Investigation of the role of sigma1-receptors in inositol 1,4,5-trisphosphate dependent calcium signaling in hepatocytes

In hepatocytes, as in other cell types, Ca(2+) signaling is subject to complex regulations, which result largely from the intrinsic characteristics of the different inositol 1,4,5-trisphosphate receptor (InsP(3)R) isoforms and from their interactions with other proteins. Although sigma1 receptors (Sig-1Rs) are widely expressed in the liver, their involvement in hepatic Ca(2+) signaling remains unknown. We here report that in this cell type Sig-1R interact with type 1 isoforms of the InsP(3) receptors (InsP(3)R-1). These results obtained by immunoprecipitation experiments are confirmed by the observation that Sig-1R proteins and InsP(3)R-1 colocalize in hepatocytes. However, Sig-1R ligands have no effect on InsP(3)-induced Ca(2+) release in hepatocytes. This can be explained by the rather low expression level expression of InsP(3)R-1. In contrast, we find that Sig-1R ligands can inhibit agonist-induced Ca(2+) signaling via an inhibitory effect on InsP(3) synthesis. We show that this inhibition is due to the stimulation of PKC activity by Sig-1R, resulting in the well-known down-regulation of the signaling pathway responsible for the transduction of the extracellular stimulus into InsP(3) synthesis. The PKC sensitive to Sig-1R activity belongs to the family of conventional PKC, but the precise molecular mechanism of this regulation remains to be elucidated.

Pregnenolone sulfate enhances long-term potentiation in CA1 in rat hippocampus slices through the modulation of N-methyl-D-aspartate receptors

Among the different steroids found in the brain, pregnenolone sulfate (3beta-hydroxy-5-pregnen-20-one-3-sulfate; PREGS) is known to enhance hippocampal-associated memory. The present study employs rat hippocampal slices to investigate the ability of PREGS to modulate long-term potentiation (LTP), a phenomenon considered as a model of synaptic plasticity related to memory processes. LTP (3 x 100 Hz/1 sec within 2 min), implicated essentially glutamatergic transmission, for which the different synaptic events could be pharmacologically dissociated. We show that PREGS enhances LTP in CA1 pyramidal neurons at nanomolar concentrations and exhibits a bell-shaped concentration-response curve. The maximal effect of PREGS on both induction and maintenance phases of LTP is observed at 300 nM and requires 10 min of superfusion. Although PREGS does not change the N-methyl-D-aspartate (NMDA) component of the field potentials (fEPSPs) isolated in the presence of 10 microM 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX) in Mg2+-free artificial cerebrospinal fluid, PREGS does enhance the response induced by NMDA application (50 microM, 20 sec). PREGS does not modify the alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) component of the fEPSPs isolated in the presence of 100 microM DL-2-amino-7-phosphopentanoic acid (DL-AP5) or its potentiation induced by a single tetanic stimulation and the response induced by AMPA application (10 microM, 10 sec). Furthermore, PREGS does not affect the recurrent inhibition of the fEPSPs mediated by gamma-aminobutyric acid type A (GABA(A)) receptor. In conclusion, this study shows the ability of PREGS to enhance LTP in CA1 by accentuating the activity of NMDA receptors. This modulation of LTP might mediate the steroid-induced enhancement of memory.

Protein kinase C-dependent potentiation of intracellular calcium influx by sigma1 receptor agonists in rat hippocampal neurons

Intracellular calcium concentration ([Ca2+]i) plays a major role in neuronal excitability, especially that triggered by the N-methyl-d-aspartate (NMDA)-sensitive glutamatergic receptor. We have previously shown that sigma1 receptor agonists potentiate NMDA receptor-mediated neuronal activity in the hippocampus and recruit Ca2+-dependent second messenger cascades (e.g., protein kinase C; PKC) in brainstem motor structures. The present study therefore assessed whether the potentiating action of sigma1 agonists on the NMDA response observed in the hippocampus involves the regulation of [Ca2+]i and PKC. For this purpose, [Ca2+]i changes after NMDA receptor activation were monitored in primary cultures of embryonic rat hippocampal pyramidal neurons using microspectrofluorometry of the Ca2+-sensitive indicator Fura-2/acetoxymethyl ester in the presence of sigma1 agonists and PKC inhibitors. We show that successive activations of the sigma1 receptor by 1-min pulses of (+)-benzomorphans or (+)-N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride (JO-1784) concomitantly with glutamate time dependently potentiated before inconstantly inhibiting the NMDA receptor-mediated increase of [Ca2+]i, whereas 1,3-di-o-tolyl-guanidine, a mixed sigma1/sigma2 agonist, did not significantly modify the glutamate response. Both potentiation and inhibition were prevented by the selective sigma1 antagonist N,N-dipropyl-2-[4-methoxy-3-(211phenylethoxy) phenyl]-ethylamine monohydrochloride (NE-100). Furthermore, only (+)-benzomorphans could induce [Ca2+]i influx by themselves after a brief pulse of glutamate. A pretreatment with the conventional PKC inhibitor 12-(2-cyanoethyl)-6,7,12,13-tetrahydro-13-methyl-5-oxo-5H-indolo [2,3-a] pyrrolo [3,4-c] carbazole (Gö-6976) prevented the potentiating effect of (+)-benzomorphans on the glutamate response. Our results provide further support for a general mechanism for the intracellular sigma1 receptor to regulate Ca2+-dependent signal transduction and protein phosphorylation.

Functional cooperation between neurosteroids and D2 dopamine antagonists on KCl-evoked [3H]noradrenaline release: modulation by calcium channel blockers

It has recently been proposed that neurosteroids, such as dehydroepiandrosterone sulphate and pregnenolone sulphate, interfere with the dopamine system in the central nervous system. According to our previous report showing that the butyrophenone, spiperone, slightly enhances the evoked release of [3H]-noradrenaline ([3H]NA) in the presence of these sulphated steroids, the present study was carried out to document the putative interplay between steroids and spiperone, which is known to be a prototypic D2 dopamine antagonist and also a 5-HT2 serotonin antagonist. For this purpose, the paradigm of KCl-evoked [3H]NA release from preloaded rat hippocampal slices was used to investigate the interactions between neurosteroids, spiperone and the voltage-sensitive calcium channels (VSCCs). The selective 5-HT2 serotonin antagonist ritanserine was ineffective, whereas sulpiride, a selective D2 dopamine antagonist mimicked the action of spiperone, thus suggesting that the blockade of D2 dopamine receptors accounted for the modulatory effect of spiperone on neurosteroid-induced modulation of evoked [3H]NA release. In addition, this facilitation of KCl-evoked [3H]NA release by the combination of a steroid and a D2 dopamine antagonist was partially inhibited by the L- and N-type VSCC blockers nifedipine and omega-conotoxin GVIA, respectively. The present results provide in-vitro functional evidence for the putative role of VSCCs in the interplay between steroids and D2 dopamine receptors.

Melatonin modulates [3h]serotonin release in the rat hippocampus: effects of circadian rhythm

Serotonin (5-HT) participates as a neurotransmitter in the control of the circadian sleep/wake rhythm, feeding and sexual behaviours, and emotional and affective states. The present study investigated whether melatonin affects the circadian rhythm of 5-HT neurotransmission in the hippocampus, a major target for serotoninergic antidepressants. The present results show a daytime dependency of [3H]5-HT uptake insensitive to melatonin, with a peak from 14.00 h to 22.00 h and a trough from 02.00 h to 06.00 h. They also indicate that melatonin reduced the spontaneous efflux of [3H]5-HT as well as KCl-evoked release of [3H]5-HT during the dark phase, while it increased the evoked release during the light phase. Both effects were concentration-dependent; the facilitatory effect was maximum at high nanomolar concentrations of melatonin, whereas the inhibition preferentially occurred at low concentrations. Finally, nifedipine, an effective antagonist of L-type voltage-sensitive calcium channels, prevented the effects of melatonin on KCl-evoked [3H]5-HT release during the light but not the dark phase. Together, these data suggest the involvement of two distinct mechanisms by which melatonin might regulate both spontaneous efflux and evoked release of 5-HT in the hippocampus.

Intracellular sigma1 receptor modulates phospholipase C and protein kinase C activities in the brainstem

Most physiological effects of sigma1 receptor ligands are sensitive to pertussis toxin, suggesting a coupling with cell membrane-bound G proteins. However, the cloning of the sigma1 receptor has allowed the identification of an intracellular protein anchored on the endoplasmic reticulum. Here, we show, using the isolated adult guinea pig brainstem preparation, that activation of the sigma1 receptor results in its translocation from the cytosol to the vicinity of the cell membrane and induces a robust and rapid decrease in hypoglossal activity, which is mediated by phospholipase C. The subsequent activation of protein kinase C beta1 and beta2 isoforms and the phosphorylation of a protein of the same molecular weight as the cloned sigma1 receptor lead to a desensitization of the sigma1 motor response. Our results indicate that the intracellular sigma1 receptor regulates several components implicated in plasma membrane-bound signal transduction. This might be an example of a mechanism by which an intracellular receptor modulates metabotropic responses.

A-Current down-modulated by sigma receptor in frog pituitary melanotrope cells through a G protein-dependent pathway

Gramicidin perforated patch-clamp recordings were used to study the effects of two sigma 1 receptor ligands, (+)-N-cyclopropylmethyl-N-methyl-1, 4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride (JO 1784) and (+)-pentazocine, on the transient outward potassium current (IA) in cultured frog melanotrope cells. (+)-Pentazocine reversibly decreased the current amplitude in a dose-dependent manner. The effects of (+)-pentazocine were mimicked by JO 1784 and were markedly reduced by the sigma 1 receptor antagonist, N, N-dipropyl-2-[4-methoxy-3-2(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE 100). Inactivation rate of IA was best fitted with a double exponential function, yielding time constants of 23.7 and 112.5 ms. (+)-Pentazocine (20 microM) accelerated the current decay, decreasing the time constants to 10.7 and 59 ms, respectively. Current-voltage experiments revealed that (+)-pentazocine (20 microM) did neither modify the open-state I/V curves nor the voltage dependence of IA. However, (+)-pentazocine (20 microM) shifted the steady-state inactivation curve toward more negative potentials and increased the time constant of the time-dependent removal of inactivation. In whole-cell experiments, internal dialysis of guanosine-5'-O-(3-thiophosphate) (100 microM) irreversibly prolonged the response to (+)-pentazocine. In addition, cholera toxin pretreatment (1 microgram. ml-1; 12 h) suppressed the inhibition of IA by (+)-pentazocine (20 microM). It is concluded that in frog melanotrope cells, a cholera toxin-sensitive, G protein-dependent inhibition of IA through a sigma 1 receptor activation, at least partially, underlies the excitatory effect of sigma ligands.

Differentiation of sigma ligand-activated receptor subtypes that modulate NMDA-evoked [3H]-noradrenaline release in rat hippocampal slices

1. It is now widely accepted that there are two classes of sigma (sigma) binding sites, denoted sigma(1) and sigma(2), and recently sigma(3) subtype has been proposed. Selective sigma(1) and sigma(2) receptor agonists are known to modulate the neuronal response to N-methyl-D-aspartate (NMDA) in vivo and in vitro. To identify the site of action of a series of recently synthesised high affinity sigma ligands, the present in vitro series of experiments was carried out on NMDA-evoked [3H]-noradrenaline ([3H]-NA) overflow from preloaded hippocampal slices of the rat. 2. The ligands (+)-cis-N-methyl-N-[2,(3,4-dichlorophenyl) ethyl]-2-(1-pyrrolidinyl) cyclohexylamine (BD-737) and (+)-pentazocine, considered as the prototypic sigma(1) agonists, potentiated the NMDA response from 10 nM to 100 nM. This potentiation faded between 100 nM and 1 microM ligand concentrations. On the other hand, 1,3-di(2-tolyl)guanidine (DTG), a mixed sigma(1)/sigma(2) agonist, at concentrations greater than 100 nM inhibited the NMDA-evoked [3H]-NA release. Spiperone, considered as active on putative sigma(3) receptors, was without effect on the NMDA response, or on the potentiating effect of BD-737. 3. The high affinity sigma antagonists haloperidol and 1[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine (BD-1063), inactive by themselves on the NMDA-induced response, at concentrations above 30 nM totally prevented the potentiating effect of (+)-pentazocine (100 nM) as well as the inhibitory effect of DTG (300 nM) on NMDA-evoked [3H]-NA release. Whereas haloperidol and BD-1063, at concentrations < 1 microM, were inactive on the potentiating effect of BD-737 (100 nM). 4. 4-(4-Chlorophenyl)-alpha-4-fluorophenyl-4-hydroxy-1-piperidinebutanol (reduced haloperidol), N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (BD-1008), inactive by themselves on the NMDA-evoked [3H]-NA release, failed to reverse the effects of (+)-pentazocine and DTG, but at concentrations of 30 nM to 1 microM antagonised the BD-737-induced potentiation of the NMDA response. Conversely, N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100) blocked the effects of (+)-pentazocine as well as those of BD-737, but not those of DTG. 5. The present results provide in vitro functional evidence for a sigma receptor type preferentially sensitive to BD-737, reduced haloperidol, BD-1008 and also to NE-100, that differs from the already identified sigma(1), sigma(2) and sigma(3) sites.

Differential effects of sigma ligands on the N-methyl-D-aspartate response in the CA1 and CA3 regions of the dorsal hippocampus: effect of mossy fiber lesioning

In the CA3 region of rat dorsal hippocampus, several sigma ligands, such as 1,3-di(2-tolyl)guanidine (DTG), (+)-pentazocine and (+)-N-cyclopropylmethyl-N-methyl-1, 4-diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride (JO-1784), administered intravenously at low doses, potentiate selectively the pyramidal neuron firing activity induced by microiontophoretic applications of N-methyl-D-aspartate, without affecting those induced by quisqualate, kainate or acetylcholine. A similar potentiation of the N-methyl-D-aspartate response has also been found with microiontophoretic applications of neuropeptide Y, an effect exerted via delta receptors. The present experiments were carried out to determine the effects of these sigma ligands and of neuropeptide Y; in the CA1 and CA3 regions following unilateral destruction by a local injection of colchicine of the mossy fiber system, which is a major afference to CA3 pyramidal neurons. In the CA1 region, DTG, JO-1784 and neuropeptide Y did not potentiate the activation induced by microiontophoretic applications of N-methyl-D-aspartate. However, (+)-pentazocine potentiated the N-methyl-D-aspartate response, similarly to its effect in the CA3 region on the intact side. In the CA3 region, on the intact side, (+)-pentazocine, DTG, JO-1784 and neuropeptide Y induced a selective potentiation of N-methyl-D-aspartate-induced activation, in keeping with previous reports. On the lesioned side, the effect of (+)-pentazocine on the N-methyl-D-aspartate response was still present, but those of DTG, JO-1784 and neuropeptide Y were abolished. These results suggest that (+)-pentazocine, on the one hand, and DTG, JO-1784 and neuropeptide Y, on the other, are not acting on the same subtype of sigma receptors. Since (+)-pentazocine, JO-1784 and neuropeptide Y have been suggested to act on the sigma 1 subtype of receptors, these data suggest the existence of two subtypes of sigma 1 receptors. They also suggest that the receptors on which DTG, JO-1784 and neuropeptide Y are acting are located on the mossy fiber terminals in the CA3 region and are absent in the CA1 region.

Neurosteroids, via sigma receptors, modulate the [3H]norepinephrine release evoked by N-methyl-D-aspartate in the rat hippocampus

N-Methyl-D-aspartate (NMDA, 200 microM) evokes the release of [3H]norepinephrine ([3H]NE) from preloaded hippocampal slices. This effect is potentiated by dehydroepiandrosterone sulfate (DHEA S), whereas it is inhibited by pregnenolone sulfate (PREG S) and the high-affinity sigma inverse agonist 1,3-di(2-tolyl)guanidine, at concentrations of > or = 100 nM. Neither 3 alpha-hydroxy-5 alpha-pregnan-20-one nor its sulfate ester modified NMDA-evoked [3H]NE overflow. The sigma antagonists haloperidol and 1-[2-(3,4-dichlorophenyl)-ethyl]-4-methylpiperazine, although inactive by themselves, completely prevented the effects of DHEA S, PREG S, and 1,3-di(2-tolyl)guanidine on NMDA-evoked [3H]NE release. Progesterone (100 nM) mimicked the antagonistic effect of haloperidol and 1-[2-(3,4-dichlorophenyl)ethyl]-4-methyl-piperazine. These results indicate that the tested steroid sulfate esters differentially affected the NMDA response in vitro and suggest that DHEA S acts as a sigma agonist, that PREG S acts as a sigma inverse agonist, and that progesterone may act as a sigma antagonist. Pertussis toxin, which inactivates the Gi/o types of guanine nucleotide-binding protein (Gi/o protein) function, suppresses both effects of DHEA S and PREG S. Since sigma 1 but not sigma 2 receptors are coupled to Gi/o proteins, the present results suggest that DHEA S and PREG S control the NMDA response via sigma 1 receptors.

The effects of sigma ligands and of neuropeptide Y on N-methyl-D-aspartate-induced neuronal activation of CA3 dorsal hippocampus neurones are differentially affected by pertussin toxin

1. The in vivo effects of the high affinity sigma ligands 1,3-di(2-tolyl)guanidine (DTG), (+)-N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1- ethyl-but-3-en-1-ylamine hydrochloride (JO-1784), (+)-pentazocine and haloperidol, as well as of those of neuropeptide Y (NPY), on N-methyl-D-aspartate (NMDA)- and quisqualate (Quis)-induced neuronal activations of CA3 pyramidal neurones were assessed, using extracellular unitary recording, in control rats and in rats pretreated with a local injection of pertussis toxin (PTX), to evaluate the possible involvement of Gi/o proteins in mediating the potentiation of the neuronal response to NMDA by the activation of sigma receptors in the dorsal hippocampus. 2. Microiontophoretic applications as well as intravenous injections of (+)-pentazocine potentiated selectively the NMDA response in control rats as well as in PTX-pretreated animals. In contrast, the PTX pretreatment abolished the potentiation of the NMDA response by DTG, JO-1784 and NPY. Moreover, microiontophoretic applications of DTG induced a reduction of NMDA-induced neuronal activation. Neither in control nor in PTX-treated rats, did the sigma ligands and NPY have any effect on Quis-induced neuronal response. 3. In PTX-treated rats, the potentiation of the NMDA response induced by (+)-pentazocine was suppressed by haloperidol, whereas the reduction of the NMDA response by DTG was not affected by haloperidol. 4. This study provides the first in vivo functional evidence that sigma ligands and NPY modulate the NMDA response by acting on distinct receptors, differentiated by their PTX sensitivity.

[Involvement of sigma receptors in schizophrenic syndromes. Pathophysiological approach]

Sigma ligands have been identified as psychotomimetic agents unrelated to opioids. A number of neuroleptics possess moderate to high affinity for sigma binding sites, raising the possibility that sigma receptors mediate some of the antipsychotic effects of neuroleptics. In addition, sigma binding sites have been reported to be reduced in the temporal cortex and in the hippocampus of schizophrenic patients. This hypothesis is further supported by the use of the sigma ligands rimcazole, BMY-14802 and remoxipride as effective antipsychotic agents. The present report, reviewing briefly the physiological effects of sigma ligands, suggests that their antipsychotic properties are related to modulation of NMDA receptors. Thus, the use of sigma ligands may provide further understanding of the pathophysiology of psychoses and open new avenues for their treatment.

The cytochromes P-450 are not involved in the modulation of the N-methyl-D-aspartate response by sigma ligands in the rat CA3 dorsal hippocampus

Recent in vitro radioligand binding studies have shown that several cytochrome P-450 inhibitors can displace [3H] sigma ligands, suggesting that these ligands might bind to the cytochrome P-450 superfamily of enzymes. Using an in vivo electrophysiological model of extracellular recordings performed in the CA3 region of the rat dorsal hippocampus, we have previously shown that intravenous administration of low doses of several sigma ligands, such as 1,3-di(2-tolyl) guanidine (DTG), JO-1784, and (+)pentazocine potentiate the neuronal response induced by microiontophoretic applications of N-methyl-D-aspartate (NMDA) without affecting those induced by quisqualate and kainate, suggesting that they act as sigma agonists. Conversely, the sigma ligands haloperidol, (+)3-PPP, and BMY-14802, which have no effect by themselves on the NMDA response, prevent and suppress the potentiating effect of sigma agonists on the NMDA response, suggesting that they act as sigma antagonists. The present studies were undertaken to determine if cytochromes P-450 could be involved in the modulation of the NMDA response by sigma ligands. For this purpose, two cytochrome P-450 inhibitors, proadifen (SKF-525A) and piperonyl butoxide (PB), have been tested in our model. Unlike sigma agonists, at low doses, neither SKF-525A nor PB affected the NMDA response of CA3 dorsal hippocampus pyramidal neurons. Unlike sigma antagonists, neither of these drugs reversed or prevented the DTG-induced potentiation of the NMDA response. In addition, following high doses of SKF-525A or PB, sufficient to induce a complete inactivation of cytochromes P-450, DTG still potentiated the NMDA response.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y potentiates the N-methyl-D-aspartate response in the CA3 dorsal hippocampus. II. Involvement of a subtype of sigma receptor

In an in vivo electrophysiological paradigm, we have shown in the companion paper that neuropeptide Y (NPY) potentiates N-methyl-D-aspartate (NMDA)-induced neuronal activation via a non-Y1, non-Y2, non-Y3 receptor subtype, in the rat CA3 dorsal hippocampus. Because sigma ligands have also been shown to potentiate NMDA-induced activation and because NPY and peptide YY have been reported to have high affinity for sigma binding sites, the present study was carried out to assess the possibility that the modulation of the NMDA response by NPY might be mediated by a sigma receptor. In the same electrophysiological paradigm, low doses of haloperidol and alpha-(4-fluorophenyl)-4-(5-fluoro-2- pyrimidinyl)-1-piperazine butanol, two antagonists of sigma receptors, reversed the potentiation of the NMDA response induced by NPY, [Leu31, Pro34]NPY or NPY13-36 and blocked the suppressant effect of desamido-NPY on the NMDA response. In contrast, spiperone, which has low affinity for sigma sites, was ineffective in suppressing NPY, as well as desamido-NPY-induced modulation of the NMDA response. In our model, peptide YY, which acts as a NPY antagonist by suppressing the potentiation of the NMDA response induced by NPY, also antagonized the potentiation of the NMDA response induced by the administration of low doses of di(2-tolyl)guanidine and (+)N-cyclopropyl-methyl-N-,methyl-1,4- diphenyl-1-ethyl-but-3-en-1-ylamine hydrochloride, two high-affinity sigma agonists.(ABSTRACT TRUNCATED AT 250 WORDS)

Neuropeptide Y potentiates selectively the N-methyl-D-aspartate response in the rat CA3 dorsal hippocampus. I. Involvement of an atypical neuropeptide Y receptor

Neuropeptide Y (NPY) has been reported to potentiate N-methyl-D-aspartate (NMDA)-induced neuronal activation in the rat CA3 region of the dorsal hippocampus in vivo. Three types of NPY receptors, denoted Y1, Y2 and Y3, have been identified thus far. The present studies were undertaken to characterize the type of NPY receptor involved in this effect of NPY on the neuronal response to NMDA. NPY, its analogs [Leu31, Pro34]NPY and desamido-NPY, the related peptides pancreatic polypeptide (PP) and peptide YY (PYY) and the C- and N-terminal NPY fragments, NPY2-36, NPY11-36, NPY13-36, NPY16-36, NPY18-36 and NPY1-24CONH2, were tested. The peptides NPY (which is active at Y1, Y2 and Y3 receptors), [Leu31, Pro34]NPY (a selective Y1 agonist) and NPY13-36 (which mimics the effects of NPY in Y2 models) dose dependently enhanced NMDA-induced activation of CA3 dorsal hippocampus pyramidal neurons, but did not alter the activation of the same neurons by quisqualate. In contrast, PYY (which mimics NPY on Y1 and Y2 receptors, but has no activity or elicits an effect opposite to that of NPY in Y3 models) and NPY18-36 (which has been reported to exert an antagonistic or a partial agonistic action at Y3 receptors) did not modify by themselves the NMDA response, but antagonized the potentiating effect of NPY on NMDA-induced activation. Additionally, the C-terminal desamido form of NPY, which has little or no activity at Y1 and Y2 receptor subtypes, reduced the neuronal response to NMDA and quisqualate.(ABSTRACT TRUNCATED AT 250 WORDS)

Modulation by sigma ligands of N-methyl-D-aspartate-induced [3H]noradrenaline release in the rat hippocampus: G-protein dependency

The effects of the high affinity sigma (sigma) ligands 1,3-di(2-tolyl)guanidine (DTG), (+)N-cyclopropylmethyl-N-methyl-1,4-diphenyl-1- ethyl-but-3-en-1-yl-amine hydrochloride (JO-1784), (+)3-[3-hydroxyphenyl]-N-(1-propyl)piperidine hydrochloride [(+)3-PPP] and haloperidol were studied on N-methyl-D-aspartate (NMDA)-evoked release of [3H]noradrenaline (NA) from preloaded hippocampal slices made from Sprague-Dawley rats. The [3H]NA release was evoked once by a 4 min exposure to NMDA, 40 min after the beginning of superfusion with a Mg+(+)-free Krebs' solution. In the absence of any drug, NMDA evoked a concentration-dependent [3H]NA release. Mg++ and EGTA abolished the [3H]NA release induced by NMDA. JO-1784 and (+)3-PPP potentiated in a concentration-dependent manner NMDA-induced [3H]NA release, without affecting the basal outflow. DTG concentration-dependently inhibited the overflow of [3H]NA evoked by NMDA, without affecting the basal efflux. Haloperidol, which did not modify NMDA-evoked [3H]NA release by itself, completely prevented the effects of JO-1784, (+)3-PPP and DTG. In contrast, spiperone, also a potent dopamine receptor antagonist but with low affinity for sigma binding sites, failed to prevent the potentiation of NMDA-evoked release of [3H]NA by JO-1784 and (+)3-PPP. The possible involvement of Gi/o proteins in the modulation by sigma ligands of NMDA-evoked [3H]NA release in the rat hippocampus was also investigated. To this end, Gi/o proteins were inactivated with pertussis toxin (PTX), injected locally 3 to 11 days prior to the experiment or with in vitro preincubation with N-ethylmaleimide (NEM) for 30 min prior the experiment.(ABSTRACT TRUNCATED AT 250 WORDS)

In vivo electrophysiological evidence for a selective modulation of N-methyl-D-aspartate-induced neuronal activation in rat CA3 dorsal hippocampus by sigma ligands

We have reported previously that the high affinity sigma ligand DTG potentiates N-methyl-D-aspartate (NMDA)-induced excitation of pyramidal neurons in the CA3 region of rat dorsal hippocampus. In the present experiments, several selective high affinity sigma ligands have been tested. At low doses, the sigma ligands DTG, JO-1784, JO-1783, AdipG, DnBG, APDQ, BD-737 and (+)-pentazocine dose-dependently enhanced selectively NMDA-induced activation of CA3 pyramidal neurons (with the exception of BD-737 which also presented a late potentiation of the neuronal response to quisqualate). However, at high doses, DTG selectively suppressed the potentiation induced by a low dose of DTG and reduced the NMDA response below base line, presumably due to its low affinity for phencyclidine sites. 2-APHB, a structural analog of DTG devoid of affinity for sigma sites, had no effect on the NMDA response. At low doses that did not by themselves affect the NMDA response, haloperidol, (+)-3-PPP and BMY-14802 reversed DTG- and JO-1784-induced potentiations of the NMDA response. Spiperone, a butyrophenone with very low affinity for sigma sites, was ineffective in this paradigm. The present data suggest that an important function of sigma receptors could be to modulate the NMDA response in this brain region.(ABSTRACT TRUNCATED AT 250 WORDS)

N-methyl-D-aspartate-induced neuronal activation is selectively modulated by sigma receptors

The effects of two high-affinity sigma ligands, DTG (1,3-di(2-tolyl)guanidine) and haloperidol, on the activation of dorsal hippocampus pyramidal neurons induced by microiontophoretic application of N-methyl-D-aspartate (NMDA) were assessed electrophysiologically. Low doses of DTG (0.5-3 micrograms/kg i.v.) potentiated the NMDA response. This effect of DTG was blocked by haloperidol (10 micrograms/kg i.v.), but not by spiperone, a potent dopamine antagonist with low affinity for sigma receptors. These results suggest that sigma receptors modulate the NMDA-induced neuronal activation.