Pharmacological behavior of spinal cord potentials relative to reflex and ascending discharge

¹ Department of Physiology and Biomechanics Laboratory, University of California Medical School, San Francisco, California

The slow negative and positive potentials recorded at the cord dorsum and at an adjacent dorsal root in response to a dorsal root volley were relatively insensitive to mephenesin, morphine, Dial, Nembutal, chloralose, eserine, amyl carbamate and, less clearly, urethane. In the doses used, mephenesin (and, to a lesser extent, morphine) markedly depressed the longer-latency, polysynaptic components of the reflex discharge and of the ascending tract responses in the contraventrolateral and ipsidorsolateral columns. The other drugs affected the monosynaptic reflex as much as or more than the polysynaptic discharge. The carbamates used depressed the monosynaptic reflex in smaller doses with increasing length of the aliphatic chain. The lack of parallelism between behavior of the slow cord potentials and the reflex or ascending discharge is explainable by the hypothesis that the slow potentials result from graded postsynaptic potentials in certain groups of interneurons. The insensitivity to eserine suggests that such postsynaptic potentials are developed at noncholinergic junctions.