RESUMEN
Nitric oxide (NO) and the C-type natriuretic peptide (CNP) exert their action on brain via the cGMP signaling pathway. NO, by activating soluble guanylyl cyclase, and CNP, by stimulating membrane-bound guanylyl cyclase, cause intracellular increases of cGMP, activating cGMP-dependent protein kinases (PKGs). We show here that injection of CNP into the rat ventral tegmental area strongly reduced cocaine-induced egr-1 expression in the nucleus accumbens in a dose-dependent manner. The effect of CNP was reversed by the previous injection of a selective PKG inhibitor, KT5823. Activation of PKG by 8-bromo-cGMP reduced, like CNP, cocaine-induced gene transcription in dopaminergic structures. To confirm the involvement of PKG, this was overexpressed in either the mesencephalon or the caudate-putamen. Using the polyethyleneimine delivery system, an active protein was expressed by injecting a plasmid vector containing the human PKG-Ialpha cDNA. PKG was overexpressed in dopaminergic and GABAergic neurons when the plasmid was injected in the ventral tegmental area, whereas overexpression was observed in medium spiny GABAergic neurons and in both cholinergic and GABAergic interneurons when the PKG vector was injected into the caudate-putamen. Activation of the overexpressed PKG reduced cocaine-induced egr-1 expression in dopaminergic structures and affected behavior (i.e., locomotor activity). These effects were again reversed by previous injection of the selective PKG inhibitor. The current data suggest that NO and the neuropeptide CNP are potential regulators of cocaine-related effects on behavior.
Asunto(s)
Estimulantes del Sistema Nervioso Central/farmacología , Cocaína/farmacología , Proteínas Quinasas Dependientes de GMP Cíclico/metabolismo , Proteínas de Unión al ADN/biosíntesis , Proteínas Inmediatas-Precoces/biosíntesis , Actividad Motora/efectos de los fármacos , Péptido Natriurético Tipo-C/fisiología , Factores de Transcripción/biosíntesis , Animales , Encéfalo/efectos de los fármacos , Encéfalo/metabolismo , Carbazoles/farmacología , Estimulantes del Sistema Nervioso Central/antagonistas & inhibidores , Cocaína/antagonistas & inhibidores , GMP Cíclico/fisiología , Proteína Quinasa Dependiente de GMP Cíclico Tipo I , Proteínas Quinasas Dependientes de GMP Cíclico/antagonistas & inhibidores , Dopamina/fisiología , Proteína 1 de la Respuesta de Crecimiento Precoz , Activación Enzimática/fisiología , Indoles/farmacología , Inyecciones Intraventriculares , Masculino , Péptido Natriurético Tipo-C/antagonistas & inhibidores , Péptido Natriurético Tipo-C/farmacología , Proteínas del Tejido Nervioso/biosíntesis , ARN Mensajero/biosíntesis , Ratas , Ratas Wistar , Transducción de Señal/efectos de los fármacos , Transducción de Señal/fisiología , Sinaptosomas/efectos de los fármacos , Sinaptosomas/metabolismoRESUMEN
Members of the Egr family of early genes are known to play a prominent role in neuronal plasticity. Using in situ hybridization, we report the induction in the rat forebrain of the immediate early gene egr-1 and of the transcriptional repressor NAB2 in response to acute or repeated cocaine administration. A single exposure to cocaine enhanced the expression of egr-1 in dopaminergic brain areas. Chronic cocaine treatment was not followed by induction of egr-1 mRNA initially, but only 12 h following the last injection, whereas Egr-1 binding activity was maintained elevated at 2 h and was increased again at 12 h. Expression of the Egr corepressor NAB2, but not NAB1, was rapidly and transiently stimulated by cocaine. Both acute and chronic cocaine treatment displayed biphasic NAB2 mRNA expression. It appears that NAB2 operates as an inducible regulator of gene expression in postmitotic neurons. Egr-3 displayed an expression profile similar to that of Egr-1 in response to acute cocaine injection and was expressed slightly earlier upon repeated cocaine treatment. Regulation of Egr transcription factors during chronic cocaine treatment appears to differ from that of the AP1 transcription factor, since Egr-1 and Egr-3 were induced after both acute and repeated cocaine administration, and that neither Egr-2 nor Egr-3 substituted for Egr-1 after chronic cocaine treatment. Our data suggest that Egr-1, Egr-3, and NAB2 are the key members of their families that regulate expression of Egr target genes.
Asunto(s)
Cocaína/farmacología , Proteínas de Unión al ADN/genética , Regulación de la Expresión Génica/efectos de los fármacos , Proteínas Inmediatas-Precoces/genética , Proteínas de Neoplasias , Prosencéfalo/metabolismo , Proteínas Represoras/genética , Factores de Transcripción/genética , Animales , Cuerpo Estriado/efectos de los fármacos , Cuerpo Estriado/metabolismo , Proteínas de Unión al ADN/metabolismo , Esquema de Medicación , Proteína 1 de la Respuesta de Crecimiento Precoz , Hibridación in Situ , Masculino , Plasticidad Neuronal , Prosencéfalo/efectos de los fármacos , ARN Mensajero/genética , Ratas , Ratas Wistar , Valores de Referencia , Transducción de Señal/efectos de los fármacos , Factores de Transcripción/metabolismo , Transcripción Genética/efectos de los fármacosRESUMEN
Acute cocaine injection to rats is known to induce the expression of immediate early genes in the forebrain, the effect being primarily mediated by the dopaminergic system. We examined the effect of the anesthetics ketamine and propofol on cocaine-induced egr-1 mRNA expression. Using in situ hybridization, we show that both compounds did not induce egr-1 gene by themselves, but were able to dose-dependently reduce cocaine-induced egr-1 mRNA synthesis in the nucleus accumbens, caudate-putamen and cingulate cortex. Our data suggest that in addition to glutamate NMDA receptors, propofol may act via GABA(A) receptors or ion channels.
Asunto(s)
Anestésicos Disociativos/farmacología , Anestésicos Intravenosos/farmacología , Química Encefálica/efectos de los fármacos , Cocaína/antagonistas & inhibidores , ADN de Cadena Simple/genética , Regulación de la Expresión Génica/efectos de los fármacos , Ketamina/farmacología , Propofol/farmacología , Prosencéfalo/metabolismo , Animales , Química Encefálica/genética , Cocaína/farmacología , Densitometría , Hibridación in Situ , Técnicas In Vitro , Masculino , Prosencéfalo/efectos de los fármacos , Ratas , Ratas Sprague-DawleyRESUMEN
Nitric oxide (NO) and the C-type natriuretic peptide (CNP) exert their action via stimulation of the cyclic GMP (cGMP)-signaling pathway, which includes the activation of cGMP-dependent protein kinases (PKG). The present report shows that the activation of PKG by local application of 8-bromo-cGMP in the caudate-putamen reduced the expression of the epigenetic markers, methyl-CpG-binding protein 2 (MeCP2) and histone deacetylase 2 (HDAC2), in dopaminergic projection areas of cocaine-treated rats. An effect of lesser amplitude was observed when rats were not injected with cocaine. We also studied the effect of PKG overexpression by injecting a plasmid vector containing the human PKG-Iα cDNA in either the caudate-putamen or the ventral tegmental area. Injection in the caudate-putamen reduced the epigenetic parameters with higher amplitude than the cGMP analog. The effect was abolished by the injection of a selective PKG inhibitor, confirming that it was due to PKG-dependent phosphorylation. As MeCP2 and HDAC2 modulate dynamic functions in the adult brain such as memory formation and synaptic plasticity, the downregulation of expression by PKG suggests that the cGMP pathway affects cognitive processes through a mechanism that comprises the MeCP2/HDAC2 complex and the subsequent control of gene silencing.