AN UPDATE OF FOWLER AND DAS - ANTICHOLINERGIC REVERSAL OF HALOPERIDOL-INDUCED, WITHIN-SESSION DECREMENTS IN RATS LAPPING BEHAVIOR

Dopamine receptor-blocking neuroleptics produce progressive decrements in response output during behavioral test sessions. If these response decrements reflect Parkinson-like motor effects of neuroleptic treatm ent, then within-session decrements should be ameliorated by concurren t anticholinergic treatment. To investigate this question, new within- session data analyses were performed on previously published data that addressed haloperidol-scopolamine influences across the entire sessio n (Fowler and Das, 1994). The peak force and duration of individual li cks were recorded for 36 rats along with the number of licks emitted i n each daily 2-min session. The effects on this behavior of vehicle an d three doses of haloperidol (0.06, 0.12, and 0.24 mg/kg, IP, 45 min b efore sessions) were evaluated alone and in combination with vehicle a nd two doses of scopolamine HCl (0.1 and 0.2 mg/kg, SC, 60 min before sessions). Despite the brief sessions, haloperidol produced pronounced within-session decrements, and pretreatment with scopolamine reversed the haloperidol-induced within-session decrements in lick emission. S copolamine by itself produced within-session increments in all three m easures of lapping behavior. The results support the idea that within- session decrements in licking behavior are Parkinson-like and diminish confidence in hedonic interpretations of neuroleptic-induced within-s ession decrements.