Spinal reflexes in the long-tailed stingray, Himantura fai |
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Authors: | Peter D Kitchener Peter J Snow |
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Institution: | (1) Department of Anatomy and Cell Biology, University of Melbourne, Parkville, VIC, 3010, Australia;(2) Department of Anatomy and Developmental Biology, University of Queensland, St Lucia, QLD, 7001, Australia |
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Abstract: | We have exploited the segregation of motor and sensory axons into peripheral nerve sub-compartments to examine spinal reflex
interactions in anaesthetized stingrays. Single, supra-maximal electrical stimuli delivered to segmental sensory nerves elicited
compound action potentials in the motor nerves of the stimulated segment and in rostral and caudal segmental motor nerves.
Compound action potentials elicited in segmental motor nerves by single stimuli delivered to sensory nerves were increased
severalfold by prior stimulation of adjacent sensory nerves. This facilitation of the segmental reflex produced by intense
conditioning stimuli decreased as it was applied to more remote segments, to approximately the same degree in up to seven
segments in the rostral and caudal direction. In contrast, an asymmetric response was revealed when test and conditioning
stimuli were delivered to different nerves, neither of which was of the same segment as the recorded motor nerve: in this
configuration, conditioning volleys generally inhibited the responses of motoneurons to stimuli delivered to more caudally
located sensory nerves. This suggests that circuitry subserving trans-segmental interactions between spinal afferents is present
in stingrays and that interneuronal connections attenuate the influence that subsequent activity in caudal primary afferents
can have on the motor elements. |
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