Potentiation in phencyclidine-induced serotonin-mediated behaviors after intracerebroventricular administration of 5,7-dihydroxytryptamine in rats

Phencyclidine (PCP)-induced behaviors were compared with 5-methoxy-N,N-dimethyltryptamine (5-MeODMT)-and p-chloroamphetamine-induced behaviors in rats pretreated with ritanserin or 5,7-dihydroxytryptamine (5,7-DHT) in order to investigate whether PCP interacts with 5-hydroxytryptamine₂ (5-HT₂) receptors. Head-twitch and wet-dog shake induced by p-chloroamphetamine, a 5-HT releaser, and head-twitch induced by PCP were blocked completely by pretreatment with ritanserin, a specific 5-HT₂ receptor blocker, but other behaviors induced by p-chloroamphetamine, PCP and 5-MeODMT, a 5-HT agonist, were not. The intensity of head-weaving, turning, backpedalling and hind-limb abduction induced by 5-MeODMT and the intensity of head-weaving, turning and head-twitch induced by PCP were markedly greater in the rats 2 weeks after the 5,7-DHT, a 5-HT neurotoxin-injection. Contrarily, 5-HT-mediated behaviors induced by p-chloroamphetamine were attenuated in the 5,7-DHT-treated rats. 5,7-DHT-treatment increased the number of 5-HT₁ ([³H]-5-HT), 5-HT₂ ([³H]ketanserin) and PCP ([³H]PCP) binding sites in the synaptic membrane of rat brain, but decreased the brain level of 5-HT (41% of control). These results may indicate that PCP as a 5-HT₂ agonist induces head-twitch via 5-HT₂ receptors, and that PCP induces head-weaving and turning via 5-HT₁ receptors and/or some other mechanisms in rats.