Specific shifts in the endocannabinoid system in hibernating brown bears

Area of Science:

• Zoology
• Physiology
• Biochemistry

Background:

• The endocannabinoid system (ECS) regulates key physiological processes, including metabolism and circadian rhythms.
• Global ECS downregulation is implicated in the adaptation of small hibernators to winter dormancy.
• Brown bears exhibit unique hibernation characteristics, such as prolonged torpor without arousal and responsiveness to stimuli.

Purpose of the Study:

• To investigate seasonal changes in circulating lipids and the ECS in hibernating brown bears.
• To determine if altered endocannabinoid profiles correlate with the unique physiological adaptations of bears during hibernation.

Main Methods:

• Analysis of serum, plasma, and tissue samples from free-ranging Scandinavian brown bears during active and hibernating states.
• Quantification of circulating fatty acids, endocannabinoids, and related compounds using lipidomic techniques.
• Measurement of gene expression for cannabinoid receptors (CB1 and CB2) in muscle and adipose tissues.

Main Results:

• Hibernating bears exhibited a 2-fold increase in total serum fatty acids, including docosahexaenoic acid (C22:6 n-3), and decreased arachidonic acid (C20:4 n-6).
• Lower concentrations of 2-arachidonoylglycerol (2-AG) were observed in adipose and muscle tissues of hibernating bears.
• Reduced mRNA levels for CB1 and CB2 genes were found in winter muscle and adipose tissues, respectively.
• Elevated circulating levels of N-oleoylethanolamide (OEA) were detected in hibernating bears.

Conclusions:

• Seasonal modulation of the ECS in brown bears may facilitate metabolic adjustments, including fatty acid mobilization and utilization.
• Reduced ECS tone could promote the shift towards carbohydrate metabolism in skeletal muscle during hibernation.
• The endocannabinoid-like compound OEA might play a role in maintaining torpor, promoting lipolysis, and preserving sensory responsiveness in hibernating bears.