Maturation of glutamatergic neurotransmission in dentate gyrus granule cells

We studied the development of glutamatergic neurotransmission in dentate gyrus granule cells (GCs) in hippocampal slices from 5 to 12-day-old rats. The active postnatal neuronogenesis in dentate permits GCs with staggered birthdates to be studied in situ in a single preparation. We recorded evoked responses to medial perforant path stimulation using visually-guided whole-cell patch clamping to select immature GCs, and biocytin filling to correlate electrophysiologic responses with maturational stage. Even within this immature cell population we found four distinct electrophysiologic patterns. Type 1 cells had no glutamatergic current; Type 2 cells had only N-methyl- d-aspartate receptor (NMDA) current; Type 3 cells had both NMDA and α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) current although the NMDA component could be isolated at low stimulus intensity (NMDA threshold