Neuropeptide Y does not alter NMDA conductances in CA3 pyramidal neurons: a slice-patch study

Thinking outside the pyramidal cell: unexplored contributions of interneurons and neuropeptide Y to estrogen-induced synapse formation in the hippocampus

Since the first finding that 17beta-estradiol (E) can regulate CA1 pyramidal cell synapse formation, subsequent studies have explored many potential E-dependent mechanisms occurring within CA1 pyramidal cells. Fewer studies have focused on E-dependent processes outside of the pyramidal cell that may influence events activity of the pyramidal cells. This review considers hippocampal interneurons, which can potently regulate the excitability of simultaneously firing pyramidal cells. In particular, we discuss neuropeptide Y (NPY) expression by these interneurons because our published findings show that NPY expression is increased by E in a subset of interneurons which coincidentally exhibit E-regulated increase in GABA synthesis and are uniquely situated anatomically such that they may regulate synaptic activity. Here we review the role of different phenotypes of CA1 interneurons, and we propose a model in which E-stimulated NPY gene expression and the release of NPY by interneurons inhibits glutamate release presynaptically and alters glutamate-dependent synaptic events in the rat hippocampus during adulthood.

Changes in interneuronal phenotypes regulated by estradiol in the adult rat hippocampus: A potential role for neuropeptide Y

Ovarian hormones regulate pyramidal cell synapse formation and excitability and interneuronal GABAergic tone in the CA1 region of the adult female rat hippocampus. The role of 17beta-estradiol in these effects is complex and appears to involve a subset of hippocampal interneurons, which express different calcium-binding protein and neuropeptide phenotypes and nuclear estrogen receptor alpha. We found that, in the hippocampus, nuclear estrogen receptor alpha-immunoreactive interneurons co-express neuropeptide Y, calbindin-D28k and calretinin but do not parvalbumin or cholecystokinin. Moreover, a proportion of neuropeptide Y-immunoreactive interneurons co-expresses calbindin-D28k and calretinin. This pattern is similar in the presence or absence of 17beta-estradiol treatment in ovariectomized rats. We then used immunohistochemistry and in situ hybridization to determine whether 17beta-estradiol treatment regulates expression of CA1 interneuronal phenotypic markers via nuclear estrogen receptor alpha activation. We found that 17beta-estradiol treatment of ovariectomized rats increased neuropeptide Y mRNA levels (25%) and the neuropeptide Y mRNA-associated grain density per cell (11%), as well as the number of neuropeptide Y-immunoreactive cells (11%), predominantly in the pyramidal cell layer (stratum pyramidale). Treatment with CI628, a selective estrogen response modulator that acts as an antagonist for nuclear estrogen receptor, blocked 17beta-estradiol-induced increase of neuropeptide Y mRNA levels. 17beta-Estradiol treatment did not alter the number of parvalbumin, calretinin, and cholecystokinin immunoreactive cells, nor mRNA levels for parvalbumin and cholecystokinin. Therefore, the present study has identified neuropeptide Y expression as the main interneuronal phenotype that co-expresses nuclear estrogen receptor alpha and shown that neuropeptide Y is responsive to 17beta-estradiol in CA1 pyramidal cell layer. We suggest that 17beta-estradiol may regulate neuropeptide Y expression mediated by nuclear estrogen receptor alpha-dependent activation in a subset of hippocampal interneurons, and we speculate that subsequent neuropeptide Y release may indirectly contribute to regulate glutamate-dependent neuronal activity in the adult rat hippocampus.

Interneuron Diversity series: Interneuronal neuropeptides--endogenous regulators of neuronal excitability

Interneurons are often classified according to neuropeptide content. However, it is becoming increasingly clear that neuropeptides are more than convenient neurochemical markers and can act as important modulators of neuronal activity. Recent advances in understanding neuropeptide release and physiological actions suggest that the interneuronal system of neuropeptides is crucial for maintaining appropriate brain function under normal and pathophysiological conditions. In particular, interneuronal neuropeptides appear to play roles in cognition and as endogenous anti-epileptic agents. This article describes current understanding of the conditions under which neuropeptides are released from interneurons, their specific effects on neuronal excitability and synaptic transmission, and the consequences of their loss of function.

NPY presynaptic actions are reduced in the hypothalamic mpPVN of obese (fa/fa), but not lean, Zucker rats in vitro

1. Neuropeptide Y (NPY) profoundly enhances feeding when injected intracerebroventricularly, or directly into hypothalamic nuclei, such as the paraventricular nucleus (PVN). Paradoxically, NPY has a reduced action on feeding in obese Zucker rats relative to lean Zucker rats, although the obese rats have much higher levels of hypothalamic NPY expression. GABAergic inputs to a subpopulation of medial parvocellular PVN (mpPVN) neurons are sensitive to NPY. Here, we tested the hypothesis that the blunted eating response to NPY observed in obese Zucker rats will be reflected in a reduced NPY action at mpPVN GABAergic synapses. 2. 'Blind' whole-cell patch-clamp recordings made from mpPVN neurons in acute brain slices of lean and obese Zucker rats revealed GABAergic inhibitory postsynaptic currents (IPSC) responses which were inhibited by NPY. While the maximum response in the obese Zucker rats was significantly less than in lean Zucker or Sprague-Dawley rats, there was no difference in the EC(50). 3. Experiments using blocking concentrations of Y(1)- or Y(5)-receptor antagonists revealed no differences between lean and obese Zucker rats in the contributions of either of these receptors to the total NPY response in mpPVN. 4. NPY is less effective at the mpPVN GABA synapse in obese than in lean Zucker rats. This is not associated with a change in the proportion of Y(1) or Y(5) receptors mediating the NPY response, and is consistent with the downregulation of NPY receptors or a reduction in receptor-effector coupling, and with the reduced sensitivity of obese rats to NPY.

Neuropeptide Y and Epilepsy

It is a central tenet of the epilepsy field that seizures result from the imbalance of excitation over inhibition (1). The bulk of excitation is mediated by the neurotransmitter glutamate, whereas inhibition results mainly from the actions of gamma-aminobutyric acid (GABA). In the neocortex and hippocampus, the intrinsic sources of GABA are the interneurons, which lately have come under intense scrutiny. It has become clear that a large number of distinct types of interneurons can be differentiated in part by the array of neuropeptides they coexpress (cf. (2)). Evidence is emerging that the neuropeptide complement of interneurons plays important roles in the way that interneurons regulate excitability. Here we discuss what is known about the relation of one well-characterized neuropeptide, neuropeptide Y (NPY), and epilepsy in experimental animals and humans, and suggest possible roles for the receptors as targets for the control of excessive excitation in epilepsy.

Neuropeptide Y and Epilepsy

It is a central tenet of the epilepsy field that seizures result from the imbalance of excitation over inhibition ( 1 ). The bulk of excitation is mediated by the neurotransmitter glutamate, whereas inhibition results mainly from the actions of γ-aminobutyric acid (GABA). In the neocortex and hippocampus, the intrinsic sources of GABA are the interneurons, which lately have come under intense scrutiny. It has become clear that a large number of distinct types of interneurons can be differentiated in part by the array of neuropeptides they coexpress (cf. 2). Evidence is emerging that the neuropeptide complement of interneurons plays important roles in the way that interneurons regulate excitability. Here we discuss what is known about the relation of one well-characterized neuropeptide, neuropeptide Y (NPY), and epilepsy in experimental animals and humans, and suggest possible roles for the receptors as targets for the control of excessive excitation in epilepsy.

Antiepileptic actions of neuropeptide Y in the mouse hippocampus require Y5 receptors

PURPOSE

Recent evidence suggests an antiepileptic role for neuropeptide Y (NPY) in the central nervous system. The precise receptor subtypes mediating the inhibitory actions of NPY in the hippocampal formation, however, remain unclear. In vitro studies suggest a role for Y2 receptors in modulating excitatory hippocampal synaptic transmission and epileptiform discharge. In vivo studies implicate Y5 receptors. Here we used pharmacologic tools and Y5-receptor knockout mice to examine the role of Y5 receptors in mediating the antiexcitatory and antiepileptic actions of NPY in the hippocampal formation.

METHODS

Hippocampal slices were obtained from age-matched wild-type (WT; 129 s3/svimj) and Y5-receptor knockout (Y5R KO) mice generated on the same background strain. Extracellular or whole-cell voltage-clamp recordings were obtained in area CA3 pyramidale. Evoked population spikes or excitatory postsynaptic currents were monitored during bath application of NPY, NPY13-36, or human pancreatic polypeptide (hPP). In some slices, zero-magnesium cerebrospinal fluid (CSF) was used to evoke spontaneous epileptiform discharges.

RESULTS

NPY and NPY agonists with preference for either Y2 (NPY13-36) or Y5 (hPP) receptor subtypes caused a significant reduction in population spike and excitatory postsynaptic current (EPSC) amplitudes in slices from WT mice. NPY (and NPY agonists) also suppressed zero-magnesium epileptiform burst discharge in slices from WT mice. In contrast, bath application of NPY, NPY13-36, or hPP had no effect in slices from Y5R KO mice.

CONCLUSIONS

NPY modulates excitatory synaptic transmission and inhibits limbic seizure activity in the mouse hippocampus. The antiepileptic actions of NPY, in the mouse, appear to require activation of hippocampal Y5 receptors.

Multiple NPY receptors Inhibit GABA(A) synaptic responses of rat medial parvocellular effector neurons in the hypothalamic paraventricular nucleus

We have recently shown that NPY and alpha-melanocyte-stimulating hormone, which potently induce or inhibit feeding, respectively, have opposing modulatory actions on GABAergic synapses in the medial parvocellular region of the paraventricular hypothalamic nucleus (mpPVN). Because this action might underlie the effects of NPY on feeding, we have examined the pharmacology of NPY responses using electrophysiological recordings. Focal electrical stimulation within the PVN elicited a GABA(A) synaptic response in some mpPVN neurons, which was reversibly inhibited by NPY in a concentration-dependent manner (EC(50) = 28 nM). NPY did not alter the response to the GABA(A) agonist, muscimol. Agonist responses to NPY analogs were not consistent with a single NPY receptor subtype; the most subtype selective agonists were less effective than the more broadly selective ones. Antagonist blockade of individual receptor subtypes partly inhibited NPY action, while fully blocking effects of selective agonists. Combining Y1 and Y5 antagonists blocked actions of NPY entirely, but the Y2 antagonist also completely blocked actions of NPY in some neurons. NPY inhibits GABA(A) synaptic transmission onto mpPVN neurons, but this can be mediated by three different NPY receptors. Controversy regarding the receptor or receptor subtypes involved in NPY-mediated feeding may arise from the multiple NPY receptors present.

Y5 receptors mediate neuropeptide Y actions at excitatory synapses in area CA3 of the mouse hippocampus

Neuropeptide Y (NPY) is a potent modulator of excitatory synaptic transmission and limbic seizures. NPY is abundantly expressed in the dentate gyrus and is thought to modulate hippocampal excitability via activation of presynaptic Y2 receptors (Y2R). Here we demonstrate that NPY, and commonly used Y2R-preferring (NPY(13-36)) and Y5 receptor (Y5R)-preferring ([D-Trp(32)]NPY and hPP) peptide agonists, evoke similar levels of inhibition at excitatory CA3 synapses in hippocampal slices from wild-type control mice (WT). In contrast, NPYergic inhibition of excitatory CA3 synaptic transmission is absent in mice lacking the Y5R subtype (Y5R KO). In both analyses of evoked population spike activity and spontaneous excitatory postsynaptic synaptic currents (EPSCs), NPY agonists induced powerful inhibitory effects in all hippocampal slices from WT mice, whereas these peptides had no effect in slices from Y5R KO mice. In slices from WT mice, NPY (and NPY receptor-preferring agonists) reduced the frequency of spontaneous EPSCs but had no effect on sEPSC amplitude, rise time, or decay time. Furthermore, NPYergic modulation of spontaneous EPSCs in WT mice was mimicked by bath application of a novel Y5R-selective peptide agonist ([cpp]hPP) but not the selective Y2R agonist ([ahx(5-24)]NPY). In situ hybridization was used to confirm the presence of NPY, Y2, and Y5 mRNA in the hippocampus of WT mice and the absence of Y5R in knockout mice. These results suggest that the Y5 receptor subtype, previously believed to mediate food intake, plays a critical role in modulation of hippocampal excitatory transmission at the hilar-to-CA3 synapse in the mouse.

Neuropeptide Y(5) receptors reduce synaptic excitation in proximal subiculum, but not epileptiform activity in rat hippocampal slices

Neuropeptide Y (NPY) potently inhibits excitatory synaptic transmission in the hippocampus, acting predominantly via a presynaptic Y(2) receptor. Recent reports that the Y(5) receptor may mediate the anticonvulsant actions of NPY in vivo prompted us to test the hypothesis that Y(5) receptors inhibit synaptic excitation in the hippocampal slice and, furthermore, that they are effective in an in vitro model of anticonvulsant action. Two putative Y(5) receptor-preferring agonists inhibited excitatory postsynaptic currents (EPSCs) evoked by stimulation of stratum radiatum in pyramidal cells. We recorded initially from area CA1 pyramidal cells, but subsequently switched to cells from the subiculum, where a much greater frequency of response was observed to Y(5) agonist application. Both D-Trp(32)NPY (1 microM) and [ahx(8-20)]Pro(34)NPY (3 microM), a centrally truncated, Y(1)/Y(5) agonist we synthesized, inhibited stimulus-evoked EPSCs in subicular pyramidal cells by 44.0 +/- 5.7% and 51.3 +/- 3.5% (mean +/- SE), in 37 and 58% of cells, respectively. By contrast, the less selective centrally truncated agonist, [ahx(8-20)] NPY (1 microM), was more potent (66.4 +/- 4.1% inhibition) and more widely effective, suppressing the EPSC in 86% of subicular neurons. The site of action of all NPY agonists tested was most probably presynaptic, because agonist application caused no changes in postsynaptic membrane properties. The selective Y(1) antagonist, BIBP3226 (1 microM), did not reduce the effect of either more selective agonist, indicating that they activated presynaptic Y(5) receptors. Y(5) receptor-mediated synaptic inhibition was more frequently observed in slices from younger animals, whereas the nonselective agonist appeared equally effective at all ages tested. Because of the similarity with the previously reported actions of Y(2) receptors, we tested the ability of Y(5) receptor agonists to suppress stimulus train-induced bursting (STIB), an in vitro model of ictaform activity, in both area CA3 and the subiculum. Neither [ahx(8-20)]Pro(34)NPY nor D-Trp(32)NPY were significantly effective in suppressing or shortening STIB-induced afterdischarge, with <20% of slices responding to these agonists in recordings from CA3 and none in subiculum. By contrast, 1 microM each of [ahx(8-20)]NPY, the Y(2) agonist, [ahx(5-24)]NPY, and particularly NPY itself suppressed the afterdischarge in area CA3 and the subiculum, as reported earlier. We conclude that Y(5) receptors appear to regulate excitability to some degree in the subiculum of young rats, but their contribution is relatively small compared with those of Y(2) receptors, declines with age, and is insufficient to block or significantly attenuate STIB-induced afterdischarges.

Integration of NPY, AGRP, and melanocortin signals in the hypothalamic paraventricular nucleus: evidence of a cellular basis for the adipostat

Energy stores are held relatively constant in many mammals. The circuitry necessary for maintaining energy homeostasis should (1) sense the amount of energy stored in adipose tissue, (2) sense and integrate the multiple opposing signals regarding nutritional state, and (3) provide output regulating energy intake and expenditure to maintain energy homeostasis. We demonstrate that individual neurons within the paraventricular nucleus of the hypothalamus (PVH) are capable of detection and integration of orexigenic (neuropeptide Y [NPY]) and anorexigenic (melanocortin) signals, that NPY and melanocortins are functional antagonists of each other within the PVH in the regulation of feeding behavior, and that melanocortin administration within the PVH regulates both feeding behavior and energy expenditure. These data provide a cellular basis for the adipostat within neurons in the PVH that appear to be jointly regulated by NPY- and melanocortin-responsive neurons.

Neuropeptide Y and limbic seizures

Since its discovery in 1982, neuropeptide Y (NPY), a 36 amino-acid member of the pancreatic polypeptide family, has received considerable attention in the field of neuroscience. Originally isolated from porcine brain /86/, NPY is one of the most abundant and widely distributed peptides in the central nervous system. In the brain, NPY is present in the hypothalamus, limbic structures, cerebral cortex, brainstem and striatum /2,71/. Because of the widespread distribution of NPY, it has been implicated in the modulation of a variety of behaviors, including, but not limited to, circadian rhythms /1/, memory retention /33/, feeding /19,56/, sympathetic control of cardiovascular function /89/ and anxiety /42,43/. These functions have been reviewed elsewhere and will not be discussed in great detail here. The present review is intended to provide an overview of recent work implicating a role for NPY in limbic seizures.

Preferential expression of the neuropeptide Y Y1 over the Y2 receptor subtype in cultured hippocampal neurons and cloning of the rat Y2 receptor

1 Neuropeptide Y (NPY) and NPY receptors are most abundant in the hippocampal formation where they modulate cognitive functions. Expression of NPY receptors in rat cultured primary hippocampal cells was investigated in the present study by use of combined molecular, pharmacological and immunohistochemical approaches, including the cloning of the rat Y2 receptor described here for the first time. 2 More than 70% of the hippocampal neurones were endowed with [125I]-[Leu31,Pro34]PYY Y1-like receptor silver grain accumulations and Y1 receptor immunostaining. These radio- and immuno-labelling signals were distributed over cell bodies and processes of bipolar, stellate and pyramidal-like neuronal cells, as confirmed by neurone-specific enolase and MAP-2 staining. 3 Competition binding profiles revealed that specific [125I]-[Leu31,Pro34]PYY binding was competitively displaced according to a ligand selectivity pattern prototypical of the Y1 receptor sub-type with [Leu31,Pro34]substituted NPY/PYY analogues >> C-terminal fragments = pancreatic polypeptides, with the non-peptide antagonist BIBP3226 being most potent. This profile excludes the possible labelling by [125I]-[Leu31,Pro34]PYY of the newly cloned Y4, Y5 and Y6 receptors. 4 The expression of the genuine Y1 receptor was confirmed by RT-PCR in hippocampal cultures. In contrast, negligible levels of Y2-like/[125I]-PYY3-36 binding were detected in these cultures in spite of the presence of its mRNA, as characterized by RT-PCR. The expression of both the Y1 and the Y2 receptor mRNAs was also noted in normal embryonic hippocampal tissues showing that signals expressed in cultured neurones were also present in utero. 5 Taken together, these results suggest that the Y1 receptor subtype may be of critical importance in the normal functioning of the rat hippocampus, especially during brain development and maturation.

Effects of low and high doses of selective sigma ligands: further evidence suggesting the existence of different subtypes of sigma receptors

Several high affinity sigma (sigma) ligands, such as DTG, JO-1784, (+)-pentazocine, BD-737 and L-687,384, administered at low doses act as agonists by potentiating N-methyl-D-aspartate (NMDA)-induced activation of pyramidal neurons in the CA3 region of the rat dorsal hippocampus. This potentiation is dose-dependent at doses between 1 and 1000 micrograms/kg, IV but bell-shaped dose-response curves are obtained. Other sigma ligands like haloperidol, BMY-14802, (+)3-PPP and NE-100 administered at low doses act as sigma antagonists, since they do not modify the NMDA response but suppress the potentiation of the NMDA response induced by sigma agonists. Because high doses of the sigma agonists do not potentiate the NMDA response, the present experiments were undertaken to assess if, at high doses, these sigma ligands could also act as sigma antagonists and suppress the potentiation induced by low doses of sigma agonists. High doses of DTG, JO-1784, BD-737, and L-687,384, administered acutely, had an effect similar to that of low doses of haloperidol, by suppressing and preventing the potentiation induced by low doses of DTG, JO-1784, BD-737, L-687,384 and (+)-pentazocine. High doses of (+)-pentazocine suppressed the effect of a low dose of (+)-pentazocine but did not affect the potentiation induced by a low dose of the other sigma agonists. The potentiation induced by a low dose of a sigma 1 agonist was not further increased by the subsequent administration of another low dose of a sigma 1 agonist. All together, these results strongly suggest that more than two subtypes of sigma receptors exist in the CNS.

Selective upregulation of T alpha 1 alpha-tubulin and neuropeptide Y mRNAs after intermittent excitatory stimulation in adult rat hippocampus in vivo

Adult central neurons exhibit significant structural and molecular changes in epilepsy. We have examined changes in two markers of morphological and physiological plasticity, T alpha 1 alpha-tubulin (T alpha 1) and neuropeptide Y (NPY) mRNAs, in response to intermittent (20 Hz, 10 seconds, 1 minute-1) stimulation of the rat perforant path in vivo. Stimulus trains elicited brief (0.5-3 seconds) afterdischarges in the ipsilateral dentate gyrus (DG). Four hours of stimulation caused no significant loss of inhibition in the DG 40-48 hours after stimulation ceased. However, it did lead to an increase in NPY mRNA in neurons of the ipsilateral and, to a lesser extent, contralateral DGs and Ammon's Horn. Many of these were presumably interneurons that normally express NPY. However, dentate granule cells (DGCs), which do not normally express this peptide, also expressed robust levels of NPY mRNA bilaterally. NPY mRNA levels peaked at 4-24 hours and returned to baseline by 48 hours poststimulation. Although 24 hours of stimulation induced a similar increase in interneurons, DGCs showed no detectable NPY mRNA. Afterdischarges were necessary to elevate NPY mRNA expression. Four hours of stimulation elevated T alpha 1 mRNA expression in both ipsilateral and, to a lesser extent, contralateral DGCs; this elevation peaked at 24 hours poststimulation and declined to baseline by 72 hours. Stimulation for 24 hours caused broader changes in T alpha 1 mRNA expression, with increases in DGCs and in CA3 pyramidal cells bilaterally. Acute denervation of the DG did not affect T alpha 1 mRNA level in the hippocampal formation. Elevated synaptic input resulting in afterdischarges, but not necessarily in excitability changes in the DG, led to alterations in the expression of molecular markers of plasticity. These changes may reflect adaptive responses to physiological activation.

Sigma receptor regulation of norepinephrine release from rat hippocampal slices

Multiple sigma receptor subtypes have been identified in the hippocampus, yet their physiological role remains largely undefined. In the current study, we examined the role of sigma receptors in the regulation of N-methyl-D-aspartate (NMDA)-stimulated [3H]norepinephrine ([3H]NE) release from rat hippocampal slices. Both sigma agonists (+)pentazocine and BD737 inhibited stimulated norepinephrine release in a concentration-dependent manner. The sigma1 antagonist DuP 734 completely antagonized the inhibition of release by all concentrations of BD737 tested. However, DuP 734 only partially reversed inhibition of release by (+)pentazocine concentrations above 100 nM. 1,3 Di-o-tolylguanidine (DTG), but not haloperidol, antagonized BD737-mediated inhibition of release. DTG also completely antagonized inhibition of release by 100 nM (+)pentazocine yet haloperidol produced only a partial reversal. A combination of DuP 734 and haloperidol produced complete reversal of (+)pentazocine-mediated inhibition, suggesting potential involvement of multiple sigma receptor subtypes in the regulation of norepinephrine release. Both (+)pentazocine and BD737 failed to inhibit stimulated release in the presence of tetrodotoxin, suggesting that sigma receptors regulating NE release are not located on noradrenergic nerve terminals. These results suggest that sigma receptors may be a therapeutic target for disorders resulting from noradrenergic imbalance in hippocampus.

Neuropeptide Y immunoreactivity of a projection from the lateral thalamic nucleus to the optic tectum of the leopard frog

Using rhodamine-labelled latex beads as a retrograde tracer, we have shown that a subset of the neurons projecting from the lateral thalamic nucleus to the optic tectum of the leopard frog are neuropeptide Y-like immunoreactive (NPY-IR). In juvenile frogs, approximately twice as many lateral thalamic nucleus cells from this area project to the ipsilateral tectum as project to the contralateral tectum. NPY-IR cells make up 25% of the projection to the ipsilateral tectum and 13% of the projection to the contralateral tectum. The ipsilateral NPY-IR projection from the lateral nucleus was present in tadpoles and was similar in its characteristics to that found in the juvenile frog. However, the contralateral tectal projection was virtually nonexistent in these animals. The results of these experiments suggest that NPY from the lateral nucleus is released into the ipsilateral tectal neuropil in both the developing and adult frog.

Effects of neuropeptide Y on the electrical properties of neurons

Neuropeptide Y, one of the scions of the pancreatic polypeptide family, is found throughout the nervous system. Based on its abundance alone, one would expect neuropeptide Y to play an important role in the regulation of neuronal activity, and indeed many pharmacological studies have demonstrated neuromodulatory effects of neuropeptide Y. Here, William F. Colmers and David Bleakman review the known actions of neuropeptide Y on the electrical properties of nerve cells. Neuropeptide Y inhibits Ca2+ currents, and modulates transmitter release in a highly selective manner. Neuropeptide Y might be quite important in the regulation of neuronal state, as exemplified by its actions in the hippocampus and the dorsal raphé nucleus.

Subtypes of receptors for neuropeptide Y: implications for the targeting of therapeutics

Neuropeptide Y is a 36 amino acid peptide that was originally discovered in extracts of porcine brain. The peptide has a broad distribution in the central or peripheral nervous system. Receptors for this peptide were originally subdivided into postsynaptic Y-1 receptors and presynaptic Y-2 receptors. The Y-1 receptor has recently been cloned and appears to mediate several effects of NPY including vasoconstriction and an anxiolytic effect in animal models of anxiety. The Y-2 receptor inhibits the release of neurotransmitters in the CNS by the inhibition of the mobilization of intracellular calcium. Additional receptors have been proposed including a Y-3 receptor that recognizes NPY but not the related endocrine peptide, PYY. The functional importance of these newer receptors remains to be established. The absence of useful antagonists has made the study of NPY a challenge for investigators in the field. The potential utility of such molecules is discussed.

Electrical kindling of the hippocampus is associated with functional activation of neuropeptide Y-containing neurons

The release of neuropeptide Y (NPY) was measured from hippocampal slices of rats at stage 2 (preconvulsive stage) and stage 5 (full seizure expression) of electrical kindling of the dorsal hippocampus (upper blade of the dentate gyrus). Spontaneous release in naive rats (9.0 +/- 0.8 fmol/ml every 10 min) was independent of external Ca2+ but was reduced by 38 +/- 3.6% (P < 0.05) during 20 min incubation with 5 microM tetrodotoxin. Spontaneous efflux in naive rats did not differ from that in shams (implanted with electrodes but not stimulated) or in rats kindled to stage 2 and stage 5. Twenty-five, 50 and 100 mM KCl induced a concentration-dependent release of NPY (P < 0.05 and P < 0.01 at 25 and 50-100 mM respectively) from slices of shams. The effect of 100 mM KCl was reduced by 94 +/- 1% (P < 0.01) in the absence of Ca2+. Two days after the last stage 2 stimulation and 1 week after the last stage 5 seizure, NPY release was significantly larger than in shams at all KCl concentrations in the stimulated and contralateral hippocampus (P < 0.05 and P < 0.01). Forty-eight hours after one single after-discharge and 1 month after the last stage 5 seizure, 50 mM KCl induced a significantly larger release of NPY in the stimulated and contralateral hippocampus (P < 0.01 and P < 0.05), although the effect was less than during kindling.(ABSTRACT TRUNCATED AT 250 WORDS)

Loss of sigma binding sites in the CA1 area of the anterior hippocampus in Alzheimer's disease correlates with CA1 pyramidal cell loss

The densities of [3H]1,3-di-o-tolylguanidine ([3H]DTG) binding to sigma binding sites in the CA1 stratum pyramidale region in 7 hippocampi affected by Alzheimer's disease, were compared with densities in 7 normal hippocampi. There was an average reduction of 26% in [3H]DTG binding in this area, which was correlated with an average 29% pyramidal cell loss in the same region. These results are consistent with experiments in animals indicating that sigma binding sites are preferentially associated with the somata of large cells.

On the sites of presynaptic inhibition by neuropeptide Y in rat hippocampus in vitro

Neuropeptide Y (NPY) reduces excitatory synaptic transmission between stratum radiatum and CA1 pyramidal cells in rat hippocampal slice in vitro by a presynaptic action. To understand NPY's role in the control of excitability in hippocampus, its actions on excitatory and inhibitory synaptic transmission were examined, using intracellular, sharp microelectrode, and tight-seal, whole cell recordings from principal neurons in areas CA1, CA3, and dentate. Bath application of 1 microM NPY reversibly inhibited excitatory postsynaptic potentials (EPSPs) evoked in CA1 pyramidal cells from either stratum radiatum or stratum oriens by about 50%. Neuropeptide Y also inhibited EPSPs at mossy fiber-CA3, stratum oriens-CA3, and CA3-CA3 synapses by between 45% and 55%. As in CA1, the action of NPY was presynaptic. By contrast, NPY did not inhibit EPSPs evoked in dentate granule cells from either perforant path or commissural inputs. Neuropeptide Y did not alter postsynaptic membrane properties in any cell type. Although NPY attenuated the orthodromically evoked (stratum radiatum) inhibitory postsynaptic potentials in CA1 pyramidal cells by about the same amount as it inhibited the EPSPs, it did not affect the IPSPs evoked in the same cells by antidromic stimulation from alveus. Inhibitory postsynaptic potentials evoked in pharmacological isolation in CA1, CA3, or dentate were also not significantly affected by NPY. The evidence supports the hypothesis that NPY acts at feedforward excitatory synapses to presynaptically reduce the amplitude of excitation as it travels through hippocampal circuits. By contrast, synaptically mediated inhibition is not directly affected by NPY.(ABSTRACT TRUNCATED AT 250 WORDS)