Patterns of connectivity of spinal interneurons with single muscle afferents.

Patterns of connectivity of spinal interneurons with single muscle afferents. Research Abstract Details 

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Patterns of connectivity of spinal interneurons with single muscle afferents. Abstract Text:

J Quevedo,J R Eguibar,J Lomeli,P Rudomin,

A technique was developed to measure, in the anesthetized and paralyzed cat under artificial ventilation, changes of excitability to intraspinal stimulation simultaneously in two different afferent fibers or in two collaterals of the same afferent fiber. Intraspinal stimulation reduced the threshold of single muscle afferent fibers ending in the intermediate nucleus. This effect was seen with strengths below those required to activate the afferent fiber tested (1.5-12 microA), occurred at a short latency (1.5-2.0 ms), reached a maximum between 15 and 30 ms, and lasted up to 100 ms. The effects produced by graded stimulation applied at the shortest conditioning-testing stimulus time intervals increased by fixed steps, suggesting recruitment of discrete elements, most likely of last-order interneurons mediating primary afferent depolarization (PAD). The short-latency increases in excitability produced by the weakest effective intraspinal stimuli were usually detected only in the collateral closest to the stimulating micropipette, indicating that the stimulated interneurons mediating PAD have spatially restricted actions. The short-latency PAD produced by intraspinal stimuli, as well as the PAD produced by stimulation of the posterior biceps and semitendinosus (PBSt) nerve or by stimulation of the bulbar reticular formation (RF), was depressed 19-30 min after the i.v. injection of 0.5 mg/kg of picrotoxin, suggesting that all these effects were mediated by GABAergic mechanisms. The PAD elicited by stimulation of muscle and/or cutaneous nerves was depressed following the i.v. injection of (-)-baclofen, whereas the PAD elicited in the same collateral by stimulation of the RF was baclofen-resistant. The short-latency PAD produced by intraspinal stimulation was not always depressed by i.v. injections of (-)-baclofen. Baclofen-sensitive and baclofen-resistant monosynaptic PADs could be produced in different collaterals of the same afferent fiber. The results suggest that the intraspinal terminals of single muscle afferents receive synapses from more than one PAD-mediating GABAergic interneuron and that a single last-order interneuron has synaptic connections with a restricted number of intraspinal terminals and/or collaterals of the same afferent fiber. In addition, they support the existence of separate subsets of last-order baclofen-sensitive and baclofen-resistant interneurons that respond predominantly to segmental and to descending inputs. It is suggested that the restricted nature of the PAD plays an important role in the central control of the synaptic effectiveness of group I muscle afferents.

Patterns of connectivity of spinal interneurons with single muscle afferents. Publishing Authors By Initials

J Quevedo,JR Eguibar,J Lomeli,P Rudomin,

For similar nervous system: synapses research abstracts see: nervous system: synapses research

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Patterns of connectivity of spinal interneurons with single muscle afferents. Journal Published:

PUBLICATION TYPE: Journal Article

Journal: Experimental brain research. Experimentelle Hirnfo

VOLUME: 115

Page Numbers: 387-402

Journal Abbreviation:

ISSN: 0014-4819

DAY: 15

MONTH: Jul

YEAR: 1997

Patterns of connectivity of spinal interneurons with single muscle afferents. Information

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LANGUAGE: eng

NlmUniqueID: 43312

Patterns of connectivity of spinal interneurons with single muscle afferents. Keywords Mesh Terms:

KEYWORDS: Synapses

MESH TERMS: physiology

Chemical & Substance for Abstract: Patterns of connectivity of spinal interneurons with single muscle afferents. Information

Substance Name: Picrotoxin

Registry Number: 124-87-8

Grant and Affiliation Information for Patterns of connectivity of spinal interneurons with single muscle afferents.

AFFILIATION: Department of Physiology, Biophysics and Neurosciences, CINVESTAV-IPN, Mexico D.F., Mexico.

Country: GERMANY

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MEDLINETA: Exp Brain Res

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