Neuropeptide Y alters monoamine turnover in the rat brain

Neuropeptide Y-induced enhancement of the evoked release of newly synthesized dopamine in rat striatum: Mediation by Y2 receptors

The purpose of the present study was to determine whether or not activation of neuropeptide Y (NPY) receptors resulted in an enhancement or attenuation of the KCl (50 mM) evoked release of [3H]dopamine newly synthesized from [3H]tyrosine in superfused striatal slices and, if so to identify the NPY receptor subtype mediating the effect. Rat striatal slices were prepared and placed in microsuperfusion chambers and continuously superfused with physiological buffer containing 50 microCi/ml of l-3-5-[3H]tyrosine. Superfusate effluents were collected and analyzed for [3H]dopamine by liquid scintillation spectrometry following amberlite CG50 and alumina chromatography. NPY agonists (NPY and PYY3-36) were added 6 min prior to the addition of KCl, while the Y1, Y2, and Y5 antagonist BIBO3304, BIIE0246 and CGP71683A, respectively were added 6 min prior to the agonists. Continuous superfusion with [3H]tyrosine resulted in the production of [3H]dopamine which reached a steady state at approximately 48 min. Depolarization with KCl resulted in a 2- to 3-fold increase in [3H]dopamine overflow. NPY and PYY3-36 produced a concentration dependent enhancement in the KCl induced increase in newly synthesized [3H]dopamine overflow. The Y2 antagonist BIIE0246 produced an attenuation of both the NPY and PYY3-36 induced enhancement while the Y1 antagonist BIBO3304 and theY5 antagonist CGP71683A failed to alter the NPY or PYY3-36 induced enhancement. These results are consistent with the NPY-Y2 receptor subtype mediating the facilitatory effect.

Locus coeruleus noradrenergic lesions attenuate intraoral intake

I.p. injections of DSP-4 in male rats decreased norepinephrine (NE) levels to varying degrees throughout the brain with 66.7% reductions in the hypothalamic paraventricular nucleus. Intake of intraorally infused sucrose was reduced for 14 days but daily pellet intake recovered within 5 days post-injection. Intraventricular NE restored intraoral sucrose intake in DSP-4-lesioned rats without affecting controls. Intraventricular infusion of neuropeptide Y (NPY) reduced intraoral intake in controls but had no effect in DSP-4-lesioned rats. NPY markedly inhibited intraoral intake in DSP-4-treated rats that also received NE. These data confirm studies showing that NPY decreases consummatory ingestive behavior and suggest that this inhibition involves ascending noradrenergic projections from locus coeruleus.

Pancreatic homeodomain transcription factor IDX1/IPF1 expressed in developing brain regulates somatostatin gene transcription in embryonic neural cells

Hox-like homeodomain proteins play a critical role during embryonic development by regulating the transcription of genes that are important for the generation of specific organs or cell types. The homeodomain transcription factor IDX1/IPF1, the expression of which was thought until recently to be restricted to the pancreas and foregut, is required for pancreas development and for the expression of genes controlling glucose homeostasis. We report that IDX1/IPF1 is also expressed in embryonic rat brain at a time coincident with active neurogenesis. Electrophoretic mobility shift assays with nuclear extracts of embryonic brains indicated that IDX1/IPF1 binds to two somatostatin promoter elements, SMS-UE-B and the recently discovered SMS-TAAT3. The requirement of these elements for IDX1/IPF1 transactivation of the somatostatin gene in neural cells was confirmed in transfection studies using embryonic cerebral cortex-derived RC2.E10 cells. Immunohistochemical staining of rat embryos showed IDX1/IPF1-positive cells located near the ventricular surface in germinative areas of the developing central nervous system. Cellular colocalization of IDX1/IPF1 and somatostatin was found in several areas of the developing brain, including cortex, ganglionic eminence, hypothalamus, and inferior colliculus. These results support the notion that IDX1/IPF1 regulates gene expression during development of the central nervous system independent of its role on pancreas development and function.

Neuropeptide Y in brains of the Flinders Sensitive Line rat, a model of depression. Effects of electroconvulsive stimuli and d-amphetamine on peptide concentrations and locomotion

Neuropeptide Y (NPY), has been implicated in the pathophysiology of depression and the mechanisms of action of electroconvulsive treatment (ECT). In this series of experiments, we explored whether there are differences between Flinders Sensitive Line (FSL) rats, an animal model of depression, and controls, Flinders Resistant Line (FRL) in (1) baseline brain NPY-LI concentrations, (2) effects of ECS on locomotion and brain neuropeptides, (3) amphetamine effects on behavior, and (4) effects of ECS pretreatment on subsequent effects of amphetamine on behavior. Both strains were divided into two groups, receiving eight ECS or ShamECS. Twenty-four hours after the last session, animals were habituated in activity boxes for 45 min before given d-amphetamine (1.5 mg.kg(-1), subcutaneously) or vehicle. Locomotor activity was then recorded for an additional 45 min. Twenty-four hours later, rats were sacrificed by microwave irradiation, the brains dissected into frontal cortex, occipital cortex, hippocampus, hypothalamus and striatum, and the neuropeptides extracted and measured by radioimmunoassay. No differences between FSL and FRL rats in baseline locomotor activity were found. FSL compared to FRL animals showed a significantly larger locomotion increase following saline and a significantly smaller increase following amphetamine. ECS pretreatment significantly decreased the saline effects on locomotion in the FSL and the amphetamine effects in the FRL rats. 'Baseline' NPY-like immunoreactivity (LI) concentrations were lower in the hippocampus of the 'depressed' rats. ECS increased NPY-LI in frontal cortex, occipital cortex and hippocampus of both strains. The hippocampal NPY-LI increase was significantly larger in the FSL compared to FRL animals.

Location and electrophysiological characterization of rostral medullary adrenergic neurons that contain neuropeptide Y mRNA in rat medulla

The objective of this study was to characterize the projection pattern and electrophysiological properties of the rostral medullary adrenergic neurons (C(1)) that express neuropeptide Y (NPY) mRNA in rat. NPY mRNA was found in a variable fraction of tyrosine hydroxylase immunoreactive (TH-IR) neurons depending on the medullary level. By retrograde labeling (Fast Blue, FluoroGold), NPY mRNA was detected in virtually all C(1) cells (96%) and C(3) cells (100%) with hypothalamic projections but in only 9% of C(1) cells and 58% of C(3) cells projecting to thoracic segment 3 (T(3)) or T(6) of the spinal cord. To identify the electrophysiological properties of the C(1) cells that express NPY mRNA, we recorded from baroinhibited neurons within the C(1) region of the ventrolateral medulla (RVLM) and tested for projections to segment T(3), the hypothalamus, or both. By using the juxtacellular method, we labeled these cells with biotinamide and determined whether the recorded neurons were TH-IR and contained NPY mRNA. At rostral levels (Bregma -11.8 mm), barosensitive neurons had a wide range of conduction velocities (0.4-6.0 m/second) and discharge rates (2-28 spikes/second). Most projected to T(3) only (27 of 31 cells), and 4 projected to both the hypothalamus and the spinal cord. Most of the baroinhibited cells with spinal projections but with no hypothalamic projections had TH-IR but no NPY mRNA (11 of 17 cells). Only 1 cell had both (1 of 17 cells), and 5 cells had neither (5 of 17 cells). Both TH-IR and NPY mRNA were found in neurons with dual projections (2 of 2 cells). At level Bregma -12.5 mm, baroinhibited neurons had projections to the hypothalamus only (13 of 13 cells) and had unmyelinated axons and a low discharge rate. Four of five neurons contained both TH-IR and NPY mRNA, and 1 neuron contained neither. In short, NPY is expressed mostly by C(1) cells with projection to the hypothalamus. NPY-positive C(1) neurons are barosensitive, have unmyelinated axons, and have a very low rate of discharge. Most bulbospinal C(1) cells with a putative sympathoexcitatory role do not make NPY.

Modulation of [3H]dopamine release by neuropeptide Y in rat striatal slices

Neuropeptide Y, a 36-amino-acid peptide, has a wide and specific distribution in the central nervous system. In this study we examined the regulatory mechanisms of neuropeptide Y on dopamine release in the rat central nervous system. The effects of neuropeptide Y on the electrically stimulated [3H]dopamine release were investigated in superfused striatal slices of Sprague-Dawley rats, spontaneously hypertensive rats and Wistar-Kyoto rats. Neuropeptide Y (1 x 10(-8) - 1 x 10(-7) mol/1) reduced the stimulation (1 Hz)-induced [3H]dopamine release by a comparable amount in Sprague-Dawley rats. The blockade of dopamine D2 receptors by the dopamine D2 receptor antagonist, sulpiride, diminished the inhibitory effects of neuropeptide Y on the stimulation-evoked [3H]dopamine release. Pretreatment of slices with pertussis toxin (a potent inhibitor of G1-proteins) attenuated the suppression of the stimulation-evoked [3H]dopamine release by neuropeptide Y. Unlabelled dopamine itself reduced the stimulation-evoked [3H]dopamine release, and the inhibitory effect was also attenuated in the pertussis toxin-pretreated slices. In spontaneously hypertensive rats, the inhibitory effect of neuropeptide Y on the stimulation-evoked [3H]dopamine release was more pronounced than that in Wistar-Kyoto rats. The results of the present study showed that neuropeptide Y inhibited the stimulation-evoked dopamine release partially mediated by dopamine D2 receptors and the pertussis toxin-sensitive G1-proteins in rat striatum. Furthermore, the greater effect of neuropeptide Y on dopamine release in spontaneously hypertensive rats suggests a possible involvement of the peptide in regulating the central dopaminergic nerve activity in hypertension.

Effect on nociception of intracerebroventricular administration of low doses of neuropeptide Y in mice

The present study shows further evidence about the implication of neuropeptide Y (NPY) in nociception. The effect of NPY (1-36), when intracerebroventricularly administered, has been studied using two physical models of acute pain (hot plate test and electrical tail stimulation) and the formalin test. The animal response to these three pain models has been shown to be integrated at different levels in the CNS. A decrease in pain threshold was exhibited in both the hot plate test (10, 30, 60, 120 and 480 pmol of NPY i.c.v.) and the electrical tail simulation test (10, 30 and 60 pmol of NPY i.c.v.), while in the formalin test (10, 30, 60 and 120 pmol of NPY icv) the licking response decreased in phase I but not in phase 2. In these three tests NPY showed hyperalgesic or analgesic effects when administered at low doses, while at high doses it failed to induce any effect. Results show that the effect of NPY on nociception is clearly test-dependent and is only observed at low doses.

Effects of repeated sensory stimulation (electro-acupuncture) and physical exercise (running) on open-field behaviour and concentrations of neuropeptides in the hippocampus in WKY and SHR rats

The effects of repeated sensory stimulation (electro-acupuncture) and physical exercise (running) on open-field behaviour and on hippocampal concentrations of neuropeptide Y, neurokinin A, substance P, galanin and vasoactive intestinal peptide (VIP)-like immunoreactivities were studied in WKY (wistar-Kyoto) and SHR (spontaneously hypertensive) rats. Significantly higher concentrations of substance P-like immunoreactivity, neurokinin A-like immunoreactivity and neuropeptide Y-like immunoreactivity were found in the hippocampus immediately after 3 weeks of treatment (electro-acupuncture and running), but not 1 week after the last (tenth) changes in neuropeptide concentrations were similar in the two rat strains. Open-field behaviour was significantly reduced during the treatment period in both strains. There were significant negative correlations between behaviour and neuropeptide concentrations in SHR rats, suggesting interdependency with sympathetic activity. It is proposed that the effects of electro-acupuncture and physical exercise in rats are related to increases in neuropeptide Y, neurokinin A and substance P in the hippocampus.

Concurrent analysis of neuropeptides and biogenic amines in brain tissue of rats treated with electroconvulsive stimuli

We developed a method for measuring neuropeptides and monoamines in the same rat brain tissue and applied this method to study the effects of electroconvulsive stimuli (ECS) on these compounds. Rats were treated with repeated ECS or sham ECS. After sacrifice by focused microwave irradiation, brains were dissected and immediately frozen. The tissues were extracted in acetic acid. After lyophilization the samples were reconstituted in phosphate buffer and divided in three fractions: (1) was further purified on a cation-exchange column before catecholamines were measured on a high-performance liquid chromatography (HPLC) system, (2) for measuring serotonin on the HPLC system, (3) for measuring peptide concentrations by specific radioimmunoassays. Confirming our previous findings, ECS significantly increased neuropeptide Y-like immunoreactivity (-LI) in hippocampus and frontal cortex and neurokinin A-LI in the hippocampus, while no changes in substance P- and neurotensin-LI were detected. New findings were a decrease in noradrenaline concentrations in the frontal and occipital cortex and hippocampus, an increase in dopamine concentrations in the frontal and occipital cortex and no serotonin change. In summary, we have developed methods to measure both peptides and monoamines in the same brain tissue specimens, and have shown that ECS leads to changes in both neuropeptides and classical neurotransmitters in distinct brain regions.

Intracerebroventricular administration of neuropeptide Y inhibits release of noradrenaline in the hypothalamic paraventricular nucleus caused by manual restraint in the rat through an opioid system

Intracerebroventricular injection of 1.5 micrograms neuropeptide Y (NPY) had no effect on basal release of noradrenaline (NA) in the hypothalamic paraventricular nucleus (PVN), measured by intracerebral microdialysis in the rat. However, it blocked the increase in NA release caused by manual restraint but not that by tail-pinch, and the effect was blocked by naloxone (1.0 mg/kg body weight). Thus, NPY attenuates NA release in the PVN by a painless stressor, such as manual restraint, through an opioid system.

Ineffectiveness of hypothalamic serotonin to block neuropeptide Y-induced feeding

A variety of recent research has suggested that the feeding associated with enhanced neuropeptide Y (NPY) activity within the hypothalamus may operate in part by interacting antagonistically with other neural processes responsive to serotonin (5-hydroxytryptamine or 5-HT). To test this possibility further, experiments were performed to determine if the magnitude of feeding produced by injecting NPY into the paraventricular nucleus (PVN) or the perifornical hypothalamus (PFH) was diminished by coinjections of 5-HT into these two sites or peripheral injections of the 5-HT agonist, d-fenfluramine. Adult male Sprague-Dawley rats were implanted unilaterally with stainless steel cannulae aimed to terminate either in the PVN or the PFH. In both studies, NPY (235 pmol) produced significant feeding in both sites either 1 or 2 h after injection when compared to saline. This enhanced feeding response was significantly greater in the PFH 2 h after injection (40% in the central study; 70% in the peripheral study). Coinjection of 5-HT (6.3, 12.5, or 25.0 nmol) into either site had no effect on the induction of this NPY-induced feeding response. However, peripherally injected d-fenfluramine (0.32, 0.63, or 1.25 mg/kg) produced strong dose-dependent attenuation both 1- and 2-h food intake elicited by 235 pmol NPY in either site, with the PFH being proportionately more sensitive to this effect. Viewed together, these results suggest that the feeding-suppressant effects of systemic fenfluramine on hypothalamic NPY-induced feeding may operate largely via peripheral mechanisms and/or central ones that have little to do with its 5-HT agonistic effects within the PVN or PFH.

Role of neuropeptides in the regulation of feeding behavior: a review of cholecystokinin, bombesin, neuropeptide Y, and galanin

The purpose of this report is to provide a review of four peptides (cholecystokinin, bombesin, neuropeptide Y, galanin) and their role in feeding behavior. Cholecystokinin (CCK) and bombesin (BBS) are considered satiety peptides, and neuropeptide Y (NPY) and galanin (GAL) have been proposed as appetite peptides. For the purposes of this review, satiety refers to the physiological cessation of feeding, and appetite refers to the drive to eat and exists in gradations.

Quantitative receptor autoradiography demonstrates a differential distribution of neuropeptide-Y Y1 and Y2 receptor subtypes in human and rat brain

Quantitative receptor autoradiography was performed on sections of rat and human brain using [125I]peptide YY ([125I]PYY) to measure the anatomical distribution of neuropeptide Y (NPY) receptors. Masking Y1- and Y2-NPY subtypes with the agonists (Leu31,Pro34]NPY and NPY13-36, respectively demonstrated a differential distribution of Y1 and Y2 receptors between human and rat brain. In human brain, the highest density of [125I]PYY binding was found in pyramidal layers (CA4-CA1) of hippocampus, head and tail regions of caudate nucleus, locus coeruleus and substantia nigra. There was moderate [125I]peptide YY binding to NPY receptors in the molecular layers of the hippocampus, frontal and temporal cerebral cortex, especially in superficial layers, anterior amygdala, central grey and inferior colliculus. Low levels of binding were observed in white matter. The selective Y1 receptor agonist, [Leu31,Pro34]NPY did not effectively reduce [125I]PYY binding to any human brain region examined except for approximately 20-40% of the binding sites in the molecular layer of the dentate gyrus, layer IV of the frontal cortex and the radiatum and oriens layers of the hippocampal complex. In contrast, the Y2 agonist, NPY13-36 was effective at reducing [125I]PYY binding in all human brain regions examined. In rat brain, high densities of [125I]PYY binding was measured in cerebral cortex, thalamus and inferior colliculus which was sensitive to [Leu31,Pro34]NPY. In contrast, high densities of the NPY13-36 sensitive binding was found in the hippocampus, striatum and nucleus accumbens. Medium to low densities of NPY13-36 sensitive binding was found in medulla and pons. This data suggests that human brain contains primarily Y2-type NPY receptors with only a few regions expressing Y1-type receptors. No human brain region examined contained solely Y1-type receptors. In contrast to human brain, rat brain contains regions which express only Y1 receptors as well as regions containing only Y2 receptors and regions containing both Y1 and Y2 receptors.

Attenuation of 8-OH-DPAT induced feeding after lesions of the area postrema/immediately adjacent nucleus of the solitary tract

Rats with lesions of the area postrema/immediately adjacent nucleus of the solitary tract (AP/mNTS-lesions) have an attenuated feeding response after several manipulations that induce food intake in intact control rats. In this study we examined the ingestive response of rats with AP/mNTS-lesions after treatment with 8-OH-DPAT, a 5-HT1A agonist. Rats with AP/mNTS-lesions failed to increase their food intake after treatment with 8-OH-DPAT at doses that stimulated food intake in intact rats. These data suggest that altered serotonergic function may contribute to the attenuation of feeding observed in rats with AP/mNTS-lesions after treatment with some orexigenic stimuli.

Neuropeptide Y: intraaccumbens injections produce a place preference that is blocked by cis-flupenthixol

Neuropeptide Y (NPY) has been localized in the nucleus accumbens (NAcc), where it may influence dopamine (DA) neurotransmission. Extensive data implicate NAcc DA in reward-related learning, raising the possibility that NPY microinjected into the NAcc may induce rewarding effects mediated by DA. This hypothesis was tested using the conditioned place preference (CPP) paradigm. Each experiment consisted of three distinct phase: preconditioning (three 15-min exposures to an apparatus with two compartments connected by a tunnel); conditioning (four 30-min pairing of one compartment with drug and four similar pairings of the other compartment with vehicle); and test (three 15-min exposures to the apparatus). A significant increase in the time spent in the drug-paired compartment from preconditioning to test was taken as evidence of a CPP. Two experiments showed that systemic (2.0 mg/kg, IP) or intraaccumbens amphetamine (10.0 micrograms in 0.5 microliters on each side) produced a CPP. The third experiment showed that intraaccumbens NPY (0.1 micrograms in 0.5 microliter on each side) produced a CPP. This CPP was blocked by pretreatment with a dose of the DA receptor blocker cis-flupenthixol (20.0 micrograms in 0.5 microliter on each side in the NAcc) that, alone, produced no CPP effect. These results strongly suggest that NPY applied to the NAcc is rewarding. In addition, these rewarding properties of NPY may be mediated by DA neurotransmission.

Neuroendocrine regulation of thyrotropin-releasing hormone (TRH) in the tuberoinfundibular system

[...] It is now required to list each part needed for mucous excretion. They are two ducts in the brain substance, then a thin portion of membrane shaped as the infundibulum, then the gland that receives the tip of this infundibulum and the ducts that drive the mucus (pituita) from this gland to the palate and nares. [...] and I said that one (duct) [...] from the middle of the common cavity (third ventricle) descends [...] into the brain substance, and the end of this duct is [...] the sinus of the gland where the brain mucus is collected [...].

Effect of serotonergic agents on regional concentrations of somatostatin- and neuropeptide Y-like immunoreactivities in rat brain

A possible role for neuropeptides in affective disorders is suggested by many investigators. Somatostatin-like immunoreactivity (SS-LI) and neuropeptide Y-like immunoreactivity (NPY-LI) concentrations are demonstrated to be reduced in cerebrospinal fluid from depressed patients. We have shown that long-term treatment with serotonin uptake inhibitors, clomipramine and zimelidine, reduce brain SS-LI concentrations in the rat. We have studied the effect of serotonergic agents on regional brain SS-LI and NPY-LI concentrations in rats. Long-term treatment with 5-hydroxytryptamine (5-HTP), a serotonin precursor, caused reductions in SS- and NPY-LI levels in the hypothalamus. SS- and NPY-LI concentrations in the brain were markedly elevated by treatment with p-chlorophenylalanine, a serotonin synthesis inhibitor. Intracerebroventricular administration of 5,7-dihydroxytryptamine, a serotonin neurotoxin, resulted in elevations of both peptides in the brain. These results suggest a inhibitory role for the serotonergic system in the brain in the regulation of SS and NPY.

Dexfenfluramine treatment and hypothalamic neuropeptides in diet-induced obesity in rats

Neuropeptide Y (NPY) is a powerful appetite stimulant, and hypothalamic concentrations rise after food deprivation and in experimental diabetes. Serotonergic drugs such as dexfenfluramine are inhibitors of feeding. We measured hyothalamic NPY and NPY mRNA, along with galanin, neurotensin, and somatostatin in chow-fed rats and in rats with dietary obesity, and examined the effect of dexfenfluramine on these peptides in this model. Sixty-five rats were fed a palatable diet (condensed milk, sucrose and chow) for 6 weeks, which produced significant weight gain compared to twenty fed standard chow (145.1 +/- 2.3 g vs. 113.4 +/- 3.2 g, p less than 0.001). Groups of animals were treated for 7 days or 28 days with dexfenfluramine (1.8 mg/kg/day) or saline intraperitoneally via miniosmotic pumps. Hypothalami were dissected into medial and lateral blocks, and NPY, galanin, neurotensin, and somatostatin were measured by radioimmunoassay. Neuropeptide Y mRNA was measured by Northern blotting. Hypothalamic NPY was significantly higher in the palatable diet group compared to chow-fed controls (medial hypothalamus: 86.6 +/- 7.6 vs. 65.7 +/- 4.0 pmol/g tissue, p less than 0.02, lateral hypothalamus 71.2 +/- 6.6 vs. 53.1 +/- 3.6 pmol/g tissue, p less than 0.05), but NPY mRNA was unchanged. Although dexfenfluramine was effective at reducing weight gain in the animals fed the palatable diet, this did not result in any changes in the hypothalamic neuropeptides measured. Neuropeptide Y may be of importance in diet-induced obesity but the weight loss produced by dexfenfluramine in such animals is not mediated by changes in hypothalamic NPY.

Ultrastructural localization of neuropeptide Y-like immunoreactivity in the rat hippocampal formation

Neuropeptide Y (NPY) has been implicated in the modulation of hippocampal neuronal activity and in the pathophysiology of several neurological disorders involving the hippocampal formation. Thus, this study examines the light and electron microscopic immunoperoxidase labeling of a rabbit polyclonal antibody against porcine NPY in single sections through each lamina of the CA1 and CA3 regions of the hippocampus and the dentate gyrus (DG) of normal adult rats. By light microscopy, the majority of perikarya with intense NPY-like immunoreactivity (NPY-LI) were located in stratum oriens of CA1 and CA3 of the hippocampus and in the hilus of the DG. Fine varicose processes with NPY-LI were found in all layers of the hippocampal formation, but were densest in the outer third of the molecular layer of the DG. The density of NPY-labeling was greater in the ventral portion of the hippocampal formation. By electron microscopy, most NPY-containing perikarya in all three hippocampal regions were: small (8-12 microns) or medium-sized (12-18 microns) and elongated; or medium-sized and round. A dense accumulation of NPY-LI was commonly observed within the individual saccules of Golgi complexes and some rough endoplasmic reticulum in the cytoplasm. Perikarya and dendrites with NPY-LI usually were directly apposed to other neuronal processes (mostly terminals) and lacked astrocytic appositions. The majority of terminals in contact with NPY immunoreactive neurons were unlabeled and synapsed with the shafts of large and small dendrites. In CA1 and CA3 of the hippocampus, the types of synapses formed by the unlabeled terminals were not significantly different; however, more asymmetric synapses than symmetric synapses were formed by the unlabeled terminals on the shafts of small NPY-labeled dendrites in the DG. The terminals with NPY-LI (0.25-1.2 microns) contained many small, clear vesicles and 0-2 large, dense-core vesicles. The types of synapses (i.e., asymmetric and symmetric) and distribution of NPY-labeled terminals on the targets were remarkably similar in each lamina of the hippocampal subregions. The NPY-labeled terminals usually synapsed with one unlabeled perikaryon or dendrite. However, others synapsed either (1) with two unlabeled perikarya or dendrites simultaneously or (2) with one NPY-containing perikaryon or dendrite. Most of the terminals with NPY-LI formed symmetric junctions with the shafts of small (distal) dendrites.(ABSTRACT TRUNCATED AT 400 WORDS)

Intracerebroventricular administration of neuropeptide Y affects parameters of dopamine, glutamate and GABA activities in the rat striatum

The effects of intracerebroventricular (ICV) injection of neuropeptide Y (NPY) on parameters of dopamine (DA), glutamate (Glu) and gamma-aminobutyric acid (GABA) activities were investigated in the rat striatum. NPY (1.17-4.70 nmol) induced a dose-dependent increase in the striatal endogenous DA release monitored in freely moving animals by means of a voltammetric method. Maximal increase was observed about one hour after the peptide injection. This result is consistent with the hypothesis that NPY may influence striatal DA turnover in a facilitatory manner by activating DA release. DA, DOPAC, Glu and GABA endogenous contents as well as 3H-Glu and 3H-GABA synaptosomal high affinity uptakes were examined one hour after NPY ICV administration at the same dose range in chloral hydrate-anesthetized animals. Depending on the NPY dose injected, opposite changes in Glu uptake were observed, suggesting that NPY has a bimodal influence on glutamatergic transmission. The Glu uptake rate increased markedly at 1.17 nmol NPY and decreased at 4.70 nmol, which may reflect an activation and an inhibition of the striatal Glu transmission, respectively. In parallel, the GABA uptake was found to decrease slightly at the higher doses of NPY tested, whereas no significant alteration of the striatal concentrations of either DA, DOPAC, Glu or GABA was observed. These results indicate that NPY may be involved in regulating the activity of nigral dopaminergic and cortical glutamatergic afferent pathways and that of intrinsic GABA neurons in the rat striatum.

Neuropeptide Y innervation of retinorecipient layers of chick optic tectum

A dense laminar network of varicose neuropeptide Y immunopositive fibres, but not cells, was found to cover the retinorecipient layers of the entire optic tectum of 10- to 21-day-old domestic chicks. Unilateral enucleation resulted in no apparent loss of neuropeptide Y immunopositive fibres in the contralateral tectum, suggesting that they are not of retinal origin. To identify possible sources of neuropeptide Y immunopositive tectal input, the distribution of neuropeptide Y immunopositive perikarya was investigated in the meso-diencephalic region of the chick. A virtually continuous network of neuropeptide Y immunopositive cells and fibres was observed stretching from rostro-lateral thalamus to the pretectum in close apposition to the perirotundal belt. These neuropeptide Y immunopositive structures did not seem to respect the borders of known anatomical regions but partially co-localized with the nucl. dorsolateralis anterior pars magnocellularis and pars medialis, nucl. pretectalis diffusus, nucl. lentiformis mesencephali pars parvocellularis and pars magnocellularis, nucl. principalis precommissuralis, nucl. lateralis precommissuralis, nucl. superficialis magnocellularis (SM), nucl. posteroventralis thalami Kühlenbeck and the nucl. subrotundus. In the nucleus of the basal optic root, neuropeptide Y immunopositive perikarya were observed only within or adjacent to its dorsal and lateral subdivisions although all subdivisions were enmeshed with neuropeptide Y immunopositive fibres. The neuropeptide Y immunopositive tectal input is likely to derive from tectothalamic--presumably perirotundal--neuronal groups. The extent of this tectal afferent projection, not reported earlier in the domestic chick, suggests a powerful neuropeptide-Yergic control of retinotectal relay function.

Differential effects of galanin and neuropeptide Y on extracellular norepinephrine levels in the paraventricular hypothalamic nucleus of the rat: a microdialysis study

Evidence suggests that the peptides galanin (GAL) and neuropeptide Y (NPY) interact with the amine norepinephrine (NE) in the hypothalamic paraventricular nucleus (PVN) to stimulate feeding behavior. To directly investigate the nature of these interactions, extracellular levels of PVN NE were monitored in freely-moving rats using the microdialysis/HPLC technique. Following PVN administration of GAL (0.3 nmol), NPY (78 pmol) or Ringer's solution, local NE levels were measured at 20-min intervals for 2 hrs postinjection, under two feeding conditions, namely, in the presence or absence of food. The results demonstrate different effects of these peptides on endogenous NE levels. Following GAL administration, PVN NE levels were enhanced by 80 to 90%, up to 40 min postinjection, independent of food availability. In contrast, following NPY injection, NE levels were significantly reduced 20 min postinjection with food absent, and when food was available, NE levels tended to be enhanced. These results, consistent with pharmacological and biochemical studies, reveal different patterns of peptide-amine interactions in the PVN.

The effects of corticotropin-releasing hormone on peptidergic neurons in the rat forebrain

Our previous study showed that intracerebroventricular (ICV) administration of corticotropin-releasing hormone (CRH) produced a significant increase in locomotor activity at a dose of 1 microgram and slow stereotypy with prominent grooming at a dose of 10 micrograms. In addition, the ICV administration of CRH caused a significant increase in dopamine (DA) and norepinephrine turnover (NE) in various forebrain regions. The present study was designed to investigate the effects of the ICV administration of CRH on cholecystokinin (CCK), neuropeptide Y (NPY), somatostatin (SOM) and gamma-amino butyric acid (GABA) in the rat forebrain. The ICV administration of 1 and 10 micrograms CRH caused a marked reduction in CCK-like immunoreactivity (CCK-LI), NPY-LI and SOM-LI in the medial frontal cortex (MFC) and anterior cingulate cortex (Ant.CC), whereas it induced an increment of NPY-LI in the nucleus accumbens (NAc) and striatum. Increased SOM-LI and decreased NPY-LI were observed in the hippocampus following the ICV administration of CRH at both doses. The ICV administration of CRH caused a significant decrease in the BAGA content in the MFC, ant.CC, NAc and striatum. Taken together with our previous findings, these results indicate that the ICV administration of CRH induced classical neurotransmitter and neuropeptide abnormalities in the central nervous system which resulted increased emotionality, especially anxiety, in rats.

Inhibitory interactions between alpha 2-adrenergic and opoid but not NPY mechanisms controlling the CRF-ACTH axis in the rat

Following a series of investigations supporting the concept that the brain stem catecholaminergic (CA) system played a major stimulatory role on both basal and stress-triggered states of the hypothalamic-pituitary-adrenocortical (HPA) axis, across alpha 1 and beta receptors and also via alpha 2 receptors, the present study was designed to gain a deeper insight into the fine mechanism of functional interactions between the alpha 2 receptors mediated CA system and two peptidergic mechanisms, both shown to take part in the stimulatory control of the HPA axis: beta-endorphin and NPY. All experiments were conducted on rats whose noradrenergic bundles, which directly innervate the CRF neurons and are strongly implicated in the ether stress-induced corticotropic response, had been bilaterally obliterated by an intracerebral (i.c.) injection of 6-OHDA (NAB-X). Results showed that: (1) the blockade of the ether-stress induced ACTH response resulting from NAB-X was entirely reversed by an intraventricular (i.c.v.) infusion of the alpha 2 antagonist idazoxan (10 nmol), which appeared ineffective under basal conditions; (2) the restoration of a normal post-stress ACTH surge by i.c.v. idazoxan was itself blunted by an i.c.v. pretreatment with naloxone (10 nmol), whereas an i.c. pretreatment with an anti-NPY serum appeared ineffective. These data suggest that, in addition to a stimulatory control exerted by postsynaptic alpha 2 receptors directly on CRF neurons, other alpha 2 receptors participate, exclusively under the stress conditions above, in a tonic inhibitory control, indirectly mediated to the HPA axis across a stimulatory opioid, but not NPY regulatory component.

Cocaine-induced reduction of brain neuropeptide Y synthesis dependent on medial prefrontal cortex

Repeated administration of cocaine elicits substantial, long-lasting, but reversible reductions in neuropeptide Y (NPY) and NPY mRNA in the rat cerebral cortex and nucleus accumbens. The NPY reduction appears to be mediated through a decrease in NPY biosynthesis, occurring transneuronally, perhaps in response to changes in synaptic dopamine associated with mesolimbic and mesocortical dopamine neurons. The medial prefrontal cortex appears necessary for maintenance of cocaine's action on this neuronal network since excitotoxic lesions of this area prevented (lesion before cocaine) and reversed (lesion after cocaine) the reductions in NPY elicited by the cocaine. NPY may be a sensitive marker for chronic cocaine use. Its decrease may relate to the anxiety and depression associated with cocaine withdrawal in humans.

Neuropeptide Y and tyrosine hydroxylase mRNA levels in the locus coeruleus show similar increases after reserpine treatment

In situ hybridisation histochemistry was used to study the effect of intra-peritoneal reserpine administration on messenger RNA (mRNA) levels in the locus coeruleus (LC) of the rat. 48h after injection, levels of mRNA encoding tyrosine hydroxylase (TH) and neuropeptide Y (NPY) in the LC increased to approximately 250% of control values (p less than 0.05). The level of beta-tubulin mRNA was unaffected by reserpine administration. The similar and selective increase in TH and NPY mRNA in the LC following reserpine administration suggests that NPY may play a role in the neurotransmitter function of this catecholaminergic nucleus.

Interactions between neuropeptide Y and alpha 2-adrenoceptors in selective rat brain regions

Neuropeptide Y significantly reduced the potassium-stimulated release of [3H]norepinephrine [( 3H]NE) from slices of rat hippocampus, hypothalamus and frontal cortex but not from slices of parieto-occipital cortex. The NPY-induced inhibition of [3H]NE release from frontal cortical slices was concentration dependent, reaching statistical significance at 10 nM. The alpha 2-adrenoceptor partial agonist, clonidine, also reduced the potassium-stimulated release of [3H]NE. The combination of NPY and clonidine in hippocampal slices produced a greater reduction of stimulated [3H]NE release than either of the two compounds alone, suggesting a potentiation of their activity, whereas in frontal cortical slices, the effect was additive. When NPY and clonidine were added to frontal cortical slices, they independently produced a significant concentration-dependent reduction in forskolin-stimulated cAMP accumulation. However, NPY and clonidine combined did not produce a further reduction in forskolin-induced cAMP accumulation than either compound when used alone. These results suggest that the ability of NPY to potentiate alpha 2-adrenoceptor-induced inhibition of [3H]NE release in discrete brain regions does not depend on the reductions in cAMP.

PYY-like material and its spatial relationship with NPY, CGRP and 5-HT in the lung of the Syrian golden hamster

We investigated the presence of peptide YY, neuropeptide Y, calcitonin gene-related peptide and serotonin in the hamster lung by radioimmunoassay, high performance liquid chromatography and immunocytochemistry. Lung-tissue concentrations of peptide YY and neuropeptide Y were 1.3 +/- 0.2 and 2.5 +/- 0.2 pmol/g wet weight, respectively. These two closely related pancreatic peptides were demonstrated in separate peaks with high performance liquid chromatography. The peptide YY appeared fragmented as immunoreactive peptide YY eluted primarily late in the gradient but showed additional peaks early in the gradient. Peptide YY-like immunoreactivity (PYY-LI) was predominantly observed in one or more cells of neuroepithelial bodies in all airways peripheral to bronchioles, and in solitary neuroendocrine cells primarily located in the same peripheral areas. Neuropeptide Y-LI was seen in individual, thin nerve fibers around arteries and veins, in the airway lamina propria, and in the airway epithelium; in the latter also immunopositive nerve terminals were located. This pattern did not appear to coincide with that of calcitonin gene-related peptide-LI in epithelial nerve fibers and terminals. Peptide YY-LI, calcitonin gene-related-LI and serotonin-LI were present in cells of one and the same neuroepithelial body. However, peptide YY-LI was never found to be co-localized with calcitonin gene-related-LI or serotonin-LI, but the latter two were co-localized as previously reported.

Ultrastructural localization of neuropeptide Y in the hypothalamus

Immunoreactive NPY neurons are widely distributed in the hypothalamus of several mammalian species. In the rat, dense NPY fiber networks are found in the paraventricular, suprachiasmatic and arcuate nuclei. NPY-containing cell bodies are mostly found in the arcuate nucleus. Studies performed at the electron microscope level clearly indicate that NPY is concentrated in dense core vesicles in the cytoplasm of cell bodies as well as in terminals. Only a small percentage (about 20%) of the NPY endings are making synaptic contacts with nerve processes, especially dendrites. These ultrastructural data suggest that NPY might play a neurotransmitter/neuromodulator role. NPY has been shown, when injected into hypothalamic areas, to exert a variety of effects, including modifications in food intake, energy balance and pituitary secretion. In an attempt to define the exact role of NPY in hypothalamic functions, we have designed experiments to study the interactions of NPY with other neurotransmitter systems. In the suprachiasmatic nucleus, both NPY and 5-HT terminals have been shown to establish synaptic junctions sometimes with the same neurons. Occasionally, axoaxonic junctions between these two types of endings have been observed. These results suggested that both 5-HT and NPY might be involved in the complex regulation of circadian rythms. In the arcuate nucleus, nonsynaptic appositions between 5-HT nerve endings and NPY-containing neurons were demonstrated. In this nucleus, direct appositions between TH- and NPY-containing neurons were also detected. These appositions were of axosomatic, axodendritic or axoaxonic types. Since it has been demonstrated that arcuate NPY neurons are projected to other hypothalamic areas, such as the paraventricular and dorsomedial nuclei, it might be speculated that arcuate 5-HT/NPY and catecholamines/NPY interactions might be involved in regulation of behavior and neuroendocrine functions.

Effects of centrally administered neuropeptide Y (NPY) and NPY13-36 on the brain monoaminergic systems of the rat

The effects of centrally administered NPY on the brain monoamine systems were investigated in the rat. Neuropeptide Y (0.2-5.0 nmol), its C-terminal 13-36 amino acid (a.a.) fragment, NPY13-36 (0.4-10.0 nmol), or saline were injected into the right lateral cerebral ventricle of unrestrained rats. After 1 h the animals were decapitated, and the brains were taken out. Two cortical regions ('frontal' and 'parietal'), the striatum, the hypothalamus, and the brain stem were dissected out. The tissue contents of noradrenaline (NA), dopamine (DA) and serotonin (5-HT), as well as of their major metabolites, 3-methoxy-4-hydroxy-phenylethylene glycol (MHPG), 3,4-dihydroxyphenylacetic acid (DOPAC) and 5-hydroxy-indole acetic acid (5-HIAA) were measured. The most consistent finding was a dose-related increase of both DA and DOPAC levels after treatment with NPY. This effect was reproduced by NPY13-36 in cortical tissue, whereas, in the sub-cortical regions, NPY13-36 only reproduced the effects of NPY on the DOPAC levels. Less consistent effects were found on the NA systems, in which NA levels showed a tendency to increase following low, and decrease after high doses of NPY. These effects were largely reproduced by NPY13-36. In addition, NPY increased tissue levels of MHPG in frontal cortical tissue in a dose-related manner. The brain 5-HT systems were not affected.

Thalamic origin of neuropeptide Y innervation of the accessory optic nucleus of the pigeon (Columba livia)

Immunohistochemical and tracing techniques were used in combination to reveal the source of a neuropeptide Y-like immunoreactive (NPY-LI) plexus in the nucleus of the basal optic root (nBOR) of the pigeon accessory optic system. Injections of rhodamine-labeled latex microspheres into nBOR produced retrograde labeling of a population of neurons interposed between the principal optic nucleus of the dorsolateral thalamus (equivalent to the mammalian dorsal lateral geniculate nucleus) and the ventral lateral geniculate nucleus. The retrogradely labeled neurons were distributed mainly in the immediate vicinity of the lateral, dorsal, and ventral aspects of the nucleus rotundus. Immunohistochemical methods revealed many NPY-containing somata within the same intergeniculate thalamic area. Double-labeling immunohistochemical and retrograde tracing experiments evidenced that many NPY-LI neurons in the intergeniculate area contained rhodamine microspheres that had been previously injected into the ipsilateral nBOR. The projection of that general thalamic area to the nBOR was then confirmed by means of anterograde transport of Phaseolus vulgaris leucoagglutinin. In these experiments, the intergeniculate region was demonstrated to project to all divisions of the nBOR and to every other retino-recipient structure, including the suprachiasmatic nucleus. Finally, electrolytic lesions of the intergeniculate area produced a dramatic reduction in the number of NPY-LI axons and terminals within the ipsilateral nBOR and also within other retino-recipient structures. These data indicate the existence of a thalamic NPY-LI projection to the pigeon nBOR of the accessory optic system. This chemically specific projection originates from the intergeniculate area, which was shown in this study to project to all other retino-recipient structures. Thus, NPY may have a role in the functional organization of the accessory optic system and also of the avian visual system as a whole.

Neuropeptide Y: an overview of central distribution, functional aspects, and possible involvement in neuropsychiatric illnesses

Neuropeptide Y (NPY) was first discovered and characterized as a 36-amino-acid peptide neurotransmitter in 1982. It is widely distributed in the central nervous system, with particularly high concentrations within several limbic and cortical regions. A number of co-localizations with other neuromessengers such as noradrenaline, somatostatin, and gamma-aminobutyric acid have been demonstrated. A large number of physiological and pharmacological actions of NPY have been suggested. Recent clinical data also suggest the involvement of NPY in several neuropsychiatric illnesses, particularly in depressive and anxiety states. This article gives a comprehensive review of central distribution of NPY and its receptors, co-localizations and interactions with other neuromessengers, genetic aspects, pharmacological and physiological actions, influence on neuroendocrine functions, and possible involvement in various neuropsychiatric illnesses.

NPY-induced inhibition of male copulatory activity is a direct behavioural effect

In adult, sexually-experienced male rats, the intracerebroventricular injection of NPY caused a dose-related inhibition of copulatory behaviour, all parameters (mount, intromission and ejaculation latencies, mount and intromission frequencies, mean inter-intromission interval, post-ejaculatory interval) being significantly worsened at the dose of 8 micrograms/rat. Since rats were deprived of food during the behavioural test, it is concluded that inhibition of sexual behaviour is a 'true', direct behavioural effect of NPY, not due to a shift towards increased feeding.

Alpha 2-adrenoceptor blockade does not block feeding induced by neuropeptide Y in sheep

We tested the hypothesis that blockade of central alpha 2-adrenergic receptors would prevent neuropeptide Y (NPY)-induced feeding. Nine young female sheep were fitted with lateral ventricula cannulas. Bolus intracerebroventricular (ICV) injection of 3 nmol of NPY increased feed intake after 30 min between 45 and 153% in three experiments. A bolus ICV injection of 400 or 100 nmol of the alpha 2-antagonist, yohimbine, either 5 or 30 min before NPY injection, did not attenuate this response. Instead, yohimbine increased feed intake over NPY-induced feeding by 52 to 55%. We interpret these data as evidence that the putative NPY feeding pathway in feed-sated sheep is not dependent on the type of alpha 2-adrenergic mechanism which can be blocked by ICV injection of yohimbine.

Peptide-amine interactions in the hypothalamic paraventricular nucleus: analysis of galanin and neuropeptide Y in relation to feeding

The neuropeptide galanin (GAL) has been found to elicit feeding after injection into the paraventricular hypothalamic nucleus (PVN), where it coexists with norepinephrine (NE), a neurotransmitter believed to be important in the control of natural feeding behavior. Using pharmacological tools, this study investigated the possibility that PVN GAL influences food intake via its direct interaction with the noradrenergic system localized in this nucleus. Tests with alpha-adrenergic receptor blockers demonstrated that GAL-induced feeding, similar to NE-stimulated feeding, depends specifically upon functional alpha 2-receptor sites. Further, experimentation with the catecholamine synthesis inhibitors, alpha-methyl-p-tyrosine and Fla-63, suggested that GAL's action also depends upon the release of endogenous NE. This is in contrast to another hypothalamic peptide, neuropeptide Y, which is also a strong stimulant of food intake and coexists with NE in the PVN. Neuropeptide Y remains effective in eliciting feeding in the presence of alpha 2-receptor antagonists and catecholamine-synthesis inhibitors, suggesting that, unlike GAL, it can act independently of endogenous NE.

Neuropeptide Y receptor binding sites in human brain. Possible alteration in Alzheimer's disease

Neuropeptide Y (NPY) and peptide YY (PYY) receptor sites were studied in human brain using saturation binding experiments and receptor autoradiography. Additionally, the affinities and densities of [3H]NPY binding sites were compared in the temporal cortex, hippocampus and putamen of patients dying from Alzheimer's disease (AD) and aged matched controls. High densities of [3H]NPY binding sites were found in the putamen (192 +/- 32 fmol/mg protein), followed by the hippocampus (165 +/- 42 fmol/mg protein) and temporal cortex (118 +/- 19 fmol/mg protein). Receptor autoradiography revealed that these sites were especially concentrated in certain layers of the hippocampus, laminae I and IV-V of the temporal cortex and the amygdalo-hippocampal area. No significant changes in [3H]NPY binding affinities were seen between the AD and aged-matched groups (Kd ranges: 2.5-6.8 nM). However, significant decreases in [3H]NPY receptor densities (Bmax) were found in temporal cortex (-43%) and hippocampus (-49%) in AD brains. No significant change in [3H]NPY Bmax values was found in the putamen. It is therefore possible that decreases in [3H]NPY receptor densities may be associated to the degenerative process taking place in certain brain regions in AD, although further work will be necessary to confirm this hypothesis. Part of this work was presented at the 17th Annual Meeting of the Society for Neuroscience.

Quantitative autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites in rat brain. Comparison with [125I]peptide YY receptor sites

The autoradiographic distribution of [125I]Bolton-Hunter neuropeptide Y receptor binding sites was quantified in rat brain. The highest level of [125I]Bolton-Hunter neuropeptide Y binding sites was seen in the hippocampus (ventral stratum radiatum, CA3 subfield: 6029 +/- 250 fmol/g tissue). The distribution of these sites was clearly laminated, being particularly concentrated in the oriens layer (dorsal CA3 subfield: 2562 +/- 147 fmol/g tissue) and stratum radiatum (dorsal CA3 subfield: 2577 +/- 95 fmol/g tissue). Lower levels of sites were seen in the pyramidal cell layer (1708 +/- 105 fmol/g tissue) and the molecular layer (1155 +/- 116 fmol/g tissue). The cortical distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites was also laminated, being particularly enriched in superficial laminae (occipital cortex, layers I-II, 4038 +/- 148 fmol/g tissue; layers III-IV, 1392 +/- 97 fmol/g tissue and layers V-VI, 1522 +/- 138 fmol/g tissue). Other areas containing high amounts of sites included the anterior olfactory nuclei (ventral part, 4935 +/- 119 fmol/g tissue; lateral part, 4530 +/- 149 fmol/g tissue; dorsal part, 3378 +/- 140 fmol/g tissue and medial part, 2601 +/- 150 fmol/g tissue); anteromedial (5168 +/- 211 fmol/g tissue), medial (4611 +/- 107 fmol/g tissue) and lateral posterior thalamic nuclei (4465 +/- 189 fmol/g tissue); medial mammillary nucleus (5555 +/- 241 fmol/g tissue); medial geniculate nucleus (4747 +/- 56 fmol/g tissue); claustrum (4123 +/- 235 fmol/g tissue); posteromedial cortical amygdaloid nucleus (3524 +/- 138 fmol/g tissue), tenia tecta (2540 +/- 195 fmol/g tissue); lateral septum (1785 +/- 90 fmol/g tissue); suprachiasmatic hypothalamic nucleus (1604 +/- 115 fmol/g tissue), and substantia nigra, pars compacta (1846 +/- 142 fmol/g tissue) and pars lateralis (1750 +/- 165 fmol/g tissue). Areas moderately enriched with [125I]Bolton-Hunter neuropeptide Y binding sites included the zonal layer of the superior colliculus (1347 +/- 71 fmol/g tissue); anterior pretectal nucleus (1172 +/- 113 fmol/g tissue); ventral tegmental area (1090 +/- 97 fmol/g tissue); periventricular fibre system (1026 +/- 48 fmol/g tissue); core of nucleus accumbens (948 +/- 29 fmol/g tissue) and area postrema (799 +/- 87 fmol/g tissue). These results are discussed with regard to some of the suggested biological effects of neuropeptide Y in the central nervous system such as effects on learning, locomotion and circadian rhythms. Moreover, we also compared the distribution of [125I]Bolton-Hunter neuropeptide Y receptor sites with that of [125I]peptide YY sites in rat brain. The resolution of the autoradiographic image is better with [125I]peptide YY most likely because of higher affinity and percentage of specific labelling.(ABSTRACT TRUNCATED AT 400 WORDS)

Neuropeptide Y-immunoreactive cells in the caudal medulla project to the median preoptic nucleus

The region surrounding the anteroventral third ventricle, particularly the median preoptic nucleus, has been implicated in the control of fluid balance and blood pressure. Previous studies indicate that catecholaminergic inputs from the caudal medulla are important in these controls. In this study we report that neuropeptide Y-immunoreactive cells in the caudal medulla project to the median preoptic nucleus in the basal forebrain. Notably these cells are found in the caudal ventral lateral medulla and the nucleus of the solitary tract. Since catecholaminergic projections to the median preoptic nucleus also arise from these regions the possibility of interactions between NPY and catecholamines exists, particularly in the control of fluid balance and blood pressure.

Brain neuropeptides: actions on central cardiovascular control mechanisms

The many peptides we have not considered (e.g. gastrin, motilin, FMRFamide, carnosine, litorin, dermorphin, casomorphin, eledoisin, prolactin, growth hormone, neuromedin U, proctolin, etc.) were omitted due to lack of information as far as any putative central cardiovascular effects are concerned. However, even for some of these peptide pariahs intriguing snippets of information are available now (e.g. ref. 85), although as we write, the list of possible candidates for investigation grows longer. On an optimistic note, it is becoming clear that many brain neuropeptides may have important effects on cardiovascular regulation. It seems feasible that 'chemically coded' pathways in the brain might be the neuroanatomical correlate of a 'viscerotopic' organization of cardiovascular control mechanisms, whereby the activity of the heart and flows through vascular beds are individually controlled, but in an integrated fashion, utilizing particular combinations of neurotransmitters and neuropeptides within the brain. Such possibilities can only be investigated, properly, by measurement of changes in cardiac output and regional haemodynamics in response to appropriate interventions, in conscious, unrestrained animals.

Neuropeptide Y (NPY)-induced suppression of activity in the rat: evidence for NPY receptor heterogeneity and for interaction with alpha-adrenoceptors

The receptor mechanisms mediating the neuropeptide Y (NPY)-induced suppression of behavioural activity have been examined in the rat. The interaction of NPY with central noradrenergic mechanisms was also studied. The non-selective alpha-adrenoceptor antagonist, phentolamine (15-60 nmol intracerebroventricularly, i.c.v.), caused a dose-related antagonism (up to 50%) of the NPY-induced suppression of activity. The selective alpha 2-adrenoceptor antagonist, idazoxan (0.125 mg/kg intraperitoneally, i.p.), was even more effective, while the selective alpha 1-adrenoceptor antagonist, prazosin, was without effect. In addition, we examined whether the recently postulated subdivision of peripheral NPY receptors was also applicable to the brain. The ability of the C-terminal 13-36 amino acid fragment of NPY (postulated to activate NPY-Y2 receptors) to reproduce the effects of the full molecule (postulated to activate both NPY-Y1 and -Y2 receptors) was tested. NPY-(13-36) (0.4-10.0 nmol i.c.v.) failed to produce any suppression of activity. On the contrary, it produced an increase in locomotor activity and rearings at low doses. This effect was not blocked by phentolamine. We conclude that the NPY-induced suppression of activity is produced to a large extent by modulation of alpha 2-adrenergic transmission. Our results also provide evidence for heterogeneity among the central NPY receptors, with the NPY-induced suppression of activity being mediated by the NPY-Y1 receptor subtype.

Pharmacological characterization of dopaminergic influence on expression of neuropeptide Y immunoreactivity by rat striatal neurons

Selective unilateral lesion of the nigrostriatal dopamine pathway by the cytotoxin 6-hydroxydopamine was previously shown to enhance the number and staining intensity of neurons expressing neuropeptide Y immunoreactivity in the ipsilateral striatum. This effect was completely reversed by treatment of the 6-hydroxydopamine-injected animals with the directly acting dopamine agonist apomorphine. This finding reinforces our previous hypothesis that changes in striatal neuropeptide Y staining subsequent to 6-hydroxydopamine lesions of this kind reflect changes in intraneuronal neuropeptide Y levels which are directly attributable to the suppression of a tonic dopaminergic control. In contrast to the effect of 6-hydroxydopamine lesion, non-destructive impairment of striatal dopamine transmission by treatments with either the dual dopamine D1/D2 receptor antagonist haloperidol or the dopamine synthesis inhibitor alpha-methylparatyrosine induced a decrease in both the number of neuropeptide Y striatal cells (-29.8% and -34.8%, respectively) and in their labeling intensity. The selective D2-antagonist sulpiride also showed a tendency to reduce the number of neuropeptide Y immunoreactive cells, whereas the selective D1 antagonist SCH 23390 induced a small but constant increase in this number. Taken as a whole, these results suggest that the dopaminergic D1 and D2 receptor subtypes play opposite roles in the dopaminergic control of the striatal neuropeptide Y neuronal system, which may account for the different changes in striatal neuropeptide Y immunostaining observed after 6-hydroxydopamine injury and after non-destructive impairment of nigrostriatal dopaminergic transmission.

Differential effects of hypothalamic catecholamine depletion on the release of arginine vasopressin and CRF-41 into hypothalamo-hypophyseal portal blood

The effects of 6-hydroxydopamine lesions of the ventral noradrenergic bundle (VNAB) and of intracerebroventricular 6-hydroxydopamine on hypothalamo-hypophyseal portal blood (HPB) concentrations of arginine vasopressin (AVP), corticotrophin releasing factor (CRF-41), and noradrenaline have been investigated. VNAB lesions and intracerebroventricular 6-hydroxydopamine caused a reduction of HPB CRF-41 concentration, while AVP remained unchanged. HPB noradrenaline concentration was reduced in animals treated with lateral ventricular 6-hydroxydopamine, but was unchanged in VNAB lesioned animals. Our results suggest differential effects of noradrenaline on the release of AVP and CRF-41 into HPB.

Neuronal interactions between neuropeptide Y (NPY) and catecholaminergic systems in the rat arcuate nucleus as shown by dual immunocytochemistry

Several recent studies have suggested interactions between catecholamine (CA) and neuropeptide Y (NPY) neuronal systems in the rat brain. In order to obtain morphological evidence for such CA/NPY interactions in the arcuate nucleus, we have used a double immunostaining procedure using an anti-tyrosine hydroxylase (TH) antiserum as a marker for catecholamine neurons and an anti-NPY antiserum. This double staining, where the first staining is silver-gold intensified, was detectable at both light and electron microscopic levels. In semi-thin sections, a substantial overlap and close proximity of TH-immunopositive neurons and NPY neuronal elements could be seen within the arcuate nucleus. At the electron microscopic level, direct appositions between TH- and NPY-immunoreactive structures could be detected. These appositions were of axosomatic, axodendritic or axoaxonic types without any synaptic membrane differentiation. Moreover, direct appositions between NPY-immunoreactive structures have also been observed. This morphological study showing appositions between TH and NPY neuronal systems suggest direct interactions between these two systems in the arcuate nucleus.

Neuropeptide Y and peptide YY as possible cerebrospinal fluid markers for major depression and schizophrenia, respectively

Neuropeptide Y (NPY)-like and peptide YY (PYY)-like immunoreactivities were measured in cerebrospinal fluid (CSF) from patients with major depressive disorder or schizophrenia and from healthy volunteers without physical or mental illness. NPY-like material was significantly lower (P less than 0.001) in CSF of patients with depressive disorders than in schizophrenic patients or healthy controls. Treatment with the antidepressant, amiflamine, a selective MAO-A inhibitor, did not alter CSF peptide concentrations. In drug-free schizophrenic patients, normal NPY but reduced PYY concentrations in CSF were observed. Treatment with neuroleptics did not affect the levels of NPY or PYY in the CSF. The finding of reduced CSF concentrations of NPY in patients with major depression and of reduced PYY concentrations in schizophrenia may reflect disturbed synthesis, turnover or degradation of the peptides. These findings suggest that the reduced concentrations of NPY or PYY in the CSF may be used as trait markers of the respective illnesses.