Inhibitory effect of apomorphine on hippocampal stimulation-induced "wet-dog shakes" in rats may be due to a stereotyped behavior.

The effect of apomorphine on "wet-dog shakes" (WDS) elicited by hippocampal stimulation was investigated. Apomorphine in doses of 1.0 and 2.0 mg/kg given to rats s.c. reduced the number of WDS. Haloperidol in doses of 0.2-1.0 mg/kg given i.p. also significantly and dose-dependently reduced the number of WDS. The inhibitory effect of apomorphine in doses of 1.0 and 2.0 mg/kg on WDS was completely inhibited by haloperidol given in a dose of 0.5 mg/kg. It is, therefore, conceivable that the inhibition of WDS produced by apomorphine in doses of 1.0 and 2.0 mg/kg may result from the occurrence of stereotyped behavior and that the dopaminergic blocking action may be crucial for the inhibition of WDS induced by hippocampal stimulation. Despite a 50% increase in stimulation intensity, as compared with the afterdischarge threshold, the number of WDS remained unchanged. We tentatively concluded that apomorphine fails to increase the number of WDS, as a result of the ceiling phenomenon.