Figure 4. Relationship between protein phosphorylation (upstream of rpS6 signal transduction) and squirrel body temperature during entrance into hibernation torpor.

Squirrels at an interbout stage usually enter into torpor within 24 h after arousal. Animals which start to re-enter torpor were identified, their body temperatures measured and they were subsequently sacrificed. Protein extracts from their brain cortex were made, the phosphorylation of various proteins upstream of rpS6 signal transduction were then examined by Western blot analysis. (A) Representative images of immunoblots. (B) Dot plots of body temperature vs phosphorylation levels in individual animals. Each dot represents an animal, and 24 animals altogether were analyzed. The phosphorylation levels were shown as relative to control (the average level of 7hrIA). Three groups (Tb=15–20°C, 20–25°C, >34°C) were chosen (shown in circles) for statistical analysis (student’s t-test).