Journal of Neurophysiology, Vol 65, Issue 6 1598-1605, Copyright © 1991 by APS
Changes in central delay of soleus H reflex after facilitatory or inhibitory conditioning in humans
M. Abbruzzese, L. Reni and E. Favale
Department of Neurology, University of Genoa, Italy.
1. Central delay (CD) changes after facilitatory or inhibitory conditioning
of the soleus H reflex have been investigated in a group of normal subjects
as a function of the conditioning and test stimulus intensities and also as
a function of the Hmax/Mmax ratio. Both facilitation and inhibition of the
reflex response have been obtained by conditioning stimulation of the
ipsilateral tibial nerve at suitable conditioning-test stimulus intervals.
CD changes have been extrapolated from the variations of the time interval
between afferent and efferent neural volleys underlying the H reflex,
directly recorded from the sciatic nerve. 2. The CD was significantly
decreased by facilitatory and increased by inhibitory conditioning.
Facilitatory CD changes were positively related to test stimulus strength
(at a given conditioning stimulus intensity) and negatively related to
conditioning stimulus strength (at a given test stimulus intensity). Both
trends were reversed after inhibitory conditioning. The effectiveness of
facilitatory conditioning was positively related to the individual
Hmax/Mmax ratio whereas a negative relationship could be observed after
inhibitory conditioning. 3. Also, the "conditioning threshold" (the minimal
conditioning stimulus strength affecting the reflex size) and the "maximal
conditioning effect" (the conditioning stimulus intensities leading to
either the saturation of the facilitatory effect or the suppression of the
reflex response) were significantly related to the Hmax/Mmax ratio. 4. We
suggest that temporal changes in the H reflex pathway after facilitatory or
inhibitory conditioning stimuli depend both on the size of the motoneuronal
pool underlying the reflex response, as determined by the test stimulus
intensity, and on the individual excitability of the motoneuronal pool, as
defined by the Hmax/Mmax ratio.(ABSTRACT TRUNCATED AT 250 WORDS)
