GABAergic interneurons of the hippocampal formation are born during early prenatal development. After birth, many interneurons of the dentate gyrus migrate from the molecular layer into the hilus while others remain in this dendritic layer. We monitored the intrinsic and synaptic properties of interneurons in the molecular layer between postnatal day (p) 6 and p16. Action potential waveform became more rapid and amplitude increased. Spiking pattern showed a development towards multiple discharges upon current injection. Input resistance decreased while membrane capacitance did not change. Spontaneous synaptic currents could be recorded from p6 throughout the period of observation. Mean frequency increased with age but the amplitudes remained unchanged. Pharmacological experiments revealed that these events were exclusively GABAA receptor-mediated. Our data shows a functional maturation of intrinsic properties of interneurons in the dentate molecular layer and an early integration into synaptic networks.

Supported by SFB 488 (DFG)