A Role for Ca 2+ Stores in Kainate Receptor-Dependent Synaptic Facilitation and LTP at Mossy Fiber Synapses in the Hippocampus

Abstract

Compared with NMDA receptor-dependent LTP, much less is known about the mechanism of induction of NMDA receptor-independent LTP; the most extensively studied form of which is mossy fiber LTP in the hippocampus. In the present study we show that Ca 2+-induced Ca 2+ release from intracellular stores is involved in the induction of mossy fiber LTP. This release also contributes to the kainate receptor-dependent component of the pronounced synaptic facilitation that occurs during high-frequency stimulation. We also present evidence that the trigger for this Ca 2+ release is Ca 2+ permeation through kainate receptors. However, these novel synaptic mechanisms can be bypassed when the Ca 2+ concentration is raised (from 2 to 4 mM), via a compensatory involvement of L-type Ca 2+ channels. These findings suggest that presynaptic kainate receptors at mossy fiber synapses can initiate a cascade involving Ca 2+ release from intracellular stores that is important in both short-term and long-term plasticity.