Hippocampal Glucocorticoid Receptor Levels Research Articles

GR/P300 Regulates MKP1 Signaling Pathway and Mediates Depression-like Behavior in Prenatally Stressed Offspring.

Accumulating evidence suggests that prenatal stress (PNS) increases offspring susceptibility to depression, but the underlying mechanisms remain unclear. We constructed a mouse model of prenatal stress by spatially restraining pregnant mice from 09:00-11:00 daily on Days 5-20 of gestation. In this study, western blot analysis, quantitative real-time PCR (qRT‒PCR), immunofluorescence, immunoprecipitation, chromatin immunoprecipitation (ChIP), and mifepristone rescue assays were used to investigate alterations in the GR/P300-MKP1 and downstream ERK/CREB/TRKB pathways in the brains of prenatally stressed offspring to determine the pathogenesis of the reduced neurogenesis and depression-like behaviors in offspring induced by PNS. We found that prenatal stress leads to reduced hippocampal neurogenesis and depression-like behavior in offspring. Prenatal stress causes high levels of glucocorticoids to enter the fetus and activate the hypothalamic‒pituitary‒adrenal (HPA) axis, resulting in decreased hippocampal glucocorticoid receptor (GR) levels in offspring. Furthermore, the nuclear translocation of GR and P300 (an acetylation modifying enzyme) complex in the hippocampus of PNS offspring increased significantly. This GR/P300 complex upregulates MKP1, which is a negative regulator of the ERK/CREB/TRKB signaling pathway associated with depression. Interestingly, treatment with a GR antagonist (mifepristone, RU486) increased hippocampal GR levels and decreased MKP1 expression, thereby ameliorating abnormal neurogenesis and depression-like behavior in PNS offspring. In conclusion, our study suggested that the regulation of the MKP1 signaling pathway by GR/P300 is involved in depression-like behavior in prenatal stress-exposed offspring and provides new insights and ideas for the fetal hypothesis of mental health.

Effects of Tibetan medicine metacinnabar (β-HgS) combined with imipramine or sertraline on depression-like symptoms in mice.

Depression is a common mood disorder that has exhibited an increased incidence rate worldwide, but the overall clinical efficacy of antidepressants remains unsatisfactory. In traditional Ayurveda and Tibetan medicines, β-HgS-containing medicines have been used to treat neurological diseases for thousands of years, and our previous study found that β-HgS ameliorated depression-like behaviors in chronic restraint stress (CRS)-treated or chronic unpredictable mild stress (CUMS)-treated mice. Hence, present study investigated the effects of β-HgS combined with the clinical first-line antidepressants, imipramine (IMI) and sertraline (SER), on depression-like symptoms in CRS- and CUMS-co-treated mice. Our results revealed that β-HgS promoted the antidepressant effect of SER on depression-like behavior in mice, and enhanced its effects on promoting glucocorticoid receptor (GR) expression and neuronal proliferation in key hippocampal subregions, as well as increasing interleukin 10 (IL-10) levels and decreasing malondialdehyde levels in the sera of stress-stimulated mice. As for IMI, β-HgS enhanced its effects on preventing atrophy and severe structural damage in the hippocampus, as well as in promoting hippocampal GR levels and neuronal proliferation and serum IL-10 and superoxide dismutase (SOD) levels. Additionally, combination therapy resulted in the increased diversity of important intestinal microbiota compared to that of monotherapy, which may help sustain the health of the digestive tract and reduce inflammation to further enhance the antidepressant effects of IMI and SER in mice.

Changes in depressive-like behaviors induced by spinal cord injury based on the hypothalamic-pituitary-adrenal axis and hippocampal neurogenesis.

A reduction in sucrose preference is a key characteristic of depressive-like behaviors after spinal cord injury as judged by the sucrose preference test, the hypothalamic-pituitary-adrenal axis and adult hippocampal neurogenesis. Male rats were divided into three groups: control, sham and spinal cord injury groups. The spinal cord injury rats received a severe mid-thoracic contusion. The Basso, Beattie and Bresnahan score was used to assess motor function. The sucrose preference test and forced swim test were used to evaluate depressive-like behaviors. Serum corticosterone levels were examined by enzyme-linked immunosorbent assay and hippocampal glucocorticoid receptor levels were examined by Western blot to evaluate the function of the hypothalamic-pituitary-adrenal axis. Adult hippocampal neurogenesis was assessed by testing hippocampal brain-derived neurotrophic factor and tropomyosin receptor kinase B levels by Western blot and doublecortin levels by immunohistochemistry. Data showed that spinal cord injury impaired motor function. The spinal cord injury rats exhibited decreased sucrose preference on day six, which continued to decrease until day twelve, followed by a plateau phase. Additionally, the immobility time of the spinal cord injury rats was increased on day thirty-four. Moreover, serum corticosterone levels in the spinal cord injury group peaked on day seven, was decreased by day twenty-one and was increased again on day thirty-five. Serum corticosterone levels were significantly negatively correlated with sucrose preference and positively correlated with immobility time. Finally, hippocampal doublecortin levels on days twenty-one and thirty-five were lower in the spinal cord injury group than in the other groups. These results suggest that hyperactivation of the hypothalamic-pituitary-adrenal axis and the inhibition of adult hippocampal neurogenesis may be part of the underlying mechanism responsible for depressive-like behaviors after spinal cord injury.

Chronically infused angiotensin II induces depressive-like behavior via microglia activation

Brain inflammation is one of hypotheses explaining complex pathomechanisms of depression. Angiotensin II (ANGII), which is associated with hypertension, also induces brain inflammation. However, there is no animal study showing the direct relationship between ANGII and depression. To address this issue, ANGII-containing osmotic pumps were implanted into adult male C57BL/6 mice subcutaneously for subacute (7 days) and chronic (at least 21 days) periods and behavioral and molecular analyses were conducted. Chronic infusion of ANGII into mice induced depressive-like behaviors, including the tail suspension test and forced swimming test, which were reversed by imipramine. Chronic infusion of ANGII also induced microglial activation in the hippocampus with increase of Il-1β mRNA and decrease of Arg1 mRNA. In addition, chronic ANGII infusion activated the hypothalamic–pituitary–adrenal axis (HPA axis) and resulted in decreased hippocampal glucocorticoid receptor level. However, subacute ANGII infusion did not induce significant molecular and behavioral changes in mice compared to that of control. The molecular and behavioral changes by chronic ANGII infusion were reversed by co-treatment of minocycline or telmisartan. In addition, ANGII treatment also induced the pro-inflammatory changes in BV-2 microglial cells. Our results indicate that ANGII can induce depressive-like behaviors via microglial activation in the hippocampus and HPA axis hyperactivation in mice. These might suggest possible mechanism on depressive symptom in chronic hypertensive state.

Effects of body weight-supported treadmill training at different speeds on the motor function and depressive behaviors after spinal cord injury in rats.

Spinal cord injury (SCI) causes motor dysfunction and depression, which hinders the recovery of motor function. Body weight-supported treadmill training (BWSTT) should be considered an effective method for functional rehabilitation after SCI, as it is an efficacious intervention in healthcare with no side effects. Because exercise exerts different effects on motor function recovery and inhibiting depression after SCI, we aimed to determine the appropriate intensity of BWSTT. In this study, fixed durations, frequencies, and percentages of BWSTT with different speeds of BWSTT (7, 15, and 21 cm/s) were chosen to explore the appropriate intensity, which affected the recovery of motor function and antidepressant effects on SCI rats. Based on our results, BWSTT at 21 cm/s produced the best outcomes for motor function recovery and the spinal cord levels of brain-derived neurotrophic factor (BDNF) and tropomyosin receptor kinase B (TrkB). The antidepressant effects of BWSTT at 15 and 21 cm/s were confirmed based on the increasing sucrose preference, the time spent in the central area and social time, and reduced immobility time. BWSTT at 15 and 21 cm/s improved the modulation of the hypothalamic-pituitary-adrenal axis by decreasing serum corticosterone levels and increasing hippocampal glucocorticoid receptor levels. In addition, higher levels of neurogenesis-related proteins were observed in the hippocampus of the group subjected to BWSTT at 21 cm/s than in the other groups. Thus, BWSTT at 21 cm/s is a potentially favorable treatment that synchronously improves motor function recovery and exerts an antidepressant effect.

Glucocorticoid receptor dysfunction orchestrates inflammasome effects on chronic obstructive pulmonary disease-induced depression: A potential mechanism underlying the cross talk between lung and brain

Depression is highly prevalent among patients with chronic obstructive pulmonary disease (COPD). However, depression with COPD comorbidity is often underdiagnosed and undertreated, and pathogenic research is also insufficient. In the present study, we characterised pulmonary and hippocampal dysfunction by researching the interaction between inflammasome-regulated cytokines and glucocorticoid receptor (GR) signalling by investigating the role of fluoxetine (FLU), one of the most widely used antidepressants in clinical practice. Mice were exposed to cigarette smoke (CS) to induce the model of COPD with comorbid depression, and pathological alterations in serum, hippocampus, lung, and bronchoalveolar lavage fluid were determined. Our results showed that the CS procedure induced the accumulation of inflammatory cells (macrophages, neutrophils, and lymphocytes), the production of cytokines, the activation of inflammasome components (NLRP3, ASC, caspase-1), depression-related behaviours, and the stimulation of GR signalling. Intriguingly, glucocorticoid resistance occurred in CS-exposed mice, with elevated serum corticosterone and suppressed hippocampal GR levels, which suggested a novel potential regulatory mechanism underlying COPD-induced depression comorbidity. Furthermore, chronic CS exposure decreased the pGR-S211/pGR-S226 ratio, increased the active nuclear GR, and impaired cytosolic GR binding capacity and GR transcriptional activity, which might be responsible for the activation of the inflammasome-induced inflammatory cascade. These alterations were reversed by chronic FLU treatment, indicating that FLU-mediated GR signalling was involved in the COPD induced inflammasome activation. Our research explored the underlying molecular mechanism of comorbid COPD/depression and provided in vivo evidence that glucocorticoid resistance occurred during CS-induced central nervous system inflammation, a potential mechanism underlying the cross talk between the lung and brain.

Modulation of central glucocorticoid receptors in short- and long-term experimental hyperthyroidism.

Hyperthyroidism is associated with a significant increase in circulating glucocorticoid levels and hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis. The aim of this study was to examine whether the HPA axis hyperactivity observed in hyperthyroidism may be explained by a disturbed feedback inhibition of endogenous glucocorticoids through two specific intracellular receptors in the brain: the high affinity mineralocorticoid receptor (MR) and the lower affinity glucocorticoid receptor (GR). Cytosolic receptor binding and gene expression was assessed in rats with short (7 days) and long standing (60 days) eu- and hyperthyroidism. Glucocorticoid receptor number and binding affinity (Kd) in the hippocampus were measured using [(3)H2]-dexamethasone radioreceptor assay. In situ hybridization was employed to examine the effects of hyperthyroidism on the GR and MR mRNA levels in the hippocampus and the pituitary. Both short- and long-term hyperthyroid rats showed pronounced reduction in the concentration of cytosolic GR in the hippocampus, without changes in binding affinity or changes in GR expression. In contrast, GR mRNA in the pituitary increased after 7 days and decreased after 60 days of thyroxin treatment. MR mRNA was moderately affected. Hyperthyroidism is associated with significant decreases in hippocampal GR levels supporting the hypothesis that hyperactivity of the HPA axis observed in experimentally induced hyperthyroidism may be attributed, at least in part, to decreased negative feedback at the level of the hippocampus. These findings further support the notion that a central locus is principally responsible for the hyperactivity of the HPA axis observed in hyperthyroidism.

Sex differences in the single prolonged stress model

Post traumatic stress disorder (PTSD) is a debilitating anxiety disorder resulting from traumatic stress exposure. Females are more likely to develop PTSD than males, but neurobiological mechanisms underlying female susceptibility are lacking. This can be addressed by using nonhuman animal models. Single prolonged stress (SPS), a nonhuman animal model of PTSD, results in cued fear extinction retention deficits and hippocampal glucocorticoid receptor (GR) upregulation in male rats. These effects appear linked in the SPS model, as well as in PTSD. However, the effects of SPS on cued fear extinction retention and hippocampal GRs in female rats remain unknown. Thus, we examined sex differences in SPS-induced cued fear extinction retention deficits and hippocampal GR upregulation. SPS induced cued fear extinction retention deficits in male rats but not female rats. SPS enhanced GR levels in the dorsal hippocampus of female rats, but not male rats. SPS had no effects on ventral hippocampal GR levels, but ventral hippocampal GR levels were attenuated in female rats relative to males. These results suggest that female rats are more resilient to the effects of SPS. The results also suggest that GR upregulation and cued fear extinction retention deficits can be dissociated in the SPS model.

Spatial memory impairments in a prediabetic rat model

Diabetes is associated with an increased risk for brain disorders, namely cognitive impairments associated with hippocampal dysfunction underlying diabetic encephalopathy. However, the impact of a prediabetic state on cognitive function is unknown. Therefore, we now investigated whether spatial learning and memory deficits and the underlying hippocampal dysfunction were already present in a prediabetic animal model. Adult Wistar rats drinking high-sucrose (HSu) diet (35% sucrose solution during 9weeks) were compared to controls’ drinking water. HSu rats exhibited fasting normoglycemia accompanied by hyperinsulinemia and hypertriglyceridemia in the fed state, and insulin resistance with impaired glucose tolerance confirming them as a prediabetic rodent model. HSu rats displayed a poorer performance in hippocampal-dependent short- and long-term spatial memory performance, assessed with the modified Y-maze and Morris water maze tasks, respectively; this was accompanied by a reduction of insulin receptor-β density with normal levels of insulin receptor substrate-1 pSer636/639, and decreased hippocampal glucocorticoid receptor levels without changes of the plasma corticosterone levels. Importantly, HSu animals exhibited increased hippocampal levels of AMPA and NMDA receptor subunits GluA1 and GLUN1, respectively, whereas the levels of protein markers related to nerve terminals (synaptophysin) and oxidative stress/inflammation (HNE, RAGE, TNF-α) remained unaltered. These findings indicate that 9weeks of sucrose consumption resulted in a metabolic condition suggestive of a prediabetic state, which translated into short- and long-term spatial memory deficits accompanied by alterations in hippocampal glutamatergic neurotransmission and abnormal glucocorticoid signaling.

Neuropeptide Y (NPY) infusion attenuates development of PTSD‐like symptoms to traumatic stress in rats

NPY has anxiolytic properties associated with resilience to stress‐related disorders, such as PTSD. However, due to its hypertensive effects, peripheral administration is undesirable, thus we used intranasal (IN) infusion. Rats were pretreated with single IN NPY or vehicle before exposure to single prolonged stress (SPS) animal model of PTSD and compared to untreated controls. Thirty min after SPS the elevation of plasma ACTH and corticosterone was not as pronounced in NPY‐infused rats and the induction of tyrosine hydroxylase (TH) in locus coeruleus (LC) was attenuated. Seven days after SPS, they displayed reduction in development of anxiety, depressive‐like behavior and hyperarousal. Plasma ACTH, corticosterone, and hippocampal glucocorticoid receptor levels were significantly above controls only in the vehicle, but not IN NPY‐treated. Baseline TH mRNA levels in LC did not differ among groups, but increased with forced swim in the vehicle‐, but not NPY‐pretreated animals. Administration of IN NPY immediately post‐SPS led to a similar reduction in PTSD associated behaviors. The results show that IN NPY can alter stress‐triggered dysregulation of the HPA axis and activation of central noradrenergic activity and provide proof of concept for potential of IN NPY as a non‐invasive prophylactic treatment or early intervention in response to traumatic stress. Supported by US army grant DM102881.

Single intranasal neuropeptide Y infusion attenuates development of PTSD-like symptoms to traumatic stress in rats

Exposure to severe stress leads to development of neuropsychiatric disorders, including depression and Post-Traumatic Stress Disorder (PTSD) in at-risk individuals. Neuropeptide Y (NPY) is associated with resilience or improved recovery. Therefore exogenous administration to the brain has therapeutic potential although peripheral administration can trigger undesirable side effects. Here, we established conditions with intranasal (IN) NPY infusion to rats to obtain CSF concentrations in the proposed anxiolytic range without significant change in plasma NPY. Rats were pretreated with IN NPY or vehicle before exposure to single prolonged stress (SPS) animal model of PTSD and compared to untreated controls. The IN NPY appeared to lessen the perceived severity of stress, as these animals displayed less time immobile in forced swim part of the SPS. Thirty minutes after SPS the elevation of plasma adrenocorticotropic hormone (ACTH) and corticosterone was not as pronounced in NPY-infused rats and the induction of tyrosine hydroxylase (TH) in locus coeruleus (LC) was attenuated. Seven days after SPS, they displayed lower depressive-like behavior on Forced Swim Test and reduced anxiety-like behavior on Elevated Plus Maze. The prolonged effect of SPS on Acoustic Startle Response was also lower in NPY-infused rats. Plasma ACTH, corticosterone, and hippocampal glucocorticoid receptor levels were significantly above controls only in the vehicle – but not IN NPY-treated group 1week after SPS. Baseline TH mRNA levels in LC did not differ among groups, but increased with forced swim in the vehicle – but not NPY-pretreated animals. Administration of IN NPY after exposure to SPS led to similar, but not identical, reduction in development of anxiety, depressive-like behavior and hyperarousal. The results show that single IN NPY can alter stress-triggered dysregulation of the hypothalamic–pituitary–adrenal (HPA) axis and activation of central noradrenergic activity. These findings provide proof of concept for potential of IN NPY for non-invasive prophylactic treatment or early intervention in response to traumatic stress.

Reduced expression of MAPK/ERK genes in perinatal arsenic-exposed offspring induced by glucocorticoid receptor deficits

Changes within the glucocorticoid receptor (GR) cellular signaling pathway were evaluated in adolescent mice exposed to 50 ppb arsenic during gestation. Previously, we reported increased basal plasma corticosterone levels, decreased hippocampal GR levels and deficits in learning and memory performance in perinatal arsenic-exposed mice. The biosynthesis of members of the mitogen-activated protein kinase (MAPK) signaling pathway, known to be involved in learning and memory, is modulated by the binding of GR to glucocorticoid response elements (GREs) in the gene promoters. Two genes of the MAPK pathway, Ras and Raf, contain GREs which are activated upon binding of GRs. We evaluated the activity of GRs at Ras and Raf promoters using chromatin immunoprecipitation and real-time PCR and report decreased binding of the GR at these promoters. An ELISA-based GR binding assay was used to explore whether this decreased binding was restricted to in vivo promoters and revealed no differences in binding of native GR to synthetic GREs. The decreased in vivo GR binding coincides with significantly decreased mRNA levels and slight reductions of protein of both H-Ras and Raf-1 in perinatally arsenic-exposed mice. Nuclear activated extracellular-signal regulated kinase (ERK), a downstream target of Ras and Raf, whose transcriptional targets also play an important role in learning and memory, was decreased in the hippocampus of arsenic-exposed animals when compared to controls. GR-mediated transcriptional deficits in the MAPK/ERK pathway could be an underlying cause of previously reported learning deficits and provide the link to arsenic-induced deficiencies in cognitive development.

Hyperactivity of the hypothalamus–pituitary–adrenal axis in lipopolysaccharide-induced neurodevelopmental model of schizophrenia in rats: Effects of antipsychotic drugs

Recent data indicate that a significant number of schizophrenic patients are hypercortisolemic and that glucocorticoids are involved in the pathogenesis of schizophrenia. The aim of the present study was to evaluate whether behavioural schizophrenia-like changes in the lipopolysaccharide (LPS)-induced neurodevelopmental model of this brain disorder are associated with alterations in the level of plasma corticosterone, the concentration of glucocorticoid receptors and the amount of the immunophilin FKBP51, the glucocorticoid receptor co-chaperone, in the hippocampus and frontal cortex. We found that the adult offspring of prenatally LPS-treated rats showed a deficit in prepulse inhibition (PPI), an enhancement of amphetamine-induced locomotor activity, an elevated plasma level of corticosterone and a decrease in both the glucocorticoid receptor level in the hippocampus and the FKBP51 concentration in the frontal cortex. Most of these changes were reversed by the atypical antipsychotic drug clozapine, whereas chlorpromazine had no effect on PPI but attenuated the amphetamine-induced hyperactivity and normalised the hippocampal level of glucocorticoid receptors. The changes in the level of plasma corticosterone and cortical FKBP51 were attenuated by chlorpromazine in female offspring only. This study supports the hypothesis of hypothalamic–pituitary–adrenal (HPA) axis hyperactivity in schizophrenia and suggests that this hyperactivity results from a decrease in the hippocampal glucocorticoid receptor level and a decrease in FKBP51 in the frontal cortex.

Differential expression of glucocorticoid receptor transcripts in major depressive disorder is not epigenetically programmed

Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis is one of the most consistent findings in major depressive disorder (MDD). Impaired HPA feedback may be due to the lower glucocorticoid receptor (GR) or mineralocorticoid receptor (MR) levels in the forebrain. GR levels are transcriptionally controlled by multiple untranslated alternative first exons, each with its own promoter providing a mechanism for tissue-specific fine-tuning of GR levels. Recently epigenetic methylation of these GR promoters was shown to modulate hippocampal GR levels. Here we investigate in post-mortem brain tissues whether in MDD HPA axis hyperactivity may be due to epigenetic modulation of GR transcript variants. Levels of GRalpha, GRbeta and GR-P transcripts were homogeneous throughout the limbic system, with GRalpha being the most abundant (83%), followed by GR-P (5-6%) while GRbeta was barely detectable (0.02%). Among the alternative first exons, 1B and 1C were the most active, while 1E and 1J showed the lowest expression and transcript 1F expressed intermediate levels of about 1%. In MDD, total GR levels were unaltered, although GRalpha was decreased in the amygdala and cingulate gyrus (p<0.05); transcripts containing exons 1B, 1C and 1F were lower, and 1D and1J were increased in some regions. NGFI-A, a transcription factor of exon 1F was down-regulated in the hippocampus of MDD patients; concomitantly exon 1F expression was reduced. Bisulphite sequencing of the alternative promoters showed low methylation levels in both MDD and control brains. Promoter 1F was uniformly unmethylated, suggesting that reduced 1F transcript levels are not linked to promoter methylation but to the observed dearth of NGFI-A. Previous studies showed high methylation levels in the 1F promoter, associated with childhood abuse. Provided our donors were not abused, our results suggest that the pathomechanism of MDD is similar but nevertheless distinct from that of abuse victims, explaining the clinical similarity of both conditions and that susceptibility to depression may be either predisposed by early trauma or developed independent of such a condition. However, this should be further confirmed in dedicated studies in larger cohorts.

The effect of antidepressant drugs on the HPA axis activity, glucocorticoid receptor level and FKBP51 concentration in prenatally stressed rats

Dysregulation of hypothalamic-pituitary-adrenal (HPA) axis activity is thought to be an important factor in pathogenesis of depression. In animals, stress or glucocorticoids given in prenatal period lead to long-lasting behavioral and neuroendocrine changes similar to those observed in depressed patients. However, molecular basis for HPA disturbances in animals exposed to prenatal stress - a model of depression - have been only partially recognized. Therefore, in the present study we investigated the effect of prenatal stress on behavioral changes, blood corticosterone level, concentrations of glucocorticoid receptor (GR) and its cochaperone, FKBP51, in the hippocampus and frontal cortex in adult rats. It has been found that prenatally stressed rats display high level of immobility in the Porsolt test and anxiety-like behavior. The HPA axis hyperactivity in theses animals was evidenced by corticosterone hypersecretion at the end of the light phase and 1h following acute stress. Western blot study revealed that GR level was significantly elevated in the hippocampus but not in the frontal cortex of prenatally stressed rats, whereas concentration of FKBP51 was decreased only in the former brain structure. Chronic treatment with imipramine, fluoxetine, mirtazapine and tianeptine have diminished both behavioral and biochemical alterations observed in this animal model of depression. These data indicate that the increase in hippocampal GR level and low concentration of FKBP51 in the frontal cortex may be responsible for enhanced glucocorticoid action in depression.

Neuroplasticity of the Hypothalamic–Pituitary–Adrenal Axis Early in Life Requires Recurrent Recruitment of Stress-Regulating Brain Regions

An eloquent example of experience-induced neuroplasticity involves the enduring effects of daily "handling" of rat pups on the expression of genes regulating hormonal and behavioral responses to stress. Handling-evoked augmentation of maternal care of pups induces long-lasting reduction of hypothalamic corticotropin releasing hormone (CRH) expression and upregulates hippocampal glucocorticoid receptor levels. These changes promote a lifelong attenuation of hormonal stress responses. We have found previously that handling-evoked downregulation of CRH expression occurs already by postnatal day 9, implicating it as an early step in this experience-induced neuroplasticity. Here, we investigated the neuronal pathways and cellular mechanisms involved. CRH mRNA expression in hypothalamic paraventricular nucleus (PVN) diminished after daily handling but not after handling once only, indicating that "recurrent" handling was required for this effect. Return of handled pups to their cage provoked a burst of nurturing behavior in dams that, in turn, induced transient, coordinate Fos expression in selected regions of the pups' brains. These included central nucleus of the amygdala (ACe) and bed nucleus of the stria terminals (BnST), regions that are afferent to PVN and influence CRH expression there. Whereas handling once sufficed to evoke Fos expression within ACe and BnST, expression in thalamic paraventricular nucleus, a region involved in storing and processing stress-related experience, required recurrent handling. Fos induction in all three regions elicited reduced transcription factor phosphorylation, followed by attenuated activation of CRH gene transcription within the PVN. These studies provide a neurobiological foundation for the profound neuroplasticity of stress-related genes evoked by early-life experience.

Stress (hypothalamic–pituitary–adrenal axis) and pain response in male rats exposed lifelong to high vs. low phytoestrogen diets

Estrogens exhibit complex but beneficial effects on brain structure, function and behavior. Soy-derived dietary phytoestrogens protect against hormone-dependent and age-related diseases, due to their estrogen-like hormonal actions. However, the effects of phytoestrogens on brain and behavior are relatively unknown. This study examined the influence of exposing male Long–Evans rats (lifelong) to either a phytoestrogen-rich (Phyto-600) or a phytoestrogen-free (Phyto-free) diet on body weights, behavioral pain thresholds, the hypothalamic–pituitary–adrenal (HPA) hormonal stress response, hippocampal glucocorticoid receptor and brain neural cell adhesion molecules (NCAM) and synaptophysin levels using standard behavioral and biochemical techniques. Body weights were significantly decreased in Phyto-600 fed animals compared to Phyto-free values. There were no significant changes in behavioral pain thresholds, circulating corticosterone concentrations (after acute immobilization stress) or NCAM and synaptophysin levels in various brain regions by the diet treatments. However, Phyto-600 fed males displayed significantly higher plasma adrenocorticotrophin (ACTH) (post-stress) and hippocampal glucocorticoid receptor levels vs. Phyto-free values. These data suggest that (1) body weights are significantly reduced by soy-derived phytoestrogens, (2) behavioral pain thresholds (via heat stimuli) are not influenced by dietary phytoestrogens, but (3) these estrogenic molecules in the hippocampus enhance glucocorticoid receptor abundance and alter the negative feedback of stress hormones towards a female-like pattern of higher ACTH release after activation of the HPA stress axis. This study is the first to show that lifelong consumption of dietary phytoestrogens alters the HPA stress response in male rats.

The effects of mutated skeletal ryanodine receptors on hypothalamic-pituitary-adrenal axis function in boars.

The objectives of the current experiment were to determine whether boars heterozygous for the mutation in skeletal ryanodine receptors (sRyR), known to cause porcine stress syndrome, differed from wild-type boars in hypothalamic-pituitary-adrenal axis (HPA) function. We have examined basal plasma ACTH, cortisol, and corticosteroid-binding globulin (CBG) concentrations; plasma ACTH and cortisol responses to a nose-snare stressor and at slaughter; dexamethasone suppression of plasma ACTH and cortisol concentrations; and glucocorticoid receptor (GR) density in the pituitary gland, hippocampus, hypothalamus, and frontal cortex. We have also examined carcass yields, composition, and meat quality to determine whether differences in HPA activity were accompanied by an increased incidence of meat quality characteristics associated with pale, soft, exudative (PSE) meat. Thirty boars either heterozygous or wild-type (n = 15 per genotype) for mutated sRyR were tested for HPA function at 7 mo of age. Heterozygous boars had lower basal plasma ACTH (P < .05) and cortisol (P < .04) concentrations. Integrated basal plasma ACTH and cortisol levels were also lower (P < .05 and P < .005, respectively). Genotype had no significant effect on basal CBG, stressor-induced (nose snare or slaughter) or dexamethasone suppression of plasma ACTH or cortisol concentrations. No differences in immunoreactive GR levels were found in the pituitary gland or any brain region examined. We did find a significant, negative correlation (r = -.62, P < .02) between peak (0800) basal plasma ACTH concentrations and hippocampal GR levels. The alterations in basal HPA function in heterozygous boars were accompanied by lighter body weights (P < .03), decreased carcass fat depth (P < .04), and increased carcass lean yields (P < .02). There was a higher incidence of meat quality characteristics associated with PSE meat in heterozygous boars indicated by higher carcass temperatures (P < .04) and meat brightness (P < .0001) with lower carcass pH at slaughter (P < .03) and after chilling (P < .003). In conclusion, we have found differences in basal and not stressor-induced HPA function between boars heterozygous and wild-type for mutated sRyR. This altered basal HPA activity was accompanied by an increased incidence of meat quality aspects associated with PSE meat in heterozygous boars.

Increased stress-induced adrenocorticotropin response after long-term intracerebroventricular treatment of rats with antisense mineralocorticoid receptor oligodeoxynucleotides.

Brain corticosteroid receptors, the type 1 mineralocorticoid receptor (MR) and the type 2 glucocorticoid receptor (GR), are involved in the regulation of neuroendocrine and behavioral responses during ongoing and stressful conditions. To further investigate the role of MR in these responses, we treated male Wistar rats intracerebroventricularly (icv) for 1 week with an 18-base end-capped phosphorothioate-protected antisense oligodeoxynucleotide (ODN) directed against MR mRNA (MR-AS). A mixed bases sequence (MR-MB) and vehicle (0.9% saline) served as controls. The ODN solution was administered by continuous infusion (1 microgram/0.5 microliter/h) via an icv cannula connected with polyethylene tubing to a subcutaneously implanted Alzet miniosmotic pump. No nonspecific effects of the ODNs, such as signs of sickness behavior or loss of body weight, were observed at any time during the treatment. The MR-AS treatment produced a 21% decline in hippocampal MR concentrations. Hippocampal GR levels were not affected by the treatment. MR and GR levels after MR-MB treatment were similar to those found after treatment with the vehicle. In situ hybridization experiments using an [35S]-labeled antisense MR probe showed that hippocampal MR mRNA levels were increased in MR-AS-treated rats. No changes were found in basal early morning levels of plasma ACTH and corticosterone which is consistent with the lack of any changes in adrenal and thymus weight. When rats were socially defeated for 10 min by a male and female resident and then placed for 5 min in the elevated plus-maze, no changes in the anxiety-like behavior were observed in MR-AS-treated animals. However, MR-AS-treated rats killed immediately after the behavioral test had markedly higher plasma ACTH, but not corticosterone, levels than the MR-MB and saline controls. In conclusion, down-regulation of the brain MR produces an enhanced responsiveness of ACTH to stressful situations which appears to be accompanied by a reduced sensitivity of the adrenal gland to ACTH.