Fasting or systemic des-acyl ghrelin administration to rats facilitates thermoregulatory behavior in a cold environment.

Fasted rats place their tails underneath their body trunks in the cold (tail-hiding behavior), which is a thermoregulatory behavior. The aim of the present study was to investigate the effect of fasting and des-acyl ghrelin, a hormone related to fasting, on tail-hiding behavior and neural activity in the cold. Wistar rats were divided into 'fed', '42-h fasting' and des-acyl ghrelin groups. The rats received an intraperitoneal saline or 30-μg des-acyl ghrelin injection, and were then exposed to 27 °C or 15 °C for 2-h with continuous body temperature (Tb), tail skin temperature (Ttail), and tail-hiding behavior measurements. cFos immunoreactive (cFos-IR) cells in the insula, secondary somatosensory cortex, medial preoptic nucleus, parastrial nucleus, amygdala, and lateral parabrachial nucleus were counted in four segments: seg1, 2, 3, and 4 (bregma -0.36, -1.44, -2.64, and -9.00 mm), respectively. At 15 °C, Tb and Ttail were lower in the 42-h fasting group than in the fed and des-acyl ghrelin groups, and the duration of tail-hiding behavior was longer in the 42-h fasting and des-acyl ghrelin groups than in the fed group. The onset of tail-hiding behavior more advanced in the des-acyl ghrelin group than in the fed group at 15 °C. Only at the insula in seg3 at 15 °C, the number of cFos-IR cells was greater in the 42-h fasting group than in the fed group. Both the 42-h fasting and des-acyl ghrelin groups might modulate the tail-hiding behavior of rats in a cold, and a part of the insula might be involved this response during fasting.