Inhibitory of glycine on spinal neurons in the cat.

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Abstract
Glycine mimics remarkably the action of a spinal inhibitory transmitter in cat lumbosacral spinal cord. Iontophoresis of this agent produces rapid (sometimes 10 msec) hyper-polarization of spinal neurons, block of spike invasion, reduction of EPSP''s [excitatory postsynaptic potential] and a conductance increase in spinal neurons. The critical firing level is unaffected by glycine action. Neither axons nor Renshaw cells are affected. IPSP''s [inhibitory postsynaptic potential] appear to have the same equilibrium potential as the glycine polarization. Both IPSP''s and glycine responses are converted to depolarizations when Br and I ions are introduced into neurons. The new equilibrium potentials are again identical. Higher doses of glycine appear to occupy receptor sites normally available to inhibitory transmitter. The responses to glycine are independent of the direction of driving current and may occur by diffusion from the electrode tip alone. Intracellularly delivered glycine has no activity. In view of the association of glycine with inhibitory interneurons and the similarity of its actions with transmitter released from these interneurons, glycine may be a mammalian spinal inhibitory transmitter.