Facilitation of the main generator source of earthworm muscle contraction by a peripheral neuron

Abstract

A constant facilitation of responses evoked in the earthworm muscle contraction generator neurons by responses evoked in the neurons of its peripheral nervous system was demonstrated. It is based on the proposal that these two responses are bifurcations of an afferent response evoked by the same peripheral mechanical stimulus but converging again on this central neuron. A single-peaked generator response without facilitation was demonstrated by sectioning the afferent route of the peripheral facilitatory modulatory response, or conditioning response (CR). The multipeaked response could be restored by restimulating the sectioned modulatory neuron with an intracellular substitutive conditioning stimulus (SCS). These multipeaked responses were proposed to be the result of reverberating the original single peaked unconditioned response (UR) through a parallel (P) neuronal circuit which receives the facilitation of the peripheral modulatory neuron. This peripheral modulatory neuron was named "Peri-Kästchen" (PK) neuron because it has about 20 peripheral processes distributed on the surface of a Kästchen of longitudinal muscle cells on the body wall of this preparation as revealed by the Lucifer Yellow-CH-filling method.

Persistent attenuation and enhancement of the earthworm main muscle contraction generator response induced by repeated stimulation of a peripheral neuron

“…The train of short pulses used as SCS in the present study seemed to function differently from the long pulses in the second study (2) in this series. A depolarizing long pulse evoked an action potential in the PK neuron and induced instantaneous enhancement in the M-2 neuron response while a hyperpolarizing long pulse inhibited these events.…”

“…By conditioning, we mean that these modifications induced in the response parameters will persist after cessation of their induction. The enhancement reported in the second article (2) in this series was induced by a simple facilitation but not by conditioning because it did not persist. A different method of induction with the same stimuli (1,2) will be used to induce persistent postsynaptic modifications in the form of attenuation and enhancement in the present article.…”

“…The US parameters, i.e., peak numbers and amplitude, must be maintained constant throughout the duration of the control experiment. The first parameter, the UR peak number, was always constant as 1.0 ± 0.0 (Figure 1) after sectioning the left third nerve (2). This number changed only in experiments of induced modifications.…”

“…The preparations and experimental procedures used in this article were the same as shown in Figure 2-2 of the second article (2) in this series. The main muscle contraction generator M-2 (postsynaptic mechanicalstimulus-sensitive) neuron response (1) evoked by a threshold mechanical stimulus (US) (Figure 1) was used to indicate the induced postsynaptic excitability modifications, in the control or the UR.…”

“…The purpose of the present article, third in this series (1,2), is to demonstrate that parameters such as peak number and amplitude of a response evoked in the earthworm, Amynthas hawayanus, neuron can be modified in a paradigm comparable to that of conditioning experiments of neuronal responses in other animals (3)(4)(5)(6) and in intact earthworms (7,8). By conditioning, we mean that these modifications induced in the response parameters will persist after cessation of their induction.…”