Interaction between repetitive stimulation of the sciatic nerve and functional ablation of cerebellar nucleus interpositus in the rat.

It is established that cerebellar nuclei exert a significant effect on the excitability of spinal neurons. However, their output is heterogeneous. Conditioning trains of dentate nucleus stimuli are known to modify the post-synaptic potentials evoked in motoneurons by stimulation of group Ia and Ib afferents in appropriate peripheral nerves. The role of the interpositus nucleus in the modulation of the excitability of rat spinal cord remains unclear. We investigated the interactions between tetrodotoxin (TTX)-induced inactivation of the interpositus cerebellar nuclei and repetitive electrical stimulation of the ipsilateral sciatic nerve (proximal segment) in the anesthetized rat. TTX (10 microM) was administered in cerebellar nuclei by the technique of microdialysis (coordinates of the extremity of the guide related to bregma: AP: -11.6, L: +2.3, V: -4.6). Peripheral stimulation consisted of trains of electric stimuli at a rate of 10 Hz, which were repeated every second during 1 hour. Stimulus intensity was adjusted to produce constant somatosensory evoked potentials. H-reflex, F-wave and M responses of the plantaris muscles were analysed ipsilaterally. H-reflex recruitment curve, Hmax/Mmax ratios, F-wave persistence and mean F/mean M ratios were studied. Functional blockade of cerebellar interpositus nucleus reduced the slope of H-reflex recruitment curve without affecting the Hmax/Mmax ratio, and depressed both F-waves persistence and mean F/mean M ratios. Concomitant repetitive stimulation of the sciatic nerve counteracted the depression of the H-reflex recruitment curve, without interacting with F-waves depression. Our results (1) show that TTX-sensitive sodium channels in cerebellar nucleus interpositus modulate the H-reflex recruitment, and (2) reveal an interaction between TTX-sensitive sodium channels in cerebellar nuclei and afferent repetitive activity not described so far.