Jordan C L, Letinsky M S, Arnold A P
Department of Psychology, University of California, Los Angeles 90024.
J Neurobiol. 1988 Jun;19(4):335-56. doi: 10.1002/neu.480190403.
Using tetranitroblue tetrazolium (TNBT) to stain neuromuscular synapses, we compared the development of the adult pattern of innervation in two fast-twitch muscles in the rat: the androgen-sensitive levator ani (LA) and the extensor digitorum longus (EDL), which is not thought to be androgen sensitive. We found that about 18% of adult LA muscle fibers, but only about 2% of adult EDL fibers, are multiply innervated. Moreover, synapse elimination occurs substantially later in the LA compared with the EDL. At 2 weeks after birth, the EDL is already predominantly singly innervated, whereas the LA is still predominantly multiply innervated. The apparent delay in the normal time course of synapse elimination in the LA corresponds to a similar delay in other aspects of neuromuscular development (the time course of appearance of axonal retraction bulbs, the growth of fibers, and the development of adult motor terminal morphology). Finally, motor terminals change during synapse elimination from morphologies resembling growth cones to the adult form of neuromuscular synapses. Because the period of synapse elimination is significantly different for muscles that differ in their androgen sensitivity, hormonal sensitivity may represent an important property of motoneurons or muscle fibers influencing the normal time course of neuromuscular synapse elimination in rats. Thus, androgen might regulate the normal ontogenetic process of synapse elimination.
我们使用四氮唑蓝（TNBT）对神经肌肉突触进行染色，比较了大鼠两块快肌中成年神经支配模式的发育情况：雄激素敏感的提肛肌（LA）和被认为对雄激素不敏感的趾长伸肌（EDL）。我们发现，成年LA肌纤维中约18%为多重神经支配，但成年EDL纤维中只有约2%为多重神经支配。此外，与EDL相比，LA中突触消除发生的时间要晚得多。出生后2周时，EDL已主要为单重神经支配，而LA仍主要为多重神经支配。LA中突触消除正常时间进程的明显延迟与神经肌肉发育其他方面的类似延迟相对应（轴突回缩球出现的时间进程、纤维的生长以及成年运动终末形态的发育）。最后，在突触消除过程中，运动终末从类似生长锥的形态转变为成年形式的神经肌肉突触。由于雄激素敏感性不同的肌肉，其突触消除期存在显著差异，激素敏感性可能是影响大鼠神经肌肉突触消除正常时间进程的运动神经元或肌纤维的一个重要特性。因此，雄激素可能调节突触消除的正常个体发育过程。
