EFFECT OF INTRATHECAL BACLOFEN ON THE MONOSYNAPTIC REFLEX IN HUMANS -EVIDENCE FOR A POSTSYNAPTIC ACTION

Intrathecal baclofen is a very powerful antispastic agent. Its mechani sm of action on the monosynaptic H-reflex in spinal patients was inves tigated. It could inhibit rapidly and profoundly monosynaptic reflexes in lower limbs, but did not modify la vibratory inhibition of the sol eus H-reflex. To assess more precisely its effect on Ia afferents, an experimental paradigm using Ia heteronymous facilitation of the soleus H-reflex was used. Intrathecal baclofen did not modify the amount of monosynaptic facilitation of the soleus H-reflex brought about by stim ulation of the femoral nerve. This demonstrates that the main part of the inhibitory effect of baclofen on the H-reflex in spinal patients i s not due to a presynaptic effect, suggesting a postsynaptic site of a ction.