Effect of the serotonergic system on the caudate nucleus.

Effects of L-5-hydroxytryptophan (L-5HTP), an active precursor of 5-hydroxytryptamine (5-HT), and electrical stimulation of the dorsal raphe nucleus were observed on the activity of the caudate nucleus in cats with electroencephalographic and evoked potential studies. In an electroencephalographic study, thecaudate spindle and the VA spindle, recorded in the cerebral cortex and induced by electrical stimulation of the caudate nucleus and the anterior ventral nucleus, respectively, were inhibited by L-5HTP. The inhibitory effect of L-5HTP on the caudate spindle was stronger than that on the VA spindle. These inhibitory effects of L-5HTP were observed when L-5HTP showed synchronization on spontaneous EEG and no effect on the duration of the cortical after discharge. In the evoked potential study, both electrical stimulation of the dorsal raphe nucleus and exogenous L-5HTP inhibited the activity of the potentials in the caudate nucleus induced by electrical stimulation of the radial nerve. These results suggest that the neuronal activity of the caudate nucleus is inhibited by the serotonergic system.