Electrophysiological investigations on the mode of action of nefopam, a novel analgesic agent.

The mode of action of nefopam, a novel analgesic, on the splanchnic afferent pathway was investigated using electrophysiological methods. Nefopam (2.5 and 5.0 mg/kg, i.v.) caused arousal patterns in spontaneous rabbit EEG. In intact cats, nefopam (1.0, 2.5 and 5.0 mg/kg, i.v.) suppressed the evoked potentials recorded from the posterior sigmoid gyrus of the cortex, N. ventralis posterolateralis and N. centralis medialis of the thalamus and the ventrolateral funiculus of the spinal cord following splanchnic nerve stimulation without inhibiting potentials in the thalamocortical pathways. These depressant effects were not antagonized by a narcotic antagonist, levallorphan (0.5 mg/kg, i.v.). The inhibitory effect of nefopam on the spinal potential evoked by splanchnic nerve stimulation was not observed in spinal cats (C1-C2 transection) and pentobarbital-anesthetized cats. These results suggest that nefopam may inhibit the splanchnic afferent pathways in the spinal cord by reinforcing descending inhibitory systems originating in the supra-spinal structure, in a manner which differs from that seen with morphine.