Objectives: 

Siberian hamster (Phodopus sungorus) is a seasonal species responding to short day photoperiod (SD) by reducing feeding and lowering body mass 30-40 %. AMP-activated protein kinase (AMPK) is a key regulator of energy homeostasis in peripheral tissues and has a major role in the central control of food intake and body weight regulation. Recently it has been shown that activation of hypothalamic AMPK increases food intake and prevents torpor in hibernating species. Since AMPK could be involved in the seasonal long-term regulation of body weight, the aim of this study was to investigate the effect of short day induced adaptations of Siberian hamster on AMPK expression in hypothalamus, white and brown adipose tissues (WAT and BAT, respectively).

Materials: 

Hamsters were exposed to SD (8L/16D) at 10 °C for 10 weeks (winter acclimatization, WA). Control animals were housed in a long photoperiod (14L/10D) at 22 °C. Total and phosphorylated (pAMPK, active form) AMPK protein expression were determined with Western blot from hypothalamus, WAT, and BAT. In addition, plasma leptin levels were measured.

Results: 

WA group had 19 % lower body weight compared to controls. Hypothalamic AMPK concentration was reduced in WA animals, whereas no differences in pAMPK levels were detected. In BAT the expression AMPK was increased and pAMPK decreased after WA. No changes were observed in WAT.

Conclusions: 

Lower basal levels of total AMPK in the hypothalamus of the WA group indicates that AMPK is linked in the regulation of maintenance of the reduced food intake and low body mass in seasonal hamster. Elevated expression of total AMPK and down regulated pAMPK in BAT suggests that AMPK has a role in thermoregulation as animals switch between torpid and euthermic states.