The Effect of Strychnine on Membrane Properties of Spinal Motoneurons in the Cat

ABSTRACT

Strychnine (Stry.) has been used, as an instrument for studies of experimental epilepsy, though its precise mode of action has remained obscure. One mechanism of action was partially clarified in 1954 ,by the demonstration that subconvulsive doses of Stry. reduce the amplitude of inhibitory postsynaptic potentials (IPSPs) in the cat's spinal motoneurons (MN). Because of the rapid onset of its action and the absence of effects upon monosynaptic excitatory postsynaptic potentials (EPSPs), it was proposed that Stry. competed with some unidentified transmitter for inhibitory receptor sites on the postsynaptic membrane. Electrophoresis of Stry. is known to block the inhibitory effects of glycine, a likely candidate as an inhibitory transmitter on MN in the cat spinal cord. A Stry. resistant inhibition seems to exist not only in the higher portion of the CNS, but also for the spinal MN. Gamma amino butyric acid (GABA) is a candidate for this synaptic transmitter. In Nembutal anesthetized cat, intracellular recording of spinal MN was performed during Stry. induced seizure. To conclude, it can be said that there were no consistant changes in the MN action potential which would reflect an action of Stry. upon MN's membrane properties important to seizure generation. It is still to be resolved whether the increase in polysynaptic EPSP amplitude is due to a Stry. effect upon the membrane properties of excitatory interneurons or to an effect only upon the inhibitory as well as the EPSPs.