Effects of stimulus timing on transmitter release and postsynaptic membrane potential at crayfish neuromuscular junctions.

Different synaptic terminals of the single excitor axon to the opener muscle of crayfish (Procambarus clarkii) often release transmitter in a very different manner when stimulated with the same equal-interval, doublet, or triplet patterns. Compared to synapses that show little facilitation (low Fe synapses), highly facilitating (high Fe) synapses show greater percentage increases in several measures of synaptic efficacy when stimulated with any of these patterns. Low Fe synapses usually show the greater absolute changes in these measures of synaptic efficacy. Changes in the span and pattern of doublets and triplets can independently affect both pre- and postsynaptic measures of synaptic efficacy at either low Fe or high Fe synapses.