Abstract
Amphetamine has complex behavioral actions in the rat that depend upon the release of dopamine in striatal and mesolimbic brain regions. To explore a possible role of the dopamine-sensitive cAMP second-messenger system in mediating these effects, we examined the effects of in vivo amphetamine treatments on the D1 receptor-coupled adenylate cyclase system in membranes from striatal and mesolimbic rat brain regions. The results show that amphetamine produces a regional, dose- and time- dependent down-regulation of adenylate cyclase activity. Intermediate and high doses of amphetamine (2.5 and 7.5 mg/kg, respectively), but not a low dose (1.0 mg/kg), resulted in a decrease in the apparent Vmax and/or an increase in the apparent Ka for the selective D1 partial agonist, SKF38393, in striatal membranes 30 min after amphetamine treatment. Treatment of rats with 7.5 mg/kg amphetamine for 30 and 60 min, but not 10 min, similarly resulted in a down-regulation of D1- mediated adenylate cyclase activity in striatal membranes. In contrast, in mesolimbic tissues, no amphetamine treatment at any time resulted in an alteration of SKF38393-stimulated adenylate cyclase activity relative to saline controls. The results of behavioral analyses also showed that animals exhibiting intense stereotypies had significantly lower striatal apparent Vmax values than did those animals engaged in moderate or no behavioral activity at the time of decapitation. These findings demonstrate that amphetamine treatments result in a down- regulation of striatal, but not mesolimbic, dopamine-sensitive adenylate cyclase activity that parallels the intense, stereotyped behaviors characteristic of dopaminergic activation in the striatum.
