Oral administration of a corticotropin-releasing hormone receptor antagonist significantly attenuates behavioral, neuroendocrine, and autonomic responses to stress in primates.

We evaluated the effects of the lipophilic nonpeptide corticotropin-releasing hormone (CRH) type 1 receptor antagonist antalarmin on the behavioral, neuroendocrine, and autonomic components of the stress response in adult male rhesus macaques. After oral administration, significant antalarmin concentrations were detected in the systemic circulation and the cerebrospinal fluid by a mass spectrometry-gas chromatography assay developed specifically for this purpose. Pharmacokinetic and dose-response studies suggested that an oral dose of 20 mg/kg was optimal for behavioral and endocrine effects. We then administered this dose in a double-blind, placebo-controlled fashion to monkeys exposed to an intense social stressor: namely, placement of two unfamiliar males in adjacent cages separated only by a transparent Plexiglas screen. Antalarmin significantly inhibited a repertoire of behaviors associated with anxiety and fear such as body tremors, grimacing, teeth gnashing, urination, and defecation. In contrast, antalarmin increased exploratory and sexual behaviors that are normally suppressed during stress. Moreover, antalarmin significantly diminished the increases in cerebrospinal fluid CRH as well as the pituitary-adrenal, sympathetic, and adrenal medullary responses to stress. We conclude that CRH plays a broad role in the physiological responses to psychological stress in primates and that a CRH type 1 receptor antagonist may be of therapeutic value in human psychiatric, reproductive, and cardiovascular disorders associated with CRH system hyperactivity.

Age and gender influence basal and stress-modulated hypothalamic-pituitary-thyroidal function in Fischer 344/N rats.

To investigate possible gender- and age-associated changes of the hypothalamic-pituitary-thyroid (HPT) axis at baseline and during stress, we studied healthy young (3-month) and old (23-month) female 344/N Fischer rats at the basal state and after 2 h of immobilization (IMMO), in parallel to age-matched male rats. At baseline, there were no major differences on HPT axis functions between young female and male animals. Old age was associated with impaired central thyroid function in both genders, albeit to a much lesser extent in females than in males. Plasma prolactin (PRL) levels were similar in young females and males but were higher in old females than males. IMMO inhibited HPT axis functions in both genders in young, but not old animals. Thus, plasma TSH and hypothalamic TRH mRNA levels were decreased by IMMO in young, but not in old rats of both genders. IMMO increased plasma PRL in young and old males, but did not have any effect in young and old females. In summary, these data indicate that age and gender exert diverse effects on HPT axis functions at baseline and after stress.

Identification of hypothalamic transcripts upregulated by antidepressants.

Identification of quantitative changes in gene expression that occur in the brain after antidepressant treatment can yield novel molecular markers that may be useful in the diagnosis and treatment of major depression. Using a modification of the differential display polymerase chain reaction, we describe the isolation of two transcripts that are differentially expressed in the brain after an 8-week course of antidepressant administration, compared to saline-treated control animals.

Hypothalamic corticotropin-releasing hormone suppression during the postpartum period: implications for the increase in psychiatric manifestations at this time.

The third trimester of human pregnancy is characterized by a hyperactive hypothalamic-pituitary-adrenal axis, possibly driven by progressively increasing circulating levels of placental CRH and gradually decreasing levels of CRH-binding protein. The postpartum period, on the other hand, is characterized by an increased vulnerability to psychiatric manifestations (postpartum "blues," depression, and psychosis), a phenomenon compatible with suppressed hypothalamic CRH secretion. To investigate the hypothesis that the postpartum period is associated with suppression of hypothalamic CRH secretion, we studied prospectively 17 healthy euthymic women (mean +/- SE age, 32.0 +/- 1.1 yr) with no prior history of depression, starting at the 20th week of gestation. Psychometric testing was performed monthly during pregnancy and postpartum on day 2 and weeks 2, 3, 6, 8, 12, 16, and 20, whereas serial ovine (o) CRH tests were performed postpartum at 3, 6, and 12 weeks. While pregnant, all 17 subjects remained euthymic; in the postpartum period, 7 women developed the "blues," and 1 developed depression. Overall, the mean plasma ACTH response to an iv bolus of 1 microgram/kg oCRH was markedly blunted at 3 and 6 weeks, but normal at 12 weeks postpartum, whereas the mean plasma cortisol response was at the upper limit of normal at all 3 times. These data are compatible with a suppressed hypothalamic CRH neuron that gradually returns to normal while hypertropic adrenal cortexes are progressively down-sizing. When the postpartum ACTH responses to oCRH were analyzed separately for the euthymic women and the women who had the "blues" or depression, the blunting of ACTH was significantly more severe and long lasting in the latter group; this was observed at all 3 times of testing. We conclude that there is central suppression of hypothalamic CRH secretion in the postpartum, which might explain the increased vulnerability to the affective disorders observed during this period. The suppressed ACTH response to oCRH might serve as a biochemical marker of the postpartum "blues" or depression.

Inferior petrosal sinus sampling in healthy subjects reveals a unilateral corticotropin-releasing hormone-induced arginine vasopressin release associated with ipsilateral adrenocorticotropin secretion.

Arginine vasopressin (AVP) acts synergistically with corticotropin-releasing hormone (CRH) to stimulate ACTH release from the anterior pituitary. In a previous study of bilateral simultaneous inferior petrosal sinus (IPS) sampling in healthy human subjects, we observed lateralized ACTH secretion, suggesting lateralized secretion of an ACTH-regulating hypothalamic factor. To investigate this possibility, we measured ACTH, CRH, AVP, and oxytocin (OT) levels in the IPS and the peripheral circulation in nine normal volunteers, before and after 1 microgram/kg i.v. bolus ovine CRH (oCRH). At baseline, ACTH, AVP, and OT exhibited a significant (P < 0.05) two to threefold intersinus gradient (ISG), indicating the existence of a dominant petrosal sinus. Endogenous CRH was undetectable in all samples. Despite similar exogenous oCRH levels in both petrosal sinuses, oCRH caused a significant increase (P < 0.001) in the ACTH ISG (15.8 +/- 5.6, mean +/- SEM), suggesting increased responsiveness of one dominant side of the anterior pituitary. This was associated with an ipsilateral CRH-induced AVP release and a significant increase (P < 0.01) in the AVP ISG (8.6 +/- 2.3), suggesting lateralized AVP secretion by the hypothalamus. Furthermore, the increased AVP ISG after oCRH correlated strongly with the ACTH ISG (r = 0.92, P < 0.01). oCRH administration did not affect OT. These findings suggest that there is a dominant petrosal sinus in healthy volunteers that appears to reflect a dominant side of the adenohypophysis, characterized by increased functional activity and/or responsiveness of the pituitary corticotrophs. This may reflect lateralized hypothalamic and/or suprahypothalamic function resulting in CRH-responsive lateralized secretion of AVP from parvocellular and/or magnocellular axons in the median eminence and the posterior pituitary. Although the functional and teleologic significance of these findings remains to be investigated, our data suggest a novel mechanism for CRH-mediated ACTH release, namely CRH-induced release of AVP which then enhances CRH action on the corticotrophs. Furthermore, our data represent the first direct evidence for the concept of brain lateralization with respect to neuroendocrine secretion.

Intracerebroventricularly transplanted embryonic neuronal tissue from inflammatory-resistant F344/N rats decreases acoustic startle responses in inflammatory-susceptible LEW/N rats.

Recently, we have shown that intracerebral transplantation of fetal F344/N hypothalamic tissue into LEW/N rats converts the LEW/N inflammatory-susceptible phenotype into an inflammatory-resistant phenotype in LEW/N hosts. Because LEW/N rats also exhibit relatively high acoustic startle responses (ASRs) compared to F344/N rats, in the present study we examined the effects on ASR of transplantation of F344/N hypothalamic tissue into the third ventricle of LEW/N rats. Dissected neuronal tissue from F344/N rats (Day E15-16) was implanted into the third ventricle of LEW/N rats. After 4 wk of postoperative survival, the animals' responses to acoustic startle stimuli were tested. Compared to naive and sham-operated animals, LEW/N rats transplanted with hypothalamic tissue exhibited significant decreases in ASR amplitudes. A similar decrease in ASR amplitude was observed in the group of LEW/N rats transplanted with embryonic striatal tissue. Our results indicate that the third ventricular neuronal grafts may modulate behavioral responses in the LEW/N rats. Although the mechanism of this effect is unknown, these studies suggest that intracerebral neuronal transplantation is a viable method with which to explore mechanisms of behavioral, neuroendocrine, and inflammatory response associations.

In vivo and in vitro effects of arginine-vasopressin receptor antagonists on the hypothalamic-pituitary-adrenal axis in the rat.

Arginine-vasopressin (AVP) is regarded as a potent stimulator of pituitary adrenocorticotropin (ACTH) secretion and participates therefore in the regulation of the hypothalamic-pituitary-adrenal (HPA) axis function in concert with the physiological activator of the axis, hypothalamic corticotropin-releasing hormone (CRH). We examined the effects of AVP and/or three synthetic V1b receptor antagonists on the activity of the HPA axis in vivo and in vitro in the rat. AVP was injected intravenously to Sprague-Dawley rats (1 microgram/rat) through an indwelling jugular catheter. AVP stimulated ACTH release, with maximal effect 10 min after injection. Intravenous injection of three V1b antagonists, [1-(beta-mercapto-beta,beta-cyclopentamethylenepropionic acid), 2-O-ethyltyrosine, 4-valine] arginine vasopressin (d(CH2)5[Tyr(Et2)]VAVP (WK 1-1), 9-desglycine[1-(beta-mercapto-beta,beta- cyclopentamethylenepropionic acid), 2-O-ethyltyrosine, 4-valine] arginine vasopressin desGly9d(CH2)5 [Tyr(Et2)]-VAVP (WK 3-6), and 9-desglycine [1-(beta-mercapto-beta,beta- cyclopentamethylenepropionic acid),2-D-(O-ethyl)tyrosine, 4-valine ] arginine vasopressin des Gly9d(CH2)5[D-Tyr(Et2)]VAVP (AO 3-21), prevented AVP-stimulated ACTH secretion. Explanted rat hypothalami incubated in vitro with graded concentrations of AVP (10(-14)-10(-5) M) secreted immunoreactive CRH (iCRH) in a concentration-dependent fashion. Maximal stimulatory effect occurred at the concentration of 10(-6) M. Incubation of hypothalami with WK 1-1, WK3-6, or AO 3-21 (10(-6) M) prevented AVP-stimulated iCRH secretion. Results suggest that AVP plays a relevant, multiple role in the activation of the HPA axis in the rat.(ABSTRACT TRUNCATED AT 250 WORDS)

Multiple sclerosis is associated with alterations in hypothalamic-pituitary-adrenal axis function.

In the LEW/N rat model, a decreased hypothalamic-pituitary-adrenal (HPA) axis response to inflammatory and immune mediators confers susceptibility to the development of a variety of inflammatory and immune diseases, including experimental allergic encephalomyelitis. In humans with optic neuritis, early intervention with steroids is associated with a decrease in the number of patients who go on to develop multiple sclerosis (MS). The current study was designed to determine whether patients with MS show evidence of a hypoactive HPA axis. Thirteen patients with MS were studied at baseline and with provocative tests of HPA axis function [ovine CRH, arginine vasopressin (AVP), and ACTH stimulation]. Compared to matched controls, patients with MS had significantly higher plasma cortisol levels at baseline. Despite this hypercortisolism and in contrast to patients with depression who had similar elevations in plasma cortisol levels, patients with MS showed normal, rather than blunted, plasma ACTH responses to ovine CRH, suggesting that the pathophysiology of hypercortisolism in MS is different from that in depression. Patients with MS also showed blunted ACTH responses to AVP stimulation and normal cortisol responses to high and low dose ACTH stimulation. Taken together, these findings are compatible with data from studies of experimental animals exposed to chronic inflammatory stress, which showed mild increased activation of the HPA axis with increased relative activity of AVP in the regulation of the pituitary-adrenal axis. These data do not support a role for hypocortisolism in MS once the disease is established.

Exercise-induced activation of the hypothalamic-pituitary-adrenal axis: marked differences in the sensitivity to glucocorticoid suppression.

Treadmill exercise activates the hypothalamic-pituitary-adrenal axis and evokes metabolic responses proportional to exercise intensity and duration. To determine whether glucocorticoid administration would alter humoral and metabolic regulation during exercise, we administered 4 mg dexamethasone (DEX) or placebo to 11 normal, moderately trained men (19-42 yr old) in a double blinded random fashion 4 h before high intensity intermittent treadmill running. Plasma levels of ACTH, cortisol, arginine vasopressin (AVP), lactate, and glucose were measured before, during, and after exercise. A wide range of ACTH responses were seen in the DEX-treated group and arbitrarily defined as two subsets of individuals according to their responses to dexamethasone: DEX nonsuppressors and DEX suppressors. Exercise-induced increases in heart rate and circulating concentrations of cortisol, AVP, lactate, and glucose were all significantly greater (P < 0.05) in nonsuppressors (n = 4) compared to suppressors (n = 7) after both placebo and DEX administration. Interestingly, heart rate, AVP, and lactate responses were unaltered by DEX alone in both groups. In summary, this study demonstrates that normal individuals exhibit differential neuroendocrine and metabolic responses to exercise and pituitary/adrenal suppression after pretreatment with DEX. These findings reflect marked individual differences in the stress response to exercise that may derive from or lead to differential glucocorticoid negative feedback sensitivity in humans.

Male Fischer 344/N rats show a progressive central impairment of the hypothalamic-pituitary-adrenal axis with advancing age.

We investigated the effects of aging on the regulation of hypothalamic-pituitary-adrenal function and hippocampal steroid receptors in a series of in vivo and in vitro studies conducted in healthy intact 2-, 8-, 18-, and 24-month-old male Fischer 344/N rats. Basal plasma ACTH levels were similar among age groups, and basal plasma corticosterone levels showed a significant aging-associated decline. Two i.v. doses (2 and 20 micrograms/kg BW) of rat CRF elicited significantly greater and delayed ACTH and greater corticosterone responses in older rats, consistent with the pattern encountered in hypothalamic CRF deficiency. In contrast, the i.v. injection of a muscarinic agonist, arecoline, elicited similar ACTH and corticosterone responses in all age groups. An i.v. injection of ACTH-(1-24) evoked lower corticosterone responses in the older (18- and 24-month-old) than in the younger (2- and 8-month-old) groups of rats, consistent with an impairment of hypothalamic-pituitary-adrenal axis function in older animals. Steady state mRNA levels of mineralocorticoid and glucocorticoid receptors were significantly decreased in the hippocampus of the 8-, 18-, and 24-month-old rats, compatible with maturational, rather than senescent, changes. CRF mRNA levels in the paraventricular nucleus of the hypothalamus, CRF content, and in vitro secretion by whole explanted hypothalami were progressively and significantly reduced with age, whereas the steady state levels of arginine vasopressin mRNA were significantly increased with age. Steady state levels of POMC mRNA were decreased, and ACTH content and in vitro secretion by corticotrophs were increased with age in the anterior pituitary. We conclude that male Fischer 344/N rats show a progressive hypothalamic CRH deficiency with advancing age, which appears to be associated with elevated production of arginine vasopressin in the hypothalamus.

Release of hypothalamic corticotropin-releasing hormone and arginine-vasopressin by interleukin 1 beta and alpha MSH: studies in rats with different susceptibility to inflammatory disease.

The susceptibility of Lewis rats is related to blunted hypothalamic-pituitary-adrenal (HPA) axis responsiveness to a variety of inflammatory and neuroendocrine stimuli. In contrast resistance to inflammatory disease of histocompatible Fischer rats is associated with their intact HPA axis responses to the same stimuli. We have examined the contribution of IL-1 beta to in vitro corticotropin-releasing hormone (CRH) and arginine vasopressin (AVP) release from hypothalamic explants derived from LEW/N and F344/N rats. The same animal model has been used to investigate the regulatory effect of alpha MSH, an immunosuppressive neurohormone, on IL-1 beta stimulated CRH and AVP secretion. CRH basal release in both strains was similar. However, LEW/N hypothalamic AVP basal secretion was significantly elevated. CRH relative response of LEW/N hypothalamic explants to IL-1 beta stimulation was lower compared to Fischer, which is consistent with their hyporesponsiveness to inflammatory mediators. AVP secretion however, was significantly decreased in hypothalamic explants from both strains after 40 min exposure to IL-1 beta. alpha MSH suppressed basal CRH and AVP release in both LEW/N and F344/N rats and prevented IL-1 beta stimulated CRH secretion in these strains. AVP was further diminished in F344/N explants following incubation with alpha MSH + IL-1 beta, while LEW/N level was significantly elevated. However, AVP levels remained significantly below baseline in explants from both strains after final incubation with IL-1 beta. Although our findings indicate a modulatory action of alpha MSH in HPA axis regulation in vitro, the physiological importance of this phenomenon in Lewis and Fischer rats requires further investigation.

Relation of dissociative phenomena to levels of cerebrospinal fluid monoamine metabolites and beta-endorphin in patients with eating disorders: a pilot study.

Dissociation is made manifest by a failure to integrate thoughts, feelings, memories, and actions into a unified sense of consciousness. Although dissociation is presumed to be a special state of consciousness manifested by state-dependent memory and physiology, the psychobiology of dissociation is poorly understood. In this study, we examined cerebrospinal fluid levels of the major monoamine metabolites and beta-endorphin in patients with eating disorders (11 with anorexia nervosa, 16 with bulimia nervosa), while they were acutely ill. Dissociative capacity was measured using the Dissociative Experiences Scale (DES). We provide evidence that neurochemical changes in dopaminergic, serotonergic, and opioid systems may be associated with the clinical expression of dissociation in patients with eating disorders during the acute phase of their illness. These preliminary results are compatible with previous studies of neurochemical disturbances in the eating disorders and suggest that future work in dissociation should specifically include examination of these neurobiologic systems.

Immobilization stress rapidly decreases hypothalamic corticotropin-releasing hormone secretion in vitro in the male 344/N Fischer rat.

Corticotropin-Releasing-Hormone (CRH) is the principal secretagogue for plasma ACTH and corticosterone secretion and plays an important role in coordinating a variety of physiological and behavioral responses to stress. To explore whether there is a rapid change in the secretory response of the hypothalamic CRH neuron during acute stress, we report here a study of the effects of KCl and norepinephrine (NE) on CRH release in vitro from rat hypothalami explanted after 5, 30, 60, and 120 minutes of immobilization. We also measured the plasma levels of ACTH, beta-endorphin, corticosterone, prolactin, GH, and TSH at these intervals. As the duration of immobilization increased, KCl and NE-induced CRH release in vitro progressively fell. After reaching a maximal rise after 30 minutes of immobilization, plasma ACTH, beta-endorphin, and prolactin progressively fell in plasma, whereas corticosterone remained elevated up to 120 minutes; TSH and GH secretion rapidly declined and remained suppressed. Taken together, these data suggest that during immobilization stress, the responsiveness of the hypothalamic CRH neuron rapidly falls, owing either to CRH depletion and/or desensitization to NE, and this is paralleled by a concomitant decrease in pituitary-adrenal responsiveness.

The stress response and the regulation of inflammatory disease.

The molecular and biochemical bases for interactions between the immune and central nervous systems are described. Immune cytokines not only activate immune function but also recruit central stress-responsive neurotransmitter systems in the modulation of the immune response and in the activation of behaviors that may be adaptive during injury or inflammation. Peripherally generated cytokines, such as interleukin-1, signal hypothalamic corticotropin-releasing hormone (CRH) neurons to activate pituitary-adrenal counter-regulation of inflammation through the potent antiinflammatory effects of glucocorticoids. Corticotropin-releasing hormone not only activates the pituitary-adrenal axis but also sets in motion a coordinated series of behavioral and physiologic responses, suggesting that the central nervous system may coordinate both behavioral and immunologic adaptation during stressful situations. The pathophysiologic perturbation of this feedback loop, through various mechanisms, results in the development of inflammatory syndromes, such as rheumatoid arthritis, and behavioral syndromes, such as depression. Thus, diseases characterized by both inflammatory and emotional disturbances may derive from common alterations in specific central nervous system pathways (for example, the CRH system). In addition, disruptions of this communication by genetic, infectious, toxic, or pharmacologic means can influence the susceptibility to disorders associated with both behavioral and inflammatory components and potentially alter their natural history. These concepts suggest that neuropharmacologic agents that stimulate hypothalamic CRH might potentially be adjunctive therapy for illnesses traditionally viewed as inflammatory or autoimmune.

Differential startle amplitude and corticosterone response in rats.

Different rat strains exhibit large differences in hypothalamic pituitary-adrenal activity that have been used to determine the role of the neuroendocrine system in susceptibility to autoimmune disease. To further characterize potential behavioral correlates of these differences, the amplitude of the acoustic (ASR) and tactile (TSR) startle response and the corticosterone response to acoustic startle stimuli were compared between two histocompatible strains, Lewis (LEW/N) and Fischer (F344/N) rats, as well as outbred Harlan Sprague-Dawley (SD) rats. Startle stimuli elicited larger ASR and TSR in LEW/N rats than in F344/N rats, with SD rats exhibiting an intermediate response. The ASR habituated at a similar rate in LEW/N and F344 rats, while the ASR did not habituate in SD rats. After handling and placement in the startle chambers, the three strains did not differ in control levels of corticosterone. In contrast, exposure to acoustic startle stimuli increased corticosterone 5-fold in F344/N rats and 2-fold in SD rats, but had no effect on corticosterone in LEW/N rats. These findings suggested an inverse relationship between the amplitude of the ASR and hypothalamic-pituitary-adrenal activation across strains. This relationship was further supported by a high negative correlation between corticosterone level and ASR amplitude within the F344/N group.

Chronic fluoxetine treatment reduces hypothalamic vasopressin secretion in vitro.

Patients with obsessive-compulsive disorder (OCD) hypersecrete the arousal producing neurohormone arginine vasopressin (AVP) into the cerebrospinal fluid and plasma. Because OCD responds preferentially to potent serotonin uptake inhibitors, we compared the effect of chronic fluoxetine treatment to that of other antidepressants (trazodone and desipramine) on AVP release from rat hypothalamic organ culture and showed that only fluoxetine significantly reduced in vitro AVP release.

Neutrophil-activating peptide-1/interleukin-8 mRNA is localized in rat hypothalamus and hippocampus.

Neutrophil-activating peptide-1/interleukin-8 (NAP-1/IL-8) is a cytokine synthesized by various cell types. In the immune system NAP-1/IL-8 is part of an immune cascade initiated by IL-1 production. NAP-1/IL-8 affects hypothalamic function and its production is suppressed by steroids. Therefore, it might be expected that NAP-1/IL-8 would be produced in brain areas involved in the control of the hypothalamic-pituitary-adrenocortical axis (HPA). NAP-1/IL-8 mRNA was localized by in situ hybridization in the paraventricular nucleus of the hypothalamus and hippocampus. Those areas also express the genes encoding interleukin-1-alpha (IL-1 alpha), IL-1 beta, IL-1 receptors, and IL-1 receptor antagonist (IL-1ra). This suggests that an immune cascade, which is well characterized in the immune system, may exist in brain, in areas of relevance to the regulation of stress-related neuroendocrine function.

Neurotransmitter-induced hypothalamic-pituitary-adrenal axis responsiveness is defective in inflammatory disease-susceptible Lewis rats: in vivo and in vitro studies suggesting globally defective hypothalamic secretion of corticotropin-releasing hormone.

The susceptibility of female Lewis (LEW/N) rats to the development of streptococcal cell wall (SCW)-induced arthritis and other autoimmune phenomena is associated with the inability of their hypothalamic-pituitary-adrenal (HPA) axis to adequately respond to inflammatory stimuli. In contrast, resistance to the development of SCW-induced arthritis and other inflammatory autoimmune manifestations in histocompatible female Fischer rats (F344/N) is related to their intact HPA axis response to inflammatory mediators. To evaluate the mechanism and the specificity of the HPA axis defect in LEW/N rats, we examined the ability of three major excitatory neurotransmitter systems to activate the HPA axis in both Lewis and Fisher rats. The responsiveness of plasma ACTH and corticosterone to the cholinergic muscarinic receptor agonist arecoline, the alpha 1-adrenergic receptor agonist methoxamine and the serotonin (5-HT) type 2 receptor agonist 1-(2,5-dimethoxy-4-iodophenyl)2-aminopropane were significantly blunted and/or abolished in LEW/N compared to F344/N rats. To localize the HPA axis defect to the hypothalamic CRH neuron, we evaluated the ability of explanted hypothalami from the two strains to secrete immunoreactive CRH in vitro, in response to acetylcholine (ACh), norepinephrine (NE), 5-HT and the 5-HT agonist quipazine. LEW/N hypothalami released less immunoreactive CRH (iCRH) in response to ACh, NE, 5-HT and quipazine than F344/N hypothalami. The dose-response curves of these compounds in the former were shifted to the right and/or abolished, suggesting decreased sensitivity of LEW/N hypothalami to these neurotransmitters.(ABSTRACT TRUNCATED AT 250 WORDS)

Induction of c-fos mRNA in rat brain by conditioned and unconditioned stressors.

Intense depolarizing stimuli induce the expression of the proto-oncogene c-fos which may be useful as a marker of neuronal activity. To determine if mild physical and behavioral stressors may also induce c-fos expression, we subjected rats to an unconditioned stressor (footshock) or a conditioned stressor (a tone previously paired with footshock) and measured c-fos mRNA levels in various brain regions using in situ hybridization. Removing rats from their home cage and exposing them to a tone was sufficient to cause increases in c-fos mRNA in several forebrain areas while further increases in c-fos occurred in the septum, cingulate cortex, and endopiriform nucleus in response to acute footshock stress. Both unconditioned and conditioned stressors increased c-fos mRNA levels in the locus ceruleus which correlated with stress-induced plasma corticosterone concentrations. Unconditioned footshock stress also increased c-fos mRNA in the hypothalamic paraventricular nucleus (PVN). However, neither conditioned nor unconditioned stressors induced c-fos in the PVN in rats which had been previously exposed to footshock. C-fos appears to be a sensitive marker for stress-responsive brain areas and may be important in mediating long-term neurochemical changes that result from stress.

Increased hypothalamic [3H]flunitrazepam binding in hypothalamic-pituitary-adrenal axis hyporesponsive Lewis rats.

We have previously demonstrated that susceptibility of Lewis (LEW/N) rats to inflammatory disease, compared to relatively resistant Fischer (F344/N) rats, is related to deficient glucocorticoid counter-regulation of the immune response resulting from deficient corticotropin-releasing hormone (CRH) responsiveness to inflammatory and other stress mediators. The GABA/benzodiazepine receptor complex is an important negative modulator of CRH secretion and responsiveness to excitatory stimuli. In this study, we have examined in vitro binding of [3H]flunitrazepam to hypothalamic membrane preparations from LEW/N and F344/N rats. LEW/N rats had significantly more hypothalamic benzodiazepine binding sites (Bmax) than F344/N rats, but there were no differences in benzodiazepine binding affinities (Kd) between these two strains. The differences in benzodiazepine receptor number were consistent with the respective plasma corticosterone levels in the two strains, and with previous work indicating a negative correlation between corticosterone levels and benzodiazepine binding site number. Adrenalectomy of F344/N rats increased benzodiazepine binding to levels comparable to LEW/N animals and treatment of adrenalectomized F344/N rats with DEX resulted in lowering of benzodiazepine Bmax to levels that did not differ significantly from those of intact F344/N rats. There was no significant change in receptor number in either adrenalectomized or DEX-treated LEW/N rats. These findings suggest that basal benzodiazepine receptor differences between these strains may be partially related to strain differences in corticosterone levels, however that additional factors may contribute to maintenance of these differences in LEW/N rats. Since benzodiazepines attenuate hypothalamic CRH secretion through GABAergic inhibition, we suggest that strain differences in receptor number could also augment strain differences in hypothalamic-pituitary-adrenal axis function through differential sensitivity to GABA-mediated feedback.