Hemisected Animals Research Articles

Effects of nicotine and recurrent inhibition on monosynaptic reflexes in acute and chronic spinal cats

The present experiments were undertaken to examine some of the changes which take place after spinal section in the cat. Recurrent inhibition was greater in cats 7–14 days after spinal section than in acute spinal preparations ( P < 0.05). The increased potency of the inhibitory pathway subsided by 25–30 days following spinal section. The general trend of the size of the inhibitory response to intravenous nicotine in spinal and hemisected animals, paralleled the change in recurrent inhibition observed in spinal cats, although the data did not reach statistical significance ( P ⩽ 0.05). In hemisected cats, there appeared to be an overall increase in recurrent inhibition similar to that seen in spinal preparations (not significant, P ⩽ 0.05). In addition, there appeared to be increased recurrent inhibition on the hemisected side as compared to the acute side in cats 14–32 days following hemisection. There was clearly no increase in the response to nicotine on the hemisected as compared to the acute sides. When the control animals were ranked using the strength of recurrent inhibition and the degree of depression of the monosynaptic reflex by nicotine as criteria, the rank orders for each measure were identical. No such relationship was obtained for any group of chronic animals, suggesting a differential change in sensitivity to nicotine and synaptic activation of the recurrent inhibitory system. The results are discussed from the standpoint of disuse of spinal pathways following cord injury.