Head-Twitches Induced by p-Hydroxyamphetamine in Mice

Head-twitches have been regarded as an experimental model of hallucination, and we have recently observed that p-hydroxyamphetamme (p-OHA) markedly induced head-twitches in mice. The present work was undertaken to study possible participation of a serotonergic system in the mechanism of head-twitches induced by p-OHA. Head-twitches induced by p-OHA continued for 20-80 mm. and the peak time of this effect was approximately 30-40 mm after the administration. The i.c.v. administration of p-OHA (20, 40, 80 and 160 μ/mouse) produced characteristic head-twitches in a dose-dependent manner. Simultaneous injection of serotonin (10 μg/mouse, I.C.V.) and p-OHA caused a 2-2.5-fold increase m the number of head-twitches compared with non-serotonin controls. Pretreat-ment with p-chlorophenylalanine (200 mg/kg, i.p, and 500 μ/mouse, i .C.V.), in contrast, reduced head-twitches as did the pretreatment with cyproheptadine or dimethothiazine These results suggest that p-OHA-induced head-twitches may involve the central serotonergic system which may exert an excitatory effect on head-twitches.