Facilitation At Neuromuscular Junctions in Crayfish Deep Abdominal Extensor Muscles

Date of Graduation

Fall 1975


Master of Natural and Applied Science in Biology



Committee Chair

Albert Gordon


The determination of facilitation in synaptic populations is necessary to gain insight into the mechanism of synaptic transmission and the functional significance of facilitation. Facilitation was investigated in the deep extensor muscles of the crayfish. The posterior branches of the motor nerve to these muscles were stimulated while intracellular recordings were made of the electrical responses of the muscle fibers. The excitatory junction potentials (ejp's) of the muscle fibers of the deep extensor abdominal lateralis (DEAL) were compared to those in the deep extensor abdominal medialis (DEAM). DEAL was more excitable and less facilitating than DEAM. An inverse relationship between facilitation and excitability was proposed. The neuromuscular junctions of the two muscles had significant differences in the means of ejp's at 1 Hz, ejp's at 10 Hz, and indices of facilitation (Fe). Fe decreased with fatigue in experiments where the muscle fibers were stimulated at 10 Hz until the ejp's were one-half the initial amplitude. The 1 Hz ejp's did not decrease proportionally. It was proposed that this result was due to a rate-dependent process in the quantal reoccupation of presynaptic active sites. Fe was determined in DEAM fibers not treated with picrotoxin and compared to Fe in fibers that had been treated with picrotoxin in the previous experiments. On the basis of this comparison it was suggested that the posterior branch of the inhibitory axon reduces 1 Hz ejp's but has little effect on ejp's during 10 Hz stimulating frequencies. The inverse relationship between facilitation and excitability of muscle fibers might explain the functional significance of different degrees of facilitation. It was proposed that factors responsible for the rate of quantal reoccupation of presynaptic active sites could determine the facilitory character of synapses.

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© Russell Hampton Hill