Some of us may put a few inches on over the course of winter, but not hibernating animals. They gain fat during the late summer ready for fuel when they stop feeding and begin hibernating. But what controls this dramatic switch from gorging to fasting? Gregory Florant from Colorado State University and his colleagues from the University of Arizona – Phoenix, USA, knew that AMP-activated protein kinase (AMPK) acts as an intracellular energy sensor and regulates food intake, so the team decided to test whether it may also play a role in regulating hibernator's eating habits (p. 2031).
Collecting nine yellow-bellied marmots in Colorado, the team kept the animals well supplied with food in a temperature regulated room as they simulated the onset of winter. By January all of the marmots had been fasting and hibernating for 3 months, despite being well supplied with food, so the team infused a compound that activates AMPK into the animals' brains to see what effect it had on them.
Amazingly the animals that received the AMPK activator began eating and some even gained weight, while the animals that were infused with a simple saline solution continued fasting and lost weight. Admittedly the team did have to relocate the marmots to a warmer room as they received the AMPK activator, but the saline treated animals also lowered their body temperatures and continued hibernating while the AMPK activated animals became active and stayed warm.
So a dose of an AMPK activator is able to switch on a hibernator's urge to eat, probably by activating the intracellular energy sensor AMPK, and the team are now keen to identify the neural pathways that regulate a hibernator's appetite.