Age-related impairment of food anticipatory locomotor activity in rats.

In rats of various ages (11 weeks to 24 months), restricted feeding was carried for 6 successive days and food was withheld completely on the 7th day to assess the effect of aging on food anticipatory activity. When feeding was restricted to a single meal at a fixed time of day (1330-1730), rats exhibited intense locomotor activity from 1-3 h before feeding time (prefeeding activity). This prefeeding activity was still detected on the fasting day. In addition, intense locomotor activity was observed for 1330-1730 even on the fasting day (mealtime-associated activity). Thus, mealtime-associated activity of the fasting day became an another good index for food anticipatory activity. These results indicate that the rats had come to anticipate the mealtime. Both prefeeding and mealtime-associated activities were similar at 11 weeks and 9 months of age, but they were impaired at 12 and 24 months of age. In 11-week-old rats, there was a negative correlation between the level of mealtime-associated activity and the daily duration of access to food, but this relationship was absent in 12-month-old rats. The present study suggests that aging strongly impairs the manifestation of food anticipatory activity in rats.