Changes in running-wheel activity, eating and drinking and their day/night distributions throughout the life span of the rat.

Running-wheel activity, eating and drinking of 39 male Long-Evans rats of various ages ranging from four to 33 months old, were recorded twice a day and total activity, and food and water intake per day and percentage nocturnal activity were studied. Running activity and food intake decrease as age advances and water intake first decreases from four months to 17 months of age and later increases proportionally with further increases in age. The percentage of nocturnal activity of the running-wheel decreases from 12 months of age proportionally with an increase of age; food and water intake also have this tendency. However, incidence of disappearance of diurnal difference in running activity, eating and drinking is quite low (7%, 32% and 25% respectively). Seven long-term ovariectomized Sprague-Dawley rats over 24 months of age show similar results to those with male Long-Evans rats. Reversal of the lighting schedule does not induce a phase shift of running activity, eating and drinking in two among 15 rats over 18 months of age, seven among 21 rats and four among 21 rats, respectively. Other rats over 18 months of age can recover their light/dark rhythm in a period not significantly different from rats below 13 months of age. The neuron number of the suprachiasmatic nucleus does not have significant correlations with percentage nocturnal activity in running activity, eating and drinking.