Identification of the main generator source of longitudinal muscle contraction in the earthworm ventral nerve cord

Abstract

The main generator source of a longitudinal muscle contraction was identified as an M (mechanical-stimulus-sensitive) circuit composed of a presynaptic M-1 neuron and a postsynaptic M-2 neuron in the ventral nerve cord of the earthworm, Amynthas hawayanus, by simultaneous intracellular response recording and Lucifer Yellow-CH injection with two microelectrodes. Five-peaked responses were evoked in both neurons by a mechanical, but not by an electrical, stimulus to the mechanoreceptor in the shaft of a seta at the opposite side of an epidermis-muscle-nerve-cord preparation. This response was correlated to 84% of the amplitude, 73% of the rising rate and 81% of the duration of a longitudinal muscle contraction recorded by a mechanoelectrical transducer after eliminating the other possible generator sources by partitioning the epidermis-muscle piece of this preparation. The pre-and postsynaptic relationship between these two neurons was determined by alternately stimulating and recording with two microelectrodes. Images of the Lucifer Yellow-CH-filled M-1 and M-2 neurons showed that both of them are composed of bundles of longitudinal processes situated on the side of the nerve cord opposite to stimulation. The M-1 neuron has an afferent process (A1) in the first nerve at the stimulated side of this preparation and the M-2 neuron has two efferent processes (E1 and E3) in the first and third nerves at the recording side where their effector muscle cell was identified by a third microelectrode.

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

“…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.…”