Failure of neuropeptide Y in vitro to increase the number of alpha 2-adrenergic binding sites in membranes of medulla oblongata of the spontaneous hypertensive rat

Modulating brain integrative actions as a new perspective on pharmacological approaches to neuropsychiatric diseases

A critical aspect of drug development in the therapy of neuropsychiatric diseases is the "Target Problem", that is, the selection of a proper target after not simply the etiopathological classification but rather the detection of the supposed structural and/or functional alterations in the brain networks. There are novel ways of approaching the development of drugs capable of overcoming or at least reducing the deficits without triggering deleterious side effects. For this purpose, a model of brain network organization is needed, and the main aspects of its integrative actions must also be established. Thus, to this aim we here propose an updated model of the brain as a hyper-network in which i) the penta-partite synapses are suggested as key nodes of the brain hyper-network and ii) interacting cell surface receptors appear as both decoders of signals arriving to the network and targets of central nervous system diseases. The integrative actions of the brain networks follow the "Russian Doll organization" including the micro (i.e., synaptic) and nano (i.e., molecular) levels. In this scenario, integrative actions result primarily from protein-protein interactions. Importantly, the macromolecular complexes arising from these interactions often have novel structural binding sites of allosteric nature. Taking G protein-coupled receptors (GPCRs) as potential targets, GPCRs heteromers offer a way to increase the selectivity of pharmacological treatments if proper allosteric drugs are designed. This assumption is founded on the possible selectivity of allosteric interventions on G protein-coupled receptors especially when organized as "Receptor Mosaics" at penta-partite synapse level.

Heterodimers and receptor mosaics of different types of G-protein-coupled receptors

Through an assembly of interacting GPCRs, heterodimers and high-order heteromers (termed receptor mosaics) are formed and lead to changes in the agonist recognition, signaling, and trafficking of participating receptors via allosteric mechanisms, sometimes involving the appearance of cooperativity. This field has now become a major research area, and this review deals with their physiology being integrators of receptor signaling in the CNS and their use as targets for novel drug development based on their unique pharmacology.

Neuropeptides as synaptic transmitters

Neuropeptides are small protein molecules (composed of 3-100 amino-acid residues) that have been localized to discrete cell populations of central and peripheral neurons. In most instances, they coexist with low-molecular-weight neurotransmitters within the same neurons. At the subcellular level, neuropeptides are selectively stored, singularly or more frequently in combinations, within large granular vesicles. Release occurs through mechanisms different from classical calcium-dependent exocytosis at the synaptic cleft, and thus they account for slow synaptic and/or non-synaptic communication in neurons. Neuropeptide co-storage and coexistence can be observed throughout the central nervous system and are responsible for a series of functional interactions that occur at both pre- and post-synaptic levels. Thus, the subcellular site(s) of storage and sorting mechanisms into different neuronal compartments are crucial to the mode of release and the function of neuropeptides as neuronal messengers.

Costorage and coexistence of neuropeptides in the mammalian CNS

The term neuropeptides commonly refers to a relatively large number of biologically active molecules that have been localized to discrete cell populations of central and peripheral neurons. I review here the most important histological and functional findings on neuropeptide distribution in the central nervous system (CNS), in relation to their role in the exchange of information between the nerve cells. Under this perspective, peptide costorage (presence of two or more peptides within the same subcellular compartment) and coexistence (concurrent presence of peptides and other messenger molecules within single nerve cells) are discussed in detail. In particular, the subcellular site(s) of storage and sorting mechanisms within neurons are thoroughly examined in the view of the mode of release and action of neuropeptides as neuronal messengers. Moreover, the relationship of neuropeptides and other molecules implicated in neural transmission is discussed in functional terms, also referring to the interactions with novel unconventional transmitters and trophic factors. Finally, a brief account is given on the presence of neuropeptides in glial cells.

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.

Centrally administered neuropeptide Y fails to increase food intake but enhances hypoalgesia in spontaneously hypertensive rats

The effects of intracerebroventricular (i.c.v.) administration of neuropeptide Y (NPY1-36) on food intake and pain sensitivity in hot plate test were studied in spontaneously hypertensive rats (SHRs) and in normotensive Wistar-Kyoto (WKy) rats. In satiated SHRs NPY1-36 failed to significantly increase intake at doses that produced a strong effect in satiated WKy rats (0.25-1.25 nmol). Conversely, both NPY1-36 and the C-terminal fragment NPY13-36, a putative selective agonist for the Y2-receptor for NPY, enhanced the spontaneously occurring hypoalgesia of SHRs, having no effect in WKy rats. The present results indicate that the NPY central systems involved in the control of regulatory functions are differently tuned in SHRs and WKy rats, suggesting possible involvement of these systems in the genesis of hypertension.

Neuropeptide Y interaction with the adrenergic transmission line: a study of its effect on alpha-2 adrenergic receptors

Neuropeptide Y (NPY), first isolated in 1982, is widely distributed among the neurons of the central and peripheral nervous systems, often in close association with catecholamines. Because of its wide distribution and concentrations in selected areas of the brain, NPY is considered a putative neurotransmitter with several possible physiological effects including modulation of blood pressure, food intake and pituitary hormone release at a central level. Peripherally, the peptide seems to be involved, via direct and indirect mechanisms, in noradrenaline (NA)-mediated vasoconstriction. The ability of NPY to interact with the catecholamine transmission line may underly a possible modulatory influence of NPY on catecholamine receptor characteristics. We recently observed interaction between alpha-2 adrenergic receptors and those for NPY at the presynaptic level. Additional data from our studies in spontaneously hypertensive rats suggest that impairment of these interactions may contribute to the hypertension in this strain.

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.

Effects of neuropeptide Y on norepinephrine release in hypothalamic slices of spontaneously hypertensive rats

We describe the effects of neuropeptide Y (NPY) on [3H]norepinephrine (NE) release from hypothalamic slices of spontaneously hypertensive rats (SHR). The electrical stimulation (1 Hz)-evoked [3H]NE release was significantly greater in hypothalamic slices of SHR than in those of Wistar Kyoto rats (WKY). NPY inhibited the stimulation-evoked [3H]NE release in a dose-dependent manner. The inhibitory effect of NPY was significantly attenuated in SHR compared with WKY. The results may indicate that the less inhibitory effect of NPY on NE release induces increased sympathetic nerve activity in the hypothalamus of SHR.

Norepinephrine release and neuropeptide Y in medulla oblongata of spontaneously hypertensive rats

Neuropeptide Y is colocalized with norepinephrine in both central and peripheral noradrenergic neurons. In this study, we examined the regulatory mechanisms of neuropeptide Y on norepinephrine release in the medulla oblongata of rats. Neuropeptide Y inhibited the stimulation-evoked [3H]norepinephrine release in a dose-dependent manner in slices of medulla oblongata of Sprague-Dawley rats (1 Hz, S2/S1 ratio, control, 0.946 +/- 0.040 [+/- SEM], n = 6; neuropeptide Y 1 x 10(-8) M, 0.676 +/- 0.022, n = 6, p less than 0.05; neuropeptide Y 1 x 10(-7) M, 0.589 +/- 0.014, n = 6, p less than 0.05). Neuropeptide Y potentiated inhibition of [3H]norepinephrine release by the alpha 2-agonists UK 14,304 and clonidine. The blockade of alpha 2-adrenergic receptors by RX 781,094 diminished inhibitory effects of neuropeptide Y on norepinephrine release. Pretreatment of pertussis toxin (a toxin that interferes with the coupling of inhibitory receptors to adenylate cyclase) attenuated the suppression of norepinephrine release by neuropeptide Y. In spontaneously hypertensive rats, the inhibitory effect of UK 14,304 and neuropeptide Y on norepinephrine release from the medulla oblongata was significantly less than in age-matched Wistar-Kyoto rats. These results show that neuropeptide Y inhibits norepinephrine release partially mediated by alpha 2-adrenergic receptors and the pertussis toxin-sensitive guanosine triphosphate-binding proteins in rat medulla oblongata. Furthermore, less suppression of norepinephrine release by UK 14,304 and neuropeptide Y in spontaneously hypertensive rats suggests that alpha 2-adrenergic receptors and neuropeptide Y might be involved in the regulation of central sympathetic tone in hypertension.

Suppression by neuropeptide Y of capsaicin-sensitive sensory nerve-mediated contraction in guinea-pig airways

1. In the present study we have examined whether neuropeptide Y (NPY) interferes with non-adrenergic, non-cholinergic nerve-mediated contractions and relaxations in the guinea-pig airways. In these experiments we have used ring preparations of bronchi and trachea, incubated in the presence of atropine, propranolol and indomethacin (each 1 microM). 2. The contractile response to electrical stimulation of non-adrenergic, non-cholinergic nerve fibres was suppressed by NPY and NPY 13-36 in a concentration-dependent manner, these agents having similar inhibitory potencies. NPY caused a more complete inhibition than the C terminal fragment. 3. NPY affected neither the basal tension nor the substance P-evoked contraction in the bronchi and trachea and did not interfere with nerve-mediated, non-adrenergic relaxation in the trachea. 4. On the basis of these results, it is suggested that NPY may act on the terminals of sensory neurones in the airways to prevent antidromic, excitatory neurotransmission by inhibiting transmitter release.

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.

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.

Reduced inhibitory effects of clonidine and neuropeptide Y on 3H-noradrenaline release from synaptosomes of the medulla oblongata of the spontaneously hypertensive rat

The release of 3H-noradrenaline (3H-NA) evoked by high-K+ (15 mM) was studied in synaptosomes isolated from the medulla oblongata of the normotensive Wistar-Kyoto and spontaneously hypertensive male rat (14 weeks old) using a superfusion apparatus. Based on concentration-response curves clonidine was shown to have a reduced ability to inhibit 3H-NA release in synaptosomes isolated from the spontaneously hypertensive rat (SHR) versus the normotensive rat. Furthermore, only a high concentration of NPY (100 nM) had the ability to enhance the inhibitory effects of clonidine on 3H-NA release in synaptosomes isolated from the medulla oblongata of the SH male rat, while 1 nM of NPY was effective in synaptosomes isolated from the medulla oblongata of the normotensive Wistar-Kyoto rat. These results may indicate a reduced presynaptic alpha 2-adrenoceptor and NPY receptor function to inhibit 3H-NA release from NA and/or adrenaline (A) nerve terminals in the medulla oblongata of the adult 14 weeks old SHR.

Opposite effects of centrally administered neuropeptide Y (NPY) on locomotor activity of spontaneously hypertensive (SH) and normal rats

Centrally administered neuropeptide Y has been shown to produce sedation manifested by a suppression of locomotor activity and a synchronizing effect on the EEG pattern in normal rats. It has been suggested that this sedative effect of NPY is largely due to a facilitation of the alpha 2-adrenergic transmission line. In the spontaneously hypertensive (SH) rat, the NPY-induced up-regulation of alpha 2-adrenoceptors observed in normal rats is absent, and NPY produces a desynchronization of the EEG. In the present study, we have therefore examined the effects of NPY on locomotor activity of SH rats and of inbred controls of the Wistar-Kyoto (WKy) strain, in both morning and evening sessions. In morning sessions, NPY (0.2-5.0 nmol intracerebroventricularly, i.c.v.) increased locomotor activity of SH rats in a dose-related manner. WKy rats were largely inactive per se, and no effects of NPY could be detected. In evening sessions, when spontaneous activity is high, NPY (I.0 nmol i.c.v.) still increased the activity of the SH rats. In WKy rats, an activity suppression similar to that previously reported for normal Sprague-Dawley rats was seen. The present results indicate that the sedative action of NPY in different rats strains correlates with the ability of the peptide to up-regulate alpha 2-adrenergic receptors.

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.

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.

Neuropeptide Y (NPY) and the central nervous system: distribution effects and possible relationship to neurological and psychiatric disorders

1. NPY is a 36 amino acid tyrosine-rich peptide. It is one of the most abundant and widely distributed neuropeptides known today within the central nervous system with particularly high concentrations in the hypothalamus and in several limbic regions. 2. NPY seems to coexist with other on neurotransmitters like somatostatin, galanin, GABA and the catecholamines noradrenaline and adrenaline in discrete brain regions. 3. NPY binding sites are widely distributed in the brain. However they do not always overlap with the distribution of NPY-like immunoreactivity. 4. NPY is suggested to be involved in a large number of neuroendocrine functions, stress responses, circadian rhythms, central autonomic functions, eating and drinking behaviour, and sexual and motor behaviour. 5. Psychotropic drugs and neurotoxins can alter the NPY concentrations in discrete brain regions. 6. It is possible that NPY is related to various neurological and psychiatric illnesses, like Huntington's chorea, Alzheimer's disease, Parkinson's disease, eating disorders, and major depressive illness.

Morphometrical and microdensitometrical studies on phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive neurons in the rostral medulla oblongata of the adult and old male rat

In the present paper the neuronal systems of the medulla oblongata containing phenylethanolamine-N-methyltransferase- and neuropeptide Y-like immunoreactivity have been characterized in adult (3-month-old) and old (24-month-old) male rats. The phenylethanolamine-N-methyltransferase and neuropeptide Y-immunoreactive neurons have been visualized by means of immunocytochemistry (peroxidase-antiperoxidase technique) and analysed in a quantitative fashion by means of morphometrical (phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive cell groups) and microdensitometrical (phenylethanolamine-N-methyltransferase-immunoreactive cell groups) approaches developed on the IBAS II image analyser (Zeiss-Kontron). During aging there is (a) a reduction in the area covered by the phenylethanolamine-N-methyltransferase-immunoreactive neuropil for both the C1 and C2 adrenaline cell groups; (b) a reduction in the area covered by the phenylethanolamine-N-methyltransferase-immunoreactive cell bodies, which is highly significant only for the C2 cell group; (c) a decrease in the area covered by the phenylethanolamine-N-methyltransferase-positive cell cluster for both C1 and C2 cell groups; (d) a decrease in the degree of phenylethanolamine-N-methyltransferase immunoreactivity present in the C1 and C2 cell groups; (e) a decay of neuropeptide Y immunoreactivity in the C1 and C2 groups, while the C3 group is unaffected by aging as evaluated by number of phenylethanolamine-N-methyltransferase- and neuropeptide Y-immunoreactive cell body profiles. These results indicate heterogeneities in the responses of the adrenaline-neuropeptide Y cell groups to the aging process. The possible functional consequences of aging-induced changes in the cardiovascular adrenergic neurons are discussed, especially in relation to development of hypertension.

Neuropeptide Y in the rat nucleus accumbens: ultrastructural localization in aspiny neurons receiving synaptic input from GABAergic terminals

The ultrastructure, afferent input, and sites of termination of neurons containing neuropeptide Y-like immunoreactivity (NPY-LI) were examined in the adult rat nucleus accumbens by using the peroxidase-antiperoxidase (PAP) method. The NPY-LI was seen in sparsely distributed, spindle-shaped perikarya having cross-sectional diameters of 15-20 microns. These perikarya exhibited highly invaginated nuclear membranes and thin rims of cytoplasm containing Golgi lamellae, dense-core vesicles, and other organelles. A few large, principally aspiny, dendrites also showed NPY-LI. The dendrites received synaptic input from unlabeled terminals forming both symmetric and asymmetric junctions. Immunolabeling for NPY was evident in other processes that were not clearly differentiated as dendrites or axons. These were seen primarily near glial processes and the basal laminae of blood vessels. A few myelinated and many unmyelinated axons and axon terminals also were labeled for NPY. These terminals contained numerous, small (40-60 nm), clear and one or more large (80-100 nm) dense core vesicles. Forty-seven percent (27 out of 57) of the terminals containing NPY-LI formed symmetric junctions with unlabeled dendrites or dendritic spines. The remainder lacked recognizable densities within single planes of section. The neurons exhibiting NPY-LI in the nucleus accumbens were characterized further with respect to their afferent input from terminals labeled for the GABA-synthesizing enzyme, glutamic acid decarboxylase (GAD). Immunogold labeling of a rabbit antiserum against NPY and PAP labeling for a sheep antiserum to GAD were sequentially applied to the same sections. The GAD-labeled terminals formed symmetric junctions primarily with the more numerous unlabeled dendrites. However, a few synaptic junctions also were detected between the GAD-labeled terminals and dendrites showing immunogold labeling for NPY. We conclude (1) that in the rat nucleus accumbens, NPY-LI is found principally in neurons of the aspiny type and (2) that the output from these presumably intrinsic neurons to other neighboring neurons or blood vessels is at least partially modulated by GABA.

Intracerebroventricular neuropeptide Y suppresses open field and home cage activity in the rat

Effects of intracerebroventricular administration of neuropeptide Y on open field behaviour, behavioural habituation and corticosterone response to open field testing, and on home cage activity have been investigated in the rat. In the open field, NPY reduced activity in a dose-dependent manner. Behavioural habituation was not influenced. After 5 days of recovery, NPY-treated animals did not differ from non-treated in any of the measured parameters. Peripheral corticosterone levels were not significantly affected, although there was a strong tendency towards an increase. Injection of 2 nmol NPY did not produce any gross neurological deficits. At this dose, NPY greatly suppressed home cage activity. The effect lasted throughout the recording period of 22 h, abolishing the normal circadian variation in activity. After 5 days of recovery, the effect was no longer present. Our interpretation of these findings is, that NPY is a highly potent endogenous agent capable of producing certain important aspects of behavioural sedation in a reversible manner. Since NPY did not decrease the corticosterone response to a novel stimulus, its pattern of actions seems to differ from synthetic sedative drugs.

Growth hormone responses to clonidine and GRF in spontaneously hypertensive rats: neuroendocrine evidence for an enhanced responsiveness of brain alpha 2-adrenoceptors in genetical hypertension

Clonidine induces growth hormone (GH) release in rat. According to previous investigations this effect is mediated by postsynaptic alpha 2-adrenoceptors in the hypothalamus exerting a stimulatory influence on the recently discovered GH releasing factor (GRF). In the present study it is demonstrated that spontaneously hypertensive rats (SHR) of the Wistar-Kyoto strain display enhanced GH responses to clonidine as compared to normotensive Wistar-Kyoto control rats. In contrast, the GH responses to GRF are similar in hypertensive and normotensive animals. These findings indicate that brain alpha 2-adrenoceptors are more responsive in SHR than in normotensive controls. Since the enhanced GH responses to clonidine were observed also in young, prehypertensive SHR they are probably not secondary to the elevated blood pressure. The possible importance of an altered alpha 2-adrenergic neurotransmission for the development of elevated blood pressure in SHR is discussed.

Increased neuropeptide Y (NPY) receptor binding in hippocampus and cortex of spontaneous hypertensive (SH) rats compared to normotensive (WKY) rats

Specific 125I-NPY binding in various brain regions of spontaneous hypertensive (SH) rats and age-matched normotensive (WKY) rats was compared. SH rats exhibited significantly greater 125I-NPY binding than WKY rats in the hippocampus (43%) and cortex (18%), but not hypothalamus, midbrain, striatum or pons-medulla. Scatchard analysis indicated that the increased 125I-NPY binding in the hippocampus of SH rats represents a greater number of NPY binding sites.

Neuropeptide Y (NPY) reduces field stimulation-evoked release of noradrenaline and enhances force of contraction in the rat portal vein

The effect of neuropeptide Y (NPY) on fractional tritium-noradrenaline (3H-NA) release and contractile activity was studied in the isolated portal vein of SHR and WKY rats. NPY (5 X 10(-7) M) enhanced the force of the spontaneous contractile activity by about 40%. The fractional 3H-release elicited by transmural nerve stimulation (TNS), which mainly reflects 3H-NA, was reduced by about 40% after preincubation with 5 X 10(-7) M NPY in portal veins from both SHR and WKY rats. The inhibitory effect of NPY on TNS-evoked 3H-release was more slowly reversed by washout than the facilitatory action on spontaneous contractile force. The contractile response to field stimulation was not reduced by NPY, but rather tended to be increased. It is concluded that NPY exerts a dual action in the SHR and WKY portal vein, thus enhancing the smooth muscle contractions and inhibiting sympathetic neurotransmission. The inhibitory effect of NPY on TNS-evoked NA efflux, which is present in both SHR and WKY rats, is most likely due to a presynaptic site of action.