Neuromedin U partially mediates leptin-induced hypothalamo-pituitary adrenal (HPA) stimulation and has a physiological role in the regulation of the HPA axis in the rat

Intracerebroventricular (ICV) administration of the hypothalamic neuropeptide neuromedin U (NMU) or the adipostat hormone leptin increases plasma ACTH and corticosterone. The relationship between leptin and NMU in the regulation of the hypothalamo-pituitary adrenal (HPA) axis is currently unknown. In this study, leptin (1 nm) significantly increased the release of CRH from ex vivo hypothalamic explants by 207 +/- 8.4% (P < 0.05 vs. basal), an effect blocked by the administration of anti-NMU IgG. The ICV administration of leptin (10 mug, 0.625 nmol) increased plasma ACTH and corticosterone 20 min after injection [plasma ACTH (picograms per milliliter): vehicle, 63 +/- 20, leptin, 135 +/- 36, P < 0.05; plasma corticosterone (nanograms per milliliter): vehicle, 285 +/- 39, leptin, 452 +/- 44, P < 0.01]. These effects were partially attenuated by the prior administration of anti-NMU IgG. Peripheral leptin also stimulated ACTH release, an effect attenuated by prior ICV administration of anti-NMU IgG. We examined the diurnal pattern of hypothalamic NMU mRNA expression and peptide content, plasma leptin, and plasma corticosterone. The diurnal changes in hypothalamic NMU mRNA expression were positively correlated with hypothalamic NMU peptide content, plasma corticosterone, and plasma leptin. The ICV administration of anti-NMU IgG significantly attenuated the dark phase rise in corticosterone [corticosterone (nanograms per milliliter): vehicle, 493 +/- 38; NMU IgG, 342 +/- 47 (P < 0.05)]. These studies suggest that NMU may play a role in the regulation of the HPA axis and partially mediate leptin-induced HPA stimulation.     

Centrally administered murine-leptin stimulates the hypothalamus-pituitary- adrenal axis through arginine-vasopressin

Starvation induces a decrease in circulating leptin levels and activation of the hypothalamus-pituitary-adrenal (HPA) axis. Leptin inhibits the HPA axis in unfed rodents or genetically leptin-deficient ob/ob mice, whereas it stimulates corticotropin-releasing hormone (CRH) gene expression in the paraventricular nucleus (PVN). However, the interactions between leptin, CRH and the HPA axis are poorly understood and are likely to be complex. We recently demonstrated that central leptin administration caused increases in plasma arginine-vasopressin (AVP) and AVP gene expression of the PVN in nonstressful rats. AVP stimulates the release of adrenocorticotropic hormone (ACTH), but it also potentiates the action of CRH on ACTH release. In this study, we investigated the effects of leptin on plasma ACTH and corticosterone levels, CRH mRNA of the PVN and proopiomelanocortin (POMC) mRNA of the pituitary in nonstrained rats. Intracerebroventricularly administered leptin caused increases in plasma ACTH and corticosterone levels in dose-dependent manners. In Northern blot analyses, the leptin injection induced significant increases in the expression of CRH mRNA in the PVN and POMC mRNA in the pituitary. The increased plasma ACTH and corticosterone levels by leptin were attenuated with intracerebroventricular pretreatment of a V(1a) receptor antagonist (OPC-21268) or a V(1a)/V(1b) receptor antagonist (dP[Tyr(Me)(2)]AVP), but not with that of a V(2) receptor antagonist (OPC-31260). The leptin-induced CRH mRNA expression in the PVN and POMC mRNA expression in the pituitary were also reduced by the pretreatment with OPC-21268 and dP[Tyr(Me)(2)]AVP. These results suggest that intracerebroventricular leptin administration activates the HPA axis by AVP receptor activation through V(1a) receptors in the PVN which in turn activates CRH neurons to drive ACTH and corticosterone secretion in concert with AVP in nonstrained rats.     

Neuroendocrine stress but not feeding responses to centrally administered neuropeptide Y are suppressed in pregnant rats

Metabolic peptides such as orexin and neuropeptide Y (NPY) exert profound effects on feeding but also act centrally to stimulate the hypothalamo-pituitary-adrenal (HPA) axis. In late pregnancy the HPA axis is hyporesponsive to centrally administered orexin-A, which signals to the HPA axis, in part, via arcuate NPY neurones. We investigated whether reduced HPA axis responses to orexin may be a consequence of down-regulated NPY signaling to the paraventricular nucleus (PVN) in pregnancy. Pregnant (d 21) and virgin rats were blood sampled for ACTH, corticosterone, and oxytocin (also a stress hormone in rats) before and after intracerebroventricular NPY or vehicle. Behavior was monitored. Rats were killed 4 h after NPY and brains removed for in situ hybridization. In another experiment rats were given vehicle or NPY, perfuse fixed 90 min later, and brain sections processed for Fos and oxytocin immunocytochemistry. NPY significantly increased ACTH, corticosterone and oxytocin secretion in the virgins but had no such effect on ACTH or oxytocin in the pregnant rats; the corticosterone response to NPY was markedly attenuated in pregnant rats. NPY increased CRH and vasopressin mRNA expression in the parvocellular PVN and stimulated Fos expression in magnocellular supraoptic and PVN oxytocin neurones of virgin but not pregnant rats. NPY increased food intake and drinking similarly in virgin and pregnant rats. Thus, neuroendocrine stress responses to central NPY are absent in late pregnancy, whereas ingestive behavioral responses are intact. These changes may explain the similarly attenuated HPA response to centrally administered orexin-A and will favor anabolic adaptations in pregnancy.     

Acute effects of purified and UV-inactivated Herpes simplex virus type 1 on the hypothalamo-pituitary-adrenocortical axis

Herpes simplex virus type 1 (HSV-1) is a common cause of viral encephalitis, manifested by neuroendocrine and behavioral changes. We have previously demonstrated that HSV-1 induces marked hypothalamo-pituitary-adrenocortical (HPA) axis activation. In this study we characterized the acute effects of HSV-1 on the HPA axis occurring before viral replication and appearance of clinical signs of encephalitis. Since in previous studies we used crude virus preparations which may contain immune factors produced by the infected cells, we tested here the effects of purified HSV-1 virions. HSV-1 was propagated on Vero cells and virions were purified by centrifugation in sucrose gradients. Inactivation of viral infectivity was achieved by UV-irradiation, which caused a million-fold decrease in virus titer, as determined by plaque assay. Intracerebroventricular (ICV) inoculation of crude or purified virions induced a dose dependent increase in serum corticosterone and corticotropin (ACTH). This effect was maximal within 3.5 h postinfection and lasted for 72 h. ICV inoculation of UV-inactivated purified virions caused a marked increase in serum corticosterone and ACTH at 3.5 h, but in contrast to the effect of the active virus, the hormone levels gradually decreased at 24 h, and returned to basal levels at 72 h postinfection. HSV-1-induced HPA axis activation at 3.5 h was completely abolished by pretreatment with interleukin-1 receptor antagonist, injected ICV. Adrenalectomized rats failed to respond to ICV inoculation of purified HSV-1 by increase in ACTH. In contrast, these rats responded to ICV injection of LPS. In conclusion: (1) HSV-1 can acutely activate the HPA axis before and independently of any viral replication; (2) HSV-1-induced HPA axis activation depends on a permissive action of circulating glucocorticoids and on host derived brain interleukin-1.     

Influence of the paraventricular nucleus of the hypothalamus in the alteration of neuroendocrine functions induced by intermittent footshock or interleukin.

The documented ability of physical stress and cytokines to increase the secretion of corticotropin-releasing factor CRF by the paraventricular nucleus of the hypothalamus (PVN), coupled with our earlier demonstration that CRF acts within the brain to interfere with reproductive functions, led us to investigate the effect of lesions of the PVN on LH, testosterone, ACTH, and corticosterone (CORT) secretion. Bilateral lesions of the PVN were done electrolytically, and 2 weeks later a series of acute and chronic experiments were performed in intact or castrated male rats bearing indwelling jugular and/or intracerebroventricular cannulas. The first study involved a single 2-h exposure of intact male rats to footshocks (2 mA, 2-sec duration, 4 per min). Although PVN lesions did not measurably alter the ability of intermittent footshock to lower plasma testosterone levels, this treatment attenuated the rise in plasma ACTH and CORT. In a second study, which was done in castrated rats, shocks were delivered 2 h daily for 7 days, and circulating hormone levels were measured at the end of the last shock period. Plasma LH levels of stressed rats showed statistically comparable decreases in both sham- and PVN-lesioned animals. Chronic exposure to footshocks induced smaller increases of ACTH and CORT secretion in PVN-lesioned compared to sham-lesioned rats, but the lesions did not completely abolish stress-induced activation of the hypothalamic-pituitary adrenal (HPA) axis. The third experiment involved the central injection of the vehicle or 40 ng interleukin-1 beta (IL-1 beta) to castrated rats. As expected, IL-1 beta dramatically decreased plasma LH values and increased circulating ACTH and CORT levels measured 2 h later. Bilateral PVN lesion did not influence LH secretion after injection of the vehicle or IL-1 beta. In contrast, destruction of the PVN completely blocked the increase of HPA axis activity observed in sham-operated rats 2 h after the intracerebroventricular infusion of IL-1 beta. These results confirm our previous observation that exposure to either footshocks or interleukins alters the activity of the hypothalamic-pituitary gonadal and HPA axis. Additionally, the present studies suggest that the PVN, which represents the predominant hypothalamic nucleus controlling the response of the HPA axis to a number of stimuli, does not appear to be necessary for the antireproductive effects of intermittent footshock or immune activation.     

Effects of chronic 'Binge' cocaine administration on plasma ACTH and corticosterone levels in mice deficient in DARPP-32.

The product of the DARPP-32 gene mediates intracellular signals initiated by the binding of dopamine to its receptors. Cocaine administration leads to increased activation of dopamine receptors, and causes activation of the stress-responsive hypothalamic-pituitary-adrenal (HPA) axis. We determined the effects of chronic 'binge' pattern cocaine on HPA activity in mice containing a targeted disruption of the DARPP-32 gene. Mice received three daily injections of cocaine (15 mg/kg/injection) for 14 days, and were sacrificed 30 min after the last injection. We measured the levels of plasma adrenocorticotropin (ACTH) and corticosterone which reflect HPA activity. In wild-type controls, 'binge' cocaine administration significantly increased plasma ACTH and corticosterone levels. In contrast, DARPP-32-deficient mice failed to show a significant elevation of either plasma ACTH or corticosterone levels following 'binge' cocaine. The results indicate that DARPP-32 plays a role in mediating the stimulatory effects of cocaine on the HPA axis.     

The amygdala regulates the pituitary-adrenocortical response and release of hypothalamic serotonin following electrical stimulation of the dorsal raphe nucleus in the rat

The amygdala is known to modulate the function of the hypothalamo-pituitary-adrenocortical (HPA) axis, but the mechanism of this effect is still not clear. In the present study we examined the specific role of the serotonin (5-HT) system in mediating the effect of the amygdala on the activity of the HPA axis. Bilateral lesions of the amygdala in rats reduced the adrenocorticotropin (ACTH) and corticosterone responses to electrical stimulation of the dorsal raphe nucleus, where the cell bodies of serotonergic neurons are located. Amygdala lesions had no effect on the ACTH and corticosterone responses to administration of a 5-HT(1A) receptor agonist directly into the paraventricular nucleus (PVN) of the hypothalamus, indicating that there was no impairment in the activity of postsynaptic 5-HT(1A) receptors in the hypothalamus. In vivo microdialysis showed that amygdala lesions markedly attenuated the effect of electrical stimulation of the dorsal raphe to increase extracellular secretion of 5-HT in the PVN. This is the first demonstration that the amygdala has a facilitatory effect on the function of dorsal raphe 5-HT neurons which project to the PVN, and suggests a mechanism by which the amygdala may modulate the function of the HPA axis.     

Hypothalamo-pituitary-adrenal axis sensitization after chronic salt loading

Hypothalamic parvocellular vasopressin (VP) and corticotropin-releasing hormone (CRH) in the paraventricular nucleus (PVN) are major secretagogues of corticotropin (ACTH), and central plasticity including their alteration is closely related to hypothalamic-pituitary-adrenal (HPA) axis modulation. Chronic hyperosmotic stress caused by 2% salt loading has been known to alter VP and CRH expression. We recently reported that rehydration, a recovery stage from salt loading, induced a prolonged increase in parvocellular VP mRNA expression and suggested that rehydration can modulate HPA axis function without obvious external stress. In the present study, we examined hypothalamic VP and CRH mRNA expression and their responsiveness to acute immobilization stress in control, salt-loaded and rehydrated animals, in order to clarify the precise mechanism of HPA axis regulation during rehydration. The results were further compared with plasma corticosterone and ACTH levels. Plasma corticosterone decreased during salt loading, whereas it increased during rehydration at 1 week. Basal ACTH concentration increased in 1-week-rehydrated animals, with enhanced responsiveness to the acute immobilization stress. In the hypothalamic parvocellular PVN, basal CRH mRNA levels also decreased during salt loading and increased during rehydration. Basal VP mRNA was up-regulated during both salt loading and rehydration. VP mRNA responded to additional acute stress during salt loading and rehydration, but CRH mRNA did not. These results indicate that the HPA axis activity of parvocellular neurons is still altered at 1 week of rehydration and that VP plays a dominant role in regulating ACTH release in response to acute stress. This rehydration stage may thus be a good model for analysis of post-stress sensitization of the HPA axis.     

Endomorphins and activation of the hypothalamo-pituitary-adrenal axis

Endomorphin (EM)-1 and EM-2 are opioid tetrapeptides recently located in the central nervous system and immune tissues with high selectivity and affinity for the mu-opioid receptor. Intracerebroventricular (i.c.v.) administration of morphine stimulates the hypothalamo-pituitary-adrenal (HPA) axis. The present study investigated the effect of centrally administered EM-1 and EM-2 on HPA axis activation. Rats received a single i.c.v. injection of either EM-1 (0.1, 1.0, 10 microg), EM-2 (10 microg), morphine (10 microg), or vehicle (0.9% saline). Blood samples for plasma corticosterone determinations were taken immediately prior to i.c.v. administration and at various time points up to 4 h post-injection. Trunk blood, brains and pituitaries were collected at 4 h. Intracerebroventricular morphine increased plasma corticosterone levels within 30 min, whereas EM-1 and EM-2 were without effect. In addition, pre-treatment of i.c.v. EM-1 did not block the rise in corticosterone after morphine. Corticotrophin-releasing factor (CRF) mRNA and arginine vasopressin (AVP) mRNA in the paraventricular nucleus (PVN) and POMC mRNA in the anterior pituitary were found to be unaffected by either morphine or endomorphins. Since release of other opioids are elevated in response to acute stress, we exposed rats to a range of stressors to determine whether plasma EM-1 and EM-2 can be stimulated by HPA axis activation. Plasma corticosterone, ACTH and beta-endorphin were elevated following acute restraint stress, but concentrations of plasma EM-1-immunoreactivity (ir) and EM-2-ir did not change significantly. Corticosterone, ACTH and beta-endorphin were further elevated in adjuvant-induced arthritis (AA) rats by a single injection of lipopolysaccharide (LPS), but not by restraint stress. In conclusion, neither EM-1 or EM-2 appear to influence the regulation of the HPA axis. These data suggest that endomorphins may be acting on a different subset of the mu-opioid receptor than morphine. The failure to induce changes in plasma EM-ir in response to the chronic inflammatory stress of AA, the acute immunological stress of LPS, or the psychological stress of restraint, argues against an important role for endomorphins in mediating HPA axis activity.     

Centrally administered neuropeptide S activates orexin-containing neurons in the hypothalamus and stimulates feeding in rats

Neuropeptide S (NPS) is a newly identified transmitter that modulates arousal and anxiety. To determine potential neuronal targets for NPS, we studied the pattern of neuronal activation as indicated by the expression of Fos. Centrally administered NPS increased Fos-like immunoreactivity (FLI) in the paraventricular, dorsomedial nuclei and lateral hypothalamic area (LHA) of the hypothalamus, the midline thalamic nuclei, and the amygdala, many parts of which are involved in the regulation of emotion, arousal, and feeding. In particular, we noted that Fos-immunoreactive (Fos-ir) levels were increased in orexin-expressing neurons in the LHA. We then studied whether an icv injection of NPS increased food intake. The injection of NPS (1 nmol) significantly stimulated feeding at 2 h in rats, but there was no difference in food intake at 4 h or 24 h. These results suggest that arousal and feeding induced by NPS in the central nervous system may be related to the activation of orexin-expressing neurons.     

Hypoactivity of the hypothalamo-pituitary-adrenocortical axis during recovery from chronic variable stress

Chronic stress induces both functional and structural adaptations within the hypothalamo-pituitary-adrenocortical (HPA) axis, suggestive of long-term alterations in neuroendocrine reactivity to subsequent stressors. We hypothesized that prior chronic stress would produce persistent enhancement of HPA axis reactivity to novel stressors. Adult male rats were exposed to chronic variable stress (CVS) for 1 wk and allowed to recover. Plasma ACTH and corticosterone levels were measured in control or CVS rats exposed to novel psychogenic (novel environment or restraint) or systemic (hypoxia) stressors at 16 h, 4 d, 7 d, or 30 d after CVS cessation. Plasma ACTH and corticosterone responses to psychogenic stressors were attenuated at 4 d (novel environment and restraint) and 7 d (novel environment only) recovery from CVS, whereas hormonal responses to the systemic stressor were largely unaffected by CVS. CRH mRNA expression was up-regulated in the paraventricular nucleus of the hypothalamus (PVN) at 16 h after cessation of CVS, but no other alterations in PVN CRH or arginine vasopressin mRNA expression were observed. Thus, in contrast to our hypothesis, reductions of HPA axis sensitivity to psychogenic stressors manifested at delayed recovery time points after CVS. The capacity of the HPA axis to respond to a systemic stressor appeared largely intact during recovery from CVS. These data suggest that chronic stress selectively targets brain circuits responsible for integration of psychogenic stimuli, resulting in decreased HPA axis responsiveness, possibly mediated in part by transitory alterations in PVN CRH expression.     

Hypothalamic-pituitary-adrenal axis hyporesponsiveness to restraint stress in mice deficient for large-conductance calcium- and voltage-activated potassium (BK) channels

Stress activates the hypothalamic-pituitary-adrenal (HPA) axis, releasing ACTH from the anterior pituitary gland and glucocorticoids from the adrenal cortex. Stress also activates the sympathetic nervous system, evoking adrenaline release from the adrenal medulla. Large-conductance calcium- and voltage-activated potassium (BK) channels have been implicated in regulation of cellular excitability in these systems. Here, we examine the functional role of BK channels in HPA axis regulation in vivo using female mice genetically deficient (BK(-/-)) for the pore-forming subunits of BK channels. BK(-/-) phenotype in the HPA was confirmed by immunohistochemistry, Western blot analysis, and corticotrope patch-clamp recording. Restraint stress-induced plasma concentrations of ACTH and corticosterone were significantly blunted in BK(-/-) mice compared with wild type (WT) controls. This stress hyporesponsiveness was associated with reduced activation of hypothalamic paraventricular nucleus (PVN) neurons. Basal expression of CRH, but not arginine vasopressin mRNA in the PVN was significantly lower in BK(-/-) mice compared with WT controls. Total anterior pituitary ACTH peptide content, but not proopiomelanocortin mRNA expression or corticotrope number, was significantly reduced in BK(-/-) mice compared with WT. However, anterior pituitary corticotropes from BK(-/-) mice fully supported ACTH output, releasing a significantly greater proportion of stored ACTH in response to secretagogue in vitro compared with WT. These results support an important role for BK channels in both the neural circuitry and endocrine output of the HPA axis and indicate that the stress hyporesponsiveness in BK(-/-) mice primarily results from reduced activation of hypothalamic PVN neurosecretory neurons.     

Androgenic influence on serotonergic activation of the HPA stress axis

The higher incidence of stress-mediated affective disorders in women may be a function of gonadal hormone influence on complex interactions between serotonin and neural circuits that mediate the hypothalamic-pituitary-adrenal (HPA) stress axis. The paraventricular nucleus of the hypothalamus (PVN) receives serotonergic innervation, and selective serotonin reuptake inhibitors such as citalopram activate the HPA axis independent of stress. We have previously demonstrated that the magnitude of this serotonergic activation was greater in females and was attenuated by testosterone administration; however, the potential central sites of action where androgens reduce these serotonergic effects have not been determined. Therefore, we examined a time course of corticosterone production and used central c-Fos protein levels to assay neuronal activation in stress-related brain regions in female, male, and gonadectomized male mice after an acute citalopram injection (15 mg/kg). In the hippocampus, c-Fos-immunoreactivity was greater in males than in females or gonadectomized males. This same pattern emerged in the lateral septum after vehicle and gonadectomy reversed the effect of citalopram. These regions are important for inhibitory influences on the PVN, and accordingly, hippocampal c-Fos levels were negatively correlated with corticosterone production. No sex differences in c-Fos were detected in the PVN, cingulate cortex, or paraventricular thalamus in response to vehicle or citalopram. These data support brain region-specific regulation of the HPA axis where sex differences may be mediated partly through androgen enhancement of signaling in inhibitory regions.     

Differential actions of acute and chronic citalopram on the rodent hypothalamic-pituitary-adrenal axis response to acute restraint stress

Serotonin re-uptake inhibitors (SSRIs) can affect the basal activity of the hypothalamic-pituitary-adrenal (HPA) axis in rats. A single injection of citalopram has been shown to stimulate the HPA axis while repeated administration leads to attenuation of the corticosterone response to the SSRI. The purpose of this work was to investigate the rodent HPA axis response to restraint stress, following acute and chronic treatment with the SSRI citalopram. We have demonstrated that a single injection of citalopram is able to prolong acute restraint-induced increases in plasma levels of corticosterone and adrenocorticotrophin (ACTH). This is possibly mediated by arginine vasopressin (AVP) in the parvocellular cells of the paraventricular nucleus (pPVN), as treatment with citalopram or restraint alone did not increase AVP mRNA in pPVN while the combination of treatments resulted in a significant increase in AVP mRNA in the pPVN. In contrast, the increase in corticotrophin-releasing factor (CRF) mRNA in the pPVN in response to acute restraint stress was not altered by citalopram. Oxytocin (OT) mRNA was also increased in the magnocellular PVN (mPVN) by the solo treatments of citalopram and restraint, and was not further enhanced by the dual treatment of restraint and citalopram. Chronic treatment with citalopram did not alter basal plasma levels of corticosterone or ACTH. However, the ACTH response to acute restraint was attenuated following chronic citalopram treatment. AVP mRNA in the pPVN was significantly elevated in response to chronic citalopram compared with saline controls suggesting an effect mediated through the AVP subset of pPVN neurones. The CRF mRNA response to acute restraint was not altered in rats treated chronically with citalopram. OT mRNA was not enhanced in the mPVN following chronic infusion of citalopram but was increased by acute restraint stress. We conclude from these data that both acute and chronic citalopram treatment has the potential to alter the rodent response to acute restraint stress. These effects appear to be regulated by the AVP-containing subset of CRF neurons in the pPVN and thus suggest that parvocellular AVP may have an important role in mediating the actions of SSRIs.     

The role of endogenous interleukin-1 in stress-induced adrenal activation and adrenalectomy-induced adrenocorticotropic hormone hypersecretion

To examine the role of IL-1 in the regulation of the hypothalamo-pituitary-adrenal (HPA) axis, mice with knockout of the IL-1 receptor type I (IL-1rKO) were exposed to psychological and metabolic stressors. When exposed to mild stressors (auditory stress or a low dose of 2-deoxyglucose), IL-1rKO mice displayed a significantly diminished corticosterone secretion, compared with wild-type (WT) controls. In response to more severe stressors (60-min restraint or a high dose of 2-deoxyglucose), both groups exhibited a similar increase in corticosterone secretion. To examine the role of IL-1 in HPA axis feedback regulation, serum ACTH levels were measured after adrenalectomy (ADX) in IL-1rKO mice and in mice with transgenic overexpression of IL-1 receptor antagonist within the brain (IL-1raTG). As expected, WT controls exhibited ADX-induced ACTH hypersecretion, whereas IL-1rKO and IL-1raTG mice showed no increase in ACTH levels, suggesting that brain IL-1 has a critical role in ADX-associated ACTH hypersecretion. Similarly, WT mice that were chronically exposed to IL-1ra in utero displayed a diminished ADX-induced ACTH hypersecretion, compared with vehicle-treated controls, suggesting a developmental role of IL-1 in HPA axis regulation. In conclusion, our results suggest that endogenous IL-1 plays a critical role in HPA axis activation after stress and ADX.     

The endogenous cannabinoid, anandamide, activates the hypothalamo-pituitary-adrenal axis in CB1 cannabinoid receptor knockout mice

The purpose of this study was to investigate the effects of the endogenous cannabinoid arachidonoyl-ethanolamide, anandamide (AEA), on the activity of the hypothalamo-pituitary-adrenal (HPA) axis in cannabinoid receptor (CB(1) receptor) inactivated (KO) mice. A low dose (0.01 mg/kg i.p.) of AEA significantly increased plasma corticotropin (ACTH) and corticosterone concentrations in both wild-type (+/+) and in mutant (-/-) animals. In each case, hormone levels reached their peaks at 90 min after AEA administration. In a parallel experiment, AEA administration was preceded by the injection of SR 141716A (1.0 mg/kg), a selective and potent CB(1) receptor antagonist, or of capsazepine (5.0 mg/kg), a potent vanilloid receptor of type 1 (VR1) antagonist. The latter drugs did not prevent the effects of AEA on the HPA axis. Using Fos protein immunohistochemistry, we observed that the parvocellular part of the hypothalamic paraventricular nucleus (PVN) was activated as early as 45 min after AEA injection and reached peak levels after 60 min in both +/+ and -/- mice. Furthermore, the CB(1) and VR1 receptor antagonists did not block the effects of AEA on Fos immunoreactivity. The results strongly support the view that activation of the HPA axis produced by AEA possibly occurs via a currently unknown (CB(x)) cannabinoid receptor present in PVN.     

Lack of decrease in hypothalamic and hippocampal glucocorticoid receptor mRNA during starvation

We have shown in a previous study that high corticosterone levels during repeated immobilization stress result in a reduction of glucocorticoid receptor (GR) mRNA in the hypothalamic paraventricular nucleus (PVN) and the hippocampus. The reduction of GR presumably accounts for loss of or decrease in glucocorticoid-negative feedback, and thus hyperfunction of the hypothalamic-pituitary-adrenocortical (HPA) axis persists during chronic stress. Starvation is a stress state in which the counterregulatory responses against the loss of food occur in the central nervous system. We explored the impact of starvation on the HPA axis, GR and mineralocorticoid receptor (MR) mRNAs in the hippocampus, the PVN, and the anterior pituitary (AP) of rats. Rats were starved for 4 days and sacrificed in the morning. Starved rats showed high levels of plasma corticosterone, whereas neither plasma corticotropin (ACTH), AP proopiomelanocortin (POMC) mRNA nor AP type-1 corticotropin-releasing hormone (CRH) receptor mRNA was altered in the starved rats. In the presence of high corticosterone, starvation resulted in a decrease in both CRH mRNA and type-1 CRH receptor mRNA in the PVN. Consistently, the starved rats did not show any changes in GR mRNA in the hippocampus (CA1-2, CA3, and dentate gyrus), the PVN or the AP despite the elevation of plasma corticosterone. A significant decrease in MR mRNA was seen in the dentate gyrus and the AP, but not in CA1-2, CA3 or PVN. The lack of reduction of GR may be one of the organism's counterregulatory responses during starvation, which allows an intact glucocorticoid negative feedback, thereby resulting in decreased anorectic neuropeptide levels, namely CRH, in the PVN. The results also indicate that GR mRNA in the hippocampus and other brain regions is not solely regulated by circulating glucocorticoids. The mechanism underlying the regulation of GR mRNA in the central nervous system remains to be clarified.     

Altered control of the hypothalamo-pituitary-adrenal axis in adult male rats exposed perinatally to food deprivation and/or dehydration

Dehydration, a classic homeostatic stressor in rats, leads to a series of well characterized endocrine responses including stimulation of the hypothalamo-pituitary-adrenal (HPA) axis. In this study, the hypothesis to be tested was that a 50% maternal food restriction (FR50) in late gestation and lactation may have long-term repercussions on HPA axis responsiveness to dehydration in offspring. For this purpose, we studied HPA axis activity in 4-month-old control (C) and perinatally malnourished male rats after a 72-hour water deprivation period. Furthermore, we investigated the long-lasting effects of perinatal maternal malnutrition on the basal activity of the HPA axis. Under basal conditions, rats exposed to perinatal malnutrition showed reduced body weight, enhanced mineralocorticoid receptor (MR) mRNA levels in CA2 and CA3 hippocampal areas, but decreased glucocorticoid receptor (GR) mRNA levels in CA1, CA3 and dentate gyrus (DG) areas. In contrast, the levels of corticotropin-releasing hormone (CRH) and vasopressin (VP) mRNAs in the hypothalamic paraventricular nucleus (PVN) as well as of VP mRNA in the supraoptic nucleus (SON) were unaffected by maternal undernutrition. Expression of proopiomelanocortin (POMC) in the adenohypophysis was significantly enhanced, whereas prohormone convertase-1 (PC1) was not affected. Perinatal malnutrition reduced absolute adrenal weight but did not affect circulating levels of adrenocorticotropin (ACTH), corticosterone and free corticosterone as well as corticosteroid-binding globulin (CBG) binding capacity. Seventy-two hours of dehydration induced a decrease in body weight and CRH mRNA levels in PVN of controls as well as of FR50 rats, but also led to a rise in plasma corticosterone and free corticosterone without changing CBG binding capacity. Dehydration also induced an increase in adenopituitary POMC (C) and PC1 (FR50), PVN and SON VP (C) and GR in CA1 hippocampal area (FR50) mRNA levels and plasma ACTH (C), but a decrease in MR in DG (C) and GR in CA3 and DG (C) mRNA levels. We conclude that maternal food restriction during the perinatal period affects (1) the adult basal activity of the HPA axis with mainly opposite effects on hippocampal MR and GR gene expression and an increase in adenopituitary POMC gene expression, and (2) the responsiveness to water deprivation in adults. In the latter case, the rise in plasma ACTH levels, adenopituitary POMC gene expression, hypothalamic VP gene expression, and the decrease in hippocampal MR gene expression in DG and GR gene expression in CA3 and DG observed in controls are lacking in FR50 rats. In contrast, drastic adenopituitary PC1 gene expression occurred in FR50 rats but not in control animals.