Sm. Gatesy et Aw. English, EVIDENCE FOR COMPARTMENTAL IDENTITY IN THE DEVELOPMENT OF THE RAT LATERAL GASTROCNEMIUS-MUSCLE, Developmental dynamics, 196(3), 1993, pp. 174-182
In adult rats, each neuromuscular compartment of the lateral gastrocne
mius muscle (LG) is exclusively innervated by a primary branch of the
LG nerve. In neonates, however, a small percentage of LG cells receive
s inputs from more than one primary nerve branch; these inputs are kno
wn as cross-compartmental. Cross-compartmental inputs are normally los
t from the medial compartment of LG (LGm) by the 8th postnatal day. To
investigate the mechanisms involved in the elimination of cross-compa
rtmental inputs, muscle fibers in the LGm compartment were denervated
by cutting the LGm nerve branch in 1-4 day old rat pups and in adult r
ats. We then assessed the degree of cross-compartmental innervation wi
thin the ''denervated'' compartment using intracellular recordings fro
m neonatal muscle fibers or immunohistochemical staining for nerve cel
l adhesion molecule (N-CAM) and neurofilament protein in adult muscles
. Following LGm axotomy in neonates, cross-compartmental innervation i
s more extensive than in controls and is present as late as 20 days af
ter birth. Thus, in the absence of ''native'' LGm axons, neonatal cros
s-compartmental inputs proliferate by axonal sprouting and the formati
on of new synapses on vacant LGm fibers. In contrast, axotomized adult
s do not form new cross-compartmental inputs over the same time period
. The differential response of neonates and adults to muscle nerve bra
nch denervation is evidence for the existence of some form of compartm
ent-specific recognition. We propose that compartmental identity eithe
r arises or becomes relatively more potent during ontogeny and normall
y acts selectively to eliminate foreign axons and deter the formation
of new cross-compartmental inputs. (C) 1993 Wiley-Liss, Inc.