EFFECT OF APOMORPHINE ON RAT MOTOR-ACTIVITY INDUCED BY FENCAMFAMINE AND OTHER INDIRECT PSYCHOSTIMULANT DRUGS

We evaluated the effects of low doses of apomorphine on the stimulant behavioral effects induced by amphetamine (2.5 mg/kg), fencamfamine (6 .0 mg/kg) and cocaine (15.0 mg/kg). Rats received 0.02 mg/kg of apomor phine (sc) and 30 min later were injected with one of the stimulants. Motor activity including locomotion, rearing and sniffing was quantifi ed in the animals home cages for 60 min at 15-min intervals. All stimu lant drugs induced hyperactivity. When apomorphine was administered be fore cocaine, but not when administered before fencamfamine or ampheta mine, distinctive changes occurred. The behavioral pattern resulting f rom high stimulation was replaced by that related to low stimulation, suggesting that apomorphine induces a transfer in the predominant beha vior in cocaine-, and partially in fencamfamine-, but not in amphetami ne-treated animals, by decreasing the intensity of the stereotyped eff ect. While no changes occurred when apomorphine was administered befor e amphetamine, the fencamfamine group showed intermediate alterations (nonsignificant changes in sniffing but a significant increase in rear ing behavior). These results are discussed in terms of the different m echanisms of presynaptic action of the drugs studied.