Simultaneous evaluation of drug effects on both the spinal cord and the descending pathways in rats

Effects of drugs affecting the central nervous system on the spinal reflexes and the descending modulations of the reflexes were simultaneously evaluated in rats. Mono- and polysynaptic reflexes were, respectively, increased and decreased by conditioning stimulation of the nucleus raphe in the medulla, with a deflection in resting dorsal root potential being evoked by the stimulation. Baclofen exclusively depressed the segmental responses without affecting the descending modulatory systems. On the other hand, KW-6629 (7-chloro-N,N,3-trimethylbenzo[b]furan-2-carboxamide) significantly depressed the descending modulations without affecting the segmental responses which were sensitive to baclofen. Diazepam and suriclone reduced the descending influence without affecting the ventral root reflexes. Tolperisone and chlorphenesin carbamate as well as tizanidine depressed not only the segmental reflexes but also the descending modulations. Thus, sites of drug actions were estimated.