Seasonal weight gain is attenuated in food-restricted ground squirrels with lesions of the suprachiasmatic nuclei.

The role of seasonal hyperphagia in the genesis of prehibernation fattening was assessed in golden-mantled ground squirrels. One group of animals was fed ad lib throughout the weight gain phase of the annual body weight cycle (June-October); a group of neurologically intact animals and one of squirrels with brain lesions incorporating the suprachiasmatic nuclei (SCN) were fed amounts of food equivalent to quantities consumed prior to the body weight trough (May). Part of the seasonal increase of body mass is independent of increases in food consumption; intact animals fed ad lib or restricted to prefattening food intakes underwent similar increases in body mass and possessed equivalent amounts of abdominal white adipose tissue. Food restriction combined with SCN lesions attenuated seasonal weight gain and reduced abdominal fat mass. However, some of the brain-damaged squirrels still evidenced weight gain, a result supporting a previous conclusion that the SCN are involved in circannual body weight rhythm generation but their contribution to this process is not essential for continued rhythmicity in most individuals.