Effect of denervation on neuromuscular transmission and glutamate sensitivity of the locust wing muscle fibers.

Changes in neuromuscular transmission and ultrastructure of synapses taking place after motor nerve cutting during 20 subsequent days were studied on the wing muscle of the locust (muscle 120) using intracellular recording from phasic fibres. The membrane potential (MP) and the excitatory postsynaptic potential (EPSP) showed practically no changes in comparison with the controls through day 8 after denervation. After the development of a neuromuscular transmission block between days 8 and 14, EPSP and miniature EPSP (MEPSP) disappeared, and the MP level somewhat decreased in comparison with controls. MEPSP frequency and amplitude increased in the first days after denervation. The sensitivity to glutaminic acid (Glu) gradually increased after nerve cutting, reached maximum on day 8 and remained at the same level subsequently (threshold concentration 0.003 mmol/l vs 0.3 mmol/l in the control). At the same time, the maximum amplitude of depolarization produced by Glu increased 1.5-2 times but slightly decreased subsequently. Beginning from day 4 after denervation synaptic vesicles began forming separate groups. On day 14 vesicles were grouped in macroconglomerates at a distance from the presynaptic membrane. On day 20 no axon profiles could be detected. The results suggest a similarity of denervation changes in insect wing and leg muscles.