MECHANISMS OF DEPRESSANT ACTION OF BACLOFEN ON THE SPINAL REFLEX IN THE RAT

The experiments were performed on spinal rats transected at Cl level. Baclofen (2 mg/kg, i.v.) produced a significant reduction in monosynaptic reflex (MSR), dorsal root potential (DRP) and focal synaptic potential without affecting resting DRP, post-tetanic hyperpolarization in the dorsal root and excitability of the primary afferent fiber and the motoneuron soma. Mephenesin (50 mg/kg, i.v.) reduced MSR, DRP and excitability of the primary afferent fiber and motoneuron soma, but did not change post-tetanic hyperpolarization in the dorsal root or focal synaptic potential. These findings suggest that the depression of the spinal cord by baclofen is due to either reduction of transmitter release from the primary afferent terminal or antagonism of the action of the transmitter(s) released from the terminal. It is also suggested that the effect of mephenesin may be attributable to stabilization of the motoneuron membrane, and resulting inhibition of the spike generation. © 1979.