RESUMO
This study investigated the role of cyclic AMP in the inhibition of [3H]5-hydroxytryptamine ([3H]5-HT) release mediated through the 5-HT1D autoreceptor using slices of guinea-pig cerebral cortex. Forskolin, dibutyryl-cyclic AMP and rolipram, which increase intracellular cyclic AMP by different mechanisms, all attenuated the inhibitory effect of the autoreceptor agonist 5-carboxamidotryptamine. These results indicate that modulation of cyclic AMP production affects 5-HT1D autoreceptor function.
Assuntos
Córtex Cerebral/metabolismo , AMP Cíclico/farmacologia , Receptores de Serotonina/efeitos dos fármacos , Serotonina/metabolismo , Animais , Bucladesina/farmacologia , Córtex Cerebral/efeitos dos fármacos , Colforsina/farmacologia , Cobaias , Técnicas In Vitro , Indóis/antagonistas & inibidores , Indóis/farmacologia , Inibidores de Fosfodiesterase/farmacologia , Potássio/farmacologia , Pirrolidinonas/farmacologia , Receptores de Serotonina/metabolismo , Rolipram , Serotonina/análogos & derivados , Serotonina/farmacologia , Agonistas do Receptor de Serotonina/farmacologia , Sulfonamidas/antagonistas & inibidores , Sulfonamidas/farmacologia , SumatriptanaRESUMO
Previous studies with lithium have shown that it potentiated the in vivo response to cholinomimetics in rats, resulting in seizures at otherwise non-convulsant doses, but did not affect seizure activity induced by a number of chemical convulsants including kainic acid and N-methyl-D-aspartate (NMDA). In vitro experiments have suggested that lithium interferes with receptor-mediated second messenger production, possibly due to an action at G-proteins. The present study tested the hypothesis that selective inhibition of G-proteins by in vivo administration of pertussis toxin would induce effects similar to those of lithium. The results reported here demonstrate that pertussis toxin mimics lithium in potentiating the convulsant response to pilocarpine in rats. The effect of pertussis toxin was dose-dependent and the extent of potentiation was over 13-fold, which was remarkably similar to lithium. The seizures were prevented by pretreatment with atropine, phenobarbital or diazepam. L-Phenylisopropyladenosine (L-PIA) and MK-801 also demonstrated anticonvulsant activity, with MK-801 also protecting the rats against the rapid death associated with pertussis toxin/pilocarpine-induced seizures. Thus, seizures were cholinergically initiated and were controlled by the same drugs as were lithium/pilocarpine-induced seizures. The results illustrate that in several respects the response to cholinomimetics is modified in a similar manner by lithium and pertussis toxin. However, pertussis toxin lacks the specificity of lithium as it also potentiated the convulsant effects of kainic acid and NMDA.