The area postrema is a medullary structure lying at the base of the fourth ventricle. The area postrema's privileged location outside of the blood-brain barrier make this sensory circumventricular organ a vital player in the control of autonomic functions by the central nervous system. By virtue of its lack of tight junctions between endothelial cells in this densely vascularized structure and the presence of fenestrated capillaries, peptide and other physiological signals borne in the blood have direct access to neurons that project to brain areas with important roles in the autonomic control of many physiological systems, including the cardiovascular system and systems controlling feeding and metabolism. However, the area postrema is not simply a conduit through which signals flow into the brain, but it is now being recognized as the initial site of integration for these signals as they enter the circuitry of the central nervous system.

Somatostatin is important in the regulation of diverse neuroendocrine functions. Based on bioinformatic analyses of evolutionarily conserved sequences, we predicted another peptide hormone in pro-somatostatin and named it neuronostatin. Immuno-affinity purification allowed the sequencing of an amidated neuronostatin peptide of 13 residues from porcine tissues. In vivo treatment with neuronostatin induced c-Fos expression in gastrointestinal tissues, anterior pituitary, cerebellum, and hippocampus. In vitro treatment with neuronostatin promoted the migration of cerebellar granule cells and elicited direct depolarizing actions on paraventricular neurons in hypothalamic slices. In a gastric tumor cell line, neuronostatin induced c-Fos expression, stimulated SRE reporter activity, and promoted cell proliferation. Furthermore, intracerebroventricular treatment with neuronostatin increased blood pressure but suppressed food intake and water drinking. Our findings demonstrate diverse neuronal, neuroendocrine, and cardiovascular actions of a somatostatin gene-encoded hormone and provide the basis to investigate the physiological roles of this endogenously produced brain/gut peptide.Originally discovered in 1972 based on its ability to inhibit pituitary growth hormone release (1, 2), somatostatin is one of the most extensively studied peptide hormones (3, 4). Somatostatin is widely expressed in neuronal, neuroendocrine, gastrointestinal, inflammatory, immune, and cancer cells and plays important roles in the regulation of neuromodulation, hormone secretion, gastrointestinal functions, immune responses, cell growth, and exocrine secretion (5). Two somatostatin isoforms, somatostatin-14 and somatostatin-28, activate five related G protein-coupled receptors with different affinity (6 -8). Somatostatin receptors are also activated by two cortistatin isoforms secreted from different brain regions (9). Based on bioinformatic analysis of evolutionarily conserved sequences in the pro-somatostatin protein, we predicted the existence of another peptide hormone encoded by the somatostatin gene. We generated antibodies against the putative peptide, isolated the endogenous peptide, and found it to be an amidated peptide of 13 residues. This peptide hormone, named neuronostatin, induced c-Fos and c-Jun expression in diverse brain/gut tissues, regulated neuronal functions in vitro, and modulated blood pressure as well as food intake and drinking behavior in vivo. EXPERIMENTAL PROCEDURESPeptide Hormones-All peptides used were synthesized by Phoenix Pharmaceuticals Inc. (Burlingame, CA) or the PAN facility at Stanford University. Peptide purity was verified by analytical reverse phase HPLC and matrix-assisted laser desorption/ionization time-of-flight (MALDI-TOF) 4 mass spectrometry. Unless indicated otherwise, all functional tests utilized human amidated neuronostatin-13.Purification of Endogenous Neuronostatin-To purify endogenous neuronostatin, frozen porcine pancreas and spleen were obtained from Pel-Freez (Rogers, AK) and extracted ...

Adiponectin is an adipocyte-derived peptide hormone involved in energy homeostasis and the pathogenesis of obesity, including hypertension. Area postrema (AP) lacks a blood-brain barrier and is a critical homeostatic integration center for humoral and neural signals. Here we investigate the role of AP in adiponectin signaling. We show that rat AP expresses AdipoR1 and AdipoR2 adiponectin receptor mRNA. We used current-clamp electrophysiology to investigate whether adiponectin influenced membrane properties of AP neurons and found that ϳ60% of rat AP neurons tested were sensitive to adiponectin. Additional electrophysiology experiments coupled with single-cell reverse transcription-PCR indicated that all neurons that expressed both subtypes of receptor were sensitive to adiponectin, whereas neurons expressing only one subtype were predominantly insensitive. Last, microinjection of adiponectin into AP caused significant increases in arterial blood pressure, with no change in heart rate, suggesting that adiponectin acts at AP to provide a possible link between control of energy homeostasis and cardiovascular function.

Adiponectin is an adipocyte derived hormone which acts in the brain to modulate energy homeostasis and autonomic function. The paraventricular nucleus of the hypothalamus (PVN) which plays a key role in controlling pituitary hormone secretion has been suggested to be a central target for adiponectin actions. A number of hormones produced by PVN neurons have been implicated in the regulation of energy homeostasis including oxytocin, corticotropin releasing hormone and thyrotropin releasing hormone. In the present study we investigated the role of adiponectin in controlling the excitability of magnocellular (MNC -oxytocin or vasopressin secreting) neurons within the PVN. Using RT-PCR techniques we have shown expression of both adiponectin receptors in the PVN. Patch clamp recordings from MNC neurons in hypothalamic slices have also identified mixed (27% hyperpolarization, 42% depolarization) effects of adiponectin in modulating the excitability of the majority of MNC neurons tested. These effects are maintained when cells are placed in synaptic isolation using tetrodotoxin. Additionally we combined electrophysiological recordings with single cell RT-PCR to examine the actions of adiponectin on MNC neurons which expressed oxytocin only, vasopressin only, or both oxytocin and vasopressin mRNA and assess the profile of receptor expression in these subgroups. Adiponectin was found to hyperpolarize 100% of oxytocin neurons tested (n = 6), while vasopressin cells, while all affected (n = 6), showed mixed responses. Further analysis indicates oxytocin neurons express both receptors (6/7) while vasopressin neurons express either both receptors (3/8) or one receptor (5/8). In contrast 6/6 oxytocin/vasopressin neurons were unaffected by adiponectin. Co-expressing oxytocin and vasopressin neurons express neither receptor (4/6). The results presented in this study suggest that adiponectin plays specific roles in controlling the excitability oxytocin secreting neurons, actions which correlate with the current literature showing increased oxytocin secretion in the obese population.

Recent attempts to find novel molecules involved with regulating appetite and energy balance have identified nesfatin-1 as a potent inhibitor of feeding activity (1). This peptide, arising from cleavage of the calcium-binding protein nucleobindin2, is expressed in many hypothalamic nuclei, including the paraventricular (PVN), arcuate, lateral hypothalamic and supraoptic nuclei (1). Significantly, in starved rats, nesfatin-1 levels decreased only in the PVN, a nucleus with a well known association with the control of feeding behaviour and metabolism (2, 3). These data identify the PVN as a location where signals associated with the depletion of energy reserves are received, resulting in the inhibition of the synthesis of this satiety signal (1). Although the PVN has been identified as a source for nesfatin-1, to date, no information is available regarding the roles of nesfatin-1 in controlling the excitability of the neurones in this vital hypothalamic autonomic control centre. Therefore, using whole-cell patch-clamp recordings from PVN neurones in rat brain slices, we performed experiments examining the effect of nesfatin-1 on the membrane potential and excitability of PVN neurones. Materials and methods Slice preparationAll animal procedures conformed to the standards of the Canadian Council on Animal Care and were approved by the Queen's University Animal Care Committee. Male Sprague-Dawley rats (Charles River, Quebec, Canada), postnatal days 21-27 (approximately 50-100 g), were used in the preparation of hypothalamic slices. Rats were quickly decapitated and the brain dissected out and placed into ice cold carbogenated slicing solution, consisting of (in mM): 87 NaCl, 2.5 KCl, 25 NaHCO 3 , 0.5 CaCl 2 , 7 MgCl 2 , 1.25 NaH 2 PO 4 , 25 glucose and 75 sucrose. A tissue block containing the hypothalamus was obtained and 300 lm coronal slices cut using a vibratome. Slices were then stored in a water bath at 32°C for at least 1 h, before recordings commenced, in carbogenated artificial cerebrospinal fluid (ACSF) composed of (in mM): 126 NaCl, 2.5 KCl, 26 NaHCO 3 , 2 CaCl 2 , 2 MgCl 2 1.25 NaH 2 PO 4 and 10 glucose. ElectrophysiologySlices were placed in a chamber that was continuously perfused at approximately 2 ml ⁄ min with carbogenated ACSF heated to between 28 and 32°C.These authors contributed equally to this paper.Nesfatin-1 is a newly-discovered satiety peptide found in several nuclei of the hypothalamus, including the paraventricular nucleus. To begin to understand the physiological mechanisms underlying these satiety-inducing actions, we examined the effects of nesfatin-1 on the excitability of neurones in the paraventricular nucleus. Whole-cell current-clamp recordings from rat paraventricular nucleus neurones showed nesfatin-1 to have either hyperpolarising or depolarising effects on the majority of neurones tested. Both types of response were observed in neurones irrespective of classification based on electrophysiological fingerprint (magnocellular, neuroendocrine or pre-autonomic) or molecular phenotyp...