Changes of excitatory and inhibitory amino acid responses in the relay neurons of lateral geniculate nucleus by optic nerve denervation

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In order to clarify the factors contributing to the activities of dorsal lateral geniculate nucleus (LGNd) neurons, we analyzed the physiological properties of excitatory and inhibitory amino acid receptors of the neurons freshly dissociated from animals with or without optic nerve denervation.(1) The LGNd neurons identified by injection of a retrograde tracer, DiI,were prepared for the electrophysiological study using nystatin perforated patch recording mode under voltageclamp condition.(2) The effect of excitatory amino acids on the neurons was stronger in the order of KA>NMDA>AMPA>Glu.(3) A neurotransmitter candidate at retino-geniculate synapses, NAAG,mainly acted at NMDA receptors with a weak KA-like action on non-NMDA receptors.(4) The values of relative permeability of Ca^<2+> for Cs^+ (Pc_a/Pc_S) were 9.57 and 0.16 for NMDA-and KA-induced responses, respectively.(5) Intracellular C1^- concentration increased with aging : i. e. 35 mM for 0-2-day-old rat neuron, 22 mM for 2-week-old one, and 15 mM for 6-month-old one. Consequently, GABA depolarizes the neurons of immature rat.(6) Denervation induced the rise of intracellular C1^- concentration and also decreased Mg^<2+>blockade of NMDA response.(7) It was found in the study using 'synaptic bouton' preparation that NMDA,AMPA,KA receptors existed on GABAergic nerve endings. THese receptores facilitated tha GABA release from its nerve terminals. Both GABA_B and mGlu receptors also exist on GABA ergic nerve endigs and act as autoreceptors.