Interaction between chronic amphetamine and neuroleptic treatments on oral behavior in rats.

The interaction of concurrently administered amphetamine (AMPH) and haloperidol (HAL) on behavior was examined. Rats were divided into four groups: drug naive controls; HAL-treated for 6 months; AMPH-treated for 1 month; and rats administered both continuous HAL for 6 months and concurrent AMPH treatment during the 2nd month of HAL administration. AMPH alone increased locomotor activity, and this effect was blocked by concurrent haloperidol administration; however, the AMPH-induced reduction of body weight was unaltered by concurrent haloperidol treatment. Oral behavior, monitored both by a human observer and a computerized system, was not significantly altered by HAL alone, or by AMPH alone, but increases in tremorous oral behavior appeared in the concurrent administration group 4 months after AMPH treatment was discontinued. These results could have implications for tardive dyskinesia.