title: 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.
authors.affiliation: Departamento de Fisiologia, Universidade Federal do Paraná, Curitiba, Brasil. changyc@cce.ufpr.br
authors.forename: Y C
authors.initials: YC
authors.lastname: Chang
authors.forename: Z
authors.initials: Z
authors.lastname: Assmé
authors.forename: E C
authors.initials: EC
authors.lastname: Caffaro
authors.forename: A B
authors.initials: AB
authors.lastname: Bartoszeck
mesh_terms: D000818:Animals; D004558:Electric Stimulation; D019706:Excitatory Postsynaptic Potentials; D009119:Muscle Contraction / Q000502:physiology*; D009474:Neurons / Q000502:physiology*; D009835:Oligochaeta / Q000502:physiology*; D010812:Physical Stimulation