Phencyclidine-induced wet-dog shakes observed in rats after withdrawal from reserpine treatment

This study was designed to assess the involvement of serotonergic neurons in phenycyclidine (PCP)-induced wet-dog shakes in rats after termination of reserpine treatment. Administration of L-5-hydroxytryptophan (7.5-12.5 mg/kg) to rats 30 min following pretreatment with pargyline induced wet-dog shakes which included head shake and whole body shake. p-Chloroamphetamine (PCA) (5 mg/kg) alone also produced wet-dog shakes in the vehicle-pretreated rats, but PCP (2.5-7.5 mg/kg) and tryptophan (100 mg/kg) alone did not. The number of wet-dog shakes significantly increased after the injection of PCA (2.5 and 5 mg/kg) in the reserpine-pretreated rats, in which the 5-hydroxyindoleacetic acid/serotonin (5-HT) ratio was significantly higher and postsynaptic 5-HT receptors were also in a state of supersensitivity, compared to that of the vehicle-pretreated rats. PCP (2.5-7.5 mg/kg) also produced wet-dog shakes in a dose-dependent fashion in rats after pretreatment with reserpine. Furthermore, PCP-induced wet-dog shakes were potentiated by imipramine, a 5-HT-uptake blocker, and prevented by mianserin, a 5-HT receptor-blocker. Tryptophan (100 mg/kg) alone produced wet-dog shakes in the reserpine-pretreated rats and it was enhanced in combination with imipramine. These results may indicate that the PCP-induced wet-dog shakes after reserpine withdrawal are due to an increased release of 5-HT from the functional pool and supersensitivity of postsynaptic 5-HT receptors.