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

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 per cent of the amplitude, 73 per cent of the rising rate and 81 per cent of the duration of a longitudinal muscle contraction recorded by a mechano-electrical 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.

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

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 multi-peaked 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

Responses evoked in the earthworm, Amynthas hawayanus, main muscle contraction generator M-2 (postsynaptic mechanical-stimulus-sensitive) neuron by threshold mechanical stimuli in 2-s intertrial intervals (ITI) were used as the control or unconditioned responses (UR). Their attenuation induced by decreasing these intervals in non-associative conditioning and their enhancement induced by associating the unconditioned stimuli (US) to a train of short (0.1 s) hyperpolarizing electrical substitutive conditioning stimuli (SCS) in the Peri-Kästchen (PK) neuron were measured in four parameters, i.e., peak numbers (N) and amplitude (AMP )averaged from 120 responses, sum of these amplitudes (SAMP) and the highest peak amplitude (V) over a period of 4 min. Persistent attenuation similar to habituation was induced by decreasing the control ITI to 0.5 s and 2.0 s in non-associative conditioning within less than 4 min. Dishabituation was induced by randomly pairing one of these habituated US to an electrical stimulus in the PK neuron. All four parameters of the UR were enhanced by forward (SCS-US), but not backward (US-SCS), association of the US with 25, 100 and 250-Hz trains of SCS with 40-ms interstimulus intervals (ISI) for 4 min and persisted for another 4 min after turning off the SCS. The enhancement of these parameters was proportional to the SCS frequencies in the train. No UR was evoked by the SCS when the US was turned off after 4 min of classical conditioning.

Identification of efferent-stimulus-responding neurons in the earthwoem 3rd segmental nerve by Lucifer yellow-ch backfilling

The objective of the present study was to identifify the mechanism for the decreased efferent reflex response recorded extracellulary from an earthworm 3rd segmental nerve after the nerve had been cut. Four neurons which showed a correlated decrease in their efferent responses were identified in the ventral nerve cord by the broken-microelectrode-backfilling method using Lucifer Yellow-CH. The long processes of these neurons extended into the 3 rd nerve trunk.Thus teses neurons may neurons mayrepresent an efferent link in the this complicated reflex are

Decremental propagation of reflex spikes along giant axons of the earthworm amynthas hawayanus

the constant-velocity conduction of an action potential evoked by stimulating the isolated nerve cord of the earthworm Amynthas hawayanus differs from the propagation of a reflex spilke evoked by stimulating the epithelium of an epithelio-muscular-nerve-cord (EMNC) preparation and recorded between pairs of microelectrodes spaced every 10 segments along either giant axon. The refloex spike is decrmental and lasts for no more than 20 segments before it eventually disappears. Secondary and tertiary spikes sometimes arise even before the disapperance of the primary spike, and disappear after propating for a short distance. This decremental propagation is tentatively attributed to the summation of excitatory postsynaptic potentials from the synaptic impingngs of afferent interneurons in a polysynaptic reflex arc