Receptor autoradiographical evidence for high densities of 125I-neuropeptide Y binding sites in the nucleus tractus solitarius of the normal male rat

Studies on the relationship of tyrosine hydroxylase, dopamine and cyclic amp-regulated phosphoprotein-32 immunoreactive neuronal structures and d1 receptor antagonist binding sites in various brain regions of the male rat-mismatches indicate a role of d1 receptors in volume transmission

The relationship between tyrosine hydroxylase (TH), dopamine (DA) and cyclic AMP-regulated phosphoprotein-32 (DARPP-32) immunoreactive (IR) neuronal structures and D1 receptor antagonist binding sites has been analysed in various brain regions in the male rat, using immunocytochemistry and receptor autoradiography with the iodinated analogue of SCH 23390 ([(125)I]SCH 23982) as radioligand. Two-colour immunocytochemistry was used to establish in detail the relationship between DARPP-32 and the TH IR neuronal structures in mes-, di- and telencephalon. The analysis reveals complex matches and mismatches between central DARPP-32 immunoreactive neurones, DA neurones and D1 DA receptors. The results inter alia indicate a probable release of DA from the dendritic plexus of the zona reticulata of the substantia nigra to reach D1 DA receptors via extracellular pathways. DA released from the few DA terminals present in the entopeduncular nucleus and from adjacent dopamine axons may also reach D1 DA receptors in this nucleus by extracellular diffusion. A similar situation may also exist in the globus pallidus. Thus, DA may in some regions be released as a paracrine signal to reach distant D1 DA receptors. This type of chemical transmission has been called volume transmission and D1 receptors may thus participate in volume transmission. The mismatch obtained in, for example, the amygdaloid cortex and hypothalamus between D1 receptor antagonist binding sites and DARPP-32 IR nerve cell profiles, is compatible with the possibility that some D1 receptors linked to adenylate cyclase may not involve DARPP-32 as a substrate protein for the cyclic AMP-dependent protein kinase. In addition the possibility should be considered that D1 receptors may not always be linked to adenylate cyclase. Finally, the mismatch in the median eminence between [(125)I]SCH 23982 binding sites and DARPP-32 IR profiles may indicate the existence of D1 receptors which are masked under basal conditions in the male rat.

Peripheral tissue-brain interactions in the regulation of food intake

More than 70 years ago the glucostatic, lipostatic and aminostatic hypotheses proposed that the central nervous system sensed circulating levels of different metabolites, changing feeding behaviour in response to the levels of those molecules. In the last 20 years the rapid increase in obesity and associated pathologies in developed countries has involved a substantial increase in the knowledge of the physiological and molecular mechanism regulating body mass. This effort has resulted in the recent discovery of new peripheral signals, such as leptin and ghrelin, as well as new neuropeptides, such as orexins, involved in body-weight homeostasis. The present review summarises research into energy balance, starting from the original classical hypotheses proposing metabolite sensing, through peripheral tissue-brain interactions and coming full circle to the recently-discovered role of hypothalamic fatty acid synthase in feeding regulation. Understanding these molecular mechanisms will provide new pharmacological targets for the treatment of obesity and appetite disorders.

Role of neuropeptides in appetite regulation and obesity--a review

Obesity represents the most prevalent nutritional problem worldwide which in the long run predisposes to development of diabetes mellitus, hypertension, endometrial carcinoma, osteoarthritis, gall stones and cardiovascular diseases. Despite significant reductions in dietary fat consumption, the prevalence of obesity is on a rise and is taking on pandemic proportions. Obesity develops when energy intake exceeds energy expenditure over time. Recently, a close evolutionary relationship between the peripheral and hypothalamic neuropeptides has become apparent. The hypothalamus being the central feeding organ mediates regulation of short-term and long-term dietary intake via synthesis of various orexigenic and anorectic neuropeptides. The structure and function of many hypothalamic peptides (neuropeptide Y (NPY), melanocortins, agouti-related peptide (AGRP), cocaine and amphetamine regulated transcript (CART), melanin concentrating hormone (MCH), orexins have been characterized in rodent models The peripheral neuropeptides such as cholecystokinin (CCK), ghrelin, peptide YY (PYY3-36), amylin, bombesin regulate important gastrointestinal functions such as motility, secretion, absorption, provide feedback to the central nervous system on availability of nutrients and may play a part in regulating food intake. The pharmacological potential of several endogenous peripheral peptides released prior to, during and/or after feeding are being explored. Long-term regulation is provided by the main circulating hormones leptin and insulin. These systems implicated in hypothalamic appetite regulation provide potential targets for treatment of obesity which could potentially pass into clinical development in the next 5 years. This review summarizes various effects and interrelationship of these central and peripheral neuropeptides in metabolism, obesity and their potential role as targets for treatment of obesity.

Hormonal regulation of food intake

Our knowledge of the physiological systems controlling energy homeostasis has increased dramatically over the last decade. The roles of peripheral signals from adipose tissue, pancreas, and the gastrointestinal tract reflecting short- and long-term nutritional status are now being described. Such signals influence central circuits in the hypothalamus, brain stem, and limbic system to modulate neuropeptide release and hence food intake and energy expenditure. This review discusses the peripheral hormones and central neuronal pathways that contribute to control of appetite.

Neurobiologic processes in drug reward and addiction

Neurophysiologic processes underlie the uncontrolled, compulsive behaviors defining the addicted state. These"hard-wired"changes in the brain are considered critical for the transition from casual to addictive drug use. This review of preclinical and clinical (primarily neuroimaging) studies will describe how the delineation between pleasure, reward, and addiction has evolved as our understanding of the biologic mechanisms underlying these processes has progressed. Although the mesolimbic dopaminergic efflux associated with drug reward was previously considered the biologic equivalent of pleasure, dopaminergic activation occurs in the presence of unexpected and novel stimuli (either pleasurable or aversive) and appears to determine the motivational state of wanting or expectation. The persistent release of dopamine during chronic drug use progressively recruits limbic brain regions and the prefrontal cortex, embedding drug cues into the amygdala (through glutaminergic mechanisms) and involving the amygdala, anterior cingulate, orbitofrontal cortex, and dorsolateral prefrontal cortex in the obsessive craving for drugs. The abstinent, addicted brain is subsequently primed to return to drug use when triggered by a single use of drug, contextual drug cues, craving, or stress, with each process defined by a relatively distinct brain region or neural pathway. The compulsive drive toward drug use is complemented by deficits in impulse control and decision making, which are also mediated by the orbitofrontal cortex and anterior cingulate. Within this framework, future targets for pharmacologic treatment are suggested.

Cardiorespiratory responses to intracerebroventricular injection of neuropeptide Y in anaesthetised dogs

Cardiovascular and respiratory effects of intracerebroventricular (icv) administration of neuropeptide Y (NPY) and separate, preferential agonists for NPY Y1 and Y2 receptors were observed in anaesthetised dogs. Central injections of NPY resulted in significant cardiac slowing and decreases in arterial pressure. These cardiovascular effects were blocked by central injection of the NPY Y1- preferring antagonist 1229U91. Central injection of NPY did not have a significant effect on ventilation, but the NPY Y1 antagonist 1229U91 administered alone caused a significant increase in ventilation. The NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreased ventilation while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24--36 significantly increased it. A similar inverse relationship was seen with respect to blood pressure, with the NPY Y1-receptor agonist [Leu31Pro34] NPY significantly decreasing blood pressure, while the NPY Y2 receptor agonist N-acetyl [Leu28Leu31] NPY 24-36 significantly increased it. These findings suggest a role for NPY Y1 receptors in pathways mediating decreases in ventilation and blood pressure, and for NPY Y2 receptors in those mediating increased ventilation and blood pressure.

Neuropeptide Y stimulates bile secretion via Y1 receptor in the left dorsal vagal complex in rats

Neuropeptide Y (NPY) injected into the cerebrospinal fluid and the left dorsal vagal complex enhances bile acid-independent and bicarbonate-dependent bile secretion through vagal muscarinic pathways in animal models. NPY binds to and activates six different receptor subtypes, and NPY Y1 and Y2 receptors are distributed in the dorsal vagal complex. We sought to determine which NPY receptor subtypes are involved in central stimulation of bile secretion by examining the effect of microinjection of specific NPY receptor agonists into the dorsal vagal complex. The bile duct was cannulated in urethane-anesthetized and bile acid-compensated rats. After measuring basal secretion, NPY, peptide YY (PYY), [Leu31, Pro34]NPY, NPY(13-36), or NPY(3-36) was microinjected into the either right or left dorsal vagal complex and bile secretion was observed for 100 minutes. Hepatic branch vagotomy was performed 2 hours before the peptide injection. Microinjection of NPY and PYY (8 pmol) into the left dorsal vagal complex increased bile secretion. [Leu31, Pro34]NPY microinjected into the left dorsal vagal complex also dose-dependently (1-8 pmol) stimulated bile acid-independent and bicarbonate-dependent bile secretion. Microinjection of NPY(13-36) into the left dorsal vagal complex did not stimulate and NPY(3-36) dose-dependently inhibited bile secretion. Stimulation of bile secretion by [Leu31, Pro34]NPY was abolished by hepatic branch vagotomy. NPY acts in the left dorsal vagal complex to stimulate bile acid-independent and bicarbonate-dependent bile secretion via Y1 receptor subtype.

Increased potency of neuropeptide Y to antagonize alpha2-adrenoceptor function in the nucleus tractus solitarii of the spontaneously hypertensive rat

The regulation by neuropeptide Y of alpha2-adrenoceptors in the nucleus tractus solitarii was evaluated in the adult normotensive Wistar Kyoto rat and the adult spontaneously hypertensive rat. The microinjection of a submaximal dose of l-noradrenaline (800 pmol in 50 nl) alone into the nucleus tractus solitarii produced a significant reduction in the mean arterial blood pressure in either strain. The threshold dose (1 pmol in 50 nl) of neuropeptide Y(1-36) for the vasodepressor response in the Wistar Kyoto rat was five times higher than that (0.2 pmol in 50 nl) in the spontaneously hypertensive rat. Furthermore, neuropeptide Y(1-36) at 0.2 pmol in 50 nl could significantly counteract the vasodepressor response to l-noradrenaline (800 pmol in 50 nl) in the spontaneously hypertensive rat, but not in the Wistar Kyoto rat, in which 1 pmol in 50 nl of neuropeptide Y(1-36) must be employed to counteract the vasodepressor response to l-noradrenaline (800 pmol in 50 nl), although the vasodepressor responses are of a similar magnitude. The in situ hybridization and quantitative receptor autoradiographical experiments showed that the alpha2A-adrenoceptor messenger RNA levels and the B(max) value of the alpha2-adrenoceptor agonist [3H]p-aminoclonidine binding sites measured in the nucleus tractus solitarii of the spontaneously hypertensive rat were substantially lower than those in the Wistar Kyoto rat. The quantitative receptor autoradiographical results were consistent with the cardiovascular results and showed that in the spontaneously hypertensive rat, neuropeptide Y(1-36) at 1 nM led to a significant increase in the K(d) value of [3H]p-aminoclonidine binding sites. In the Wistar Kyoto rat, neuropeptide Y(1-36) produced this effect only at 10 nM. The present study provides evidence for an increase of the potency of neuropeptide Y(1-36) to antagonistically modulate alpha2-adrenoceptors in the nucleus tractus solitarii of the spontaneously hypertensive rat. This enhanced antagonistic action may partly be related to a reduction in the number of alpha2A-adrenoceptors in the nucleus tractus solitarii of the spontaneously hypertensive rat, since a decrease has been observed in the alpha2A-adrenoceptor messenger RNA levels and the alpha2-adrenoceptor binding sites in the spontaneously hypertensive rat. This increased potency of neuropeptide Y(1-36) to antagonize alpha2-adrenoceptor function in the nucleus tractus solitarii of the spontaneously hypertensive rat may contribute to the development of high blood pressure in this hypertensive strain.

Autoradiographic localization of receptors for neuropeptide Y (NPY) in the brain of broiler and leghorn chickens (Gallus domesticus)

Broiler and leghorn chickens show an extreme difference in ingestive and reproductive behavior. As neuropeptide Y (NPY) influences both behaviors the goal of this study was to elucidate the distribution, expression and affinity of NPY binding sites in broiler and leghorn chicken brain. By means of in vitro autoradiography, sections of chicken brains were incubated with 3H-NPY as tracer and NPY as displacer. Scatchard analysis revealed a curvilinear plot suggesting two subtypes of the NPY binding site in the chicken brain, a high affinity one (KD = 2-4 nM) and one with a lower affinity (KD = 18-24 nM). Binding sites for NPY are localized with high density in the different subdivisions of the neostriatum and the hyperstriatum, the cerebellum, the nucleus septalis lateralis and medialis, the nucleus ruber and the nucleus tractus solitarii. A lower density of NPY binding sites was found in the different subdivisions of the striatum, the nucleus mesencephalicus lateralis pars dorsalis, the paleostriatum, the archistriatum intermedium pars ventralis, the nucleus geniculatus lateralis, the nucleus taeniae, the locus ceruleus, the nucleus rotondus, the nucleus habenularis medialis, the nucleus dorsomedialis anterior (rostralis) thalami, the pituitary and the area of the hypothalamus with its nuclei such as the nucleus paraventricularis magnocellularis and the nucleus preopticus medialis. Comparison of the localization of NPY binding sites in the brains of broilers and leghorns showed no differences but the density of both receptor types is two to three times higher in broilers than in leghorns.

Neuropeptide Y gene expression and receptor autoradiography in hypertensive and normotensive rat brain

Neurones containing neuropeptide Y (NPY) may participate in central cardiovascular control by tonically influencing barosensitive neurones within the nucleus tractus solitarius. The present study has employed both in situ hybridisation histochemistry and receptor autoradiography, to visualise the expression of prepro-NPY mRNA in the forebrain and to determine the NPY receptor subtype(s) in the brainstem, respectively. Prepro-NPY gene expression was visualised in the hypothalamus, cortex, dentate gyrus and lateral reticular thalamus from age-matched spontaneously hypertensive rats (SHR) and normotensive Don Ryu rats (DRY) and Wistar Kyoto rats (WKY). Quantitative densitometry revealed an increase in the NPY transcript in the arcuate nucleus of SHR rats compared to their normotensive counterparts. Autoradiography using [125I]Bolton-Hunter-NPY (BH-NPY, 15 pM) demonstrated NPY binding sites in the area postrema, the commissural nucleus tractus solitarius (cNTS) and the inferior olivary complex. NPY (1 microM) and peptide YY (1 microM), but not [Leu31,Pro34]NPY (10-100 nM), fully inhibited the binding of [125I]BH-NPY. These results indicate that NPY receptors of the Y2 subtype predominate in the dorsal vagal complex. Unilateral nodose ganglionectomy resulted in a partial loss of NPY binding sites in the commissural NTS, but not the area postrema, suggesting that a proportion of binding sites (Y2 subtype) are present on central vagal terminals. While all three rat strains appear to have the same relative proportions of NPY receptor subtypes in the brainstem, the relevance of the differential NPY gene expression in the arcuate nucleus regarding central cardiovascular control mechanisms and/or the pathogenesis of hypertension remains to be elucidated.

Pancreatic polypeptide, microinjected into the dorsal vagal complex, potentiates glucose-stimulated insulin secretion in the rat

Specific binding sites for circulating pancreatic polypeptide (PP) have been found within the dorsal vagal complex (DVC) in the caudal medulla oblongata. Therefore, the effects of rat PP on pancreatic hormone secretion upon its microinjection into the DVC in halothane-anesthetized rats at doses of 0.4-40 pmol were investigated. At this range of doses, the changes in plasma concentrations of insulin, glucagon and glucose over basal levels did not differ from those after vehicle microinjection. In a separate series of experiments, vehicle and PP at doses of 0.4 and 4 pmol were microinjected into the right DVC 40 min after the continuous infusion of D-glucose had been started. In animals receiving continuous infusion of D-glucose, PP microinjected into the DVC (4 pmol), resulted in markedly higher insulin levels at corresponding time points compared to those with vehicle microinjected into the DVC. These data indicate, for the first time, that microinjection of PP into the DVC may potentiate glucose-stimulated insulin secretion in halothane-anesthetized rats.

Central neuropeptide Y enhances bile secretion through vagal and muscarinic but not nitric oxide pathways in rats

Neuropeptide Y (NPY) acts in the central nervous system to regulate gastrointestinal functions in rats and dogs. The effects of intracisternal injection of NPY on bile secretion and biliary components were investigated in urethane-anesthetized rats with bile duct cannula. Intracisternal NPY (0.02-0.12 nmol) dose-dependently increased bile secretion by 9.2-19.5%. The secretory response occurred within the first 20-40 min and lasted for the 120-min observation period. Intravenous injection of NPY (0.12 nmol) did not modify bile secretion under identical conditions. Biliary bile acid, phospholipid, and cholesterol secretion were not modified by intracisternal injection of NPY (0.12 nmol), whereas bicarbonate was increased by 19.0 +/- 1.7% from 40 to 120 min after NPY injection. Cervical cord transection at the C6 level, acute bilateral adrenalectomy (-120 min), or injection of NG-nitro-L-arginine methyl ester (10 mg/kg, IV, -15 min), an inhibitor of nitric oxide biosynthesis, did not alter intracisternal NPY (0.12 nmol)-induced stimulation of bile secretion. Atropine (2.0 mg/kg, IP, -30 min) and bilateral cervical vagotomy (-120 min) completely abolished the stimulatory effect of intracisternal NPY (0.12 nmol) on bile secretion. These findings indicate that NPY acts in the brain to stimulate bicarbonate-dependent bile secretion through vagal and muscarinic pathways and suggest that peptides in the central nervous system may be involved in the vagal regulation of bile secretion.

Antagonistic regulation of alpha 2-adrenoceptors by neuropeptide Y receptor subtypes in the nucleus tractus solitarii

The modulation of alpha 2-adrenoceptors by neuropeptide Y Y1 and neuropeptide Y Y2 receptor subtypes has been studied in the nucleus tractus solitarii of the male rat. The autoradiographical experiments showed that neuropeptide Y-(1-36), neuropeptide Y-(13-36), a selective neuropeptide Y Y2 receptor agonist, and [Leu31,Pro34]neuropeptide Y, a selective neuropeptide Y Y1 receptor agonist, in the nanomolar range increased the Kd value of the [3H]p-aminoclonidine binding sites in the above rank order of potency without changing the Bmax values. In contrast, in the competition experiments, the neuropeptide Y Y1 and the neuropeptide Y Y2 receptor agonists decreased and increased, respectively, with the same potency the IC50 value of l-adrenaline and especially of clonidine for the alpha 2-adrenoceptor agonist binding sites associated with an increase and a decrease of the B0 value, respectively. Cardiovascular experiments showed that microinjections of clonidine into the nucleus tractus solitarii induced dose-dependent vasodepressor and bradycardiac responses. Threshold doses for vasodepressor effects of neuropeptide Y-(1-36) and of the neuropeptide Y Y1 receptor agonist and for vasopressor effects of the neuropeptide Y Y2 receptor agonist significantly counteracted the vasodepressor action elicited by an ED50 dose of clonidine in the nucleus tractus solitarii, the bradycardiac action of clonidine also being counteracted by the neuropeptide Y Y2 but not the neuropeptide Y Y1 receptor agonist. The present results give indications for the existence of an antagonistic modulation of high affinity alpha 2-adrenoceptors by the neuropeptide Y Y1 and neuropeptide Y Y2 receptor subtype in the nucleus tractus solitarii which may contribute to a reduction of alpha 2-adrenoceptor-mediated cardiovascular depression.

Selective modulation of the NPY receptors of the Y2 subtype by alpha 2 receptors in the nucleus tractus solitarii of the rat. A cardiovascular and quantitative receptor autoradiographical analysis

The modulation of neuropeptide Y (NPY) receptors by alpha 2 receptors in the nucleus tractus solitarii (Sol) of the rat was evaluated using quantitative receptor autoradiography and measurements of mean arterial blood pressure and heart rate. The receptor autoradiographical experiments showed that clonidine (10 nM), a selective alpha 2 receptor agonist, induced a 59% increase in the B0 value and a 47% decrease in the IC50 value of NPY(1-36) when competing for [125I]peptide YY ([125I]PYY)-binding sites in the presence of [Leu31, Pro34]NPY (100 nM), a selective NPY Y1 receptor agonist, to block the binding to NPY Y1 receptors. In contrast, when NPY(13-36) (300 nM), a selective NPY Y2 receptor agonist, was used to block the binding to NPY Y2 receptors, clonidine (1-30 nM) did not affect the B0 value and the IC50 value of NPY(1-36) when competing for [125I]PYY-binding sites, suggesting that the stimulation of alpha 2 receptors can selectively increase the affinity of NYP(1-36) for the NPY Y2 receptor. Microinjections of threshold doses of adrenaline or clonidine into the Sol not only counteracted the vasopressor action of a close to ED50 dose of coinjected NPY(13-36), but also changed the vasopressor and tachycardic response produced by NPY(13-36) into a vasodepressor and bradycardic response. However, threshold doses of adrenaline or of clonidine microinjected into the Sol did not modify the vasodepressor responses to a close to ED50 dose of NPY(1-36) or of [Leu31, Pro34]NPY.(ABSTRACT TRUNCATED AT 250 WORDS)

Coinjections of NPY(1-36) or [Leu31,Pro34]NPY with adrenaline in the nucleus tractus solitarius of the rat counteract the vasodepressor responses to adrenaline

The cardiovascular effects of adrenaline microinjected alone or together with neuropeptide Y (NPY) receptor agonists into the nucleus tractus solitarius (Sol) of the anaesthetized rat have been investigated in order to evaluate NPY/adrenergic receptor interactions. In the dose range 0.05-20 nmol, adrenaline microinjected unilaterally into the Sol produced significant dose-related reductions in mean arterial blood pressure and heart rate. The vasodepressor action of a close to ED50 dose of adrenaline (0.5 nmol) was significantly counteracted by a threshold dose of NPY (1-36) (1 pmol) and of the NPY Y1 receptor agonist [Leu31,Pro34]NPY (2.5 pmol) microinjected into the Sol, but not by a threshold dose of NPY(13-36)(50 fmol), a selective Y2 receptor agonist. The present study provides evidence for an antagonistic NPY Y1/adrenergic receptor interaction in the Sol of the rat, involved in cardiovascular regulation.

Participation of endogenous neuropeptide Y in the suppression of baroreceptor reflex response by locus coeruleus in the rat

We evaluated the potential participation of endogenous brain neuropeptide Y (NPY) in the suppression of baroreceptor reflex (BRR) response by locus coeruleus (LC), using adult male Sprague-Dawley rats anesthetized with pentobarbital sodium (40 mg/kg, i.p.). Bilateral microinjection of an antiserum against NPY (1:20, 20 nl) into the caudal one-third level of the nucleus tractus solitarii (NTS), the terminal site for baroreceptor afferent fibers, significantly reversed the suppressive effect of electrical or chemical activation of the LC on the BRR response. Treatments with NPY (4.65 pmol, 20 nl), normal rabbit serum, aCSF and heat-inactivated NPY or NPY antiserum, on the other hand, were ineffective. The LC-promoted inhibition of the BRR response was also attenuated by the alpha 1-adrenoceptor antagonist prazosin (50 pmol, 20 nl), either microinjected alone or in combination with NPY antiserum into the bilateral NTS. Mathematical treatment of our data revealed that the depressive effect on the BRR response of NPY or NE released at the NTS following LC activation manifested different time-course and magnitude. The one by endogenous NPY maximized at 40 min and amounted to no more than 20% of, whereas that by NE peaked at 10 min and contributed no less than 30% to, the suppression. These results suggest that both endogenous NPY and NE may participate in the suppression of BRR response by the LC at the NTS.

Subpicomolar amounts of NPY(13-36) injected into the nucleus tractus solitarius of the rat counteract the cardiovascular responses to L-glutamate

The effects of NPY(13-36) on cardiorespiratory responses elicited by microinjections of L-glutamate into the nucleus tractus solitarius (NTS) have been studied in anaesthetized (alpha-chloralose + urethane) Sprague-Dawley rats. NPY(13-36) in doses ranging from 50 to 500 fmol produces a significant increase in mean arterial pressure (MAP) without significant effects on heart rate (HR) and respiratory rate (RR). The ED50 dose (100 fmol) of NPY(13-36) counteracts significantly the decrease in MAP and HR elicited by L-glutamate (1500 pmol) microinjected into NTS. Similar results are obtained using a threshold dose of the peptide (50 fmol) and an ED50 dose of L-glutamate (300 pmol). These results indicate that the Y2 receptors in NTS can mediate vasopressor responses to femtomolar amounts of NPY(13-36) and counteract cardiovascular responses to L-glutamate.

Cerebrospinal fluid norepinephrine, 3-methoxy-4-hydroxyphenylglycol and neuropeptide Y levels in Parkinson's disease, multiple system atrophy and dementia of the Alzheimer type

Neuropeptide Y, one of the most abundant polypeptides within the nervous system, is co-stored with catecholamines, especially norepinephrine (NE), thus suggesting its possible involvement in pathologies characterized by a noradrenergic impairment. In Parkinson's disease (PD), as well as in multiple system atrophy (MSA), a central noradrenergic deficit has been demonstrated, and in the dementia of Alzheimer type (DAT) an impaired noradrenergic transmission has been postulated. In this study we determined CSF NE and MHPG levels in 29 PD, 15 MSA, 22 DAT patients and in 36 controls, while CSF NPY-immunoreactivity (NPY-ir) levels were measured in 10 PD, 7 MSA, 10 DAT patients and 20 controls. PD, MSA, and DAT patients showed a significant reduction in CSF NPY-ir and NE levels compared with controls, while CSF MHPG levels resulted in a reduction in only the MSA group. Furthermore, an inverse correlation between either NE or MHPG levels and the duration of the orthostatic hypotension was found in MSA patients while for DAT patients the MHPG levels were directly correlated to the severity of cognitive impairment, and inversely to the duration of illness.

Neuropeptide Y/angiotensin II interactions in central cardiovascular regulation of the rat

Neuropeptide Y (NPY)/angiotensin II (ANG II) interactions have been studied in the central nervous system of the rat in view of their co-distribution and their opposing role in central cardiovascular control using quantitative receptor autoradiography and measurements of mean arterial blood pressure (MAP), heart rate and respiratory rate. The receptor autoradiographical experiments show that incubation with ANG II (10 nM) produces an increase in porcine (p) iodinated NPY-(1-36) [125I]pNPY-(1-36) binding within the dorsal strip (ds) of the nucleus tractus solitarius (nTS). Immunocytochemical analysis of intracisternally injected ANG II indicated that it could reach this area, in addition to the periventricular gray of the medulla oblongata, the pons and the periventricular part of the dorsal thalamus and dentate gyrus. Furthermore, a threshold dose of ANG II given intracisternally (3 nmol/rat) together with a dose (75 pmol/rat) of pNPY-(1-36) close to its ED50 value for reducing MAP, not only counteracts the vasodepressor action of pNPY-(1-36) but also leads to a marked increase of MAP. Also the bradycardic and bradypneic actions of pNPY-(1-36) are counteracted by this dose of ANG II. In contrast, a threshold dose of pNPY-(1-36) does not counteract the pressor action of an ED50 dose of ANG II (10 nmol/rat) but even enhances the peak pressor action of ANG II. These results may be explained on the basis that central ANG II receptor activation leads to an uncoupling of the NPY Y1 receptor, which mediate the vasodepressor action of pNPY-(1-36) and which is preferentially labeled by [125I]pNPY-(1-36).(ABSTRACT TRUNCATED AT 250 WORDS)

Receptor-selective analogs demonstrate NPY/PYY receptor heterogeneity in rat brain

Neuropeptide Y (NPY) receptors are heterogeneous, consisting of at least two subclasses, Y1 and Y2. We sought evidence for differential expression of NPY receptor subtypes in the rat brain. Tissue was incubated with 125I-peptide YY (PYY) which labels NPY and PYY binding sites. The Y1-selective agonist, p[Pro34]NPY, and the Y2-selective agonist, pNPY 13-36, were used as displacing ligands. Autoradiographic analyses of regional receptor binding demonstrated heterogeneity across brain regions. We conclude that Y1- and Y2-receptors may be independently expressed in the brain. While the predominate NPY/PYY receptor subtype in the brain is Y2, there are also Y1-receptors in some brain regions such as the superficial layers of the parietal cortex.

Neuropeptide Y levels in central and peripheral cerebrospinal fluid in patients with intracranial disorders

Neuropeptide Y (NPY) was measured in central and peripheral cerebrospinal fluid (CSF) in patients suffering from various intracranial disorders. The central NPY-like immunoreactivity (LI) level showed a concentration of 129 +/- 19 pmol.l-1 and was significantly increased (p less than 0.05) compared to peripheral CSF (73 +/- 9 pmol.l-1). From five patients with subarachnoid haemorrhage the CSF NPY-LI levels reached 154 +/- 47 pmol.l-1. In five patients peripheral and central CSF was collected at the same occasion and the CSF NPY-LI concentration was 76 +/- 17 pmol.l-1 in peripheral and 142 +/- 23 pmol.l-1 in central CSF (p less than 0.01), respectively. In a reference group of 9 patients, who were examined by lumbar myelography because of suspected intervertebral herniated discs, the peripheral CSF NPY-LI concentration was 59 +/- 5 pmol.l-1 a value which was also significantly lower compared to NPY-LI levels in central CSF. Thus it is obvious that NPY is present in human CSF with a relatively higher concentration in central than in peripheral CSF at least in patients with disorders of the central nervous system, suggesting a central origin of the NPY.

[The nucleus tractus solitarius: neuroanatomic, neurochemical and functional aspects]

The nucleus tractus solitarii (NTS) has long been considered as the first central relay for gustatory and visceral afferent informations only. However, data obtained during the past ten years, with neuroanatomical, biochemical and electrophysiological techniques, clearly demonstrate that the NTS is a structure with a high degree of complexity, which plays, at the medullary level, a key role in several integrative processes. The NTS, located in the dorsomedial medulla, is a structure of small size containing a limited number of neurons scattered in a more or less dense fibrillar plexus. The distribution and the organization of both the cells and the fibrillar network are not homogeneous within the nucleus and the NTS has been divided cytoarchitectonically into various subnuclei, which are partly correlated with the areas of projection of peripheral afferent endings. At the ultrastructural level, the NTS shows several complex synaptic arrangements in form of glomeruli. These arrangements provide morphological substrates for complex mechanisms of intercellular communication within the NTS. The NTS is not only the site of vagal and glossopharyngeal afferent projections, it receives also endings from facial and trigeminal nerves as well as from some renal afferents. Gustatory and somatic afferents from the oropharyngeal region project with a crude somatotopy within the rostral part of the NTS and visceral afferents from cardiovascular, digestive, respiratory and renal systems terminate viscero-topically within its caudal part. Moreover the NTS is extensively connected with several central structures. It projects directly to multiple brain regions by means of short connections to bulbo-ponto-mesencephalic structures (parabrachial nucleus, motor nuclei of several cranial nerves, ventro-lateral reticular formation, raphe nuclei...) and long connections to the spinal cord and diencephalic and telencephalic structures, in particular the hypothalamus and some limbic structures. The NTS is also the recipient of several central afferent inputs. It is worth to note that most of the structures that receive a direct projection from the NTS project back to the nucleus. Direct projections from the cerebral cortex to the NTS have also been identified. These extensive connections indicate that the NTS is a key structure for autonomic and neuroendocrine functions as well as for integration of somatic and autonomic responses in certain behaviors. The NTS contains a great diversity of neuroactive substances. Indeed, most of the substances identified within the central nervous system have also been detected in the NTS and may act, at this level, as classical transmitters and/or neuromodulators.(ABSTRACT TRUNCATED AT 400 WORDS)

Y2 receptors for neuropeptide Y in the nucleus of the solitary tract mediate depressor responses

In anesthetized, spontaneously breathing rats, microinjections of selective agonists of neuropeptide Y (NPY) receptor subtypes were made into the medial region of the caudal nucleus of the solitary tract (NTS) at the level of the area postrema. This region of the rat NTS exhibits very high densities of NPY binding sites. Microinjections of the long C-terminal NPY fragment, NPY(13-36), a selective agonist at Y2 receptors, into the caudal NTS elicited pronounced, dose-related reductions in blood pressure and respiratory minute volume. Moreover, the specific pattern of cardiorespiratory responses elicited by NPY(13-36) was remarkably similar, over approximately the same dosage range, with the cardiorespiratory response pattern elicited by intact NPY. In contrast to the potent NTS-mediated responses evoked by NPY(13-36), similar microinjections conducted with either NPY(26-36), an inactive C-terminal NPY fragment, or [Leu31,Pro34]NPY, a NPY analog with specific agonist properties at Y1 receptors, into the same caudal NTS sites did not appreciably affect cardiorespiratory parameters even at 10-20-fold higher dosages. The present results with selective agonists for NPY receptor subtypes suggest that the depressor responses and reductions in minute volume elicited by microinjections of intact NPY and NPY(13-36) were mediated by Y2 receptors in the caudal NTS, likely distributed at presynaptic sites in the medial region of the subpostremal NTS.

Subregional topography of capillaries in the dorsal vagal complex of rats: I. Morphometric properties

Cytoarchitectonic and neurochemical studies of the dorsal vagal complex in the caudal medulla oblongata of rats indicate the existence of distinct anatomical and functional compartments within its components. We applied morphometric methods to discern whether capillary networks differed quantitatively between subregions and zones of area postrema, nucleus tractus solitarii (NTS), and dorsal motor nucleus of the vagus nerve (DMN) of rats. Analysis of 11 subdivisions of area postrema identified both "true" (range in luminal diameter of 3-7.5 microns) and sinusoidal (luminal diameter greater than 7.5 microns) capillaries that, together, made the capillary density for most of area postrema 75% greater than that found in NTS and DMN (526/mm2 vs about 300/mm2). The rank order of true capillary density in area postrema along its rostracaudal axis was caudal greater than central greater than rostral, whereas the reverse order was true for sinusoidal capillaries. Dorsal (periventricular) and medial zones of area postrema throughout its rostrocaudal axis tended to have higher values for capillary density, volume, surface area, luminal diameter, and pericapillary space volume than lateral or ventral zones bordering NTS. Within 200 microns of obex, the ventral zone of rostral area postrema was distinct, having a relatively sparse capillary density that may indicate morphological specializations limiting blood-tissue communication in this subregion. There were no quantitative differences in capillary dimensions between DMN and three subnuclei of NTS. These studies add to extant evidence that the dorsal vagal complex is differentiated for specific functions. Area postrema, especially, has topographical diversity in its capillary organization that likely corresponds to complex roles in neuroendocrine, autonomic, and chemosensory mechanisms.

Long-lasting inhibition of the cardiovascular responses to glutamate and the baroreceptor reflex elicited by neuropeptide Y injected into the nucleus tractus solitarius of the rat

Neuropeptide Y (NPY) microinjected unilaterally into the nucleus tractus solitarii (NTS) of anesthetized paralyzed rats elicits a gradual dose-dependent and reversible fall in arterial pressure (AP) and heart rate (HR) lasting 20 min. It also abolished the brief (less than 1 min) dose-dependent and reversible fall of AP and HR elicited by L-glutamate (L-Glu) injected into the nucleus. The blockade of L-Glu by NPY appeared gradually and was prolonged, lasting over 2 h, and recovering by 24 h. It was not replicated by desamido-NPY or galanin. Unlike 2% lidocaine it did not block the hypotension elicited by focal electrical stimulation at the injection site indicating the response was not that of a local anesthetic. Bilateral injection of NPY into the NTS resulted, after an initial fall, in an elevation of AP (+48 +/- 10.6 mmHg). At this time the reflex bradycardia evoked by elevating AP with phenylephrine was markedly reduced. We conclude that in the NTS, NPY antagonizes the actions of L-Glu and may attenuate baroreceptor reflexes. Since the NTS is richly innervated by NPY neurons and contains many NPY binding sites and since primary baroreceptor afferents appear to be glutamatergic the results suggested that NPY may serve in NTS as a long-term regulator of baroreceptor reflex activity.

Neuropeptide Y (NPY) and peptide YY (PYY) receptors in rat brain

1. Specific binding sites for neuropeptide Y (NPY) and peptide YY (PYY) were investigated in rat brain areas using quantitative receptor autoradiography with 125I-Bolton-Hunter NPY (125I-BH-NPY) and 125I-PYY, radioligands for PP-fold family peptides receptors. 2. There were no differences between localization of 125I-BH-NPY and 125I-PYY binding sites in the rat brain. High densities of the binding sites were present in the anterior olfactory nucleus, lateral septal nucleus, stratum radiatum of the hippocampus, posteromedial cortical amygdaloid nucleus, and area postrema. 3. In cold ligand-saturation experiments done in the presence of increasing concentrations of unlabeled NPY and PYY, 125I-BH-NPY and 125I-PYY binding to the stratum radiatum of the hippocampus, layer I of the somatosensory frontoparietal cortex, molecular layer of the cerebellum, and area postrema was single and of a high affinity. There was a significant difference between the affinities of 125I-BH-NPY (Kd = 0.96 nM) and 125I-PYY binding (Kd = 0.05 nM) to the molecular layer of the cerebellum. The binding of the two radioligands to the other areas examined had the same affinities. 4. When comparing the potency of unlabeled rat pancreatic polypeptide (rPP), a family peptide of NPY and PYY, to inhibit the binding to the areas examined, rPP displaced 125I-BH-NPY and 125I-PYY binding to the area postrema more potently than it did the binding to the stratum radiatum of the hippocampus, layer I of the somatosensory frontoparietal cortex, and molecular layer of the cerebellum. 5. Thus, the quantitative receptor autoradiographic method with 125I-BH-NPY and 125I-PYY revealed differences in binding characteristics of specific NPY and PYY binding sites in different areas of the rat brain. The results provide further evidence for the existence of multiple NPY-PYY receptors in the central nervous system.

Synaptic connections of neuropeptide Y (NPY) immunoreactive neurons in the hilar area of the rat hippocampus

Synaptic connections and fine structural characteristics of neuropeptide Y-immunoreactive (NPY-i) neurons in the fascia dentata were studied using an antiserum against NPY. Normal and colchicine pretreated rats were examined to study the synaptic connections of NPY-i neurons in the normal fascia dentata. The perforant pathway and fimbria fornix were transected to label afferent fibers to NPY-positive cells. Horseradish peroxidase conjugated with wheat germ agglutinin (HRP-WGA) was injected into the contralateral hippocampus to study commissural projections of hippocampal NPY-i neurons, and to search for NPY-i synaptic contacts on immunonegative commissural cells. Since earlier reports have shown that at least half of the NPY-i neurons also contain somatostatin (SS), the distribution of NPY-i neurons in the hilar area was determined and compared with that of SS-i neurons. Four types of dentate NPY-i neurons were distinguished: Type 1: large multipolar cells in the deep hilus (9%). Type 2: medium-sized multipolar and fusiform hilar neurons with dendrites occasionally reaching the outer molecular layer (64%). Type 3: pyramidal shaped cells in the granule cell layer with long apical dendrites reaching the outer molecular layer (20%). Type 4: small multipolar NPY-i cells located in the molecular layer (7%). Our results indicate two overlapping but not identical cell populations of NPY-i and SS-i neurons. Light and electron microscopic analysis of the normal fascia dentata demonstrated that the majority of NPY-i terminals are located in the outer molecular layer of the dentate gyrus, where they establish symmetric synaptic contacts on dendritic shafts and occasionally on spines of granule cells. A moderate number of NPY-i synapses were also found on dendrites in the inner molecular layer and on the cell body of granule cells. Numerous symmetric NPY-i synapses were found on dendrites and somata of neurons in the hilar area. Some NPY-i dendrites in the hilar area received mossy axon collateral input. After transection of the perforant pathway degenerated axon terminals could be found in synaptic contact with NPY-i dendrites in the outer molecular layer. Commissurotomy revealed direct commissural input to NPY-i dendrites in the inner molecular layer and in the hilus. After injection of HRP-WGA into the contralateral hippocampus 2% of hilar NPY-i neurons were retrogradely labeled and symmetric NPY-i synapses were found on the cell bodies and dendrites of unstained HRP-WGA labeled neurons.(ABSTRACT TRUNCATED AT 400 WORDS)

A comparison of the binding of [3H]proprionyl-neuropeptide Y to rat and human frontal cortical membranes

The binding characteristics of [3H]proprionyl-neuropeptide Y ([3H]proprionyl-NPY) were studied in frontal cortical membranes prepared from rat and human postmortem tissue. The specific binding of NPY decreased as the magnesium concentration increased from 1.05 to 10 mM. The binding was also influenced by the concentration of GTP in the buffer medium, with a resulting 45% decrease in NPY binding in the presence of 10(-6) M GTP. Using equilibrium binding studies, [3H]proprionyl-NPY was found to bind in both tissues with high affinity to a single class of receptors with a similar KD (0.035 nM). However, kinetic experiments in both tissues provided evidence for two components of [3H]proprionyl-NPY binding which may be related to receptor states. Competition binding experiments showed that peptide YY (PYY) was equal to NPY in its ability to displace [3H]proprionyl-NPY, whereas rat and human pancreatic polypeptide were without effect up to a concentration of 10(-6) M. This suggests that, whereas PYY and NPY may compete for the same receptor(s), the pancreatic polypeptides probably act on a separate population of receptors.

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.

Distribution of neuropeptide Y-like immunoreactive perikarya and processes in the medulla of the cat

Neuropeptide Y-like immunoreactive (NPY-LI) perikarya and processes have been identified in the medulla of the cat. NPY-LI perikarya were found in 4 regions; (1) the medial N. of the solitary tract (MNTS), (2) the lateral tegmental field (LTF), (3) the ventrolateral medullary surface (VLMS), and (4) in the spinal trigeminal nucleus. Tyrosine hydroxylase-like immunoreactive (TH-LI) neurons were also found in the first 3 regions noted above. NPY-LI and TH-LI neurons had a similar morphology and distribution. NPY-LI and TH-LI neurons were counted in sections from 3 representative levels of the medulla. NPY-LI cells were most numerous in the LTF, especially at the level of the area postrema and more rostrally. The lowest number of NPY-LI cells was seen in the MNTS, particularly at a level caudal to the area postrema. NPY-LI cells were at least 3-fold less numerous than TH-LI cells at all levels of the MNTS, but there was a 27-fold greater number of TH-LI neurons at a level of MNTS caudal to the area postrema. In the LTF, NPY-LI cells were 2- to 5-fold less common than TH-LI cells. Approximately equal numbers of NPY-LI and TH-LI cells were counted in the VLMS at the level of the area postrema and rostrally. These data indicate that the majority of TH-LI cells in the MNTS of the cat probably do not contain NPY as a co-transmitter.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y: localization in the central nervous system and neuroendocrine functions

Neuropeptide Y (NPY) is a 36-amino acid peptide first isolated and characterized from porcine brain extracts. A number of immunocytochemical investigations have been conducted to determine the localization of NPY-containing neurons in various animal species including both vertebrates and invertebrates. These studies have established the widespread distribution of NPY in the brain and in sympathetic neurons. In the rat brain, a high density of immunoreactive cell bodies and fibers is observed in the cortex, caudate putamen and hippocampus. In the diencephalon, NPY-containing perikarya are mainly located in the arcuate nucleus of the hypothalamus; numerous fibers innervate the paraventricular and suprachiasmatic nuclei of the hypothalamus, as well as the paraventricular nucleus of the thalamus and the periaqueductal gray. At the electron microscope level, using the pre- and post-embedding immunoperoxidase techniques, NPY-like immunoreactivity has been observed in neuronal cell body dendrites and axonal processes. In nerve terminals of the hypothalamus, the product of the immunoreaction is associated with large dense core vesicles. In lower vertebrates, including amphibians and fish, neurons originating from the diencephalic (or telencephalic) region innervate the intermediate lobe of the pituitary where a dense network of immunoreactive fibers has been detected. At the ultrastructural level, positive endings have been observed in direct contact with pituitary melanotrophs of frog and dogfish. These anatomical data suggest that NPY can act both as a neurotransmitter (or neuromodulator) and as a hypophysiotropic neurohormone. In the rat a few NPY-containing fibers are found in the internal zone of the median eminence and high concentrations of NPY-like immunoreactivity are detected in the hypothalamo-hypophyseal portal blood, suggesting that NPY may affect anterior pituitary hormone secretion. Intrajugular injection of NPY causes a marked inhibition of LH release but does not significantly affect other pituitary hormones. Passive immunoneutralization of endogenous NPY by specific NPY antibodies induces stimulation of LH release in female rats, suggesting that NPY could affect LH secretion at the pituitary level. However, NPY has no effect on LH release from cultured pituitary cells or hemipituitaries. In addition, autoradiographic studies show that sites for 125I-labeled Bolton-Hunter NPY or 125I-labeled PYY (2 specific ligands of NPY receptors) are not present in the adenohypophysis, while moderate concentrations of these binding sites are found in the neural lobe of the pituitary. It thus appears that the inhibitory effect of NPY on LH secretion must be mediated at the hypothalamic level.(ABSTRACT TRUNCATED AT 400 WORDS)

Cardiorespiratory response patterns elicited by microinjections of neuropeptide Y in the nucleus tractus solitarius

A limited occipital craniotomy was conducted on anesthetized, spontaneously breathing rats to expose the caudal medulla in the region of the obex. Microinjections of neuropeptide Y (NPY), a putative neuromodulator associated with catecholaminergic (CA) synapses, were made into the medial region of the caudal nucleus tractus solitarius (NTS) at the level of the posterior portion of the area postrema, an area of the NTS in which there is known to be a functional coexistence of cardiovascular and respiratory-related neuronal elements. This region of the caudal NTS in the rat is not only the principal site of termination of baro- and chemoreceptor afferents, but it also has profuse reciprocal connections with NPY-containing cardiorespiratory control regions in the hypothalamus and with other brainstem regulatory nuclei. Moreover, this same region of the rat NTS also shows very high densities of NPY binding sites. Cardiorespiratory responses were subsequently recorded for a 60-min test period following NPY administration. Microinjections of NPY, in the dose range of 10-100 pmol/rat, into the caudal NTS of intact rats produced significant dose-related reductions in mean arterial blood pressure, pulse pressure and minute volume. To a lesser extent, NPY microinjections also produced significant reductions in heart rate, respiratory rate and tidal volume. In a series of separate experiments, in an effort to ascertain the modulatory influences of rostral brain regions on these NPY-evoked, NTS-mediated cardiorespiratory response patterns, microinjections of NPY were made under identical anesthetic and experimental conditions in a group of rats wherein reciprocal connections between the NTS and rostral brain regions had been disrupted via supracollicular decerebration. In addition, since NPY microinjections were made into specific loci wherein afferent inputs from cardiopulmonary receptors are known to converge in the rat NTS, the effects of bilateral vagotomy on NPY-evoked, NTS-mediated cardiorespiratory response patterns were also examined in otherwise intact rats and under the same experimental conditions. The effects of NPY microinjections at the same dosage on NTS-mediated cardiorespiratory response patterns were subsequently compared among the intact, decerebrate and vagotomized rats. The results showed that whereas the hypotensive actions of NPY were not affected by decerebration, vagotomy significantly increased the magnitude of the hypotension elicited by NPY microinjections in comparison to the intact and decerebrate groups of rats. On the other hand, vagotomy abolished the NPY-evoked bradycardia which had a similar magnitude in both intact and decerebrate rats.(ABSTRACT TRUNCATED AT 400 WORDS)

On the role of neuropeptide Y in information handling in the central nervous system in normal and physiopathological states. Focus on volume transmission and neuropeptide Y/alpha 2 receptor interactions

The NPY neurons play an important role in information handling in the CNS by their ability to interact in both wiring and volume transmission at the network, local circuit and synaptic level. The importance of NPY/alpha 2 receptor-receptor interactions in cardiovascular, neuroendocrine and vigilance control is emphasized. Alterations in these receptor-receptor interactions take place in the spontaneously hypertensive rats as well as in the ischemic brain, which may have profound consequences for the information handling and contribute to the functional alterations found in these pathophysiological states. Finally, in the aging brain there appears to exist a marked reduction in NPY transmission line, which may affect higher brain functions, such as learning and memory retrieval. The most impressive result is, however, the indications of a role for NPY in volume transmission, where NPY appears to produce syndromic actions via its conversion into biologically active fragments, which may have preferential actions at Y2 NPY receptors. These syndromic pathways may be altered in the spontaneously hypertensive rat and may be controlled by gonadal steroids and glucocorticoids. Glucocorticoid receptors have been demonstrated in all arcuate NPY neurons and all NA/NPY and A/NPY costoring neurons.

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)

Pertussis toxin treatment counteracts intramembrane interactions between neuropeptide Y receptors and alpha 2-adrenoceptors

The effect of intracerebroventricular injections of pertussis toxin were investigated on the neuropeptide Y-induced modulation of alpha 2-adrenoceptor binding in membranes from the dorsomedial medulla oblongata of the rat. Concentration-response experiments showed that neuropeptide Y reduced the binding affinity of the alpha 2-agonist, p-[3H]aminoclonidine, with a maximal effect of 30% at 3-30 nM. Pertussis toxin treatment (10 micrograms, 24 h) counteracted this modulation, without reducing the binding of neuropeptide Y to its own receptor. The results indicate that pertussis toxin-sensitive G-proteins are essential for the mediation of the intramembrane interaction between neuropeptide Y receptors and alpha 2-adrenoceptors.

The cardiovascular actions of clonidine and neuropeptide-Y in the ventrolateral medulla of the rat

1. The cardiovascular responses to neuropeptide-Y (NPY) (25 and 50 pmol) and clonidine (10 and 20 nmol) were examined following microinjection into the rostral ventrolateral medulla (RVLM) and the caudal ventrolateral medulla (CVLM). Mean arterial pressure (MAP) and heart rate (HR) were measured in anaesthetized rats, pre- and post-injection. 2. The alpha 2-adrenoceptor agonist clonidine (10 and 20 nmol) reduced MAP and HR significantly when microinjected into the CVLM and RVLM. 3. NPY (25 and 50 pmol) microinjected into the CVLM decreased MAP and HR. However, in the RVLM neither dose had a significant cardiovascular effect. 4. The possibility of a functional interaction between the adrenergic system and NPY was examined by co-administration of clonidine and NPY in doses that gave submaximal blood pressure responses. In the CVLM this produced hypotension and bradycardia which was similar in magnitude to the sum of their individual responses, indicating that in this area their actions appear to be independent. 5. In the RVLM, where NPY has no significant cardiovascular effects, co-administration with clonidine, did not alter the response to clonidine. 6. It appears that in the areas investigated, there is no functional interaction between NPY and clonidine.

Pertussis toxin treatment counteracts the cardiovascular effects of neuropeptide Y and clonidine in the awake unrestrained rat

The role of G-proteins in the mediation of the cardiovascular effects of neuropeptide Y and the alpha 2-adrenoceptor agonist clonidine was investigated by injections of pertussis toxin (10 micrograms/30 microliters, i.v.t., 24 h) in the awake unrestrained male rat. Treatment with pertussis toxin was found to inhibit the hypotensive and bradycardic actions of neuropeptide Y (1250 pmol) and the hypotensive actions of clonidine (1875 pmol). Control experiments showed that treatment with pertussis toxin caused an approximately 50% reduction in the back-ADP-ribosylation of GTP-binding proteins. These results suggest that G-proteins mediate the central cardiovascular actions of neuropeptide Y and clonidine.

Reciprocal interactions between alpha 2-adrenoceptor agonist and neuropeptide Y binding sites in the nucleus tractus solitarius of the rat. A biochemic and autoradiographic analysis

Interactions between a alpha 2-adrenoceptor agonist and neuropeptide Y (NPY) binding sites have been studied in the rat medulla oblongata (MO) using biochemical binding techniques as well as quantitative autoradiography. Tritiated para-amino clonidine (3H-PAC; alpha 2-adrenoceptor agonist), idazoxan (3H-IDA; alpha 2-adrenoceptor antagonist) and iodinated neuropeptide Y (125I-NPY) were used as radioligands. (1) Neuropeptide Y (NPY; 10(-8) M) but not bovine pancreatic polypeptide (BPP) nor peptide YY (PYY 10 nM) increased the KD value of 3H-PAC binding sites. However, intraventricular administration of a high dose of NPY (1.25 nmol) did not change the 3H-PAC binding characteristics in MO membrane preparations of these animals. (2) GTP 10(-4) lowered the affinity of 3H-PAC binding. NPY (10 nM) had no additional effect, nor did NPY influence the GTP induced shift in potency of clonidine to displace 3H-IDA from its binding sites. (3) In the autoradiographical experiments NPY (10 nM) significantly reduced 3H-PAC binding (2 nM) in the nucleus tractus solitarius (NTS) area by 35%. (4) When clonidine, either given centrally in vivo (3.75 nmol) or in vitro (10 nM) the binding of 125I-NPY was reduced (34 and 24%, respectively) in the NTS. When the monoamine receptors were irreversibly blocked in vivo by N-ethoxycarbonyl-2-ethoxy-1,2-dihydroquinoline (EEDQ, 10 micrograms i.c. 24 h) 125I-NPY (0.5 nM) binding was increased by 137% in the NTS. This effect of EEDQ was prevented by pretreatment with the alpha 2-adrenoceptor antagonist idazoxan. These results provide support for a direct intramembrane interaction between the alpha 2-receptor and the NPY receptor within the NTS and may be of importance in central cardiovascular regulation.