Meeting Abstract
Mammalian hibernation is normally viewed as a state of relative stasis as animals dramatically reduce activity and metabolic rate to weather periods of low resource availability. However, in many species, the end of hibernation involves a transition from fasting to a fed state and is closely followed by seasonal reproduction. These transitions require extensive changes to the brain, physiology, and behavior. This raises the question: does the hibernating brain anticipate this seasonal transition and begin to prepare for spring activity before hibernation ends? We used in-situ hybridization, immunohistochemistry, and electron microscopy to examine neuroendocrine and structural changes in the brains of hibernating male and female arctic ground squirrels. We found significant changes in gene expression across hibernation within the thyroid hormone signaling pathway, including upregulation of TSH-β and changes in deiodinases in the mediobasal hypothalamus. Additionally, ependymal tanyctes lining the third ventricle exhibited striking changes; during early hibernation, tanycytic processes were scant within the mediobasal hypothalamus but process density increased late in hibernation. This suggests that the hibernating brain, instead of remaining in stasis, undergoes extensive remodeling. We propose that periodic arousals from torpor, which are typically viewed as functioning in maintaining homeostatic processes, also enable circannual modulation of hypothalamic plasticity.
