Discrimination of the amphetamine cue. Effects of A, B and mixed type inhibitors of monoamine oxidase.

Rats were trained to discriminate between the effects of 0.6 mg/kg of (+)-amphetamine given intraperitoneally saline in a two-lever operant task, according to a fixed ratio ( FR10 ) schedule of food reinforcement. Once trained (greater than 90% responding on the appropriate lever during sessions with drug and saline, respectively over 2 weeks), they were given tests of generalization with various type A, type B or mixed type monoamine oxidase inhibitors (MAOI). Generalization was tested during the first 100 sec of a 15 min trial during which no reinforcements were given (extinction) followed by reinforcement on both levers for the rest of the session. Generalization to amphetamine was estimated using both the percentage of responding on the "drug lever" and a measure of choice of lever. None of the type A MAOI's tested [ cimoxatone (MD 780515), clorgyline, LY 51641, moclobemide (Ro 11-1163), toloxatone] showed generalization towards the lever for amphetamine. Clear or partial amphetamine-like responding was observed with the B type MAOI (+/-)-deprenyl and LY 54761 but not with two other type B MAOI's MD 240928 or pargyline. (+/-)-Tranylcypromine, but not nialamide (mixed type MAOI's), induced dose-dependent responding on the lever for amphetamine. It was concluded that amphetamine-like activity was not an intrinsic property of A or B type MAOI's.