Osmolyte Depletion and Thirst Suppression Allow Hibernators to Survive for Months without Water

• Published in: Current biology 2019-09, Vol.29 (18), p.3053-3058.e3
• Main Authors: Feng, Ni Y., Junkins, Madeleine S., Merriman, Dana K., Bagriantsev, Sviatoslav N., Gracheva, Elena O.
• Format: Article
• Language: English
• Subjects: blood osmolality; fluid homeostasis; hibernation; thirst; thirteen-lined ground squirrel; vasopressin; water deprivation
• ISSN: 0960-9822; 1879-0445
• DOI: 10.1016/j.cub.2019.07.038

Thirteen-lined ground squirrels (Ictidomys tridecemlineatus) are obligatory hibernators who can survive over 6 months of the year in underground burrows or laboratory hibernaculum without access to food or water [1]. Hibernation consists of prolonged periods of torpor, lasting up to 18 days, which are characterized by low body temperature and suppressed metabolism. This torpidity is interspersed with short periods of interbout arousal, lasting up to 48 h, during which squirrels temporarily return to an active-like state and lose small amounts of water to urination and evaporation [2]. Water is also lost during torpor due to a positive vapor pressure difference created by the slightly higher temperature of the body compared to its surroundings [2, 3]. Here, we investigate the physiological mechanism of survival during prolonged water loss and deprivation throughout hibernation. By measuring hydration status during hibernation, we show that squirrels remain hydrated during torpor by depleting osmolytes from the extracellular fluid. During brief periods of arousal, serum osmolality and antidiuretic hormone levels are restored, but thirst remains suppressed. This decoupling of thirst and diuresis enables water retention by the kidney while suppressing the drive to leave the safety of the underground burrow in search of water. An acute increase in serum osmolality reinstates water-seeking behavior, demonstrating preservation of the physiological thirst circuit during hibernation. Better mechanistic understanding of internal osmolyte regulation and thirst suppression could translate to advancements in human medicine and long-term manned spaceflight. [Display omitted] [Display omitted] •Hibernating squirrels employ several strategies to survive for months without water•Hibernating squirrels have decreased blood osmolality despite water deprivation•Basal thirst is inhibited in ground squirrels during hibernation•Antidiuretic hormonal release and water seeking are uncoupled during hibernation Feng et al. reveal strategies that allow hibernating ground squirrels to survive for months without water, including depletion of blood osmolytes, inhibition of thirst, and uncoupling of the circuits for antidiuretic hormonal release and water-seeking. These strategies help avoid the potentially detrimental drive to leave the burrow to seek water.