RESUMEN

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.

Asunto(s)

Encéfalo/metabolismo , Cocaína/antagonistas & inhibidores , Inhibidores de Captación de Dopamina/antagonistas & inhibidores , Dopamina/metabolismo , Genes Inmediatos-Precoces/fisiología , Péptido Natriurético Tipo-C/metabolismo , Neuronas/metabolismo , Regulación hacia Arriba/fisiología , Animales , Encéfalo/efectos de los fármacos , Trastornos Relacionados con Cocaína/tratamiento farmacológico , Trastornos Relacionados con Cocaína/metabolismo , Trastornos Relacionados con Cocaína/fisiopatología , Regulación de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica/fisiología , Genes Inmediatos-Precoces/efectos de los fármacos , Inmunohistoquímica , Masculino , Actividad Motora/efectos de los fármacos , Actividad Motora/fisiología , Péptido Natriurético Tipo-C/farmacología , Neuronas/efectos de los fármacos , Ratas , Ratas Sprague-Dawley , Receptores de Superficie Celular/efectos de los fármacos , Receptores de Superficie Celular/metabolismo , Activación Transcripcional , Regulación hacia Arriba/efectos de los fármacos

RESUMEN

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.

Asunto(s)

Cuerpo Estriado/metabolismo , Dopamina/biosíntesis , Ratas/metabolismo , Oxibato de Sodio/metabolismo , Sustancia Negra/enzimología , Ácido gamma-Aminobutírico/biosíntesis , Animales , Cuerpo Estriado/citología , Inmunohistoquímica , Masculino , Neuronas/enzimología , Ratas Wistar , Sustancia Negra/citología , Distribución Tisular

RESUMEN

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.

Asunto(s)

Encéfalo/metabolismo , Hidroxibutiratos/metabolismo , Transducción de Señal , Animales , Humanos , Hidroxibutirato Deshidrogenasa/metabolismo , Hidroxibutiratos/farmacología , Neuronas/enzimología , Receptores de Superficie Celular/fisiología , Ácido gamma-Aminobutírico/metabolismo

RESUMEN

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.

Asunto(s)

Amígdala del Cerebelo/química , Ansiedad/genética , Receptores de GABA-A/análisis , Animales , Ansiedad/metabolismo , Diazepam/metabolismo , Miedo , Cinética , Masculino , Ratones , Ratones Endogámicos BALB C , Ratones Endogámicos C57BL , Especificidad de la Especie

RESUMEN

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.

Asunto(s)

Óxido Nítrico Sintasa/metabolismo , Corteza Prefrontal/metabolismo , Receptores de Superficie Celular/metabolismo , Animales , Relación Dosis-Respuesta a Droga , Activación Enzimática , Técnicas In Vitro , Masculino , Óxido Nítrico Sintasa/efectos de los fármacos , Óxido Nítrico Sintasa de Tipo I , Corteza Prefrontal/enzimología , Ratas , Ratas Wistar , Oxibato de Sodio/análogos & derivados , Oxibato de Sodio/síntesis química , Oxibato de Sodio/farmacología , Factores de Tiempo , Veratrina/farmacología

RESUMEN

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.

Asunto(s)

Regulación de la Expresión Génica/efectos de los fármacos , ARN Mensajero , Receptores de Dopamina D1/genética , Receptores de Dopamina D2/genética , Adyuvantes Anestésicos/farmacología , Animales , Autorradiografía , Cocaína/farmacología , Inhibidores de Captación de Dopamina/farmacología , Lóbulo Frontal/efectos de los fármacos , Lóbulo Frontal/metabolismo , Lóbulo Frontal/fisiología , Hipocampo/efectos de los fármacos , Hipocampo/metabolismo , Hipocampo/fisiología , Hibridación in Situ , Masculino , Neostriado/efectos de los fármacos , Neostriado/metabolismo , Neostriado/fisiología , Vías Olfatorias/efectos de los fármacos , Vías Olfatorias/metabolismo , Vías Olfatorias/fisiología , Ratas , Ratas Wistar , Oxibato de Sodio/farmacología , Radioisótopos de Azufre

RESUMEN

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.

Asunto(s)

Encéfalo/efectos de los fármacos , Oxibato de Sodio/metabolismo , Ácido gamma-Aminobutírico/biosíntesis , Aminoácidos/metabolismo , Animales , Benzocicloheptenos/farmacología , Encéfalo/anatomía & histología , Encéfalo/metabolismo , Espacio Extracelular/efectos de los fármacos , Espacio Extracelular/metabolismo , Masculino , Microdiálisis , Ratas , Ratas Wistar , Oxibato de Sodio/agonistas , Oxibato de Sodio/farmacología , Ácido gamma-Aminobutírico/metabolismo

RESUMEN

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.

Asunto(s)

5,7-Dihidroxitriptamina/farmacología , Condicionamiento Clásico/efectos de los fármacos , Dextroanfetamina/farmacología , Inhibición Neural/efectos de los fármacos , Neurotoxinas/farmacología , Receptores de Serotonina/efectos de los fármacos , Animales , Reacción de Prevención/efectos de los fármacos , Mapeo Encefálico , Relación Dosis-Respuesta a Droga , Electrochoque , Hipocampo/efectos de los fármacos , Masculino , Ratas , Ratas Long-Evans , Tiempo de Reacción/efectos de los fármacos , Receptores Dopaminérgicos/efectos de los fármacos , Gusto/efectos de los fármacos

RESUMEN

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.

Asunto(s)

Encefalinas/genética , Precursores de Proteínas/genética , ARN Mensajero/metabolismo , Oxibato de Sodio/administración & dosificación , Adyuvantes Anestésicos/administración & dosificación , Anestésicos Intravenosos/administración & dosificación , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Relación Dosis-Respuesta a Droga , Encefalinas/biosíntesis , Encefalinas/metabolismo , Inyecciones Intraperitoneales , Masculino , Precursores de Proteínas/biosíntesis , Precursores de Proteínas/metabolismo , ARN Mensajero/efectos de los fármacos , Ratas , Ratas Wistar

RESUMEN

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.

Asunto(s)

Encéfalo/enzimología , Hidroxibutirato Deshidrogenasa/genética , Hidroxibutirato Deshidrogenasa/metabolismo , Oxibato de Sodio/metabolismo , Aldehído Reductasa/química , Secuencia de Aminoácidos , Animales , Secuencia de Bases , Clonación Molecular , Secuencia de Consenso , Femenino , Biblioteca de Genes , Hipocampo/enzimología , Humanos , Hidroxibutirato Deshidrogenasa/química , Hidroxibutirato Deshidrogenasa/aislamiento & purificación , Cinética , Datos de Secuencia Molecular , Sistemas de Lectura Abierta , Fragmentos de Péptidos/química , Reacción en Cadena de la Polimerasa , Embarazo , Ratas , Proteínas Recombinantes/química , Proteínas Recombinantes/aislamiento & purificación , Proteínas Recombinantes/metabolismo , Alineación de Secuencia , Homología de Secuencia de Aminoácido , Homología de Secuencia de Ácido Nucleico , Transcripción Genética

RESUMEN

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.

Asunto(s)

Encéfalo/fisiología , Cocaína/farmacología , Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica/fisiología , Genes fos/genética , Proteínas Inmediatas-Precoces , Serotonina/fisiología , Factores de Transcripción/genética , 5,7-Dihidroxitriptamina/farmacología , Animales , Encéfalo/efectos de los fármacos , Encéfalo/patología , Proteína 1 de la Respuesta de Crecimiento Precoz , Expresión Génica/efectos de los fármacos , Masculino , Ratas , Ratas Wistar , Serotonina/análogos & derivados , Serotonina/farmacología , Agonistas de Receptores de Serotonina/farmacología

RESUMEN

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.

Asunto(s)

Antagonistas de Dopamina/farmacología , Haloperidol/farmacología , Receptores de Superficie Celular/efectos de los fármacos , Sulpirida/farmacología , Regulación hacia Arriba/efectos de los fármacos , Animales , Química Encefálica/efectos de los fármacos , Línea Celular , Células Cultivadas , Inyecciones Intraventriculares , Cinética , Masculino , Ratas , Ratas Wistar , Receptores de Superficie Celular/biosíntesis , Oxibato de Sodio/farmacología

RESUMEN

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.

Asunto(s)

Ansiolíticos/antagonistas & inhibidores , Ansiolíticos/farmacología , Flumazenil/farmacología , Moduladores del GABA/farmacología , Oxibato de Sodio/antagonistas & inhibidores , Oxibato de Sodio/farmacología , Animales , Anticonvulsivantes/farmacología , Conducta Animal/efectos de los fármacos , Benzocicloheptenos/farmacología , Diazepam/farmacología , Relación Dosis-Respuesta a Droga , Masculino , Actividad Motora/efectos de los fármacos , Naloxona/farmacología , Antagonistas de Narcóticos/farmacología , Ratas

RESUMEN

Transcription regulatory factors are rapidly induced in brain by a wide variety of stimuli and may be important in coordinating changes in gene expression underlying 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-methyl-serotonin induced the expression of these early genes in structures including the caudate putamen and nucleus accumbens.

RESUMEN

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.

Asunto(s)

Anticonvulsivantes/uso terapéutico , Discinesia Inducida por Medicamentos/prevención & control , Haloperidol/antagonistas & inhibidores , Ácido gamma-Aminobutírico/análogos & derivados , 4-Aminobutirato Transaminasa/metabolismo , Animales , Anticonvulsivantes/farmacocinética , Peso Corporal/efectos de los fármacos , Encéfalo/patología , Discinesia Inducida por Medicamentos/patología , Ingestión de Alimentos/efectos de los fármacos , Glutamato Descarboxilasa/metabolismo , Haloperidol/toxicidad , Masculino , Ratas , Ratas Sprague-Dawley , Receptores de Dopamina D2/metabolismo , Conducta Estereotipada/efectos de los fármacos , Sulpirida/farmacología , Vigabatrin , Ácido gamma-Aminobutírico/metabolismo , Ácido gamma-Aminobutírico/farmacocinética , Ácido gamma-Aminobutírico/uso terapéutico

RESUMEN

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.

Asunto(s)

Cuerpo Estriado/metabolismo , Encefalina Metionina/metabolismo , Oxibato de Sodio/farmacología , Ácido 3,4-Dihidroxifenilacético/análisis , Animales , Benzocicloheptenos/farmacología , Cuerpo Estriado/efectos de los fármacos , Dopamina/análisis , Masculino , Microdiálisis , Oxidopamina/toxicidad , Ratas , Ratas Wistar , Receptores Dopaminérgicos/efectos de los fármacos , Sulpirida/farmacología , Tetrodotoxina/farmacología , Veratridina/farmacología

RESUMEN

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.

Asunto(s)

Antipsicóticos/farmacocinética , Benzamidas/farmacocinética , Proclorperazina/farmacocinética , Receptores de Superficie Celular/metabolismo , Oxibato de Sodio/farmacocinética , Animales , Unión Competitiva , Técnicas In Vitro , Masculino , Ratas , Ratas Wistar

RESUMEN

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.

Asunto(s)

Epéndimo/citología , Glicoproteínas/farmacología , Manosa/farmacología , Animales , Células Cultivadas , Endotelio Vascular/metabolismo , Epéndimo/efectos de los fármacos , Epéndimo/metabolismo , Fluoresceína-5-Isotiocianato/análogos & derivados , Fluoresceína-5-Isotiocianato/metabolismo , Colorantes Fluorescentes , Galactosa/metabolismo , Glucosa/metabolismo , Glicoproteínas/metabolismo , Uniones Intercelulares/efectos de los fármacos , Manosa/metabolismo , Microscopía Fluorescente , Ratas , Ratas Wistar , Albúmina Sérica Bovina/metabolismo

RESUMEN

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.

Asunto(s)

Antipsicóticos/farmacología , Antagonistas de Dopamina , Oxibato de Sodio/farmacología , Animales , Apomorfina/antagonistas & inhibidores , Conducta Animal/efectos de los fármacos , Sitios de Unión , Temperatura Corporal/efectos de los fármacos , Cuerpo Estriado/metabolismo , Antagonistas de los Receptores de Dopamina D2 , Técnicas In Vitro , Masculino , Ratas , Ratas Wistar , Oxibato de Sodio/análogos & derivados , Oxibato de Sodio/metabolismo , Conducta Estereotipada/efectos de los fármacos

RESUMEN

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.

Asunto(s)

Animales Recién Nacidos/metabolismo , Cerebelo/lesiones , Glicoproteínas/biosíntesis , Lectinas/biosíntesis , Regeneración Nerviosa/fisiología , Sinapsis/fisiología , Animales , Cerebelo/metabolismo , Glicoproteínas/análisis , Inmunohistoquímica , Lectinas/análisis , Peso Molecular , Ratas , Ratas Wistar