Investigations on the CNS sites of action of the discriminative stimulus effects of arecoline and nicotine.

The role of the dorsal hippocampus (DH) and mesencephalic reticular formation (MRF) in mediating the discriminative stimulus (DS) effects of nicotine and arecoline was assessed. In rats trained to discriminate nicotine (1.14 mg/kg) from saline, peripherally administered nicotine generalized to injection of nicotine, but not arecoline, directly into the DH and MRF. The stimulus effect of centrally administered nicotine was antagonized by peripherally administered mecamylamine, but not atropine. Response rate decreases were also observed after nicotine injection into either site. In rats trained to discriminate arecoline (1.74 mg/kg) from saline, peripherally administered arecoline did not generalize to the direct injection of arecoline into the DH and MRF. However, a decrease in response rates was observed after arecoline injection into either site. Thus, The DH and MRF are important in mediating the DS effect of nicotine but not arecoline.