Presynaptic kainate receptors play different physiological roles in mossy fiber and associational-commissural synapses in CA3 of hippocampus from adult rats.

Mossy fiber (MF) and Associational-commissural (Assoc-com) synaptic responses were recorded simultaneously in CA3 from the same hippocampal slice. Low concentrations of Kainate (KA) (50 and 100 nM) reversibly increased the synaptic response and decreased the paired-pulse facilitation (PPF) in the MF synapse, while reversibly decreasing the synaptic response and increasing the PPF in the Assoc-com synapse. The same concentration of KA had no effect on synaptic transmission or the induction and expression of long-term potentiation (LTP) in area CA1. MF LTP partially occluded the effect of KA on MF responses. These results suggest that KARs function as presynaptic autoreceptors in both MF and Assoc-com synapses but play different roles.