Acquisition of an appetitive behavior prevents development of stress-induced neurochemical modifications in rat nucleus accumbens

In rats, exposure to chronic unavoidable stress produces a decrease in dopamine output in the nucleus accumbens shell that is accompanied by a decreased density of the dopamine transporter and an increased activity of the dopamine-D(1) receptor complex. These modifications have been hypothesized to be adaptive to decreased dopamine output in stressed rats. We investigated whether the learning of an appetitive behavior sustained by palatable food, which is associated with increased dopamine output in the nucleus accumbens shell as measured by microdialysis experiments, would affect the modifications induced by chronic stress exposure on dopamine transporter density and dopamine-D(1) receptor complex activity in the nucleus accumbens. Rats exposed to chronic unavoidable stress after acquisition of the appetitive behavior showed a higher dopamine extraneuronal release in the nucleus accumbens shell than that of stressed animals, and similar to that of control rats. Moreover, previous acquisition of the appetitive behavior prevented development of a stress-induced decrease in dopamine transporter density, measured by [(3)H]-WIN 35428 binding, a stress-induced increase in dopamine-D(1) receptor density, measured by binding of [(3)H]-SCH 23390, and SKF 38393-stimulated adenylyl cyclase activity in the nucleus accumbens. These results support the hypothesis that changes induced in pre- and postsynaptic dopaminergic transmission by chronic stress exposure are related to decreased dopamine output.