The development of vesicular acetylcholine transporter immunoreactivity inthe hindlimbs of the opossum Monodelphis domestica

Vesicular acetylcholine transporter (VAChT) was revealed immunohistochemic ally in light microscopy on hindlimb sections of developing opossums, Monod elphis domestica. In the immobile hindlimbs of the newborn, which comprise cartilaginous bones and loose, unstriated myofibers, scant immunolabeled ne rve segments and small spherical terminals, presumably growth cones or imma ture neuromuscular junctions, are found in the muscle tissue of the thigh, lea and proximal foot, decreasing in number and size proximodistally. When the hindlimbs start moving at I week, terminals are more numerous and large r, still decreasing proximodistally, and occur in the newly formed inteross eous foot muscles. At 4 weeks, when the hindlimbs start supporting weight a nd quadrupedal locomotion appears, terminals are more numerous, flattened a nd in comparable size and density in thigh, leg and foot muscles. By 7 week s, large and completely flat terminals are observed in groups of 3 to 4 at regular intervals along muscle fibers. VAChT expression develops largely po stnatally in the opossum hindlimbs, along a proximodistal gradient that par allels somatic and reflex development. (C) 2001 Published by Elsevier Scien ce B.V.