Animals at the extremes: Hibernation and torpor
Animals at the extremes: Hibernation and torpor

This free course is available to start right now. Review the full course description and key learning outcomes and create an account and enrol if you want a free statement of participation.

Free course

Animals at the extremes: Hibernation and torpor

6.6.2 Hibernation-induction trigger

Researchers have devoted much effort to the search for a possible blood-borne chemical messenger that might communicate a signal within the brain and to other body tissues, causing entry to hibernation. Serum from hibernating animals such as the woodchuck (Marmota monax; Figure 8), when injected into active animals, can induce torpor. Partly purified serum extracts are also able to induce hibernation-like behavioural changes in a variety of mammalian species. Chemical analysis of the serum extracts reveals two components, one of high molecular mass (M r = 88 000) which has a structure closely resembling a natural protease inhibitor, and the other of low molecular mass (M r < 5000) which is a member of the family of natural morphine-like or ‘opioid’ compounds. Pure samples of an opioid called enkephalin also induce hibernation in Colombian ground squirrels (Spermophilus columbianus). Dynorphin A is another opioid present in the ground squirrel brain. It acts at so-called delta receptor sites similar to those for enkephalin and rises during hibernation to a level 15 times higher than in non-hibernating euthermia, reaching an intermediate level in euthermia between bouts of hibernation. The origin of the different hibernation-inducing trigger components is not certain, but these observations point to the possibility that the blood circulation does contribute to the transmission of the signal to enter hibernation from one tissue to another. Opioids also have remarkable properties in inducing survival of cells in the brain and other organs under anoxic conditions. This discovery has led to an interest in the chemical induction of hibernation amongst medical researchers seeking ways in which to prolong tissue survival after trauma, or during and after transplantion.


Take your learning further

Making the decision to study can be a big step, which is why you'll want a trusted University. The Open University has 50 years’ experience delivering flexible learning and 170,000 students are studying with us right now. Take a look at all Open University courses.

If you are new to university level study, find out more about the types of qualifications we offer, including our entry level Access courses and Certificates.

Not ready for University study then browse over 900 free courses on OpenLearn and sign up to our newsletter to hear about new free courses as they are released.

Every year, thousands of students decide to study with The Open University. With over 120 qualifications, we’ve got the right course for you.

Request an Open University prospectus