Forebrain NMDA receptors contribute to neuronal spike responses in adult mice.

Glutamate is the major fast excitatory transmitter in the central nervous system. While normal synaptic transmission is mediated by alpha-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) and kainate receptors, N-methyl-D-aspartate (NMDA) receptors are thought to selectively contribute to plasticity. Genetically enhancing NMDA receptor functions enhances animal behavior in normal physiological learning and enhances their sensitivity in the case of tissue injury. One major mechanism for NMDA receptors is synaptic long-term potentiation (LTP). Here we present evidence that NMDA receptors not only contribute to normal synaptic responses induced by stimulation of local layer V or white matters, but also contribute to generation of action potentials induced by a depolarizing step applied to the soma. Calcium-calmodulin sensitive adenylyl cyclase 1 and cAMP signal pathways likely mediate these effects. Considering the importance of cingulate neurons in nociception and pain, our results provide a new mechanism for NMDA receptor contributing to neuronal synaptic transmission, spiking properties in forebrains, and possible forebrain-related behavioral nociceptive responses and pain.