Content of DSIP, enkephalins and ACTH in some tissues of active and hibernating ground squirrels (Citellus suslicus).

Seasonal changes in the amount of DSIP-like material have been measured in extracts from the brain of Citellus suslicus. 2. Analysis of extracts from the brain of deeply sleeping ground squirrels shows that the level of enkephalin-like material reliably increases while that of ACTH-like material decreases. 3. It is concluded that the opiate brain activation system is among the factors participating in the induction of hibernation in ground squirrels.