Homosynaptic and heterosynaptic changes in driving of dentate gyrus interneurons after brief tetanic stimulation in vivo.

This study addressed changes in interneuron driving in the dentate gyrus (DG) of urethane-anaesthetized rats in response to tetanic stimulation of the perforant path (PP) or the converging dentate commissural pathway (CP). Using an extracellular tungsten electrode, we recorded from putative interneurons in the DG that fired to stimulation of both the PP and the CP. Conditioning trains (400 Hz, 17.5 ms) were delivered to each pathway individually and to the two pathways together. The primary measure of synaptic drive was the latency of interneuron discharge. High-intensity PP tetany, CP tetany, and paired tetany consistently reduced firing latency to CP driving (P < .05 for all three), indicating an LTP-like increase in synaptic activation through the CP. High-intensity PP tetany decreased latency to PP driving in only two of seven cases. Heterosynaptic changes occurred frequently in individual experiments. Activity-mediated adjustments in synaptic driving of inhibitory interneurons could play a role in normal physiological function.