Two antagonistic functions of neural groups of the femoral chordotonal organ underlie thanatosis in the cricket Gryllus bimaculatus DeGeer |
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Authors: | H Nishino M Sakai L H Field |
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Institution: | (1) Department of Zoology, University of Canterbury, Private Bag 4800, Christchurch, New Zealand e-mail: h.nishino@zool.canterbury.ac.nz Tel.: +64-3-364-2860; Fax: +64-3-364-2024, NZ;(2) Department of Biology, Faculty of Science, Okayama University, Tsushima-Naka-3-1-1, Okayama 700-0082, Japan, JP |
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Abstract: | The cricket Gryllus bimaculatus displayed freezing (thanatosis) after struggling while the femoro-tibial joints of the walking legs were forcibly restrained.
Myographic recording indicated that strong contraction of the flexor tibia muscle “leg flexion response” occurred under this
restrained condition. During thanatosis, when the femoro-tibial joint was passively displaced and held for several seconds,
it maintained its new position (catalepsy). Only discharge of the slow flexor units was mechanically indispensable for maintaining
thanatosis and catalepsy. Differing roles of identified neuron subgroups of the femoral chordotonal organ were elucidated
using this behavioral substrate. Ablation of the dorsal group neurons in the ventral scoloparium strengthened the leg flexion
response and the normal resistance reflex, while ablation of the ventral group weakened both motor outputs. Ablation of the
dorsal scoloparium neurons, or other main sensory nerves caused no detectable deficiency in femoro-tibial joint control. These
results imply that both modes of flexor muscle activation promoted by the ventral group neurons are normally held under inhibitory
control by the dorsal group. It is hypothesized that this antagonistic function causes immobilization of the femoro-tibial
joint in a wide range of angles in thanatosis and catalepsy.
Accepted: 12 November 1998 |
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Keywords: | Femoral chordotonal organ Thanatosis Catalepsy Cricket Gryllus bimaculatus |
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