Involvement of the serotonergic system in depression of the caudate spindle.

The involvement of the serotonergic system on the caudate spindle recorded from the posterior sigmoid gyrus was examined in cats. L-5-Hydroxytryptophan injected intravenously inhibited the caudate spindle significantly. On the other hand, the caudate spindle was inhibited by high frequency stimulation of the dorsal raphe nucleus where many serotonergic fibers originate: this inhibitory effect was antagonized by cyproheptadine but not by atropine. These results suggest an involvement of serotonergic mechanisms in depression of the caudate spindle.