Synaptic transmission of nervous impulses through the last abdominal ganglion of the cockroach

Publisher Website
Google Scholar
Abstract
The purely afferent cereal nerve proper in Periplaneta americana was separated from the motor cereal nerve. It connects with anterior regions of the nerve cord by "through" fibres, running through the ganglion without synapse, and with a smaller number of "giant fibres" through synapses in the ganglion. Antidromic stimulation of the giant fibres, unlike that of the through fibres produces no response in the cereal nerve. Maximal single shock stimulation of the cereal nerve produces an immediate response in the through fibres, a volley of impulses in the giant after a synaptic delay of about 1 msec. With repetitive maximal stimulation of the pre-ganglionic fibres at low frequency each volley in the giant fibres is approximately identical. At higher frequencies the number of fibres responding falls off, although the inactive fibres may still be stimulated directly; the failure is due to fatigue at the synapses. With repetitive sub-maximal stimulation of the cereal nerve above a critical frequency for any given intensity, the magnitude of the postganglionic giant fibre response falls off. It may be restored by increasing the intensity (increasing the number of pre-ganglionic fibres stimulated) or frequency of the stimulus, or by interpolating an extra stimulus. The through fibre response is maintained throughout the expt. The postganglionic decline in amplitude is considered to be an adaptation of the synapses, consisting in prolongation of the relative refractory state of the synaptic terminations of the preganglionic fibres. Temporal summation in the classical sense does not occur, but in the adapted preparation a summation is evident in the augmentation of the post-ganglionic response on increasing the frequency of the stimulus. The oscillator, amplifier and double gas-discharge tube for stimulation were essentially those previously described by the authors.

This publication has 4 references indexed in Scilit: