Role of the neural pathway from hindbrain to hypothalamus in the regulation of energy homeostasis in rats.

Recent evidence suggests that neural pathways from the hindbrain to the hypothalamus are important for informing the hypothalamus of the body's condition with regard to energy metabolism. Here we examined energy metabolism in rats with transections of the midbrain that severed the neural pathway from the hindbrain to the hypothalamus, and then investigated the levels of various molecules associated with control of energy metabolism in these rats. Food intake and body weight were higher in the midbrain-transected rats than in sham-operated rats. In addition, the midbrain-transected rats showed insulin resistance and hyperleptinemia. Furthermore, the hypothalamic mRNA levels of anorectic proopiomelanocortin and cocaine- and amphetamine-related transcript were significantly lower in midbrain-transected rats than in sham-operated rats. Our findings elucidate the mechanisms of food intake and energy balance from the perspective of multifactorial regulatory systems that underlie functions such as neurohormonal integration.

Coinjection of CCK and leptin reduces food intake via increased CART/TRH and reduced AMPK phosphorylation in the hypothalamus.

CCK and leptin are anorectic hormones produced in the small intestine and white adipose tissue, respectively. Investigating how these hormones act together as an integrated anorectic signal is important for elucidating the mechanisms by which energy balance is maintained. We found here that coadministration of subthreshold CCK and leptin, which individually have no effect on feeding, dramatically reduced food intake in rats. Phosphorylation of AMP-activated protein kinase (AMPK) in the hypothalamus significantly decreased after coinjection of CCK and leptin. In addition, coadministration of these hormones significantly increased mRNA levels of anorectic cocaine- and amphetamine-regulated transcript (CART) and thyrotropin-releasing hormone (TRH) in the hypothalamus. The interactive effect of CCK and leptin on food intake was abolished by intracerebroventricular preadministration of the AMPK activator AICAR or anti-CART/anti-TRH antibodies. These findings indicate that coinjection of CCK and leptin reduces food intake via reduced AMPK phosphorylation and increased CART/TRH in the hypothalamus. Furthermore, by using midbrain-transected rats, we investigated the role of the neural pathway from the hindbrain to the hypothalamus in the interaction of CCK and leptin to reduce food intake. Food intake reduction induced by coinjection of CCK and leptin was blocked in midbrain-transected rats. Therefore, the neural pathway from hindbrain to hypothalamus plays an important role in transmitting the anorectic signals provided by coinjection of CCK and leptin. Our findings give further insight into the mechanisms of feeding and energy balance.

Role of the neural pathway from hindbrain to hypothalamus in interaction of GLP1 and leptin in rats.

Glucagon-like peptide-1 (GLP1) and leptin are anorectic hormones. Previously, we have shown that i.p. coadministration of subthreshold GLP1 with leptin dramatically reduced food intake in rats. In this study, by using midbrain-transected rats, we investigated the role of the neural pathway from the hindbrain to the hypothalamus in the interaction of GLP1 and leptin in reducing food intake. Food intake reduction induced by coinjection of GLP1 and leptin was blocked in midbrain-transected rats. These findings indicate that the ascending neural pathway from the hindbrain plays an important role in transmitting the anorectic signals provided by coinjection of GLP1 and leptin.

Neuropeptide W: an anorectic peptide regulated by leptin and metabolic state.

Neuropeptide W (NPW) is an anorectic peptide produced in the brain. Here, we showed that NPW was present in several hypothalamic nuclei, including the paraventricular hypothalamic nucleus, ventromedial hypothalamic nucleus, lateral hypothalamus, and hypothalamic arcuate nucleus. NPW expression was significantly up-regulated in leptin-deficient ob/ob and leptin receptor-deficient db/db mice. The increase in NPW expression in ob/ob mice was abrogated to control levels after leptin replacement. Leptin induced suppressors of cytokine signaling-3 after phosphorylation of signal transducer and activator of transcription-3 in NPW-expressing neurons. In addition, we demonstrated that NPW reduces feeding via the melanocortin-4-receptor signaling pathway. We also showed that NPW activates proopiomelanocortin and inhibits neuropeptide Y neurons using loose-patch extracellular recording of these neurons identified by promoter-driven green fluorescent protein expression. This study indicates that NPW may play an important role in the regulation of feeding and energy metabolism under the conditions of leptin insufficiency.

Distribution of neuropeptide W in the rat brain.

Neuropeptide W (NPW), which was recently isolated from the porcine hypothalamus, has been identified as the endogenous ligand of the orphan G protein-coupled receptors GPR7 (NPBWR1) and GPR8 (NPBWR2). Infusion of NPW increases food intake in the light phase, whereas in the dark phase, it has the opposite effect. In this study, we used RT-PCR analysis to examine the gene expression of NPW mRNA in the rat brain, and performed a detailed analysis of the distribution of NPW-positive neurons by use of immunohistochemistry at both the light and electron microscopic levels. NPW mRNA expression was demonstrated in the hypothalamic paraventricular nucleus (PVN), arcuate nucleus (ARC), ventromedial nucleus (VMH) and lateral hypothalamus (LH). At the light microscopic level, NPW-like immunoreactive (NPW-LI) cell bodies were found in the preoptic area (POA), PVN, ARC, VMH, LH, PMD (dorsal premammillary nucleus), periaqueductal gray (PAG), lateral parabrachial nucleus (LPB), and prepositus nucleus (Pr). NPW-LI axon terminals were shown in the POA, bed nucleus of the stria terminalis (BST), amygdala, PVN, ARC, VMH, LH, and PAG, LPB. In addition, at the electron microscopic level, NPW-LI cell bodies and dendritic processes were often seen to receive inputs from other unknown neurons in the ARC, PVN, VMH and amygdala. Our observations indicate that NPW-LI neurons widely distributed in the rat brain region. These finding suggest that NPW may have important roles in feeding behavior, energy homeostasis, emotional response and regulation of saliva secretion.

Neuronal interactions between neuropeptide W- and orexin- or melanin-concentrating hormone-containing neurons in the rat hypothalamus.

Neuropeptide W (NPW) was recently discovered as the endogenous ligand for GPR7 and GPR8, which are orphan G protein-coupled receptors isolated from the porcine brain. These receptors are assumed to be involved in feeding regulation and/or energy homeostasis. Recent anatomical studies have revealed that high levels of GPR7 mRNA are distributed in the brain, including the hypothalamus and amygdala. However immunohistochemical studies on the distribution and localization of NPW have revealed differing results concerning whether or not NPW-containing cell bodies and their processes are present in the hypothalamus. Only a few immunohistochemical reports have been published concerning the presence of NPW-containing neurons in the brains of rodents, while there have been no anatomical studies of the co-localization of this neuropeptide with other transmitters. On this basis, we used a specific antiserum against NPW to determine immunohistochemically the presence of NPW-containing neurons in the rat hypothalamus. Many NPW-like immunoreactive cell bodies and their processes could be detected in the caudal region of the lateral hypothalamus but not in its anterior or middle regions. Given this positive identification of NPW-containing neurons in the lateral hypothalamus, we further studied the nature of interaction between NPW-containing neurons and neurons containing feeding regulating peptides such as orexin- and melanin-concentrating hormone (MCH). Very close interactions between NPW-containing nerve processes and orexin- and MCH-containing neuronal cell bodies and processes could be observed. These morphological findings strongly suggest that NPW is involved in the regulation of feeding and/or sleep/arousal behavior through orexin- and/or MCH-mediated neuronal pathways.

Peripheral ghrelin transmits orexigenic signals through the noradrenergic pathway from the hindbrain to the hypothalamus.

Ghrelin, a gastrointestinal peptide, stimulates feeding when administered peripherally. Blockade of the vagal afferent pathway abolishes ghrelin-induced feeding, indicating that the vagal afferent pathway may be a route conveying orexigenic ghrelin signals to the brain. Here, we demonstrate that peripheral ghrelin signaling, which travels to the nucleus tractus solitarius (NTS) at least in part via the vagus nerve, increases noradrenaline (NA) in the arcuate nucleus of the hypothalamus, thereby stimulating feeding at least partially through alpha-1 and beta-2 noradrenergic receptors. In addition, bilateral midbrain transections rostral to the NTS, or toxin-induced loss of neurons in the hindbrain that express dopamine beta hydroxylase (an NA synthetic enzyme), abolished ghrelin-induced feeding. These findings provide new evidence that the noradrenergic system is necessary in the central control of feeding behavior by peripherally administered ghrelin.

Des-acyl ghrelin induces food intake by a mechanism independent of the growth hormone secretagogue receptor.

Ghrelin, an acylated peptide produced predominantly in the stomach, stimulates feeding and GH secretion via interactions with the GH secretagogue type 1a receptor (GHS-R1a), the functionally active form of the GHS-R. Ghrelin molecules exist in the stomach and hypothalamus as two major endogenous forms, a form acylated at serine 3 (ghrelin) and a des-acylated form (des-acyl ghrelin). Acylation is indispensable for the binding of ghrelin to the GHS-R1a. Ghrelin enhances feeding via the neuronal pathways of neuropeptide Y and orexin, which act as orexigenic peptides in the hypothalamus. We here studied the effect of des-acyl ghrelin on feeding behavior. Intracerebroventricular (icv) administration of rat des-acyl ghrelin to rats or mice fed ad libitum stimulated feeding during the light phase; neither ip nor icv administration of des-acyl ghrelin to fasting mice suppressed feeding. The icv administration of des-acyl ghrelin induced the expression of Fos, a marker of neuronal activation, in orexin-expressing neurons of the lateral hypothalamic area, but not neuropeptide Y-expressing neurons of the arcuate nucleus. Peripheral administration of des-acyl ghrelin to rats or mice did not affect feeding. Although icv administration of ghrelin did not induce food intake in GHS-R-deficient mice, it did in orexin-deficient mice. In contrast, icv administration of des-acyl ghrelin stimulated feeding in GHS-R-deficient mice, but not orexin-deficient mice. Des-acyl ghrelin increased the intracellular calcium concentrations in isolated orexin neurons. Central des-acyl ghrelin may activate orexin-expressing neurons, perhaps functioning in feeding regulation through interactions with a target protein distinct from the GHS-R.

Central actions of neuromedin U via corticotropin-releasing hormone.

Neuromedin U (NMU), a hypothalamic peptide, has been known to be involved in feeding behavior as a catabolic signaling molecule. However, little is known about the participation of NMU in the neuronal network. One NMU receptor, NMU2R, is abundantly expressed in the hypothalamic paraventricular nucleus, where corticotrophin-releasing hormone (CRH) is synthesized. The functions of CRH, regulation of stress response and feeding behavior, are comparable with those of NMU. Here, we have investigated the functional relationships between NMU and CRH using CRH knockout (KO) mice. Intracerebroventricular administration of NMU suppressed dark-phase food intake and fasting-induced feeding in wild-type mice. In contrast, these suppressions were not observed in CRH KO mice. NMU-induced increases in oxygen consumption and body temperature were attenuated in CRH KO mice. These results suggest that NMU plays a role in feeding behavior and catabolic functions via CRH. This study demonstrates a novel hypothalamic pathway that links NMU and CRH in the regulation of feeding behavior and energy homeostasis.

The role of the gastric afferent vagal nerve in ghrelin-induced feeding and growth hormone secretion in rats.

BACKGROUND & AIMS: Visceral sensory information is transmitted to the brain through the afferent vagus nerve. Ghrelin, a peptide primarily produced in the stomach, stimulates both feeding and growth hormone (GH) secretion. How stomach-derived ghrelin exerts these central actions is still unknown. Here we determined the role of the gastric afferent vagal nerve in ghrelin's functions. METHODS: Food intake and GH secretion were examined after an administration of ghrelin intravenously (IV) to rats with vagotomy or perivagal application of capsaicin, a specific afferent neurotoxin. We investigated Fos expression in neuropeptide Y (NPY)-producing and growth hormone-releasing hormone (GHRH)-producing neurons by immunohistochemistry after administration IV of ghrelin to these rats. The presence of the ghrelin receptor in vagal afferent neurons was assessed by using reverse-transcription polymerase chain reaction and in situ hybridization histochemistry. A binding study on the vagus nerve by (125)I-ghrelin was performed to determine the transport of the ghrelin receptor from vagus afferent neurons to the periphery. We recorded the electric discharge of gastric vagal afferent induced by ghrelin and compared it with that by cholecystokinin (CCK), an anorectic gut peptide. RESULTS: Blockade of the gastric vagal afferent abolished ghrelin-induced feeding, GH secretion, and activation of NPY-producing and GHRH-producing neurons. Ghrelin receptors were synthesized in vagal afferent neurons and transported to the afferent terminals. Ghrelin suppressed firing of the vagal afferent, whereas CCK stimulated it. CONCLUSIONS: This study indicated that the gastric vagal afferent is the major pathway conveying ghrelin's signals for starvation and GH secretion to the brain.