The Journal of Neuroscience, April 1, 2003, 23(7):2980
Transmission Security for Single Kinesthetic Afferent Fibers of
Joint Origin and Their Target Cuneate Neurons in the Cat
Gordon T.
Coleman,
Hong-Qi
Zhang, and
Mark J.
Rowe
School of Medical Sciences, The University of New South Wales,
Sydney, Australia 2052
Transmission between single identified, kinesthetic afferent fibers
of joint origin and their central target neurons of the cuneate nucleus
was examined in anesthetized cats by means of paired
electrophysiological recording. Fifty-three wrist joint afferent-cuneate neuron pairs were isolated in which the single joint
afferent fiber exerted suprathreshold excitatory actions on the target
cuneate neuron. For each pair, the minimum kinesthetic input, a single
spike, was sufficient to generate cuneate spike output, often amplified
as a pair or burst of spikes, particularly at input rates up to 50-100
impulses per second. The high security was confirmed quantitatively by
construction of stimulus-response relationships and calculation of
transmission security measures in response to both static and dynamic
vibrokinesthetic disturbances applied to the joint capsule. Graded
stimulus-response relationships demonstrated that the output for this
synaptic connection between single joint afferents and cuneate neurons
could provide a sensitive indicator of the strength of joint capsule
stimuli. The transmission security measures, calculated as the
proportion of joint afferent spikes that generated cuneate spike
output, were high (>85-90%) even at afferent fiber discharge rates
up to 100-200 impulses per second. Furthermore, tight phase locking in
the cuneate responses to vibratory stimulation of the joint capsule
demonstrated that the synaptic linkage preserved, with a high level of
fidelity, the temporal information about dynamic kinesthetic
perturbations that affected the joint. The present study establishes
that single kinesthetic afferents of joint origin display a capacity
similar to that of tactile afferent fibers for exerting potent synaptic actions on central target neurons of the major ascending kinesthetic sensory pathway.
Key words:
cuneate nucleus; kinesthetic input; joint afferent
fiber; paired recording; synaptic transmission; dorsal column
nuclei
Copyright © 2003 Society for Neuroscience 0270-6474/03/2372980-13$05.00/0
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