Patterns of neuronal activation in the rat brain and spinal cord in response to increasing durations of restraint stress

Central amygdala corticotropin-releasing factor neurons promote hyponeophagia but do not control alcohol drinking in mice

Corticotropin-releasing factor (CRF) signaling in the central nucleus of the amygdala (CeA) plays a critical role in rodent models of excessive alcohol drinking. However, the source of CRF acting in the CeA during alcohol withdrawal remains to be identified. In the present study, we hypothesized that CeA CRF interneurons may represent a behaviorally relevant source of CRF to the CeA increasing motivation for alcohol via negative reinforcement. We first observed that Crh mRNA expression in the anterior part of the mouse CeA correlates positively with alcohol intake in C57BL/6J males with a history of chronic binge drinking followed by abstinence and increases upon exposure to chronic intermittent ethanol (CIE) vapor inhalation. We then found that chemogenetic activation of CeA CRF neurons in Crh-IRES-Cre mouse brain slices increases gamma-aminobutyric acid (GABA) release in the medial CeA, in part via CRF1 receptor activation. While chemogenetic stimulation exacerbated novelty-induced feeding suppression (NSF) in alcohol-naïve mice, thereby mimicking the effect of withdrawal from CIE, it had no effect on voluntary alcohol consumption, following either acute or chronic manipulation. Furthermore, chemogenetic inhibition of CeA CRF neurons did not affect alcohol consumption or NSF in chronic alcohol drinkers exposed to air or CIE. Altogether, these findings indicate that CeA CRF neurons produce local release of GABA and CRF and promote hyponeophagia in naïve mice, but do not drive alcohol intake escalation or negative affect in CIE-withdrawn mice. The latter result contrasts with previous findings in rats and demonstrates species specificity of CRF circuit engagement in alcohol dependence.

Hormonal and neural responses to restraint stress in an animal model of perimenopause in female rats

The present study investigated the hormonal and neural responses to stress in a perimenopause animal model induced by 4-vinylcyclohexene diepoxide (VCD), which induces progressive follicular depletion in rodents, allowing studies on the transition to ovarian failure. Female rats, aged 28 days old, were s.c. injected for 15 consecutive days with corn oil or VCD. At 85 ± 5 days after the onset of treatment, the jugular vein was cannulated in the afternoon of metoestrus and in next morning (dioestrus) at 10.00 am, rats were subjected to 30 minutes of restraint stress. Blood samples were withdrawn before (-5 minutes), during (2, 5, 15 and 30 minutes) and after (45, 60 and 90 minutes) stress and plasma prolactin, progesterone and corticosterone levels were measured. Animals were perfused, brains processed for c-Fos/tyrosine hydroxylase (TH) in the locus coeruleus (LC) and c-Fos/corticotrophin-releasing factor (CRF) in the paraventricular nucleus (PVN). In unstressed rats the density of β-endorphin fibres was assessed in LC and PVN. In VCD-treated rats, stress-induced prolactin peak was higher, basal and peak progesterone levels were lower, and both levels of corticosterone were similar to controls. However, the recovery period was longer for both adrenal hormones. In VCD-treated rats the number of c-Fos/TH and c-Fos/CRF-immunoreactive neurones was higher whereas the density of β-endorphin fibres was lower in LC and PVN. We surmise that the hyperactivity of the LC and PVN neurones in VCD-treated rats may be a result of the lower progesterone levels that resulted in the decrease of β-endorphin content in both nuclei, thus impairing the negative-feedback mechanism in the recovery period.

Prepubertal and adult male rats differ in the degree and pattern of stress reactive neurons in brain regions that project to the paraventricular nucleus of the hypothalamus

The hormonal stress response, mediated by the hypothalamic-pituitary-adrenal (HPA) axis, shows greater responsiveness to various stressors in prepubertal compared to adult animals. Though the implications of this age-related change are unclear, this heightened reactivity might contribute to the increase in stress-related dysfunctions observed during adolescence. Interestingly, prepubertal animals show greater stress-induced neural activation compared to adults in the paraventricular nucleus of the hypothalamus (PVN), the area responsible for initiating the hormonal stress response. Thus, it is possible that direct afferents to the PVN, such as the anterior bed nucleus of the stria terminalis (aBST), nucleus of the solitary tract (NTS), posterior BST (pBST), medial preoptic area (MPOA), and dorsomedial nucleus (DMN), contribute to this age-dependent change in reactivity. To investigate these possibilities, two separate experiments were conducted in prepubertal (30 days old) and adult (70 days old) male rats using the retrograde tracer, Fluoro-Gold (FG), and FOS immunohistochemistry to study neural connectivity and activation, respectively. Though there was no difference in the number or size of FG-positive cells in the PVN afferents we examined, we found a significantly greater number of stress-induced FOS-like-positive cells in the aBST and significantly fewer in the DMN in prepubertal compared to adult animals. Together these data suggest that functional, instead of structural, changes in nuclei that project to the PVN may lead to the greater PVN stress responsiveness observed prior to adolescence. Furthermore, these data indicate that nuclei known to directly modulate HPA stress responsiveness show differential activation patterns before and after adolescent development.

Far-infrared Ray-mediated Antioxidant Potentials are Important for Attenuating Psychotoxic Disorders

Far-infrared ray (FIR) is an electromagnetic wave that produces various health benefits against pathophysiological conditions, such as diabetes mellitus, renocardiovascular disorders, stress, and depression etc. However, the therapeutic ap-plication on the FIR-mediated protective potentials remains to be further extended. To achieve better understanding on FIR-mediated therapeutic potentials, we summarized additional findings in the present study that exposure to FIR ameliorates stressful condition, memory impairments, drug dependence, and mitochondrial dysfunction in the central nervous system. In this review, we underlined that FIR requires modulations of janus kinase 2 / signal transducer and activator of transcription 3 (JAK2/STAT3), nuclear factor E2-related factor 2 (Nrf-2), muscarinic M1 acetylcholine receptor (M1 mAChR), dopamine D1 receptor, protein kinase C δ gene, and glutathione peroxidase-1 gene for exerting the protective potentials in response to neuropsychotoxic conditions

Hypoxia-ischemia in the immature rodent brain impairs serotonergic neuronal function in certain dorsal raphé nuclei

Neonatal hypoxia-ischemia (HI) results in losses of serotonergic neurons in specific dorsal raphé nuclei. However, not all serotonergic raphé neurons are lost and it is therefore important to assess the function of remaining neurons in order to understand their potential to contribute to neurological disorders in the HI-affected neonate. The main objective of this study was to determine how serotonergic neurons, remaining in the dorsal raphé nuclei after neonatal HI, respond to an external stimulus (restraint stress). On postnatal day 3 (P3), male rat pups were randomly allocated to one of the following groups: (i) control + no restraint (n = 5), (ii) control + restraint (n = 6), (iii) P3 HI + no restraint (n = 5) or (iv) P3 HI + restraint (n = 7). In the two HI groups, rat pups underwent surgery to ligate the common carotid artery and were then exposed to 6% O₂ for 30 minutes. Six weeks after P3 HI, on P45, rats were subjected to restraint stress for 30 minutes. Using dual immunolabeling for Fos protein, a marker for neuronal activity, and serotonin (5-hydroxytrypamine; 5-HT), numbers of Fos-positive 5-HT neurons were determined in five dorsal raphé nuclei. We found that restraint stress alone increased numbers of Fos-positive 5-HT neurons in all five dorsal raphé nuclei compared to control animals. However, following P3 HI, the number of stress-induced Fos-positive 5-HT neurons was decreased significantly in the dorsal raphé ventrolateral, interfascicular and ventral nuclei compared with control animals exposed to restraint stress. In contrast, numbers of stress-induced Fos-positive 5-HT neurons in the dorsal raphé dorsal and caudal nuclei were not affected by P3 HI. These data indicate that not only are dorsal raphé serotonergic neurons lost after neonatal HI, but also remaining dorsal raphé serotonergic neurons have reduced differential functional viability in response to an external stimulus. Procedures were approved by the University of Queensland Animal Ethics Committee (UQCCR958/08/NHMRC) on February 27, 2009.

Corticotropin-Releasing Factor-Producing Cells in the Paraventricular Nucleus of the Hypothalamus and Extended Amygdala Show Age-Dependent FOS and FOSB/DeltaFOSB Immunoreactivity in Acute and Chronic Stress Models in the Rat

Corticotropin-releasing factor (CRF) immunoreactive (ir) neurons of the paraventricular nucleus of the hypothalamus (PVN) play pivotal role in the coordination of stress response. CRF-producing cells in the central nucleus of amygdala (CeA) and oval division of the bed nucleus of stria terminalis (BNSTov) are also involved in stress adaptation and mood control. Immediate early gene products, subunits of the transcription factor activator protein 1 (AP1) are commonly used as acute (FOS) and/or chronic (FOSB/deltaFOSB) markers for the neuronal activity in stress research. It is well known that the course of aging affects stress adaptation, but little is known about the aging-related stress sensitivity of CRF neurons. To the best of our knowledge, the stress-induced neuronal activity of CRF neurons in the course of aging in acute and chronic stress models was not studied systematically yet. Therefore, the aim of the present study was to quantify the acute restraint stress (ARS) and chronic variable mild stress (CVMS) evoked neuronal activity in CRF cells of the PVN, CeA, and BNSTov using triple-label immunofluorescence throughout the whole lifespan in the rat. We hypothesized that the FOS and FOSB content of CRF cells upon ARS or CVMS decreases with age. Our results showed that the FOS and FOSB response to ARS declined with age in the PVN-CRF cells. BNSTov and CeA CRF cells did not show remarkable stress-induced elevation of these markers neither in ARS, nor in CVMS. Exposure to CVMS resulted in an age-independent significant increase of FOSB/delta FOSB immunosignal in PVN-CRF neurons. Unexpectedly, we detected a remarkable stress-independent FOSB/deltaFOSB signal in CeA- and BNSTov-CRF cells that declined with the course of aging. In summary, PVN-CRF cells show decreasing acute stress sensitivity (i.e., FOS and FOSB immunoreactivity) with the course of aging, while their (FOSB/deltaFOSB) responsivity to chronic challenge is maintained till senescence. Stress exposure does not affect the occurrence of the examined Fos gene products in CeA- and BNSTov-CRF cells remarkably suggesting that their contribution to stress adaptation response does not require AP1-controlled transcriptional changes.

PACAP regulation of central amygdala GABAergic synapses is altered by restraint stress

The pituitary adenylate cyclase-activating polypeptide (PACAP) system plays a central role in the brain's emotional response to psychological stress by activating cellular processes and circuits associated with threat exposure. The neuropeptide PACAP and its main receptor PAC1 are expressed in the rodent central amygdala (CeA), a brain region critical in negative emotional processing, and CeA PACAPergic signaling drives anxiogenic and stress coping behaviors. Despite this behavioral evidence, PACAP's effects on neuronal activity within the medial subdivision of the CeA (CeM, the major output nucleus for the entire amygdala complex) during basal conditions and after psychological stress remain unknown. Therefore, in the present study, male Wistar rats were subjected to either restraint stress or control conditions, and PACAPergic regulation of CeM cellular function was assessed using immunohistochemistry and whole-cell patch-clamp electrophysiology. Our results demonstrate that PACAP-38 potentiates GABA release in the CeM of naïve rats, via its actions at presynaptic PAC1. Basal PAC1 activity also enhances GABA release in an action potential-dependent manner. Notably, PACAP-38's facilitation of CeM GABA release was attenuated after a single restraint stress session, but after repeated sessions returned to the level observed in naïve animals. A single restraint session also significantly decreased PAC1 levels in the CeM, with repeated restraint sessions producing a slight recovery. Collectively our data reveal that PACAP/PAC1 signaling enhances inhibitory control of the CeM and that psychological stress can modulate this influence to potentially disinhibit downstream effector regions that mediate anxiety and stress-related behaviors. This article is part of the special issue on 'Neuropeptides'.

Both Basal and Acute Restraint Stress-Induced c-Fos Expression Is Influenced by Age in the Extended Amygdala and Brainstem Stress Centers in Male Rats

The hypothalamus-pituitary-adrenal axis (HPA) is the main regulator of the stress response. The key of the HPA is the parvocellular paraventricular nucleus of the hypothalamus (pPVN) controlled by higher-order limbic stress centers. The reactivity of the HPA axis is considered to be a function of age, but to date, little is known about the background of this age-dependency. Sporadic literature data suggest that the stress sensitivity as assessed by semi-quantitation of the neuronal activity marker c-Fos may also be influenced by age. Here, we aimed at investigating the HPA activity and c-Fos immunoreactivity 2 h after the beginning of a single 60 min acute restraint stress in eight age groups of male Wistar rats. We hypothesized that the function of the HPA axis (i.e., pPVN c-Fos and blood corticosterone (CORT) level), the neuronal activity of nine stress-related limbic areas (i.e., magnocellular PVN (mPVN), medial (MeA), central (CeA), basolateral nuclei of the amygdala, the oval (ovBNST), dorsolateral (dlBNST), dorsomedial (dmBNST), ventral and fusiform (fuBNST) divisions of the bed nucleus of the stria terminalis (BNST)), and two brainstem stress centers such as the centrally projecting Edinger-Westphal nucleus (cpEW) and dorsal raphe nucleus (DR) show age dependency in their c-Fos response. The somatosensory barrel cortex area (S1) was evaluated to test whether the age dependency is specific for stress-centers. Our results indicate that the stress-induced rise in blood CORT titer was lower in young age reflecting relatively low HPA activity. All 12 stress-related brain areas showed c-Fos response that peaked at 2 months of age. The magnitude of c-Fos immunoreactivity correlated negatively with age in seven regions (MeA, CeA, ovBNST, dlBNST, dmBNST, fuBNST and pPVN). Unexpectedly, the CeA, ovBNST and cpEW showed a considerable basal c-Fos expression in 1-month-old rats which decreased with age. The S1 showed a U-shaped age-related dynamics in contrast to the decline observed in stress centers. We conclude that the age- and brain area dependent dynamics in stress-induced neuronal activity pattern may contribute to the age dependance of the stress reactivity. Further studies are in progress to determine the neurochemical identity of neurons showing age-dependent basal and/or stress-induced c-Fos expression.

RDoC-based categorization of amygdala functions and its implications in autism

Confusion endures as to the exact role of the amygdala in relation to autism. To help resolve this we turned to the NIMH's Research Domain Criteria (RDoC) which provides a classification schema that identifies different categories of behaviors that can turn pathologic in mental health disorders, e.g. autism. While RDoC incorporates all the known neurobiological substrates for each domain, this review will focus primarily on the amygdala. We first consider the amygdala from an anatomical, historical, and developmental perspective. Next, we examine the different domains and constructs of RDoC that the amygdala is involved in: Negative Valence Systems, Positive Valence Systems, Cognitive Systems, Social Processes, and Arousal and Regulatory Systems. Then the evidence for a dysfunctional amygdala in autism is presented with a focus on alterations in development, prenatal valproic acid exposure as a model for ASD, and changes in the oxytocin system therein. Finally, a synthesis of RDoC, the amygdala, and autism is offered, emphasizing the task of disambiguation and suggestions for future research.

Brain c-fos expression patterns induced by emotional stressors differing in nature and intensity

Regardless of its particular nature, emotional stressors appear to elicit a widespread and roughly similar brain activation pattern as evaluated by c-fos expression. However, their behavioral and physiological consequences may strongly differ. Here we addressed in adult male rats the contribution of the intensity and the particular nature of stressors by comparing, in a set of brain areas, the number of c-fos expressing neurons in response to open-field, cat odor or immobilization on boards (IMO). These are qualitatively different stressors that are known to differ in terms of intensity, as evaluated by biological markers. In the present study, plasma levels of the adrenocorticotropic hormone (ACTH) demonstrated that intensity increases in the following order: open-field, cat odor and IMO. Four different c-fos activation patterns emerged among all areas studied: (i) positive relationship with intensity (posterior-dorsal medial amygdala, dorsomedial hypothalamus, lateral septum ventral and paraventricular nucleus of the hypothalamus), (ii) negative relationship with intensity (cingulate cortex 1, posterior insular cortex, dorsal striatum, nucleus accumbens and some subdivisions of the hippocampal formation); (iii) activation not dependent on the intensity of the stressor (prelimbic and infralimbic cortex and lateral and basolateral amygdala); and (iv) activation specifically associated with cat odor (ventromedial amygdala and ventromedial hypothalamus). Histone 3 phosphorylation at serine 10, another neuronal activation marker, corroborated c-fos results. Summarizing, deepest analysis of the brain activation pattern elicit by emotional stressor indicated that, in spite of activating similar areas, each stressor possess their own brain activation signature, mediated mainly by qualitative aspects but also by intensity.

Stress-Dependent Changes in the CacyBP/SIP Interacting Protein S100A6 in the Mouse Brain

The CacyBP/SIP target S100A6 is widely present in the nervous system, and its up-regulation is associated with certain neurodegenerative diseases. Here, we examined the involvement of S100A6 protein in stress responses in mice. Using Western blotting, we observed a marked change in brainstem structures, whereby stressed mice showed approximately one-third the protein level produced in the control group. A decreased level of S100A6 protein in stressed animals was also detected in the olfactory bulb and the cerebellum and stress-related structures such as the hippocampus and the hypothalamus. Additionally, using immunohistochemistry, high levels of S100A6 expression were observed in astrocytes localized in the border zones of all brain ventricles, tanycytes of the ventro-lateral walls of the hypothalamus, including the arcuate nucleus (ARH) and low levels of this protein were in neurons of the olfactory bulb, the hippocampus, the thalamus, the cerebral cortex, the brainstem and the cerebellum. Although S100A6-expressing cells in all these brain structures did not change their phenotype in response to stress, the intensity of immunofluorescent labeling in all studied structures was lower in stressed mice than in control animals. For example, in the ARH, where extremely strong immunostaining was observed, the number of immunolabeled fibers was decreased by approximately half in the stressed group compared with the controls. Although these results are descriptive and do not give clue about functional role of S100A6 in stress, they indicate that the level of S100A6 decreases in several brain structures in response to chronic mild stress, suggesting that this protein may modify stress responses.

Repeated exposure to far infrared ray attenuates acute restraint stress in mice via inhibition of JAK2/STAT3 signaling pathway by induction of glutathione peroxidase-1

Exposure to far-infrared ray (FIR) has been shown to exert beneficial effects on cardiovascular and emotional disorders. However, the precise underlying mechanism mediated by FIR remains undetermined. Since restraint stress induces cardiovascular and emotional disorders, the present study investigated whether exposure to FIR affects acute restraint stress (ARS) in mice. c-Fos-immunoreactivity (IR) was significantly increased in the paraventricular hypothalamic nucleus (PVN) and dorsomedial hypothalamic nucleus (DMH) in response to ARS. The increase in c-Fos-IR parallels that in oxidative burdens in the hypothalamus against ARS. Exposure to FIR significantly attenuated increases in the c-Fos-IR, oxidative burdens and corticosterone level. ARS elicited decreases in GSH/GSSG ratio, cytosolic Cu/Zn-superoxide dismutase (SOD-1), glutathione peroxidase (GPx), and glutathione reductase (GR) activities. FIR-mediated attenuation was particularly observed in ARS-induced decrease in GPx, but not in SOD-1 or GR activity. Consistently, ARS-induced decreases in GPx-1-immunoreactivity in PVN and DMH, and decreases in GPx-1 expression in the hypothalamus were significantly attenuated by FIR. ARS-induced significant increases in phosphorylation of JAK2/STAT3, and nuclear translocation and DNA-binding activity of NFκB were observed in the hypothalamus. Exposure to FIR selectively attenuated phosphorylation of JAK2/STAT3, but did not diminish nuclear translocation and DNA-binding activity of NFκB, suggesting that JAK2/STAT3 constitutes a critical target for FIR-mediated pharmacological potential. ARS-induced increase in c-Fos-IR in the PVN and DMH of non-transgenic mice was significantly attenuated by FIR exposure or JAK2/STAT3 inhibitor AG490. GPx-1 overexpressing transgenic mice significantly protected increases in the c-Fos-IR and corticosterone level induced by ARS. However, neither FIR exposure nor AG490 significantly affected attenuations by genetic overexpression of GPx-1. Moreover, AG490 did not exhibit any additional positive effects against the attenuation by genetic overexpression of GPx-1 or FIR exposure. Our results indicate that exposure to FIR significantly protects ARS-induced increases in c-Fos-IR and oxidative burdens via inhibition of JAK2/STAT3 signaling by induction of GPx-1.

The neuroendocrine response to stress under the effect of drugs: Negative synergy between amphetamine and stressors

There have been numerous studies into the interaction between stress and addictive drugs, yet few have specifically addressed how the organism responds to stress when under the influence of psychostimulants. Thus, we studied the effects of different acute stressors (immobilization, interleukin-1β and forced swimming) in young adult male rats simultaneously exposed to amphetamine (AMPH, 4 mg/kg SC), evaluating classic biological markers. AMPH administration itself augmented the plasma hypothalamic-pituitary-adrenal (HPA) hormones, adrenocorticotropin (ACTH) and corticosterone, without affecting plasma glucose levels. By contrast, this drug dampened the peripheral HPA axis, as well as the response of glucose to the three stressors. We also found that AMPH administration completely blocked the forced swim-induced expression of the corticotropin-releasing hormone (hnCRH) and it partially reduced c-fos expression in the paraventricular nucleus of the hypothalamus (PVN). Indeed, this negative synergy in the forced swim test could even be observed with a lower dose of AMPH (1mg/kg, SC), a dose that is usually received in self-administration experiments. In conclusion, when rats that receive AMPH are subjected to stress, a negative synergy occurs that dampens the prototypic peripheral physiological response to stress and activation of the PVN.

To stress or not to stress: a question of models

Stress research is a rapidly evolving field that encompasses numerous disciplines ranging from neuroscience to metabolism. With many new researchers migrating into the field, navigating the hows and whys of specific research questions can sometimes be enigmatic given the availability of so many models in the stress field. Additionally, as with every field, there are many seemingly minor experimental details that can have dramatic influences on data interpretation, although many of these are unknown to those not familiar with the field. The aim of this overview is to provide some suggestions and points to guide researchers moving into the stress field and highlight relevant methodological points that they should consider when choosing a model for stress and deciding how to structure a study. We briefly provide a primer on the basics of endpoint measurements in the stress field, factors to consider when choosing a model for acute stress, the difference between repeated and chronic stress, and importantly, influencing variables that modulate endpoints of analysis in stress work.

Effects of mild calorie restriction on anxiety and hypothalamic-pituitary-adrenal axis responses to stress in the male rat

Chronic calorie restriction (CR) is one of the few interventions to improve longevity and quality of life in a variety of species. It also reduces behavioral indices of anxiety and influences some stress hormones under basal conditions. However, it is not known how CR influences hypothalamic–pituitary–adrenal (HPA) axis function or if those on a CR diet have heightened HPA axis responses to stress. We hypothesized elevated basal glucocorticoid levels induced by CR would lead to exacerbated HPA axis responses to the psychological stress, restraint, in the male rat. We first confirmed rats fed 75% of their normal calorie intake for 3 weeks were less anxious than ad libitum‐fed (AD) rats in the elevated plus maze test for anxiety. The anxiolytic effect was mild, with only grooming significantly attenuated in the open field and no measured behavior affected in the light/dark box. Despite elevated basal glucocorticoids, CR rats had very similar hormonal and central responses to 15‐min restraint to the AD rats. Both CR and AD rats responded to restraint stress with a robust increase in glucocorticoids that was resolved by 60 min. Both groups also showed robust neuronal activation in the paraventricular nucleus of the hypothalamus and in other stress‐ and feeding‐sensitive brain regions that was not substantially affected by calorie intake. Our findings thus demonstrate chronic mild CR is subtly anxiolytic and is not likely to affect HPA axis responses to psychological stress. These findings support research suggesting a beneficial effect of mild CR.

Oxidative stress--implications, source and its prevention

Oxidative stress has been a major predicament of present day living. It has been the product of imbalance between the processes involved in free radical generation and their neutralization by enzymatic and non-enzymatic defence mechanisms. The oxidative stress has been contributed by numerous factors including heavy metals, organic compound-rich industrial effluents, air pollutants and changing lifestyle pattern focussing mainly on alcohol consumption, dietary habits, sun exposure, nuclear emissions, etc. The most common outcome of oxidative stress is the increased damage of lipid, DNA and proteins that resulted in the development of different pathologies. Among these pathologies, cancer is the most devastating and linked to multiple mutations arising due to oxidative DNA and protein damage that ultimately affect the integrity of the genome. The chemopreventive agents particularly nutraceuticals are found to be effective in reducing cancer incidences as these components have immense antioxidative, antimutagenic and antiproliferative potentials and are an important part of our dietary components. These secondary metabolites, due to their unique chemical structure, facilitate cell-to-cell communication, repair DNA damage by the downregulation of transcription factors and inhibit the activity of protein kinases and cytochrome P450-dependent mixed function oxidases. These phytochemicals, therefore, are most appropriate in combating oxidative stress-related disorders due to their tendency to exert better protective effect without having any distinct side effect.

Being suckled in a large litter mitigates the effects of early-life stress on hypothalamic-pituitary-adrenal axis function in the male rat

The perinatal environment influences stress responses in the long-term, as does body composition. Male rats suckled in large litters, where they have reduced access to milk and attention from the dam, are less anxious and have attenuated hypothalamic-pituitary-adrenal (HPA) axis responses to stress compared to rats from control litters. In the present study, we investigated whether this early-life environment can also ameliorate anxiety and HPA axis function in rats prone to be stress-sensitive. We conducted these experiments in male rats from control litters (n = 12) or large litters (n = 20). Half were given 24 h of maternal separation on postnatal day 10 to induce HPA axis hyperactivity; the remainder staying undisturbed with their dam. When the rats reached adulthood, we examined behavioural indices of anxiety (elevated plus maze) and depression (Porsolt's forced swim test) under basal conditions and after 15 min of restraint stress. We also examined neuronal activation in the paraventricular nucleus of the hypothalamus (PVN) as an index of HPA axis function. Being suckled in a large litter led to a significantly attenuated PVN response to stress in adulthood. Maternal separation strongly exacerbated the stress-induced increase in PVN neuronal activation in control rats but did not affect the PVN response in large-litter rats. Immobility in the forced swim after restraint was also exacerbated in neonatally maternally separated control rats but not in those from large litters. Our findings show that being suckled in large litters mitigates the effects of early-life stress on HPA axis function and indices of depression in the rat.

Angiotensin 1A receptors transfected into caudal ventrolateral medulla inhibit baroreflex gain and stress responses

AIMS

The caudal ventrolateral medulla (CVLM) is important for autonomic regulation and is rich in angiotensin II type 1A receptors (AT(1A)R). To determine their function, we examined whether the expression of AT(1A)R in the CVLM of mice lacking AT(1A)R (AT(1A)(-/-)) alters baroreflex sensitivity and cardiovascular responses to stress.

METHODS AND RESULTS

Bilateral microinjections into the CVLM of AT(1A)(-/-) mice of lentivirus with the phox-2 selective promoter (PRSx8) were made to express either AT(1A)R (Lv-PRSx8-AT(1A)) or green fluorescent protein (Lv-PRSx8-GFP) as a control. Radiotelemetry was used to record mean arterial pressure (MAP), heart rate (HR), and locomotor activity. Following injection of Lv-PRSx8-GFP, robust neuronal expression of GFP was observed with ∼60% of the GFP-positive cells also expressing the catecholamine-synthetic enzyme tyrosine hydroxylase. After 5 weeks, there were no differences in MAP or HR between groups, but the Lv-PRSx8-AT(1A)- injected mice showed reduced baroreflex sensitivity (-25%, P = 0.003) and attenuated pressor responses to cage-switch and restraint stress compared with the Lv-PRSx8-GFP-injected mice. Reduced MAP mid-frequency power during cage-switch stress reflected attenuated sympathetic activation (Pgroup × stress = 0.04). Fos-immunohistochemistry indicated greater activation of forebrain and hypothalamic neurons in the Lv-PRSx8-AT(1A) mice compared with the control.

CONCLUSION

The expression of AT(1A)R in CVLM neurons, including A1 neurons, while having little influence on the basal blood pressure or HR, may play a tonic role in inhibiting cardiac vagal baroreflex sensitivity. However, they strongly facilitate the forebrain response to aversive stress, yet reduce the pressor response presumably through greater sympatho-inhibition. These findings outline novel and specific roles for angiotensin II in the CVLM in autonomic regulation.

Pancreatic insulin and exocrine secretion are under the modulatory control of distinct subpopulations of vagal motoneurones in the rat

Brainstem vago-vagal neurocircuits modulate upper gastrointestinal functions. Derangement of these sensory-motor circuits is implicated in several pathophysiological states, such as gastroesophageal reflux disease (GERD), functional dyspepsia and, possibly, pancreatitis. While vagal circuits controlling the stomach have received more attention, the organization of brainstem pancreatic neurocircuits is still largely unknown. We aimed to investigate the in vitro and in vivo modulation of brainstem vagal circuits controlling pancreatic secretion. Using patch clamp techniques on identified vagal pancreas-projecting neurones, we studied the effects of metabotropic glutamate receptor (mGluR) agents in relation to the effects of exendin-4, a glucagon-like peptide 1 analogue, cholecystokinin (CCK) and pancreatic polypeptide (PP). An in vivo anaesthetized rat preparation was used to measure pancreatic exocrine secretion (PES) and plasma insulin following microinjection of metabotropic glutamate receptor (mGluR) agonists and exendin-4 in the brainstem. Group II and III mGluR agonists (2R,4R-4-aminopyrrolidine-2,4-dicarboxylate (APDC) and L(+)-2-amino-4-phosphonobutyric acid (L-AP4), respectively) decreased the frequency of miniature inhibitory and excitatory postsynaptic currents (mIPSCs and mEPSCs, respectively) in the majority of the neurones tested. All neurones responsive to L-AP4 were also responsive to APDC, but not vice versa. Further, in neurones where L-AP4 decreased mIPSC frequency, exendin-4 increased, while PP had no effect upon, mIPSC frequency. Brainstem microinjection of APDC or L-AP4 decreased plasma insulin secretion, whereas only APDC microinjections increased PES. Exendin-4 microinjections increased plasma insulin. Our results indicate a discrete organization of vagal circuits, which opens up promising avenues of research aimed at investigating the physiology of homeostatic autonomic neurocircuits.

α1 and α2-adrenoceptors in the medial amygdaloid nucleus modulate differently the cardiovascular responses to restraint stress in rats

Medial amygdaloid nucleus (MeA) neurotransmission has an inhibitory influence on cardiovascular responses in rats submitted to restraint, which are characterized by both elevated blood pressure (BP) and intense heart rate (HR) increase. In the present study, we investigated the involvement of MeA adrenoceptors in the modulation of cardiovascular responses that are observed during an acute restraint. Male Wistar rats received bilateral microinjections of the selective α1-adrenoceptor antagonist WB4101 (10, 15, and 20 nmol/100 nL) or the selective α2-adrenoceptor antagonist RX821002 (10, 15, and 20 nmol/nL) into the MeA, before the exposure to acute restraint. The injection of WB4101 reduced the restraint-evoked tachycardia. In contrast, the injection of RX821002 increased the tachycardia. Both drugs had no influence on BP increases observed during the acute restraint. Our findings indicate that α1 and α2-adrenoceptors in the MeA play different roles in the modulation of the HR increase evoked by restraint stress in rats. Results suggest that α1-adrenoceptors and α2-adrenoceptors mediate the MeA-related facilitatory and inhibitory influences on restraint-related HR responses, respectively.

Comparison of CRF-immunoreactive neurons distribution in mouse and rat brains and selective induction of Fos in rat hypothalamic CRF neurons by abdominal surgery

Mice and rats are widely used in stress-related behavioral studies while little is known about the distribution of the stress hormone, corticotropin-releasing factor (CRF) in the mouse brain. We developed and characterized a novel rat/mouse CRF polyclonal antibody (CURE ab 200101) that was used to detect and compare the brain distributions of CRF immunoreactivity in naïve and colchicine-treated rats and mice. We also assessed whether the visceral stressor of abdominal surgery activated brain CRF neurons using double labeling of Fos/CRF in naïve rats. CRF-ir neurons were visualized in the cortex, bed nucleus of the stria terminalis, central amygdala, hypothalamic paraventricular nucleus (PVN), Barrington's nucleus and dorsolateral tegmental area in naïve rats. CRF-immunoreactive (ir) neurons in the mouse brain were detected only after colchicine. The pattern shows fundamental similarity compared to the colchicine-treated rat brain, however, there were differences with a lesser distribution in both areas and density except in the lateral septum and external subnucleus of the lateral parabrachial nucleus which contained more CRF-ir neurons in mice, and CRF-ir neurons in the dorsal motor nucleus of the vagus were found only in mice. Abdominal surgery in naïve rats induced Fos-ir in 30% of total CRF-ir neurons in the PVN compared with control (anesthesia alone) while Fos was not co-localized with CRF in other brain nuclei. These data indicate that CRF-ir distribution in the brain displays similarity as well as distinct features in mice compared to rats that may underlie some differential stress responses. Abdominal surgery activates CRF-ir neurons selectively in the PVN of rats without colchicine treatment.

Anxiety and hypothalamic-pituitary-adrenal axis responses to psychological stress are attenuated in male rats made lean by large litter rearing

An excellent strategy to treat overactive responses to stress is to exploit the body's inherent stress-inhibitory mechanisms. Stress responses are known to differ between individuals depending upon their level and distribution of adiposity and their experiences in early life. For instance, we have recently shown that female rats made obese by overfeeding during the neonatal period have exacerbated responses to psychological stress. The converse may be true for those that are underfed during this period. In this investigation we hypothesized that rats made lean by neonatal underfeeding would have reduced anxiety and attenuated hypothalamic-pituitary-adrenal (HPA) axis responses to psychological stress. Our findings show that male (but not female) rats, made smaller by being suckled in a large litter, show reduced anxiety-related behaviour compared with those from normal litters when tested in the elevated plus maze. These smaller males also have attenuated activation of the paraventricular nucleus of the hypothalamus in response to the psychological stress, restraint, and corticosterone responses to restraint that return more quickly to baseline than controls. These findings are exciting from the perspective of understanding and potentially exploiting the body's inherent stress-inhibitory mechanisms to treat overactive responses to stress. They also provide an indication that being lean may be able to ameliorate overactive stress responses. Understanding the mechanisms by which these stress responses are attenuated in lean animals will be important for future strategies to treat diseases associated with overactive HPA axes in humans.

Central neural responses to restraint stress are altered in rats with an early life history of repeated brief maternal separation

Repeated brief maternal separation (i.e. 15 min daily, MS15) of rat pups during the first one to two postnatal weeks enhances active maternal care received by the pups and attenuates their later behavioral and neuroendocrine responses to stress. In previous work, we found that MS15 also alters the developmental assembly and later structure of central neural circuits that control autonomic outflow to the viscera, suggesting that MS15 may alter central visceral circuit responses to stress. To examine this, juvenile rats with a developmental history of either MS15 or no separation (NS) received microinjection of retrograde neural tracer, FluoroGold (FG), into the hindbrain dorsal vagal complex (DVC). After 1 week, FG-injected rats and surgically intact littermates were exposed to either a 15-min restraint stress or an unrestrained control condition, and then perfused 1 h later. Brain tissue sections from surgically intact littermates were processed for Fos alone or in combination with phenotypic markers to examine stress-induced activation of neurons within the paraventricular nucleus of the hypothalamus (PVN), bed nucleus of the stria terminalis (BNST), and hindbrain DVC. Compared to NS controls, MS15 rats displayed less restraint-induced Fos activation within the dorsolateral BNST (dBNST), the caudal PVN, and noradrenergic neurons within the caudal DVC. To examine whether these differences corresponded with altered neural inputs to the DVC, sections from tracer-injected rats were double-labeled for FG and Fos to quantify retrogradely labeled neurons within hypothalamic and limbic forebrain regions of interest, and the proportion of these neurons activated after restraint. Only the dBNST displayed a significant effect of postnatal experience on restraint-induced Fos activation of DVC-projecting neurons. The distinct regional effects of MS15 on stress-induced recruitment of neurons within hypothalamic, limbic forebrain, and hindbrain regions has interesting implications for understanding how early life experience shapes the functional organization of stress-responsive circuits.

Stress-induced decreases in local cerebral glucose utilization in specific regions of the mouse brain

Background

Restraint stress in rodents has been reported to activate the hypothalamic-pituitary-adrenocortical (HPA) axis and to increase c-fos expression in regions that express components of the corticotropin-releasing factor (CRF) system. We have previously reported that acute central administration of CRF increased a measure of relative local cerebral glucose utilization (LCGU), a measure of neuronal activity in specific brain regions, and activated the HPA axis in mice. It was hypothesized that the involvement of the CRF system in the stress response would lead to similar changes in relative LCGU after restraint stress. In the present studies the effect of restraint stress on relative LCGU and on the HPA axis in C57BL/6N mice were examined.

Findings

Restraint stress activated the HPA axis in a restraint-duration dependent manner, but in contrast to the reported effects of CRF, significantly decreased relative LCGU in frontal cortical, thalamic, hippocampal and temporal dissected regions. These findings support evidence that stressors enforcing limited physical activity reduce relative LCGU, in contrast to high activity stressors such as swim stress.

Conclusions

In conclusion, the present studies do not support the hypothesis that stress-induced changes in relative LCGU are largely mediated by the CRF system. Further studies will help to delineate the role of the CRF system in the early phases of the relative LCGU response to stress and investigate the role of other neurotransmitter systems in this response.

A protease inhibitor against acute stress-induced visceral hypersensitivity and paracellular permeability in rats

In the present study, we investigated the effects of camostat mesilate (CM), a synthetic protease inhibitor, on visceral sensitivity and paracellular permeability induced by the acute restraint stress. We also explored the possible mechanisms underlying these effects. The acute restraint stress was induced by wrapping the fore shoulders, upper forelimbs and thoracic trunk of Sprague-Dawley rats for 2h. Either CM (30, 100 and 300mg/kg) or saline was intragastrically administrated to the rats 30min before the acute restraint stress. Visceral perception was quantified as visceral motor response with an electromyography in a subset of rats. Paracellular permeability was determined in another subset of rats. We found that the visceral sensitivity and paracellular permeability were significantly reduced in the CM-treated rats. Moreover, the fecal protease activity was decreased in the CM-treated rats. The ZO-1 protein expression was markedly reduced by the stress treatment, but this decrease was suppressed by CM administration. Our data indicated that CM could efficiently inhibit visceral sensitivity and paracellular permeability induced by the acute restraint stress in rats. Therefore, CM might be an effective drug for the treatment of irritable bowel syndrome.

The role of the bed nucleus of the stria terminalis in stress-induced inhibition of pulsatile luteinising hormone secretion in the female rat

The bed nucleus of the stria terminalis (BNST) occupies a central position in the neural circuitry regulating the hypothalamic-pituitary-adrenocortical axis response to stress. The potential role of the BNST in stress-induced suppression of the gondotrophin-releasing hormone (GnRH) pulse generator, the central regulator of the reproductive system, was assessed by examining the effects of micro-infusion of corticotrophin-releasing factor (CRF) or its antagonist into the BNST on pulsatile luteinising hormone (LH) secretion or stress-induced inhibition of LH pulses, respectively. Ovariectomised oestrogen-treated rats were implanted chronically with bilateral cannulae in the dorsolateral BNST and i.v. catheters. CRF (25, 50 or 100 pmol in 200 nl of artificial cerebrospinal fluid) administered bilaterally into the BNST resulted in a dose-dependent decrease in LH pulse frequency, and induced Fos expression in glutamic acid decarboxylase immunostained neurones in the medial preoptic area. These results suggest that the activation of hypothalamic GABAergic neurones in response to intra-BNST administration of CRF may be involved in the suppression of LH pulses. Furthermore, administration of CRF antagonist (280 pmol astressin-B, three times at 20-min intervals) into the BNST effectively blocked the suppression of pulsatile LH secretion in response to restraint (1 h) but not hypoglycaemic (0.25 U insulin/kg, i.v.) stress. These data suggest that CRF innervation of the dorsolateral BNST plays a key, but differential, role in stress-induced suppression of the GnRH pulse generator.

c-Fos expression in the supraoptic nucleus is the most intense during different durations of restraint water-immersion stress in the rat

Restraint water-immersion stress (RWIS) can induce anxiety, hypothermia, and severe vagally-mediated gastric dysfunction. The present work explored the effects of different durations of RWIS on neuronal activities of the forebrain by c-Fos expression in conscious rats exposed to RWIS for 0, 30, 60, 120, or 180 min. The peak of c-Fos induction was distinct for different forebrain regions. The most intense c-Fos induction was always observed in the supraoptic nucleus (SON), and then in the hypothalamic paraventricular nucleus (PVN), posterior cortical amygdaloid nucleus (PCoA), central amygdaloid nucleus (CeA), and medial prefrontal cortex (mPFC). Moreover, body temperature was reduced to the lowest degree after 60 min of RWIS, and the gastric lesions tended to gradually worsen with the prolonging of RWIS duration. These data strongly suggest that these nuclei participate in the organismal response to RWIS to different degrees, and may be involved in the hypothermia and gastric lesions induced by RWIS.

Catecholaminergic systems in stress: structural and molecular genetic approaches

Stressful stimuli evoke complex endocrine, autonomic, and behavioral responses that are extremely variable and specific depending on the type and nature of the stressors. We first provide a short overview of physiology, biochemistry, and molecular genetics of sympatho-adrenomedullary, sympatho-neural, and brain catecholaminergic systems. Important processes of catecholamine biosynthesis, storage, release, secretion, uptake, reuptake, degradation, and transporters in acutely or chronically stressed organisms are described. We emphasize the structural variability of catecholamine systems and the molecular genetics of enzymes involved in biosynthesis and degradation of catecholamines and transporters. Characterization of enzyme gene promoters, transcriptional and posttranscriptional mechanisms, transcription factors, gene expression and protein translation, as well as different phases of stress-activated transcription and quantitative determination of mRNA levels in stressed organisms are discussed. Data from catecholamine enzyme gene knockout mice are shown. Interaction of catecholaminergic systems with other neurotransmitter and hormonal systems are discussed. We describe the effects of homotypic and heterotypic stressors, adaptation and maladaptation of the organism, and the specificity of stressors (physical, emotional, metabolic, etc.) on activation of catecholaminergic systems at all levels from plasma catecholamines to gene expression of catecholamine enzymes. We also discuss cross-adaptation and the effect of novel heterotypic stressors on organisms adapted to long-term monotypic stressors. The extra-adrenal nonneuronal adrenergic system is described. Stress-related central neuronal regulatory circuits and central organization of responses to various stressors are presented with selected examples of regulatory molecular mechanisms. Data summarized here indicate that catecholaminergic systems are activated in different ways following exposure to distinct stressful stimuli.

Lactobacillus farciminis treatment attenuates stress-induced overexpression of Fos protein in spinal and supraspinal sites after colorectal distension in rats

Abstract Irritable bowel syndrome (IBS), frequently associated with psychological distress, is characterized by hypersensitivity to gut wall distension. Some probiotics are able to alleviate IBS symptoms and reduce visceromotor response to mechanical stimuli in animals. Moreover, we have previously shown that Lactobacillus farciminis treatment abolished the hyperalgesia to colorectal distension (CRD) induced by acute stress. The aims of the present study were to determine whether (i) stress-induced visceral hyperalgesia modifies the expression of Fos, a marker of general neuronal activation, induced by CRD, (ii) this activation can be modulated by L. farciminis treatment. Female rats were treated by L. farciminis and CRD was performed after partial restraint stress (PRS) or sham-PRS. The expression of Fos protein was measured by immunohistochemistry. After CRD or PRS, Fos expression was increased in spinal cord section (S1), nucleus tractus solitarius (NTS), paraventricular nucleus (PVN) of the hypothalamus, and in the medial nucleus of the amygdala (MeA). The combination of both stimuli, PRS and CRD, markedly increased this Fos overexpression in the sacral spinal cord section, PVN and MeA, but not in NTS. By contrast, a pretreatment with L. farciminis significantly reduced the number of Fos positive cells in these area. This study shows that PRS enhances Fos protein expression induced by CRD at the spinal and supraspinal levels in rats. Lactobacillus farciminis treatment inhibited this enhancing effect, suggesting that the antinociceptive effect of this probiotic strain results from a decrease of the stress-induced activation/sensitization of sensory neurons at the spinal and supraspinal level.

Reduced anxiety in the mice expressing mutant (N141I) presenilin 2

Alzheimer's disease (AD) is characterized by progressive cognitive impairment. The effect of presenilin 1 (PS1) and PS2 mutation on cognition has been well characterized in a variety of transgenic mice. However, noncognitive behaviors have not been considered in these mice. In the present study, we found that transgenic mice expressing mutant PS2 (N141I) displayed decreased anxiety behavior determined by the elevated plus maze test and the light dark box test. However, these mice showed biphasic ambulatory activity (hyperactivity followed by hypoactivity) in an open field test. Correlated well with the reduced anxiety, expression of GABA(A)alpha(1) receptor was higher whereas c-Fos was lower in the cortex, hippocampus, and amygdala of the mice expressing PS2 mutation than those of the wild-type PS2 or nontransgenic control mice. These data indicate that PS2 mutation causes reduction of anxiety, and this effect may be related to the change of the expression of GABA(A)alpha(1) receptor and c-Fos. These findings could be useful in the understanding and the treatment of AD patients.

Ingestion of non-caloric liquid diet is sufficient to restore plasma corticosterone level, but not to induce the hypothalamic c-Fos expression in food-deprived rats

Male Sprague-Dawley rats were subjected to four different conditions; free fed control (FC), 48 h of food deprivation (FD), 1 h of refeeding with chow (RF/CW) or with a non-caloric liquid diet following FD (RF/NC) and then sacrificed for c-Fos immunohistochemistry in the hypothalamic paraventricular nucleus (PVN) and the nucleus tractus of solitarius (NTS). Plasma corticosterone level and the postmortem weight of gastric contents were measured. Plasma level of corticosterone significantly increased during FD, and then decreased within 1 h after ad libitum access to chow or non-caloric liquid diet. c-Fos-ir in the brain regions was not changed by FD; however, significantly increased by chow refeeding, but not by non-caloric diet. Chow, but not the non-caloric, refeeding significantly increased gastric contents. Results suggest that caloric load and/or gastric distension may require for the postprandial activation of neurons in the PVN and NTS, but ingestion of non-caloric palatable mixture may be sufficient to normalize the fasting-induced increase of plasma corticosterone. In conclusion, feeding-related changes in the HPA axis activity may not be related with meal-induced c-Fos expression in the PVN and NTS.

Neonatal amygdala lesions: co-occurring impact on social/fear-related behavior and cocaine sensitization in adult rats

Neurodevelopmental abnormalities of temporal-limbic structures may underlie both adult psychiatric syndromes and increased addiction vulnerability, leading to high frequencies of "dual diagnosis" disorders. Although the amygdala is implicated in various mental disorders and drug addiction, no studies have explored the impact of early developmental damage to the amygdala on phenotypes relating to mental illness and addictions as co-occurring processes. We tested rats with neonatal amygdala lesions (NAML) vs. SHAM-operated controls in a battery of tests--novel field activity, elevated plus maze (EPM), and social interaction (SI) at baseline and after odor and restraint stress--followed by measures of cocaine sensitization (15 mg/kg vs. saline x 5 days + challenge session 2 weeks later) and remeasurement of SI. NAMLs showed increased novelty-related locomotion, less fear responding in the EPM, and resistance to predator-odor- but not to restraint-induced suppression of SI. NAMLs also had elevated cocaine sensitization profiles, and cocaine history differentially affected subsequent SI in NAMLs compared with SHAMs. NAMLs may provide models for understanding a shared neurobiological basis for and complex interactions among psychiatric symptoms, drug exposure history, and addiction vulnerability.

Restraint-induced fra-2 and c-fos expression in the rat forebrain: relationship to stress duration

The protein product of the fra-2 gene (Fra-2), a fos-family member, can compete with Fos protein for participation in activating protein-1 (AP-1) transcription factor complexes and each protein can contribute different transactivational consequences to an AP-1 complex. To date, there is limited characterization of fra-2 mRNA expression in the rat forebrain. We examined basal and restraint-induced mRNA expression (in situ hybridization) of fra-2 in the rat forebrain and compared its temporal-spatial pattern to c-fos. In contrast to the very low basal expression of c-fos, fra-2 basal expression was moderately high throughout cortex and some subcortical structures, including prominent basal expression in the hypothalamic paraventricular nucleus (PVN). Restraint-induced fra-2 expression was quantified in the prefrontal cortex (PFC), lateral septum (LS) and PVN. Maximal fra-2 gene induction in the PFC and LS was delayed (60 min) after restraint onset with respect to c-fos (15 min), whereas in the PVN, fra-2 mRNA increased within 15 min of restraint. Additionally we compared c-fos and fra-2 gene expression in rats given shorter or longer restraint durations, but equal total time from stress onset to sample collection, to determine the extent to which the kinetics of gene induction matched that of a hypothalamic-pituitary-adrenal axis hormone response. Rats given 45 min recovery after 15 min restraint showed less c-fos expression in the PVN, less fra-2 expression in the prelimbic and infralimbic PFC, and no difference in the LS compared with rats restrained for 60 min. Thus, the expression of both genes was sensitive to stressor duration, but this sensitivity varied with brain region. Differential basal and stress-induced expression patterns of the fra-2 and c-fos genes are likely to have important functional consequences for AP-1 transcription factor dependent regulation of neural plasticity.

Intra-amygdala injection of GABAA agonist, muscimol, reduces tachycardia and modifies cardiac sympatho-vagal balance during restraint stress in rats

At present, little is known about the brain origin of stress-induced cardiac sympathetic drive responsible for stress-induced tachycardia. Our aim was to determine the effect of bilateral microinjections of the GABA(A) receptor agonist, muscimol, into the amygdaloid complex on both the heart rate and cardiac autonomic activity during restraint stress. Experiments were performed in male Sprague-Dawley rats (n=9), with pre-implanted electrocardiographic electrodes. Heart rate increased sharply after the onset of the restraint and reached a peak 1-2 min later (from 344+/-6-440+/-20 BPM). Subsequently, heart rate began to fall, and during the next 10-15 min approached the steady-state level of 384+/-11. After vehicle, mean heart rate during each of three 10-min restraint epochs was significantly higher compared with the pre-restraint level. After muscimol, mean heart rate was significantly elevated only during the first 10 min of restraint. There was no difference in the early peak tachycardia between both conditions. Muscimol substantially accelerated the fall of the HR from the peak to the steady-state level, and thus the area under the curve value for muscimol (503+/-162 BPM x min) was significantly smaller than that for vehicle (1221+/-231 BPM x min); P<0.05. After vehicle, the high-frequency spectral power of the heart rate decreased and the low-frequency power increased during the restraint, resulting in a significant rise of the low frequency/high frequency ratio from 1.2+/-0.2-2.8+/-0.6 (n=9, P<0.05). Muscimol suppressed these stress-induced effects. We conclude that inhibition of the amygdala neurons abolishes the sustained component of tachycardia during the restraint, has no effect on the early tachycardic component, and prevents stress-induced alterations in the heart rate variability indices.

Adaptation in the corticosterone and hyperthermic responses to stress following repeated stressor exposure

Previous studies have shown that repeated daily exposure to the same (homotypic) stressor results in habituation of the corticosterone (CORT) response. Others have found that the stress response to a more ethologically relevant stressor, social defeat, does not habituate and, in some cases, sensitisation has been observed. Similar observations have been noted when core temperature is examined. Although habituation and/or sensitisation have been reported during stressor exposure, little is known about the development of an anticipatory fever in response to daily stressor exposure. The aim of the present study was to compare systematically commonly used laboratory stressors (i.e. restraint, cage confinement and social defeat) using a common set of procedures and analyses. Specifically, we examined: (i) the development of an anticipatory fever to repeated (5 days) homotypic stressor exposure; (ii) the adaptation of the fever response during stressor exposure; and (iii) the resolution of the fever response to stressors presented at the same time each day. For comparison, adaptation of the CORT response was also examined to assess the degree to which habituation to repeated stressor exposure may represent a more general response observed across diverse physiological measures. Habituation was observed after restraint and cage confinement, but not observed in either the CORT or hyperthermic responses to repeated social defeat. Furthermore, no anticipatory fever response was observed with repeated exposure to restraint, cage confinement, or social defeat. These data suggest that habituation to repeated stressor exposure may not occur with all homotypic stressor paradigms. In addition, rats do not appear to entrain an anticipatory fever response to a stressor presented at the same time each day, at least not within 5-6 days of repeated exposure.

Dendritic spines in the posterodorsal medial amygdala after restraint stress and ageing in rats

Several evidences suggest that the posterodorsal medial amygdala (MePD) can be a relevant part of the rat neural circuitry for the regulation of hypothalamic neuroendocrine secretion and for ontogenetically different behavioral displays. The dendritic spine density of Golgi-impregnated neurons from the MePD was evaluated in young rats following acute or chronic restraint stress and in aged animals (24 months old). Compared to the control group, a single 1 h restraint stress session promoted a decreased spine density (p<0.01) whereas a single 6 h restraint stress session or daily 6-h restraint sessions for 28 consecutive days did not lead to the same effect (p>0.05). Aged rats showed no difference in this dendritic spine parameter when compared to young adults (p>0.05). These results indicate that short-term stress (1 h) can affect MePD dendritic spines and that neural plasticity is involved with adaptive responses onwards in restrained rats. On the other hand, brain structural modifications related with ageing appear not to influence the number of certain postsynaptic sites in the MePD of rats.

Acute effects of nicotine on restraint stress-induced anxiety-like behavior, c-Fos expression, and corticosterone release in mice

Clinical evidence suggests that nicotine reduces anxiety in stressful situations. In the present study, we investigated the effect of nicotine on restraint-enhanced anxiety-like behavior, c-Fos expression, an index of neuronal activation in the brain, and plasma corticosterone. Two-hour restraint stress-enhanced anxiety-like behavior in the elevated plus-maze (EPM) and nicotine hydrogen tartrate (0.25 mg/kg, i.p.) attenuated the stress-induced changes. Pretreatment with the centrally acting nicotinic antagonist, mecamylamine (2 mg/kg), blocked nicotine's effects. In addition, restraint led to significant increases of c-Fos expression in several brain regions related to stress or anxiety including paraventricular hypothalamic nucleus (PVN), lateral hypothalamic area (LH), central amygdaloid nucleus (CeA), medial amygdaloid nucleus (MeA) and cingulate and retrosplenial cortices (Cg/RS), paraventricular thalamic nucleus (PVT), and basolateral amygdaloid nucleus (BLA). Nicotine attenuated the restraint-induced expression of c-Fos in the PVN, LH, CeA, MeA, and Cg/RS, while leaving the BLA and PVT unaffected. In contrast, nicotine did not reverse the increased levels of plasma corticosterone induced by restraint. These findings suggest that nicotine may modify the stress-induced behavioral changes via regulating the neuronal activation in selected brain regions rather than affecting hypothalamo-pituitary-adrenocortical axis hormone responses.

Androgen and estrogen receptor-beta distribution within spinal-projecting and neurosecretory neurons in the paraventricular nucleus of the male rat

Activation of the hypothalamic-pituitary-adrenal (HPA) axis is initiated by neurosecretory neurons residing within the medial parvicellular part of the hypothalamic paraventricular nucleus (PVN). Despite the potency by which sex steroids operate on HPA and medial parvocellular responses to stress, previous topographic and phenotypic studies suggest that gonadal steroid hormone receptors are scarcely, if at all, expressed by PVN neurons controlling anterior pituitary corticotropes. Guided by the pattern of retrograde accumulation of fluorogold, we used a direct connectional approach to define the distribution of androgen receptors (AR) and estrogen-beta receptors (ER-beta) within populations of neurosecretory vs. nonneurosecretory neurons in the PVN. Juxtaposition of AR-immunoreactivity (ir) and ER-beta mRNA to the pattern of intravenous fluorogold labeling showed these steroid hormone receptors to be concentrated within portions of the PVN devoid of neurosecretory neurons. Superimposing receptor profiles onto the pattern of spinal retrograde labeling confirmed a selective distribution of AR-ir within autonomic-related cells of the medial parvocellular division, including its dorsal, lateral, and ventral medial components. ER-beta mRNA expression was likewise concentrated within regions accumulating spinal tracer, highest within the ventral aspect of the PVN. These results indicate a direct influence of gonadal hormones on preautonomic effector neurons and remain in keeping with an indirect influence of androgens on adrenocorticotropin-regulating neurons in the PVN.

Stress history and pubertal development interact to shape hypothalamic-pituitary-adrenal axis plasticity

Both the magnitude and the duration of the hormonal stress response change dramatically during neonatal development and aging as well as with prior experience with a stressor. However, surprisingly little is known with regard to how pubertal maturation and experience with stress interact to affect hypothalamic-pituitary-adrenal axis responsiveness. Because adolescence is a period of neurodevelopmental vulnerabilities and opportunities that may be especially sensitive to stress, it is imperative to more fully understand these interactions. Thus, we examined hormonal and neural responses in prepubertal (28 d of age) and adult (77 d of age) male rats after exposure to acute (30 min) or more chronic (30 min/d for 7 d) restraint stress. We report here that after acute stress, prepubertal males exhibited a significantly prolonged hormonal stress response (e.g. ACTH and total and free corticosterone) compared with adults. In contrast, after chronic stress, prepubertal males exhibited a higher response immediately after the stressor, but a faster return to baseline, compared with adults. Additionally, we demonstrate that this differential stress reactivity is associated with differential neuronal activation in the paraventricular nucleus of the hypothalamus, as measured by FOS immunohistochemistry. Using triple-label immunofluorescence histochemistry, we found that a larger proportion of CRH, but not arginine vasopressin, cells are activated in the arginine vasopressin in response to both acute and chronic stress in prepubertal animals compared with adults. These data indicate that experience-dependent plasticity of the hypothalamic-pituitary-adrenal neuroendocrine axis is significantly influenced by pubertal maturation.

Cortico-amygdala circuits: role in the conditioned stress response

The amygdala plays a crucial role in the orchestration and modulation of the organism response to aversive, stressful events. This response could be conceived as the result of two interdependent components. The first is represented by sets of visceral and motor responses aimed at helping the organism to cope with the present event. The second is the acquisition and modulation of memories relative to the stressful stimulus and its context. This latter component contributes to the instatement of conditioned stress responses that are essential to the capability of the organism to predict future exposures to similar stimuli in order to avoid them or counteract them effectively. In the amygdala, these two components become fully integrated. Massive networks link the amygdala to the hypothalamus, midbrain and brainstem. These networks convey visceral, humoral and nociceptive information to the amygdala and mediate its effects on the hypothalamic-pituitary-adrenal axis as well on autonomic and motor centers. On the other hand, interactions between the amygdala and interconnected cortical networks play a crucial role in acquisition, consolidation and extinction of learning relative to the stressful stimulus. Within the scope of this review, current evidence relative to the interaction between the amygdala and cortical networks will be considered in relationship to the integration of the conditioned response to stress.