RESUMO
In this study, the involvement of nitric oxide (NO) in the mechanism of anxiety was investigated. The rats received an intraamygdaline or intrahippocampal injection of the nitric oxide synthase inhibitor, N(G)-nitro-l-arginine (L-NOARG), and were then tested in the plus-maze test. L-NOARG induced a decrease in the time spent by rats in the open arms. Conversely, the administration of the melanin-concentrating hormone (MCH) into these structures increased the number of entries into the open arms as well as the time spent on them. MCH injected in rats pretreated with L-NOARG also was able to revert the anxiogenic effects of L-NOARG in amygdala.
Assuntos
Encéfalo/enzimologia , Inibidores Enzimáticos/farmacologia , Hormônios Hipotalâmicos/farmacologia , Melaninas/farmacologia , Neovascularização Patológica , Óxido Nítrico Sintase/antagonistas & inibidores , Oxigênio/metabolismo , Hormônios Hipofisários/farmacologia , Tonsila do Cerebelo/efeitos dos fármacos , Tonsila do Cerebelo/enzimologia , Animais , Hipocampo/efeitos dos fármacos , Hipocampo/enzimologia , Masculino , Aprendizagem em Labirinto/efeitos dos fármacos , Óxido Nítrico/metabolismo , Nitroarginina/farmacologia , Ratos , Ratos Wistar , Fatores de TempoRESUMO
Some behavioral response of rats to spatial novelty after i.c.v. administration of melanin-concentrating hormone (MCH) were evaluated. To this purpose, an open-field test was used, as well as an elevated plus-maze to study the possible anxiolytic effect of this peptide. In the open field, the frequency of exploratory components (locomotion and rearing) increased after MCH administration in comparison to controls. Moreover, in the plus-maze, MCH increased the number of entries into the open arms as well as the time spent on them, whereas no changes in the number of entries onto the closed arms were found. The data indicate that MCH exerts an anxiolytic effect, and suggests a physiological role for this.
Assuntos
Ansiolíticos/farmacologia , Comportamento Animal/efeitos dos fármacos , Meio Ambiente , Hormônios Hipotalâmicos/farmacologia , Melaninas/farmacologia , Hormônios Hipofisários/farmacologia , Animais , Ansiolíticos/administração & dosagem , Ansiedade/psicologia , Comportamento Exploratório/efeitos dos fármacos , Hormônios Hipotalâmicos/administração & dosagem , Injeções Intraventriculares , Masculino , Melaninas/administração & dosagem , Atividade Motora/efeitos dos fármacos , Periodicidade , Hormônios Hipofisários/administração & dosagem , Ratos , Ratos Wistar , Proteínas Recombinantes/administração & dosagem , Proteínas Recombinantes/farmacologiaRESUMO
The purpose of the present study was to evaluate the possible effect of melanin-concentrating hormone (MCH) on learning and memory by using the one-trial step-down inhibitory avoidance test in rats. The peptide was infused into hippocampus, amygdala, and entorhinal cortex. MCH caused retrograde facilitation when given at 0 or 4 h post-training into hippocampus, but only at 0 h into amygdala. From these results, it seems that MCH modulates memory early after training by acting on both the amygdala and hippocampus and, 4 h after training, on the hippocampus.