Maintenance of Bat Skeletal Muscle during Hibernation Kevin Ornee

Exercise Change in skeletal muscle is dependent on use. Change in skeletal muscle is dependent on use. Two muscle types: Fast (more glycolytic) Slow (more oxidative) Two muscle types: Fast (more glycolytic) Slow (more oxidative) Aerobic exercise increases mass and oxidative capacity of the muscle. Aerobic exercise increases mass and oxidative capacity of the muscle. Disuse decreases mass and oxidative capacity of the muscle. Disuse decreases mass and oxidative capacity of the muscle.

Atrophy Humans experience profound disuse atrophy up to 50% reduction in mass in just 4 weeks. Humans experience profound disuse atrophy up to 50% reduction in mass in just 4 weeks. Hibernating animals show reduced <30% to no atrophy over a period of 6 months. Hibernating animals show reduced <30% to no atrophy over a period of 6 months. Hibernating animals show increased oxidative capacity. Hibernating animals show increased oxidative capacity.

Hibernation Freezing temperatures, photoperiod and lack of food. Freezing temperatures, photoperiod and lack of food. Torpor – Enter state of reduced body temp and metabolic rate. Torpor – Enter state of reduced body temp and metabolic rate. Thermogenesis – quivering rapidly increases body temp. Thermogenesis – quivering rapidly increases body temp.

Hibernation Habits Hang upside-down from ceiling of caves Hang upside-down from ceiling of caves Cave shelter 5-10°C Cave shelter 5-10°C Arousal and relocation observed Arousal and relocation observed Drafts/cold spots Drafts/cold spots Cold temps, food unlikely Cold temps, food unlikely Great risk of starvation Great risk of starvation

Weight and Energy Issues Little brown bats begin hibernation from grams and lose ~ 35% of their body mass. Little brown bats begin hibernation from grams and lose ~ 35% of their body mass. Able to fly upon arousal, great strength and fatigue resistance. Able to fly upon arousal, great strength and fatigue resistance.

Flight Pectoralis muscle, highest oxidative capacity of mammalian skeletal muscle >90%. Pectoralis muscle, highest oxidative capacity of mammalian skeletal muscle >90%. Over six month hibernation period there is no change in fiber makeup of the pectoralis. Over six month hibernation period there is no change in fiber makeup of the pectoralis.

Atrophy Prevention May be attributed to many factors: May be attributed to many factors: An adaptation An adaptation Tension created by wings Tension created by wings Muscle activity during arousal and relocation Muscle activity during arousal and relocation

Flight Experiment Limiting flight to stimulate disuse atrophy, small cage, large cage and wild. Limiting flight to stimulate disuse atrophy, small cage, large cage and wild. Expected reduction in strength and oxidative capacity. Expected reduction in strength and oxidative capacity. Contractile force measured. Contractile force measured. Section of the muscle will be stained and analyzed to determine cross sectional area. Section of the muscle will be stained and analyzed to determine cross sectional area. Immunoblots for CS and Akt. Immunoblots for CS and Akt.

Wing Tension Experiment While hanging, tension created by bats wings may initiate exercise feedback. While hanging, tension created by bats wings may initiate exercise feedback. Increasing and decreasing tension would be expected to decrease and increase atrophy, respectively. Increasing and decreasing tension would be expected to decrease and increase atrophy, respectively.

Relocation Telemetry Hibernation induced in cold rooms. Hibernation induced in cold rooms. Bats subject to cold, drafty conditions are expected to relocate. Bats subject to cold, drafty conditions are expected to relocate. Bats with available food expected to benefit if aroused. Bats with available food expected to benefit if aroused. Control monitored for muscle activity during a full six month hibernation. Control monitored for muscle activity during a full six month hibernation. Electromyography use to remotely monitor muscle activity. Electromyography use to remotely monitor muscle activity.

Benefits Comparison of bat to other hibernating species should show an increase in the mechanism to prevent disuse atrophy. Comparison of bat to other hibernating species should show an increase in the mechanism to prevent disuse atrophy. Application to human skeletal muscle would greatly benefit clinical orthopedics and space exploration. Application to human skeletal muscle would greatly benefit clinical orthopedics and space exploration.