Ghrelin-induced Food Intake, but not GH Secretion, Requires the Expression of the GH Receptor in the Brain of Male Mice

Ghrelin stimulates both GH secretion and food intake. The orexigenic action of ghrelin is mainly mediated by neurons that coexpress agouti-related protein (AgRP) and neuropeptide Y (NPY) in the arcuate nucleus of the hypothalamus (ARH). GH also stimulates food intake and, importantly, ARHAgRP/NPY neurons express GH receptor (GHR). Thus, ghrelin-induced GH secretion may contribute to the orexigenic effect of ghrelin. Here, we investigated the response to ghrelin in male mice carrying GHR ablation specifically in neurons (brain GHR knockout [KO] mice) or exclusively in ARHAgRP/NPY neurons (AgRP GHR KO mice). Although brain GHR KO mice showed normal ghrelin-induced increase in plasma GH levels, these mutants lacked the expected orexigenic response to ghrelin. Additionally, brain GHR KO mice displayed reduced hypothalamic levels of Npy and Ghsr mRNA and did not elicit ghrelin-induced c-Fos expression in the ARH. Furthermore, brain GHR KO mice exhibited a prominent reduction in AgRP fiber density in the ARH and paraventricular nucleus of the hypothalamus (PVH). In contrast, AgRP GHR KO mice showed no changes in the hypothalamic Npy and Ghsr mRNAs and conserved ghrelin-induced food intake and c-Fos expression in the ARH. AgRP GHR KO mice displayed a reduced AgRP fiber density (~16%) in the PVH, but this reduction was less than that observed in brain GHR KO mice (~61%). Our findings indicate that GHR signaling in the brain is required for the orexigenic effect of ghrelin, independently of GH action on ARHAgRP/NPY neurons.

Tanycyte ablation in the arcuate nucleus and median eminence increases obesity susceptibility by increasing body fat content in male mice

Tanycytes are radial glial cells located in the mediobasal hypothalamus. Recent studies have proposed that tanycytes play an important role in hypothalamic control of energy homeostasis, although this has not been directly tested. Here, we report the phenotype of mice in which tanycytes of the arcuate nucleus and median eminence were conditionally ablated in adult mice. Although the cerebrospinal fluid-hypothalamic barrier was rendered more permeable following tanycyte ablation, neither the blood-hypothalamic barrier nor leptin-induced pSTAT3 activation in hypothalamic parenchyma were affected. We observed a significant increase in visceral fat distribution accompanying insulin insensitivity in male mice, without significant effect on either body weight or food intake. A high-fat diet tended to accelerate overall body weight gain in tanycyte-ablated mice, but the development of visceral adiposity and insulin insensitivity was comparable to wildtype. Thermoneutral housing exacerbated fat accumulation and produced a shift away from fat oxidation in tanycyte-ablated mice. These results clarify the extent to which tanycytes regulate energy balance, and demonstrate a role for tanycytes in regulating fat metabolism.

Action spectrum for photoperiodic control of thyroid-stimulating hormone in Japanese quail (Coturnix japonica)

At higher latitudes, vertebrates exhibit a seasonal cycle of reproduction in response to changes in day-length, referred to as photoperiodism. Extended day-length induces thyroid-stimulating hormone in the pars tuberalis of the pituitary gland. This hormone triggers the local activation of thyroid hormone in the mediobasal hypothalamus and eventually induces gonadal development. In avian species, light information associated with day-length is detected through photoreceptors located in deep-brain regions. Within these regions, the expressions of multiple photoreceptive molecules, opsins, have been observed. However, even though the Japanese quail is an excellent model for photoperiodism because of its robust and significant seasonal responses in reproduction, a comprehensive understanding of photoreceptors in the quail brain remains undeveloped. In this study, we initially analyzed an action spectrum using photoperiodically induced expression of the beta subunit genes of thyroid-stimulating hormone in quail. Among seven wavelengths examined, we detected maximum sensitivity of the action spectrum at 500 nm. The low value for goodness of fit in the alignment with a template of retinal1-based photopigment, assuming a spectrum associated with a single opsin, proposed the possible involvement of multiple opsins rather than a single opsin. Analysis of gene expression in the septal region and hypothalamus, regions hypothesized to be photosensitive in quail, revealed mRNA expression of a mammal-like melanopsin in the infundibular nucleus within the mediobasal hypothalamus. However, no significant diurnal changes were observed for genes in the infundibular nucleus. Xenopus-like melanopsin, a further isoform of melanopsin in birds, was detected in neither the septal region nor the infundibular nucleus. These results suggest that the mammal-like melanopsin expressed in the infundibular nucleus within the mediobasal hypothalamus could be candidate deep-brain photoreceptive molecule in Japanese quail. Investigation of the functional involvement of mammal-like melanopsin-expressing cells in photoperiodism will be required for further conclusions.

Effects of dihydrotestosterone administration on the expression of reproductive and body weight regulatory factors in ovariectomized and estradiol-treated female rats

To clarify the direct effects of androgens, the changes in the hypothalamic levels of reproductive and appetite regulatory factors induced by chronic dihydrotestosterone (DHT) administration were evaluated in female rats. DHT treatment increased the BW and food intake of the ovariectomized rats, but not the estradiol (E2)-treated rats. DHT administration suppressed the expression of a hypothalamic anorexigenic factor. Although the kisspeptin (Kiss1) mRNA levels of the anterior hypothalamic block (the anteroventral periventricular nucleus, AVPV) were increased in the E2-treated rats, DHT administration did not affect the Kiss1 mRNA levels of the AVPV in the ovariectomized or E2-treated rats. Conversely, DHT administration reduced the Kiss1 mRNA levels of the posterior hypothalamic block (the arcuate nucleus, ARC) in the ovariectomized rats. Although the Kiss1 mRNA levels of the posterior hypothalamic block (ARC) were decreased in the E2-treated rats, DHT administration did not affect the Kiss1 mRNA levels of the ARC in these rats. Serum luteinizing hormone levels of these groups exhibited similar patterns to the Kiss1 mRNA levels of the ARC. These results showed that DHT affects the production of hypothalamic reproductive and appetite regulatory factors, and that these effects of DHT differ according to the estrogen milieu.

Hypothalamic effects of neonatal diet: reversible and only partially leptin dependent

Early life diet influences metabolic programming, increasing the risk for long-lasting metabolic ill health. Neonatally overfed rats have an early increase in leptin that is maintained long term and is associated with a corresponding elevation in body weight. However, the immediate and long-term effects of neonatal overfeeding on hypothalamic anorexigenic pro-opiomelanocortin (POMC) and orexigenic agouti-related peptide (AgRP)/neuropeptide Y (NPY) circuitry, and if these are directly mediated by leptin, have not yet been examined. Here, we examined the effects of neonatal overfeeding on leptin-mediated development of hypothalamic POMC and AgRP/NPY neurons and whether these effects can be normalised by neonatal leptin antagonism in male Wistar rats. Neonatal overfeeding led to an acute (neonatal) resistance of hypothalamic neurons to exogenous leptin, but this leptin resistance was resolved by adulthood. While there were no effects of neonatal overfeeding on POMC immunoreactivity in neonates or adults, the neonatal overfeeding-induced early increase in arcuate nucleus (ARC) AgRP/NPY fibres was reversed by adulthood so that neonatally overfed adults had reduced NPY immunoreactivity in the ARC compared with controls, with no further differences in AgRP immunoreactivity. Short-term neonatal leptin antagonism did not reverse the excess body weight or hyperleptinaemia in the neonatally overfed, suggesting factors other than leptin may also contribute to the phenotype. Our findings show that changes in the availability of leptin during early life period influence the development of hypothalamic connectivity short term, but this is partly resolved by adulthood indicating an adaptation to the metabolic mal-programming effects of neonatal overfeeding.

Central precocious puberty caused by mutations in the imprinted gene MKRN3

BACKGROUND

The onset of puberty is first detected as an increase in pulsatile secretion of gonadotropin-releasing hormone (GnRH). Early activation of the hypothalamic-pituitary-gonadal axis results in central precocious puberty. The timing of pubertal development is driven in part by genetic factors, but only a few, rare molecular defects associated with central precocious puberty have been identified.

METHODS

We performed whole-exome sequencing in 40 members of 15 families with central precocious puberty. Candidate variants were confirmed with Sanger sequencing. We also performed quantitative real-time polymerase-chain-reaction assays to determine levels of messenger RNA (mRNA) in the hypothalami of mice at different ages.

RESULTS

We identified four novel heterozygous mutations in MKRN3, the gene encoding makorin RING-finger protein 3, in 5 of the 15 families; both sexes were affected. The mutations included three frameshift mutations, predicted to encode truncated proteins, and one missense mutation, predicted to disrupt protein function. MKRN3 is a paternally expressed, imprinted gene located in the Prader-Willi syndrome critical region (chromosome 15q11-q13). All affected persons inherited the mutations from their fathers, a finding that indicates perfect segregation with the mode of inheritance expected for an imprinted gene. Levels of Mkrn3 mRNA were high in the arcuate nucleus of prepubertal mice, decreased immediately before puberty, and remained low after puberty.

CONCLUSIONS

Deficiency of MKRN3 causes central precocious puberty in humans. (Funded by the National Institutes of Health and others.).

High-fat diet-induced alterations in the feeding suppression of low-dose nisoxetine, a selective norepinephrine reuptake inhibitor

Central noradrenergic pathways are involved in feeding and cardiovascular control, physiological processes altered by obesity. The present studies determined how high-fat feeding and body weight gain alter the sensitivity to the feeding suppression and neural activation to a selective norepinephrine reuptake inhibitor, nisoxetine. Acute administration of nisoxetine (saline: 0, 3, 10, and 30 mg/kg; i.p.) resulted in a dose-dependent reduction in the 24 h refeeding response in male Sprague Dawley rats maintained on standard chow. In a similar fashion, nisoxetine resulted in reductions in blood pressure and a compensatory increase in heart rate. From these studies, the 3 mg/kg dose was subthreshold. In a separate experiment, however, 10 wk exposure to a high-fat diet (60% fat) resulted in weight gain and significant feeding suppression following administration of nisoxetine (3 mg/kg) compared with animals fed a control diet (10% fat). Nisoxetine (3 mg/kg) also resulted in greater neural activation, as measured by c-Fos immunohistochemistry, in the arcuate nucleus of the hypothalamus in animals exposed to the high-fat diet. Such data indicate acute nisoxetine doses that suppress food intake can impact cardiovascular measures. It also suggests that the feeding suppression to a low-dose nisoxetine is enhanced as a result of high-fat diet and weight gain.

Sex differences in the neurokinin B system in the human infundibular nucleus

CONTEXT

The recent report that loss-of-function mutations in either the gene encoding neurokinin B (NKB) or its receptor (NK3R) produce gonadotropin deficiencies in humans strongly points to NKB as a key regulator of GnRH release.

OBJECTIVES

We used NKB immunohistochemistry on postmortem human brain tissue to determine: 1) whether the human NKB system in the infundibular nucleus (INF) is sexually dimorphic; 2) at what stage in development the infundibular NKB system would diverge between men and women; 3) whether this putative structural difference is reversed in male-to-female (MtF) transsexual people; and 4) whether menopause is accompanied by changes in infundibular NKB immunoreactivity.

METHODS

NKB immunohistochemical staining was performed on postmortem hypothalamus material of both sexes from the infant/pubertal period into the elderly period and from MtF transsexuals.

RESULTS

Quantitative analysis demonstrated that the human NKB system exhibits a robust female-dominant sexual dimorphism in the INF. During the first years after birth, both sexes displayed a moderate and equivalent level of NKB immunoreactivity in the INF. The adult features emerged progressively around puberty until adulthood, where the female-dominant sex difference appeared and continued into old age. In MtF transsexuals, a female-typical NKB immunoreactivity was observed. Finally, in postmenopausal women, there was a significant increase in NKB immunoreactivity compared to premenopausal women.

CONCLUSION

Our results indicate that certain sex differences do not emerge until adulthood when activated by sex steroid hormones and the likely involvement of the human infundibular NKB system in the negative and positive feedback of estrogen on GnRH secretion.

Normal Distribution of Body Weight Gain in Male Sprague-Dawley Rats Fed a High-Energy Diet

OBJECTIVE

To investigate the effect of a high-energy (HE) diet on caloric intake, body weight, and related parameters in outbred male Sprague-Dawley (SD) rats.

RESEARCH METHODS AND PROCEDURES

Twenty-eight SD rats were fed either chow (C) for 19 weeks or HE diet for 14 weeks and then C for 5 weeks. Blood hormones and metabolites were assayed, and expression of uncoupling protein-1 and hypothalamic energy-balance-related genes were determined by Northern blotting and in situ hybridization, respectively.

RESULTS

HE rats gained body weight more rapidly than C animals with a range of weight gains, but there was no evidence that weight gain was bimodally distributed. Caloric intake was transiently elevated after introduction of the HE diet. Transfer of HE rats back to C resulted in a drop in caloric intake, but a stable body weight. In terminal analysis, two of four dissected adipose tissue depots were heavier in rats that had previously been fed HE diet. Blood leptin, insulin, glucose, and nonesterified fatty acids were not different between the groups. Uncoupling protein-1 mRNA was elevated in interscapular brown adipose tissue from HE rats. There was a trend for agouti-related peptide mRNA in the hypothalamic arcuate nucleus to be higher in HE rats.

DISCUSSION

Contrary to other studies of the SD rat on HE diet, body weight and other measured parameters were normally distributed. There was no segregation into two distinct populations on the basis of susceptibility to diet-induced obesity. This characteristic may be dependent on the breeding colony from which animals were sourced.

Morphological evidence for direct interaction between kisspeptin and gonadotropin-releasing hormone neurons at the median eminence of the male goat: an immunoelectron microscopic study

Kisspeptin has been thought to play pivotal roles in the control of both pulse and surge modes of gonadotropin-releasing hormone (GnRH) secretion. To clarify loci of kisspeptin action on GnRH neurons, the present study examined the morphology of the kisspeptin system and the associations between kisspeptin and GnRH systems in gonadally intact and castrated male goats. Kisspeptin-immunoreactive (ir) and Kiss1-positive neurons were found in the medial preoptic area of intact but not castrated goats. Kisspeptin-ir cell bodies and fibers in the arcuate nucleus (ARC) and median eminence (ME) were fewer in intact male goats compared with castrated animals. Apposition of kisspeptin-ir fibers on GnRH-ir cell bodies was very rare in both intact and castrated goats, whereas the intimate association of kisspeptin-ir fibers with GnRH-ir nerve terminals was observed in the ME of castrated animals. Neurokinin B immunoreactivity colocalized not only in kisspeptin-ir cell bodies in the ARC but also in kisspeptin-ir fibers in the ME, suggesting that a majority of kisspeptin-ir fibers projecting to the ME originates from the ARC. A dual immunoelectron microscopic examination revealed that nerve terminals containing kisspeptin-ir vesicles made direct contact with GnRH-ir nerve terminals at the ME of castrated goats. There was no evidence for the existence of the typical synaptic structure between kisspeptin- and GnRH-ir fibers. The present results suggest that the ARC kisspeptin neurons act on GnRH neurons at the ME to control (possibly the pulse mode of) GnRH secretion in males.

Identification of salsolinol in the mediobasal hypothalamus of lactating ewes and its relation to suckling-induced prolactin and GH release

The push-pull perfusions of the infundibular nucleus-median eminence (IN/ME) were made in lactating ewes (n=7) twice, to identify dopamine (DA)-derived salsolinol and the changes in its extracellular concentration in response to suckling. The perfusate collecting period in every ewe consisted of control non-suckling period, 1000-1230 h (five perfusates), and suckling period, 1230-1500 h (next five perfusates). Simultaneously, blood samples were collected from 1000 to 1500 h at 10-min intervals. The perfusate concentrations of salsolinol and DA were measured by HPLC, and plasma prolactin and GH concentrations were assayed by the RIA. Mean concentrations of salsolinol in perfusates collected from the anterior and posterior parts of the IN/ME (according to post-mortem localization of a perfusion site) increased significantly (P<0.05 and P<0.001 respectively) during the suckling period, when compared with those noted during the non-suckling period. While no DA was found in the anterior part, only vestigial amounts of DA were found in a few perfusates collected from the posterior part. Salsolinol was not detected in the IN/ME of ewes 10 weeks after weaning (seasonal anoestrus). Mean plasma prolactin and GH concentrations during suckling were significantly (P<0.001) higher than those noted during the non-suckling period. In conclusion, our current study reveals that salsolinol is present in the IN/ME of lactating ewes and that its extracellular concentration increases during suckling. Moreover, it supports the role of salsolinol as a neurotransmitter involved in the regulatory process of prolactin secretion at least during lactation.

Divergent regulation of proopiomelanocortin neurons by leptin in the nucleus of the solitary tract and in the arcuate hypothalamic nucleus

Proopiomelanocortin (POMC) neurons in the arcuate nucleus (ARC) of the hypothalamus are activated by leptin and mediate part of leptin's central actions to influence energy balance. However, little is known about potential leptin signaling in POMC neurons located in the nucleus of the solitary tract (NTS), the only other known population of POMC neurons. Leptin-responsive neurons do exist in the NTS, but their neurochemical phenotype is largely unknown. The contribution of NTS POMC neurons versus ARC POMC neurons in leptin action is thus undetermined. We show here that in contrast to POMC neurons in the ARC, leptin does not stimulate phosphorylation of signal-transducer and activator of transcription 3 in NTS POMC neurons of POMC-EGFP reporter mice. In addition, leptin does not induce c-Fos expression in NTS POMC neurons unlike ARC POMC neurons. Fasting induces a fall in POMC mRNA in both the ARC and the NTS, but different from the ARC, the reduction in NTS POMC mRNA is not reversed by leptin. We conclude that POMC neurons in the NTS do not respond to leptin unlike ARC POMC neurons. POMC neurons in the hypothalamus may therefore mediate all of leptin's signaling via POMC-derived peptides in the central nervous system.

Distribution of somatostatin immunoreactivity in the brain of the snake Bothrops jararaca

The distribution of perikarya and fibers containing somatostatin was studied in the brain of the snake Bothrops jararaca by means of immunohistochemistry using an antiserum against synthetic somatostatin. Immunoreactive perikarya and fibers were localized in telencephalic, diencephalic and mesencephalic areas. In the telencephalon, numerous immunoreactive perikarya were found in the medial, dorsomedial, dorsal and lateral cortex, mainly in the deep plexiform layer, less so in the cellular layer, but not in the superficial plexiform layer. Immunoreactive perikarya were also observed in the dorsal ventricular ridge, the nucleus of the diagonal band of Broca, amygdaloid complex, septum and lamina terminalis. In the diencephalon, labelled cells were observed in the paraventricular, periventricular hypothalamic and in the recessus infundibular nuclei. In the mesencephalon, immunoreactive perikarya were seen in the mesencephalic reticular formation, reticular nucleus of the isthmus and torus semicircularis. Labelled fibers ran along the diencephalic floor and the inner zone of the median eminence, and ended in the neural lobe of the hypophysis. Other fibers were observed in the outer zone of the median eminence close to the portal vessels and in the septum, lamina terminalis, retrochiasmatic nucleus, deep layers of the tectum, periventricular gray and granular layer of the cerebellum. Our data suggest that somatostatin may function as a mediator of adenohypophysial secretion as well as neurotransmitter and/or neuromodulator which can regulate the neurohypophysial peptides in the snake B. jararaca.

Lack of involvement of dopamine and serotonin during the orphanin FQ/Nociceptin (OFQ/N)-induced prolactin secretory response

The purpose of these studies was to examine possible mechanisms of Orphanin FQ/Nociceptin (OFQ/N)-induced prolactin release. We investigated the involvement of the dopaminergic neurons by quantifying DOPAC:DA levels in the median eminence and neurointermediate lobe following central administration of OFQ/N to female Sprague-Dawley rats. To specifically determine the involvement of the tuberoinfundibular dopaminergic neurons, immunocytochemical studies were conducted to visualize c-fos protein expression in the arcuate nucleus following central administration of OFQ/N. In addition, the role of serotonergic activation was examined in dose response studies using the selective serotonin antagonist ritansarin and the nonselective antagonist metergoline. Finally, the pharmacological specificity of the prolactin response was examined by pretreating animals with [Nphe1] NC (1-13)NH2, a drug reported to antagonize OFQ/N effects. The results of these studies indicate that the increase in prolactin release following central administration of OFQ/N does not inhibit tuberoinfundibular, tuberohypophyseal or periventricular hypophysial dopaminergic neuronal activity at 10 min after drug administration, a time when prolactin levels were significantly elevated. Furthermore, serotonergic activation is not involved since pharmacological blockade of serotonergic receptors did not alter the prolactin secretory response to OFQ/N. NC (1-13)NH2 did not antagonize the stimulatory effects of OFQ/N on prolactin secretion. The neural effects of OFQ/N on dopaminergic neuronal activity may occur following a different time course than that of the prolactin increase.

PAC1 receptors mediate pituitary adenylate cyclase-activating polypeptide- and progesterone-facilitated receptivity in female rats

Pituitary adenylate cyclase-activating polypeptide (PACAP) acts as a feed-forward, paracrine/autocrine factor in the hypothalamic ventromedial nucleus (VMN) for receptivity and sensitizes pituitary hormone release for ovulation. The present study examined receptor(s) and signaling pathway by which PACAP enhances rodent lordosis. PACAP binds to PACAP (PAC1)- and vasoactive intestinal peptide-preferring receptors (VPAC1, VPAC2). Ovariectomized rodents primed with estradiol (EB) were given PACAP or vasoactive intestinal peptide directly onto VMN cells. Only PACAP facilitated receptivity. Pretreatment with VPAC1 and VPAC2 inhibitors blocked both PACAP- and progesterone (P)-induced receptivity. Antisense (AS) oligonucleotides to PAC1 (not VPAC1 or VPAC2) inhibited the behavioral effect of PACAP and P. By real-time RT-PCR, EB, P and EB+P enhanced VMN mRNA expression of PAC1. Within the total PAC1 population, EB and EB+P induced expression of short form PAC1 and PAC1hop2 splice variants. Finally, blocking cAMP/protein kinase A signaling cascade by antagonists to cAMP activity and protein kinase A or by antisense to dopamine- and cAMP-regulated phosphoprotein of 32 kDa blocked the PACAP effect on behavior. Collectively, these findings provide evidence that progesterone receptor-dependent receptivity is, in part, dependent on PAC1 receptors for intracellular VMN signaling and delineate a novel, steroid-dependent mechanism for a feed-forward reinforcement of steroid receptor-dependent reproductive receptivity.

Role of neuropeptide Y and proopiomelanocortin in fluoxetine-induced anorexia

Fluoxetine is an anorexic agent known to reduce food intake and weight gain. However, the molecular mechanism by which fluoxetine induces anorexia has not been well-established. We examined mRNA expression levels of neuropeptide Y (NPY) and proopiomelanocortin (POMC) in the brain regions of rats using RT-PCR and in situ hybridization techniques after 2 weeks of administering fluoxetine daily. Fluoxetine persistently suppressed food intake and weight gain during the experimental period. The pair-fed group confirmed that the reduction in body weight in the fluoxetine treated rats resulted primarily from decreased food intake. RT-PCR analyses showed that mRNA expression levels of both NPY and POMC were markedly reduced by fluoxetine treatment in all parts of the brain examined, including the hypothalamus. POMC mRNA in situ signals were significantly decreased, NPY levels tended to increase in the arcuate nucleus (ARC) of fluoxetine treated rats (compared to the vehicle controls). In the pair-fed group, NPY mRNA levels did not change, but the POMC levels decreased (compared with the vehicle controls). These results reveal that the chronic administration of fluoxetine decreases expression levels in both NPY and POMC in the brain, and suggests that fluoxetine-induced anorexia may not be mediated by changes in the ARC expression of either NPY or POMC. It is possible that a fluoxetine raised level of 5-HT play an inhibitory role in the orectic action caused by a reduced expression of ARC POMC (alpha-MSH).

The role of the vagal nerve in peripheral PYY3-36-induced feeding reduction in rats

Peptide YY (PYY), an anorectic peptide, is secreted postprandially from the distal gastrointestinal tract. PYY(3-36), the major form of circulating PYY, binds to the hypothalamic neuropeptide Y Y2 receptor (Y2-R) with a high-affinity, reducing food intake in rodents and humans. Additional gastrointestinal hormones involved in feeding, including cholecystokinin, glucagon-like peptide 1, and ghrelin, transmit satiety or hunger signals to the brain via the vagal afferent nerve and/or the blood stream. Here we determined the role of the afferent vagus nerve in PYY function. Abdominal vagotomy abolished the anorectic effect of PYY(3-36) in rats. Peripheral administration of PYY(3-36) induced Fos expression in the arcuate nucleus of sham-operated rats but not vagotomized rats. We showed that Y2-R is synthesized in the rat nodose ganglion and transported to the vagal afferent terminals. PYY(3-36) stimulated firing of the gastric vagal afferent nerve when administered iv. Considering that Y2-R is present in the vagal afferent fibers, PYY(3-36) could directly alter the firing rate of the vagal afferent nerve via Y2-R. We also investigated the effect of ascending fibers from the nucleus of the solitary tract on the transmission of PYY(3-36)-mediated satiety signals. In rats, bilateral midbrain transections rostral to the nucleus of the solitary tract also abolished PYY(3-36)-induced reductions in feeding. This study indicates that peripheral PYY(3-36) may transmit satiety signals to the brain in part via the vagal afferent pathway.

Inhibition of appetite by nasal leptin administration in rats

OBJECTIVE

Leptin inhibits appetite and reduces body weight. However, subcutaneous leptin administration is not very effective on weight reduction. The present studies were undertaken to test the hypotheses that nasally administered leptin effectively accesses to the brain and inhibits appetite.

METHODS

Recombinant leptin (0.5 mg/rat) was administered into the bilateral nasal spaces of rats (i.n.). Changes in serum immunoreactive leptin (IRL) and cerebrospinal fluid (CSF)-IRL concentrations after i.n. leptin administration were compared after intraperitoneal (i.p.) administration. The influence of 0.1 or 0.5% lysophosphatidylcholine (LPC) as an optimizer of leptin absorption was examined. The anorexic effects of i.n. leptin were compared with i.p. leptin in ad libitum fed rats.

RESULTS

The i.n. leptin increased CSF-IRL concentrations, although serum IRL concentrations of rats administered leptin i.n. were lower than those administered i.p. The addition of 0.1 and 0.5% LPC dose-dependently increased serum IRL concentrations, but did not modify CSF-IRL concentrations in i.n. leptin-treated rats. The i.n. leptin inhibited dark-time food consumption at 0-1 h and 3-6 h in ad libitum fed rats. In contrast, i.p. leptin reduced food consumption only for an hour. Phosphorylated signal transducer and activator of transcription (STAT) 3 immunoreactive cells increased in the arcuate nucleus (ARC) of the hypothalamus at 3 h only following i.n. leptin.

CONCLUSION

The present study demonstrated that i.n. leptin caused longer inhibition of appetite and phosphorylation of STAT3 in ARC. It is concluded that the trans-nasal route may be useful for the selective access of leptin to the brain in obese people.

Increased melanin concentrating hormone receptor type I in the human hypothalamic infundibular nucleus in cachexia

Melanin-concentrating hormone (MCH) exerts a positive regulation on appetite and binds to the G protein-coupled receptors, MCH1R and MCH2R. In rodents, MCH is produced by neurons in the lateral hypothalamus with projections to various hypothalamic and other brain sites. In the present study, MCH1R was shown, by immunocytochemistry, to be present in the human infundibular nucleus/median eminence, paraventricular nucleus, lateral hypothalamic area, and perifornical area, although in the latter two regions, only a few MCH1R-containing cells were found. In addition, MCH1R staining was found in nerve fibers in the periventricular nucleus, dorsomedial and ventromedial nucleus, suprachiasmatic nucleus, and tuberomammillary nucleus. A significant 1.6 times increase in the number of MCH1R cell body staining was found in the infundibular nucleus in postmortem brain material of cachectic patients, compared with matched controls, supporting a role for this receptor in energy homeostasis in the human.

Nuclear Factor of Activated T Cells (NFAT) Is Involved in the Depolarization-Induced Activation of Growth Hormone-Releasing Hormone Gene Transcription in Vitro

GHRH plays a pivotal role in the regulation of both synthesis and secretion of GH in the anterior pituitary. In this study, we examined the molecular mechanism of depolarization-induced GHRH gene transcription using the hypothalamus cell line, Gsh+/+, revealing the involvement of the transcription factor called nuclear factor of activated T cells (NFAT). GHRH, NFAT1, NFAT4, and related genes were endogenously expressed in Gsh+/+ cells and the rat arcuate nucleus, where NFAT1 and GHRH were colocalized. Cellular excitation with high potassium potently stimulated endogenous GHRH gene 5′-promoter activity as well as the NFAT-mediated gene transcription, the former being further enhanced by coexpression of NFAT. On the other hand, cyclosporin A (a calcineurin-NFAT inhibitor) or EGTA (a calcium chelator) significantly blocked the depolarization-induced GHRH gene transcription. EMSA and site-directed mutagenesis experiments showed the direct binding of NFAT at five sites of the GHRH promoter, among which the relative importance of three distal sites (−417/−403, −402/−387, −317/−301) was suggested. Finally, elimination of all five sites completely abolished the NFAT-induced GHRH gene up-regulation. Altogether, our results suggest that the transcription factor NFAT is involved in the depolarization-induced transcriptional activation of GHRH gene in the neuronal cells.

Expressional changes of neuropeptide Y and cholecystokinin in the arcuate and paraventricular nuclei after capsaicin administration

Despite its toxicity, a great deal of attention has been paid to the anorexic effect of capsaicin in the treatment of obesity-related neurotransmitters/neuromodulators. To determine if capsaicin has any effects on the orexigenic or anorexigenic peptides, the neuropeptide Y (NPY)- and cholecystokinin (CCK)-immunoreactivities were demonstrated in the rat hypothalamus by immunohistochemistry after capsaicin administration. There was a significantly lower concentration of NPY immunopositive cells in the arcuate and paraventricular nuclei of the capsaicin treated rats. In contrast, the CCK expressions level was higher in the paraventricular nucleus of the capsaicin treated rats than in the control rats. These results suggest that capsaicin influence neuropeptides such as orexigenic NPY and anorexigenic CCK related to control food intake.

Galanin-like peptide gene expression in the hypothalamus and posterior pituitary of the obese fa/fa rat

We examined the galanin-like peptide (GALP) gene expression in the arcuate nucleus (ARC) and posterior pituitary (PP) in 6- and 18-week-old male obese fa/fa rats. GALP mRNA in the ARC in fa/fa rats was significantly decreased in 6- and 18-week-old and GALP mRNA in the PP in fa/fa rats was significantly increased in 18-week-old compared to lean Fa/? rats. Insulin treatment in hyperglycemic fa/fa rats partially reversed those changes. These results suggest that the GALP gene expression in fa/fa rats might be regulated in part by leptin-independent mechanisms.

Estrogen regulation of neurokinin B gene expression in the mouse arcuate nucleus is mediated by estrogen receptor alpha

Neurokinin B (NKB) gene expression is elevated in the infundibular (arcuate) nucleus of the hypothalamus in postmenopausal women. Estrogen replacement decreases both the number of NKB mRNA-expressing neurons and the level of expression within individual cells. Similarly, NKB gene expression is elevated in ovariectomized rats and reduced after estrogen treatment. The actions of estrogen in the brain can be mediated via either estrogen receptor alpha (ERalpha) or estrogen receptor beta (ERbeta). In the rodent arcuate nucleus (ARC), more ERalpha- than ERbeta-containing cells are present, suggesting that ERalpha might be directly responsible for estrogen regulation of NKB gene expression. However, an indirect effect via ERbeta could not be ruled out. Here we used ERalpha knockout and ERbeta knockout mice to identify the type of ER responsible for mediating estrogen action on NKB gene expression in the ARC. Using in situ hybridization histochemistry, we have found that estrogen treatment significantly reduced NKB gene expression in the ARC of ovariectomized ERbeta knockout mice, but had no effect on NKB mRNA levels in ERalpha knockout mice. These data indicate that ERalpha mediates the increase in NKB gene expression associated with ovariectomy in rodents and might also be responsible for the increase in NKB in postmenopausal women.

Regulation of hypothalamic neuropeptide Y messenger ribonucleic acid expression during lactation: role of prolactin

In the present study, we investigated the role of prolactin (PRL) in the suckling-induced increase in hypothalamic neuropeptide Y (NPY) gene expression in the dorsomedial nucleus of the hypothalamus (DMH) and the caudal portion of the arcuate nucleus of the hypothalamus (ARH-C). Lactating rats were deprived of their eight-pup litters on d 9 postpartum. After 48 h, the animals were randomly divided into two groups: nonsuckled controls and eight pups suckling for 24 h. In addition, some of the suckled animals received two injections of bromocriptine (0.5 mg/rat per injection) to inhibit suckling-induced PRL secretion. Some bromocriptine-treated rats also received ovine PRL (1 mg/rat per injection). In situ hybridization was performed to measure NPY mRNA levels. Suckling for 24 h induced a significant increase in NPY mRNA levels in the DMH and ARH-C. Bromocriptine treatment greatly attenuated the increase of NPY mRNA in the DMH but not in the ARH. Injections of ovine PRL in bromocriptine-treated rats greatly restored DMH NPY mRNA levels but had no additional effects on the ARH NPY expression. Double-label in situ hybridization for NPY and PRL receptor (PRL-R) in the lactating rat brains showed that NPY-positive neurons in the DMH also express PRL-R mRNA. On the contrary, few ARH NPY neurons expressed PRL-R. These data suggest that PRL could act directly on DMH NPY neurons to modulate NPY gene expression during lactation. Thus, the results from the present study demonstrate that NPY neurons in the DMH and ARH are differentially regulated by PRL during lactation.

Abnormalities of leptin and ghrelin regulation in obesity-prone juvenile rats

Rats selectively bred to develop diet-induced obesity (DIO) spontaneously gain more body weight between 5 and 7 wk of age than do those bred to be diet resistant (DR). Here, chow-fed DIO rats ate 9% more and gained 19% more body weight from 5 to 6 wk of age than did DR rats but had comparable leptin and insulin levels. However, 6-wk-old DIO rats had 29% lower plasma ghrelin levels at dark onset but equivalent levels 6 h later compared with DR rats. When subsequently fed a high-energy (HE; 31% fat) diet for 10 days, DIO rats ate 70% more, gained more body and adipose depot weight, had higher leptin and insulin levels, and had 22% lower feed efficiency than DR rats fed HE diet. In DIO rats on HE diet, leptin levels increased significantly at 3 days followed by increased insulin levels at 7 days. These altered DIO leptin and ghrelin responses were associated with 10% lower leptin receptor mRNA expression in the arcuate (ARC), dorsomedial (DMN), and ventromedial hypothalamic nuclei and 13 and 15% lower ghrelin receptor (GHS-R) mRNA expression in the ARC and DMN than in the DR rats. These data suggest that increased ghrelin signaling is not a proximate cause of DIO, whereas reduced leptin sensitivity might play a causal role.

Early social stress in male Guinea-pigs changes social behaviour, and autonomic and neuroendocrine functions

The present study was undertaken to investigate the effects of pre- and early postnatal social stress on the functioning of hormonal, autonomic and behavioural systems, by studying the distribution of sex hormone receptors in limbic brain systems. Dams had either lived in groups with a constant composition (= stable social environment) or in groups with changing compositions, i.e. every third day, two females from different groups were exchanged (= unstable social environment). The subjects were male offspring of dams who had either lived in a stable social environment during pregnancy and lactation (= control males) or in an unstable social environment during this period of life (= early stressed males). From days 20-80, the spontaneous behaviour of control males and early stressed males was recorded in their home cages. Five control males and five early stressed males were killed at 75 days, and five control males and five early stressed males at 120 days. Blood samples were taken to determine serum concentrations of cortisol, testosterone, dehydroepiandrosterone, dehydroepiandrosterone sulphate and oestrogen. The adrenals were prepared to determine tyrosine hydroxylase activities and the brains were used to investigate the distribution of sex-hormone receptors in specific hypothalamic and hippocampal brain areas. Early stressed males showed a behavioural infantilization that was accompanied by significantly decreased adrenal tyrosine hydroxylase activities and dehydroepiandrosterone levels. Furthermore, early stressed males showed a down-regulation of androgen receptors in the medial preoptic area and the nucleus arcuatus of the hypothalamus, as well as of oestrogen receptor alpha in the hippocampus compared to control males. Thus, the present study provides clear evidence that early social stress induces changes in endocrine, autonomic and limbic brain function, which is mirrored by changes in male social behaviour.

Changes in hypothalamic expression levels of galanin-like peptide in rat and mouse models support that it is a leptin-target peptide

Galanin-like peptide (GALP) is a novel peptide that has been isolated from the porcine hypothalamus. The expression of GALP mRNA is localized to the hypothalamic arcuate nucleus and is thought to be under the regulation of leptin. First, we confirmed by real-time PCR analysis that sc administration of leptin to Wistar rats under food-deprived conditions resulted in a 1.5-fold increase in hypothalamic GALP mRNA levels. Next, GALP mRNA levels were found to be reduced by 50% in 11-wk-old male Zucker obese rats compared with age-matched Zucker lean rats, whereas neuropeptide Y mRNA levels were increased by 55% and proopiomelanocortin mRNA levels were reduced by 53% in Zucker obese rats. Analysis using a two-site enzyme immunoassay revealed a lower level of hypothalamic GALP immunoreactivity in 11-wk-old Zucker obese rats (5.9 fmol/mg protein) than in age-matched Zucker lean rats (19.6 fmol/mg protein). Immunohistochemical studies demonstrated that Zucker obese rats (11 wk old) had a reduced number of GALP immunoreactivity-positive cells (29.4 cells/3 slices) in the arcuate nucleus compared with age-matched Zucker lean rats (115 cells/3 slices). Furthermore, Zucker obese rats showed increased sensitivity to intracerebroventricularly administered GALP compared with Zucker lean rats, in that a lower dose of GALP increased plasma LH levels in male Zucker obese rats, but not in male Zucker lean rats. In addition, a reduction in the level of hypothalamic GALP mRNA was found in db/db and ob/ob mice. The result supports the hypothesis that the hypothalamic GALP gene expression is controlled by leptin signals and suggests possible involvement of GALP in the reproductive abnormalities of the Zucker obese rat.

Co-existence of leptin- and orexin-receptors in feeding-regulating neurons in the hypothalamic arcuate nucleus-a triple labeling study

The arcuate nucleus (ARC) of the hypothalamus has been identified as a prime feeding regulating center in the brain. Several feeding regulating peptides, such as neuropeptide Y (NPY) and proopiomelanocortin (POMC), are present in neurons of the ARC, which also serves as a primary targeting site for leptin, a feeding inhibiting hormone secreted predominantly by adipose tissues, and for orexin (OX)-containing neurons. OX is expressed exclusively around the lateral hypothalamus, an area also established as a feeding regulating center. Some recent physiological analyses have shown that NPY- and POMC-containing neurons are activated or inactivated by leptin and OX. Moreover, we have already shown, using double immunohistochemical staining techniques, that NPY- and POMC-containing neurons express leptin receptors (LR) and orexin type 1 receptors (OX-1R). However, no morphological study has yet described the possibility of whether or not these arcuate neurons are influenced by both leptin and OX simultaneously. In order to address this issue, we performed histochemistry on ARC neurons using a triple immunofluorescence method. We found that 77 out of 213 NPY- and 99 out of 165 POMC-immunoreactive neurons co-localized with both LR- and OX-1R-immunoreactivities. These findings strongly suggest that both NPY- and POMC-containing neurons are regulated simultaneously by both leptin and OX.

Targeting sst2A receptor-expressing cells in the rat hypothalamus through in vivo agonist stimulation: neuroanatomical evidence for a major role of this subtype in mediating somatostatin functions

Numerous physiological studies as well as in situ hybridization and PCR experiments concur in reporting a role for the sst2A receptor in transducing somatostatin (SRIF) actions in the rat hypothalamus. However, the distribution of this receptor protein is not known within this structure. Regional and cellular localization of the sst2A receptor was therefore examined in the rat hypothalamus using highly sensitive immunohistochemical techniques. In close correspondence with the distribution of SRIF-immunoreactive fibers, numerous hypothalamic areas displayed sst2A receptor immunoreactivity. Receptor labeling was, however, diffusely distributed over the tissue, and few immunopositive cells were apparent. Unraveling the distribution of receptor-expressing cells was achieved through acute in vivo agonist stimulation and subsequent receptor internalization. At the cellular level, double-immunolabeling experiments with synaptophysin and microtubule-associated protein 2 demonstrated that sst2A receptors were predominantly internalized in perikarya and dendrites. Double-labeling experiments with SRIF revealed that 93% of arcuate, but only 18% of periventricular, SRIF-positive neurons expressed internalized receptors. Taken together, these results demonstrate for the first time that the sst2A receptor protein is widely, but selectively, distributed in the hypothalamus, and that postsynaptic sst2A auto- and heteroreceptors are well poised to play an important role in the somatostatinergic regulation of hypothalamic endocrine and metabolic processes.

Interrelationship between the novel peptide ghrelin and somatostatin/growth hormone-releasing hormone in regulation of pulsatile growth hormone secretion

GH is an anabolic hormone that is essential for normal linear growth and has important metabolic effects throughout life. The ultradian rhythm of GH secretion is generated by the intricate patterned release of two hypothalamic hormones, somatostatin (SRIF) and GHRH, acting both at the level of the pituitary gland and within the central nervous system. The recent discovery of ghrelin, a novel GH-releasing peptide identified as the endogenous ligand for the GH secretagogue receptor and shown to induce a positive energy balance, suggests the existence of an additional neuroendocrine pathway for GH control. To further understand how ghrelin interacts with the classical GHRH/SRIF neuronal system in GH regulation, we used a combined physiological and histochemical approach. Our physiological studies of the effects of ghrelin on spontaneous pulsatile GH secretion in conscious, free-moving male rats demonstrate that 1) ghrelin, administered either systemically or centrally, exerts potent, time-dependent GH-releasing activity under physiological conditions; 2) ghrelin is a functional antagonist of SRIF, but its GH-releasing activity at the pituitary level is not dependent on inhibiting endogenous SRIF release; 3) SRIF antagonizes the action of ghrelin at the level of the pituitary gland; and 4) the GH response to ghrelin in vivo requires an intact endogenous GHRH system. Our dual chromogenic and autoradiographic in situ hybridization experiments provide anatomical evidence that ghrelin may directly modulate GHRH mRNA- and neuropeptide Y mRNA-containing neurons in the hypothalamic arcuate nucleus, but that SRIF mRNA-expressing cells are not major direct targets for ghrelin. Together, these findings support the idea that ghrelin may be a critical hormonal signal of nutritional status to the GH neuroendocrine axis serving to integrate energy balance and the growth process.

A confocal microscopic study of gonadotropin-releasing hormone (GnRH) neuron inputs to dopaminergic neurons containing estrogen receptor alpha in the arcuate nucleus of GnRH-green fluorescent protein transgenic mice

The purpose of the present study was to determine whether the septo-preoptico-tuberoinfundibular gonadotropin-releasing hormone (GnRH) pathway comes in close juxtaposition with tyrosine hydroxylase immunoreactive (TH-IR) neurons in the arcuate nucleus of female mice. Immunohistochemical staining with a TH monoclonal antibody coupled with confocal microscopy was employed on vibratome-cut brain sections of female GnRH-green fluorescent protein (GFP) transgenic mice to evaluate possible appositions between GnRH and tuberoinfundibular dopaminergic (TIDA) neurons. TH-IR neurons of the arcuate nucleus received GnRH neuronal appositions in adult female mice at proestrus and estrus stages. In contrast, no GnRH appositions were observed in adult females at diestrus. Subsequently, double immunohistochemical staining for TH and estrogen receptor-alpha (ERalpha) was performed to examine the role of estradiol on this relationship. We found that most TH-IR neurons contacted by GnRH fibers were immunoreactive for ERalpha. Our observations suggest that GnRH neurons communicate directly with TIDA neurons in the adult female. Furthermore, ERalpha activation in TIDA neurons may be involved in the formation of connections between GnRH neurons and TIDA neurons.

Chemical coding of GABA(B) receptor-immunoreactive neurones in hypothalamic regions regulating body weight

Gamma-aminobutyric acid (GABA) interacts with hypothalamic neuronal pathways regulating feeding behaviour. GABA has been reported to stimulate feeding via both ionotropic GABA(A) and metabotropic GABA(B) receptors. The functional form of the GABA(B) receptor is a heterodimer consisting of GABA(B) receptor-1 (GABA(B)R1) and GABA(B) receptor-2 (GABA(B)R2) proteins. Within the heterodimer, the GABA-binding site is localized to GABA(B)R1. In the present study, we used an antiserum to the GABA(B)R1 protein in order to investigate the cellular localization of GABA(B)R1-immunoreactive neurones in discrete hypothalamic regions implicated in the control of body weight. The colocalization of GABA(B)R1 immunoreactivity with different chemical messengers that regulate food intake was analysed. GABA(B)R1-immunoreactive cell bodies were found in the periventricular, paraventricular (PVN), supraoptic, arcuate, ventromedial hypothalamic, dorsomedial hypothalamic, tuberomammillary nuclei and lateral hypothalamic area (LHA). Direct double-labelling showed that glutamic acid decarboxylase (GAD)-positive terminals were in close contact with GABA(B)R1-containing cell bodies located in all these regions. In the ventromedial part of the arcuate nucleus, GABA(B)R1-immunoreactive cell bodies were found to contain neuropeptide Y, agouti-related peptide (AGRP) and GAD. In the ventrolateral part of the arcuate nucleus, GABA(B)R1-immunoreactive cell bodies were shown to contain pro-opiomelanocortin and cocaine- and amphetamine-regulated transcript. In the LHA, GABA(B)R1 immunoreactivity was present in both melanin-concentrating hormone- and orexin-containing cell populations. In the tuberomammillary nucleus, GABA(B)R1-immunoreactive cell bodies expressed histidine decarboxylase, a marker for histamine-containing neurones. In addition, GAD and AGRP were found to be colocalized in some nerve terminals surrounding GABA(B)R1-immunoreactive cell bodies in the parvocellular part of the PVN. The results may provide a morphological basis for the understanding of how GABA regulates the hypothalamic control of food intake and body weight via GABA(B) receptors.

AMPA glutamate receptor subunits in the guinea pig hypothalamus: distribution and colocalization with progesterone receptor

Excitatory amino acids (EAAs), particularly glutamate, have been implicated in the control of luteinizing hormone (LH) secretion through facilitation of gonadotropin-releasing hormone release. The effects of EAAs are mediated by means of ionotropic glutamate receptors, which are divided into N-methyl-D-aspartate (NMDA) and non-NMDA (kainate and AMPA) subtypes. Moreover, ovarian steroids are responsible for inducing the preovulatory surge of LH and are involved in the actions of EAAs on LH release. Progesterone is directly involved in the potentiating effect of ovarian steroids on the stimulating effect of AMPA neurotransmission on gonadotropin secretion. To broaden our understanding of the role of hypothalamic AMPA receptors in the steroid-induced LH surge, we determined the cellular localization of AMPA receptors in the hypothalamus of guinea pigs by using antibodies that recognize the GluR1, GluR2, GluR2/3, or GluR4 subunits, and then we examined the neuroanatomic relationships between these receptors and the progesterone receptor (PR). Different patterns of immunostaining within the preoptic area and hypothalamus were evident with the antibodies to the four subunits with marked contrasts between moderate staining for GluR1, intensely stained structures for GluR2 and GluR2/3, and little specific staining for GluR4. Immunoreactive (IR) neurons were visualized in many regions, including the two regions known to contain a dense population of estradiol-induced PR-IR cells: the preoptic periventricular and ventrolateral hypothalamic nuclei. Approximately 60% of GluR1-IR and 39% of GluR2-IR cells in the preoptic region possessed PR, whereas 46% of GluR1-IR and 54% of GluR2-IR cells in the ventrolateral nucleus expressed PR. These neuroanatomic results suggest that the coordinated actions of progesterone and glutamatergic inputs on mammalian reproductive functions are integrated at the cellular level.

Colocalization of progesterone receptors in parvicellular dynorphin neurons of the ovine preoptic area and hypothalamus

Recent evidence suggests that the dynorphin-kappa receptor opioid system acts to mediate the inhibitory effect of progesterone (P) on GnRH pulse frequency during the luteal phase of the ovine estrous cycle. It is known that progesterone receptors (PRs) are required for the actions of P on GnRH secretion. Therefore, if P acts directly on dynorphin (DYN) neurons, then these neurons should contain PRs. To test this hypothesis, we used a dual-label immunoperoxidase procedure to visualize PRs and DYN in the preoptic area (POA) and hypothalamus of ovary-intact ewes killed during the luteal phase of the estrous cycle. The PR was colocalized in more than 90% of parvicellular DYN neurons in the POA, anterior hypothalamus (AHA), and arcuate nucleus (ARC). By contrast, none of magnocellular DYN cells of the paraventricular and supraoptic nuclei coexpressed immunoreactive PRs. The high percentage of colocalization of PRs in parvicellular DYN cells of the POA, AHA, and ARC suggests that these cells are prime targets of P. In addition, DYN cells in the ARC, but not the POA or AHA, were found to receive synaptic inputs from DYN-positive axon terminals. This observation raises the possibility that an ultrashort feedback loop controls the release of DYN from ARC neurons.

Influence of estradiol on NADPH diaphorase/neuronal nitric oxide synthase activity and colocalization with progesterone or type II glucocorticoid receptors in ovine hypothalamus

Nitric oxide (NO) has been shown to play an important role in both the neuroendocrine reproductive and stress axes, which are closely linked. Because progesterone (P4) receptors (PRs) and glucocorticoid receptors (GRs) are not found in GnRH neurons and the NOergic system has been implicated in the control of GnRH secretion, this study aimed to ascertain whether steroids altered the NOergic system. Our first objective was to map the distribution of NO synthase (NOS) cells in the ovine preoptic area (POA) and hypothalamus and to determine whether NOS activity is enhanced by estradiol (E2) treatment. Using NADPH diaphorase (NADPHd) histochemistry, we found that NADPHd-positive neurons were spread throughout the ovine POA and hypothalamus, and that all NADPHd cells were immunoreactive for NOS. In response to estradiol, a significant increase in the number of NADPHd cells was noted only in the ventrolateral region of the ventromedial nucleus (VMNvl), with no significant difference in the POA or arcuate nucleus. Progesterone and glucocorticoid receptors were colocalized with NADPHd reactive neurons in the POA, arcuate nucleus, and VMNvl of ewes in both treatment groups. In ewes receiving estradiol, the number of NADPHd-positive cells containing steroid receptors in the POA (PR, 81%; GR, 79%) and arcuate nucleus (PR, 89%; GR, 84%) was similar, but in the VMNvl, fewer NADPHd-positive cells contained GR (PR, 88%, GR, 31%). These data show that estradiol up-regulates NOS activity in a site-specific manner and that the influence and possible interaction of progesterone and corticosteroids on NO producing cells may differ according to the neural location.

Ultrastructural localization of orexin-1 receptor in pre- and post-synaptic neurons in the rat arcuate nucleus

The distribution and ultrastructural localization of the orexin-1 receptor (OX(1)R) in the rat arcuate nucleus were studied using immunocytochemical techniques. OX(1)R-containing neurons were found throughout the nucleus, but were concentrated in its posterior region. Both OX(1)R-positive perikarya and dendrites were found to receive synapses from other unknown axon terminals. In addition, a small number of OX(1)R-positive axon terminals were observed. These OX(1)R-immunoreactive axon terminals were often found to make synapses on unidentified immunonegative dendritic processes. The present results indicate that orexin may act on food intake regulating neurons through both pre- and post-synaptic OX(1)R.

Regulation by gonadal steroids of the mRNA encoding for a type I receptor for TGF-beta in the female rat hypothalamus

We have recently shown that the mRNA encoding for a type I receptor for transforming growth factor beta and activin - named B1 - is expressed in hypothalamic areas implicated in gonadotropin-releasing hormone regulation, particularly in estrogen-receptive regions. In the present study, we examined whether ovarian steroids may regulate expression of B1 mRNA in the hypothalamus. Comparing relative levels of B1 mRNA expression in ovariectomized (OVX), OVX + estradiol-treated, and OVX + estradiol + progesterone-treated female rats, we observed that estrogen significantly (p < 0.05) downregulated B1 mRNA levels in the anteroventral periventricular nucleus (by 12.5%), medial preoptic nucleus (by 27.5%), and arcuate nucleus (by 29.5%). In contrast, no effects of gonadal steroids were observed in the median preoptic nucleus. We next examined whether cells expressing B1 mRNA may be direct targets for the action of estrogen. Using an in situ hybridization coupled to immunohistochemical labeling, we found that many B1-mRNA-expressing cells also exhibited estrogen receptor alpha immunoreactvity in anteroventral periventricular nucleus, medial preoptic nucleus, and arcuate nucleus. Taken together, these results reveal that estrogen may directly modulate expression of B1 mRNA in the hypothalamus and support the idea that transforming growth factors beta play an important role in the hypothalamic control of gonadotropin-releasing hormone function.

Effects of dietary fat types on body fatness, leptin, and ARC leptin receptor, NPY, and AgRP mRNA expression

Some, but not all, fats are obesogenic. The aim of the present studies was to investigate the effects of changing type and amount of dietary fats on energy balance, fat deposition, leptin, and leptin-related neural peptides: leptin receptor, neuropeptide Y (NPY), agouti-related peptide (AgRP), and proopiomelanocortin (POMC), in C57Bl/6J mice. One week of feeding with a highly saturated fat diet resulted in ~50 and 20% reduction in hypothalamic arcuate NPY and AgRP mRNA levels, respectively, compared with a low-fat or an n-3 or n-6 polyunsaturated high-fat (PUFA) diet without change in energy intake, fat mass, plasma leptin levels, and leptin receptor or POMC mRNA. Similar neuropeptide results were seen at 7 wk, but by then epididymal fat mass and plasma leptin levels were significantly elevated in the saturated fat group compared with low-fat controls. In contrast, fat and leptin levels were reduced in the n-3 PUFA group compared with all other groups. At 7 wk, changing the saturated fat group to n-3 PUFA for 4 wk completely reversed the hyperleptinemia and increased adiposity and neuropeptide changes induced by saturated fat. Changing to a low-fat diet was much less effective. In summary, a highly saturated fat diet induces obesity without hyperphagia. A regulatory reduction in NPY and AgRP mRNA levels is unable to effectively counteract this obesogenic drive. Equally high fat diets emphasizing PUFAs may even protect against obesity.

Several subpopulations of neuropeptide Y-containing neurons exist in the infundibular nucleus of sheep: an immunohistochemical study of animals on different diets

Conversely to rodents, the involvement of hypothalamic neuropeptide Y (NPY) neurons in the control of nutrition is poorly understood in ruminants such as sheep. Therefore, the aim of this work was to describe the NPY neurons of the diencephalon in ewes submitted to different diets. In colchicine-treated animals, large populations of NPY-immunoreactive (-ir) neurons were observed in a ventral and a lateral subpopulation of the infundibular nucleus (IN), in the median eminence, the pituitary stalk, and the dorsomedian and dorsocaudal nuclei. No labeled perikaryon was observed in the magnocellular neurons of the hypothalamus, although numerous labeled fibers were noted in the neural part of the pituitary. The pattern of distribution of NPY-ir neurons in the sheep hypothalamus is similar in many ways to those of rodents, but it presents also many specific characteristics that have not been previously described. In ewes that were fasted for 24 hours, or fed ad libitum, the number of NPY-ir neurons was the same whatever the hypothalamic structures. In underfed ewes (40% of maintenance for 24 weeks), the lateral subpopulation of the IN presented a higher number of NPY-ir neurons than observed in the 100% fed ewes. Conversely, in the ventral subpopulation, the animals refed ad libitum (at least 150% of maintenance for 4 days) presented a lower number of NPY-ir neurons than the other groups. The other NPY neuronal populations of the hypothalamus were not significantly modified by the dietary treatments. For the first time, we demonstrated the presence of two functionally distinct subpopulations of NPY neurons in the sheep IN. The variations of labeled neurons were correlated with plasma nonesterified fatty acid levels but not with leptinemia.

Attenuation of diabetic hyperphagia in neuropeptide Y--deficient mice

The combined effects of increased hypothalamic signaling by neuropeptide Y (NPY) and decreased signaling by melanocortins are hypothesized to stimulate food intake when body fat stores are depleted. To investigate NPY's role in the hyperphagic response to uncontrolled diabetes, streptozotocin (STZ) (200 mg/kg intraperitoneally) or saline vehicle was given to NPY-deficient (Npy(--/--)) and wild-type (Npy(+/+)) mice. In Npy(+/+) mice, STZ-induced diabetes increased mean daily food intake to plateau values 50% above baseline intake (+2.0 +/- 0.6 g/day; P < or = 0.05), an effect that was not seen in STZ-treated Npy(--/--) mice (+0.8 +/- 0.1 g/day; NS), despite comparably elevated levels of plasma glucose and comparably decreased levels of body weight, fat content, and plasma leptin. Unlike the impaired feeding response to uncontrolled diabetes, Npy(--/--) mice exhibit intact hyperphagic responses to fasting (Erickson et al. [1], Nature 381:415-418, 1996). To investigate whether differences in hypothalamic melanocortin signaling can explain this discrepancy, we used in situ hybridization to compare the effects of STZ-diabetes and fasting on pro-opiomelanocortin (POMC) and agouti-related peptide (AgRP) mRNA levels in the hypothalamic arcuate nucleus (ARC) of Npy(--/--) and Npy(+/+) mice. AgRP mRNA levels were increased by both fasting and STZ-diabetes, but the increase in STZ-diabetes was small (50-80%) compared with the effect of fasting (approximately 20-fold increase of AgRP mRNA). STZ-diabetes also lowered POMC mRNA levels by 65% in the ARC of Npy(+/+) mice (P less-than-or-equal 0.05) but by only 11% in Npy(--/--) mice (NS); fasting significantly lowered POMC mRNA levels in both genotypes. We conclude that NPY is required for both the increase of food intake and the decrease of hypothalamic POMC gene expression induced by uncontrolled diabetes. In contrast, NPY is not required for either of these responses when the stimulus is food deprivation. Moreover, fasting is a more potent stimulus to hypothalamic AgRP gene expression than is STZ-diabetes. Therefore, central nervous system melanocortin signaling appears to be suppressed more effectively by fasting than by uncontrolled diabetes, which provides a plausible explanation for differences in the feeding response to these two stimuli in mice lacking NPY.

Decreased expression of fos-related antigens (FRAs) in the hypothalamic dopaminergic neurons after immunoneutralization of endogenous prolactin

In our previous studies we found that administration of exogenous prolactin increased dopamine turnover in the terminal areas of the hypothalamic dopaminergic neurons controlling prolactin secretion from pituitary lactotrophs. In this study we investigated the effect of immunoneutralization of endogenous prolactin on the expression of FRAs in the tuberoinfundibular dopaminergic (TIDA), tuberohypophysial dopaminergic (THDA), and periventricular hypothalamic dopaminergic (PHDA) subpopulations of the hypothalamic dopaminergic neurons. Female rats were ovariectomized on d 0 of the experiment. At 1000 h of d 10, all animals were injected with 20 microg of 17-beta-estradiol sc to induce a proestrous-like surge of prolactin at 1700 h the next day. At 1000 h on d 11, half of the animals were injected with 200 microL of rabbit anti-rat prolactin antiserum ip, while the controls received normal rabbit serum. Groups of animals were sacrificed for immunocytochemistry in 2 h intervals between 1300 and 2100 h. Double-label immunocytochemistry for FRAs and tyrosine hydroxylase (TH) was performed and the results are presented as percentage of TH-immunoreactive neurons expressing FRAs. In the control animals, expression of FRAs decreased at 1500 h, gradually increased by 1900 h, but was lower than the basal levels by 2100 h. Expression of FRAs was significantly lower at 1900 h in the PHDA, THDA and TIDA neurons of prolactin antiserum treated rats than in the controls. These results indicate that elimination of endogenous prolactin from the circulation lowers the activity and/or prevents the reactivation of neuroendocrine dopaminergic neurons at the beginning of the dark phase.

Immunohistochemical analyses of thyroid-specific enhancer-binding protein in the fetal and adult rat hypothalami and pituitary glands

Thyroid-specific enhancer-binding protein (T/EBP), also known as NKX2.1 or TTF-1, regulates the expression of thyroid- and lung-specific genes. The t/ebp/Nkx2.1-null mutant mouse was stillborn but lacked the thyroid gland, pituitary gland, ventral region of the forebrain and normal lungs. These data demonstrated that T/EBP/NKX2.1 plays an important role not only in tissue-specific gene expressions in adults but also in genesis of these organs during development. Although the expression of t/ebp/Nkx2.1 in the brain has been reported, its function in the brain remains unknown. The present study was designed to determine the localization of T/EBP/NKX2.1 in the hypothalamus and pituitary gland of fetal and adult rats by immunohistochemistry as the first step toward understanding the function of T/EBP/NKX2.1 in the rat brain. In the fetal rat hypothalamus, T/EBP/NKX2.1 was localized widely in the ventral hypothalamic areas. In the adult rat brain, T/EBP/NKX2.1 was localized in the ventromedial hypothalamic nucleus, medial tuberal nucleus, arcuate nucleus and mammillary body. No T/EBP/NKX2.1 immunoreactivity was observed in the anterior or intermediate lobe of the pituitary gland in either fetal or adult rats. On the other hand, immunoreactive T/EBP/NKX2.1 was found in the posterior lobe of the pituitary gland. This paper presents results of detailed analyses of the distributions of T/EBP/NKX2.1 protein in the fetal and adult rat hypothalami and pituitary glands, and these results should provide important information for understanding the function of T/EBP/NKX2.1 in the brain.

Role of alpha-MSH in the regulation of consummatory behavior: immunohistochemical evidence

Central injection of alpha-melanocyte-stimulating hormone (alpha-MSH) decreases food intake, suggesting a role for this peptide in the mediation of satiety. Inasmuch as alpha-MSH also supports the development of taste aversions under certain conditions, the nature of its influence on ingestive behavior, i.e., whether it is related to satiety or aversion, remains unclear. In the present studies, we used immunostaining, including that for c-Fos as a marker of neuronal activation, to further substantiate the physiological role for alpha-MSH in the regulation of consummatory behavior. We found that an increase in activation of alpha-MSH neurons in the arcuate nucleus coincided with meal termination. Administration of powerful aversive agents, LiCl and CuSO(4), did not stimulate alpha-MSH cells but did induce pronounced activation of oxytocin (OT) and vasopressin (VP) neurons, the final components of circuitry mediating aversion. We observed fewer Fos-positive OT/VP neurons after alpha-MSH injection into the lateral ventricle or into the hypothalamic paraventricular nucleus, treatments that cause mild or no aversion, respectively. The degree of activation of OT/VP neurons paralleled the magnitude of aversive response to a given treatment. Our data support the hypothesis that, in the arcuate nucleus, alpha-MSH acts as a satiety mediator independent from aversion-related mechanisms.

Expression of the melanin-concentrating hormone (MCH) receptor mRNA in the rat brain

The melanin-concentrating hormone (MCH) system is thought to be an important regulator of food intake. Recently the orphan G protein-coupled receptor SLC-1 was identified as the MCH receptor (MCHR). Preliminary analyses of MCHR mRNA distribution have supported a role for the MCH system in nutritional homeostasis. We report here a complete anatomical distribution of the MCHR mRNA. We have found high levels of expression of MCHR mRNA in most anatomical areas implicated in control of olfaction, with the exception of the main olfactory bulb. Dense labeling was also detected in the hippocampal formation, subiculum, and basolateral amygdala, all of which are important in learning and memory, and in the shell of the nucleus accumbens, a substrate for motivated behavior and feeding. Within the hypothalamus, MCHR mRNA was moderately expressed in the ventromedial nucleus, arcuate nucleus, and zona incerta, all of which serve key roles in the neuronal circuitry of feeding. In the brainstem, strong expression was observed in the locus coeruleus, which is implicated in arousal, as well as in nuclei that contribute to orofacial function and mastication, including the facial, hypoglossal, motor trigeminal, and dorsal motor vagus nuclei. In most regions there was a good correspondence between MCHR mRNA distribution and that of MCH-immunoreactive fibers. Taken together, these data suggest that MCH may act at various levels of the brain to integrate various aspects of feeding behavior. However, the extensive MCHR distribution throughout the brain suggests that this receptor may play a role in other functions, most notably reinforcement, arousal, sensorimotor integration, and autonomic control.

Hypothalamic control of photoperiod-induced cycles in food intake, body weight, and metabolic hormones in rams

This study used a hypothalamo-pituitary disconnected (HPD) sheep model to investigate the central regulation of long-term cycles in voluntary food intake (VFI) and body weight (BW). VFI, BW, and circulating concentrations of metabolic hormones [alpha-melanocyte-stimulating hormone (alpha-MSH), insulin-like growth factor-1 (IGF-1), insulin, and leptin] were measured in HPD and control Soay rams exposed to alternating 16 weekly periods of long and short days for 80 wk. In the controls, the physiology was cyclical with a 32-wk periodicity corresponding to the lighting regimen. VFI and BW increased under long days to a maximum early into short days, and there were associated increases in blood concentrations of alpha-MSH, insulin, and leptin. In the HPD rams, there were no significant photoperiod-induced changes in any of the parameters. VFI increased after surgery for 8 wk and then gradually declined, although BW increased progressively and the HPD rams became obese. Concentrations of alpha-MSH, insulin, and leptin in peripheral blood were permanently increased (>200%), and levels of IGF-1 decreased (<55%). The HPD lesion effectively destroyed the entire median eminence [no nerve terminals immunostained for tyrosine hydroxylase (TH) and gonadotropin-releasing hormone] and the adjacent arcuate nucleus (no perikarya immunostained for proopiomelanocortin or TH, and no cells expressed neuropeptide Y mRNA). The results support the conclusion that arcuate hypothalamic systems generate long-term rhythms in VFI, BW, and energy balance.

Homologous upregulation of sst2 somatostatin receptor expression in the rat arcuate nucleus in vivo

In vitro studies using various cell systems have provided conflicting results regarding homologous regulation of somatostatin (SRIH) receptors, and information on whether SRIH regulates the expression of its own receptors in vivo is lacking. In the present study we examined, by in situ hybridization, the effects of pretreatment with the sst2-preferring SRIH analog, octreotide, in vivo, on mRNA levels of two SRIH receptor subtypes, sst1 and sst2, in rat brain and pituitary. (125)I-[DTrp(8)]-SRIH binding was also measured in these regions. Three hours after the iv injection of 50 microg octreotide to conscious adult male rats, there was a 46% increase (p < 0.01) in the labeling density of sst2 mRNA-expressing cells in the hypothalamic arcuate nucleus compared to normal saline-pretreated controls, but not in any of the other brain regions examined. Computer-assisted image analysis revealed that 3 h exposure to octreotide significantly (p < 0.01) augmented both the number and labeling density of sst2 mRNA-expressing cells in the arcuate nucleus, compared to those in saline-treated controls. By contrast, within the anterior pituitary gland, in vivo exposure to octreotide did not affect the expression of sst2 mRNA. No changes in sst1 mRNA-expressing cells were observed after octreotide treatment in any of the regions measured, indicating that the observed effects were homologous, i.e. specific of the receptor subtype stimulated. Octreotide pretreatment was also without effect on the density of (125)I-[DTrp(8)]-SRIH binding in either the arcuate nucleus or pituitary. These results demonstrate, for the first time, that SRIH preexposure in vivo upregulates the expression of a subtype of its own receptors, sst2, within the central nervous system. They further suggest that pretreatment with SRIH in vivo does not cause sst2 receptor desensitization in arcuate nucleus and pituitary. Such homologous regulatory mechanisms may play an important role in the neuroendocrine control of growth hormone (GH) secretion by the arcuate nucleus.

GABAergic nature of hypothalamic leptin target neurones in the ventromedial arcuate nucleus

Leptin is an adipose tissue-derived cytokine hormone, which reduces body weight via interactions with hypothalamic neurones. Leptin receptors capable of activating the JAK-STAT signal transduction pathway are expressed at high levels in the hypothalamus, particularly in the arcuate nucleus. In order to identify the chemical mediators of leptin's action in the hypothalamus, we have examined whether GABA neurones of the hypothalamic arcuate nucleus contain leptin receptors and the leptin-activated transcription factor STAT3. GABAergic neurones, as visualized by antisera to the GABA-synthesizing enzyme glutamic acid decarboxylase (GAD) and GABA, were demonstrated in the ventromedial and ventrolateral parts of the arcuate nucleus. GABA neurones in the ventromedial arcuate nucleus were shown to contain leptin receptor immunoreactivity, as revealed using an antiserum generated to a sequence common to all isoforms of the leptin receptor (Ob-R), as well as an antiserum generated to the carboxy-terminal end of the long leptin receptor (Ob-Rb), and immunoreactivity for the leptin-induced signal transduction molecule STAT3. Ventromedial GABA neurones were also shown to contain neuropeptide Y, whereas ventrolateral proopiomelanocortin-containing neurones lacked GAD and GABA immunoreactivity. Levels of mRNA for GAD65, GAD67 and the vesicular GABA transporter (VGAT) were analysed in the arcuate nucleus of leptin-deficient ob/ob mice and lean control mice by in situ hybridization. No significant differences in GAD65, GAD67 or VGAT mRNA were detected in the arcuate nucleus of ob/ob mice as compared to lean control mice. The presence of leptin receptor and STAT3 in GABAergic arcuate neurones, but absence of changes in gene transcription for GAD and VGAT mRNA suggests, that leptin does not transcriptionally regulate the expression of proteins involved in GABAergic transmission in arcuate neurones. However, mechanisms other than transcriptional regulation for leptin to influence arcuate GABA neurones may exist.

A possible role of neuropeptide Y as a mediator of undernutrition to the hypothalamic gonadotropin-releasing hormone pulse generator in goats

To understand central mechanisms for nutritional infertility, the activity of the GnRH pulse generator was directly assessed in ovariectomized (OVX) goats under several experimental conditions by recording characteristic increases in the multiple-unit activity (volleys). When estradiol (E(2))-treated animals were fasted for 4-5 days, the activity of the GnRH pulse generator was gradually suppressed, and the volley interval at the end of fasting was significantly prolonged, compared with that during the feeding period (67.4 vs. 49.3 min, n = 5, P < 0.01). On the other hand, such a significant effect on the pulse generator was not observed in OVX goats. In the second experiment, the animals received a bolus intracerebroventricular injection of several doses (0, 2, 5, and 20 microg/400 microl) of neuropeptide Y (NPY). Exogenous NPY dose-dependently inhibited the pulse generator activity. At the highest dosage, the 1st posttreatment volley interval was significantly longer than that of the pretreatment (112.4 vs. 32.6 min, n = 5, P < 0.01) in OVX goats. The suppressive effect of NPY was similarly observed in OVX+E(2) goats. Further, when NPY was infused (10 microg/200 microl.h for 6 h) into OVX goats, the activity of the GnRH pulse generator was almost completely inhibited during the infusion period. Hypothalamic sites responding to fasting were immunohistochemically evaluated using an antibody for Fos in castrated goats. Fos-immunoreactive neurons were found in areas adjacent to the third ventricle. Double-labeling immunohistochemistry revealed that a subpopulation of NPY neurons in the arcuate nucleus was activated in response to fasting. These results demonstrate that: 1) the activity of the GnRH pulse generator is suppressed by fasting in the presence of E(2); 2) exogenous NPY inhibits the activity of the GnRH pulse generator regardless of the presence of E(2); and 3) several hypothalamic neurons or regions, including those containing NPY in the arcuate nucleus, are activated by fasting. Collectively, these observations suggest that NPY acts as a mediator of undernutrition to the GnRH pulse generator.

Neuropeptide Y has a central inhibitory action on the hypothalamic-pituitary-thyroid axis

Recent evidence suggests that neuropeptide Y (NPY), originating in neurons in the hypothalamic arcuate nucleus, is an important mediator of the effects of leptin on the central nervous system. As these NPY neurons innervate hypophysiotropic neurons in the hypothalamic paraventricular nucleus (PVN) that produce the tripeptide, TRH, we raised the possibility that NPY may be responsible for resetting of the hypothalamic-pituitary-thyroid (HPT) axis during fasting. To test this hypothesis, the effects of intracerebroventricularly administered NPY on circulating thyroid hormone levels and proTRH messenger RNA in the PVN were studied by RIA and in situ hybridization histochemistry, respectively. NPY administration suppressed circulating levels of thyroid hormone (T(3) and T(4)) and resulted in an inappropriately normal or low TSH. These alterations were associated with a significant suppression of proTRH messenger RNA in the PVN, indicating that NPY infusion had resulted in a state of central hypothyroidism. Similar observations were made in NPY-infused animals pair fed to the vehicle-treated controls. These data are reminiscent of the effect of fasting on the thyroid axis and indicate that NPY may play a major role in the inhibition of HPT axis during fasting.