Maintenance of Bat Skeletal Maintenance of Bat Skeletal Muscle during HibernationMuscle during Hibernation

Kevin OrneeKevin Ornee

ExerciseExercise

Change in skeletal muscle is dependent Change in skeletal muscle is dependent on use.on use.

Two muscle types: Fast (more glycolytic) Two muscle types: Fast (more glycolytic) Slow (more oxidative)Slow (more oxidative)

Aerobic exercise increases mass and Aerobic exercise increases mass and oxidative capacity of the muscle.oxidative capacity of the muscle.

Disuse decreases mass and oxidative Disuse decreases mass and oxidative capacity of the muscle.capacity of the muscle.

AtrophyAtrophy

Humans experience profound disuse Humans experience profound disuse atrophy up to 50% reduction in mass in atrophy up to 50% reduction in mass in just 4 weeks.just 4 weeks.

Hibernating animals show reduced <30% Hibernating animals show reduced <30% to no atrophy over a period of 6 months.to no atrophy over a period of 6 months.

Hibernating animals show Hibernating animals show increasedincreased oxidative capacity.oxidative capacity.

HibernationHibernation

Freezing Freezing temperatures, temperatures, photoperiod and lack photoperiod and lack of food.of food.

Torpor – Enter state Torpor – Enter state of reduced body temp of reduced body temp and metabolic rate.and metabolic rate.

Thermogenesis – Thermogenesis – quivering rapidly quivering rapidly increases body temp.increases body temp.

Hibernation HabitsHibernation Habits

Hang upside-down Hang upside-down from ceiling of cavesfrom ceiling of caves

Cave shelter 5-10°CCave shelter 5-10°C Arousal and Arousal and

relocation observedrelocation observed Drafts/cold spotsDrafts/cold spots Cold temps, food Cold temps, food

unlikelyunlikely Great risk of Great risk of

starvationstarvation

Weight and Energy IssuesWeight and Energy Issues

Little brown bats begin hibernation from 20-25 Little brown bats begin hibernation from 20-25 grams and lose ~ 35% of their body mass.grams and lose ~ 35% of their body mass.

Able to fly upon arousal, great strength and Able to fly upon arousal, great strength and fatigue resistance.fatigue resistance.

FlightFlight

Pectoralis muscle, Pectoralis muscle, highest oxidative highest oxidative capacity of capacity of mammalian skeletal mammalian skeletal muscle >90%.muscle >90%.

Over six month Over six month hibernation period hibernation period there is no change in there is no change in fiber makeup of the fiber makeup of the pectoralis.pectoralis.

Atrophy PreventionAtrophy Prevention

May be attributed to many factors:May be attributed to many factors:An adaptationAn adaptationTension created by wingsTension created by wingsMuscle activity during arousal and Muscle activity during arousal and

relocationrelocation

Flight ExperimentFlight Experiment

Limiting flight to stimulate disuse atrophy, Limiting flight to stimulate disuse atrophy, small cage, large cage and wild.small cage, large cage and wild.

Expected reduction in strength and Expected reduction in strength and oxidative capacity.oxidative capacity.

Contractile force measured.Contractile force measured.Section of the muscle will be stained and Section of the muscle will be stained and

analyzed to determine cross sectional analyzed to determine cross sectional area.area.

Immunoblots for CS and Akt.Immunoblots for CS and Akt.

Wing Tension ExperimentWing Tension Experiment

While hanging, While hanging, tension created by tension created by bats wings may bats wings may initiate exercise initiate exercise feedback.feedback.

Increasing and Increasing and decreasing tension decreasing tension would be expected to would be expected to decrease and decrease and increase atrophy, increase atrophy, respectively.respectively.

Relocation TelemetryRelocation Telemetry

Hibernation induced in cold rooms.Hibernation induced in cold rooms.Bats subject to cold, drafty conditions are Bats subject to cold, drafty conditions are

expected to relocate.expected to relocate.Bats with available food expected to Bats with available food expected to

benefit if aroused.benefit if aroused.Control monitored for muscle activity Control monitored for muscle activity

during a full six month hibernation.during a full six month hibernation.Electromyography use to remotely monitor Electromyography use to remotely monitor

muscle activity. muscle activity.

BenefitsBenefits

Comparison of bat to other hibernating Comparison of bat to other hibernating species should show an increase in the species should show an increase in the mechanism to prevent disuse atrophy.mechanism to prevent disuse atrophy.

Application to human skeletal muscle Application to human skeletal muscle would greatly benefit clinical orthopedics would greatly benefit clinical orthopedics and space exploration.and space exploration.