C-type natriuretic peptide (CNP) regulates cocaine-induced dopamine increase and immediate early gene expression in rat brain

The neuropeptide C-type natriuretic peptide (CNP) is the primary biologically active natriuretic peptide in brain. Using in situ hybridization, the present report demonstrates that CNP regulates egr-1, c-fos and junB immediate early gene expression in rat brain. In the frontal cortex, CNP induced immediate early gene expression whereas it inhibited dose-dependently the cocaine-induced early gene expression in the dopaminergic projection fields nucleus accumbens and caudate-putamen. CNP may produce its effect directly on dopaminergic neurons because we found that its receptor, guanylyl cyclase GC-B, was expressed in the mesencephalon where dopaminergic neurons originate, as well as in their projection fields. The inhibition by CNP of the early gene expression elicited by cocaine in the caudate-putamen is correlated with a CNP-evoked decrease in cocaine-induced rise in extracellular dopamine, measured by in vivo microdialysis experiments. The significance of the inhibition of cocaine-induced dopamine release and early gene induction by the endogenous peptide CNP is demonstrated by data indicating that CNP reduced the cocaine-induced spontaneous locomotor activation. By inhibiting dopaminergic neuronal activity, CNP represents a potential negative regulator of related behavioural effects of cocaine.

Immunohistochemical studies of the localization of neurons containing the enzyme that synthesizes dopamine, GABA, or gamma-hydroxybutyrate in the rat substantia nigra and striatum

gamma-Hydroxybutyrate (GHB) is an endogenous metabolite of gamma-aminobutyric acid (GABA), which is synthesized in the neuronal compartment of the central nervous system. This substance possesses several properties that support its role as a neurotransmitter/neuromodulator in brain. In particular, it is synthesized by a specific pathway that transforms GABA into succinic semialdehyde via GABA-T activity; then succinic semialdehyde is converted into GHB by a specific succinic semialdehyde reductase (SSR). The last enzyme is considered as a marker for neurons that synthesize GHB. This compound binds in brain to receptors whose distribution, ontogenesis, kinetics, and pharmacology are specific. Endogenous GHB, but also GHB exogenously administered to rats, participate in the regulation of dopaminergic activity of the nigrostriatal pathway. To investigate the distribution of GHB neurons in this pathway and the anatomic relationships between dopaminergic and GHB neurons, immunocytochemical identification of dopamine, GABA, and GHB neurons was carried out in the substantia nigra and striatum of the rat. The following markers for these neurons were used: anti-tyrosine hydroxylase (TH) antibodies for dopamine neurons, anti-glutamate decarboxylase (GAD) antibodies for GABA neurons, and anti-succinic semialdehyde reductase (SSR) antibodies for GHB neurons. GABA neurons were studied because GAD and SSR co-exist frequently in the same neuron, and GABA alone also exerts its own regulatory effects on dopaminergic neurons. This study reveals the co-existence of GAD/SSR and GAD/SSR/TH in numerous neurons of the substantia nigra. However, some neurons appear to be only GAD or SSR positive. In the striatum, TH-positive terminals surround many GHB neurons. GAD innervation is abundant in close contact with unlabeled neurons in the caudate-putamen, whereas distinct SSR-positive punctuates are also present. The existence of SSR-reactive synapses and neurons was confirmed in the striatum at the electron microscopic level. On the basis of these results, a clear anatomo-functional relationship between GHB and dopamine networks cannot be defined; however, we propose the modulation by GHB of striatal intrinsic neurons that could then interfere with the presynaptic control of dopaminergic activity.

Gamma-hydroxybutyric acid as a signaling molecule in brain

Gamma-hydroxybutyric acid was synthesized 35 years ago to obtain a GABAergic substance that penetrates the brain freely. Since then, gamma-hydroxybutyric acid has been used in human beings for its sedative and anesthetic properties when administered at high doses, and most of the studies on gamma-hydroxybutyric acid have focused on its pharmacological effects. However, gamma-hydroxybutyric acid is also an endogenous substance, which is synthesized and released in the brain by specific neuronal pathways, implicated in the control of the GABAergic, dopaminergic, and opioid systems. This control is mediated by specific gamma-hydroxybutyric acid receptors with a unique distribution in brain and a specific ontogenesis and pharmacology. Stimulation of these receptors induces specific cellular responses. Taken together, these results suggest that gamma-hydroxybutyric acid possesses most of the properties required of a neurotransmitter/neuromodulator in the brain.

Hypoexpression of benzodiazepine receptors in the amygdala of neophobic BALB/c mice compared to C57BL/6 mice

The distribution of benzodiazepine receptors in the brain of neophobic BALB/c mice was studied by autoradiographic analysis using [3H]-diazepam and compared to that of the same receptors of the "nonemotional" C57BL/6 mice. This technique revealed no significant interstrain difference except for a lower density of diazepam binding sites in the amygdala of BALB/c mice. Therefore, the expression of benzodiazepine receptors in the amygdala of the two strains of mice were quantified by binding studies on brain membranes. The amygdala of BALB/c mice exhibited a fivefold decrease in the density of benzodiazepine receptors compared to C57BL/6 mice. These results suggest that the trait anxiety (neophobia) that characterizes BALB/c mice could be due, at least in part, to a genetic modulation of benzodiazepine receptor expression in the amygdala, a structure known to be strongly involved in fear behavior.

Gamma-hydroxybutyrate receptor function studied by the modulation of nitric oxide synthase activity in rat frontal cortex punches

Previous results have shown that stimulation of the gamma-hydroxybutyrate (GHB) receptor modulates Ca2+ channel permeability in cell cultures. In order to confirm this result, we investigated the consequence of GHB receptor stimulation on nitric oxide synthase (NOS) activity in rat brain cortical punches rich in GHB receptors. The stimulation of these receptors by increasing amounts of GHB induced a progressive decrease in NOS activity. However, for GHB doses above 10 microM, this reduction was progressively lost, either after receptor desensitization or after stimulation of an additional class of GHB receptor having lower affinity. The effect of GHB was reproduced by the GHB receptor agonist NCS-356 and blocked by the GHB receptor antagonist NCS-382. The GHB-induced effect on Ca2+ movement was additive to those produced by veratrine, indicating that GHB modulates a specific Ca2+ conductance, which explains the modification in NOS activity and the increase in cyclic guanosine monophosphate levels previously reported.

Gamma-hydroxybutyrate and cocaine administration increases mRNA expression of dopamine D1 and D2 receptors in rat brain

The effects of acute and repeated gamma-hydroxybutyrate (GHB) and cocaine administration on D1 and D2 dopamine receptor mRNA expression were examined using in situ hybridization histochemistry in different rat brain structures rich in GHB receptors. Six hours after a single GHB administration (500 mg/kg i.p.), an increase in D1 and D2 mRNA expression was observed in almost all regions examined; whereas, acute cocaine injection (20 mg/kg i.p.) had no effect. Repeated exposure to GHB (500 mg/kg i.p. twice daily) for 10 days, followed by a 14-h withdrawal period, induced increasing effects on D1 and D2 dopamine receptor mRNA expression, similar to those caused by chronic treatment with cocaine (20 mg/kg i.p. once a day). These effects of GHB and cocaine on dopamine receptor mRNA expression could be a consequence, for both compounds, of the modulation of dopaminergic activity; thus, supporting the benefit of GHB in cocaine substitution therapy.

gamma-Hydroxybutyrate modulates synthesis and extracellular concentration of gamma-aminobutyric acid in discrete rat brain regions in vivo

gamma-Hydroxybutyrate possesses most of the properties of a neurotransmitter/neuromodulator that acts via specific pathways and receptors in brain. Beside its regulatory effects on dopaminergic transmission, gamma-hydroxybutyrate was thought for many years to interfere with gamma-aminobutyric acid (GABA)ergic processes in the brain. The present study demonstrates that in the rat frontal cortex in vivo, gamma-hydroxybutyrate or its agonist NCS-356 administered systemically at a high dose (500 mg/kg) increases GABA contents in dialysates via a mechanism blocked by the peripheral administration of the gamma-hydroxybutyrate antagonist NCS-382. Under the same conditions, the extracellular concentration of this amino acid was not modified in the hippocampus. However, when administered at a low dose (250 mg/kg), gamma-hydroxybutyrate decreases GABA content of the dialysates of the frontal cortex by an NCS-382-sensitive mechanism. Spontaneous [3H]GABA release was observed in the frontal cortex of rats at 160 min after i.p. [3H]-gamma-hydroxybutyrate administration. This result indicates that gamma-hydroxybutyrate in vivo could be the precursor of an extracellular GABA pool in the frontal cortex. After i.p. [3H]-gamma-hydroxybutyrate administration in the rat, the amino acid contents of several brain regions were quantified 160 min later, and the radioactivity in each region was measured. [3H]GABA, [3H]glutamate, and [3H]glycine were detected in most, but not all, of the brain regions studied. In particular, radioactive GABA was not detected in the hippocampus. The other amino acids were not labeled. These results show that gamma-hydroxybutyrate modulates the synthesis and the extracellular concentrations of GABA in specific regions of the rat brain. Identification of these GABA pools and determination of their functional role remain to be defined.

A neurotoxic lesion of serotonergic neurones using 5,7-dihydroxytryptamine does not disrupt latent inhibition in paradigms sensitive to low doses of amphetamine

Testing the effects of low doses of d-amphetamine on latent inhibition (LI) in two different conditioning paradigms, passive avoidance and conditioned taste aversion, provided evidence of their pharmacological equivalence. For passive avoidance, LI was expressed by the decreased latency to enter a shock compartment in preexposed rats placed 5 min in the compartment during 3 consecutive days before conditioning. In the conditioned taste aversion paradigm, a group of rats was preexposed to a solution of sucrose also for 3 consecutive days prior to the establishment of an association between sucrose and sickness elicited by an injection of LiCl. On the following day, the preexposed rats drunk more sucrose when allowed to choose between one tube containing water and an other containing sucrose. In both paradigms, 0.25 mg/kg d-amphetamine, injected daily on the 3 preexposure days and on the conditioning day, decreased LI. A dose of 0.5 mg/kg suppressed LI in the passive avoidance paradigm. The effect of a serotonergic lesion induced by i.c.v. injection of 5,7-dihydroxytryptamine (5,7-DHT) was evaluated in the same paradigms. The lesion procedure that lowered hippocampal serotonin and 5 HIAA levels by more than 80% did not affect LI. Taken together, the present results lessens the hypothesis that LI is prone to an opposing influence of the two monoaminergic systems considered in this work.

Prodynorphin and proenkephalin mRNAs are increased in rat brain after acute and chronic administration of gamma-hydroxybutyrate

The effects of gamma-hydroxybutyrate (GHB) on prodynorphin (PD) and proenkephalin (PE) mRNA expression were examined using in situ hybridization histochemistry in discrete rat brain structures rich in GHB receptors. A single dose of GHB (500 mg/kg i.p.) increased striatal PE mRNA levels (+60%) between 15 and 90 min after injection. An increase in PD mRNA expression was observed in the frontal cortex (+90%) 6 h after GHB administration. Chronic exposure to GHB (500 mg/kg i.p. twice a day) for 10 days induced significant increases in both PE and PD mRNA levels in different brain regions examined, suggesting that PD and PE mRNA expressions are modulated by the endogenous GHBergic system.

Cloning of a rat brain succinic semialdehyde reductase involved in the synthesis of the neuromodulator gamma-hydroxybutyrate

The gamma-hydroxybutyrate biosynthetic enzyme succinic semialdehyde reductase (SSR) was purified to homogeneity from rat brain. Peptides were generated by tryptic cleavage and sequenced. PCR primers were designed from the amino acid sequences of two of the peptides showing a similarity (75-85%) to a mitochondrial aldehyde dehydrogenase. A PCR-amplified DNA fragment was generated from recombinant plasmids prepared by a mass excision procedure from a rat hippocampal cDNA library and used as a probe to screen this cDNA library. One cDNA of 1341 bp had an open reading frame encoding a protein of 447 residues with a deduced molecular mass of 47967 Da. The enzyme was expressed in Escherichia coli. Immunoblotting analysis revealed the existence of a protein with the same electrophoretic mobility as the SSR purified from rat brain and with an estimated molecular mass of 45 kDa. Northern blot experiments showed that this enzyme was not expressed in the kidney or in the liver. In the brain tissue, a single but rather broad band was labelled under high stringency conditions, suggesting the presence of more than one messenger species coding for SSR. Hybridization in situ performed on brain tissue slices showed specific labelling of the hippocampus, the upper cortex layer, the thalamus, the substantia nigra, the cerebellum, the pons medulla and the olfactory tract. The recombinant enzyme showed catalytic properties similar to those of the SSR purified from rat brain, particularly in regard to its substrate affinities and Ki for inhibition by phthalaldehydic acid. Valproic acid did not inhibit the cloned SSR. This enzyme had 20-35% identity in highly conserved regions involved in NADPH binding with four other proteins belonging to the aldo-oxo reductase family.

The serotonergic system modulates the cocaine-induced expression of the immediate early genes egr-1 and c-fos in rat brain

Transcription regulatory factors are rapidly induced in brain by a wide variety of stimuli and may be important in coordinating changes in gene expression under-lying neuronal plasticity. Using in situ hybridization, we found that acute cocaine administration (20 mg/kg, intraperitoneally (i.p.)) produced a robust induction of both c-fos and egr-1 immediate early genes. Egr-1 messenger RNA induction was highest in the caudate putamen and in the shell of the nucleus accumbens. No significant induction was noticed after injection of fluoxetine, a selective inhibitor of serotonin uptake. Cocaine-induced egr-1 and c-fos expression was substantially reduced in the brain areas from rats in which the serotonergic projections were lesioned by injection of the neurotoxin 5,7-dihydroxytryptamine and in rats that have been injected with tropisetron, an antagonist of the 5-hydroxytryptamine (5-HT3) receptor. Conversely, the 5-HT3 receptor agonist 2-methylserotonin induced the expression of these early genes in structures including the caudate putamen and nucleus accumbens.

Sulpiride, but not haloperidol, up-regulates gamma-hydroxybutyrate receptors in vivo and in cultured cells

Five days of gamma-hydroxybutyrate (GHB) administration (3 x 500 mg kg(-1) day(-1) i.p.) to rats resulted in a significant decrease in the density of GHB receptors measured in the whole rat brain without modification of their corresponding affinity. Similar administration of (-)-sulpiride (2 X 100 mg kg(-1) day(-1) i.p. for 5 days) induces an up-regulation of GHB receptors without change in their dissociation constants (Kd). Haloperidol (2 X 2 mg day(-1) i.p. for 5 days) showed no effect. Administered chronically via osmotic minipumps directly into the lateral ventricles, (-)-sulpiride (60 microg day(-1) for 7 days) and GHB (600 microg day(-1) for 7 days) up-regulated and down-regulated rat brain GHB receptors, respectively. Finally, in a mouse hybridoma cell line (NCB-20 cells) expressing GHB receptors, the treatment of these cells with 1 mM GHB, 100 microM (-)-sulpiride or 1 mM GABA decreases, increases and induces no change, respectively, in the density of GHB receptors after 3 days of treatments. These results indicate that chronic GHB treatment modifies the expression of its receptor and that sulpiride also induces plastic changes in GHB receptors perhaps via antagonistic properties.

The anxiolytic effect of gamma-hydroxybutyrate in the elevated plus maze is reversed by the benzodiazepine receptor antagonist, flumazenil

The effects of gamma-hydroxybutyrate (GHB), a product of gamma-aminobutyric acid (GABA) metabolism which possesses neuromodulatory properties in brain, were investigated in the elevated plus maze in rats. The number of entries and the time spent in the open arms of the maze were increased by GHB (50, 150, 250 mg/kg i.p.). This is classically considered as indicative of an anxiolytic effect of the drug. There was no sedative effect at these doses as measured by the spontaneous locomotor activity in the actimeter or the total number of arm entries. The anxiolytic properties of GHB were reversed by neither the GHB receptor antagonist, NCS-382 (6,7,8,9-tetrahydro-5(H)-5-olylidene acetic acid) (300 mg/kg i.p.), nor the opioid receptor antagonist, naloxone (10 mg/kg i.p.). However the anti-anxiety effect of GHB was antagonized by the benzodiazepine receptor antagonist, flumazenil (10 mg/kg i.p.), suggesting an interaction of GHB with the GABA(A) receptor complex which mediates the anti-anxiety effect of benzodiazepines.

Suppression of haloperidol-induced oral dyskinesias in rats by vigabatrin

Acute and chronic administration of vigabatrin, a selective inactivator of GABA-T, suppresses haloperidol-induced dyskinesias at low doses without preventing the enhancement of striatal dopamine D2 receptor density or the development of vacuous chewing movements. The long-term administration of vigabatrin does not attenuate its effect. The observations presented in this work support the GABA hypothesis of haloperidol-induced vacuous chewing behavior in rats, and suggest that vigabatrin is an appropriate means to enhance nigral GABAergic activity.

Characterization of methionine-enkephalin release in the rat striatum by in vivo dialysis: effects of gamma-hydroxybutyrate on cellular and extracellular methionine-enkephalin levels

The opioïd system is implicated in mediating the effects produced upon administration of gamma-hydroxybutyrate. Gamma-hydroxybutyrate occurs endogenously in the mammalian brain, and is most probably involved in the regulation of some basic brain functions, particularly those concerning the dopaminergic nigrostriatal pathway, which is closely linked to the expression of enkephalins in the striatum. In the present study, in vivo microdialysis was used to examine the basic characteristics of methionine-enkephalin (met-enkephalin) release in the striatum of Wistar rats, using a high performance radioimmunoassay. Administration of gamma-hydroxybutyrate to the rats induced a dose-dependent decrease in the extracellular release of met-enkephalin. In parallel, a dose- and time-dependent gamma-hydroxybutyrate-induced accumulation of met-enkephalin in striatum was observed. These two phenomena (tissue accumulation and inhibition of release) were blocked by NCS-382, a gamma-hydroxybutyrate receptor antagonist. The striatal met-enkephalin accumulation does not seem to be exclusively due to the inhibition of its release. Thus, a gamma-hydroxybutyrate mediating effect on met-enkephalin synthesis is suggested, most probably occurring via functional modulation of striatal dopamine synthesis and release. To understand the role of this dopaminergic mechanism, unilateral lesions of the nigrostriatal dopaminergic pathway were carried out. In gamma-hydroxybutyrate-treated rats, striata exhibited a similar increase in met-enkephalin content. In untreated rats, only the lesioned striatum showed an identical increase in met-enkephalin levels. Thus, striatal met-enkephalin accumulation could be attributed to the suppression of the dopaminergic impulse flow, due to gamma-hydroxybutyrate or to the action of 6-hydroxydopamine. In the extracellular spaces (microdialysis experiments), gamma-hydroxybutyrate administration induced identical modifications of met-enkephalin release in lesioned or non-lesioned striata. These modifications could be reproduced by peripheral or striatal administration of sulpiride, a D2/D3 antagonist. From a functional point of view, the dopaminergic D2 receptor blockade or the gamma-hydroxybutyrate-induced inhibition of dopamine release could be considered to induce similar results, with identical consequences on striatal met-enkephalin accumulation and release. These results suggest that gamma-hydroxybutyrate-induced modifications in met-enkephalin release, presumably potentiated by 6-hydroxydopamine treatment, act via a functional modification of the nigrostriatal dopaminergic pathway.

Displacement of [3H] gamma-hydroxybutyrate binding by benzamide neuroleptics and prochlorperazine but not by other antipsychotics

Since gamma-hydroxybutyrate receptor agonists exhibit dopaminergic regulatory properties and neuroleptic-like effects in neuropharmacological tests, the common neuroleptics were tested for [3H] gamma-hydroxybutyrate binding activity on rat brain membranes. (-)-Sulpiride, sultopride, amisulpride and prochlorperazine possess affinity for the gamma-hydroxybutyrate site(s), consistent with their therapeutic dosage. This study has revealed that gamma-hydroxybutyrate receptors represent an additional target for antipsychotics.

Mannose dependent tightening of the rat ependymal cell barrier. In vivo and in vitro study using neoglycoproteins

The possible role of carbohydrate binding proteins (lectins) and glycoconjugates in the formation of junctions ensuring tightening between ependymal cells was studied using synthetic glycoconjugates, the neoglycoproteins. These compounds are prepared by substituting bovine serum albumin with sugar residues and additional labelling (or not) with fluorescein or biotin. Injections of these components into the cerebral ventricles of adult rats resulted in a binding pattern which could be related to their carbohydrate composition. Mannose-containing neoglycoproteins were bound to ependymal cell cilia and penetrated rapidly the brain tissue. Such phenomenon was not seen with glucose- or galactose-containing neoglycoprotein molecules. In contrast, mannose-, galactose- and glucose-containing neoglycoproteins bound strongly to some endothelial cells around blood vessels. Fluorescent unglycosylated serum albumin did not bind to any brain structures. In contrast, co-injection of mannose-containing non-fluorescent neoglycoproteins with the other fluorescent compounds (including fluorescent sugar-free BSA) resulted in the penetration of the fluorescent compounds into the brain tissue. This internalization into brain was attributed to disaggregation of junctions between ependymal cells. Cultured ependymal cells behaved likewise. In short term experiments (5 min-1 h), only the mannose-containing neoglycoproteins bound strongly to the ependymal cells, particularly to the cilia. In long term experiments (1-9 days), mannose-containing neoglycoproteins specifically induced the disappearance of junctions between the cultured cells. These results emphasize the importance of mannose-dependent recognition system in the maintenance of junctions between ependymal cells, where a mannose-binding lectin has been previously detected.

gamma-Hydroxybutyrate ligands possess antidopaminergic and neuroleptic-like activities

The action of agonists or antagonists at the gamma-hydroxybutyrate (GHB) receptor represents a possibility to modulate dopaminergic activities in brain. In the present study, GHB and six structural analogs were tested for their ability to displace [3H] GHB binding from striatal membranes. All the analogs tested exhibited higher affinity for GHB as compared with GHB itself. Parallel experiments were carried out on striatal slices in order to determine IC50 values for inhibition of dopamine release in the presence of these compounds. All substances inhibited dopamine release with higher potency as compared with GHB itself. These antidopaminergic activities were confirmed in several neuropharmacological tests, usually used to predict neuroleptic activities in vivo. There appears to be a relationship between the affinity for the GHB striatal low-affinity receptor and the inhibition of dopamine release on one hand, and the antidopaminergic activity (as revealed by the in vivo tests) on the other hand. Thus, it is suggested that GHB agonists possessing antidopaminergic activities, may represent potential drugs endowed with neuroleptic properties.

Lesion-induced re-expression of neonatal recognition molecules in adult rat cerebellum

It has been previously shown that sectioning of parallel fibers in the cerebellar molecular layer of adult rats gave rise to rapid reinnervation of the target cells, i.e., Purkinje cells. This paper reports that such a reinnervation is accompanied by reexpression (partial and total) of two developmentally regulated complementary molecules. These are an endogenous mannose-binding lectin, called R1, which reappears at the surface of the dendrites of Purkinje cells, and an endogenous glycoprotein ligand of R1, the 31 kDa glycoprotein, which seems to be neosynthetized and transported to the surface of parallel fibers. In this system, embryonic N-CAM is not reexpressed in neurons but reappears in reactive astrocytes in the vicinity of the lesion. The reexpression of recognition molecules (lectin and glycoprotein ligand) involved in normal synaptogenesis, may constitute the molecular basis for repair of nervous circuits in the adult as well.

Selective distribution pattern of gamma-hydroxybutyrate receptors in the rat forebrain and midbrain as revealed by quantitative autoradiography

Using quantitative autoradiography to study the precise distribution of gamma-hydroxybutyrate high-affinity binding sites, the present results showed the heterogeneous localization of these sites in cortical and hippocampal layers and also in some diencephalic and mesencephalic nuclei. In frontal, parietal and temporal cortex, GHB binding sites are generally distributed in three distinct layers. The olfactory system, the amygdala, septum, basal ganglia and substantia nigra also exhibited significant amounts of GHB receptors. In thalamus, the radioactivity was heterogeneously distributed, the highest amounts being in the lateral posterior nucleus. Hypothalamus, cerebellum, colliculi and pons-medulla were apparently devoid of binding sites. This more accurate mapping of GHB high-affinity receptors in rat brain is due to some technical improvements and the use of [3H]GHB of higher specific activity.

Anti-sedative and anti-cataleptic properties of NCS-382, a gamma-hydroxybutyrate receptor antagonist

NCS-382 possesses antagonistic properties at gamma-hydroxybutyrate receptor sites. Its effect on the sedative/cataleptic behaviour observed in rats after gamma-hydroxybutyrate administration was investigated. NCS-382 diminished, in a dose-dependent manner, the sedative and/or cataleptic effects of gamma-hydroxybutyrate, as revealed by a variety of sensorimotor tests. These results indicate that the well-known sedative/anaesthetic effects induced by gamma-hydroxybutyrate administration are provoked via stimulation of a specific class(es) of gamma-hydroxybutyrate receptors which exist in the rat brain and which could mediate a local stimulation of opiate synthesis and release.

Extracellular events induced by gamma-hydroxybutyrate in striatum: a microdialysis study

The modification of dopamine release and accumulation induced by gamma-hydroxybutyrate (GHB) was studied using both striatal slices and in vivo microdialysis of caudate-putamen. GHB inhibited dopamine release for approximately 5-10 min in vitro, and this was associated with an accumulation of dopamine in the tissue. Subsequently, there was an increase in dopamine release. In the microdialysis experiments, low doses of GHB inhibited dopamine release, whereas higher doses strongly increased release; the initial decrease seen in slices could not be detected in vivo. Thus, GHB had a biphasic effect on the release of dopamine: An initial decrease in the release of transmitter was followed by an increase. A time-dependent biphasic effect was observed when GHB was added to brain slices, and a dose-dependent biphasic effect was seen in dialysate after systemic administration of GHB. Naloxone blocked GHB-induced dopamine accumulation and release both in vitro and in vivo. GHB also increased the release of opioid-like substances in the striatum. A specific antagonist of GHB receptors completely blocked both the dopamine response and the release of opioid-like substances. These data suggest that GHB increases dopamine release via specific receptors that may modulate the activity of opioid interneurons.

Suppressive effects of dehydroepiandrosterone and 3 beta-methyl-androst-5-en-17-one on attack towards lactating female intruders by castrated male mice. II. Brain neurosteroids

Dehydroepiandrosterone (DHA) and 3 beta-methyl-androst-5-en-17-one (CH3-DHA) suppress attacks by castrated male mice towards lactating female intruders (Haug et al. Physiol. Behav. 46:955, 1989). Their effects on the concentrations of DHA, pregnenolone (delta 5P), and their sulfate ester (S) have been investigated in the brain of control and treated mice. A more than 2 fold, significant, decrease of delta 5P-S was the only change common to both steroids. DHA and CH3-DHA effects might be related to the antagonistic action of delta 5P-S on GABAA receptors.

Alterations in synaptosomal neurotransmitter amino acids in "petit-mal" rats at a daytime and a nighttime

The synaptosomal fractions of 6 brain areas-olfactory tubercles (OT), frontal cortex (FC), striatum (Sr), amygdala (A), thalamus (Th), hypothalamus (Hy) - have been analyzed for their neurotransmitter amino acids (AA) content in Wistar rats exhibiting "petit-mal" epilepsy (PM-E) and in controls (C). The analysis was carried out at 11 p.m. (nighttime corresponding to the acrophase for the hourly number of spike-wave complexes) and at 11 a.m. (daytime). A day versus night rhythmicity is recorded for synaptosomal inhibitory AA in control and in PM-E rats. However, day versus night variations are more frequent and more prominent in C rats than in PM-E rats. Two day versus night variations exist only in PM-E rats: increases of GABA level in Sr and of Asp in Hy. Differences between PME-and C in synaptosomal AA content are more likely to be present during the nighttime. During this period lower AA values for PM-E rats are found for one or several inhibitory AA in OT, Th, and FC. It seems that the differences between PM-E and C concerning the inhibitory AA correlate with the number of spike-wave discharges. Only in one brain area is there a similar difference for PM-E and C during daytime and nighttime: a decreased GABA content for PM-E rats in OT. The decrease is larger in nighttime than in daytime. This difference may serve as a marker for this epileptic disorder. Moreover, it is in OT that the greatest number of PM-E versus C differences in synaptosomal neurotransmitter AA are observed.(ABSTRACT TRUNCATED AT 250 WORDS)

A specific gamma-hydroxybutyrate receptor ligand possesses both antagonistic and anticonvulsant properties

Administration of gamma-hydroxybutyrate (GHB) to animals induces electroencephalographic and behavioral changes that resemble petit-mal seizures. Furthermore, these GHB-induced electroencephalogram-behavioral changes can be blocked by anticonvulsant drugs, which are specific in their action against petit-mal seizures. These effects of GHB on electroencephalogram and behavior may well be due to an effect of exogenously administrated GHB on GHB-mediated systems in the brain. GHB has many properties of a neuromodulator including the existence of receptors with a specific affinity for this compound. A synthetic structural analog of GHB, NCS-382, possessed anticonvulsant activity against several animal models of seizure and, in particular, against that induced by GHB administration. NCS-382 was also shown to be an antagonist at GHB receptor sites and blocked the neuropharmacologic effects induced in the striatum and hippocampus by GHB administration. In particular, NCS-382 inhibited the increase in cGMP levels and in inositol phosphate turnover induced by GHB in hippocampus. Furthermore, in vivo dialysis demonstrated that NCS-382 blocked the increased release of dopamine in striatum after GHB administration in vivo. Thus, this ligand appears to be the first described antagonist substance for GHB receptor(s). These results suggest that NCS-382 may represent a harbinger for a new class of anticonvulsant drugs that most probably act by modifying the endogenous GHB system.

Localization studies of gamma-hydroxybutyrate receptors in rat striatum and hippocampus

Quantitative autoradiography using [3H] gamma-hydroxybutyrate was used in combination with anatomic and neurotoxic lesions to localize the gamma-hydroxybutyrate (GHB) receptors in the striatum and hippocampus of rat brain. 6-Hydroxydopamine (6-OHDA) lesions of the nigro-striatal pathway failed to reduce [3H] gamma-hydroxybutyrate binding in the striatum. In contrast, kainic acid (KA) lesions of the caudate-putamen (CPu) resulted in about 45% loss of binding. For hippocampus, lesions of septo-hippocampal pathway did not modify receptor density but intrahippocampal kainic acid injection largely attenuated (50%) [3H] GHB binding. These results demonstrate that gamma-hydroxybutyrate receptors in the CPu and dorsal hippocampus are principally located on intrinsic neurons which may participate in the functional expression of the role gamma-hydroxybutyrate has in these structures.

Endogenous lectin CSL is present on the membrane of cilia of rat brain ependymal cells

An endogenous brain lectin, with a great affinity for oligomannosidic glycans, called CSL (for 'cerebellar soluble lectin'), was detected on the surface of the cilia of ependymal cells both in cultures and in vivo. The lectin is not synthesized by the ependymal cells themselves. In vivo it is neither found in cerebrospinal fluid nor in cells of the choroid plexus. Probably, lectin CSL is produced by subependymal astrocytic cells. The membranes of ependymal cells seem to possess glycoprotein ligands for the lectin which explain the specific adhesion of CSL on the surface of these cells, particularly on the cilia. The localization of this adhesive molecule on cilia of ependymal cells suggests that it may play a role in trapping foreign cells, micro-organisms or debris.

Alterations of serotonin neurotransmission and inhibition of mouse killing behavior: II. Effects of selective and reversible monoamine oxidase inhibitors of type A

Three groups of rats were tested for mouse killing behavior after IP injection of selective and reversible type A monoamine oxidase inhibitors. The rats were either spontaneous killers, or non-killers which acquired killing behavior following para-chlorophenylalanine treatment or electrolytical destruction of dorsal and median raphe nuclei. Moclobemide (para-chloro-N-(2-morpholinoethyl)-benzamide), cimoxatone (3-(4-(3-cyanophenyl-methoxy)phenyl)-5-(methoxy-methyl)-2-oxazo lid inone, MD 780515), toloxatone (5-(hydroxymethyl)-3-(3-methylphenyl)-2-oxazolidinone) and amiflamine ((+)-4-dimethylamino-2, alpha-dimethylphenethyl amine, FLA 336 (+)) were used as selective and reversible monoamine oxidase inhibitors of type A. Cimoxatone, toloxatone and amiflamine inhibited mouse killing behavior of spontaneous killer rats without apparent sedation, whereas moclobemide was not efficient at doses which did not decrease locomotor activity. A similar inhibition of mouse killing behavior was obtained in spontaneous and serotonin depleted killer rats. The results are discussed in relation to the behavioral expression of serotoninergic supersensitivity in the three groups of killer rats described earlier using serotonin agonist and uptake inhibitors.

3'-5' cyclic-guanosine monophosphate increase in rat brain hippocampus after gamma-hydroxybutyrate administration. Prevention by valproate and naloxone

An increase (123%) of cyclic GMP (cGMP) was observed in the hippocampus of the rat killed by microwave irradiation 45 min after administration of 500 mg/kg gamma-hydroxybutyrate (GHB) IP. This increase is time and dose dependent. No modification in cyclic nucleotide content was observed in striatum and in cerebellum. As the role of GHB has been implicated in neurotransmission, the fact that this compound increases cyclic GMP accumulation in hippocampus in vivo may represent a mechanism by which the actions of GHB are mediated at the cellular level. Valproate (400 mg/kg) or naloxone (10 mg/kg) pretreatment completely abolish the cGMP increase due to GHB. A GABAergic and/or opiate phenomenon may be involved in the mechanism of GHB induced increase of cGMP.

Inhibition of mouse killing behavior by serotonin-mimetic drugs: effects of partial alterations of serotonin neurotransmission

Rats which do not kill mice and which acquire mouse killing behavior after partial lesion of the serotonin neurotransmission, either by p-chlorophenylalanine treatment or by electrolytical lesions of dorsal and median raphe nucleus, were treated by IP injection of serotonin-mimetics. The following drugs were used: 5-methoxy-N-N-dimethyl-tryptamine and 8-hydroxy-2-(di-n-propylamino)tetralin hydrobromide, serotonin-agonists, fluoxetine and citalopram, inhibitors of serotonin uptake. All these serotonin-mimetics inhibit mouse killing behavior without apparent secondary effects. When these compounds were tested on killer rats, a stronger antimuricidal effect was observed in rats having altered serotonin neurotransmission. These results support a role for the serotoninergic supersensitivity in a model of aggressive behavior.

Regional distribution in rat brain of tryptophan hydroxylase apoenzyme determined by enzyme-linked immunoassay

Tryptophan hydroxylase apoenzyme was measured in 21 regions of the rat brain by a competitive enzyme-linked immunoassay (ELISA) technique using a recently developed antiserum from the sheep to this protein. Highest apoenzyme levels were found in the pineal gland and in the dorsal raphé. An insignificant level was observed in the cerebellum. In general, the distribution of tryptophan hydroxylase apoenzyme follows the distribution of serotonin previously detected by immunocytochemistry. A turnover number for tryptophan hydroxylase in a rat brain supernatant fraction of 7.5 s-1 was estimated, a value far higher than that estimated for serotonin turnover in vivo. This result confirms that serotonin biosynthesis is additionally regulated by factors other than tryptophan hydroxylase apoenzyme concentration.

A new immunization procedure for obtention of anti-leucine-enkephalin antibodies. Part II. Effects of olfactory bulb removal on pro-enkephalin related peptides in rat brain

Bilateral Olfactory Bulb Removal (OBR) induced both complex behavioral alterations and a decrease of many neurotransmitter levels. We studied brain levels of the pro-enkephalin related peptides 45 days after OBR. Opioid levels were studied using three different highly specific antisera exhibiting very high affinities in radioimmunoassays in striatum, hypothalamus, hypophysis, brain stem and cortex. Methionine enkephalin levels increase significantly in striatum (42%), hypophysis (94%) and hypothalamus (25%) and non-significantly in the other areas. Leucine-enkephalin levels tended to increase in all dissected structures but a significant increase only occurred in striatum (42%). Octapeptide levels (Methionine-enkephalin-Arg-Gly-Leu) significantly increase in striatum (22%) and decrease in hypophysis (97%) and in brain stem (76%). All these results are partially consistent with the decrease of opiate binding described previously after OBR and suggest a complex imbalance in neurotransmitters after such a sensorial deprivation. It is suggested that the modifications of enkephalinergic neurotransmission might be related to the stressful state induced by OBR.

Effects of the potentiation of the GABAergic neurotransmission in the olfactory bulbs on mouse-killing behavior

Intra olfactory bulb administration of three classes of GABA-mimetics (GABAa agonists, inhibitors of reuptake, inhibitors of GABA degradation) clearly inhibit mouse-killing behavior, without sedation. A linear correlation is observed between GABA levels increase in the olfactory bulbs and muricidal inhibition following local injection of valproic acid and gamma-vinyl GABA, two GABA-T inhibitors; the differences observed between these two compounds may be due to the differences in their mechanism of action on GABA-T activity and to the different pool of GABA on which they act. No diffusion to extra bulbar sites were observed after local administration of gamma-vinyl GABA. This evidence suggests an inhibitory role of GABA from olfactory bulbs in the modulation of mouse-killing behavior.

Distribution of sodium valproate and GABA metabolism in CNS of the rat

The distribution of VPA has been investigated in several brain areas of the rat, and GABA increases were measured. A biphasic exponential decay was observed for VPA; the slowest decrease was noted in the olfactory bulbs and in the hypothalamus where GAD and GABA-T activities were the highest. The data may be correlated with the prolonged effect of VPA in these areas.