RECOVERY OF MUSCLE SPINDLE ACTIVITY IN CATS AFTER CEREBELLAR ABLATION

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Abstract
In a series of 59 cats utilized for direct spindle afferent recordings, 12 underwent acute or chronic ablation of the anterior lobe of cerebellum and 9 had total cerebellectomy. In the remainder, recordings were made after decerebration without cerebellar lesion. Acute total cerebellectomy in the decerebrate cat results in diminished sensitivity of flexor as well as extensor muscle spindles. Alpha motoneuron activity is enhanced and is no longer dependent upon spindle mediation. During the process of recovery from cerebellectomy, spindle bias is restored and can mediate reflex alpha discharge. The recovery of spindle sensitivity occurs in parallel with the clinical restoration of some degree of maintained proprioceptive positive supporting. During this late phase of recovery some degree of enhanced alpha excitability persists, independent of spindle input. Flexor muscle spindles recover activity to a degree that exceeds extensors and in fact is greater than that present in cats with cerebellum intact. The increased activity of flexor muscle spindles may relate to the exaggerated phase of flexion that characterizes the hopping abnormality seen during recovery from cerebellectomy. The findings in animals with anterior lobe ablation alone are similar to those after total cerebellectomy, however, in these animals recovery occurs sooner and is more complete.

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