RESUMO
The present study investigated the effects of the GABA agonist muscimol on the behaviors produced by acute injections of selective D1 and D2 agonists and antagonists. Muscimol potentiated the intensity of stereotyped behaviors shown by rats treated with the D2 agonist quinpirole; in contrast, it suppressed the repetitive bouts of grooming shown by rats treated with SKF38393. Muscimol potentiated the catalepsy produced by either a D1 (SCH23390) or D2 (metoclopramide) antagonist, suggesting that the cataleptic behaviors produced by these compounds may contain a common GABAergic mechanism.
Assuntos
2,3,4,5-Tetra-Hidro-7,8-Di-Hidroxi-1-Fenil-1H-3-Benzazepina/farmacologia , Ergolinas/farmacologia , Muscimol/farmacologia , Receptores Dopaminérgicos/fisiologia , Comportamento Estereotipado/efeitos dos fármacos , Animais , Masculino , Quimpirol , Ratos , Ratos Endogâmicos , Receptores Dopaminérgicos/efeitos dos fármacos , Receptores de Dopamina D1 , Receptores de Dopamina D2RESUMO
Recent electrophysiological findings have indicated that D1 dopamine (DA) receptor stimulation by SKF 38393 enables the inhibitory effects of the D2 receptor agonist quinpirole on nucleus accumbens neurons. In the present study, a similar interaction was shown for quinpirole-induced stereotyped behaviors. In control rats, SKF 38393 enhanced the stereotyped responses induced by quinpirole, converting lower-level stereotypies (sniffing and rearing) to more intense oral behaviors (licking and gnawing). In rats depleted of DA (79% reduction) by the tyrosine hydroxylase inhibitor alpha-methyl-p-tyrosine (AMPT), the behavioral effects of quinpirole were abolished. However, quinpirole-induced stereotyped responses were reinstated by SKF 38393 suggesting that D1 receptor stimulation by endogenous DA is necessary for D2 receptor-mediated stereotyped responses (sniffing, rearing). In support of this suggestion, stereotyped behaviors produced by the non-selective D1/D2 agonist apomorphine were not affected by AMPT pretreatment. In contrast to the effects of quinpirole, the ability of SKF 38393 to induce grooming responses was not abolished by AMPT pretreatment or by combined pretreatment with AMPT and reserpine (greater than 99% DA depletion). These results indicate that D1 receptor stimulation enables D2 receptor-mediated stereotyped responses, but that this relationship is not reciprocal since D2 receptor stimulation is not necessary for the grooming response elicited by SKF 38393.
