EFFECT OF RESTRAINT STRESS ON FOOD-INTAKE AND BODY-WEIGHT IS DETERMINED BY TIME OF DAY

Three experiments were conducted to investigate the effect of restrain t stress applied at different times of the light-dark cycle on feeding behavior and body weight of rats. Sprague-Dawley rats were restrained for 3 h in restraining tubes either at the start or the end of the li ght cycle. There was a significant reduction in food intake on the day of restraint and no change in food intake during a 10-day recovery pe riod in either experiment. Reductions of food intake on the day of res traint were about the same for both restrained groups compared with th eir controls. When stress was applied Ln the evening, eating was inhib ited during the first 2 h after restraint, whereas in rats restrained in the morning, feeding was suppressed twice: during the 4 h after res traint and during the first 2 h of the dark cycle. Restraint induced a significant weight loss that was greater in the rats stressed in the morning. Neuropeptide Y (NPY) levels determined at the time of food su ppression for both experiments (beginning of the dark cycle) revealed an elevation of NPP in the paraventricular nucleus of rats stressed in the morning compared with other groups, but no difference in hypothal amic NPY mRNA expression. Expression of uncoupling protein mRNA in bro wn adipose tissue and leptin mRNA in epididymal fat, measured at the s tart of the dark period, was not altered by stress. There was an eleva tion of dopamine turnover in the hypothalami of rats restrained at, th e end of light cycle, but not those restrained in the morning. These r esults show that restraint stress has a greater effect on metabolism a nd energy balance when it is applied in the morning. Additional studie s are needed to elucidate mechanisms involved in the suppression of fo od intake 9 h after restraint.