The effect of neonatal deafferentation or deefferentation on the immunocytochemistry of muscle spindles in the rat.

Immature muscle spindles were either deafferented or deefferented by selectively severing the sensory or motor nerve supply to the soleus muscle in neonatal rats. Experimental spindles were examined two months after the surgery using monoclonal antibodies specific for myosin heavy chains of slow-tonic and fast-twitch chicken muscles. The deefferented spindles exhibited a pattern of antibody binding that closely resembled that of normal adult intrafusal fibers, whereas deafferented intrafusal fibers were unreactive with the two antibodies. These observations suggest that sensory innervation is responsible for the expression of myosins in developing intrafusal muscle fibers of rat.