SYNAPTIC CONDUCTION TO GIANT FIBERS OF THE COCKROACH AND THE ACTION OF ANTICHOLINESTERASES

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Abstract
Afferent fibers from hair sensilla on the cerci of the cockroach, Periplaneta americana, synapse with a small number of giant fibers in the 6th abdominal ganglion. The ganglionic delay is 0.6 to 1.5 msecs. These synapses conduct synchronously on afferent stimulation up to frequencies of 400/sec. Treatment of the ganglion with di-isopropyl fluorophosphate 10-4 [image] at first interferes with the synchrony of the response. After 15 mins., a few afferent stimuli cause a prolonged after-discharge and synaptic block. Conduction returns spontaneously after a few mins. rest, to be followed by another after-discharge and block. The change produced is presumably due to cholinesterase in-activation, and cannot be removed by washing. This, and higher concns. (10-3 [image]) of DFP have no detectable effect on axonic conduction in the giant fibers in the cord, Other cholinesterases (physostigmine, prostigmine, and strychnine) reversably block trans-synaptic conduction without the preliminary facilitation produced by DFP. The significance of this difference is discussed.

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