Neuroleptic-induced reduction of quipazine-elicited head-twitches in rats: possible involvement of striatal dopaminergic supersensitivity.

Rats were treated with a single large dose of various neuroleptic compounds and, 5-7 days after, they were assayed for either behavioral sensitivity to apomorphine (hypermotility and stereotyped behavior) or head-twitch response to the mixed serotonin-dopamine agonist quipazine. The animals withdrawn from chlorpromazine, fluphenazine, haloperidol, metoclopramide and the D1 selective blocker SCH 23390, showed enhanced hypermotility and/or stereotyped responses to apomorphine and reduced head-twitch response to quipazine. The rats withdrawn from thioridazine, (-)-sulpiride and sultopride responded to apomorphine only with enhanced hypermotility while their response to quipazine was either unchanged or even increased. The results are discussed in terms of dopaminergic brain areas and/or receptor subtypes involved in the modulation of the head-twitch response to quipazine. We concluded that an enhancement of dopaminergic tone at the striatal level could be related to the reduced head-twitch response to quipazine.