Effects of amino acids on cat red nucleus neurons in vitro.

Intracellular records were obtained from neurons in the region of the red nucleus (RN) of cat brain slices. Both EPSPs and IPSPs were recorded in response to local electrical stimulation and these resembled similar electrophysiological responses observed in experiments conducted in vivo. Monosynaptic and polysynaptic IPSPs were observed, suggesting the existence of inhibitory interneurons near or within the RN region. When added to the bathing solution, L-glutamate and L-aspartate depolarized RN neurons with a decrease in input resistance. gamma-Aminobutyric acid (GABA) and glycine hyperpolarized the cells with a decrease in input resistance. GABA also elicited a depolarizing response. These amino acid actions had direct postsynaptic effects, since the experiments were conducted in a low Ca2+/high Mg2+ medium which blocked synaptic transmission.