Spatial recognition test: A novel cognition task for assessing topographical memory in mice

NMDA receptors containing GluN2C and GluN2D subunits have opposing roles in modulating neuronal oscillations; potential mechanism for bidirectional feedback

NMDA receptor (NMDAR) antagonists such as ketamine, can reproduce many of the symptoms of schizophrenia. A reliable indicator of NMDAR channel blocker action in vivo is the augmentation of neuronal oscillation power. Since the coordinated and rhythmic activation of neuronal assemblies (oscillations) is necessary for perception, cognition and working memory, their disruption (inappropriate augmentation or inhibition of oscillatory power or inter-regional coherence) both in psychiatric conditions and with NMDAR antagonists may reflect the underlying defects causing schizophrenia symptoms. NMDAR antagonists and knockout (KO) mice were used to evaluate the role of GluN2C and GluN2D NMDAR subunits in generating NMDAR antagonist-induced oscillations. We find that basal oscillatory power was elevated in GluN2C-KO mice, especially in the low gamma frequencies while there was no statistically significant difference in basal oscillations between WT and GluN2D-KO mice. Compared to wildtype (WT) mice, NMDAR channel blockers caused a greater increase in oscillatory power in GluN2C-KO mice and were relatively ineffective in inducing oscillations in GluN2D-KO mice. In contrast, preferential blockade of GluN2A- and GluN2B-containing receptors induced oscillations that did not appear to be changed in either KO animal. We propose a model wherein NMDARs containing GluN2C in astrocytes and GluN2D in interneurons serve to detect local cortical excitatory synaptic activity and provide excitatory and inhibitory feedback, respectively, to local populations of postsynaptic excitatory neurons and thereby bidirectionally modulate oscillatory power.