Behavioural effects of chronic treatment with apomorphine in combination with neuroleptic drugs

Groups of male Wistar rats were injected with either apomorphine alone twice daily for one week or with apomorphine in combination with chlorpromazine or thioridazine. The neuroleptics were administered once daily so that it was possible to assess their duration of effect on the apomorphine responses. Other groups were injected with saline (controls) chlorpromazine or thioridazine. The nature and time of onset and duration of the stereotyped response following apomorphine injection was determined twice daily. In addition, the behaviour of the rats on the hole board apparatus was also assessed after seven days of drug treatment. Apomorphine was found to induce either a "sniffing/burrowing" or a "fighting" stereotypy. Chlorpromazine increased the latency and reduced the duration of both types of stereotypy. In contrast thioridazine only increased the latency and reduced the duration of response the "fighting" group. On the hole board apparatus, both neuroleptics reduced the ambulation and rearing scores of the "fighting groups alone. It is suggested that the different types of stereotypy induced by chronic apomorphine administration, and their sensitivity to the two neuroleptics, are mediated by different types of dopamine receptors.