NMDAr BLOCKING BY MK801 ALTERS HIPPOCAMPAL AND PREFRONTAL CORTEX OSCILLATIONS AND IMPAIRS SPATIAL WORKING MEMORY IN MICE.

Abnormal NMDAr function has been linked to rhythmopathies, psychosis, and cognitive dysfunction in schizophrenia (SCZ). Here, we investigate the role of NMDAr hypofunction in pathological oscillations and behavior. We implanted mice with tetrodes in the dorsal hippocampus and medial prefrontal cortex (mPFC), administered the NMDAr antagonist MK801, and recorded oscillations during spontaneous exploration in an open field and in the y-maze spatial working memory test. Our results show that NMDAr blockade increased locomotor activity, impaired spatial working memory, and disrupted the correlation between oscillations and speed of movement, which is crucial for internal representations of distance. In the hippocampus, MK801 increased gamma oscillations and disrupted theta/gamma coupling. In the mPFC, MK801 increased the power of theta and gamma, generated high-frequency oscillations (HFO 155-185 Hz), and disrupted theta/gamma coupling. The performance of mice in the spatial working memory version of the y-maze was strongly correlated with CA1-PFC theta/ low gamma co-modulation. Thus, theta/gamma mediated by NMDAr function might be essential to explaining several of SCZs cognitive symptoms and might be crucial to explaining hippocampal-PFC interaction. Significance StatementNMDAr hypofunction might be the basis of cognitive symptoms and oscillopathies found in SCZ. In this work, we aimed to understand this link further. We found that NMDAr hypofunction altered theta/gamma co-modulation in the hippocampus and the PFC, explaining spatial working memory deficits.