CSF1R inhibitor PLX5622 and environmental enrichment additively improve metabolic outcomes in middle-aged female mice.

As the elderly population grows, chronic metabolic dysfunction including obesity and diabetes are becoming increasingly common comorbidities. Hypothalamic inflammation through CNS resident microglia serves as a common pathway between developing obesity and developing systemic aging pathologies. Despite understanding aging as a life-long process involving interactions between individuals and their environment, limited studies address the dynamics of environment interactions with aging or aging therapeutics. We previously demonstrated environmental enrichment (EE) is an effective model for studying improved metabolic health and overall healthspan in mice, which acts through a brain-fat axis. Here we investigated the CSF1R inhibitor PLX5622 (PLX), which depletes microglia, and its effects on metabolic decline in aging in interaction with EE. PLX in combination with EE substantially improved metabolic outcomes in middle-aged female mice over PLX or EE alone. Chronic PLX treatment depleted 75% of microglia from the hypothalamus and reduced markers of inflammation without affecting brain-derived neurotrophic factor levels induced by EE. Adipose tissue remodeling and adipose tissue macrophage modulation were observed in response to CSF1R inhibition, which may contribute to the combined benefits seen in EE with PLX. Our study suggests benefits exist from combined drug and lifestyle interventions in aged animals.

Role of oxidative stress in disrupting the function of negative glucocorticoid response element in daily amphetamine-treated rats.

Amphetamine (AMPH)-induced appetite suppression is associated with changes in hypothalamic reactive oxygen species (ROS), antioxidants, neuropeptides, and plasma glucocorticoid. This study explored whether ROS and glucocorticoid response element (GRE), which is the promoter site of corticotropin-releasing hormone (CRH) gene, participated in neuropeptides-mediated appetite control. Rats were treated daily with AMPH for four days, and changes in food intake, plasma glucocorticoid and expression levels of hypothalamic neuropeptide Y (NPY), proopiomelanocortin (POMC), superoxide dismutase (SOD), CRH, and glucocorticoid receptor (GR) were examined and compared. Results showed that food intake decreased and NPY gene down-regulated, while POMC, SOD, and CRH gene up-regulated during AMPH treatment. GR and GRE-DNA bindings were disrupted on Day 1 and Day 2 when glucocorticoid levels were still high. Pretreatment with GR inhibitor or ROS scavenger modulated mRNA levels in NPY, POMC, SOD and CRH in AMPH-treated rats. We suggest that disruptions of negative GRE (nGRE) on Day 1 and Day 2 are associated with an increase in oxidative stress during the regulation of NPY/POMC-mediated appetite control in AMPH-treated rats. These results advance the understanding of molecular mechanism in regulating AMPH-mediated appetite suppression.

Chlorella vulgaris reduces the impact of stress on hypothalamic-pituitary-adrenal axis and brain c-fos expression.

Predominantly emotional stressors activate a wide range of brain areas, as revealed by the expression of immediate early genes, such as c-fos. Chlorella vulgaris (CV) is considered a biological response modifier, as demonstrated by its protective activities against infections, tumors and stress. We evaluated the effect of acute pretreatment with CV on the peripheral and central responses to forced swimming stress in adult male rats. Pretreatment with CV produced a significant reduction of stress-related hypothalamic-pituitary-adrenal activation, demonstrated by decreased corticotrophin releasing factor gene expression in the hypothalamic paraventricular nucleus (PVN) and lower ACTH response. Hyperglycemia induced by the stressor was similarly reduced. This attenuated neuroendocrine response to stress occurred in parallel with a diminished c-fos expression in most evaluated areas, including the PVN. The data presented in this study reinforce the usefulness of CV to diminish the impact of stressors, by reducing the HPA response. Although our results suggest a central effect of CV, further studies are necessary to understand the precise mechanisms underpinning this effect.

Intermittent access ethanol consumption dysregulates CRF function in the hypothalamus and is attenuated by the CRF-R1 antagonist, CP-376395.

Corticotrophin-releasing factor (CRF) is a mediator of stress responses and a key modulator of ethanol-mediated behaviors. We report here that the CRF receptor 1 (CRF-R1) antagonist, CP-376395 reduces 20% ethanol consumption in animals trained to consume ethanol on an intermittent, but not a continuous, schedule. Furthermore, using [(35) S]GTPγS binding assays, we demonstrate that CRF-mediated G-protein signaling in the hypothalamus of the intermittent drinkers is decreased when compared to controls suggesting that the effects of CP-376395 are mediated by extrahypothalamic mechanisms. The present study provides further support for the use of CRF-R1 antagonists for the treatment of alcohol use disorders and suggests that ethanol consumption dysregulates CRF function in the hypothalamus.

Glucocorticoid inhibition in the treatment of depression: can we think outside the endocrine hypothalamus?

BACKGROUND: Major depressive disorder affects a substantial percentage of the U.S. population, and can be highly debilitating. Selective serotonin reuptake inhibitors are commonly prescribed to treat depression, but may not be as effective for more severe or persistent depression. METHODS: The authors review data concerning the effects of corticosteroid synthesis inhibitors (CSIs) in the management of depressive disorders, present a hypothesis as to their possible mechanisms of action based on recent data suggesting synergistic effects of glucocorticoids on extrahypothalamic corticotropin-releasing hormone (CRH), and consider alternative hypotheses. Published reports evaluating the efficacy of CSIs in treating depression are reviewed and presented in light of recent findings regarding actions of glucocorticoids on the central CRH system. RESULTS: Results from open label and double-blind studies by several groups have indicated that CSIs may be efficacious or of adjunctive value in some patients with depression, including those refractory to other agents; however, there is a need for more controlled studies. Several lines of data suggest that the mechanism of action of these agents may not be solely a function of inhibition of adrenal cortisol production. CONCLUSIONS: The authors propose that CSIs may be efficacious in part by reducing glucocorticoid enhancement of CRH action in neurons of the central nucleus of the amygdala and other structures outside the endocrine hypothalamus. Possible effects of systemically administered CSIs on glucocorticoid receptor regulation, neuroactive steroids, and classical monoamine systems are also discussed. We conclude that available clinical data suggest a potential role for CSIs in the management of depressive disorders, especially major depression with psychotic features.

A single administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin that produces reduced food and water intake induces long-lasting expression of corticotropin-releasing factor, arginine vasopressin, and proopiomelanocortin in rat brain.

The mechanism by which a single administration of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) reduces food and water intake is unclear. We examined whether such a food and water intake-reducing single administration of TCDD induced changes in corticotropin-releasing factor (CRF), arginine vasopressin (AVP), and proopiomelanocortin (POMC) expression in rat brain. To observe time-dependent changes in these neuropeptides, male Sprague-Dawley rats were given TCDD (50 microg/kg) and terminated 1, 2, 4, or 7 days later. In addition, to observe dose-dependent changes in feeding and neuropeptides, rats were also given a range of TCDD doses (12.5, 25, or 50 microg/kg) and terminated 14 days later. TCDD suppressed food and water intake over 14 days in a dose-dependent manner. TCDD treatment also increased CRF and POMC mRNA levels in the hypothalamic paraventricular nucleus (PVN) and arcuate nucleus, respectively, in a dose- and time-dependent manner. These increases were related to decreased food intake following TCDD administration. TCDD treatment increased AVP and CRF mRNA levels in the PVN, and these increases were related to decreased water intake. Interestingly, the increases in CRF, AVP and POMC expression were observed 7 to 14 days after TCDD administration. These results suggest that a single administration of TCDD induced long-lasting increases in CRF, AVP, and POMC mRNA levels in the hypothalamus and that these changes are related to reduced food and water intake 7 to 14 days after TCDD administration.

The probiotic Bifidobacteria infantis: An assessment of potential antidepressant properties in the rat.

It is becoming increasingly apparent that probiotics are important to the health of the host. The absence of probiotic bacteria in the gut can have adverse effects not only locally in the gut, but has also been shown to affect central HPA and monoaminergic activity, features that have been implicated in the aetiology of depression. To evaluate the potential antidepressant properties of probiotics, we tested rats chronically treated with Bifidobacteria infantis in the forced swim test, and also assessed the effects on immune, neuroendocrine and central monoaminergic activity. Sprague-Dawley rats were treated for 14 days with B. infantis. Probiotic administration in naive rats had no effect on swim behaviours on day 3 or day 14 following the commencement of treatment. However, there was a significant attenuation of IFN-gamma, TNF-alpha and IL-6 cytokines following mitogen stimulation (p<0.05) in probiotic-treated rats relative to controls. Furthermore, there was a marked increase in plasma concentrations of tryptophan (p<0.005) and kynurenic acid (p<0.05) in the bifidobacteria-treated rats when compared to controls. Bifidobacteria treatment also resulted in a reduced 5-HIAA concentration in the frontal cortex and a decrease in DOPAC in the amygdaloid cortex. The attenuation of pro-inflammatory immune responses, and the elevation of the serotonergic precursor, tryptophan by bifidobacteria treatment, provides encouraging evidence in support of the proposition that this probiotic may possess antidepressant properties. However, these findings are preliminary and further investigation into the precise mechanisms involved, is warranted.

Hydroxyurea induces vasopressin release and cytokine gene expression in the rat hypothalamus.

We previously showed that the cytostatic drug hydroxyurea (HU) activates the hypothalamo-pituitary-adrenal (HPA) axis in intact rats, whereas it is lethal in rats with impaired HPA function. In these animals, HU toxicity is mediated by increased circulating levels of proinflammatory cytokines, whose secretion cannot be counteracted by glucocorticoids, suggesting that HPA activation blunts HU toxicity. Here we investigated the mechanisms through which HU activates the HPA axis, looking at the direct effects of the drug on the isolated hypothalamus. We found that HU significantly increases the release of arginine vasopressin but not that of corticotrophin-releasing hormone in short-term incubation experiments. The levels of arginine vasopressin are also increased in the hypothalamus and systemic circulation 2 h after the in vivo administration of the drug. Furthermore, HU increased significantly the expression of interleukin-6 and, to a lesser extent, interleukin-1beta in the hypothalamus. Interestingly, experiments with HU on primary cultures of rat microglia and astrocytes suggested that the increase in cytokine gene expression observed in hypothalamic explants is not accounted for by glial cells. Since both vasopressin and cytokines can activate the HPA axis, our present findings provide a reasonable explanation of the HPA activation elicited by HU in vivo in the rat.

Antidepressant-like activity of a Kampo (Japanese herbal) medicine, Koso-san (Xiang-Su-San), and its mode of action via the hypothalamic-pituitary-adrenal axis.

Koso-san (Xiang-Su-San in Chinese), a Kampo (Japanese herbal) medicine, is used clinically in East Asia for the treatment of depression-like symptoms associated with the initial stage of the common cold, allergic urticaria due to food ingestion, irritable bowel syndrome, chronic fatigue syndrome, insomnia, and autonomic imbalance. However, the antidepressant-like activity of Koso-san has never been evaluated scientifically. In this study, ddY mice subjected to a combination of forced swimming and chronic mild stresses were termed depression-like model mice. The degree of the depression-like state was measured by the animal's duration of immobility using the forced swimming test (FST). Oral administration of Koso-san (1.0 g/kg/body wt./day, 9 days) significantly shortened the duration of immobility of the depression-like model mice in the FST; however, locomotor activity was not affected. Hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis plays an important role in the pathophysiology of depression. Levels of corticotropin-releasing hormone mRNA expression in the hypothalamus and proopiomelanocortin mRNA expression in the pituitary were significantly increased, and glucocorticoid receptor protein expression in the hypothalamus paraventricular nucleus was downregulated in the depression-like model mice. However, Koso-san ameliorated these alterations to the normal conditions. The results of this study suggest that Koso-san shows the antidepressant-like effect through suppressing the hyperactivity of the HPA axis in depression-like model mice.

Mode of leptin action in chicken hypothalamus.

While there have been many studies in various species examining the mode of central leptin action on food intake, there is however a paucity of data in birds. We have, therefore, addressed this issue in broiler chickens because this strain was selected for high growth rate, hence high food intake. Continuous infusion of recombinant chicken leptin (8 microg/kg/h) during 6 h at a constant rate of 3 ml/h resulted in a significant reduction (49-57%) of food intake in 3-week-old broiler chickens (P < 0.05). The effect of leptin within the central nervous system (CNS) was mediated via selective hypothalamic neuropeptides. Leptin significantly decreased the expression of its receptor (Ob-R), neuropeptide Y (NPY), orexin (ORX), and orexin receptor (ORXR) (P < 0.05), but not that of agouti-related protein (AgRP) (anabolic/orexigenic effectors) in chicken hypothalamus. However, the catabolic/anorexigenic neuropeptides namely proopiomelanocortin (POMC) and corticotropin-releasing hormone (CRH) mRNA levels remained unchanged after leptin treatment. Despite the absence of leptin effect on AgRP (the antagonist of melanocortin receptor MCR) and POMC (the precursor of alpha-melanocyte stimulating hormone which is a potent agonist for MCR), leptin significantly decreased the expression of MCR-4/5 gene in chicken hypothalamus (P < 0.05) suggesting that leptin acts directly (as ligand) or indirectly (via other ligands) on MCRs to regulate food intake in birds. Additionally, leptin down-regulated the expression of fatty acid synthase (FAS) gene in chicken hypothalamus, indicating an additional pathway of leptin action on food intake such as described for FAS inhibitors. These findings provide new insight into the mechanism of leptin control of food intake in chickens.

Hypothalamic neurons of postnatally overfed, overweight rats respond differentially to corticotropin-releasing hormones.

Adult overweight rats previously subjected to early postnatal overnutrition in small litters are hyperphagic, hyperleptinemic and differ in emotional behaviour from rats of control litters. We proved the hypothesis that neurons of the hypothalamic regulatory system of body weight differentially react to peptides of the corticotropin-releasing factor (CRF) family in these overweight rats. Single unit activity was recorded in brain slices. In controls, CRF and the CRF(2) receptor agonist stresscopin-related peptide (SRP) predominantly activated neurons of the dorsomedial part of ventromedial hypothalamic nucleus (VMHDM), but in overweight rats, SRP induced a significant inhibition. Increased neuronal firing to CRF and SRP of the medial parvocellular part of paraventricular hypothalamic nucleus (PaMP) in controls similarly changed to more inhibition in overweight rats. Inhibition of neuronal activity in VMHDM and PaMP can contribute to reduce satiety signals and to decrease energy expenditure in rats. In contrast, medial arcuate (ArcM) neurons of controls were significantly inhibited by SRP, whereas neurons of overweight rats could also be activated. The difference in the expression of these response types was significant. Activation of ArcM neurons known to produce neuropeptide Y can increase food intake. The results are discussed in terms of a trophic action of leptin changing synaptic wiring and the expression of excitatory and inhibitory synapses. The altered responses of hypothalamic neurons in adult small-litter rats may reflect a general mechanism of neurochemical plasticity acquired during the postnatal critical differentiation period, thus leading to permanently altered function of the regulatory system of body weight.

Acute glucocorticoid pretreatment suppresses stress-induced hypothalamic-pituitary-adrenal axis hormone secretion and expression of corticotropin-releasing hormone hnRNA but does not affect c-fos mRNA or fos protein expression in the paraventricular nucleus of the hypothalamus.

Corticosterone regulates both basal and stress-induced hypothalamic-pituitary-adrenal (HPA) axis activity in a negative-feedback fashion. However, the cellular and molecular mechanisms of this negative feedback have yet to be explicitly characterized. By comparing stress-induced c-fos and corticotropin-releasing hormone (CRH) expression in the paraventricular nucleus (PVN), we may be able to determine whether acute glucocorticoid treatment affects the net neural excitatory input to the PVN (represented primarily by c-fos mRNA expression) or directly affects the ability of cells in the PVN to respond to that input (represented primarily by CRH hnRNA expression). In the following studies, we observed the effect of acute glucocorticoid (RU28362) treatment on subsequent HPA axis reactivity by measuring stress-induced plasma hormone concentration [corticosterone and adrenocorticotropic hormone (ACTH)] and gene expression (c-fos and CRH) in the PVN. First, we examined the dose-response relationship between systemically administered RU28362 (1-150 microg/kg, i.p) and suppression of the stress-induced corticosterone response. We then confirmed central nervous system access of the maximally suppressive dose of RU28362 (150 microg/kg) by an ex vivo radioligand binding assay. RU28362 selectively occupied the majority of glucocorticoid receptors in the hippocampus and hypothalamus while having no effect on mineralocorticoid receptors. In separate studies, RU28362 (150 microg/kg) and corticosterone (5 mg/kg) were injected i.p. 1 h before restraint stress. Compared to vehicle-treated controls, rats treated with RU28362 and corticosterone had substantially blunted stress-induced corticosterone and ACTH production, respectively. Furthermore, treatment with RU28362 significantly blunted stress-induced CRH hnRNA expression in the PVN. By contrast, neither RU28362 nor corticosterone treatment had an effect on stress-induced neuronal activation as measured by c-fos mRNA and its protein product in the PVN. This dissociation between c-fos and CRH gene expression suggests that glucocorticoid suppression of HPA activity within this time-frame is not a result of decreased excitatory neural input to the PVN, but instead depends on some direct effect of RU28362 on cells intrinsic to the HPA axis.

Effect of interleukin 1beta on the HPA axis in H1-receptor knockout mice.

OBJECTIVES AND METHODS: Circulating cytokines such as interleukin-1 (IL-1), and tumor necrosis factor-alpha as well as lipopolysaccharide (LPS) are potent ACTH secretagogues, acting via stimulation of corticotropin-releasing hormone (CRH) and vasopressinergic neurons in the paraventricular nucleus of the hypothalamus (PVN). Histamine (HA) has been shown to stimulate ACTH secretion in rats, an effect in part mediated by CRH and arginine vasopressin (AVP). We have previously shown that inhibition of neuronal HA synthesis or central blockade of H(1) receptors (H(1)R) decreased the ACTH response to LPS in male rats. To further elucidate the role of neuronal HA in cytokine-induced activation of the HPA axis, we compared the effect of H(1)R knockout on IL-1beta-induced ACTH secretion in adult male mice. RESULTS: In H(1)R knockout mice, ACTH secretion increased from basal levels of 261 to 492 pmol/l in response to IL-1beta whereas the cytokine-induced ACTH secretion increased from 140 to 406 pmol/l in wild-type mice. Plasma corticosterone (CORT) rose from basal levels of 99 to 831 nmol/l in knockout mice upon IL-1beta stimulation, whereas in wild-type mice CORT levels rose from 112 to 841 nmol/l. There was no significant difference in IL-1beta-stimulated plasma ACTH or CORT levels between wild-type and knockout mice. Furthermore, there was no significant difference in basal or IL-1beta-stimulated hypothalamic levels of histamine and tele-methyl-histamine between wild-type and knockout mice. HDC gene expression was significantly lower in knockout mice than in wild-type mice both under basal and IL-1beta-stimulated conditions, while there were no significant differences in CRH gene expression in the PVN in knockout mice under basal and IL-1beta-stimulated conditions. Increased basal expression of AVP in the PVN of knockout mice was observed in this study compared to wild-type mice. CONCLUSION: We conclude that the lack of the gene for histamine H(1)R does not seem to be crucial for the ACTH and CORT response to IL-1beta, either due to possible functional compensation in the H(1)R knockout mouse or due to activation of pathways other than the neuronal histaminergic system.

Estrogen and androgen influence hypothalamic AVP and CRF concentrations in fetal and adult sheep.

The present study tested the hypothesis that action of sex steroids on the hypothalamus-pituitary-adrenal (HPA) axis is measurable in the hypothalamus. Late-gestation fetal sheep were treated (5 mg/21 days) with either estradiol, androstenedione, or tamoxifen and compared to age-matched control fetuses. Tamoxifen significantly increased hypothalamic corticotropin releasing factor (CRF) and arginine vasopressin (AVP) concentrations, and androstenedione significantly decreased hypothalamic CRF concentration. Adult sheep were treated with estrone (10 mg/21 days), and responded with significant increases in hypothalamic AVP concentration, but not in immunoreactive ACTH concentration or processing within the pituitary. The results demonstrate that the effect of estrogen on the HPA axis is measurable in the hypothalamus, and is therefore not primarily at the anterior pituitary.

Cytokine and adrenal axis responses to endotoxin.

The push-pull cannula (PPC) technique was applied to examine the kinetics of in vivo concentration changes in male rat brain extracellular fluid (ECF) of endogenous interleukin-1beta (IL-1beta) and corticotrophin releasing hormone (CRH) after a peripheral injection of lipopolysaccharide (LPS) (25 microg/100 g b.wt. intravenously). In addition, IL-1beta, adrenocorticotropin hormone (ACTH) and corticosterone concentrations in plasma were also measured at selected intervals after LPS challenge. Administration of LPS resulted in a progressive increase in the concentrations of IL-1beta in brain hypothalamic ECF. A significant increase from the zero time mean value of 77+/-10 to 393+/-88 pg/ml at the 15-min interval was recorded. The increase in IL-1beta concentration in hypothalamic ECF reached a peak of 883+/-237 pg/ml at 30 min post-LPS. CRH concentration in the same hypothalamic ECF was 41+/-17 pg/ml at time zero, 97+/-15 pg/ml at 15 min and at 30 min was significantly increased (215+/-56 pg/ml). A time course of significant increases at 30 min in plasma concentrations of IL-1beta, ACTH and corticosterone was also recorded in the same animals described above. The data show that a peripherally administered LPS bolus elicited an early (over 15 min post-injection) increase in brain ECF IL-1beta concentration; additional significant increases in hormones released from the hypothalamic-pituitary-adrenal (HPA) axis were recorded at 30 min post-LPS injection. These observations support the concept of an early change in hypothalamic ECF concentration of IL-1beta preceding LPS-induced activation of the HPA axis.

Neuronal histamine and expression of corticotropin-releasing hormone, vasopressin and oxytocin in the hypothalamus: relative importance of H1 and H2 receptors.

Centrally administered histamine (HA) stimulates the secretion of the pro-opiomelanocortin-derived peptides ACTH and beta-endorphin as well as prolactin. The effect of HA on secretion of these adenohypophysial hormones is indirect and may involve activation of hypothalamic neurons containing corticotropin-releasing hormone (CRH), arginine-vasopressin (AVP) or oxytocin (OT). We studied the effect of activating central HA receptors by central infusion of HA, HA agonists or antagonists on expression of CRH, AVP and OT mRNA in the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. Intracerebroventricular infusion of HA (270 nmol), the H1-receptor agonist 2-thiazolylethylamine or the H2-receptor agonist 4-methylhistamine increased the level of CRH mRNA in the PVN, and OT mRNA in the SON. In contrast, none of these compounds had any effect on expression of AVP mRNA in the PVN or SON. Administration of the H1-receptor antagonist mepyramine or the H2-receptor antagonist cimetidine had no effect on basal expression of CRH, AVP or OT mRNA in the PVN and/or SON except for a slight inhibitory effect of cimetidine on CRH mRNA expression in the PVN. Pretreatment with mepyramine or cimetidine before HA administration inhibited the HA-induced increase in OT mRNA levels but had no effect on the HA-induced increase in CRH mRNA levels in the PVN. We conclude that HA stimulates hypothalamic CRH and OT neurons by increasing mRNA levels, and this effect seems to be mediated via activation of both HA H1 and H2 receptors.

Differential regulation of corticotropin-releasing factor and vasopressin in discrete brain regions after morphine administration: correlations with hypothalamic noradrenergic activity and pituitary-adrenal response.

The changes in the content of corticotropin-releasing factor (CRF) and arginine vasopressin (AVP) in discrete brain nuclei during chronic opioids administration have not been well established. We evaluated the effects of acute and chronic morphine administration on the content of CRF and AVP in different hypothalamic and extrahypothalamic (bed nucleus of the stria terminalis, BNST) nuclei in rats. Concomitantly, changes in hypothalamic noradrenaline (NA) turnover [estimated by the 3-methoxy-4-hydroxyphenylethyleneglycol MHPG/NA ratio] and in plasma corticosterone release (as a marker of the activity of the hypothalamus-pituitary-adrenal axis) were determined. Male rats were implanted with placebo (naïve) or morphine (tolerant) pellets for 7 days. On day 8, groups of rats received an acute injection of either saline i.p. or morphine (30 mg/kg i.p.) and were sacrificed 30 min later. Acute morphine injection to naïve rats increased both the release of corticosterone and the hypothalamic NA turnover. CRF and AVP showed no modifications in the paraventricular nucleus (PVN) or in the median eminence (ME). CRF content decreased in the ventromedian nucleus (VMN) and increased in the BNST, but did not change in the arcuate nucleus (AN). AVP was elevated in the supraoptic nucleus (SON) but not changed in the suprachiasmatic nucleus (SCN). In chronic morphine-treated rats, there was a pronounced decrease in the NA turnover and in the release of corticosterone, which indicates that tolerance develops to the acute effects of morphine. Correspondingly, CRF and AVP were enhanced in the PVN and decreased in the ME, when compared with naïve rats injected with morphine. CRF content was decreased in the AN and in the BNST, but increased in the VMN. The AVP content was decreased in the SON, and no modifications were seen in the SCN. The present study shows that, in addition to the modifications in corticosterone secretion and in hypothalamic NA turnover, chronic morphine administration produces a complex response in the CRF and AVP systems. These modifications might contribute to the behavioral, emotional and neuroendocrine alterations produced during opioid tolerance.

Involvement of nitric oxide in basal and interleukin-1 beta-induced CRH and ACTH release in vitro.

NG-Nitro-L-arginine, an inhibitor of nitric oxide synthase, does not influence CRH basal release but is able to modify ACTH basal secretion and to block interleukin-1 beta-induced CRH and ACTH release from rat hypothalamic and anterior pituitary cell cultures in vitro. The data suggest a different involvement of NO at hypothalamic and pituitary level.