Ultrastructural changes in the glial cells at neuromuscular synapses of Locusta migratoria occurring after nerve stimulation and subsequent rest: a morphometric analysis.

The glial processes ensheathing the motor nerve terminals on the retractor unguis muscle of Locusta migratoria are described. Ultrastructural changes observed after electrical nerve stimulation (20 Hz, 7 min) without or with subsequent rest (2 min, 1 h) are analysed morphometrically. Immediately after stimulation both the average terminal circumference (+ 23%) and its proportion covered by glial processes (+ 16%) are significantly increased. The mean number of Schwann cell processes per micron of terminal circumference (without stimulation: 0.86 +/- 0.04) is also affected: Immediately after stimulation it is increased by about 15% and after 2 min of rest even by 36%. The periaxonal cleft (without stimulation: 16.5 nm +/- 0.36) becomes wider immediately after stimulation by about 19%, an effect which is almost reversed after 1 h of rest. It is suggested that these changes are a consequence of the enlargement of the nerve terminal's surface upon massive exocytotic activity and that they are possibly mediated by mechanical attachment between glial and terminal plasma membranes.