Terminal sprouting in the sternocostalis muscle of the rat. Effects of increasing extent of partial denervation.

Partial denervation of the sternocostalis muscle was achieved by sectioning two out of the five of its intercostal nerves. The terminal sprouting response was markedly increased compared to that found following section of only one nerve. The increase in the response was greater for B type than for C type end plates, although B type end plates appear unable to produce terminal sprouts longer than 20 micron after partial denervation. Double nerve section allowed terminal sprouts from C type end plates to increase the length up to three days, after which time they appeared to retract. It is postulated that the onset of collateral sprouting resulted in reinnervation of empty end plate sites and hence removed the target for terminal sprouts.