5-Methoxytryptamine-induced head twitches in rats.
In rats pretreated with pargyline ip injection of 5-methoxytryptamine (5-MT), but not of 5-HT, produced characteristic head twitches. 5-HT receptor blocking agents (cyproheptadine, methergoline, mianserine, WA-335-BS, and methsergide) reduced the effect of 5-MT. These substances in doses 20-160 times higher than their ED50 in head twitch test did not antagonize the pinna reflex. 5-MT-induced head twitches were also inhibited by imipramine, morphine, phenoxybenzamine and aceperone. However, their ED50 were only 3-8 times below the doses necessary to inhibit the pinna reflex. Reserpine, phentolamine, spiroperidol, pimozide and LiCl did not modify head twitches produced by 5-MT, while PCPA even potentiated them. Our results suggest the 5-MT-induced head twitches are due to the activation of the central 5-HT mechanisms probably as a result of direct stimulation of 5-HT receptors by 5-MT. Antagonism of 5-MT-induced head twitches and the dissociation of doses effective in this test from those inhibiting the pinna reflex may be of value in the prediction of central 5-HT receptor blocking properties.
D008735:5-Methoxytryptamine / Q000494:pharmacology*; D000818:Animals; D001522:Behavior, Animal / Q000187:drug effects*; D001921:Brain / Q000187:drug effects; D003533:Cyproheptadine / Q000494:pharmacology; D006257:Head / Q000294:innervation; D008297:Male; D008711:Metergoline / Q000494:pharmacology; D008803:Mianserin / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects; D010579:Petrous Bone / Q000187:drug effects; D051381:Rats; D014363:Tryptamines / Q000494:pharmacology*
D014363:Tryptamines; D008711:Metergoline; D008803:Mianserin; D003533:Cyproheptadine; D008735:5-Methoxytryptamine