Prenatal Hyperhomocysteinemia Impairs Hypothalamic Regulation of Reproductive Cycles in Rat Progeny.

Effects of prenatal hyperhomocysteinemia on hypothalamic regulation of estrous cycles were studied in female rats. In mature rats exposed to prenatal hyperhomocysteinemia, changes in the catecholamine content in hypothalamic areas responsible for the formation of the preovulatory surge of gonadotropin-releasing hormone were revealed: the level of norepinephrine in the medial preoptic area decreased and concentration of dopamine in the median eminence with arcuate nuclei increased. Administration of melatonin attenuated the observed changes, which can be related to neuroprotective effects of this hormone determined by its antioxidant properties.

NaCl preference and water intake effects of food availability in median eminence polydipsia.

Lesions in the median eminence (ME) produce a well-known neurological model of polydipsia and polyuria in rats. The effect of food availability (ad lib/deprivation) on the polydipsic/polyuric behaviour of animals was tested. As expected, all lesioned rats developed strong polyuria and polydipsia during the first postoperative 24h. This effect was maintained during day 2 when food was available ad lib (experiment A), but both polyuria and polydipsia were abolished when animals were deprived of food during the next 24h (day 3). Animals deprived of food from the first post-operative day (experiment B) showed a significant reduction in the initial polyuria and polydipsia (day 1) on day 2, but these effects were again observed on day 3 when food was available ad lib. Finally, when food-deprived animals were able to choose between a 1.5% sodium chloride solution and water (experiment C), they preferentially chose (82% of total liquid consumed) the hypertonic saline solution (day 1); during the next 24h (day 2), when only water was available, the polyuric/polydipsic effect was abolished but returned when food became available ad lib on day 3. Hence, the polyuria/polydipsia effect produced by ME lesions appears to be consistent during the first 24h but might later be related to the availability of standard food and is completely abolished under food deprivation conditions. Preference for the hypertonic solution supports the volemic component of this syndrome and demonstrates the need for appropriate amounts of hypertonic nutrients to be consumed during the first 24h.

The role of hypothalamic mammalian target of rapamycin complex 1 signaling in diet-induced obesity.

The mammalian target of rapamycin (mTOR) kinase is a key regulator of several cellular functions, including cell growth and differentiation. Because hypothalamic mTOR complex 1 (mTORC1) signaling has been implicated as a target of leptin in the regulation of energy balance, we investigated its role in obesity-induced leptin resistance. In contrast to rats maintained on a low-fat (LF) diet for 3 weeks, rats maintained on a high-fat (HF)-diet had no anorexic response to intracerebroventricular leptin. Western blot analysis revealed that leptin was unable to modulate hypothalamic mTORC1 signaling in the HF group, whereas it significantly induced phosphorylation of both S6 kinase 1 (S6K1) and S6 ribosomal protein (S6) in the LF group. Similar to leptin, the cytokine ciliary neurotrophic factor (CNTF) induces hypophagia and increases signal transduction activator of transcription 3 phosphorylation. However, CNTF and its analog CNTF(Ax15) activate leptin-like pathways in the hypothalamus, even in leptin-resistant states, including diet-induced obesity. Intracerebroventricular CNTF(Ax15) decreased 24 h food intake and body weight in rats on HF or LF diets and increased the phosphorylation of hypothalamic S6K1 and S6 in a comparable way in both diets. Importantly, mice lacking the expression of S6K1 (S6K1(-/-)) did not respond to the anorectic action of either leptin or CNTF(Ax15), implying a crucial role for S6K1 in modulating the actions of these two cytokines. Finally, exposure to HF diet decreased mTORC1 signaling within the hypothalamus. Overall, these findings point strongly to the possibility that reduced hypothalamic mTORC1 signaling contributes to the development of hyperphagia, weight gain, and leptin resistance during diet-induced obesity.

Steroid-induced polycystic ovaries in rats: effect of electro-acupuncture on concentrations of endothelin-1 and nerve growth factor (NGF), and expression of NGF mRNA in the ovaries, the adrenal glands, and the central nervous system.

Previous studies on the effect of repeated electro-acupuncture (EA) treatments in rats with steriod-induced polycystic ovaries (PCO), EA has been shown to modulate nerve growth factor (NGF) concentration in the ovaries as well as corticotropin releasing factor (CRF) in the median eminence (ME). In the present study we tested the hypothesis that repeated EA treatments modulates sympathetic nerve activity in rats with PCO. This was done by analysing endothelin-1 (ET-1), a potent vasoconstrictor involved in ovarian functions, as well as NGF and NGF mRNA expression involved in the pathophysiological process underlying steroid-induced PCO. The main result in the present study was that concentrations of ET-1 in the ovaries were significantly lower in the PCO group receiving EA compared with the healthy control group (p < 0.05). In the hypothalamus, however, ET-1 concentrations were found to be significantly higher in the PCO group receiving EA than in the healthy control group (p < 0.05). Concentrations of ovarian NGF protein were significantly higher in the PCO control group compared with the healthy control group (p < 0.001), and these concentrations decreased significantly after repeated EA treatments compared with those in the PCO control group (p < 0.05) and were found to be the same as those in the healthy control group. In conclusion, these results indicate that EA modulates the neuroendocrinological state of the ovaries, most likely by modulating the sympathetic nerve activity in the ovaries, which may be a factor in the maintenance of steroid-induced PCO.

Increased synaptic input to gonadotropin releasing hormone cells in preoptic area grafts that support reproductive development in female hypogonadal mice.

Ultrastructural studies have established that gonadotropin releasing hormone (GnRH) neuronal cell bodies receive sparse synaptic input compared to other neuronal cell types. In the present studies, immunocytochemistry for the presynaptic marker synaptophysin, coupled with confocal microscopy, was employed to evaluate whether there was a difference in synaptic input to GnRH cells within preoptic area grafts (hypogonadal, HPG; preoptic area, POA) in hypogonadal female mice that did or did not show ovarian development. GnRH cells in HPG/POA mice with ovarian development exhibited significantly higher numbers of synaptophysin immunoreactive (syn-IR) appositions as compared with HPG/POA mice without ovarian development. This suggests that synaptic input to the grafted GnRH cells is important for the correction of reproductive functions in HPG/POA mice. Following mating, Fos immunoreactivity was present in several GnRH cells in HPG mice with successful POA grafts, indicating the establishment of neuronal projections conveying somatosensory information to the GnRH cells in these mice. The presence of a higher number of syn-IR appositions to GnRH cells in the successful grafts supports this hypothesis.

Increased activity of the hypothalamic-pituitary-adrenal axis of rats exposed to alcohol in utero: role of altered pituitary and hypothalamic function.

Prenatal exposure to ethanol (E) enhances the offspring's ACTH and corticosterone responses to stressors. Here, we determined the role of increased pituitary responsiveness and/or PVN neuronal activity in this phenomenon. Pregnant rats were exposed to E vapors during days 7-18 of gestation, and we compared the responses of their 55- to 60-day-old offspring (E rats) to those of control (C) dams. PVN mRNA levels of the immediate early genes (IEGs) c-fos and NGFI-B, which were low under basal conditions in all groups, showed a peak response 15 min after shocks and 45 min after LPS treatment. These responses were significantly enhanced in E, compared to C offspring of both genders. CRF, but not VP hnRNA levels were also significantly higher in the PVN of shocked E offspring. Resting median eminence content of CRF and VP, and pituitary responsiveness to CRF, were unchanged, while responsiveness to VP was marginally increased in females. These results indicate that prenatal alcohol selectively augments the neuronal activity of hypothalamic CRF perikarya.

Activation of the adrenocortical axis by surgical stress: involvement of central norepinephrine and interleukin-1.

In the present study, we examined the mechanisms involved in the activation of the adrenocortical axis following surgical stress. Adult male rats underwent surgical laparotomy or craniotomy under ether anesthesia while control rats were only ether-anesthetized. Four hours following laparotomy or craniotomy, serum adrenocorticotropin (ACTH) and corticosterone (CS) were significantly increased and returned to almost basal levels after 24 h. Laparotomy also caused a significant depletion of corticotropin-releasing hormone (CRH-41) in the median eminence (ME). Pretreatment with dexamethasone 50 microg/kg completely abolished the pituitary-adrenal response while pretreatment with type II corticosteroid receptor antagonist caused a significant hypersecretion of both ACTH and CS and inhibited the effect of dexamethasone. The response to laparotomy was markedly attenuated in rats injected with 6-hydroxydopamine into the paraventricular nucleus (PVN) which significantly depletes norepinephrine (NE) PVN content. Intracerebroventricular injection of interleukin-1 receptor antagonist (IL-1ra) also inhibited the pituitary-adrenal response to laparotomy. The results suggest that (1) surgical stress activates the hypothalamo-pituitary-adrenal (HPA) axis via a mechanism which involves the release of CRH from the ME and NE input to the PVN; (2) the adrenocortical response is sensitive to the negative feedback of glucocorticoids via the mediation of type II glucocorticoid receptors, and (3) central IL-1 may be a mediator in the HPA axis response to surgical stress.

Hypoxia influences somatostatin release in rats.

The impact of hypoxia on somatostatin (SS) secretion from the median eminence (ME) of the hypothalamus and the possible glucocorticosteroid involvement in modulating secretion, were investigated in adult male rats exposed to hypoxia. SS levels were measured by specific radioimmunoassay during acute and prolonged hypoxia as well as after bilateral adrenalectomy (ADX) with or without a replacement with dexamethasone (DEX). The results were as follows: (a) acute hypoxia (5 km altitude, 10.8% O(2)) for 2 and 24 h markedly increased SS content in ME, but acute severe hypoxia (7 km, 8.2% O(2) for 24 h) markedly decreased SS level in ME. (b) Chronic hypoxia (10.8% O(2)) from 5 to 25 days exposure did not significantly affect SS content of ME. (c) ADX alone increased SS content of ME and this increase was further enhanced after 2 h exposure to hypoxia. (d) The increased SS in ME of ADX rats was blocked by replacement with DEX (500 microg/rat i.p.). The data presented suggest that acute hypoxia stress may increase or decrease SS content of ME in rats, depending on the severity and duration of the hypoxia and that the stimulatory action of hypoxia on SS content of ME be may in part mediated by the increased corticosterone levels during hypoxia.

The human hypothalamo-neurohypophysial system in health and disease.

The present paper reviews the changes observed in the human supraoptic (SON) and paraventricular (PVN) nuclei, and their projections to the neurohypophysis, median eminence and to other brain areas in health and disease.

Alcohol stimulates ACTH secretion in the rat: mechanisms of action and interactions with other stimuli.

This review discusses some of the mechanisms through which alcohol (EtOH) alters the activity of the hypothalamic-pituitary-adrenal (HPA) axis. In adult rats, acute EtOH treatment increases plasma ACTH and corticosteroids levels primarily by stimulating the release of corticotropin-releasing factor (CRF) and possibly vasopressin (VP) from nerve terminals in the median eminence. Increased CRF gene transcription in the hypothalamus may also be important. The HPA axis remains activated during chronic EtOH exposure, although habituation may take place. Changes in the responsiveness of hypothalamic neurons, a phenomenon itself dependent in part on a number of intermediate secretagogues, as well as decreased pituitary responsiveness to VP, all play a role. Finally, the activity of the HPA axis is influenced by exposure to EtOH during embryonic development, with mature offspring showing hyporesponsiveness to many stimuli. These altered responses appear to be caused in part by changes in the synthesis/release CRF, possibly under the influence of nitric oxide. CRF, VP, ACTH, and corticosteroids are important regulators of the immune system, behavior, metabolic pathways, and reproductive parameters. Alcohol therefore may influence such functions through the pathological secretion of these hormones. A better understanding of the mechanisms through which the drug alters their release thus may permit the development of therapies designed to alleviate some of the consequences of alcoholism.

Prenatal alcohol exposure alters the hypothalamic-pituitary-adrenal axis response of immature offspring to interleukin-1: is nitric oxide involved?

We have previously shown that following prenatal alcohol exposure, immature offspring showed blunted ACTH released in response to the peripheral administration of interleukin-1 beta (IL-1 beta). The present studies were conducted to investigate the role of changes in corticosteroid feedback (measured by altered adrenal responses to ACTH), corticotropin-releasing factor (CRF) content of the median eminence (ME), and the influence of endogenous nitric oxide (NO). The injection of several doses of ACTH failed to indicate measurable differences between the corticosterone responses of offspring born to dams fed ad libitum [control (C)], pair-fed (PF), or fed alcohol [ethanol (EtOH) = E]. CRF content in the ME, taken as an index of the amount of releasable peptide, showed a small, but statistically significant, decrease following prenatal alcohol exposure. A comparable change, however, was also noted in PF rats. As expected, the subcutaneous injection of IL-1 beta (0.5 microgram/kg) induced smaller increases in plasma ACTH levels of E than C pups. The response of PF animals was intermediate between that of E and C rats. Finally, we observed that inhibition of NO formation by the administration of the arginine derivative L omega nitro-L-arginine-methylester significantly augmented ACTH secretion in all three experimental groups, and reversed the decreased corticotrophs' response to IL-1 beta caused by prenatal alcohol. Taken together, our results suggest that the ability of prenatal alcohol exposure to alter ACTH released by immature pups in response to blood-borne IL-1 beta is probably not mediated through changes in adrenal responsiveness.(ABSTRACT TRUNCATED AT 250 WORDS)

Effect of median eminence lesion on the hypertensive response due to acute aortic coarctation.

The present study was designed to investigate the effect of a lack of vasopressin resulting from electrolytic lesion of the median eminence of the hypothalamus on the acute 45-min aortic coarctation hypertension elicited in conscious rats by means of a pneumatic cuff placed around the aorta above the renal arteries. Forty-eight hours after lesion, aortic constriction elicited a prompt (5-min) rise in mean carotid pressure from 115 +/- 2 to 149 +/- 2 mmHg, followed by a gradual decline to 129 +/- 2 mmHg. In contrast, sham-lesioned rats exhibited a prompt hypertensive response from 118 +/- 2 to 157 +/- 2 mmHg that leveled off throughout the experiment. Lesioned rats treated with saralasin presented a blunted hypertensive response (within 125 +/- 2 to 130 +/- 2 mmHg), whereas sham-lesioned rats showed only a delay in the onset of hypertension. The hypertensive response of lesioned rats was unaffected by the vasopressin antagonist [d(CH2)5Tyr(Me)]AVP, whereas sham-lesioned rats submitted to this treatment presented a prompt rise in pressure followed by a gradual decline at the end of the experiment. Lesioned and sham-lesioned rats treated with saralasin plus vasopressin antagonist showed a blunted hypertensive response throughout the experiment. These data demonstrate that the integrity of the median eminence plays a pivotal role in the maintenance (30-45 min) of acute aortic coarctation hypertension, presumably involving the release of vasopressin from the neurohypophysis, whereas angiotensin II mainly accounts for the prompt (5-15 min) rise in pressure.

Effect of postnatal exposure of female rats to an alcohol diet: influence of age and circulating sex steroids.

We have previously reported that when compared with animals fed ad libitum, adult ovariectomized (OVX) female rats fed an alcohol diet, but not its isocaloric equivalent control, showed a blunted ACTH response to the intravenous injection of interleukin-1 beta (IL-1 beta). The present work was undertaken to determine whether this finding could be extended to intact rats, and whether the stage of sexual maturation and/or circulating sex steroids of ovarian origin modulated the inhibitory influence of alcohol. Intact female rats were exposed to alcohol or pair-fed between postnatal days 25-35 (group I), 35-45 (group II), or 45-55 (group III). Animals of comparable age and fed ad libitum served as controls. All alcohol-exposed animals had similar blood alcohol levels measured during the eighth night of treatment. Group I lost the most weight following exposure to alcohol, but did not show measurable changes in ACTH released in response to 20 or 100 ng IL-1 beta/kg. Both alcohol and pair-feeding caused a modest decrease in IL-1-stimulated ACTH in rats of group II, but only alcohol significantly blunted corticotrophs' activity in group III. Group III, when fed alcohol, also showed lower CRF content in the median eminence compared with absolute controls or the isocaloric diet. No measurable changes, however, were observed in steady-state CRF mRNA levels in the hypothalamus of animals fed any of the diets. When intact and OVX rats were compared at 55 days of age, alcohol feeding caused a decrease in IL-1-induced ACTH secretion which was slightly, though not significantly, larger in intact animals.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of interleukin-1 on the stress-responsive and -nonresponsive subtypes of corticotropin-releasing hormone neurosecretory axons.

Administration of interleukin-1 (IL-1) induces increases in plasma ACTH and glucocorticoids. Numerous experiments have implicated the hypothalamic CRH neurosecretory system in these responses, but have failed to provide evidence for involvement of the ACTH secretagogue vasopressin (VP). The rat CRH neurosecretory system contains two types of cells: VP expressing and VP deficient. Hence, the above findings suggested that IL-1 may selectively activate the VP-deficient subtype of CRH neurosecretory cells. In this study we employed postembedding electron microscopic immunocytochemistry to directly assay IL-1-induced depletion of secretory vesicles from identified VP-expressing and VP-deficient CRH neurosecretory axons. IL-1-induced depletion of secretory vesicles from these axons was correlated with increases in plasma ACTH and decreases in plasma PRL. No dose of IL-1 was found that could selectively activate one subtype of CRH neurosecretory axons; at doses of 0.67 microgram/100 g and above for both IL-1 alpha and IL-1 beta, equal depletion of vesicles from the two subtypes was observed. Similar results were previously found after the injection of bacterial lipopolysaccharide, which induces the release of IL-1 from macrophages. The findings unequivocally establish for the first time that IL-1 activates hypothalamic CRH neurosecretory cells in the absence of surgical stress, anesthesia, disruption of the infundibular area, or administration of toxic drugs. In addition, these data clearly demonstrate that IL-1 induces the release of VP from neurosecretory axons in the portal capillary zone of the external zone of the median eminence. Previous studies have shown that the VP-deficient subtype of CRH neurosecretory axons is not strongly activated by several types of stress; therefore, activation of the system by inflammatory mediators involves mechanisms different from those mediating the stress response.

Effect of lesioning of medullary catecholamine neurons or the median eminence on the development of cerebral vasospasm in the squirrel monkey.

Injections of blood into the interpeduncular fossa and cisterna magna in the squirrel monkey produce an angiographically demonstrable, biphasic cerebral vasospasm with a maximal acute spasm at ten minutes and a maximal late spasm at six days after the subarachnoid haemorrhage (SAH). Selective lesioning of the A2 nucleus in the medulla oblongata or the median eminence in the hypothalamus prior to the SAH prevents the development of both the acute and late cerebral vasospasm. The present data indicate that the A2 nucleus and the median eminence participate in the development of vasospasm in the squirrel monkey.

A study of the response to several dipsogenic treatments in rats with mammillary polydipsia and with centrally induced diabetes insipidus.

Several brain areas have been implicated in the regulation of water intake and body fluid homeostasis. Electrolytic lesions located in the mammillary area have proved to induce a strong polydipsia. The cause of this overconsumption is not understood, although other studies have indicated a possible relationship with the mechanisms involved in sodium control. In this paper, we consider whether mammillary polydipsia is related to diabetes insipidus. In this regard, animals with mammillary lesions were submitted to several dipsogenic treatments, both osmotic and volemic. These subjects showed a differential response to hypertonic NaCl compared with controls. No effect could be seen in relation to the other treatments employed, that is, sucrose and polyethylene glycol. On the other hand, this differential response to NaCl was not observed in those animals with diabetes insipidus centrally induced by means of lesions in the median eminence. Thus, mammillary polydipsia and diabetes insipidus-related water intake seem to be different phenomena. The possible relationship between mammillary polydipsia and sodium control is discussed.

The regional hypothalamic distribution of type II 5'-monodeiodinase in euthyroid and hypothyroid rats.

The brain topographical distribution of type II 5'-monodeiodinase (5'D-II), which converts thyroxine (T4) to triiodothyronine (T3), was studied in euthyroid and hypothyroid rats. Low levels of 5'D-II activity were detected in the median eminence, but not in any other brain regions of euthyroid rats. The arcuate nucleus and median eminence were also the sites of highest 5'D-II activity in brains of hypothyroid rats. Under these conditions, the paraventricular nucleus contained almost no detectable 5'D-II, while intermediate enzyme activity was present in other medial basal hypothalamic sites.