Document Detail

Selective depression of medium-latency leg and foot muscle responses to stretch by an alpha 2-agonist in humans.
MedLine Citation:
PMID:  7623294     Owner:  NLM     Status:  MEDLINE    
1. In standing humans, toe-up rotation of a platform induces a short-latency (SLR) and a medium-latency response (MLR) in both soleus (Sol) and flexor digitorum brevis (FDB) muscles. Toe-down rotation evokes a MLR in the tibialis anterior (TA). The SLR is the counterpart of the monosynaptic stretch reflex, but the origin of the MLR is still debated. By means of tizanidine (an alpha 2-adrenergic receptor agonist) we tested the hypothesis that the MLR is relayed by group II afferent fibres, since animal data indicate that tizanidine or stimulation of monoaminergic brainstem centres decrease the excitability of spinal interneurones supplied by those fibres. In addition, we compared the effect of the drug on these responses with that induced by stabilization of posture. 2. Eight subjects received tizanidine (150 micrograms kg-1 orally) or placebo, in a single-blind design. Platform rotations were delivered prior to administration and for 3 h afterwards. Both TA- and FDB-MLRs decreased in size, starting from about 1 h after tizanidine administration. Sol-SLR was unaffected. Response latencies were unchanged. Placebo induced no changes in any response. In each subject, the extent of TA-MLR depression induced by holding onto a frame and by tizanidine was superimposable. 3. The selective effect of tizanidine on MLR supports the notion that it is relayed through group II afferent fibres. The similar effects of holding and tizanidine on the response suggests that it is modulated by monoaminergic centres.
S Corna; M Grasso; A Nardone; M Schieppati
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Publication Detail:
Type:  Clinical Trial; Comparative Study; Controlled Clinical Trial; Journal Article    
Journal Detail:
Title:  The Journal of physiology     Volume:  484 ( Pt 3)     ISSN:  0022-3751     ISO Abbreviation:  J. Physiol. (Lond.)     Publication Date:  1995 May 
Date Detail:
Created Date:  1995-08-28     Completed Date:  1995-08-28     Revised Date:  2010-09-13    
Medline Journal Info:
Nlm Unique ID:  0266262     Medline TA:  J Physiol     Country:  ENGLAND    
Other Details:
Languages:  eng     Pagination:  803-9     Citation Subset:  IM    
Posture and Movement Laboratory, Clinica del Lavoro Foundation, IRCCS, Veruno (NO), Italy.
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MeSH Terms
Adrenergic alpha-Agonists / pharmacology*
Clonidine / analogs & derivatives,  pharmacology
Middle Aged
Muscle, Skeletal / drug effects,  physiology*
Physical Stimulation
Reaction Time
Reflex, Stretch / physiology
Reg. No./Substance:
0/Adrenergic alpha-Agonists; 4205-90-7/Clonidine; 51322-75-9/tizanidine

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