Physiological study of amino acid uptake and receptor desensitization: the GABA system in dorsal root ganglia

GABA applied under microscopic vision (x320) to neurones of isolated DRG, triggers a depolarizing outflow of Cl-, as seen in intracellular recordings of large somata with myelinated fibres. Group C neurones have now also been examined with respect to diversity of GABA receptors. Cells of small diametre (less than 30 micrometers) responding to stimulation of slow conducting, (less than 2.5 m/sec) unmyelinated C fibres were studied for 2 reasons: 1) GABA probably depolarizes nerve endings and C fibres but conductance changes have not been determined, 2) the inference that, unlike group A, the group C neurones show an additional response to GABA by reducing the net influx of Ca++ during action potentials. As a first step in comparing group A with C neurones, it was found that all ganglion cells responded similarly to GABA with Cl--dependent depolarization and a rapid desensitization. This conclusion relies on combined physiological and pharmacological data and also on autoradiographs of glial GABA uptake. Results are considered to reflect direct actions of GABA on neuronal membranes and to be independent of secondary effects due to Na+-dependent transport of GABA into glia.