RESUMO
Results of two experiments revealed that morphine produced both time-and dose-dependent effects on the general activity of rats following a single acute administration, depression being observed 30 min after the injection and hyperactivity at 150 min. Tolerance to the depressive effects of morphine was observed within 7 days of chronic, once daily treatments, the depression being replaced by a hyperactivity that included a high degree of self-directed oral stereotyped behaviour. Dose-response analyses of the effects of d-amphetamine, an indirectly acting dopamine agonist, and apomorphine, a directly acting dopamine agonist, revealed a shift in the dose-response curves following chronic morphine treatment, indicating that the animals were supersensitive to these agents. Conversely, the dose-response curve for pimozide, a directly acting dopamine antagonist, was shifted in a direction indicating that the animals were subsensitive to this agent. The dose-response curve for haloperidol, another dopamine antagonist, was unchanged. These findings are consistent with the hypothesis that an increase in the number of dopamine receptors may develop during chronic treatment with morphine.
Assuntos
Dopamina/fisiologia , Morfina/farmacologia , Atividade Motora/efeitos dos fármacos , Animais , Apomorfina/farmacologia , Dextroanfetamina/farmacologia , Relação Dose-Resposta a Droga , Tolerância a Medicamentos , Haloperidol/farmacologia , Masculino , Atividade Motora/fisiologia , Pimozida/farmacologia , Ratos , Fatores de TempoAssuntos
Comportamento Animal/efeitos dos fármacos , Dopamina/farmacologia , Morfina/farmacologia , Animais , Apomorfina/farmacologia , Dextroanfetamina/farmacologia , Antagonistas de Dopamina , Tolerância a Medicamentos , Haloperidol/farmacologia , Humanos , Masculino , Atividade Motora/efeitos dos fármacos , Pimozida/farmacologia , Ratos , Comportamento Estereotipado/efeitos dos fármacos , Fatores de TempoRESUMO
The general activity of rats in an open field test situation was observed following the central administration of isotonic saline and 0.5 and 2.0 mug of noradrenaline into the locus coeruleus. A significant increase in activity was found following the 0.5 mug, but not the 2.0 mug dose. The results are consistent with other reports indicating that low doses of centrally administered noradrenaline produce behavioural arousal whereas higher doses may result in behavioural depression. In addition, these findings suggest that the noradrenergic neurons arising from the locus coeruleus may be important for the arousal status of rats.
