Development of sensitivity to GABA and glycine in cultured cerebellar neurons

The effects of iontophoretically applied gamma-aminobutyric acid (GABA) and glycine on developing cerebellar neurons cultured for 7-40 days were intracellularly investigated. All neurons tested dose-dependently responded to both GABA and glycine. In mature neurons (after 25 days in culture) these amino acids inhibited spontaneous spikes, decreased the membrane input resistance and induced either hyperpolarization or depolarization of membrane potential. The mean reversal potential was -47 mV for GABA and -43 mV for glycine. Immature neurons, 7-12 days in culture, which were not spontaneously firing, also behaved in a similar manner as the mature ones, though the membrane resistance was not so largely changed by GABA or glycine and the reversal potential was more positive (-39 mV for GABA, -37 mV for glycine). These reversal potentials were shifted toward 0 mV by lowering the external Cl- concentration in either mature or immature neurons. The effects of GABA and glycine on mature or immature neurons were more or less inhibited by all of picrotoxin, bicuculline and strychnine. The effective concentrations of these antagonists, however, were lower in general in immature neurons. In mature neurons, picrotoxin and bicuculline became more selective to GABA than glycine and strychnine became more selective to glycine than GABA. These results suggest that sensitivities to GABA and glycine differentiate into selective types in the course of maturing of cerebellar cultured neurons.