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 treatment, then within-session decrements should be ameliorated by concurrent 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 session (Fowler and Das, 1994). The peak force and duration of individual licks were recorded for 36 rats along with the number of licks emitted in each daily 2-min session. The effects on this behavior of vehicle and three doses of haloperidol (0.06, 0.12, and 0.24 mg/kg, IP, 45 min before sessions) were evaluated alone and in combination with vehicle and 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. Scopolamine by itself produced within-session increments in all three measures 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-session decrements.