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Differential action of (−)-baclofen on the primary afferent depolarization produced by segmental and descending inputs

Differential action of (−)-baclofen on the primary afferent depolarization produced by segmental... 221 91 91 1 1 J. Quevedo J. R. Eguibar I. Jiménez P. Rudomin Department of Physiology, Biophysics and Neurosciences Centro de Investigatión y de Estudios Avanzados del IPN Apartado Postal 14-740 07000 México D.F. México Department of Physiological Sciences, Instituto de Ciencias UAP 07000 México D.F. México Summary The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed cats, the effects of (-)-baclofen and picrotoxin on the primary afferent depolarization (PAD) generated in single Ib afferent fibers by either intraspinal microstimulation or stimulation of the segmental and descending pathways. PAD was estimated by recording dorsal root potentials and by measuring the changes in the intraspinal activation threshold of single Ib muscle afferent fibers. The PAD elicited by stimulation of group I muscle or cutaneous afferents was readily depressed and often abolished 20–40 min after the intravenous injection of 1–2 mg/kg (-)-baclofen. In contrast, the same amounts of (-)-baclofen produced a relatively small depression of the PAD elicited by stimulation of the brainstem reticular formation (RF). The monosynaptic PAD produced in single Ib fibers by intraspinal microstimulation within the intermediate nucleus was depressed and sometimes abolished following the i.v. injections of 1–2 mg/kg (-)-baclofen. Twenty to forty minutes after the i.v. injection of picrotoxin (0.5–1 mg/kg), there was a strong depression of the PAD elicited by stimulation of muscle and cutaneous afferents as well as of the PAD produced by stimulation of the RF and the PAD produced by intraspinal microstimulation. The results obtained suggest that, in addition to its action on primary afferents, (-)-baclofen may depress impulse activity and/or transmitter release in a population of last-order GABAergic interneurons that mediate the PAD of Ib fibers. The existence of GABA b autoreceptors in last-order interneurons mediating the PAD may function as a self-limiting mechanism controlling the synaptic efficacy of these interneurons. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png Experimental Brain Research Springer Journals

Differential action of (−)-baclofen on the primary afferent depolarization produced by segmental and descending inputs

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References (38)

Publisher
Springer Journals
Copyright
Copyright © 1992 by Springer-Verlag
Subject
Biomedicine; Neurosciences; Neurology
ISSN
0014-4819
eISSN
1432-1106
DOI
10.1007/BF00230011
Publisher site
See Article on Publisher Site

Abstract

221 91 91 1 1 J. Quevedo J. R. Eguibar I. Jiménez P. Rudomin Department of Physiology, Biophysics and Neurosciences Centro de Investigatión y de Estudios Avanzados del IPN Apartado Postal 14-740 07000 México D.F. México Department of Physiological Sciences, Instituto de Ciencias UAP 07000 México D.F. México Summary The purpose of the present series of experiments was to analyze, in anesthetized and paralyzed cats, the effects of (-)-baclofen and picrotoxin on the primary afferent depolarization (PAD) generated in single Ib afferent fibers by either intraspinal microstimulation or stimulation of the segmental and descending pathways. PAD was estimated by recording dorsal root potentials and by measuring the changes in the intraspinal activation threshold of single Ib muscle afferent fibers. The PAD elicited by stimulation of group I muscle or cutaneous afferents was readily depressed and often abolished 20–40 min after the intravenous injection of 1–2 mg/kg (-)-baclofen. In contrast, the same amounts of (-)-baclofen produced a relatively small depression of the PAD elicited by stimulation of the brainstem reticular formation (RF). The monosynaptic PAD produced in single Ib fibers by intraspinal microstimulation within the intermediate nucleus was depressed and sometimes abolished following the i.v. injections of 1–2 mg/kg (-)-baclofen. Twenty to forty minutes after the i.v. injection of picrotoxin (0.5–1 mg/kg), there was a strong depression of the PAD elicited by stimulation of muscle and cutaneous afferents as well as of the PAD produced by stimulation of the RF and the PAD produced by intraspinal microstimulation. The results obtained suggest that, in addition to its action on primary afferents, (-)-baclofen may depress impulse activity and/or transmitter release in a population of last-order GABAergic interneurons that mediate the PAD of Ib fibers. The existence of GABA b autoreceptors in last-order interneurons mediating the PAD may function as a self-limiting mechanism controlling the synaptic efficacy of these interneurons.

Journal

Experimental Brain ResearchSpringer Journals

Published: Oct 1, 1992

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