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By Root 1268 0

ground squirrels may hold keys to the riddle of why we need sleep, and also some medical problems, such as stroke. In hibernating ground squirrels, it is difficult to detect any heartbeat. It is difficult to tell if the animal, with a body temperature less than the freezing point of water, is dead or alive. In a deathlike state of torpor, the animals are cold little balls in which there is only a minute trickle of blood to the brain. In humans when a blood clot or a ruptured blood vessel interrupts blood flow to a part of the brain, there is an almost immediate die-off of brain cells, because our brain cells require a continuous supply of oxygen and glucose that the continuously flowing blood normally supplies. Hypoxia (insufficient oxygen) is the primary deleterious consequence of a stroke, but not in a hibernating squirrel. In the hibernating squirrel’s brain there is a metabolic shutdown, so that lack of oxygen and nutrient is less harmful. Do they warm up to oxygenate the brain?

The primary metabolic shutdown in hibernators is due simply to the temperature drop. Human car crash victims who fall unconscious through the ice and whose brain is immediately chilled are also able to survive prolonged hypoxia. But there are also active metabolic processes in the squirrels; brain tissues show suppressed protein synthesis even when warmed to 37°C. A second recent interesting finding is that hibernating squirrels as well as hibernating turtles accumulate five times as much ascorbic acid (vitamin C) in their, as opposed to human, brains. When the squirrels arise from torpor, the vitamin C levels return to normal within hours. It is thought that the vitamin C, a powerful antioxidant, protects the brain from the sudden rush of oxygen that they take in after their long oxygen “fast.”

Barnes’s interest in hibernation research is motivated by the discovery of basic phenomena, not practical applications. Many others’ interest in the hibernating ground squirrel is clinically, rather than intellectually, motivated. They wonder how halting blood supply and hence oxygen and glucose to the brain might be relevant to treating stroke victims, where insufficient oxygen to the brain is the main cause of cell death. They wonder how hibernating animals maintain strong bones despite months of inactivity, why their blood clots so slowly, and why they accumulate huge amounts of vitamin C in their brains and cerebrospinal fluids. I suspect that, with biology becoming ever more applied, research relating to such questions of how to harness hibernation will be increasingly funded in preference to those inquiries motivated purely by intellectual curiosity. That is unfortunate and shortsighted.

08

THE KINGLET’S FEATHERS

The wind whipping through the northern spruce-fir forest sounds like pounding surf, even as the thermometer routinely reads -20°C—and sometimes -30°C. I wear wool pants, two sweaters, a windbreaker, a woolen cap, gloves with liners, wool stockings, and insulated boots. My fingers become stiff in minutes when I take off my gloves. Clothing is essential to staying alive, even in the daytime. The cold is no mere abstraction. How do kinglets, who are out there day and night and who are no bigger than the end of my thumb, maintain their body temperature near 43° to 44°C? They maintain a body temperature some 3°C higher than that of most birds. For added perspective, that’s 6° to 7°C higher than that of a healthy human—a temperature at which most of us would die of heat stroke.

Puffed out in its drab-olive garb, a hummingbird-size kinglet looks like a fuzzy little ball. The physics of heating and cooling dictate that small objects cool quickly, since every point within them is close to the surface where heat is lost. The smaller the animal, the proportionally larger is its surface area, which is the drain whereby it loses heat. How can these tiny birds possibly survive even five minutes on a winter day? I know they are there.

After searching in the woods only an hour or so on any morning, I can usually hear the thin tsees of a