Ground squirrel hibernation cycle
Fall active Full torpor
Body temperature (ºC)
40
35
25
30
20
15
10
5
Active bout
Spring active
Treatment extends survival in rats
0
0
30 60 90 120 150 180 210 240 270
October November December January February March April
Squirrel cycle During hibernation, the body temperatures of 13-lined ground squirrels yo-yo, leading to a repeated loss and restoration of blood
;ow that would be dangerous during the summer. Researchers hope a cocktail of compounds inspired by the squirrels’ ability to withstand this
cycle could buy time for people experiencing blood loss. When tested in rats with 60 percent blood loss, the treatment extended survival.
Minutes after 60% blood loss
SOURCES, FROM LEFT: M. T. ANDREWS/BIOESSAYS 2007; A.H. KLEIN E T AL/SHOCK 2010
excreting anything at all, though they too
stir occasionally.
The 13-lined ground squirrels hibernating in Cohn’s refrigerator go from
dormant to alert within minutes. “They
will all be as active as this guy,” Cohn
says, tapping a gloved finger on the cage
of a bright-eyed ground squirrel, sending it darting for cover. It’s soon out front
again, whistling curiously
at Cohn and his company.
By-products of the energy-producing
reactions — molecules called oxidants
or oxygen radicals — can damage the proteins, DNA and fats that make up cells.
If the damage is bad enough, the cells
will die and may contribute to tissue
damage or organ failure.
Ground squirrels are susceptible
to this type of damage in the summer,
After a few hours, the ani-
mal will curl into a tor-
pid ball with no regard
for Cohn, who is trying
to understand how the
ground squirrels maintain
muscles during torpor.
but come winter, hibernating squirrels become
impervious to the effects
of oxygen deprivation and
restored blood flow.
The ground squirrels’
up-and-down cycles cause
repeated loss and restoration of blood flow to parts
of the animals’ bodies, a
situation most humans
face only when something
has gone horribly wrong.
A hormone from black
bears maintained bone
health in rats at risk of
osteoporosis (treated rat
tibia at top, untreated
tibia at bottom).
To find out how the
squirrels handle the constant near-freezing and
thawing, Andrews and his
colleagues compared gene
activity in summer ground
squirrels with activity in
hibernating animals, during full torpor and bouts
of activity.
In people, blood clots,
heart attacks, strokes,
accidents or even sitting or
lying too long in one position may shut off blood supply to cells
that need it. Oxygen deprivation from
reduced blood supply can damage tissues and organs. But restoring blood flow
comes with its own problems, Carey says.
S. DONAHUE
The influx of oxygen-rich blood causes
little power plants called mitochon-dria to go wild churning out molecular
energy for the cell in which they reside.
The team found that
hibernating ground squir-
rels keep their bodies
going during the temper-
ature drop by fueling the
organs with breakdown
products from fat, rather than glucose as
summer ground squirrels do. During brief
active bouts, levels of a chemical called
melatonin shoot up in the ground squir-
rels’ blood. Melatonin is known mainly as
a hormone that helps regulate the body’s
daily rhythms, but it is also a powerful
antioxidant — just what ground squirrels
need to fight off damage from oxygen
radicals as their blood begins to surge.
Explore more
s Scandinavian brown bear project:
www.bearproject.info
www.sciencenews.org
February 25, 2012 | SCIENCE NEWS | 29
