Maintenance of neurite contacts at junctional regions of cultured individual muscle fibers from aged rats is correlated with the presence of a synapse-associated protein, gelasmin

When adult skeletal muscle is denervated as a result of injury or disease, it can usually be reinnervated [1–5]. Throughout the life of an animal, some skeletal muscles are thought to undergo cycles of denervation and reinnervation with concomitant remodeling of the neuromuscular junction, even in the absence of injury or disease [6–8]. In old animals, this reinnervation process may be faulty and may not occur at all in some aged muscle fibers, leaving them permanently denervated [6–8]. In general, the former endplate is the preferred site of reinnervation [4,5,9], which had led to the speculation that specific molecular cues persist, particularly in the basal lamina of this region, that may mediate endplate reinnervation [4,5,9,10]. Although these molecular cues are as yet unidentified, one candidate is gelasmin, a 93 kD glycoprotein we have isolated and characterized from preparations of rat synaptic extracellular matrix [11,12].