Meal patterns associated with the age-related decline in food intake in the Fischer 344 rat

We previously reported that aging Fischer 344 (F344) rats display a spontaneous, rapid loss in body weight associated with decreased food intake near the end of life. Here, we describe the specific changes in feeding patterns underlying this reduced intake. Nine male F344 rats, aged 25 mo, were monitored continuously until 7 days after the onset of spontaneous rapid weight loss (i.e., senescence). Regardless of age at death (25.5-32.5 mo), all senescent rats demonstrated a similar pattern of decreased food intake. They ate significantly smaller meals (g/meal) of shorter duration during spontaneous rapid weight loss compared with their period of weight stability (presenescence). However, no differences occurred in the number of meals eaten per day. Rapid weight loss had no effect on the rats' selection of preferred diets. Serum levels of the hormone leptin were not higher in the senescent vs. age-matched presenescent rats, nor was the incidence of common disease different in senescent animals. Moreover, the area of the pituitary-hypothalamus interface, measured to identify possible hypothalamic compression, was similar in the senescent rats and an age-matched, presenescent control group despite significantly greater pituitary size in the former. Our data show that simultaneous with rapid spontaneous weight loss, aging rats demonstrate significant changes in feeding patterns suggestive of earlier satiation. These feeding alterations do not result from loss of ability to select for palatable food, elevated serum leptin levels, specific pathology, or hypothalamic compression.