Slow kinetics of miniature IPSCs during early postnatal development in granule cells of the dentate gyrus

Whole-cell patch-clamp recordings were used to investigate the properties of GABA(A) receptor-mediated postsynaptic currents during development in dentate gyrus granule cells from neonatal [postnatal day 0 (P0)] to adult rats in brain slices, The frequency of miniature lPSCs (mlPSCs) was low at birth and increased progressively with age, The mlPSCs of all ages could be satisfactorily fitted with the sum of a single exponential rise and single exponential decay, From P0 to P14, both the rise time and the decay time constants were significantly longer than in the adult. The mlPSC rise and decay kinetics did not change during the first 2 postnatal weeks, but during the third week the kinetics sped up and by P21 attained adult values, In contrast, the amplitude of the mlPSCs did not change during development, The synaptic GABA(A) receptors in immature and adult cells showed differential sensitivity to modulators. The subunit-specific benzodiazepine agonist zolpidem increased the decay time constant of the lPSCs of immature granule cells with a reduced potency compared with the adult, Furthermore, zinc decreased the amplitude and decay time constant of mlPSCs from developing granule cells, whereas it had no effect on mlPSCs in adult neurons. The results reveal for the first time that until the end of the second postnatal week the synaptic GABA(A) receptor-mediated currents in dentate granule cells display slower rise and decay kinetics but similar amplitudes compared with adult, resulting in a net decrease in synaptic charge transfer during development.