Characteristics of activated neurons in the suprachiasmatic nucleus when mice become hypothermic during fasting and cold exposure

Cold defense mechanisms in mice are attenuated in the light phase during fasting, resulting in hypothermia. The present study examined whether specific neurons and areas in the SCN are related to the response. Mice were fasted over 47h or remained fed, during which they were placed at 20 or 27°C for 3h in the light or dark phases. Body temperature (T_b) was monitored. After the exposure, immunoreactive (IR) cells of cFos, arginine vasopressin (AVP), and vasoactive intestinal polypeptide (VIP) in the SCN were assessed. T_b at 20°C during fasting was lower in the light phase than in the dark phase. Both AVP/cFos-IR and VIP/cFos-IR cells increased when mice were at 20°C during fasting in the light phase. Such increase was observed in the central part of the SCN. These responses in the SCN may be related to the hypothermia in the light phase.