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

Putative neurochemical and cell type contributions to hemodynamic activity in the rodent caudate putamen

Functional magnetic resonance imaging (fMRI) is widely used by researchers to noninvasively monitor brain-wide activity. The traditional assumption of a uniform relationship between neuronal and hemodynamic activity throughout the brain has been increasingly challenged. This relationship is now believed to be impacted by heterogeneously distributed cell types and neurochemical signaling. To date, most cell-type- and neurotransmitter-specific influences on hemodynamics have been examined within the cortex and hippocampus of rodent models, where glutamatergic signaling is prominent. However, neurochemical influences on hemodynamics are relatively unknown in largely GABAergic brain regions such as the rodent caudate putamen (CPu). Given the extensive contribution of CPu function and dysfunction to behavior, and the increasing focus on this region in fMRI studies, improved understanding of CPu hemodynamics could have broad impacts. Here we discuss existing findings on neurochemical contributions to hemodynamics as they may relate to the CPu with special consideration for how these contributions could originate from various cell types and circuits. We hope this review can help inform the direction of future studies as well as interpretation of fMRI findings in the CPu.

Neuropeptide Y modifies a part of diencephalic catecholamine but not indolamine metabolism in chicks depending on feeding status

The role of the monoaminergic system in the feeding behavior of neonatal chicks has been reported, but the functional relationship between the metabolism of monoamines and appetite-related neuropeptides is still unclear. This study aimed to investigate the changes in catecholamine and indolamine metabolism in response to the central action of neuropeptide Y (NPY) in different feeding statuses and the underlying mechanisms. In Experiment 1, the diencephalic concentrations of amino acids and monoamines following the intracerebroventricular (ICV) injection of NPY (375 pmol/10 μl/chick), saline solution under ad libitum, and fasting conditions for 30 min were determined. Central NPY significantly decreased L-tyrosine concentration, the precursor of catecholamines under feeding condition, but not under fasting condition. Central NPY significantly increased dopamine metabolites, including 3,4-dihydroxyphenylacetic acid and homovanillic acid (HVA). The concentration of 3-methoxy-4-hydroxyphenylglycol was significantly reduced under feeding condition, but did not change under fasting condition by NPY. However, no effects of NPY on indolamine metabolism were found in either feeding status. Therefore, the mechanism of action of catecholamines with central NPY under feeding condition was elucidated in Experiment 2. Central NPY significantly attenuated diencephalic gene expression of catecholaminergic synthetic enzymes, such as tyrosine hydroxylase, L-aromatic amino acid decarboxylase, and GTP cyclohydrolase I after 30 min of feeding. In Experiment 3, co-injection of α-methyl-L-tyrosine, an inhibitor of tyrosine hydroxylase with NPY, moderately attenuated the orexigenic effect of NPY, accompanied by a significant positive correlation between food intake and HVA levels. In Experiment 4, there was a significant interaction between NPY and clorgyline, an inhibitor of monoamine oxidase A with ICV co-injection which implies that co-existence of NPY and clorgyline enhances the orexigenic effect of NPY. In conclusion, central NPY modifies a part of catecholamine metabolism, which is illustrated by the involvement of dopamine transmission and metabolism under feeding but not fasting conditions.

Sex Differences in the Neuropeptide Y System and Implications for Stress Related Disorders

The neuropeptide Y (NPY) system is emerging as a promising therapeutic target for neuropsychiatric disorders by intranasal delivery to the brain. However, the vast majority of underlying research has been performed with males despite females being twice as susceptible to many stress-triggered disorders such as posttraumatic stress disorder, depression, anorexia nervosa, and anxiety disorders. Here, we review sex differences in the NPY system in basal and stressed conditions and how it relates to varied susceptibility to stress-related disorders. The majority of studies demonstrate that NPY expression in many brain areas under basal, unstressed conditions is lower in females than in males. This could put them at a disadvantage in dealing with stress. Knock out animals and Flinders genetic models show that NPY is important for attenuating depression in both sexes, while its effects on anxiety appear more pronounced in males. In females, NPY expression after exposure to stress may depend on age, timing, and nature and duration of the stressors and may be especially pronounced in the catecholaminergic systems. Furthermore, alterations in NPY receptor expression and affinity may contribute to the sex differences in the NPY system. Overall, the review highlights the important role of NPY and sex differences in manifestation of neuropsychiatric disorders.

The Role of Neuropeptide Y (NPY) in Alcohol and Drug Abuse Disorders

Neuropeptide Y (NPY) is a neuromodulator that is widely expressed throughout the central nervous system (CNS) and which is cosecreted with classic neurotransmitters including GABA and glutamate. There is a long history of research implicating a role for NPY in modulating neurobiological responses to alcohol (ethanol) as well as other drugs of abuse. Both ethanol exposure and withdrawal from chronic ethanol have been shown to produce changes in NPY and NPY receptor protein levels and mRNA expression in the CNS. Importantly, manipulations of NPY Y1 and Y2 receptor signaling have been shown to alter ethanol consumption and self-administration in a brain region-specific manner, with Y1 receptor activation and Y2 receptor blockade in regions of the extended amygdala promoting robust reductions of ethanol intake. Similar observations have been made in studies examining neurobiological responses to nicotine, psychostimulants, and opioids. When taken together with observations of potential genetic linkage between the NPY system and the human alcohol abuse disorders, NPY represents a promising target for treating problematic alcohol and drug use, and in protecting individuals from relapse during abstinence.

Neuropeptide-Y alters VTA dopamine neuron activity through both pre- and postsynaptic mechanisms

The mesocorticolimbic dopamine system, the brain's reward system, regulates many different behaviors including food intake, food reward, and feeding-related behaviors, and there is increasing evidence that hypothalamic feeding-related neuropeptides alter dopamine neuron activity to affect feeding. For example, neuropeptide-Y (NPY), a strong orexigenic hypothalamic neuropeptide, increases motivation for food when injected into the ventral tegmental area (VTA). How NPY affects the activity of VTA dopamine neurons to regulate feeding behavior is unknown, however. In these studies we have used whole cell patch-clamp electrophysiology in acute brain slices from mice to examine how NPY affects VTA dopamine neuron activity. NPY activated an outward current that exhibited characteristics of a G protein-coupled inwardly rectifying potassium channel current in ~60% of dopamine neurons tested. In addition to its direct effects on VTA dopamine neurons, NPY also decreased the amplitude and increased paired-pulse ratios of evoked excitatory postsynaptic currents in a subset of dopamine neurons, suggesting that NPY decreases glutamatergic transmission through a presynaptic mechanism. Interestingly, NPY also strongly inhibited evoked inhibitory postsynaptic currents onto dopamine neurons by a presynaptic mechanism. Overall these studies demonstrate that NPY utilizes multiple mechanisms to affect VTA dopamine neuron activity, and they provide an important advancement in our understanding of how NPY acts in the VTA to control feeding behavior.NEW & NOTEWORTHY Neuropeptide-Y (NPY) has been shown to act on mesolimbic dopamine circuits to increase motivated behaviors toward food, but it is unclear exactly how NPY causes these responses. Here, we demonstrate that NPY directly inhibited a subset of ventral tegmental area (VTA) dopamine neurons through the activation of G protein-coupled inwardly rectifying potassium currents, and it inhibited both excitatory postsynaptic currents and inhibitory postsynaptic currents onto subsets of dopamine neurons through a presynaptic mechanism. Thus NPY uses multiple mechanisms to dynamically control VTA dopamine neuron activity.

The role of melanocortins and Neuropeptide Y in food reward

The Neuropeptide Y and the melanocortin peptides are two well-described hypothalamic feeding peptides regulating energy balance. Predominantly expressed within the arcuate nucleus, these neurons project to different brain areas and modulate various aspects of feeding. Hedonic feeding, where one overindulges in palatable food consumption beyond one's nutritional necessities, is one such aspect regulated by NPY/melanocortin signaling. Research suggests that NPY/melanocortin regulate hedonic aspects of feeding through its projections to the brain reward circuitry (ventral tegmental area, lateral hypothalamus, nucleus accumbens etc.), however, exact target areas have not yet been identified. The current work explores literature to provide a mechanistic explanation for the effects of these peptides on food reward.

Neuropeptide Y Y5 receptor antagonism causes faster extinction and attenuates reinstatement in cocaine-induced place preference

Several studies have suggested a role for neuropeptide Y (NPY) in addiction to drugs of abuse, including cocaine. Recently, our group showed a role for the NPY Y5 receptor in the modulation of acute reinforcing effects of cocaine using self-administration and hyperlocomotion paradigms. In the present study, we further explored potential anti-addiction-related effects of Y5 antagonism in another murine model of cocaine addiction-related behavior: conditioned place-preference (CPP). Using this model, it was tested whether blockade or deficiency of the NPY Y5 receptor could influence the induction, extinction or reinstatement of a conditioned cocaine response. We found that the Y5 antagonist L-152,804 causes faster extinction and reduced reinstatement of cocaine-induced CPP but did not reduce the ability of cocaine to induce CPP. Similarly, Y5-KO mice displayed faster extinction, and reinstatement of cocaine-induced CPP was absent. The development of CPP for cocaine was similar between Y5-KO and WT mice. Taken together, the present data show that Y5 antagonism attenuates relapse to cocaine addiction-related behavior. Prevention of relapse is considered to be of pivotal importance for the development of an effective treatment against cocaine addiction and therefore Y5 receptors could be a potential future therapeutic target in cocaine addiction.

Neuropeptide Y and its role in CNS disease and repair

Neuropeptide Y (NPY) is widely expressed throughout the CNS and exerts a number of important physiological functions as well as playing a role in pathological conditions such as obesity, anxiety, epilepsy, chronic pain and neurodegenerative disorders. In this review, we highlight some of the recent advances in our understanding of NPY biology and how this may help explain not only its role in health and disease, but also its possible use therapeutically.

Neuropeptide Y Y5 receptor antagonism attenuates cocaine-induced effects in mice

RATIONALE

Several studies suggest a role for neuropeptide Y (NPY) in addiction to drugs of abuse, including cocaine. However, the NPY receptors mediating addiction-related effects remain to be determined.

OBJECTIVES

To explore the potential role of Y5 NPY receptors in cocaine-induced behavioural effects.

METHODS

The Y5 antagonist L-152,804 and Y5-knockout (Y5-KO) mice were tested in two models of cocaine addiction-related behaviour: acute self-administration and cocaine-induced hyperactivity. We also studied effects of Y5 receptor antagonism on cocaine-induced c-fos expression and extracellular dopamine with microdialysis as well as dopamine transporter-mediated uptake of dopamine in vitro. Immunocytochemistry was used to determine whether dopamine neurons express Y5-like immunoreactivity.

RESULTS

In self-administration, L-152,804 prominently decreased nose-poking for the peak dose of cocaine and shifted the dose-response curve for cocaine downward. Y5-KO mice also showed modestly attenuated self-administration. Cocaine-induced hyperactivity was attenuated by L-152,804 and in Y5-KO mice. Cocaine failed to increase c-fos expression in the nucleus accumbens and striatum of L-152,804-treated mice, indicating that the Y5 antagonist could act by influencing neural activity in these regions. Accordingly, the cocaine-induced increase in accumbal extracellular dopamine was attenuated by L-152,804 and in Y5-KO mice, suggesting that Y5 antagonism influences cocaine-induced behaviour by regulating dopamine. Consistent with this concept, dopamine neurons in the ventral tegmental area appeared to contain Y5 receptors. In contrast, neither L-152,804 nor NPY influenced dopamine transporter-mediated dopamine uptake.

CONCLUSIONS

The present data indicate that Y5 antagonism may attenuate cocaine-induced behavioural effects, suggesting that Y5 receptors could be a potential therapeutic target in cocaine addiction.

Ghrelin interacts with neuropeptide Y Y1 and opioid receptors to increase food reward

Ghrelin, a stomach-derived hormone, is an orexigenic peptide that was recently shown to potently increase food reward behavior. The neurochemical circuitry that links ghrelin to the mesolimbic system and food reward behavior remains unclear. Here we examined the contribution of neuropeptide Y (NPY) and opioids to ghrelin's effects on food motivation and intake. Both systems have well-established links to the mesolimbic ventral tegmental area (VTA) and reward/motivation control. NPY mediates the effect of ghrelin on food intake via activation of NPY-Y1 receptor (NPY-Y1R); their connection with respect to motivated behavior is unexplored. The role of opioids in any aspect of ghrelin's action on food-oriented behaviors is unknown. Rats were trained in a progressive ratio sucrose-induced operant schedule to measure food reward/motivation behavior. Chow intake was measured immediately after the operant test. In separate experiments, we explored the suppressive effects of a selective NPY-Y1R antagonist or opioid receptor antagonist naltrexone, injected either intracerebroventricularly or intra-VTA, on ghrelin-induced food reward behavior. The ventricular ghrelin-induced increase in sucrose-motivated behavior and chow intake were completely blocked by intracerebroventricular pretreatment with either an NPY-Y1R antagonist or naltrexone. The intra-VTA ghrelin-induced sucrose-motivated behavior was blocked only by intra-VTA naltrexone. In contrast, the intra-VTA ghrelin-stimulated chow intake was attenuated only by intra-VTA NPY-Y1 blockade. Finally, ghrelin infusion was associated with an elevated VTA μ-opioid receptor expression. Thus, we identify central NPY and opioid signaling as the necessary mediators of food intake and reward effects of ghrelin and localize these interactions to the mesolimbic VTA.

Central administration of NPY or an NPY-Y5 selective agonist increase in vivo extracellular monoamine levels in mesocorticolimbic projecting areas

Selective NPY-Y5 antagonists are known to reduce NPY-evoked increase of food intake under free feeding conditions and drug-reinforced operant responding in rodents suggesting that NPY-Y5 receptors can regulate reinforcers, potentially by modulating the hypothalamic-limbic reward system. However, evidence published to date has revealed a limited expression of NPY-Y5 in the limbic areas. Thus, the first aim of the present study was to investigate the distribution of NPY-Y5 receptor binding sites in rat mesocorticolimbic projection areas such as the nucleus accumbens (NAc), medial prefrontal cortex (mPFC), and lateral hypothalamus (LH). Since mesocorticolimbic release of monoamines has been typically associated to the rewarding and motivational significance of reinforcers, we then compared the ability of NPY and an NPY-Y5 selective agonist, [cPP1-7,NPY19-23,Ala31,Aib32,Gln34]hPP, to evoke changes in extracellular monoamines from these brain regions using in vivo microdialysis techniques. Intracerebral doses of each compound were selected on the basis of those previously demonstrated to trigger food intake in a separate set of animals. We found that NPY-Y5 receptors were widely distributed in both the NAc and mPFC but not in the LH nuclei. Central administration of either NPY (4.5 nmol/rat) or the NPY-Y5 agonist (0.6 nmol/rat) induced a significant increase of dopamine (DA) output of up to 150% of basal values in the NAc. In addition, NPY induced a stepped increase of norepinephrine (NE) outflow in the NAc area. Also extracellular levels of NE levels were increased by both treatments in the mPFC (150% vs basal concentration). Hypothalamic monoamine levels were unaffected by both treatments. Extracellular serotonin (5-HT) levels were also unchanged in all regions. Given the NPY-Y5 agonist paralleled the in vivo ability of NPY to increase DA, these data suggest that the release of NPY may modulate behaviours associated to accumbal DA release such reward and reinforcement by, at least in part, acting on mesocorticolimbic NPY-Y5 receptors.

An NMDA antagonist inhibits light but not GRP-induced phase shifts when administered after the phase-shifting stimulus

Brief light pulses or microinjection of gastrin-releasing peptide (GRP) into the third ventricle or near the suprachiasmatic nucleus (SCN) induce phase shifts of circadian rhythms during the subjective night. It has previously been reported that these effects are strongly influenced by the activation of N-methyl-d-aspartate (NMDA) receptors and the availability of glutamate. We hypothesized that the photic signaling pathway in the SCN was dependent on glutamate neurotransmission even after the completion of a photic stimulus. Adult male Syrian hamsters equipped with a surgically implanted guide cannula aimed at the SCN region were housed in constant darkness until stable free-running rhythms of wheel-running activity were apparent. Light pulses administered in the early night induced phase delays of circadian rhythms which were attenuated by the co-administration of (+/-)-2-amino-5-phosphonopentanoic acid (AP5), an NMDA antagonist. Microinjection of AP5 also inhibited light-induced shifts, to a lesser extent, immediately after and 15 min after, but not 30 min after the light pulse. A second experiment was designed to test whether AP5 would be able to attenuate GRP-induced shifts 15 min following microinjection of GRP. Phase shifts of animals that received microinjection of AP5 15 min after the administration of GRP were not different from those that received microinjection of GRP and vehicle. These data suggest that glutamate signaling remains necessary for a full photic response in the SCN even after the termination of the photic signal, but that this dependency ends once GRP-dependent signaling is complete.

Neuropeptidergic mediators of spontaneous physical activity and non-exercise activity thermogenesis

Lean individuals have high levels of spontaneous physical activity (SPA) and the energy expenditure derived from that activity, termed non-exercise activity thermogenesis or NEAT, appears to protect them from obesity. Conversely, obesity in different human populations is characterized by low levels of SPA and NEAT. Like in humans, elevated SPA in rats appears to protect against obesity: obesity-resistant rats have significantly greater SPA and NEAT than obesity-prone rats. We review the literature on brain mechanisms important in mediating SPA and NEAT. The focus is on neuropeptides, including cholecystokinin, corticotropin-releasing hormone (also known as corticotropin-releasing factor), neuromedin U, neuropeptide Y, leptin, agouti-related protein, orexin-A (also known as hypocretin-1), and ghrelin. We also review information regarding interactions between these neuropeptides and dopamine, a neurotransmitter important in mediating motor function. Finally, we present evidence that elevated signaling of pathways mediating SPA and NEAT may protect against weight gain and obesity.

Sigma 1 receptor-mediated increase in hippocampal extracellular dopamine contributes to the mechanism of the anticonvulsant action of neuropeptide Y

The potent anticonvulsant properties of neuropeptide Y (NPY) are generally attributed to a Y2 receptor-mediated inhibition of glutamatergic synaptic transmission. Independent studies have shown that NPY increases brain dopamine content, possibly via interaction with sigma 1 receptors. Recently, we showed that increased extracellular hippocampal dopamine attenuates pilocarpine-induced limbic seizures via activation of hippocampal D2 receptors. Our aim in this study was to elucidate the role of increased hippocampal dopamine in the mechanism of the anticonvulsant action of NPY and to investigate the involvement of Y2 and sigma 1 receptors in this process. Limbic seizures were evoked in freely moving rats by intrahippocampal administration of pilocarpine via a microdialysis probe. NPY was administered intracerebroventricularly, intrahippocampally via the microdialysis probe, or coadministered intrahippocampally with the D2 receptor antagonist remoxipride, the Y2 receptor antagonist BIIE0246 or the sigma 1 receptor antagonist BD1047. Changes in hippocampal extracellular dopamine were monitored, and behavioural changes indicative of seizure activity were scored. Intracerebroventricular (10 nmol/3 microL) and intrahippocampal (20-50 microm) NPY administration increased hippocampal dopamine and attenuated pilocarpine-induced seizures. Hippocampal D2 receptor blockade (4 microm remoxipride) reversed the anticonvulsant effect of NPY. Y2 receptor blockade (1 microm BIIE0246) reversed the anticonvulsant effect of NPY but did not prevent NPY-induced increases in hippocampal dopamine. Sigma 1 receptor blockade (10 microm BD1047) abolished NPY-induced increases in hippocampal dopamine and reversed the anticonvulsant effect of NPY. Our results indicate that NPY-induced increases in hippocampal dopamine are mediated via sigma 1 receptors and contribute to the anticonvulsant effect of NPY via increased activation of hippocampal D2 receptors. This novel mechanism of anticonvulsant action of NPY is separate from, and may be complementary to, the well established Y2 receptor-mediated inhibition of hippocampal excitability.

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

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

Effects of acute and subchronic d-amphetamine on ventral striatal concentrations of neurotensin and neuropeptide Y in rats treated with antipsychotic drugs

We have reported that acute d-amphetamine increases extracellular concentrations (efflux) of neurotensin-like immunoreactivity (NT-LI) and neuropeptide Y-LI (NPY-LI) in the ventral striatum (VSTR) of freely moving rats, effects that are abolished by chronic administration of haloperidol and risperidone admixed to food pellets. In this study we further investigated the d-amphetamine effects on NT-LI and NPY-LI efflux in VSTR and their content in selected brain regions. Rats received haloperidol, risperidone or vehicle for 30days and saline or d-amphetamine either on days 22-29 and/or day 30. Seven day d-amphetamine administration decreased basal NT-LI and NPY-LI efflux in vehicle-treated rats; pretreatment with haloperidol counteracted these effects, while pretreatment with risperidone had effect only on NT-LI. Acute d-amphetamine after the seven day d-amphetamine increased NT-LI only. Pretreatment with haloperidol or risperidone abolished the effects of acute d-amphetamine on NT-LI and NPY-LI. Acute and seven day d-amphetamine increased NT-LI and NPY-LI contents in striatum; seven day d-amphetamine also increased NT-LI in frontal and occipital cortex and both NT-LI and NPY-LI in hippocampus. Our results suggest that NT and NPY are involved in both the pathophysiology and the therapeutics of schizophrenia.

Effects of maternal separation on neuropeptide Y and calcitonin gene-related peptide in "depressed" Flinders Sensitive Line rats: a study of gene-environment interactions

Interactions between genetic vulnerability to stress/depression and early life experience may play a crucial role in the pathogenesis of mood disorders. Here we explore this hypothesis by superimposing early life trauma in the form of maternal deprivation for 180 min per day from postnatal day 2 to 14 onto a genetic model of depression/susceptibility to depression, Flinders Sensitive Line (FSL) and their controls, Flinders Resistant Line (FRL) rats. We investigate effects on neuropeptide Y (NPY) and calcitonin gene-related peptide (CGRP) like immunoreactivity (LI) in 10 brain regions as these neuropeptides are affected by antidepressants and are altered in cerebrospinal fluid of depressed patients. NPY-LI was reduced while CGRP-LI was elevated in hippocampus and frontal cortex of "genetically depressed" FSL rats. The two peptides displayed a significant negative correlation in these regions that was strongest in the FSL strain. Maternal deprivation exacerbated the strain difference in hippocampal CGRP-LI, while it was without effect on NPY-LI. FSL rats had higher tissue concentration of both neuropeptides in periaqueductal grey and higher NPY-LI in caudate/putamen. Maternal deprivation selectively raised CGRP-LI in amygdala of the FRL control stain. Thus, in two brain regions implicated in the neurobiology of depression, hippocampus and frontal cortex, changes in CGRP-LI and NPY-LI were in opposite direction, and CGRP-LI appears to be more responsive to adverse experience. Our findings thus support the hypothesis that genetic disposition and developmental stress may contribute to the susceptibility to depression by exerting selective neuropeptide- and brain region-specific effects on adult neurobiology.

Alterations in striatal neuropeptide Y system activity of rats with haloperidol-induced behavioral supersensitivity

The study was conducted to determine whether the expression of behavioral supersensitivity induced by haloperidol (HAL) administered once daily (2 mg/kg i.p.) for 14 days is associated with the alterations in activity of neuropeptide Y (NPY) system in the striatum (caudate-putamen) and nucleus accumbens. Dopamine supersensitivity was tested by measurement of locomotor activity and stereotyped behavior after administration of the dopamine D2/D3 receptor agonist quinpirole (1 mg/kg i.p.) on day 1, 3 and 7 after HAL withdrawal. Neuropeptide Y-like immunoreactivity (NPY-LI) was determined in the striatum and nucleus accumbens isolated 6 h after quinpirole injection on day 1, 3 and 7 after the end of HAL treatment. NPY mRNA was quantified in these structures on day 7 after HAL withdrawal. HAL increased spontaneous locomotor activity and prevalence of rearing, grooming and head-down sniffing. At the same time, striatal NPY-LI increased progressively from the reduced level found on day 1 of haloperidol withdrawal. NPY mRNA remained unchanged. In saline-treated rats, quinpirole enhanced locomotion, rearing, and induced intense head-down sniffing and oral activity. These behavioral effects were accompanied by a decrease in striatal NPY-LI. NPY mRNA was slightly increased. HAL treatment altered response to quinpirole, namely it increased locomotion, intensified oral activity and reduced rearing and head-down sniffing. The second and the third quinpirole injection decreased NPY-LI levels. NPY mRNA was unchanged. In the nucleus accumbens, apart from a decrease in NPY-LI on day 1 after the last haloperidol dose, the level of NPY-LI and NPY mRNA in any experimental group did not differ from the control value. The presented results suggest that the alterations in the activity of the striatal but not nucleus accumbens NPY system contribute to adaptive changes induced by long-term haloperidol treatment and may be of significance to the motor hyperactivity induced by intermittent stimulation of postsynaptic dopamine D2 receptors.

Growth hormone-induced stimulation of swimming and feeding behaviour of rainbow trout is abolished by the D1 dopamine antagonist SCH23390

The effects of GH on various types of behaviour in fish are well documented although the underlying mechanisms are not fully understood. In rainbow trout, an involvement of the brain dopaminergic system in mediating the behavioural effects of GH has been indicated, as GH can alter the brain dopaminergic activity. To further examine the role of the dopaminergic system in the mediation of GH effects on locomotion and foraging, GH- and sham-implanted juvenile rainbow trout were injected with the selective D1 dopamine antagonist SCH23390 or vehicle. Swimming and feeding activity was then studied by direct observation. Brains were thereafter sampled and analysed for the content of serotonin, dopamine and their metabolites in the hypothalamus, optic tectum, cerebellum, telencephalon, and brain stem. GH increased swimming activity as well as feed intake, effects which were abolished by SCH23390. By itself, the antagonist did not affect behaviour, nor did it affect the brain monoamines. In contrast, treatment with GH, with or without SCH23390, decreased the content of the dopamine metabolite homovanillic acid (HVA) in the optic tectum and the cerebellum, as well as the serotonin content (5-HT) in the optic tectum. It is concluded that the D1 dopamine receptor of the dopaminergic system appears to be of importance in the mediation of the effects of GH on behaviour.

Reduced feeding response to muscimol and neuropeptide Y in senescent F344 rats

Many mammals experience spontaneous declines in their food intake and body weight near the end of life, a stage we refer to as senescence. We have previously demonstrated that senescent rats have blunted food intake responses to intracerebroventricular injections of neuropeptide Y (NPY). In the present study, we tested the hypothesis that responsiveness to GABA, a putative potentiator of NPY's effect, is also diminished. Young and old male F344 rats received injections of NPY, muscimol, (MUS, a GABA-A receptor agonist), combinations of these two agents, and vehicle [artificial cerebrospinal fluid (aCSF)] into the hypothalamic paraventricular nucleus (PVN). Both young and old presenescent rats increased their food intake in response to NPY, MUS, and the combination of the two (in comparison to injections of aCSF). The combination treatment was generally more effective than either NPY or MUS alone. These data are consistent with suggestions that both NPY and GABA play a role in the regulation of feeding behavior. Senescent rats exhibited an attenuated NPY-induced food intake, no increase in response to MUS, and a response to NPY + MUS that was no larger than that of NPY alone. We conclude that PVN injections of GABA, as well as NPY, are less effective in stimulating feeding in senescent rats and suggest that alterations in their signaling pathways play a role in the involuntary feeding decrease seen near the end of life.

Effects of haloperidol and clozapine on neuropeptide Y-like immunoreactivity in the nucleus accumbens and striatum of rats pretreated with psychostimulants

It has been shown that the synthesis, release and levels of neuropeptide Y (NPY), a peptide linked to the dopamine system, are altered by stimulants with psychotomimetic properties and by antipsychotic drugs. This study was designed to evaluate the effect of 3-day haloperidol (HAL) (2 mg/kg i.p.) or clozapine (CLOZ) (25 mg/kg i.p.) treatment on neuropeptide Y-like immunoreactivity (NPY-LI) in nucleus accumbens and striatum (caudate-putamen) in rats pretreated with d-amphetamine or phencyclidine. D-amphetamine (5 mg/kg s.c. twice daily for 6 days and once on day 7) and phencyclidine (10 mg/kg i.p. once daily for 2 days and 15 mg/kg once on day 3) induced marked stereotypy with different symptomatology. Stereotypy is thought to resemble psychosis-related behavior. The first dose of either HAL or CLOZ was given 3 or 2h after the final d-amphetamine or phencyclidine injection, respectively. The control groups were injected with either saline alone, saline instead of psychostimulants, which was followed by antipsychotics, or psychostimulants followed by saline. Rats were sacrificed 24h after antipsychotics or 72 h after the last psychostimulant dose. Both psychostimulants similarly reduced nucleus accumbens and striatal NPY-LI. In saline-pretreated rats, HAL and CLOZ decreased nucleus accumbens NPY-LI, but only HAL decreased striatal NPY-LI. In both the structures examined the effects of HAL and d-amphetamine on NPY-LI were additive. HAL slightly enhanced but CLOZ reversed the phencyclidine-induced decrease in accumbens NPY-LI. The present study has shown that HAL and CLOZ produce different effects on nucleus accumbens and striatal NPY-LI in d-amphetamine or phencyclidine pretreated rats, and it suggests that these effects are related particularly to the dopaminergic and glutamatergic systems whose activities were altered by psychostimulants.

d-Amphetamine-induced increase in neurotensin and neuropeptide Y outflow in the ventral striatum is mediated via stimulation of dopamine D1 and D2/3 receptors

The neuroanatomical and functional relationships between dopamine (DA) and neurotensin (NT) and DA and neuropeptide Y (NPY) suggest a role for these neuropeptides in DA-related neuropsychiatric disorders. By employing a microdialysis technique in conjunction with radioimmunoassay (RIA), the effects of d-amphetamine per se or after pretreatment with DA receptor antagonists on NT and NPY outflow were determined in the ventral striatum (VSTR) of the rat. One hour after a subcutaneous (s.c.) injection of saline, the DA-D(1) receptor antagonist SCH 23390 (0.3 mg/kg), or the DA-D(2/3) receptor antagonist raclopride (1.0 mg/kg), animals were injected s.c. with either saline or d-amphetamine (1.5 mg/kg). d-Amphetamine significantly increased extracellular NT- and NPY-like immunoreactivity (LI) concentrations compared with control animals. Administration of SCH 23390 or raclopride did not significantly affect NT-LI or NPY-LI concentrations. However, pretreatment with either SCH 23390 or raclopride abolished the stimulatory effect of d-amphetamine on NT-LI and NPY-LI. These findings demonstrate that d-amphetamine increases extracellular concentrations of NT-LI and NPY-LI in the VSTR through a mechanism that initially involves stimulation of either DA-D(1) or DA-D(2/3) receptors but appears to require both. In conclusion, changes in dopaminergic neurotransmission via DA-D(1) and DA-D(2/3) receptors affect the outflow of both NT and NPY in the VSTR.

Suppression of BDNF-induced expression of neuropeptide Y (NPY) in cortical cultures by oxygen-glucose deprivation: a model system to study ischemic mechanisms in the perinatal brain

The aim of this study was to establish a culture system that can serve as a model to study hypoxic-ischemic mechanisms regulating the functional expression of NPY neurons in the perinatal brain. Using an aggregate culture system derived from the rat fetal cortex, we defined the effects of oxygen and glucose deprivation on NPY expression, using BDNF-induced production of NPY as a functional criterion. NPY neurons exhibited a differential susceptibility to oxygen and glucose deprivation. Although the neurons could withstand oxygen deprivation for 16 hr, they were dramatically damaged by 8 hr of glucose deprivation and by 1-4 hr of deprivation of both oxygen and glucose (N+Glu-). One-hour exposure to N+Glu- led to a transient inhibition ( approximately 50%) of NPY production manifesting within 24 hr and recovering by 5 days thereafter, a 2-hr exposure to N+Glu- led to a sustained inhibition (50-75%) manifesting 1-5 days thereafter, and a 4-hr exposure to N+Glu- led to a total irreversible suppression of BDNF-induced production of NPY manifesting within 24 hr and lasting 8 days after re-supply of oxygen and glucose. Moreover, 1-hr exposure to N+Glu- led to a substantial and 4-hr exposure led to a total disappearance of immunostaining for MAP-2 and NPY but not for GFAP; indicating that neurons are the primary cell-type damaged by oxygen-glucose deprivation. Analysis of cell viability (LDH, MTT) indicated that progressive changes in cell integrity take place during the 4-hr exposure to N+Glu- followed by massive cell death 24 hr thereafter. Thus, we defined a culture system that can serve as a model to study mechanisms by which ischemic insult leads to suppression and eventually death of NPY neurons. Importantly, changes in NPY neurons can be integrated into the overall scheme of ischemic injury in the perinatal brain.

Neuropeptide Y-Y1 receptor antisense oligodeoxynucleotide increases the infarct volume after middle cerebral artery occlusion in rats

An antisense oligodeoxynucleotide selective for the rat neuropeptide Y1 receptor gene was given into the left lateral ventricle in the experimental group of rats, whereas a missense oligodeoxynucleotide or saline was given in the control groups. Some rats were decapitated at 1-2h after the last injection of the oligodeoxynucleotides to examine their effects on the Y1 receptor density in the insular cortex. When compared to the Y1 and Y2 binding density of the untreated rats, the antisense-treated rats had reduced Y1 binding in the insular cortex but the Y2 binding was unaffected; treatment with missense oligodeoxynucleotide had no effect. Other rats underwent a right-sided middle cerebral artery occlusion at 1-2h after the last injection of the oligodeoxynucleotides or saline to examine the effect on the infarction volume at three days following stroke. The antisense treatment resulted in a doubling of the mean infarction volume when compared to the missense or saline treatment.Thus, reducing the Y1 receptor density prior to middle cerebral artery occlusion is harmful. Neuropeptide Y may mediate neuroprotection against focal ischemia via the cortical Y1 receptor, since the immunoreactivity for neuropeptide Y has been shown to increase within the peri-infarct cortex after middle cerebral artery occlusion.

Effects of typical and atypical antipsychotics on neuropeptide Y in rat brain tissue and microdialysates from ventral striatum

The main goal of this study was to investigate effects of typical (haloperidol) and atypical (risperidone) antipsychotic drugs on brain regional neuropeptide Y (NPY)-like immunoreactivity (-LI) tissue concentrations and on release of NPY-LI in freely moving rats. An additional aim was to explore the effect of d-amphetamine on NPY-LI release following pretreatment with typical and atypical antipsychotics. During a 4-week period, male Wistar rats were fed chow to which vehicle, risperidone (1.15 mg/100 g food or 2.3 mg/100 g food), or haloperidol (1.15 mg/100 g food) were added. In one series of experiments, the animals were sacrificed on day 30 with focused microwave irradiation, the brain regions dissected and extracted for radioimmunoassay of NPY-LI. In another experimental series, probes were inserted into the ventral striatum. The perfusates were collected at 60-min intervals; NPY-LI was determined by radioimmunoassay. Haloperidol significantly increased NPY-LI in hypothalamus and the occipital cortex. In contrast, haloperidol decreased tissue levels of NPY-LI in striatum. Moreover, haloperidol and risperidone also significantly decreased extracellular NPY-LI concentrations in the ventral striatum. d-amphetamine (1.5 mg/kg) significantly increased extracellular NPY-LI in the vehicle group. Both haloperidol and risperidone pretreatments abolished the effect of d-amphetamine. The results show that d-amphetamine as well as haloperidol and risperidone selectively and specifically affect NPY-LI concentrations in brain tissue and microdialysates and that the effect of d-amphetamine is abolished by both typical and atypical antipsychotics.

Ultrastructural and metabolic changes in the neuropeptide Y-containing striatal neuronal network after thermocoagulatory cortical lesion in adult rat

This study examined the effects of unilateral thermocoagulatory cortical lesion on the pattern of neuropeptide Y immunostaining in the rat ipsilateral striatum at 4 and 21 days post-lesion. Light microscopic analysis showed a significant increase in the number of neuropeptide Y-positive neurons vs. control at both time points; paradoxically, the intraneuronal level of labelling significantly decreased at 4 days post-lesion but increased at 21 days post-lesion. Ultrastructural analysis in control condition showed a higher proportion of dendritic versus axonal labelled processes (3.5 ratio); all the neuropeptide Y synaptic terminals formed symmetrical contacts, mostly onto unlabelled dendrites. At 4 days post-lesion, the neuropeptide Y-positive axon density dramatically increased (+576%) without significant change in the labelled dendrite density, vs. control values; the density of neuropeptide Y synaptic terminals increased in parallel by 233%. In addition, a significant proportion of large neuropeptide Y boutons forming asymmetrical synapses onto unlabelled spines were observed. At 21 days post-lesion, densities of neuropeptide Y dendrites, axons, and synaptic terminals increased by 68, 246 and 125%, respectively, vs. control. But, the morphological features of the neuropeptide Y axonal processes and synaptic specializations of the boutons were similar to those observed in control condition. These data (1) raise an important issue regarding the origin of the terminals forming asymmetrical synapses in the striatum, (2) suggest that adaptative changes in the neuropeptide Y neuronal network may be a main component of striatal remodelling resulting from the progressive loss of cortical inputs, and (3) reinforce the view that neuropeptide Y and excitatory amino acid functions may be tightly linked in the striatum.

CART peptide-immunoreactive neurones in the nucleus accumbens in monkeys: ultrastructural analysis, colocalization studies, and synaptic interactions with dopaminergic afferents

Cocaine- and amphetamine-regulated transcript (CART) is a novel mRNA whose level of expression was found to be increased in the striatum after acute administration of psychomotor stimulants in rats. To define better the potential role of CART peptides in behavioural and physiologic changes induced by psychomotor stimulants, we analyzed the distribution, ultrastructural features, synaptic connectivity, and transmitter content of CART peptide-immunoreactive neurones in the nucleus accumbens in monkeys. Medium-sized CART peptide-immunoreactive neurones within a rich plexus of labelled varicosities were found mostly in the medial division of the shell of the nucleus accumbens in monkeys. At the electron microscope level, CART peptide immunoreactivity was exclusively associated with neuronal structures that included perikarya, dendrites, spines as well as nerve terminals packed with electron-lucent and dense-core vesicles. Most CART peptide-containing somata displayed the ultrastructural features of striatal output neurones. The majority of labelled terminals formed symmetric axodendritic synapses and displayed gamma-aminobutyric acid (GABA) immunoreactivity. CART peptide-immunoreactive somata were not immunoreactive for parvalbumin and somatostatin, two markers of striatal interneurones, nor for calbindin D-28k, a marker of a subpopulation of projection neurones. In double-immunostained sections, CART peptide-immunoreactive dendrites were found to be contacted by tyrosine hydroxylase-positive terminals which displayed the ultrastructural features of dopamine-containing boutons. These findings strongly suggest that CART peptides may be a cotransmitter with GABA in a subpopulation of projection neurones in the monkey accumbens. Furthermore, the fact that CART peptide-immunoreactive neurones receive direct synaptic inputs from dopaminergic afferents and are particularly abundant in the caudomedial division of the shell of the nucleus accumbens suggest that CART peptides might be involved in neuronal and behavioural changes that underlie addiction to psychomotor stimulants and feeding in primates.

Influence of typical and atypical antipsychotics on neuropeptide Y-like immunoreactivity and NPY mRNA expression in rat striatum

Striatal neuropeptide Y-like immunoreactivity (NPY-LI) levels were investigated in naive rats after acute, subchronic (14 days) or chronic (28 days) intraperitoneal (i.p.) treatment with chlorpromazine (2 or 10mg/kg), haloperidol (0.5 or 2 mg/kg), (+/-)sulpiride (50 or 100 mg/kg) or clozapine (10 or 25 mg/kg), and in chronically treated rats after 8-day drug withdrawal. The most pronounced changes in NPY-LI levels were found 24 h after acute chlorpromazine or haloperidol administration (a decrease) and after withdrawal of chlorpromazine, haloperidol or sulpiride (an increase). The effect of clozapine on NPY-LI differed from those of the other antipsychotics: both single doses had no effect, the higher chronic dose increased NPY-LI levels, and its withdrawal resulted in their decrease. No significant alterations were detected in the hybridization signal of NPY mRNA in response to acute or subchronic administration of haloperidol or clozapine. Our results suggest that the effects of antipsychotics are in part mediated by blockade of dopamine D2-like (D2/D3) or serotonin 5HT2A receptors but not dopamine D1, D4 or alpha1-adrenergic receptors. The antipsychotic-induced changes in NPY system activity has been discussed in connection with adaptive alterations in the dopamine system.

Neuropeptide Y and glutamate block each other's phase shifts in the suprachiasmatic nucleus in vitro

The suprachiasmatic nuclei contain a circadian clock whose activity can be recorded in vitro for several days. Photic information is conveyed to the nuclei primarily via a direct projection from the retina, the retinohypothalamic tract, utilizing an excitatory amino acid neurotransmitter. Photic phase shifts may be mimicked by application of glutamate in vitro. A second, indirect pathway to the suprachiasmatic nuclei via the geniculohypothalamic tract utilizes neuropeptide Y as a transmitter. Phase shifts to neuropeptide Y in vitro are similar to those seen to non-photic stimuli in vivo. We have used the hypothalamic slice preparation to examine the interactions of photic and non-photic stimuli in the suprachiasmatic nuclei. Coronal hypothalamic slices containing the suprachiasmatic nuclei were prepared from Syrian hamsters and 3 min recordings of the firing rate of individual cells were performed throughout a 12 h period. Control slices receiving either no application or application of artificial cerebrospinal fluid to the suprachiasmatic nucleus showed a consistent daily peak in their rhythms. Glutamate produces phase shifts of the circadian clock in the hamster hypothalamic slice preparation during the subjective night but not during the subjective day. These phase shifts were similar in timing and direction to the photic phase response curve in vivo confirming previous work with the rat slice preparation. Neuropeptide Y produces phase shifts of the circadian clock during the subjective day but not during the subjective night. The phase shifts are similar in timing and direction to the non-photic phase response curve in vivo, confirming previous in vitro work. We then examined the interaction of these neurochemicals with each other at various times during the circadian cycle. We found that both advances and delays to glutamate in the slice are blocked by application of neuropeptide Y. We also found that phase shifts to neuropeptide Y in the slice are blocked by application of glutamate. These results indicate that photic and non-photic associated neurochemicals can block each others phase shifting effects within the suprachiasmatic nucleus in vitro. These experiments demonstrate the ability of photic and non-photic associated neurochemicals to interact at the level of the suprachiasmatic nucleus. It is clear that neuropeptide Y antagonizes the effect of glutamate during the subjective night, and that glutamate antagonizes the effect of neuropeptide Y during the subjective day. Great care must be taken when devising treatments where photic and non-photic signals may interact.

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

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

Neuropeptide Y perfused in the preoptic area of rats shifts extracellular efflux of dopamine, norepinephrine, and serotonin during hypothermia and feeding

This study examined the localized action of neuropeptide Y (NPY) on monoamine transmitter activity in the hypothalamus of the unrestrained rat as this peptide induced hypothermia, spontaneous feeding or both responses simultaneously. A guide tube was implanted in the anterior hypothalamic pre-optic area (AH/POA) of Sprague-Dawley rats. Then either control CSF vehicle or NPY in a dose of either 100 ng/microliter or 250 ng/microliter was perfused by push-pull cannulae in this structure in the fully sated, normothermic rat. Successive perfusions were carried out at a rate of 20 microliters/min for 6.0 min with an interval of 6.0 min elapsing between each. Samples of perfusate were assayed by HPLC for their levels of dopamine (DA), norepinephrine (NE), serotonin (5-HT) and their respective metabolites. Whereas control CSF was without effect on body temperature (Tb) or feeding, repeated perfusions of NPY over 3.0 hr caused dose-dependent eating from 4 to 39 g of food, hypothermia of 0.9 to 2.3 degrees C or both responses concurrently. As the rats consumed 11-39 g of food, the efflux of NE, MHPG, DOPAC and 5-HT was enhanced significantly, whereas during the fall in Tb the efflux of NE, DOPAC and 5-HIAA from the AH/POA increased. When the Tb of the rat declined simultaneously with eating behavior, the levels in perfusate of DOPAC and HVA increased significantly while MHPG declined. During perfusion of the AH/POA with NPY the turnover of NE declined while DA and 5-HT turnover increased during hypothermia alone or when accompanied by feeding. These results demonstrate that the sustained elevation in NPY within the AH/POA causes a selective alteration in the activity of the neurotransmitters implicated in thermoregulation, satiety and hunger. These findings suggest that both DA and NE comprise intermediary factors facilitating the action of NPY on neurons involved in thermoregulatory and ingestive processes. The local activity of NPY on hypothalamic neurons apparently shifts the functional balance of serotonergic and catecholaminergic neurons now thought to play a primary role in the control of energy metabolism and caloric intake.

Autoradiographic distribution of [125I]Leu31,Pro34]PYY and [125I]PYY3-36 binding sites in the rat brain evaluated with two newly developed Y1 and Y2 receptor radioligands

The peptide YY derivatives [Leu31,Pro34]PYY and PYY3-36 are highly selective Y1 and Y2 agonists, devoid of activity on the Y3 receptor subtype [Dumont et al. (1994) Molec. Brain Res., 26:3220-3324]. These selective ligands were iodinated and used to evaluate the respective quantitative autoradiographic distribution of the Y1 and Y2 receptor subtypes in the rat brain, excluding a potential contamination from Y3 receptor. Specific [125I][Leu31,Pro34]PYY (Y1), and [125I]PYY3-36 (Y2) binding sites are detected in various brain regions, but each showed a differential distribution profile. Y1/[125I][Leu31,Pro34]PYY sites are especially concentrated in superficial layers of the cortex, the olfactory tubercle, islands of Calleja, tenia tecta, molecular layer of the dentate gyrus, several thalamic nuclei, and the posterior part of the medial mammaliary nucleus. These areas generally contained only low densities of Y2/[125I]PYY3-36 binding sites. In contrast, [125I]PYY3-36 binding is most abundant in multiple other regions including the lateral septum, piriform cortex, triangular septal nucleus, bed nucleus of the stria terminalis, oriens layer and stratum radiatum of the dorsal hippocampus, ventral tegmental area, substantia nigra, dorsal raphe nucleus, and the granular cell layer of the cerebellum. Few areas of the rat brain contained significant amounts of both [125I][Leu31,Pro34]PYY and [125I]PYY3-36 binding sites such as the anterior olfactory nuclei, oriens layer and stratum radiatum of the ventral hippocampus, nucleus tractus solitarius, area postrema, and inferior olive. Taken together, these results and the use of two selective radioligands demonstrate further the discrete, differential distribution of the Y1 and Y2 receptor subtypes in the rat brain.

Neuropeptide changes following excitotoxic lesion of the insular cortex in rats

Following middle cerebral artery occlusion in Wistar rats, the immunoreactivity of neuropeptide Y increased ipsilaterally in the insular cortex and basolateral nucleus of the amygdala. In addition, the immunoreactivity of leucine-enkephalin, dynorphin, and neurotensin increased in the ipsilateral central nucleus of the amygdala. The amygdalar neurochemical changes are likely the result of damage to the insular cortex, although other cortical areas were also affected by the ischemia. To investigate whether damage to the insular cortex is essential in eliciting these changes, a localized lesion of the right or left insular cortex was produced by microinjection of D,L-homocysteic acid. Control animals received injections of vehicle into the right or left insular cortex or D,L-homocysteic acid into the right primary somatosensory cortex. Neurochemical changes were examined immunohistochemically with the peroxidase-antiperoxidase reaction 5 days after the injection. The immunoreactivity of neuropeptide Y increased locally after excitotoxic damage to the insular cortex or primary somatosensory cortex. The amygdalar neurochemical changes, including neuropeptide Y increase in the basolateral nucleus and leucine-enkephalin, dynorphin, and neurotensin increase in the central nucleus, were seen only when the ipsilateral insular cortex was lesioned. These neurochemical changes were similar to those seen 5 days after middle cerebral artery occlusion. Our findings indicate that damage to the insular cortex is essential in eliciting the neurochemical changes in the ipsilateral amygdala. In addition, the change in neuropeptide Y in the cortex appears to be a local reaction occurring irrespective of location of the lesion and glutamate receptor activation may be involved.

Neurochemical changes following occlusion of the middle cerebral artery in rats

We have developed a stroke model involving middle cerebral artery occlusion in the rat which elicits changes in cardiac and autonomic variables that are similar to those observed clinically. It is likely that these neurogenic autonomic responses are mediated by changes in neurotransmitter systems subsequent to the stroke. This possibility was investigated by examining changes in immunohistochemical staining for tyrosine hydroxylase, neuropeptide Y, leu-enkephalin, neurotoxins and dynorphin following middle cerebral artery occlusion in the rat. Computerized image analysis was used to provide semi-quantitative measurements of the changes. The ischemic region was centered primarily in the insular cortex. The results indicate that there are significant increases in immunostaining for tyrosine hydroxylase and neuropeptide Y in the insular cortex within the peri-infarct region. Neuropeptide Y staining was also significantly increased in the basolateral nucleus of the amygdala, ipsilateral to the middle cerebral artery occlusion, which did not appear to be included in the infarct. Leu-enkephalin, neurotensin and dynorphin staining was significantly elevated in the central nucleus of the amygdala ipsilateral to the occlusion of the middle cerebral artery. These neurochemical changes are discussed as possible mechanisms mediating the cardiac and autonomic consequences of stroke or as part of a process to provide neuro-protection following focal cerebral ischemia.

Time-course of neuropeptide changes in peri-ischemic zone and amygdala following focal ischemia in rats

Previously, using a middle cerebral artery occlusion model in Wistar rat, we showed autonomic disturbances similar to those seen clinically and observed striking neurochemical changes in cortical and subcortical sites at 5 days following stroke. The neurochemical changes may account for functional recovery and/or autonomic disturbances after focal ischemia. To understand the possible mechanisms and to facilitate future studies, it is necessary to define the time-courses of these changes. Using immunohistochemical staining with the peroxidase-antiperoxidase reaction, the changes in several neuropeptides over the peri-ischemic region and the ipsilateral central and basolateral nucleus of the amygdala were investigated at different times after middle cerebral artery occlusion. In the experimental group, neuropeptide Y immunoreactivity appeared to increase by 6 hours in the peri-ischemic region. Using image analysis to quantify the staining intensity, the change became statistically significant at 1 day, peaked around 3 days, and subsided at 10 days. There was a delayed increase in neuropeptide Y in the ipsilateral basolateral nucleus of the amygdala with a peak around 3 days. Immunoreactive staining for leucine-enkephalin, dynorphin, and neurotensin demonstrated an increase that was localized to the ipsilateral central nucleus of the amygdala with a peak around 3 days and a return to baseline levels by 10 days. The results support a specific time-course for each of the neuropeptides studied and indicate that a survival time of 3 days after focal ischemia is the critical period for examining the relationship between neuropeptide responses and neuronal or functional recovery.

Colocalization of somatostatin, neuropeptide Y, and NADPH-diaphorase in the caudate-putamen of the rat

Somatostatin, neuropeptide Y, and nicotinamide adenine dinucleotide phosphate-diaphorase are colocalized within a small population of medium aspiny neurons in the caudate-putamen of the rat. The extent of colocalization, however, appears to be in dispute. In order to examine the question of colocalization between these three neuroactive substances, a series of double-labelling experiments was performed. This was accomplished by combining immunocytochemistry for somatostatin or neuropeptide Y or enzyme histochemistry for nicotinamide adenine dinucleotide phosphate-diaphorase with in situ hybridization for somatostatin and/or neuropeptide Y mRNA. The results of such analysis indicate that nicotinamide adenine dinucleotide phosphate-diaphorase and somatostatin mRNA are 100% colocalized throughout the caudate-putamen, except for the area bordering the globus pallidus. All neurons that contain neuropeptide Y contain somatostatin message. Only 84% of the neurons that contain somatostatin mRNA, however, also contain neuropeptide Y. Neurons that contain somatostatin 28 but not neuropeptide Y are found throughout the caudate-putamen. These results indicate that the somatostatin neuron population in the rat caudate-putamen is not homogeneous. Instead, the medium aspiny neuron population is actually composed of several subpopulations based on the content of neuroactive substances.

Reversal of the adaptive response of neuropeptide Y neurons in the rat striatum to nigrostriatal dopamine deafferentation by the N-methyl-D-aspartate antagonist dizocilpine maleate

This study examined the effects of systemic treatments with dizocilpine maleate alone or in combination with unilateral 6-hydroxydopamine-induced lesion of the nigrostriatal dopaminergic neurons on the number and staining intensity of neuropeptide Y-immunoreactive neurons in the rat striatum. In the combined condition, short-term and long-term treatments with dizocilpine maleate were started 19 days and 12 days after the lesion of the nigrostriatal dopaminergic pathway, respectively. As reported previously, the unilateral dopaminergic lesion elicited an increase in both the number and staining intensity of neuropeptide Y-immunoreactive neurons in the ipsilateral striatum. Short-term treatment with dizocilpine maleate at the dose of 0.2 mg/kg (four injections, 6 h apart, sacrifice 2 h after the final dose), which by itself did not modify neuropeptide Y immunostaining, totally suppressed the effect of the dopaminergic deafferentation on the number of neuropeptide Y-positive neurons but not that on the intraneuronal amount of labelling. When administered twice a day for eight days at the same dose of 0.2 mg/kg, dizocilpine maleate by itself elicited an increase in the number of neuropeptide Y-immunodetectable cells, paradoxically concomitant with a decrease in the levels of intraneuronal labelling. After combination of this treatment with unilateral lesion of the nigrostriatal dopaminergic pathway, the changes related to either the dizocilpine maleate treatment or the 6-hydroxydopamine-induced lesion totally disappeared, so that the number and staining intensity of neuropeptide Y-immunoreactive neurons in that condition did not differ from control values.(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative study of the effects of mu, delta and kappa opioid agonists on 3H-dopamine uptake in rat striatum and nucleus accumbens

The effect of the mu opioid agonist DAGO, delta opioid agonist DPDPE and kappa opioid agonist U50,488H on 3H-dopamine (3H-DA) uptake was studied in synaptosomes prepared from rat striatum and nucleus accumbens. Over the range of concentrations tested (1 nM-10 microM) DAGO and DPDPE were devoid of effects on 3H-DA uptake in the striatum and the nucleus acumbens. In contrast, U50,488H significantly decreased 3H-DA uptake in both structures. The inhibition of uptake induced by the kappa agonist was not reversed in the presence of the opiate antagonists naloxone (10 microM) or nor-binaltorphimine (0.1 microM). Dynorphin A (1-13) also induced a significant reduction in 3H-DA uptake in both structures at the concentrations of 10 and 30 microM. This inhibitory effect was not reversed by naloxone (10 microM). These data suggest that kappa opioid agonists modulate dopamine uptake in the striatum and the nucleus accumbens and their effects may not be due to an activation of opioid receptors.

Local injections of excitatory amino acid agonists alter the glutamatergic and dopaminergic transmissions in the rat striatum

This study examined the effects of kainic, ibotenic, and quisqualic acid-induced lesions of the rat striatum on biochemical markers of the glutamatergic corticostriatal and dopaminergic nigrostriatal afferent transmissions. Fifteen to 21 days after striatal injections of these various compounds, significant reductions in the high-affinity glutamate uptake rate, due to decreases in the Vmax of the transport process, were measured. Interestingly, the relationship between these decreases in the Vmax and the decreases in the levels of biochemical markers for the intrinsic striatal cholinergic and GABAergic neurons differed depending on the excitotoxin used. These findings suggest that excitatory amino acid agonists-induced alterations of the glutamatergic terminal activity may not depend only on the loss of cholinergic and GABAergic striatal neurons. In contrast, the observed changes in the dopamine and metabolite contents seemed to be related to the extent of the striatal neuronal degeneration induced by each excitotoxin. All in all, these results indicate that excitatory amino acid agonists can impair the activity and/or the integrity of the two main striatal afferent pathways, through presumably different mechanisms.