VON DER OHE, C.G.*; DARIAN-SMITH, C; HELLER, H.C.; Stanford University; Stanford University; Stanford University: Neural Plasticity in Hibernation

Hibernators provide a uniquely informative system for studying neural structural plasticity because these animals exhibit an extreme spectrum of neural activity, virtually ceasing electrical activity as body temperature drops during torpor. We investigated whether changes in neural activity over the course of a torpor bout in adult hibernating golden-mantled ground squirrels are associated with corresponding changes in neural structure. Neural activity is known to influence parameters of neural structure such as dendritic arbors and spines, but malleability of neural structure is thought to be limited in adulthood. We detailed the time course of neural structural changes over the course of a torpor bout in disparate regions of the brain. Squirrels were sacrificed at several time points in torpor, and neurons were imaged by injecting Lucifer Yellow into cortical, thalamic, and hippocampal neurons in fixed slices. Cell body size, dendritic length and complexity, and spine density all decrease by 20-30% during torpor. The majority of decrease occurs during entry into torpor, and the majority of the recovery takes place within 2 hours of arousal induction. These rates of structural change are among the most dramatic found in nature, suggesting that adult mammals are capable of greater neural plasticity than previously thought.