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Biomedical subjects

A Sahu

Publications and source records attributed to A Sahu.

At least 91 records · Page 5Linked to original sources
PubMed1992

Neuropeptide Y release is elevated from the microdissected paraventricular nucleus of food-deprived rats: an in vitro study.

Intracerebroventricular injection of neuropeptide Y (NPY) stimulates a robust dose-related feeding response in the rat. Experimental evidence attests to the view that the release of NPY in the paraventricular nucleus (PVN), a site richly innervated by NPY immunopositive fibers, is responsible for stimulation of feeding behavior. However, there is little information on the neuroendocrine factors involved in regulation of NPY release, in part due to the unavailability of reliable techniques to monitor PVN NPY release. In this study, we have validated an in vitro technique to assess NPY release from the PVN and other neighboring hypothalamic sites of the rat brain. In the first experiment, freshly dissected brains from male rats were processed for 300-microns thick sections with a vibratome. The PVNs were microdissected from the brain sections under a stereomicroscope and incubated in 250 microliters Krebs Ringer bicarbonate buffer at 37 C for basal and KCl-induced NPY release. The results showed that basal NPY efflux from the excised PVN was detectable and increased in relation to the number of PVNs in the incubation chambers. Addition of KCl at the end of the 60-min basal incubation period increased NPY release further, the increments were again closely related to the number of PVN punches in the incubation chambers. In the second experiment, the assumption that in vitro basal and KCl-evoked NPY release from the PVN reflected the in vivo pattern of PVN NPY secretion was validated. The effects of 4-day food deprivation (FD), an experimental paradigm known to augment in vivo PVN NPY secretion, on the in vitro NPY release from PVN and ventromedial nucleus were evaluated. The results showed that both basal and KCl-evoked NPY release was significantly higher from the PVN of food-deprived than control rats on ad libitum rat chow. This FD-induced incremental NPY response was site-specific because the basal and KCl-evoked NPY effluxes from the ventromedial nucleus of FD and control rats were similar. Thus, in agreement with previous in vivo findings, NPY release in vitro is also augmented selectively from the PVN in response to fasting. Cumulatively, these results demonstrate that NPY release in vitro from hypothalamic sites microdissected from fresh brains can be assessed in a reliable fashion and are in accord with the proposal that enhanced NPY action within the PVN is responsible for increased drive for food.

Animals↗
PubMed1992

Diverse effects of tachykinins on luteinizing hormone release in male rats: mechanism of action.

The tachykinins are a group of structurally related peptides found in the rat hypothalamus and anterior pituitary. We have evaluated the effects of four tachykinins on LH release in male rats. In intact male rats, intracerebroventricular (icv) injection of neurokinin A (NKA), neuropeptide K (NPK), and neuropeptide-gamma (NP gamma) elicited dose-related, transient increases in plasma LH. Substance P (SP) was ineffective under these conditions. A further examination showed that in vitro incubation with either NPK or NP gamma of hemipituitaries from intact but not castrated male rats promoted release of LH into the medium, thereby revealing that the excitatory effects of tachykinins in intact male rats may, in part, be a result of stimulation of LH release directly from the anterior pituitary. On the other hand, the effects of these four tachykinins on LH release were different in castrated rats. Intracerebroventricular injection of NPK, NKA, and NP gamma as well as SP, which was ineffective in intact male rats, evoked a long-lasting suppression of LH release. Comparatively, NPK was the most effective tachykinin in eliciting LH responses in both of these tests involving different endocrine environments. We next evaluated the possibility that the inhibitory effects of tachykinins (NPK) may be mediated by activation of inhibitory endogenous opioid peptides. The results showed that iv infusion of the opiate receptor antagonist naloxone, to block the possible inhibitory effects of endogenous opioid peptides, only partially counteracted the suppressive effects of icv NPK on plasma LH levels. Thus, in addition to revealing the diverse effects of structurally related tachykinins on LH release, the results of these investigations showed specifically that the NK-2 receptor agonists NPK, NP gamma, and NKA stimulated LH release in intact rats, in part, by a direct action at the level of the pituitary, whereas the NK-1 receptor agonist SP was inactive under these conditions. These findings imply a paracrine/autocrine mode of excitatory action on LH release involving pituitary NK-2 receptor subtypes. On the other hand, in castrated rats, all four tachykinins readily suppressed LH release by a central action involving, in part, an activation of hypothalamic opioid systems.

Animals↗
PubMed1992

Neuropeptide Y release from the paraventricular nucleus increases in association with hyperphagia in streptozotocin-induced diabetic rats.

We tested the hypothesis that the hyperphagia observed in streptozotocin (STZ)-induced diabetic rats is due to increased release of neuropeptide Y (NPY) in the paraventricular nucleus (PVN) of the hypothalamus. In the first experiment, male rats were injected with STZ or vehicle (control) via the tail vein and 18-20 days later, NPY levels in seven hypothalamic sites and release in vitro from selected hypothalamic sites were evaluated. The results showed that in association with STZ-produced marked hyperglycemia and hyperphagia, NPY concentrations were increased in four hypothalamic sites, including the PVN. Evaluation of NPY release in vitro showed that both basal and KCl-induced release was significantly higher from the micro-dissected PVN of STZ-treated than control rats. A similar augmentation in the NPY efflux in vitro was detected from the median eminence arcuate nucleus, but not from the neighboring ventromedial nucleus of STZ-treated rats. In the second experiment, rats were treated with STZ or vehicle and received permanent push-pull cannula (PPC) in the PVN for evaluation of NPY release in vivo 18-21 days after STZ treatment. The results showed that mean NPY levels in the perfusates collected from the PVN of diabetic rats were significantly higher as compared to control rats. Since NPY is the most potent naturally occurring orexigenic signal and the PVN is an important initial site of NPY action in the stimulatory pathway regulating feeding, our findings of augmented PVN NPY release in vivo and in vitro are in accord with the hypothesis that increased NPY secretion in the PVN may be responsible for hyperphagia in diabetic rats.

Animals↗
PubMed1992

Delayed clearance of circulating immune complexes in mice following administration of antileprosy drugs.

In this report we describe an animal experiment which showed delayed clearance of preformed 125I-HSA-anti-HSA immune complexes (with five times excess HSA) from the circulation of mice treated with antileprosy drugs (dapsone, clofazimine, and rifampin--multidrug therapy for 7 days) in comparison with normal (untreated) mice. The results also showed delayed retention of the preformed immune complexes in the spleen and kidneys of the antileprosy-drug-treated animals. The exact mechanism of the delayed handling of preformed immune complexes in mice fed antileprosy drugs could not be ascertained. However, in light of the anticomplementary effects of clofazimine and dapsone, as reported earlier, and in light of the large accumulation of clofazimine and rifampin in macrophages, it has been postulated that in the drug-fed animals either the immune complexes could not be phagocytosed by macrophages, through the avenue of their C3b receptors, or the immune complexes could not be downgraded easily within the macrophages overloaded with clofazimine and rifampin. These results might have clinical significance and might throw some light on the prolonged persistence of circulating immune complexes in the vascular bed of lepromatous patients even after clinical remission of erythema nodosum leprosum.

Animals↗
PubMed1991

Neuropeptide Y secretion increases in the paraventricular nucleus in association with increased appetite for food.

Feeding in mammals is a periodic behavior; however, knowledge of how the brain signals an intermittent eating pattern is scanty. Recent indirect evidence indicates that one of the signals encoded in the structure of neuropeptide Y (NPY) is to stimulate robust feeding. Therefore, two series of experiments were undertaken to characterize NPY secretion within the paraventricular nucleus (PVN) in association with eating behavior in the rat. Dynamic changes in NPY concentration in several hypothalamic sites and release in the PVN were assessed before and during the course of food consumption in rats trained to eat daily only for 4 h. Only in the PVN were NPY concentrations elevated before the introduction of food and, thereafter, levels decreased significantly during the course of eating. A similar temporal pattern in NPY release into the PVN interstitium was evident in samples collected by push-pull cannula perfusion in unrestrained rats. In addition, in food-deprived rats displaying a robust drive for feeding, NPY release in the PVN was also markedly enhanced in the shape of high-amplitude secretory episodes as compared to a lower release rate in rats receiving food ad libitum. The higher rate of NPY release in fasted rats returned to the control range after 24 h of ad libitum food supply. These findings of intense and dynamic NPY neurosecretory activity within a discrete hypothalamic site in association with an increased drive for food consumption demonstrate that NPY release in the PVN is an important orexigenic signal for periodic eating behavior. These results have important global implications for elucidating the underlying causes of the pathophysiology of eating disorders--anorexia nervosa, bulimia, and obesity--as well as constituting a specific contextual model for the formulation and testing of suitable NPY receptor agonists and antagonists for therapeutic intervention.

Animals↗
PubMed1991

Effect of anti-leprosy drugs on superoxide anion production by rat peritoneal macrophage with special reference to light exposed clofazimine.

The present study describes the in vitro effect of anti-leprosy drugs on superoxide anion (O2-) production by rat resident peritoneal macrophages. Of the three drugs tested i.e. clofazimine, rifampicin and dapsone, the first was most effective in increasing O2- production in a dose dependent manner, while rifampicin had some stimulatory effect and dapsone exhibited minimal action. Furthermore, when clofazimine and dapsone were added together it was observed that the increase of O2- production by macrophages due to clofazimine was not significantly altered by the addition of dapsone. Moreover, it was found that killed Mycobacterium leprae could induce a lesser amount of O2- production in comparison to that of Staphylococcus aureus and the enhancement of O2- release due to clofazimine was stimulus dependent. This increase of O2- release after addition of clofazimine was inhibited by the addition of p-bromophenacyl bromide. Another interesting finding was that the enhancement of O2- production by clofazimine gradually decreased as clofazimine was exposed to light for days. On further investigation it was found that ultraviolet, NMR, infrared and mass spectra of the light unexposed and exposed drug were similar, but the diffusion current of the polarogram of light exposed drug was remarkably more than that observed in light unexposed drug, indicating, thereby, a possible increase in the electron accepting capacity of the light reacted molecule. As far as we know this is the first report describing the effect of light exposed clofazimine on the respiratory burst activity of macrophages.

Animals↗
PubMed1991

Effects of various tachykinins on pituitary LH secretion, feeding, and sexual behavior in the rat.

Our investigations of the four tachykinines tested have shown that NPK characteristically evoked a spectrum of biological effects in male and female rats. NPK suppressed pituitary LH release by inhibiting the release of hypothalamic LHRH, presumably by activation of NK-2 tachykinin receptor subtypes. However, NPK may also act at the level of gonadotrophs to stimulate LH release in male rats. Central injection of NPK rapidly disrupted copulatory behavior in sexually active male rats. NPK also suppressed feeding, but, in this case, peripheral injections were more effective than central injections. Taken together, these observations strongly imply that NPK may be an inhibitory messenger molecule in the hypothalamic control of reproduction, sexual, and feeding behaviors.

Animals↗
PubMed1991

Sexual function and neuropeptide Y levels in selected brain regions in male spontaneously hypertensive rats.

Sexual function was examined in spontaneously hypertensive rats (SHR) from 8 to 20 wk of age and compared with normotensive Wistar-Kyoto (WKY) and Long-Evans rats (LE). Blood pressures (evaluated indirectly) were elevated in SHR (185 +/- 2 and 195 +/- 3 mmHg at 16 and 19 wk of age, respectively) relative to WKY and LE (135-144 mmHg). SHR exhibited good copulatory behavior but displayed fewer erections (less than 20% of the number displayed by WKY or LE) in ex copula tests. At the conclusion of the study (20 wk of age), body weights were lowest in SHR, intermediate in WKY, and greatest in LE. Relative weights of testes were greater in SHR, whereas relative weights of accessory organs, pituitary and adrenal glands, and kidneys were equivalent across strains, as were circulating levels of aldosterone. Circulating levels of testosterone were higher in SHR and WKY than in LE. Neuropeptide Y (NPY) levels in the median preoptic and arcuate nuclei were significantly greater in SHR than in WKY or LE, whereas NPY levels in the medial preoptic area and the suprachiasmatic, hypothalamic dorsomedial, and hypothalamic paraventricular nuclei were equivalent in SHR and WKY, with both greater than LE. No strain differences were evident in the medial nucleus of the amygdala, the bed nucleus of the stria terminalis, the median eminence, the anterior hypothalamic nucleus, or the hypothalamic dorsomedial nucleus.

Aldosterone↗
PubMed1990

Aging in male rats modifies castration and testosterone-induced neuropeptide Y response in various microdissected brain nuclei.

Neuropeptide Y (NPY) is localized in several hypothalamic sites which are implicated in the control of hypothalamic luteinizing hormone-releasing hormone (LHRH) and pituitary luteinizing hormone (LH) release. We have observed previously that in young rats castration decreases and testosterone (T) replacement restores NPY levels in selected hypothalamic sites. However, in aged male rats, NPY levels were decreased in all hypothalamic sites studied. Since testicular function is diminished in aged rats, we reasoned that decreased T feedback may be responsible for the reduction of NPY in the hypothalamus. Therefore, we compared the effects of castration and T-replacement on NPY levels in microdissected hypothalamic sites of 2.5-month- (young) and 15-month-old (aged) male rats. Serum LH and T levels were markedly reduced in aged as compared to those observed in young rats. In association with the decreased hormone levels, NPY levels were significantly reduced in each of the 7 hypothalamic sites of aged as compared to young rats. Further, in young rats, castration reduced and T-replacement prevented the castration-induced depletion in only 3 sites, viz. the ventromedial hypothalamic nucleus (VMN), arcuate nucleus (ARC) and median eminence (ME). In contrast, castration in aged rats reduced NPY levels not only in the VMN as in young rats, but also in the medial preoptic area (MPOA) and dorsomedial nucleus (DMN). However, the marked reduction in the ME and ARC NPY levels of young rats following castration was not observed in the ME and ARC of aged rats.(ABSTRACT TRUNCATED AT 250 WORDS)

Aging↗
PubMed1990

A decrease in opioid tone amplifies the luteinizing hormone surge in estrogen-treated ovariectomized rats: comparisons with progesterone effects.

It is well known that the estrogen-induced LH surge in ovariectomized (ovx) rats is invariably far less in magnitude than the preovulatory LH surge or that induced by progesterone (P) in estrogen-primed ovx rats. Recent studies show that a decrease in hypothalamic inhibitory opioid tone by the neural clock (NC) is responsible for the induction of the preovulatory LH surge on proestrus. Therefore, we hypothesized that the diminished LH response in estrogen-treated ovx rats may be due to an inadequate reduction in opioid tone. To test this hypothesis the effects of transiently decreasing the opioid tone with an opiate receptor antagonist, naloxone (NAL), on LH secretion in estrogen-primed, short term (5 days) and long term (4 weeks) ovx rats were examined. NAL (2 mg/h) was infused iv from 1100-1400 h on day 2 in rats receiving either sc implants (two, 15 mm each) filled with 17 beta-estradiol (300 micrograms/ml in oil) or sc estradiol benzoate (EB; 10 micrograms/rat) injections at 1000 h on day 0. For comparison of NAL- and P-induced LH responses, EB-primed short and long term ovx rats received P injection (2 mg/rat, sc) instead of NAL infusion at 1100 h. Estrogen treatment alone induced a spontaneous rise in plasma LH on the afternoon of day 2, with peak LH levels ranging between 1.5-2.4 ng/ml. NAL infusion markedly enhanced the LH surge in both groups of ovx rats. In short term ovx rats NAL-induced peak LH levels (5-6 ng/ml) were less than those observed in rats receiving supplemental P treatment or that observed previously on proestrus (10-15 ng/ml). However, in long term EB-primed ovx rats, NAL infusion evoked LH surges equivalent to those observed after P injection. In addition, analysis of the episodic LH secretion pattern showed that NAL infusion accelerated the frequency and amplitude of LH discharge and significantly changed the contour of LH episodes. These results show that a transient decrease in inhibitory opioid tone before a spontaneous LH rise in estrogen-treated ovx rats can accelerate episodic LH secretion to culminate in LH surges that resemble those induced by P and the preovulatory LH surge. Therefore, these observations are in accord with the view that the NC-induced curtailment in the inhibitory opioid tone may be inadequate in estrogen-treated rats; NAL infusion and P treatment intensify decrements in inhibitory opioid tone to reinstate the preovulatory-type LH surge in these rats.

Animals↗
PubMed1990

Neuropeptide-Y concentration in microdissected hypothalamic regions and in vitro release from the medial basal hypothalamus-preoptic area of streptozotocin-diabetic rats with and without insulin substitution therapy.

Experimental diabetes adversely affects hypothalamic control of gonadotropin secretion and sex behavior and induces hyperphagia accompanied by severe body weight loss. Neuropeptide-Y (NPY) stimulates pituitary gonadotropin release, inhibits sexual behavior, and stimulates robust feeding in rats by acting at different sites in the hypothalamus. Therefore, we tested the hypothesis that altered hypothalamic NPY neurosecretion may mediate the constellation of effects observed in streptozotocin-induced diabetic (STZ-D) rats. Adult male rats were made diabetic by a single injection of STZ (50 mg/kg). Five months later, in vitro NPY release from the hypothalamic fragment encompassing the medial basal hypothalamus and preoptic area and NPY concentrations in seven hypothalamic sites were assessed. Basal NPY release was not significantly changed after STZ treatment. However, in response to a 30-min pulse of KCl (45 mM), NPY release from the medial basal hypothalamus-preoptic area of STZ-D rats was significantly increased compared to that in age-matched controls. In the STZ-D rats, NPY concentrations in six of the seven microdissected nuclei, including those mediating control of pituitary gonadotropin, sexual, and feeding behaviors, were increased compared to control values. In an additional study similar increments in NPY concentrations in the hypothalamic sites were observed 6 months after STZ treatment. The effects of insulin on NPY levels in microdissected hypothalamic sites in STZ-treated and BB diabetic rats was next assessed. One group of rats was treated with STZ, and the other group of rats was additionally treated with insulin (6 U/kg.day) for 3 months after development of diabetes with STZ. Again, STZ treatment alone, even for 3 months, increased NPY levels in all seven nuclei, including the suprachiasmatic nuclei. Insulin therapy completely prevented the STZ-induced increments in NPY levels in all hypothalamic sites, and the blood glucose level was 233 +/- 22 mg/dl in insulin-treated STZ-D rats and 496 +/- 6 mg/dl in untreated STZ-D rats. Similarly, NPY concentrations in five of the seven nuclei were unchanged in spontaneously diabetic BB rats (blood glucose, 435 +/- 67 mg/dl) maintained on insulin (5-8 U/kg.day). These results demonstrate that STZ-D rats have a widespread increase in NPY levels in hypothalamic sites, and there is an increase in the evoked release of NPY from the hypothalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

An opioid-neuropeptide-Y transmission line to luteinizing hormone (LH)-releasing hormone neurons: a role in the induction of LH surge.

We tested the hypothesis that a decrease in hypothalamic inhibitory opioid tone produced by naloxone (NAL) will activate neuropeptide-Y (NPY) neurosecretion in 17 beta-estradiol (E2)-primed ovariectomized (ovx) rats. NPY neurosecretion was assessed in two ways. First, we studied the effects of iv saline (controls) or NAL infusion (2 mg/h) between 1100-1400 h on NPY concentrations in seven microdissected sites in the medial basal hypothalamus (MBH) and preoptic area in association with the increase in the rate of LH secretion, and then we examined the effects of NAL on the in vitro release of NPY and LHRH from the MBH of E2-primed ovx rats. We observed that in control rats, NPY concentrations in selected hypothalmic sites (median eminence, medial preoptic area, and arcuate nucleus) increased either just before LH rise at 1400 h or in association with the moderate LH surge in the afternoon. NAL infusion advanced the onset and amplified the magnitude of LH surge in the afternoon. In association with this augmentation of LH response, NAL infusion significantly increased NPY concentrations selectively in the median eminence, medial preoptic area, and arcuate nucleus. During NAL infusion at 1300 h and at the end of infusion at 1400 h, NPY concentrations in these sites increased compared to preinfusion levels at 1100 h and corresponding control levels at 1300 h. During the post-NAL infusion period until 1800 h, NPY levels remained elevated in these sites, but were not significantly different from those in control rats, which also displayed increments at this time. Further, NAL increased the in vitro efflux of both NPY and LHRH from the MBH; the increased release of two neuropeptides was dose related between 0.01-0.5 mg/ml, with the maximal increase occurring at 1.0 mg/ml NAL. Cumulatively, these studies show that 1) in association with the spontaneous LH surge in E2-primed rats, NPY concentration increased only in sites confined to the preoptic-tuberal pathway, which previously has been shown to mediate the induction of the LH surge; and 2) a decrease in the inhibitory opioid tone imposed by NAL readily augmented the hypothalamic NPY neurosecretion concomitant with an increase in duration and magnitude of the LH surge. These findings are in accord with the thesis that a decrease in the inhibitory opioid tone by the neural clock, postulated to occur before the LH surge, initiates a chain of neurosecretory events that may include a site-specific activation of NPYergic neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Interleukin-1 inhibits the ovarian steroid-induced luteinizing hormone surge and release of hypothalamic luteinizing hormone-releasing hormone in rats.

Interleukin-1 (IL-1), a polypeptide cytokine secreted by activated macrophages, has been postulated as a chemical messenger between the immune and endocrine systems. IL-1-immunopositive neurons and fibers have been visualized in the human and rat hypothalamus, and IL-1 receptors are present in the rat brain. We have examined the effects of human recombinant IL-1 (alpha- and beta-subtypes) on LH release in vivo and hypothalamic LHRH release in vitro. Ovariectomized rats were primed with estradiol benzoate, and progesterone was injected 48 h later to elicit a LH surge in the afternoon. IL-1 alpha and IL-1 beta were injected either intracerebroventricularly (icv) via a preimplanted cannula in the third ventricle of the brain or iv. Systemic injection of IL-1 alpha or IL-1 beta (58.8 pmol at 1300 and 1500 h) failed to influence the afternoon LH surge seen in saline-injected control rats. However, IL-1 beta (1.76 pmol) administered icv at 1300 and 1500 h or a single icv injection at 1300 h blocked the progesterone-induced LH surge. Similar icv injections of IL-1 alpha also significantly suppressed the afternoon LH surge compared to that in saline-injected control rats. However, IL-1 alpha was relatively less effective than the beta-subtype, since the LH surge was detected in some rats. To ascertain whether suppression of the LH surge was due to inhibition of LHRH release, the medial basal hypothalamus-preoptic area of estradiol benzoate-progesterone-treated ovariectomized rats was incubated with and without IL-1. Both IL-1 alpha and IL-1 beta, at concentrations of 0.1 nM and higher, significantly suppressed LHRH release in vitro from the medial basal hypothalamus-preoptic area. In contrast, IL-1 (10 nM) was completely ineffective in suppressing LHRH release from the microdissected median eminence. These results demonstrated an overall inhibitory effect of icv IL-1 on the LHRH-LH axis and suggest that suppression of the steroid-induced LH surge by IL-1 may primarily be due to inhibition of LHRH release at hypothalamic sites located within the blood-brain barrier.

Animals↗
PubMed1990

Functional heterogeneity in neuropeptide-Y-producing cells in the rat brain as revealed by testosterone action.

Despite the widespread distribution of neuropeptide-Y (NPY) in various hypothalamic sites, castration reduced and testosterone (T) replacement restored NPY levels selectively in the median eminence (ME), arcuate nucleus (ARC), and ventromedial nucleus (VMN). Since androgen-concentrating cells and NPY-producing cells display overlapping distribution in the ARC and brain stem (BS), we assessed the participation of BS NPY cells in the steroid-dependent site-specific effects on NPY levels. The BS projections to the hypothalamus were severed by bilateral neural transection (BNT) with a knife lowered on either side of the sagittal sinus to the depth of the dorsal tegmentum in the mesencephalon in intact, castrated, or castrated rats that additionally received sc T implants to maintain physiological T levels. Two weeks later, NPY concentrations in microdissected hypothalamic sites and serum LH and T levels were quantitated by RIA. Castration decreased and T replacement increased NPY concentrations in only three sites, such as the VMN, ARC, and ME. In response to BNT in gonadally intact rats, a different site-specific response of NPY levels was observed; NPY levels decreased in the ME, as seen after castration, and, additionally, decreased in the medial preoptic area, paraventricular nucleus, and dorsomedial nucleus, suggesting that BS NPY neurons innervate these four sites. When castration and BNT were performed simultaneously, a combined regional response was evident. NPY levels decreased in six sites, including two sites (ARC and VMN) that normally respond to castration alone, three sites (medial preoptic area, paraventricular nucleus, and dorsomedial nucleus) that normally respond to BNT alone, and the ME, the only site that showed reduction of NPY levels of similar magnitude after either castration or BNT, but the response of combined surgery was not additive. This observation suggested that gonadal steroids act outside the hypothalamus to raise ME NPY levels, and therefore, BNT in intact rats impaired the effectiveness of steroids. To test this hypothesis, the effects of physiological T replacement in the castrate plus BNT group were studied. We observed that whereas T replacement readily raised NPY levels in the VMN and ARC, it was completely ineffective in the third T-dependent site, the ME. Collectively, these findings revealed a functional heterogeneity among NPY-producing cells in response to T. Apparently, there are two distinct neural sites in the rat brain where T acts to exert a site-specific stimulatory effect on NPY in the hypothalamus.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1990

Endogenous opioid peptides mediate the interleukin-1-induced inhibition of the release of luteinizing hormone (LH)-releasing hormone and LH.

We have reported recently that central administration of both the alpha- and beta-subtypes of the cytokine interleukin-1 (IL-1) inhibited the estrogen-progesterone-induced LH surge in ovariectomized (ovx) rats. This inhibition was probably due to a central effect, since IL-1 alpha and IL-1 beta also suppressed the in vitro LHRH output from the hypothalami of steroid-primed ovx rats. Whether IL-1 inhibits LHRH release by a direct action or via some other neuronal system is not known. Since IL-1 reportedly stimulates the release of POMC peptides, which are known to be inhibitory to the LHRH-LH axis, we have tested the hypothesis that the inhibitory influence of IL-1 may be mediated via activation of hypothalamic opioid peptides. Ovx rats, preimplanted with cannulae in the third ventricle of the brain, were injected with 30 micrograms estradiol benzoate, followed by 2 mg progesterone 48 h later. Three hours after P injection, IL-1 alpha, IL-1 beta, or saline (SAL) was injected intracerebroventricularly (30 ng/3 microliters) at 1300 h, followed immediately by iv infusion of SAL or the opiate antagonist naloxone hydrochloride (NAL; 2 mg/0.6 ml.h) for 2 h. Plasma LH levels were measured in blood samples withdrawn hourly until 1800 h. Both IL-1 alpha and IL-1 beta blocked the afternoon LH surge. NAL infusion into control SAL-injected rats did not alter the LH surge; however, it reversed the IL-1 alpha- and IL-1 beta-induced suppression of the LH surge. To determine whether this reversal of IL-1 suppression of the LH surge was due to NAL action at the hypothalamic level, the preoptic area-medial basal hypothalamus of similarly primed ovx rats was obtained at 1300 h and incubated in vitro in the presence of 10 nM IL-1 alpha or IL-1 beta with or without 100 micrograms/ml NAL. Both subtypes of IL-1 suppressed LHRH output significantly. NAL alone did not affect LHRH release, but it completely reversed the inhibitory effects of the cytokine on LHRH release. These results suggest that IL-1 alpha and IL-1 beta inhibit LHRH-LH release by stimulating the activity of hypothalamic endogenous opioid peptide systems.

Animals↗
PubMed1990

Localization of neuropeptide-Y immunoreactivity in estradiol-concentrating cells in the hypothalamus.

Considerable evidence shows that gonadal steroids exert a facilitatory influence on levels and release of neuropeptide-Y (NPY) from the hypothalamus. However, it is not known whether gonadal steroids act directly on NPY-producing cells in the arcuate nucleus (ARC) of the hypothalamus to produce these facilitatory effects on NPY or whether they act on other cells that have a modulatory influence via synapses on ARC NPY cells. We applied the combined method of steroid autoradiography and immunocytochemistry to assess the localization of [3H]estradiol in relation to NPY-producing cells in the hypothalamus. Rats (n = 6) were bilaterally ovariectomized and injected intracerebroventricularly with colchicine. Twenty-four hours later each rat received an iv injection of 17 beta-[2,4,6,7,16,17(-3)H]estradiol (SA, 166 Ci/mmol) at a dose of 5.0 micrograms/kg BW. One hour after the injection of [3H]estradiol, the rats were perfused with 4% paraformaldehyde; brains were removed, frozen in isopentane precooled in liquid nitrogen (-190 C), sectioned, and processed for autoradiography. The autoradiograms were then incubated with specific antibodies for NPY immunostaining by the avidin-biotin-peroxidase method. The results revealed NPY-immunopositive cells in the ARC, striatum, hippocampus, amygdala, and cerebral cortex and a few cells in the median eminence. NPY-immunoreactive fibers were also detected in the internal layer of the median eminence. The largest number of neurons showing NPY immunoreactivity in the cytoplasm was detected in the ARC, and only in this nucleus did we observed colocalization of [3H]estradiol and NPY immunoreactivity in neurons. A population of NPY-immunopositive cells in the ARC (10-20%) exhibited nuclear [3H]estradiol; the majority of these cells were located in the lateral and ventral portions of the ARC. Since gonadal steroids stimulate hypothalamic NPY levels and release, this anatomical evidence of colocalization is suggestive of a direct genomic modulation of NPY neurosecretion by steroids in a subpopulation of hypothalamic NPY-immunopositive neurons.

Animals↗