Structure-activity analysis of the motor effects of neuropeptide Y

Neuropeptide-Y modulates eating patterns and masticatory muscle activity in rats

Neuropeptide Y (NPY) is a powerful orexigenic peptide secreted by hypothalamic neurons. The present study investigates how NPY injection into the lateral ventricle modulates masticatory movements and eating behavior. Behavioral experiments showed that cumulative food intake over a 4-h period and latency to eating were increased and decreased, respectively, in NPY-injected rats compared to saline-injected control rats. The feeding time for 2 g pellets was shorter in NPY-injected rats and resulted in an increased feeding rate, with more potent effects observed at 1 μg compared to 10 μg NPY. After injection of 10 μg NPY, a greater number of bouts with shorter average bout duration for eating 2g, compared to 1 μg NPY, were observed. Furthermore, 10 μg NPY injection resulted in prolonged periods of moving and shortened sleep and grooming. Electromyography recordings from the digastric and masseter muscles showed two distinct patterns of bursts corresponding to the gnawing and chewing phases. After the injection of 1 μg NPY, the burst magnitude of masseter muscle during the gnawing phase increased, reflecting strong jaw-closing muscle activity. The relative integrated EMG of masseter muscle in both phases was smaller following injection of 10 μg NPY in comparison with that of 1 μg NPY. The present study indicates that 1 μg NPY administration promotes feeding behavior together with increased feeding rate and powerful jaw-closing muscle activity; whereas 10 μg NPY administration lowers jaw-closing muscle activity during biting and produces mastication with shorter and more frequent feeding bouts than 1 μg NPY.

Central administration of ghrelin and agouti-related protein (83-132) increases food intake and decreases spontaneous locomotor activity in rats

Ghrelin was recently identified as an endogenous ligand of the GH secretagogue receptor. The novel peptide hormone is produced by gastric A-like cells, and circulating levels rise before feeding, suggestive of ghrelin as an endogenous hunger factor. ghrelin stimulates food intake and promotes adiposity after peripheral or central administration, likely by activating hypothalamic neurons expressing the orexigenic neuropeptides neuropeptide Y (NPY) and agouti-related protein (AGRP). To examine whether ghrelin-induced feeding resembles NPY and AGRP [AGRP fragment (83-132)] induced orexia, we compared the short- and long-term orexigenic capacity of the three peptides. A single intracerebroventricular injection of ghrelin (0.2, 1.0, and 5.0 microg) increased food intake in a dose-dependent manner. A prolonged and uncompensated increase in feeding was seen after the highest dose of ghrelin. The prolonged effects on feeding (+72 h) closely resembled those of AGRP (83-132) but not NPY. Surprisingly, ghrelin injections reduced overall locomotor activity by 20% during the first 24-h observation period. AGRP (83-132) had similar effects on locomotor behavior, whereas NPY had no effect. In summary, ghrelin causes long-term increases of food intake and, like AGRP, plays a previously unknown role as a suppressor of spontaneous physical activity. Expanding the current model of food intake control to include mechanisms regulating physical activity may promote our understanding of two major etiological factors causing obesity.

Receptor autoradiography as mean to explore the possible functional relevance of neuropeptides: focus on new agonists and antagonists to study natriuretic peptides, neuropeptide Y and calcitonin gene-related peptides

Over the past 20 years, receptor autoradiography has proven most useful to provide clues as to the role of various families of peptides expressed in the brain. Early on, we used this method to investigate the possible roles of various brain peptides. Natriuretic peptide (NP), neuropeptide Y (NPY) and calcitonin (CT) peptide families are widely distributed in the peripheral and central nervous system and induced multiple biological effects by activating plasma membrane receptor proteins. The NP family includes atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP) and C-type natriuretic peptide (CNP). The NPY family is composed of at least three peptides NPY, peptide YY (PYY) and the pancreatic polypeptides (PPs). The CT family includes CT, calcitonin gene-related peptide (CGRP), amylin (AMY), adrenomedullin (AM) and two newly isolated peptides, intermedin and calcitonin receptor-stimulating peptide (CRSP). Using quantitative receptor autoradiography as well as selective agonists and antagonists for each peptide family, in vivo and in vitro assays revealed complex pharmacological responses and radioligand binding profile. The existence of heterogeneous populations of NP, NPY and CT/CGRP receptors has been confirmed by cloning. Three NP receptors have been cloned. One is a single-transmembrane clearance receptor (NPR-C) while the other two known as CG-A (or NPR-A) and CG-B (or NPR-B) are coupled to guanylate cyclase. Five NPY receptors have been cloned designated as Y(1), Y(2), Y(4), Y(5) and y(6). All NPY receptors belong to the seven-transmembrane G-protein coupled receptors family (GPCRs; subfamily type I). CGRP, AMY and AM receptors are complexes which include a GPCR (the CT receptor or CTR and calcitonin receptor-like receptor or CRLR) and a single-transmembrane domain protein known as receptor-activity-modifying-proteins (RAMPs) as well as an intracellular protein named receptor-component-protein (RCP). We review here tools that are currently available in order to target each NP, NPY and CT/CGRP receptor subtype and establish their respective pathophysiological relevance.

Behavioral effects of neuropeptide Y in F344 rat substrains with a reduced dipeptidyl-peptidase IV activity

Dipeptidyl-peptidase IV (DPPIV/CD26) is involved in several physiological functions by cleavage of dipeptides with a Xaa-Pro or Xaa-Ala sequence of regulatory peptides such as neuropeptide Y (NPY). Cleavage of NPY by DPPIV results in NPY(3-36), which lacks affinity for the Y(1) but not for other NPY receptor subtypes. Among other effects, the NPY Y(1) receptor mediates anxiolytic-like effects of NPY. In previous studies with F344 rat substrains lacking endogenous DPPIV-like activity we found a reduced behavioral stress response, which might be due to a differential degradation of NPY. Here we tested this hypothesis and administered intracerebroventricularly two different doses of NPY (0.0, 0.2, 1.0 nmol) in mutant and wildtype-like F344 substrains. NPY dose-dependently stimulated food intake and feeding motivation, decreased motor activity in the plus maze and social interaction test, and exerted anxiolytic-like effects. More important for the present hypothesis, NPY administration was found to be more potent in the DPPIV-negative substrains in exerting anxiolytic-like effects (increased social interaction time in the social interaction test) and sedative-like effects (decreased motor activity in the elevated plus maze). These data demonstrate for the first time a differential potency of NPY in DPPIV-deficient rats and suggest a changed receptor-specificity of NPY, which may result from a differential degradation of NPY in this genetic model of DPPIV deficiency. Overall, these results provide direct evidence that NPY-mediated effects in the central nervous system are modulated by DPPIV-like enzymatic activity.

The neurocircuitry and receptor subtypes mediating anxiolytic-like effects of neuropeptide Y

This review aims to give a brief overview of NPY receptor distribution and physiology in the brain and summarizes series of studies, test by test and region by region, aimed at identification receptor subtypes and neuronal circuitry mediating anxiolytic-like effects of NPY. We conclude that from four known NPY receptor subtypes in the rat (Y(1), Y(2), Y(4), Y(5)), only the NPY Y(1) receptor can be linked to anxiety-regulation with certainty in the forebrain, and that NPY Y(2) receptor may have a role in the pons. Microinjection studies with NPY and NPY receptor antagonists support the hypothesis that the amygdala, the dorsal periaqueductal gray matter, dorsocaudal lateral septum and locus coeruleus form a neuroanatomical substrate that mediates anxiolytic-like effects of NPY. The release of NPY in these areas is likely phasic, as NPY receptor antagonists are silent on their own. However, constant NPY-ergic tone seems to exist in the dorsal periaqueductal gray, the only brain region where NPY Y(1) receptor antagonists had anxiogenic-like effects. We conclude that endogenous NPY has an important role in reducing anxiety and serves as a physiological stabilizer of neural activity in circuits involved in the regulation of arousal and anxiety.

Neurochemical effects of neuropeptide Y (NPY) and NPY2-36

Our previous in vivo structure-activity studies suggested that the putative receptors mediating the effects of NPY and NPY2-36 on food intake and body temperature following ICV administration are pharmacologically different. In the present study, we examined and compared dose related effects of NPY and NPY2-36 on levels of norepinephrine (NE), dopamine (DA) and its main metabolites, dihydroxyphenylacetic acid (DOPAC) and homovanilic acid (HVA), as well as serotonin (5-HT) and its metabolite, 5-hydroxyindolacetic acid (5-HIAA), in several brain regions of the rat, including: frontal cortex, hypothalamus, amygdala, septum, nucleus accumbens, corpus striatum, globus pallidus, substantia nigra and hippocampus. NPY and NPY2-36 (10 or 20 micrograms) were administered intraventricularly and the regional levels of the amines and metabolites were assessed 30 min following administration. Results indicate that both doses of NPY decreased NE levels within the hypothalamus. Furthermore, DOPAC concentrations were increased in this region while DA and HVA remained unchanged. The most pronounced neurochemical effects of NPY were found in the hippocampus, where the peptide produced dose related increases in DA, DOPAC and HVA. On the other hand, NPY2-36 significantly increased NE, DA and its metabolite DOPAC in both the amygdala and septum. The metabolism of DA was most obviously affected in the hippocampus and frontal cortex where levels of DA and DOPAC were significantly increased. 5-HT was affected in both the hypothalamus and globus pallidus where DA and its metabolite HVA were also increased.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo central actions of NPY(1-30), an N-terminal fragment of neuropeptide Y

The purpose of the present study was to examine the possible central actions of a N-terminal fragment of NPY, NPY(1-30), on five measures typically influenced by the native peptide: decreased spontaneous activity, enhancement of muscle tone (increased grasping response), catalepsy, hypothermia, and stimulation of food intake. The peptides were administered ICV in doses ranging from 2.5 to 160 micrograms (0.75-48 nmol) and their effects on the three motor variables as well as thermal and feeding responses were evaluated and compared. Globally, results indicate that, similarly to NPY, the N-terminal fragment NPY(1-30), decreased spontaneous activity and induced hypothermia. However, the fragment displayed approximately half of the potency of NPY for producing these effects. On the other hand, contrary to NPY, NPY(1-30) did not affect muscle tone or food consumption and did not induced catalepsy in animals. These results demonstrate for the first time central actions of a N-terminal fragment of NPY and lend further support to the hypothesis that the receptors mediating the central actions of NPY are pharmacologically different.