Ubiquitous and temperature-dependent neural plasticity in hibernators

Area of Science:

• Neuroscience
• Mammalian Physiology
• Cell Biology

Background:

• Hibernating mammals survive extreme cold with reduced neural activity.
• Previous studies noted synaptic changes in hippocampal neurons during hibernation.
• The ubiquity and temperature-dependence of these changes across the brain were unclear.

Purpose of the Study:

• To investigate if neuronal structural changes during hibernation are widespread throughout the brain.
• To determine if these changes are driven by temperature.
• To analyze the dynamics of neuronal retraction and regrowth during torpor and rewarming.

Main Methods:

• Iontophoretic injection of Lucifer yellow into neurons of hibernating ground squirrels.
• Analysis of neuronal microstructure (cell bodies, dendrites, spines) in fixed brain slices.
• Comparison of animals at different torpor stages, ambient temperatures, and during summer.

Main Results:

• Neuronal cell bodies, dendrites, and spines retracted upon entry into torpor across multiple brain regions (hippocampus, cortex, thalamus).
• Structural changes showed a linear relationship with minimum body temperature during hibernation.
• Neurons regrew to original complexity within 2 hours of rewarming, irrespective of prior retraction extent.

Conclusions:

• Hibernation induces large-scale, ubiquitous neural plasticity in ground squirrel brains.
• A temperature-driven model of dramatic neural plasticity is defined.
• This plasticity offers insights into neural regrowth mechanisms and the impact of remodeling on cognition.