Ninjin'yoeito modulates feeding and activity under negative energy balance conditions via the NPY system.

The central and peripheral neuropeptide Y (NPY) system is critically involved in feeding and energy homeostasis control. Disease conditions as well as aging can lead to reduced functionality of the NPY system and boosting it represents a promising option to improve health outcomes in these situations. Here we show that Ninjin-yoeito (NYT), a Japanese kampo medicine comprising twelve herbs, and known to be effective to treat anorexia and frailty, mediates part of its action via NPY/peptide YY (PYY) related pathways. Especially under negative energy homeostasis conditions NYT is able to promote feeding and reduces activity to conserve energy. These effects are in part mediated via signalling through the NPY system since lack of Y4 receptors or PYY leading to modification in these responses highlighting the possibility for combination treatment to improve aging related conditions on energy homeostasis control.

Actions of NPY, and its Y1 and Y2 receptors on pulsatile growth hormone secretion during the fed and fasted state.

The hypothalamic NPY system plays an important role in regulating food intake and energy expenditure. Different biological actions of NPY are assigned to NPY receptor subtypes. Recent studies demonstrated a close relationship between food intake and growth hormone (GH) secretion; however, the mechanism through which endogenous NPY modulates GH release remains unknown. Moreover, conclusive evidence demonstrating a role for NPY and Y-receptors in regulating the endogenous pulsatile release of GH does not exist. We used genetically modified mice (germline Npy, Y1, and Y2 receptor knock-out mice) to assess pulsatile GH secretion under both fed and fasting conditions. Deletion of NPY did not impact fed GH release; however, it reversed the fasting-induced suppression of pulsatile GH secretion. The recovery of GH secretion was associated with a reduction in hypothalamic somatotropin release inhibiting factor (Srif; somatostatin) mRNA expression. Moreover, observations revealed a differential role for Y1 and Y2 receptors, wherein the postsynaptic Y1 receptor suppresses GH secretion in fasting. In contrast, the presynaptic Y2 receptor maintains normal GH output under long-term ad libitum-fed conditions. These data demonstrate an integrated neural circuit that modulates GH release relative to food intake, and provide essential information to address the differential roles of Y1 and Y2 receptors in regulating the release of GH under fed and fasting states.

The identification of neuropeptide Y receptor subtype involved in phenylpropanolamine-induced increase in oxidative stress and appetite suppression.

Hypothalamic neuropeptide Y (NPY) and superoxide dismutase (SOD) have been reported to participate in the regulation of appetite-suppressing effect of phenylpropanolamine (PPA), a sympathomimetic agent. This study explored whether Y1 receptor (Y1R) and/or Y5 receptor (Y5R) was involved in this regulation. Wistar rats were treated with PPA for 24 h. Changes in food intake and hypothalamic NPY, Y1R, Y5R, and SOD contents were assessed and compared. Results showed that food intake and NPY contents were decreased following PPA treatment, while Y1R and SOD contents were increased and Y5R contents remained unchanged. Moreover, although Y1R or Y5R knockdown by themselves could modify the food intake, Y1R but not Y5R knockdown could modify PPA-induced anorexia as well as NPY and SOD contents. In addition, selective inhibition of Y1R but not Y5R could modulate PPA-induced anorexia. It is suggested that Y1R but not Y5R participates in the anorectic response of PPA via the modulation of NPY and SOD. Results provide molecular mechanism of NPY-mediated PPA anorexia and may aid the understanding of the toxicology of PPA.

Y1 receptor knockout increases nociception and prevents the anti-allodynic actions of NPY.

OBJECTIVE: Recent pharmacologic studies in our laboratory have suggested that the spinal neuropeptide Y (NPY) Y1 receptor contributes to pain inhibition and to the analgesic effects of NPY. To rule out off-target effects, the present study used Y1-receptor-deficient (-/-) mice to further explore the contribution of Y1 receptors to pain modulation. METHODS AND RESULTS: Y1(-/-) mice exhibited reduced latency in the hotplate test of acute pain and a longer-lasting heat allodynia in the complete Freund's adjuvant (CFA) model of inflammatory pain. Y1 deletion did not change CFA-induced inflammation. Upon targeting the spinal NPY systems with intrathecal drug delivery, NPY reduced tactile and heat allodynia in the CFA model and the partial sciatic nerve ligation model of neuropathic pain. Importantly, we show for the first time that NPY does not exert these anti-allodynic effects in Y1(-/-) mice. Furthermore, in nerve-injured CD1 mice, concomitant injection of the potent Y1 antagonist BIBO3304 prevented the anti-allodynic actions of NPY. Neither NPY nor BIBO3304 altered performance on the Rotorod test, arguing against an indirect effect of motor function. CONCLUSION: The Y1 receptor contributes to pain inhibition and to the analgesic effects of NPY.

Regulation of bone remodeling by the central and peripheral nervous system.

The homeostatic nature of bone remodeling has become a notion further supported lately by the demonstration that neuropeptides and their receptors regulate osteoblast and osteoclast function in vivo. Following initial studies reporting the presence of nerves and nerve-derived products within the bone microenvironment and the expression of receptors for these neuropeptides in bone cells, new experimental and mechanistic evidence based on in vivo murine genetic and pharmacologic models recently demonstrated that inputs from the central and peripheral nervous system feed into the already complex regulatory machinery controlling bone remodeling. The function of a number of "osteo-neuromediators" has been characterized, including norepinephrine and the beta2-adrenergic receptor, Neuropeptide Y and the Y1 and Y2 receptors, endocannabinoids and the CB1 and CB2 receptors, as well as dopamine, serotonin and their receptors and transporters, Calcitonin gene-related peptide, and neuronal NOS. This new body of evidence suggests that neurons in the central nervous system integrate clues from the internal and external milieux, such as energy homeostasis, glycemia or reproductive signals, with the regulation of bone remodeling. The next major tasks in this new area of bone biology will be to understand, at the molecular level, the mechanisms by which common central neural systems regulate and integrate these major physiological functions, the relative importance of the central and peripheral actions of neuropeptides present in both compartments and their relationship, and how bone cells signal back to central centers, because the definition of a homeostatic function implies the existence of feedback signals. Together, these findings shed a new light on the complexity of the mechanisms regulating bone remodeling and uncovered new potential therapeutic strategies for the design of bone anabolic treatments. This review summarizes the latest advances in this area, focusing on investigations based on in vivo animal studies.

Selective role of neuropeptide Y receptor subtype Y2 in the control of gonadotropin secretion in the rat.

Different signals with key roles in energy homeostasis regulate the reproductive axis. These include neuropeptide Y and polypeptide YY(3-36), whose type Y(2) receptor is the most abundant of this family in the brain. We evaluated herein the putative roles of Y(2) receptors in the control of gonadotropin secretion by means of central administration of PYY(13-36) (agonist of Y(2) receptors) and BIIE 0246 (antagonist of Y(2) receptors) to intact and orchidectomized male rats. In addition, the ability of PYY(13-36) to elicit GnRH and gonadotropin secretion in vitro and the impact of fasting on LH responses to PYY(13-36) in vivo were also monitored. Central administration of PYY(13-36) significantly decreased the circulating levels of both gonadotropins, an effect that was observed in prepubertal and adult rats. Yet a dual action of Y(2) receptors in the control of male gonadotropic axis was evidenced as their activation induced 1) stimulation of gonadotropin responses to GnRH at the pituitary but 2) inhibition of GnRH secretion at the hypothalamus. Antagonization of Y(2) receptors failed to modify basal LH secretion in intact males either after being fed ad libitum or after being fasted. In contrast, their central blockade in orchidectomized rats evoked a significant increase in circulating LH and FSH level, suggesting the constitutive activation of Y(2) receptor in such stimulated conditions. In summary, our data evidence a complex mode of action of Y(2) receptors in the control of gonadotropic axis, with stimulatory and inhibitory actions at different levels of the system that are sensitive to the gonadal status.

Combined deletion of Y1, Y2, and Y4 receptors prevents hypothalamic neuropeptide Y overexpression-induced hyperinsulinemia despite persistence of hyperphagia and obesity.

Neuropeptide Y (NPY) is a key regulator of energy homeostasis and is implicated in the development of obesity and type 2 diabetes. Whereas it is known that hypothalamic administration of exogenous NPY peptides leads to increased body weight gain, hyperphagia, and many hormonal and metabolic changes characteristic of an obesity syndrome, the Y receptor(s) mediating these effects is disputed and unclear. To investigate the role of different Y receptors in the NPY-induced obesity syndrome, we used recombinant adeno-associated viral vector to overexpress NPY in mice deficient of selective single or multiple Y receptors (including Y1, Y2, and Y4). Results from this study demonstrated that long-term hypothalamic overexpression of NPY lead to marked hyperphagia, hypogonadism, body weight gain, enhanced adipose tissue accumulation, hyperinsulinemia, and other hormonal changes characteristic of an obesity syndrome. NPY-induced hyperphagia, hypogonadism, and obesity syndrome persisted in all genotypes studied (Y1(-/-), Y2(-/-), Y2Y4(-/-), and Y1Y2Y4(-/-) mice). However, triple deletion of Y1, Y2, and Y4 receptors prevented NPY-induced hyperinsulinemia. These findings suggest that Y1, Y2, and Y4 receptors under this condition are not crucially involved in NPY's hyperphagic, hypogonadal, and obesogenic effects, but they are responsible for the central regulation of circulating insulin levels by NPY.

Neuropeptide Y inhibits hypocretin/orexin neurons by multiple presynaptic and postsynaptic mechanisms: tonic depression of the hypothalamic arousal system.

Neurons that release neuropeptide Y (NPY) have important effects on hypothalamic homeostatic regulation, including energy homeostasis, and innervate hypocretin neurons. Using whole-cell patch-clamp recording, we explored NPY actions on hypocretin cells identified by selective green fluorescent protein expression in mouse hypothalamic slices. NPY reduced spike frequency and hyperpolarized the membrane potential of hypocretin neurons. The NPY hyperpolarizing action persisted in tetrodotoxin (TTX), was mimicked by Y1 receptor-selective agonists [Pro34]-NPY and [D-Arg25]-NPY, and was abolished by the Y1-specific antagonist BIBP3226 [(R)-N2-(diphenylacetyl)-N-[(4-hydroxyphenyl)methyl]-D-arginine-amide], consistent with a direct activation of postsynaptic Y1 receptors. NPY induced a current that was dependent on extracellular potassium, reversed near the potassium equilibrium potential, showed inward rectification, was blocked by extracellular barium, and was abolished by GDP-betaS in the recording pipette, consistent with a G-protein-activated inwardly rectifying K+ (GIRK) current. [Pro34]-NPY evoked, and BIBP3226 blocked, the activation of the GIRK-type current, indicating mediation by a Y1 receptor. NPY attenuated voltage-dependent calcium currents mainly via a Y1 receptor subtype. BIBP3226 increased spontaneous spike frequency, suggesting an ongoing Y1 receptor-mediated NPY inhibition. In TTX, miniature EPSCs were reduced in frequency but not amplitude by NPY, NPY13-36, and [D-Trp32]-NPY, but not by [Pro34]-NPY, suggesting the presynaptic inhibition was mediated by a Y2/Y5 receptor. NPY had little effect on GABA-mediated miniature IPSCs but depressed spontaneous IPSCs. Together, these data support the view that NPY reduces the activity of hypocretin neurons by multiple presynaptic and postsynaptic mechanisms and suggest NPY axons innervating hypocretin neurons may tonically attenuate hypocretin-regulated arousal.

The neuropeptide Y Y1 receptor mediates NPY-induced inhibition of the gonadotrope axis under poor metabolic conditions.

Hypothalamic neuropeptide Y (NPY) plays a central role in the control of food intake, energy balance, and modulation of neuroendocrine functions. In particular, an increase in NPY expression participates in the inhibition of the reproductive activity under poor nutritional conditions. The present study was designed to evaluate further the involvement of the Y1 subtype of NPY receptors in these effects. Food intake, body weight gain, and the onset of puberty were studied in groups of wild-type and Y1 deficient mice that were either fed ad libitum or subjected to a 30% restriction in food intake. This moderate feeding restriction induced a similar deficit in body weight gain in wild-type and in Y1 knockout mice. However, although wild-type mice experienced the expected delay of puberty, all mice in the food restriction group and lacking Y1 could go through puberty over the time of the experiment despite decreases in circulating leptin levels and increases in hypothalamic NPY expression. This observation demonstrates that the absence of Y1 impairs the perception of decreasing energy stores by the gonadotrope axis, demonstrating a physiological role for Y1 in the sensing of endogenous metabolic parameters by the hypothalamus.

Orexin neurons express a functional pancreatic polypeptide Y4 receptor.

The receptor subtypes that mediate the effects of neuropeptide Y (NPY) on food intake have not been clearly defined. The NPY Y4 receptor has been identified recently as a potential mediator of the regulation of food intake. The purpose of the present study was to characterize the central site of action of the Y4 receptor using a combination of neuroanatomical and physiological approaches. Using immunocytochemistry, Y4-like immunoreactivity was found to be colocalized with orexin cell bodies in the lateral hypothalamic area (LHA) and orexin fibers throughout the brain. In situ hybridization confirmed the expression of Y4 mRNA in orexin neurons. To determine the functional interaction between Y4 receptors and orexin neurons, we examined the effects of rat pancreatic polypeptide (rPP), a Y4-selective ligand, or NPY, a nonselective ligand, administered directly into the LHA on the stimulation of food and water intake and c-Fos expression. Both rPP and NPY significantly increased food and water intake when they were administered into the LHA, although NPY was a more potent stimulator of food intake. Furthermore, both NPY and rPP significantly stimulated c-Fos expression in the LHA. However, whereas rPP stimulated c-Fos expression in orexin neurons, NPY did not. Neither rPP nor NPY stimulated c-Fos in melanin-concentrating hormone neurons, but both activated neurons of an unknown phenotype in the LHA. These results suggest that a functional Y4 receptor is expressed on orexin neurons and that these neurons are activated in response to a ligand with high affinity for the Y4 receptor (rPP). Although these data suggest a role for central Y4 receptors, the endogenous ligand for this receptor has yet to be clearly established.

Neuropeptide Y1 and Y5 receptors mediate the effects of neuropeptide Y on the hypothalamic-pituitary-thyroid axis.

Neuropeptide Y (NPY) is one of the most important hypothalamic-derived neuropeptides mediating the effects of leptin on energy homeostasis. Central administration of NPY not only markedly stimulates food intake, but simultaneously inhibits the hypothalamic-pituitary-thyroid axis (HPT axis), replicating the central hypothyroid state associated with fasting. To identify the specific NPY receptor subtypes involved in the action of NPY on the HPT axis, we studied the effects of the highly selective Y1 ([Phe7,Pro34]pNPY) and Y5 ([chicken pancreatic polypeptide(1-7), NPY(19-23), Ala31, Aib32 (aminoisobutyric acid), Q34]human pancreatic polypeptide) receptor agonists on circulating thyroid hormone levels and proTRH mRNA in hypophysiotropic neurons of the hypothalamic paraventricular nucleus. The peptides were administered continuously by osmotic minipump into the cerebrospinal fluid (CSF) over 3 d in ad libitum-fed animals and animals pair-fed to artificial CSF (aCSF)-infused controls. Both Y1 and Y5 receptor agonists nearly doubled food intake compared with that of control animals receiving aCSF, similar to the effect observed for NPY. NPY, Y1, and Y5 receptor agonist administration suppressed circulating levels of thyroid hormones (T3 and T4) and resulted in inappropriately normal or low TSH levels. These alterations were also associated with significant suppression of proTRH mRNA in the paraventricular nucleus, particularly in the Y1 receptor agonist-infused group [aCSF, NPY, Y1, and Y5 (density units +/- SEM), 97.2 +/- 8.6, 39.6 +/- 8.4, 19.9 +/- 1.9, and 44.6 +/- 8.4]. No significant differences in thyroid hormone levels, TSH, or proTRH mRNA were observed between the agonist-infused FSanimals eating ad libitum and the agonist-infused animals pair-fed with vehicle-treated controls. These data confirm the importance of both Y1 and Y5 receptors in the NPY-mediated increase in food consumption and demonstrate that both Y1 and Y5 receptors can mediate the inhibitory effects of NPY on the HPT axis.

Important role of hypothalamic Y2 receptors in body weight regulation revealed in conditional knockout mice.

Neuropeptide Y is implicated in energy homeostasis, and contributes to obesity when hypothalamic levels remain chronically elevated. To investigate the specific role of hypothalamic Y2 receptors in this process, we used a conditional Y2 knockout model, using the Cre-lox system and adenoviral delivery of Cre-recombinase. Hypothalamus-specific Y2-deleted mice showed a significant decrease in body weight and a significant increase in food intake that was associated with increased mRNA levels for the orexigenic NPY and AgRP, as well as the anorexic proopiomelanocortin (POMC) and cocaine- and amphetamine-regulated transcript (CART) in the arcuate nucleus. These hypothalamic changes persisted until at least 34 days after Y2 deletion, yet the effect on body weight and food intake subsided within this time. Plasma concentrations of pancreatic polypeptide and corticosterone were 3- to 5-fold increased in hypothalamus-specific Y2 knockout mice. Germ-line Y2 receptor knockout also produced a significant increase in plasma levels of pancreatic polypeptide. However, these mice differed from conditional knockout mice in that they showed a sustained reduction in body weight and adiposity associated with increased NPY and AgRP but decreased POMC and CART mRNA levels in the arcuate nucleus. The transience of the observed effects on food intake and body weight in the hypothalamus-specific Y2 knockout mice, and the difference of this model from germ-line Y2 knockout mice, underline the importance of conditional models of gene deletion, because developmental, secondary, or extrahypothalamic mechanisms may mask such effects in germ-line knockouts.

The neuropeptide Y (NPY) Y1 receptor subtype mediates NPY-induced antidepressant-like activity in the mouse forced swimming test.

The present study was undertaken to investigate the possible antidepressant-like effects of neuropeptide Y (NPY) in the mouse forced swimming test, an animal model widely used for the screening of potential antidepressant drugs. In addition, experiments were performed, using agonists and selective antagonists, to assess the potential role of NPY Y(1) and Y(2) receptor subtypes in this model. Complementary studies were performed in an open field apparatus to rule out any changes in locomotor activity that might have interfered with the interpretation of data from the mouse forced swimming test. Intracerebroventricular injections (0.03 nmole-3 nmole) of NPY, [Leu(31)Pro(34)]PYY (Y(1) agonist), NPY(13-36) (Y(2) agonist), BIBP3226, BIBO3304 (Y(1) antagonists) and BIIE0246 (Y(2) antagonist) were performed 30 min prior to testing in the mouse forced swimming test and open field. NPY administration significantly reduced immobility time in a dose dependent manner (p <.01 vs. control group), as did [Leu(31)Pro(34)]PYY (p <.01 vs. control group) and BIIE0246 (p <.05 vs. control group). In contrast, BIBO3304, BIBP3226 and NPY(13-36) did not display any activity at the doses tested. However, pretreatment with BIBO3304 or BIBP3226 significantly blocked the anti-immobility effects of NPY. Data from the open field demonstrated that BIIE0246 increased horizontal ambulation at the dose found to be active in the forced swimming test. Taken together, our results demonstrate that NPY displays antidepressant-like activity in the mouse forced swimming test, and suggest that this activity is mediated by the NPY Y(1) receptor subtype.

Hypothalamic Y2 receptors regulate bone formation.

Neuropeptide Y (NPY) is a downstream modulator of leptin action, possibly at the level of the arcuate nucleus where NPY neurons are known to express both leptin receptors and Y2 receptors. In addition to the well-described role of NPY and leptin in energy balance and obesity, intracerebroventricular administration of NPY or leptin also causes bone loss. Here we show that Y2 receptor-deficient mice have a twofold increase in trabecular bone volume as well as greater trabecular number and thickness compared with control mice. We also demonstrate that central Y2 receptors are crucial for this process, since selective deletion of hypothalamic Y2 receptors in mature conditional Y2 knockout mice results in an identical increase in trabecular bone volume within 5 weeks. This hypothalamus-specific Y2 receptor deletion stimulates osteoblast activity and increases the rate of bone mineralization and formation, with no effect on osteoblast or osteoclast surface measurements. The lack of any changes in plasma total calcium, leptinemia, or hypothalamo-pituitary-corticotropic, -thyrotropic, -somatotropic, or -gonadotropic output suggests that Y2 receptors do not modulate bone formation by humoral mechanisms, and that alteration of autonomic function through hypothalamic Y2 receptors may play a key role in a major central regulatory circuit of bone formation.

Fasting, leptin treatment, and glucose administration differentially regulate Y(1) receptor gene expression in the hypothalamus of transgenic mice.

NPY is a potent orexigenic signal and represents a key component of targets through which leptin exerts a regulatory restraint on body adiposity. Part of the orexigenic effects of NPY are mediated by hypothalamic NPY-Y(1) receptors. Here we studied the effect of fasting, leptin, and glucose administration on Y(1) receptor gene expression using a transgenic mouse model carrying a mouse Y(1) receptor/LacZ fusion gene. Transgene expression was determined by quantitative analysis of beta-galactosidase histochemical staining in the paraventricular, arcuate, ventromedial, and dorsomedial hypothalamic nuclei and in the medial amygdala, as a control region. Food deprivation for 72 h decreased transgene expression in the paraventricular nucleus but not in the arcuate nucleus. Leptin treatment, that was per se ineffective, counteracted the decrease of transgene expression induced in the paraventricular nucleus by 72 h fasting. Supplementing the drinking water with 10% glucose increased beta-galactosidase expression both in the paraventricular nucleus and arcuate nucleus of control mice. Finally, none of the treatments altered transgene expression in the dorsomedial hyphothalamic, ventromedial, and amygdaloid nuclei. Results suggest that changes in energetic balance affect Y(1) receptor expression in the paraventricular and arcuate nuclei and that leptin regulates the NPY-Y(1) system in the paraventricular nucleus. Different regulatory signals might modulate the NPY-Y(1) transmission in the dorsomedial hyphothalamic and ventromedial hyphothalamic nuclei.

Hypothalamic circuitry of neuropeptide Y regulation of neuroendocrine function and food intake via the Y5 receptor subtype.

Neuropeptide Y (NPY) displays diverse modes of action in the CNS including the modulation of feeding behavior, gonadotropin releasing hormone release, and stress responses. Many of the above physiological actions have been at least partially attributed to actions of NPY on the NPY Y5 receptor subtype. We utilized an antibody directed against the NPY Y5 receptor to characterize the distribution of this receptor in the rat brain. Using Western blot analysis, this antibody recognized a single major band at approximately 57 kD. To further verify the specificity of the antibody, animals were treated for 5 days with antisense oligonucleotides for the Y5 receptor. The antisense treatment significantly reduced food intake and body weight. Furthermore, the Y5 antibody detected a significant decrease in Y5 receptor protein. Y5-like immunoreactivity (-ir) was observed throughout the hypothalamus, thalamus, hippocampus and cortex. Double-label immunofluorescence demonstrated that Y5-ir was colocalized with the following neuronal phenotypes in the hypothalamus, gonadotropin-releasing hormone, neurophysins, corticotropin-releasing hormone, and gamma-amino butyric acid. In addition, functional interactions were demonstrated by the presence of close appositions of NPY fibers with Y5-ir expressing cells. The wide distribution of the Y5 receptor-ir, as well as the colocalization within specific neuronal populations, agrees with the distribution of the Y5 receptor mRNA and the known physiological roles of the NPY/Y5 system. The role of the NPY/Y5 receptor system as a mediator between signals of peripheral energy availability and reproductive neuroendocrine function is discussed.

Emerging functions of neuropeptide Y Y(2) receptors in the brain.

The Y(2) receptor is the predominant neuropeptide Y (NPY) receptor subtype in the brain. Y(2) receptor mRNA is discretely distributed in the brain, including specific subregions of the hippocampus and the hypothalamus, and is largely consistent with the distribution of Y(2) receptor protein demonstrated by radioligand-binding methods. Y(2) receptor-mediated effects have been reported principally based on the observations using the C-terminal fragments of NPY. Recent studies indicate an involvement of the receptor in food intake, gastrointestinal motility, cardiovascular regulation, and neuronal excitability. Very recently, Y(2) receptor selective antagonist has been developed and Y(2) receptor-deficient animals have been created. These new pharmacological tools will help to clarify the roles of this receptor in brain functions.

Acceleration of pubertal development following central blockade of the Y1 subtype of neuropeptide Y receptors.

Pubertal development results from the coordinate secretion of gonadotropin-releasing hormone (GnRH) by hypothalamic GnRH neurons. Central administration of neuropeptide Y (NPY) to prepubertal rats can indefinitely delay sexual maturation by inhibiting this GnRH secretion. The aim of the present study was to further investigate the physiological role of NPY in pubertal development, and to assess the potential involvement of its Y1 receptor subtype in this setting. The timing of pubertal development was determined in juvenile female rats receiving chronic i.c.v. infusion of a specific Y1 receptor antagonist (BIBP 3226), and compared with controls. Although treatment with BIBP 3226 did not affect the age at vaginal opening, animals receiving the Y1 antagonist experienced a quicker progression through puberty, corroborated by a significant increase in pituitary luteinizing hormone content. This effect of BIBP3226 on the gonadotrope axis occurred without apparent toxicity, but was accompanied by a transient decrease in body weight gain on the first day of treatment, suggesting an effect on appetite. Together, our results add to the evidence in favour of a role for NPY in the onset of puberty. They are entirely consistent with the proposed inhibition exerted by endogenous hypothalamic NPY before the onset of pubertal development. They also suggest that the Y1 subtype of NPY receptors is involved in this effect.

Expression of a novel neuropeptide Y receptor subtype involved in food intake: an in situ hybridization study of Y5 mRNA distribution in rat brain.

Our group has reported on the cloning of a novel rat neuropeptide Y (NPY) receptor involved in NPY-induced food intake, the Y5 receptor. The distribution in rat brain of the mRNA encoding this receptor has been determined by in situ hybridization histochemistry, using radiolabeled oligonucleotide probes. Control experiments were carried out in cell lines transfected with either rat Y1 or rat Y5 cDNAs. With the exception of the cerebellum, only the antisense probes yielded hybridization signal in rat brain tissue sections. A number of brain regions contained hybridization signals indicative of Y5 mRNA localization. Chief among these were various hypothalamic nuclei, including the medial preoptic nucleus, the supraoptic nucleus, the paraventricular nucleus, and the lateral hypothalamus. Other regions with substantial hybridization signals included the midline thalamus, parts of the amygdala and hippocampus, and some midbrain and brain-stem nuclei. In general a low density of Y5 mRNA was observed in most cortical structures, with the exception of the cingulate and retrosplenial cortices, each of which contained a moderate abundance of Y5 hybridization signal. The distribution of this receptor mRNA is consistent with a role for the Y5 receptor in food intake and also suggests involvement in other processes mediated by NPY.