Inhibition of conditional avoidance response by neuroleptics upon repeated administration

Abstract

Development of tolerance to neuroleptic compounds tested in the conditional avoidance model was investigated. Since tolerance may manifest itself by a diminished potency and/or a shortened duration of effect, the complete time course of effect was registered in these experiments. Rats were pretreated approximately 2 weeks with daily oral doses of chlorprothixene (20 mg/kg), flupenthixol (10 mg/kg), fluphenazine (2.5 mg/kg), or haloperidol (10 mg/kg) or twice a week with piflutixol (0.31 mg/kg). Three days after withdrawal chlorprothixene and flupenthixon caused a slightly but significantly weaker inhibition of avoidance performance in rats pretreated with the respective compounds and compared with non-pretreated rats, the duration of effect was shortened. Six dasy after withdrawal of piflutixol the duration of effect of a dose of piflutixol causing maximum inhibition was significantly shortened, while no homologous tolerance could be demonstrated in fluphenazine-pretreated rats. Cross tolerance was found after haloperidol-pretreatment when the rats were tested with fluphenazine 6 days after withdrawal. Homologous piflutixol tolerance could be shown 4 weeks after withdrawal. These results indicate that it is possible to demonstrate a slight tolerance to the effect of neuroleptic compounds when these are tested in conditional avoidance experiments. The cause of this tolerance is discussed.