Differential facilitation of high- and low-output nerve terminals from a single motoneuron

In the crayfish opener neuromuscular preparation, regional differences in s ynaptic transmission are observed among the terminals of a single motoneuro n. With a single stimulus, the high-output terminals of the proximal region of the muscle produce a larger excitatory postsynaptic potential than do t he low-output terminals of the central region of the muscle. We tested the hypothesis that the low-output terminals exhibit more facilitation than do high-output terminals for twin-pulse, train, and continuous-stimulation par adigms. Previous studies have not employed several stimulation paradigms to induce facilitation among high- and low-output terminals of a single moton euron. We found that the high-output terminals on the proximal fibers facil itate more than the low-output terminals on the central muscle fibers, in c ontrast with previous studies on similar muscles. The difference in measure d facilitation is dependent on the stimulation paradigm. These results are important because ultrastructural differences between these high- and low-o utput terminals are known and can be used for correlation with physiologica l measurements. Short-term facilitation is a form of short-term memory at t he synaptic level, and the processes understood at the crayfish neuromuscul ar junction may well be applicable to all chemical synapses.