[Stimulation of the dorsal raphe nucleus induced depressive effect on cerebellar Purkinje cell responses to mossy and climbing fiber afferent inputs in rat]

Abstract

In anaesthetized and paralyzed rats, the effect of dorsal raphe (DR) conditioning stimulation on cerebellar Purkinje cell (PC) responses to mossy fiber and climbing fiber inputs were examined. The main results are as follows: (1) Stimulation of cerebral sensorimotor cortex elicits widespread activation of mossy and climbing fiber inputs to PCs in contralateral VI and VII lobules of the cerebellum and generates two kinds of evoked responses, i.e. the simple spike (SS) and the complex spike (CS) responses with respectively a latency 8-25 and 12-30 ms. (2) These PC responses could be markedly suppressed by stimulation of DR at intensities which by themselves were subthreshold for directly affecting PC's spontaneous SS and CS activities. (3) This DR-induced depressive effects on evoked PC's SS and CS excitations could be attenuated or blocked by systemic administration of 5-HT receptor blocker methysergide. These results demonstrate that serotonergic fiber input from DR can suppress the efficacy of mossy and climbing fiber synaptic action on PC, or decrease the responsiveness of PC itself to afferent synaptic action. The findings of this study also suggest that the raphe-cerebellar serotonergic fiber afferent system may be involved in some of the important neuronal processing in the cerebellum.