnant mice by triggering changes in the microbiome. To that end, pregnant mice were fed different diets being zinc-adequate, deficient in zinc, or adequate in zinc but high in zinc uptake antagonists for 8 weeks. Our results show that acute zinc-deficient pregnant mice and pregnant mice on a diet high in zinc uptake antagonists have an altered composition of gastro-intestinal (GI) microbiota. These changes were accompanied by alterations in markers for GI permeability. Within the brain, we found signs of neuroinflammation. Interestingly, microbiota composition, gut pathology, and inflammatory cytokine levels were partially rescued upon supplementation of mice with zinc amino-acid conjugates (ZnAA). We conclude that zinc deficiency may contribute to abnormal gut-brain signaling by altering gut physiology, microbiota composition and triggering an increase of inflammatory markers.

Environmental noise exposure modifies astrocyte morphology in hippocampus of young male rats

Background:

Chronic exposure to noise induces changes on the central nervous system of exposed animals. Those changes affect not only the auditory system but also other structures indirectly related to audition. The hippocampus of young animals represents a potential target for these effects because of its essential role in individuals’ adaptation to environmental challenges.

Objective:

The aim of the present study was to evaluate hippocampus vulnerability, assessing astrocytic morphology in an experimental model of environmental noise (EN) applied to rats in pre-pubescent stage.

Materials and Methods:

Weaned Wistar male rats were subjected to EN adapted to the rats’ audiogram for 15 days, 24 h daily. Once completed, plasmatic corticosterone (CORT) concentration was quantified, and immunohistochemistry for glial fibrillary acidic protein was taken in hippocampal DG, CA3, and CA1 subareas. Immunopositive cells and astrocyte arborizations were counted and compared between groups.

Results:

The rats subjected to noise exhibited enlarged length of astrocytes arborizations in all hippocampal subareas. Those changes were accompanied by a marked rise in serum CORT levels.

Conclusions:

These findings confirm hippocampal vulnerability to EN and suggest that glial cells may play an important role in the adaptation of developing the participants to noise exposure.

The contribution of the locus coeruleus-norepinephrine system in the emergence of defeat-induced inflammatory priming

Exposure to psychosocial stress is known to precipitate the emergence of stress related psychiatric disorders such as depression and anxiety. While mechanisms by which this occurs remain largely unclear, recent evidence points towards a causative role for inflammation. Neurotransmitters, such as norepinephrine (NE), are capable of regulating expression of proinflammatory cytokines and thus may contribute to the emergence of stress-related disorders. The locus coeruleus (LC) is the major source of norepinephrine (NE) to the brain and therefore the current study utilized N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4), an LC selective noradrenergic neurotoxin, to determine the discrete involvement of the LC-NE system in social defeat-induced inflammation in LC projection regions including the central amygdala (CeA), dorsal raphe (DR) and plasma. In the current study, rats were exposed to brief social defeat or control manipulations on 5 consecutive days. To determine whether a history of social defeat enhanced or "primed" the inflammatory response to a subsequent defeat exposure, all rats regardless of stress history were exposed to an acute social defeat challenge immediately preceeding tissue collection. As anticipated, prior history of social defeat primed inflammatory responses in the plasma and CeA while neuroinflammation in the DR was markedly reduced. Notably, DSP-4 treatment suppressed stress-induced circulating inflammatory cytokines independent of prior stress history. In contrast, neuroinflammation in the CeA and DR were greatly augmented selectively in DSP-4 treated rats with a history of social defeat. Together these data highlight the dichotomous nature of NE in stress-induced inflammatory priming in the periphery and the brain and directly implicate the LC-NE system in these processes.

The Effect of Antenatal Betamethasone on White Matter Inflammation and Injury in Fetal Sheep and Ventilated Preterm Lambs

Antenatal administration of betamethasone (BM) is a common antecedent of preterm birth, but there is limited information about its impact on the acute evolution of preterm neonatal brain injury. We aimed to compare the effects of maternal BM in combination with mechanical ventilation on the white matter (WM) of late preterm sheep. At 0.85 of gestation, pregnant ewes were randomly assigned to receive intra-muscular (i.m.) saline (n = 9) or i.m. BM (n = 13). Lambs were delivered and unventilated controls (UVCSal, n = 4; UVCBM, n = 6) were humanely killed without intervention; ventilated lambs (VentSal, n = 5; VentBM, n = 7) were injuriously ventilated for 15 min, followed by conventional ventilation for 75 min. Cardiovascular and cerebral haemodynamics and oxygenation were measured continuously. The cerebral WM underwent assessment of inflammation and injury, and oxidative stress was measured in the cerebrospinal fluid (CSF). In the periventricular and subcortical WM tracts, the proportion of amoeboid (activated) microglia, the density of astrocytes, and the number of blood vessels with protein extravasation were higher in UVCBM than in UVCSal (p < 0.05 for all). During ventilation, tidal volume, mean arterial pressure, carotid blood flow, and oxygen delivery were higher in -VentBM lambs (p < 0.05 vs. VentSal). In the subcortical WM, microglial infiltration was increased in the VentSal group compared to UVCSal. The proportion of activated microglia and protein extravasation was higher in the VentBM group compared to VentSal within the periventricular and subcortical WM tracts (p < 0.05). CSF oxidative stress was increased in the VentBM group compared to UVCSal, UVCBM, and VentSal groups (p < 0.05). Antenatal BM was associated with inflammation and vascular permeability in the WM of late preterm fetal sheep. During the immediate neonatal period, the increased carotid perfusion and oxygen delivery in BM-treated lambs was associated with increased oxidative stress, microglial activation and microvascular injury.

Abnormal metabolite concentrations and amygdala volume in patients with recent-onset posttraumatic stress disorder

BACKGROUND

Previous psychoradiological studies of posttraumatic stress disorder (PTSD) were mainly of patients at a chronic stage, focusing on brain regions outside the amygdala. The goals of this study were to investigate the early biochemical and structural changes of anterior cingulate cortex (ACC) and amygdala in patients with PTSD and to explore their relationships.

METHODS

Seventy-eight drug-naïve PTSD subjects and 71 non-PTSD age- and sex-matched control subjects were enrolled, all of whom had suffered the same earthquake about one year before. Single-voxel proton magnetic resonance spectroscopy (¹H-MRS) was performed and absolute metabolite concentrations in ACC and bilateral amygdalae were estimated with LCModel. Bilateral amygdalae were manually outlined and their volumes were calculated and corrected for the total intracranial volume.

RESULTS

The PTSD group showed significantly increased N-acetylaspartate (NAA) concentration in the ACC, increased creatine (Cr) concentration in the left amygdala, and increased myo-inositol (mI) concentration in the right amygdala, compared to non-PTSD controls. The NAA concentration in ACC was negatively correlated with the time since trauma. The PTSD group showed significantly decreased volumes of bilateral amygdalae compared to non-PTSD controls, but amygdala volumes were not correlated with metabolite concentrations.

LIMITATIONS

Longitudinal studies are needed to explore the metabolic and structural changes of PTSD at different stages. The volume of ACC was not measured.

CONCLUSIONS

This concurrent increase in some metabolite concentrations and decrease of amygdala volumes may represent a pattern of biochemical and morphological changes in recent-onset PTSD which is different from that reported in chronic PTSD.

Distinctive stress sensitivity and anxiety-like behavior in female mice: Strain differences matter

Epidemiologic studies have shown that the prevalence of stress-related mood disorders is higher in women, which suggests a different response of neuroendocrine circuits involved in the response to stressful events, as well as a genetic background influence. The aim of this study was to investigate the baseline differences in anxiety-like behaviors of females of two commonly used mice strains. Secondly, we have also aimed to study their behavioral and biochemical alterations following stress. Naïve 3-4 months-old Swiss and C57BL/6 female mice were evaluated in the elevated plus maze (EPM) and in the acoustic startle response (ASR) for anxiety-like behaviors. Besides, an independent group of animals from each strain was exposed to cold-restraint stress (30 min/4 °C, daily) for 21 consecutive days and then evaluated in EPM and in the sucrose consumption tests. Twenty-four hours following behavioral experimentation mice were decapitated and their hippocampi (HP) and cortex (CT) dissected for further Western blotting analysis of glucocorticoid receptor (GR) and glial fibrillary acid protein (GFAP). Subsequent to each behavioral protocol, animal blood samples were collected for further plasma corticosterone analysis. C57BL/6 presented a lower anxiety profile than Swiss female mice in both behavioral tests, EPM and ASR. These phenomena could be correlated with the fact that both strains have distinct corticosterone levels and GR expression in the HP at the baseline level. Moreover, C57BL/6 female mice were more vulnerable to the stress protocol, which was able to induce an anhedonic state characterized by lower preference for a sucrose solution. Behavioral anhedonic-like alterations in these animals coincide with reduced plasma corticosterone accompanied with increased GR and GFAP levels, both in the HP. Our data suggest that in C57BL/6 female mice a dysregulation of the hypothalamus-pituitary-adrenal axis (HPA-axis) occurs, in which corticosterone acting on GRs would possibly exert its pro-inflammatory role, ultimately leading to astrocyte activation in response to stress.

Social stress during adolescence activates long-term microglia inflammation insult in reward processing nuclei

The experience of social stress during adolescence is associated with higher vulnerability to drug use. Increases in the acquisition of cocaine self-administration, in the escalation of cocaine-seeking behavior, and in the conditioned rewarding effects of cocaine have been observed in rodents exposed to repeated social defeat (RSD). In addition, prolonged or severe stress induces a proinflammatory state with microglial activation and increased cytokine production. The aim of the present work was to describe the long-term effects induced by RSD during adolescence on the neuroinflammatory response and synaptic structure by evaluating different glial and neuronal markers. In addition to an increase in the conditioned rewarding effects of cocaine, our results showed that RSD in adolescence produced inflammatory reactivity in microglia that is prolonged into adulthood, affecting astrocytes and neurons of two reward-processing areas of the brain (the prelimbic cortex, and the nucleus accumbens core). Considered as a whole these results suggest that social stress experience modulates vulnerability to suffer a loss of glia-supporting functions and neuronal functional synaptic density due to drug consumption in later life.

Effects of glucocorticoids in depression: Role of astrocytes

Astrocytes or astroglia are heterogeneous cells, similar to neurons, that have different properties in different brain regions. The implications of steroid hormones on glial cells and stress-related pathologies have been studied previously. Glucocorticoids (GCs) that are released in response to stress have been shown to be deleterious to neurons in various brain regions. Further, in the light of the effect of GCs on astrocytes, several reports have shown the crucial role of glia. Still, much remains to be done to understand the stress-astrocytes-glucocorticoid interactions associated with the pathological consequences of various CNS disorders. This review is an attempt to summarize the effects of GCs and stress on astrocytes and its implications in depression.

Chronic Social Stress Time-Dependently Affects Neuropathic Pain-Related Cold Allodynia and Leads to Altered Expression of Spinal Biochemical Mediators

Clinical data have shown that chronic exposure to stress may be accompanied by an enhancement of inflammation-related pain sensitivity. In this context, little is however known on the impact of stress on neuropathic pain. In the present study we addressed this issue by combining the chronic constriction injury (CCI) model with an ongoing social stress (OSS) paradigm. Cold plate and von Frey tests were performed in 48 rats divided into four groups: OSS exposed to OSS, CCI subjected to chronic nerve constriction, OSS+CCI with a combination of neuropathy and stress and CON, a control group lacking any manipulation. While we did not observe any stress-related differences in mechanical sensitivity throughout the observation period, CCI rats were more sensitive to cold stimulation than OSS+CCI in the initial phase of neuropathy. A switch was observed at a later stage, leading to a hypersensitivity of the OSS+CCI compared to the CCI rats. At this time point we investigated the spinal mRNA expression of neuron and glia related molecules potentially involved in neuropathic pain and stress. The combination of psychosocial stress and neuropathic pain seemed to enhance glial cell activation, pro-inflammatory cytokine and neurotrophic factor mRNA levels, rather than glutamatergic transmission. Our data show that long lasting social stress may lead to time-dependent alteration of neuropathy-related cold pain sensitivity while mechanically-induced pain remains unchanged.

The role of neuroimmune signaling in alcoholism

Alcohol consumption and stress increase brain levels of known innate immune signaling molecules. Microglia, the innate immune cells of the brain, and neurons respond to alcohol, signaling through Toll-like receptors (TLRs), high-mobility group box 1 (HMGB1), miRNAs, pro-inflammatory cytokines and their associated receptors involved in signaling between microglia, other glia and neurons. Repeated cycles of alcohol and stress cause a progressive, persistent induction of HMGB1, miRNA and TLR receptors in brain that appear to underlie the progressive and persistent loss of behavioral control, increased impulsivity and anxiety, as well as craving, coupled with increasing ventral striatal responses that promote reward seeking behavior and increase risk of developing alcohol use disorders. Studies employing anti-oxidant, anti-inflammatory, anti-depressant, and innate immune antagonists further link innate immune gene expression to addiction-like behaviors. Innate immune molecules are novel targets for addiction and affective disorders therapies. This article is part of the Special Issue entitled "Alcoholism".

Role of Glia in Stress-Induced Enhancement and Impairment of Memory

Both acute and chronic stress profoundly affect hippocampally-dependent learning and memory: moderate stress generally enhances, while chronic or extreme stress can impair, neural and cognitive processes. Within the brain, stress elevates both norepinephrine and glucocorticoids, and both affect several genomic and signaling cascades responsible for modulating memory strength. Memories formed at times of stress can be extremely strong, yet stress can also impair memory to the point of amnesia. Often overlooked in consideration of the impact of stress on cognitive processes, and specifically memory, is the important contribution of glia as a target for stress-induced changes. Astrocytes, microglia, and oligodendrocytes all have unique contributions to learning and memory. Furthermore, these three types of glia express receptors for both norepinephrine and glucocorticoids and are hence immediate targets of stress hormone actions. It is becoming increasingly clear that inflammatory cytokines and immunomodulatory molecules released by glia during stress may promote many of the behavioral effects of acute and chronic stress. In this review, the role of traditional genomic and rapid hormonal mechanisms working in concert with glia to affect stress-induced learning and memory will be emphasized.

The Omega-3 Polyunsaturated Fatty Acid Docosahexaenoic Acid (DHA) Reverses Corticosterone-Induced Changes in Cortical Neurons

BACKGROUND

Chronic exposure to the glucocorticoid hormone corticosterone exerts cellular stress-induced toxic effects that have been associated with neurodegenerative and psychiatric disorders. Docosahexaenoic acid is a polyunsaturated fatty acid that has been shown to be of benefit in stress-related disorders, putatively through protective action in neurons.

METHODS

We investigated the protective effect of docosahexaenoic acid against glucocorticoid hormone corticosterone-induced cellular changes in cortical cell cultures containing both astrocytes and neurons.

RESULTS

We found that glucocorticoid hormone corticosterone (100, 150, 200 μM) at different time points (48 and 72 hours) induced a dose- and time-dependent reduction in cellular viability as assessed by methyl thiazolyl tetrazolium. Moreover, glucocorticoid hormone corticosterone (200 μM, 72 hours) decreased the percentage composition of neurons while increasing the percentage of astrocytes as assessed by βIII-tubulin and glial fibrillary acidic protein immunostaining, respectively. In contrast, docosahexaenoic acid treatment (6 μM) increased docosahexaenoic acid content and attenuated glucocorticoid hormone corticosterone (200 μM)-induced cell death (72 hours) in cortical cultures. This translates into a capacity for docosahexaenoic acid to prevent neuronal death as well as astrocyte overgrowth following chronic exposure to glucocorticoid hormone corticosterone. Furthermore, docosahexaenoic acid (6 μM) reversed glucocorticoid hormone corticosterone-induced neuronal apoptosis as assessed by terminal deoxynucleotidyl transferase-mediated nick-end labeling and attenuated glucocorticoid hormone corticosterone-induced reductions in brain derived neurotrophic factor mRNA expression in these cultures. Finally, docosahexaenoic acid inhibited glucocorticoid hormone corticosterone-induced downregulation of glucocorticoid receptor expression on βIII- tubulin-positive neurons.

CONCLUSIONS

This work supports the view that docosahexaenoic acid may be beneficial in ameliorating stress-related cellular changes in the brain and may be of value in psychiatric disorders.

Hippocampal cytogenesis and spatial learning in senile rats exposed to chronic variable stress: effects of previous early life exposure to mild stress

In this study, we exposed adult rats to chronic variable stress (CVS) and tested the hypothesis that previous early-life exposure to stress changes the manner in which older subjects respond to aversive conditions. To this end, we analyzed the cytogenic changes in the hippocampus and hippocampal-dependent spatial learning performance. The experiments were performed on 18-month-old male rats divided into four groups as follows: Control (old rats under standard laboratory conditions), Early-life stress (ELS; old rats who were exposed to environmental noise from postnatal days, PNDs 21–35), CVS + ELS (old rats exposed to a chronic stress protocol who were previously exposed to the early-life noise stress) and CVS (old rats who were exposed only to the chronic stress protocol). The Morris Water Maze (MWM) was employed to evaluate the spatial learning abilities of the rats at the end of the experiment. Immunohistochemistry against 5′Bromodeoxyuridine (BrdU) and glial fibrillar acidic protein (GFAP) was also conducted in the DG, CA1, CA2 and CA3 regions of the hippocampus. We confocally analyzed the cytogenic (BrdU-labeled cells) and astrogenic (BrdU + GFAP-labeled cells) changes produced by these conditions. Using this procedure, we found that stress diminished the total number of BrdU+ cells over the main proliferative area of the hippocampus (i.e., the dentate gyrus, DG) but increased the astrocyte phenotypes (GFAP + BrdU). The depleted BrdU+ cells were restored when the senile rats also experienced stress at the early stages of life. The MWM assessment demonstrated that stress also impairs the ability of the rats to learn the task. This impairment was not present when the stressful experience was preceded by the early-life exposure. Thus, our results support the idea that previous exposure to mild stressing agents may have beneficial effects on aged subjects.

Is Dysregulation of the HPA-Axis a Core Pathophysiology Mediating Co-Morbid Depression in Neurodegenerative Diseases?

There is increasing evidence of prodromal manifestation of neuropsychiatric symptoms in a variety of neurodegenerative diseases such as Parkinson's disease (PD) and Huntington's disease (HD). These affective symptoms may be observed many years before the core diagnostic symptoms of the neurological condition. It is becoming more apparent that depression is a significant modifying factor of the trajectory of disease progression and even treatment outcomes. It is therefore crucial that we understand the potential pathophysiologies related to the primary condition, which could contribute to the development of depression. The hypothalamic-pituitary-adrenal (HPA)-axis is a key neuroendocrine signaling system involved in physiological homeostasis and stress response. Disturbances of this system lead to severe hormonal imbalances, and the majority of such patients also present with behavioral deficits and/or mood disorders. Dysregulation of the HPA-axis is also strongly implicated in the pathology of major depressive disorder. Consistent with this, antidepressant drugs, such as the selective serotonin reuptake inhibitors have been shown to alter HPA-axis activity. In this review, we will summarize the current state of knowledge regarding HPA-axis pathology in Alzheimer's, PD and HD, differentiating between prodromal and later stages of disease progression when evidence is available. Both clinical and preclinical evidence will be examined, but we highlight animal model studies as being particularly useful for uncovering novel mechanisms of pathology related to co-morbid mood disorders. Finally, we purpose utilizing the preclinical evidence to better inform prospective, intervention studies.

Lipopolysaccharide repeated challenge followed by chronic mild stress protocol introduces a combined model of depression in rats: reversibility by imipramine and pentoxifylline

OBJECTIVES

The present study examined the effect of combined exposure to repeated challenge using low doses of lipopolysaccharide (LPS) and chronic mild stress (CMS) together. This combined exposure is thought to expose the animals to more realistic challenges, testable on different levels (behavioral, neurochemical, immunohistochemical and gene expression). The role of glial cells was examined, as well. Additionally, the effects of chronic administration of the tricyclic antidepressant imipramine and the anti-TNF-α pentoxyphylline were investigated.

METHODS

Wistar rats were exposed to either repeated LPS (50μg/kg i.p.) over 2weeks, CMS protocol for 4weeks or LPS over 2weeks then 4weeks of CMS. Two groups of rats were exposed to LPS/CMS protocol and treated with either imipramine or pentoxifylline. Rats were examined for behavioral, neurochemical and gene expression changes.

RESULTS

Animals exposed to LPS/CMS elaborated depressive-like symptoms with significant increase in both serum corticosterone and TNF-α levels compared to those in the saline, LPS or CMS groups. Hippocampal kynurenine/tryptophan ratio and TNF-α gene expression showed significant increase in the LPS/CMS model compared to those in saline, LPS or CMS groups. The immunohistochemical findings scrutinized the topography of the examined effects. Chronic treatment with imipramine or pentoxifylline significantly ameliorated the behavioral, neurochemical, immunohistochemical and TNF-α gene expression changes induced by the LPS/CMS protocol.

CONCLUSION

This study gave a clue to the neurobiological processes underlying, at least, the subtypes of depressive disorders. It highlighted the possible interactions between stress and immune-inflammatory pathways in the pathogenesis of depression and suggested a new animal model of depression that addresses these pathways.

Neuropathology of stress

Environmental challenges are part of daily life for any individual. In fact, stress appears to be increasingly present in our modern, and demanding, industrialized society. Virtually every aspect of our body and brain can be influenced by stress and although its effects are partly mediated by powerful corticosteroid hormones that target the nervous system, relatively little is known about when, and how, the effects of stress shift from being beneficial and protective to becoming deleterious. Decades of stress research have provided valuable insights into whether stress can directly induce dysfunction and/or pathological alterations, which elements of stress exposure are responsible, and which structural substrates are involved. Using a broad definition of pathology, we here review the "neuropathology of stress" and focus on structural consequences of stress exposure for different regions of the rodent, primate and human brain. We discuss cytoarchitectural, neuropathological and structural plasticity measures as well as more recent neuroimaging techniques that allow direct monitoring of the spatiotemporal effects of stress and the role of different CNS structures in the regulation of the hypothalamic-pituitary-adrenal axis in human brain. We focus on the hypothalamus, hippocampus, amygdala, nucleus accumbens, prefrontal and orbitofrontal cortex, key brain regions that not only modulate emotions and cognition but also the response to stress itself, and discuss disorders like depression, post-traumatic stress disorder, Cushing syndrome and dementia.

Chronic psychosocial stress and citalopram modulate the expression of the glial proteins GFAP and NDRG2 in the hippocampus

RATIONALE

It has been suggested that there are causal relationships between alterations in brain glia and major depression.

OBJECTIVES

To investigate whether a depressive-like state induces changes in brain astrocytes, we used chronic social stress in male rats, an established preclinical model of depression. Expression of two astrocytic proteins, the intermediate filament component glial fibrillary acidic protein (GFAP) and the cytoplasmic protein N-myc downregulated gene 2 (NDRG2), was analyzed in the hippocampus. For comparison, expression of the neuronal protein syntaxin-1A was also determined.

METHODS

Adult male rats were subjected to daily social defeat for 5 weeks and were concomitantly treated with citalopram (30 mg/kg/day, via the drinking water) for 4 weeks.

RESULTS

Western blot analysis showed that the chronic stress downregulated GFAP but upregulated NDRG2 protein. Citalopram did not prevent these stress effects, but the antidepressant per se downregulated GFAP and upregulated NDRG2 in nonstressed rats. In contrast, citalopram prevented the stress-induced upregulation of the neuronal protein syntaxin-1A.

CONCLUSIONS

These data suggest that chronic stress and citalopram differentially affect expression of astrocytic genes while the antidepressant drug does not prevent the stress effects. The inverse regulation of the cytoskeletal protein GFAP and the cytoplasmic protein NDRG2 indicates that the cells undergo profound metabolic changes during stress and citalopram treatment. Furthermore, the present findings indicate that a 4-week treatment with citalopram does not restore normal glial function in the hippocampus, although the behavior of the animals was normalized within this treatment period, as reported previously.

Spatial memory decline after masticatory deprivation and aging is associated with altered laminar distribution of CA1 astrocytes

Background

Chewing imbalances are associated with neurodegeneration and are risk factors for senile dementia in humans and memory deficits in experimental animals. We investigated the impact of long-term reduced mastication on spatial memory in young, mature and aged female albino Swiss mice by stereological analysis of the laminar distribution of CA1 astrocytes. A soft diet (SD) was used to reduce mastication in the experimental group, whereas the control group was fed a hard diet (HD). Assays were performed in 3-, 6- and 18-month-old SD and HD mice.

Results

Eating a SD variably affected the number of astrocytes in the CA1 hippocampal field, and SD mice performed worse on water maze memory tests than HD mice. Three-month-old mice in both groups could remember/find a hidden platform in the water maze. However, 6-month-old SD mice, but not HD mice, exhibited significant spatial memory dysfunction. Both SD and HD 18-month-old mice showed spatial memory decline. Older SD mice had astrocyte hyperplasia in the strata pyramidale and oriens compared to 6-month-old mice. Aging induced astrocyte hypoplasia at 18 months in the lacunosum-moleculare layer of HD mice.

Conclusions

Taken together, these results suggest that the impaired spatial learning and memory induced by masticatory deprivation and aging may be associated with altered astrocyte laminar distribution and number in the CA1 hippocampal field. The underlying molecular mechanisms are unknown and merit further investigation.

Pregnancy and maternal behavior induce changes in glia, glutamate and its metabolism within the cingulate cortex

An upregulation of the astrocytic proteins GFAP and bFGF within area 2 of the cingulate cortex (Cg2) occurs within 3 hours of parturition in rats. These changes are the result of an interaction between hormonal state and maternal experience and are associated with increased dendritic spine density in this area. Here, we examined whether this upregulation of astrocytic proteins generalized to other glial markers and, in particular those associated with glutamate metabolism. We chose glial markers commonly used to reflect different aspects of glial function: vimentin, like GFAP, is a marker of intermediate filaments; glutamine synthetase (GS), and S-100beta, are used as markers for mature astrocytes and GS has also been used as a specific marker for glutamatergic enzymatic activity. In addition, we examined levels of proteins associated with glutamine synthetase, glutamate, glutamine and two excitatory amino acid transporters found in astrocytes, glt-1 and glast. S100beta immunoreactivity did not vary with reproductive state in either Cg2 or MPOA suggesting no change in the number of mature astrocytes across these conditions. Vimentin-ir did not differ across groups in Cg2, but expression of this protein decreased from Day 1 postpartum onwards in the MPOA. By contrast, GS-ir was increased within 24 h postpartum in Cg2 but not MPOA and similarly to GFAP and bFGF this upregulation of GS resulted from an interaction between hormonal state and maternal experience. Within Cg2, upregulation of GS was not accompanied by changes in the astrocytic glutamatergic transporters, glt-1 and glast, however, an increase in both glutamate and glutamine proteins were observed within the Cg2 of postpartum animals. Together, these changes suggest postpartum upregulation of glutamatergic activity and metabolism within Cg2 that is stimulated by pregnancy hormones and maternal experience.

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.

Responses of glial cells to stress and glucocorticoids

A growing body of evidence suggests that glial cells are involved in practically all aspects of neural function. Glial cells regulate the homeostasis of the brain, influence the development of the nervous system, modulate synaptic activity, and carry out the immune response inside the brain. In addition, they play an important role in the restoration of the nervous system after damage, and they also participate in various neurodegenerative disorders. In a similar way, the importance of stress and glucocorticoids (GCs) on brain function is being increasingly recognized. Within the brain, stress hormones target both neurons and glial cells. Through their actions on these cells, glucocorticoids exert organizational functions on various processes of the developing brain and contribute to neuronal plasticity in the adult brain. Moreover, stress and glucocorticoids have become especially attractive in the study of a number of neurodegenerative disorders. However, studies on the mechanisms behind glucocorticoid-induced regulation of brain function have been classically focused on their effects on neurons. In this review, we start by describing the main functions of glial cells and then proceed to present data highlighting the effects of stress and GCs on brain function. We conclude the review by presenting recent evidence linking stress and glucocorticoids to glial cell function.

Glucocorticoid receptor blockade normalizes hippocampal alterations and cognitive impairment in streptozotocin-induced type 1 diabetes mice

Type 1 diabetes is a common metabolic disorder accompanied by an increased secretion of glucocorticoids and cognitive deficits. Chronic excess of glucocorticoids per se can evoke similar neuropathological signals linked to its major target in the brain, the hippocampus. This deleterious action exerted by excess adrenal stress hormone is mediated by glucocorticoid receptors (GRs). The aim of the present study was to assess whether excessive stimulation of GR is causal to compromised neuronal viability and cognitive performance associated with the hippocampal function of the diabetic mice. For this purpose, mice had type 1 diabetes induced by streptozotocin (STZ) administration (170 mg/kg, i.p.). After 11 days, these STZ-diabetic mice showed increased glucocorticoid secretion and hippocampal alterations characterized by: (1) increased glial fibrillary acidic protein-positive astrocytes as a marker reacting to neurodegeneration, (2) increased c-Jun expression marking neuronal activation, (3) reduced Ki-67 immunostaining indicating decreased cell proliferation. At the same time, mild cognitive deficits became obvious in the novel object-placement recognition task. After 6 days of diabetes the GR antagonist mifepristone (RU486) was administered twice daily for 4 days (200 mg/kg, p.o.). Blockade of GR during early type 1 diabetes attenuated the morphological signs of hippocampal aberrations and rescued the diabetic mice from the cognitive deficits. We conclude that hippocampal disruption and cognitive impairment at the early stage of diabetes are caused by excessive GR activation due to hypercorticism. These signs of neurodegeneration can be prevented and/or reversed by GR blockade with mifepristone.

Effect of chronic citalopram on serotonin-related and stress-regulated genes in the dorsal raphe nucleus of the rat

Using a model of depression in which chronic social stress induces depressive-like symptoms, we investigated effects of the selective serotonin-reuptake inhibitor (SSRI) citalopram on gene expression in the dorsal raphe nucleus of male rats. Expression of tryptophan hydroxylase (TPH) protein was found to be upregulated by the stress and normalized by citalopram, while mRNAs for genes TPH 1 and 2 were differentially affected. Citalopram had no effect on serotonin transporter mRNA but reduced serotonin-1A autoreceptor mRNA in stressed animals. The SSRI prevented the stress-induced upregulation of mRNA for CREB binding protein, synaptic vesicle glycoprotein 2b and the glial N-myc downstream-regulated gene 2, but increased mRNA for neuron-specific enolase (NSE) in both stressed and unstressed animals having no effect on stress-induced upregulation of NSE protein. These findings demonstrate that in the dorsal raphe nucleus of chronically stressed rats, citalopram normalizes TPH expression and blocks stress effects on distinct genes related to neurotransmitter release and neuroplasticity.

Gel-based hippocampal proteomic analysis 2 weeks following traumatic brain injury to immature rats using controlled cortical impact

Traumatic brain injury (TBI) to postnatal day 17 rats has been shown to produce acute changes in hippocampal global protein levels and spatial learning and memory deficits. The purpose of the present study was to analyze global hippocampal protein changes 2 weeks after a moderate ipsilateral controlled cortical impact in postnatal day 17 rats using 2-dimensional difference gel electrophoresis and mass spectrometry. Paired sham and ipsilateral injured hippocampal lysates were independently labeled with different fluorescent cyanine dyes and coseparated within the same immobilized pH gradient strips and slab gel based on isoelectric point and molecular mass. Significant changes in key proteins involved in glial and neuronal stress, oxidative metabolism, calcium uptake and neurotransmitter function were found 2 weeks after injury, and their potential roles in hippocampal plasticity and cognitive dysfunction were discussed.

Hippocampal neuropathology of diabetes mellitus is relieved by estrogen treatment

1. A recently recognized complication of uncontrolled diabetes mellitus is the encephalopathy involving, among other regions, the hippocampus. Since estrogens bring neuroprotection in cases of brain injury and degenerative diseases, we have studied if estradiol (E2) administration counteracts some hippocampal abnormalities of streptozotocin (STZ)-diabetic adult mice. 2. We first report the ability of E2 to modulate neurogenesis in the dentate gyrus (DG) and subventricular zone (SVZ) of diabetic mice. Using bromodeoxyuridine (BrdU) to label newly generated cells, a strong reduction in cell proliferation was obtained in DG and SVZ of mice sacrificed 20 days after STZ administration. The reduction was completely relieved by 10 days of E2 pellet implantation, which increased 30-fold the circulating E2 levels. 3. Diabetic mice also showed abnormal expression of astrocyte markers in hippocampus. Thus, increased number of GFAP(+) cells, indicative of astrogliosis, and increased number of apolipoprotein-E (Apo-E)(+) astrocytes, a marker of ongoing neuronal dysfunction, was found in stratum radiatum below the CA1 hippocampal subfield of diabetic mice. Both parameters were reverted to normal by the E2 regime that upregulated cell proliferation. 4. The studies demonstrated that hippocampal neuropathology of uncontrolled diabetes is a reversible condition and sensitive to estrogen treatment. Studies in animal models may open up new venues for understanding the beneficial role of steroid hormones in diabetic encephalopathy.

Abnormalities of the hippocampus are similar in deoxycorticosterone acetate-salt hypertensive rats and spontaneously hypertensive rats

Hippocampal neuropathology is a recognised feature of the brain in spontaneously hypertensive rats (SHR), but similar studies are lacking in another model of hypertension, the mineralocorticoid-salt-treated rat. The present study aimed to compare changes in hippocampal parameters in 16-week-old male SHR (blood pressure approximately 190 mmHg) and their normotensive Wistar-Kyoto controls, with those of male Sprague-Dawley rats receiving (i) 10 mg deoxycorticosterone acetate (DOCA) every other day during 3 weeks and drinking 1% NaCl solution (blood pressure approximately 160 mmHg) and normotensive controls treated with (ii) DOCA and drinking water, (iii) drinking water only or (iv) 1% NaCl only. In these experimental groups, we determined: (i) cell proliferation in the dentate gyrus (DG) using the 5-bromo-2'-deoxyuridine-labelling technique; (ii) the number of glial fibrillary acidic protein (GFAP) positive astrocytes under the CA1, CA3 and DG; (iii) the number of apolipoprotein E (ApoE) positive astrocytes as a marker of potential neuronal damage; and (iv) the number of neurones in the hilus of the DG, taken as representative of neuronal density in other hippocampal subfields. Changes were remarkably similar in both models, indicating a decreased cell proliferation in DG, an increased number of astrocytes immunopositive for GFAP and ApoE and a reduced number of hilar neurones. Although hypertension may be a leading factor for these abnormalities, endocrine mechanisms may be involved, because hypothalamic-pituitary function, mineralocorticoid receptors and sensitivity to mineralocorticoid treatment are stimulated in SHR, whereas high exogenous mineralocorticoid levels circulate in DOCA-treated rats. Thus, in addition to the deleterious effects of hypertension, endocrine factors may contribute to the abnormalities of hippocampus in SHR and DOCA-treated rats.

Identification of genes regulated by chronic social stress in the rat dorsal raphe nucleus

1. Changes in the serotonergic (5-HT) system are suspected to play a role in stress-induced neuropathologies and neurochemical measures indicate that serotonergic neurons in the dorsal raphe nucleus (DRN) are activated during stress. In the present study we analyzed gene expression in the DRN after chronic social stress using subtractive cDNA hybridization. 2. In the resident intruder paradigm, male Wistar rats were chronically stressed by daily social defeat during 5 weeks, RNA was isolated from their DRN, cDNA was generated, and subtractive hybridization was performed to clone sequences that are differentially expressed in the stressed animals. 3. From the cDNA libraries that were obtained, we selected the following genes for quantitative Real-time PCR: Two genes related to neurotransmission (synaptosomal associated protein 25 and synaptic vesicle glycoprotein 2b), a glial gene presumptively supporting neuroplasticity (N-myc downstream-regulated gene 2), and a gene possibly related to stress-induced regulation of transcription (CREB binding protein). These four genes were upregulated after the chronic social stress. Quantitative Western blotting revealed increased expression of synaptosomal associated protein 25 and synaptic vesicle glycoprotein 2b. 4. Genes directly related to 5-HT neurotransmission were not contained in the cDNA libraries and quantitative Real-time PCR for the serotonin transporter, tryptophan hydroxylase 2 and the 5-HT(1A) autoreceptor confirmed that these genes are not differentially expressed after 5-weeks of daily social stress. 5. These data show that 5 weeks of daily social defeat lead to significant changes in expression of genes related to neurotransmission and neuroplasticity in the DRN, whereas expression of genes directly related to 5-HT neurotransmission is apparently normal after this period of chronic stress.

Chronic mild stress exacerbates the effects of permanent bilateral common carotid artery occlusion on CA1 neurons

The effect of chronic mild stress (CMStress) was examined in an animal model of chronic cerebral hypoperfusion. Eight-month-old male Sprague-Dawley rats underwent permanent bilateral occlusion of the carotid arteries (2VO) or sham surgery. At 7 days postsurgery, animals from these groups were randomly assigned to undergo CMStress consisting of relatively mild stressor exposure 6 days a week for 6 weeks or a no-stress regimen. They were perfused 24 h thereafter and stereology was used to estimate the total number of hippocampal CA1 and CA3 pyramidal cells. Glial fibrillary acid protein (GFAP) immunoreactivity in the hippocampus was also measured. Degenerating neurons were quantified with the Fluoro-Jade B staining technique. CMStress significantly potentiated CA1 cell loss in 2VO rats (17% loss), compared to a 7% loss of CA1 cells in nonstressed 2VO rats. CMStress had no effect on CA3 cell number. CMStress also caused a significant reduction in GFAP-immunoreactive astrocyte density in CA1, CA3, and the hilus of both sham and 2VO rats. Fluoro-Jade staining was absent, indicating that cell loss probably occurred in the early stage of combined 2VO and CMStress. It was concluded that CMStress exacerbates the consequences of chronic cerebral hypoperfusion on CA1 probably by reducing astrocytes, thereby increasing extracellular glutamate and/or diminishing free radical defense systems. These findings have particular relevance to understanding the contribution of chronic stress to Alzheimer's disease, which, in its premorbid stage, is characterized by cerebral hypoperfusion, and, in its clinical stage, is characterized by CA1 cell loss.

Coping strategies in male and female rats exposed to multiple stressors

Because of the pathogenic effects of chronic stress exposure, it is important to identify factors, such as effective coping strategies, that mitigate stress-induced pathology. Of interest in the present study was the consistency of behavioral responses across a diverse array of stressors. Sixteen male and 16 female Long-Evans rats were assigned to either a stress or control group. The stressed animals were subsequently exposed to a battery of ecologically relevant stressors (e.g., predator odor, novel stimuli, and immunological challenge) to determine trends in coping strategies. Blood was collected for corticosterone (CORT) assay and brains were harvested for assessment of fos immunoreactivity in the paraventricular hypothalamus (PVH) and central amygdala (CEA) following exposure to the final stressor of fox urine. A correlational analysis indicated that certain response strategies (e.g., latency to respond in different stress tests such as the open-field and novel item tests) persist across several behavioral tests, especially those tests involving exploratory components. A subsequent principal component factor analysis revealed the following four components: initiative to explore, low reactivity, variable reactivity, and high reactivity. Females exhibited higher recovery CORT levels than males; however, sex only affected one behavioral response measure (i.e., females demonstrated more attempts to climb the wall in the forced-swim test than their male counterparts). In conclusion, these results support the importance and prevalence of initiative to explore as a common factor in many stress tests; additionally, the principal component analysis indicated that physiological correlates of stress are more closely associated with more challenging environments and stimuli such as forced swimming, immunological challenges, and exposure to predator odors.

Behavioral training increases local astrocytic metabolic activity but does not alter outcome of mild transient ischemia

Functional neurological outcome after transient ischemia might be improved by timely therapeutic intervention. To determine if restorative behavioral therapy influences damage, improves task learning, or alters astrocyte metabolic activity after ischemia, rats (food-restricted to 85% of free-feeding weight) were (a) first trained to respond on one of two levers under a fixed-ratio 20 schedule of food presentation (FR20), then (b) subjected to sham manipulation of carotid arteries or 10 min ischemia by four-vessel occlusion, followed by (c) 4 days of operant testing or inactivity, (d) then all rats were tested under a FR20 lever reversal task for 4 weeks, and (e) 3 days after the last behavioral session astrocyte metabolism was assayed by local uptake of [2-14C]acetate. Mild loss of hippocampal neurons occurred in ischemic rats with or without training after ischemia. Glial fibrillary acidic protein-positive astrocytes were present in similar numbers throughout brains of sham control and ischemic rats. Mild ischemia did not impair learning, and no changes in FR20 reversal learning were detected in sham vs. ischemic rats. Net [14C]acetate uptake was unaffected by ischemia but [14C]acetate uptake increased 15-24% (P<0.05; n=12-15/group) in specific structures (caudate, primary motor and sensorimotor cortex, CA1 hippocampus, subcortical white matter) in the pooled groups of rats that had 4 days FR20 testing vs. inactivity before reversal learning. 'Behavioral therapy' (operant testing on the 4 days immediately following either sham manipulation or ischemia) did not alter ischemic outcome, but was associated with higher acetate utilization in regions involved in motor activities.

Increased astrocyte reactivity in the hippocampus of murine models of type 1 diabetes: the nonobese diabetic (NOD) and streptozotocin-treated mice

Diabetes can be associated with cerebral dysfunction in humans and animal models of the disease. Moreover, brain anomalies and alterations of the neuroendocrine system are present in type 1 diabetes (T1D) animals, such as the spontaneous nonobese diabetic (NOD) mouse model and/or the pharmacological streptozotocin (STZ)-induced model. Because of the prevalent role of astrocytes in cerebral glucose metabolism and their intimate connection with neurones, we investigated hippocampal astrocyte alterations in prediabetic and diabetic NOD mice and STZ-treated diabetic mice. The number and cell area related to the glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes were quantified in the stratum radiatum region of the hippocampus by computerized image analysis in prediabetic (2, 4 and 8 weeks of age) and diabetic (16-week-old) NOD female mice, age and sex-matched lymphocyte-deficient NODscid and C57BL/6 control mice and, finally, STZ-induced diabetic and vehicle-treated nondiabetic 16-week-old C57BL/6 female mice. Astrocyte number was higher early in life in prediabetic NOD and NODscid mice than in controls, when transient hyperinsulinemia and low glycemia were found in these strains. The number and cell area of GFAP(+) cells further increased after the onset of diabetes in NOD mice. Similarly, in STZ-treated diabetic mice, the number of GFAP(+) cells and cell area were higher than in vehicle-treated mice. In conclusion, astrocyte changes present in genetic and pharmacological models of T1D appear to reflect an adaptive process to alterations of glucose homeostasis.