Central action of 6-hydroxytryptamine in rats

The effects of 6-hydroxytryptamine (6-HT), an analogue of 5-hydroxytryptamine (5-HT) injected into a lateral brain ventricle of rats (i.c.v.) on the behaviour of animals spontaneous and exploratory activity as well as amphetamine and chlorpromazine influenced motor activity were studied. Moreover, 6-HT i.c.v. effect was investigated on rectal body temperature, duration and hexobarbital induced sleep, blood pressure and heart rate. In a separate series of experiments the effect of 6-HT after i.c.v. administration of 200 microgram was studied on the level of 5-HT, 5-hydroxyindoleacetic acid, noradrenaline, dopamine and acetylcholine as well as on the activity of acetylcholine esterase and acetyltransferase in the whole brain and in its various parts. It was demonstrated that 6-HT had a short-lasting inhibitory effect on the behaviour of animals and on the concentrations of biogenic amines in the brain. Although the effects of 6-HT in certain pharmacological tests used here resembled the known effects of 5-HT, it seems that the action of 6-HT on the central nervous system is of low specificity.