Various dose-dependent influences of apomorphine on the acetylcholine turnover in striatum and mesolimbic areas of rat brain.

The content of acetylcholine and choline and the acetylcholine turnover rates were determined in olfactory tubercle, n. accumbens, striatum and hippocampus after the administration of various doses of apomorphine. Whereas apomorphine failed to change the levels of both amines, the acetylcholine turnover rates were markedly influenced in a dose and time dependent manner. A clear-cut decrease of the latter parameter in all four brain structures was observed after administration of higher doses of apomorphine (1 and 2.5 mg/kg). After a low dose of apomorphine (0.25 mg/kg) the acetylcholine turnover in the striatum was depressed, too. However, the acetylcholine turnover was dramatically increased in olfactory tubercle and n. accumbens. An inhibitory dopaminergic modulation of cholinergic neurons has been postulated to exist in these four brain structures. Some functional differences between the nigrostriatal and the mesolimbic dopamine systems have been discussed.