Abnormalities of muscle spindle afferent responses in congenital feline ataxia.

Abstract

The responses of single spindle primary afferents in medial gastrocnemius muscle to passive extension of the muscle were compared in adult cats between controls, acutely decerebellate (DB), chronically DB, and chronic, congenitally ataxic (CA) animals, to determine the degree of restitution (“compensation”) of responses in the chronic groups. It was found that chronically DB cats exhibit considerable compensation of spindle afferent responses when compared with those of acutely DB cats, and that responses of CA cats demonstrate compensation similar to those of the chronically DB animals. However, de-efferentation of spindle receptors by section of either lumbosacral cord or ventral roots innervating the spindles results in a significant depression of spindle responses in controls and in chronically and acutely DB animals, but does not alter the responses in CA animals. The degree of depression of responses resulting from de-efferentation is related directly to the degree of increased firing threshold to passive muscle stretch. It is concluded that the compensatory mechanisms in the DB animals depend upon fusimotor-gamma innervation from the central nervous system, but in the CA animals the compensatory processes must occur within, the intrafusal muscle or nerve fiber itself.