Suprachiasmatic nucleus: phase-dependent activation during the hibernation cycle.

The suprachiasmatic nucleus (SCN) of the golden-mantled ground squirrel undergoes a phase-dependent change in its accumulation of 2-[14C]deoxy-D-glucose (2-DG) relative to other brain structures during the hibernation cycle. The greatest relative 2-DG uptake (R2DGU) is observed in the SCN during entrance into and during deep hibernation. A circadian fluctuation in R2DGU of the SCN is not evident in the euthermic ground squirrel but can be increased during the subjective day by photic stimulation. An increase in R2DGU by the paraventricular nucleus (PVN) correlates with the increase in R2DGU by the SCN during entrance to hibernation but not with the increase in SCN R2DGU evoked by photic stimulation during euthermia. The periventricular nuclei of the hypothalamus (PEV) also have high levels of R2DGU during the latter phase of the entrance. These observations support the hypothesis that the SCN, PEV, and PVN may play important roles in hibernation and suggest progressive activation of synaptic input to and within the SCN during entrance into this state.