Climbing-fibre activation of NMDA receptors in Purkinje cells of adult mice

Among principal neurons, adult Purkinje cells have long been considered unusual in lacking functional NMDA receptors. This view has emerged largely from studies on rats, where NMDA receptors are expressed in Purkinje cells of newborn animals, but are lost after 2 weeks. By contrast, immunolabelling data have shown that Purkinje cells from adult mice express multiple NMDA receptor subunits, suggesting a possible species difference. To investigate the presence of functional NMDA receptors in Purkinje cells of mice, and to explore the contribution of different receptor subunits, we made whole-cell and single-channel patch-clamp recordings from Purkinje cells of wild-type and NR2D-/- mice of different ages. Here we report that multiple NMDA receptor subtypes are indeed expressed in Purkinje cells of young and adult mice; in the adult, both NR2A- and NR2B-containing subtypes are present. Furthermore, we show that NMDA receptor-mediated EPSCs can be evoked by climbing fibre stimulation, and appear to be mediated mainly by NR2A-containing receptors.