Behavioural Subsensitivity Induced by Long-term Administration of a Low Dose of Haloperidol to Rats

This study examines the effects on open-field and stereotyped behaviour of rats of abrupt withdrawal from repeated treatment with a low (0.03 mg kg^?1) dose of haloperidol. Single administration of this low dose of haloperidol significantly increased open-field locomotion without modifying apomorphine (0.5 or 2.0 mg kg^?1)-induced stereotyped behaviour. Forty-eight hours after abrupt withdrawal from 0.03 mg kg^?1 haloperidol (twice daily for 15 days) a significant decrease in locomotion frequency was observed, but no change was observed in apomorphine-induced stereotypy. Our results suggest that dopamine autoreceptor supersensitivity might be evaluated in a behavioural situation of absence of postsynaptic dopamine receptor supersensitivity.