Hibernating Squirrels Resist Thirst Despite Dehydration

The thirteen-lined ground squirrel doesn't drink during its winter hibernation, even though systems throughout its body are crying out for water. Madeleine Junkins and colleagues now show that the squirrel suppresses the need to quench its thirst by reducing the activity of a set of neurons in highly vascularized brain structures called circumventricular organs, which act as a specialized connection point between brain, blood circulation and cerebrospinal fluid. The study by Junkins et al. helps explain how some hibernating animals ignore the powerful physiological drive to seek out water for months at a time. During hibernation, the squirrels cycle between periods of torpor (inactivity and suppressed metabolism) and interbout arousal (higher core temperatures and some movement in the burrow). Although squirrels in the interbout stage are deficient in fluids and are sensitive to some kidney and nervous system cues to regulate fluid homeostasis, they are less sensitive to other hormonal thirst cues. The researchers found that the baseline activity of thirst neurons in the circumventricular organs drops sharply during the months of winter hibernation, suppressing their sensitivity to physiological cues for thirst.