N-methyl-d-aspartate inhibits cerebellar Purkinje cell activity via the excitation of molecular layer interneurons under in vivo conditions in mice

• Cerebellar surface perfusion of NMDA inhibits PCs simple spike activity in vivo in mice.
• NMDA induces excitation of PCs in the absence of GABAA receptor-mediated inhibition.
• NMDA induces inhibition of PCs due to the NMDA-induced excitation of MLIs.

N-methyl-d-aspartate (NMDA) receptors play a key role in synaptic transmission, and are widely expressed on the membrane of granule cells, parallel fibers, and molecular layer interneurons (MLIs) in the cerebellar cortex of mammals. In cerebellar slices, activation of NMDA receptors increases inhibitory postsynaptic currents (IPSCs) of Purkinje cells (PCs). However, the effects of NMDA on the cerebellar network under in vivo conditions are currently unclear. In the present study, we examined the effects of NMDA on the spontaneous activity of PCs and MLIs in urethane-anesthetized mice by electrophysiological, pharmacological, and juxtacellular labeling methods. Our results revealed that cerebellar surface application of NMDA (5–200 μM) reduced the PC simple spike (SS) firing rate in a dose-dependent manner. Application of GABAA receptor antagonist, SR95531 (20 μM) abolished NMDA-induced inhibition of PCs spontaneous activity, and revealed NMDA-induced excitation of cerebellar PCs. NMDA receptor antagonist, DAP-V (250 µM) did not affect the mean frequency of SS firing, but the SS firing rate of PCs became more regular than the control. In addition, NMDA increased the spike firing of both basket-type and stellate-type MLIs. Overall, these results indicated that NMDA-induced excitation of MLIs at the cerebellar surface may inhibit PC activity. Thus, NMDA receptors of MLIs may play a key role in regulating the spontaneous activity of PCs, and in information transmission and integration in cerebellar cortex.