The suprachiasmatic nuclei (SCN) have been identified as a pacemaker for many circadian rhythms in mammals. The previous findings indicate that excitatory amino acid (EAA) receptors play an important role in the transmission of light information from the retina to the circadian clocks. The 2-deoxyglucose (2DG) uptake shows a robust circadian change: high uptake during subjective day and low uptake during subjective night. To determine whether EAA agonists regulate 2DG uptake in the SCN, we have measured 2DG uptake in the rat SCN in vitro. We report that, during the subjective night, glutamate, N-methyl-d-aspartate (NMDA) and kainic acid (KA) cause an increase in 2DG uptake and that NMDA- or KA-induced increase of 2DG uptake is blocked by co-treatments with competitive and non-competitive NMDA or KA receptor antagonists. EAA receptor agonist-induced increase in 2DG uptake occurs only during subjective night, at circadian times when photic phase shifting of activity occurs. Taken together, those data suggest that EAA may be an important transmitter of light information from retina to the SCN.
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