The effect of baclofen on the transmission in spinal pathways in spastic multiple sclerosis patients.
OBJECTIVE
To measure the effect of baclofen on the transmission in different spinal pathways to soleus motoneurones in spastic multiple sclerosis patients.


METHODS
Baclofen was administered orally in 14 and intrathecally in 8 patients. H(max)/M(max), presynaptic inhibition by biceps femoris tendon tap of femoral nerve stimulation, depression of the soleus H-reflex following previous activation of the Ia afferents from the soleus muscle (i.e. postactivation depression), disynaptic reciprocal Ia inhibition of the soleus H-reflex and the number of backpropagating action potentials in primary afferents, which may be a sign of presynaptic inhibition, were examined.


RESULTS
Baclofen depressed the soleus H(max)/M(max) ratio significantly following oral and intrathecal baclofen. None of the two tests of presynaptic inhibition, or the postactivation depression or the disynaptic reciprocal Ia inhibition of the soleus H-reflex were affected by baclofen administration. Also the action potentials of the primary afferents were unchanged during baclofen administration.


CONCLUSIONS
The antispastic effect of baclofen is not caused by an effect on the transmitter release from Ia afferents or on disynaptic reciprocal Ia inhibition. One possible explanation of the depression of the H-reflex by baclofen is suggested to be a direct depression of motoneuronal excitability.
Orsnes
G
G
Department of Neurology, Rigshospitalet, Copenhagen University Hospital, Blegdamsvej 9, 2100 Copenhagen O., Denmark. orsnes@dadlnet.dk
Crone
C
C
Krarup
C
C
Petersen
N
N
Nielsen
J
J
D000284:Administration, Oral; D000328:Adult; D001418:Baclofen / Q000008:administration & dosage*; D004558:Electric Stimulation; D004576:Electromyography; D005260:Female; D006181:H-Reflex / Q000187:drug effects / Q000502:physiology; D006801:Humans; D007278:Injections, Spinal; D008297:Male; D008875:Middle Aged; D009103:Multiple Sclerosis / Q000188:drug therapy* / Q000503:physiopathology*; D009434:Neural Pathways / Q000187:drug effects* / Q000503:physiopathology*; D013035:Spasm / Q000188:drug therapy* / Q000503:physiopathology*; D013116:Spinal Cord / Q000187:drug effects* / Q000503:physiopathology*
D001418:Baclofen