TY - JOUR
T1 - Slowing of synapse elimination by α-bungarotoxin superfusion of the neonatal rabbit soleus muscle
AU - Callaway, Edward M.
AU - Van Essen, David C.
N1 - Funding Information:
This work was supported by NSF Grant BNS 8408213 and by NIH Training Grant T32 GM07737 to E.M.C.
PY - 1989/2
Y1 - 1989/2
N2 - To examine the role of postsynaptic activity in regulating the rate of neuromuscular synapse elimination, contractile activity of neonatal rabbit soleus muscles was decreased by chronic superfusion of α-bungarotoxin (α-BGT) over their surfaces. Superfusion was begun at 6 days postnatal and continued for a variable duration (2 to 5 days) before muscles were analyzed. The percentage of polyinnervated fibers was assessed both physiologically and anatomically for α-BGT-treated muscles and their contralateral muscles, in addition to normal and control muscles of the same age. Within muscles exposed to α-BGT, polyinnervation was significantly greater than that for muscles from each of the control groups. The anatomical assay further revealed that the retention of polyinnervation in α-BGT-treated muscles was most pronounced near the muscle's surface, although end plates at the center were also affected. This finding, coupled with evidence that only a small percentage of the muscle fibers were completely inactivated, suggestst that the activity block was also most pronounced near the surface and ralatively low at the muscle's center. The percentage of end plates at which synapse elimination was delayed was greater than the estimated percentage whose activity was completely blocked, suggesting that synapse loss was slowed even in muscle fibers retaining some postsynaptic activity. These observations indicate that the rate of synapse elimination depends on the levels of functional acetylcholine receptors. This process could be mediated in a graded fashion by changes in postsynaptic activity (subthreshold or suprathreshold) or by a nonelectrical effect of blocking postsynaptic receptors.
AB - To examine the role of postsynaptic activity in regulating the rate of neuromuscular synapse elimination, contractile activity of neonatal rabbit soleus muscles was decreased by chronic superfusion of α-bungarotoxin (α-BGT) over their surfaces. Superfusion was begun at 6 days postnatal and continued for a variable duration (2 to 5 days) before muscles were analyzed. The percentage of polyinnervated fibers was assessed both physiologically and anatomically for α-BGT-treated muscles and their contralateral muscles, in addition to normal and control muscles of the same age. Within muscles exposed to α-BGT, polyinnervation was significantly greater than that for muscles from each of the control groups. The anatomical assay further revealed that the retention of polyinnervation in α-BGT-treated muscles was most pronounced near the muscle's surface, although end plates at the center were also affected. This finding, coupled with evidence that only a small percentage of the muscle fibers were completely inactivated, suggestst that the activity block was also most pronounced near the surface and ralatively low at the muscle's center. The percentage of end plates at which synapse elimination was delayed was greater than the estimated percentage whose activity was completely blocked, suggesting that synapse loss was slowed even in muscle fibers retaining some postsynaptic activity. These observations indicate that the rate of synapse elimination depends on the levels of functional acetylcholine receptors. This process could be mediated in a graded fashion by changes in postsynaptic activity (subthreshold or suprathreshold) or by a nonelectrical effect of blocking postsynaptic receptors.
UR - http://www.scopus.com/inward/record.url?scp=0024537921&partnerID=8YFLogxK
U2 - 10.1016/S0012-1606(89)80009-0
DO - 10.1016/S0012-1606(89)80009-0
M3 - Article
C2 - 2912800
AN - SCOPUS:0024537921
SN - 0012-1606
VL - 131
SP - 356
EP - 365
JO - Developmental Biology
JF - Developmental Biology
IS - 2
ER -