Distribution of NMDA receptor subunit NR1 in arctic ground squirrel central nervous system.

Hibernation is a natural model of neuroprotection and adult synaptic plasticity. NMDA receptors (NMDAR), which play key roles in excitotoxicity and synaptic plasticity, have not been characterized in a hibernating species. Tolerance to excitotoxicity and cognitive enhancement in Arctic ground squirrels (AGS, Spermophilus parryii) suggests that NMDAR expression may decrease in hibernation and increase upon arousal.

Substance P and neurokinin-1 immunoreactivities in the neural circadian system of the Alaskan northern red-backed vole, Clethrionomys rutilus.

The suprachiasmatic nucleus (SCN) of the hypothalamus houses the main mammalian circadian clock. This clock is reset by light-dark cues and stimuli that evoke arousal. Photic information is relayed directly to the SCN via the retinohypothalamic tract (RHT) and indirectly via the geniculohypothalamic tract, which originates from retinally innervated cells of the thalamic intergeniculate leaflet (IGL).

Entrainment of the master circadian clock by scheduled feeding.

The master circadian clock, located in the mammalian suprachiasmatic nuclei (SCN), generates and coordinates circadian rhythmicity, i.e., internal organization of physiological and behavioral rhythms that cycle with a near 24-h period.