Postnatal maturation of mossy fibre excitatory transmission in mouse CA3 pyramidal cells: a potential role for kainate receptors.

Kainate receptors (KARs) are abundantly expressed in the central nervous system at a period of intense synaptogenesis and might participate in the maturation of neural networks. We have described the postnatal development of mossy fibre excitatory synaptic transmission in CA3 pyramidal cells and we have explored the potential role of KARs in synaptic maturation. In CA3 pyramidal cells, mossy fibre stimulation evokes EPSCs as early as postnatal day 3 (P3). At this early stage, mossy fibre (MF)-EPSCs are fully blocked by GYKI 53655, an AMPA receptor (AMPAR) antagonist. A postsynaptic KAR component can only be detected from P6. Thus, AMPAR-EPSCs precede KAR-EPSCs during postnatal maturation at this synapse. All MF-EPSCs display a KAR component after P10. A key issue of the present work is that between P6 and P9, the presence of a postsynaptic KAR component tightly coincides with AMPAR-mediated EPSCs of large amplitude, and with the onset of low frequency facilitation (from 0.1 Hz to 1 Hz), a presynaptic form of short-term synaptic plasticity. In addition, mice lacking functional KARs throughout postnatal development display MF-EPSCs of significantly smaller amplitude at stages of maturation where synaptic KARs are normally present, due to both pre- and postsynaptic impairment of synaptic transmission. These data suggest a role for KARs in the maturation of mossy fibre synapses.