Decreases in pineal melatonin content during the hibernation bout in the golden-mantled ground squirrel, spermophilus lateralis

The role of the pineal gland in modulating the rhythmic bouts of hibernation in the golden-mantled ground squirrel (S. lateralis) was explored by comparing pineal melatonin content in hibernating animals with that of euthermic animals at the same time of year. Significant decreases in pineal melatonin content were found in hibernating versus euthermic animals In addition, significantly lower values for pineal melatonin were observed in hibernating animals that were sacrificed in the late bout period, just prior to expected spontaneous arousal, as compared to hibernating animals that were sacrificed on the first day of their respective bouts. A strong correlation was evident between pineal melatonin content and the duration of the individual hibernation bout. These data suggest that pineal melatonin may be important in determining the duration of individual bouts of hibernation in this species.