Hemicerebellectomy blocks the enhancement of cortical motor output associated with repetitive somatosensory stimulation in the rat

Abstract

Repetitive peripheral stimulation is associated with an enhancement of the intensity of corticomotor responses. We analysed the effects of hemicerebellectomy on the modulation of cortical motor output associated with repetitive electrical stimulation of the sciatic nerve in the rat. Hemicerebellectomy blocked the enhancement of the corticomotor response. The cerebellum is a key player in this form of short-term plasticity.

Figure 1. Hemicerebellectomy impairs the adaptation of motor cortex

A, corticomuscular responses evoked in left gastrocnemius muscle by electrical stimulation of the right motor cortex, before (top panels) and after (middle panels) repetitive stimulation of the left sciatic nerve. Superimposition of eight traces obtained in a control rat (left) and in a rat following left hemicerebellectomy (right, 48 h after operation). Lower panels, superimposition of compound muscle action potentials (CMAPs) of left gastrocnemius muscle before (thin trace) and after (thick trace) 1 h of repetitive stimulation. CMAPs are obtained by stimulating electrically the sciatic nerve following dissection. LW, late waves appearing after repetitive stimulation. B, upper panel, amplitudes of basal motor responses (recordings in left gastrocnemius muscle) in the two groups of rats before repetitive stimulation of the left sciatic nerve. Values are means ±s.d. and are expressed in microvolts. Group 1, no cerebellar intervention (7 rats). Group 2, left hemicerebellectomy (5 rats, 48 h after surgery). *P = 0.01, intergroup difference. Lower panel, corticomuscular responses evoked in left gastrocnemius muscle following stimulation of the right motor cortex (as compared to the basal condition; values are expressed in percentage of baseline values) in the two groups of rats. Means ±s.d. of motor responses are shown. Group 1, effects of 1 h of stimulation of the sciatic nerve in 7 control rats; group 2, effects in rats with hemicerebellectomy (n = 5). **P < 0.005, intergroup difference.

Figure 2. Effects of hemicerebellectomy on spinal cord

M responses, H-reflex and F responses in control rats (A, top panels) and in hemicerebellectomized rats 48 h after surgery (B, bottom panels), before and after repetitive stimulation of the left sciatic nerve. Recordings in left plantaris muscle resulting from stimulation of the left tibial nerve. Left panels, M responses and H-reflexes at time 0 (basal state, filled circles) and time +60 min (open circles). Mean values ±s.d. are shown. Persistence and mean F/mean M wave ratios are illustrated in right panels (means ±s.d.; filled bar, time 0; open bar, +60 min). Values are means ±s.d.*P < 0.05.