EFFECTS OF SEROTONIN ON DORSAL HORN DORSAL SPINOCEREBELLAR TRACT NEURONS

Effects of ionophoretic application of serotonin and of one of its ago nists were tested on responses of dorsal horn dorsal spinocerebellar t ract neurons evoked by electrical stimulation of peripheral nerves. Bo th drugs depressed monosynaptically evoked actions of group II muscle afferents; they decreased the number and/or increased the latency of s pike potentials evoked by these afferents. In contrast, synaptic actio ns of low-threshold cutaneous afferents (mono- or oligosynaptic) were facilitated in the majority of the neurons, as judged by decrease in t he latency of spike potentials evoked by stimulation of a cutaneous ne rve and/or an increase in the number of these potentials. It is propos ed that facilitatory actions assist in maintaining tonic discharges of dorsal spinocerebellar tract neurons in some movements and that the s elective control of group II input is used to correlate activity of sp inal and supraspinal neurons. Both actions may be subserved by tight c ontacts between serotoninergic nerve fibres and dorsal spinocerebellar tract neurons, which have been revealed in a parallel study.