Changes in the distribution and size of synaptic vesicles in neuromuscular junctions of Locusta migratoria after stimulation and rest.

The distribution and size of synaptic vesicles in excitatory terminals of the extensor tibiae muscle were determined after stimulation at frequencies varying from 0.5 to 100 Hz and after subsequent rest. Only in preparations stimulated at the higher frequencies do these parameters differ from those in the controls. The synaptic vesicles in the nonsynaptic areas of these terminals are depleted in number, and the remaining vesicles are reduced in size. These effects are reversed after a 1 h rest.