Document Detail

Changes in gain and spatiotemporal properties of the vestibulospinal reflex after injection of a GABA-A agonist in the cerebellar anterior vermis.
MedLine Citation:
PMID:  9057156     Owner:  NLM     Status:  MEDLINE    
Experiments were performed to study the influence of the cerebellar anterior vermis on both amplitude and directional properties of the vestibulospinal (VS) reflexes. In decerebrate cats, the multiunit EMG activity of the medial head of the forelimb extensor triceps brachii was recorded during wobble of the whole animal at 0.15 Hz. With this procedure the animals were submitted to a tilt characterized by a fixed amplitude (10 degrees) and by a direction moving at constant velocity over the horizontal plane, in both a clockwise (CW) and a counterclockwise (CCW) direction. These dynamic stimuli permitted characterization of the triceps muscle response to animal tilt as a single vector in the horizontal plane. The gain of this vector was taken as the mean value obtained for the CW and CCW responses, while its orientation corresponded to the direction of head displacement, lying midway between the maximal response directions to CW and CCW rotations. The temporal phase was evaluated as the half difference between the directions of the CW and CCW responses. In all the experiments the response vector of the triceps brachii was closely aligned with the transverse axis and pointed to the side-down direction. Unilateral inactivation of the cerebellar anterior vermis after microinjection, in one or two folia of lobule V, of the GABA-A agonist muscimol (0.5 microL at 8 micrograms/microL saline), consistently and reversibly reduced in 20 to 40 min the amplitude of the EMG modulation of the ipsilateral triceps brachii to 46% to 80% of the control value, while only a small shift (up to 30 degrees) of the response vector occurred either nosewards or tailwards. Small shifts in temporal phase were also observed. These findings suggest that the Purkinje (P)-cells, which usually fire out of phase with respect to the VS neurons, contribute positively to the amplitude of the VS reflexes. It was previously shown that P-cells with response vectors covering all the directions of animal displacement are present in small regions of the cerebellar anterior vermis; it is likely that these neurons represent functional units facilitating the VS reflexes elicited by animal tilt in the direction of their response vectors. By suppressing the activity of these cells, muscimol injections would lead to a general depression of the triceps responses to animal displacement, not associated with prominent changes in directional specificity.
D Manzoni; P Andre; O Pompeiano
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Publication Detail:
Type:  Journal Article; Research Support, Non-U.S. Gov't; Research Support, U.S. Gov't, P.H.S.    
Journal Detail:
Title:  Journal of vestibular research : equilibrium & orientation     Volume:  7     ISSN:  0957-4271     ISO Abbreviation:  J Vestib Res     Publication Date:    1997 Jan-Feb
Date Detail:
Created Date:  1997-06-05     Completed Date:  1997-06-05     Revised Date:  2007-11-15    
Medline Journal Info:
Nlm Unique ID:  9104163     Medline TA:  J Vestib Res     Country:  UNITED STATES    
Other Details:
Languages:  eng     Pagination:  7-20     Citation Subset:  IM; S    
Department of Physiology and Biochemistry, University of Pisa, Italy.
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MeSH Terms
Cerebellum / anatomy & histology,  drug effects,  physiology*
Decerebrate State
Forelimb / innervation,  physiology
GABA Agonists / administration & dosage,  pharmacology*
Injections, Intraventricular
Muscimol / administration & dosage,  pharmacology*
Muscle, Skeletal / physiology
Neurons / drug effects,  physiology
Receptors, GABA-A / agonists
Reflex / physiology*
Spinal Cord / physiology*
Vestibule, Labyrinth / physiology*
Grant Support
Reg. No./Substance:
0/GABA Agonists; 0/Receptors, GABA-A; 2763-96-4/Muscimol

From MEDLINE®/PubMed®, a database of the U.S. National Library of Medicine

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