Myofibrillar ATPase activity of intrafusal fibers in chronically de-afferented rat muscle spindles.

Dorsal root ganglia L4, L5 were removed to accomplish long-term (1 year) de-afferentation of the rat soleus muscle. Muscle spindles in the muscles deprived of sensory innervation were morphologically and histochemically abnormal. The spindle periaxial fluid space was greatly diminished with a thicker capsular investment. De-afferented intrafusal muscle fibers lacked either "nuclear bags" "nuclear chains" at their midlengths. The intracapsular myofibrillar ATPase staining pattern of de-afferented nuclear bag fibers resembled that which the bag fibers normally display in their extracapsular regions. These abnormalities are discussed with respect to the regulatory functions of spindle sensory and motor nerves.