Discriminative stimulus properties of arecoline: a new approach for studying central muscarinic receptors.

Rats were trained to discriminate arecoline (1.74 mg/kg) from saline in a milk-reinforced (variable interval 12s) two-lever operant paradigm. The discriminative stimulus (DS) effects of arecoline were antagonized by atropine sulfate, but not by atropine methylnitrate or mecamylamine. In contrast to the effects on discrimination, atropine did not antagonize the response rate suppressant effects of arecoline. The DS effect of arecoline completely generalized to oxotremorine, partially generalized to pilocarpine, and did not generalize to nicotine. These data demonstrate that the DS effect of arecoline depends on central muscarinic receptors.