Nighttime Food Intake Research Articles

Reduction of food intake and body weight by chronic intraventricular insulin infusion

This study examined the effect of chronic infusions of insulin in one of three doses (5, 7.5 or 10 mU/day) into the third ventricle, on food and water intake and body weight in the rat. Solutions were infused via osmotic minipumps at a rate of 1 μ1/hour for seven days. The two highest doses of insulin produced a dose-related suppression of food intake and weight loss, which was greater than the effect produced by 5 mU/day or a control infusion of Ringers solution. The effect of 5 mU/day on food and water intake and body weight was similar to the effect of the control infusion. All groups treated with insulin decreased food intake during the day and night, although only differences in nighttime food intake were statistically significant. Ten mU/day also produced a significantly greater reduction in water intake than each of the other solutions. Weight loss in the animals infused with insulin could not be explained by a decrease in caloric intake alone. Food intake returned to normal in all groups by the end of a seven day post-infusion period, with recovery being slowest among the animals receiving the highest doses of insulin. All animals recovered body weight at approximately the same rate. These results provide further evidence for the view that brain insulin plays a role in the regulation of food intake and body weight.

Increased central serotonergic activity associated with nocturnal anorexia induced by Walker 256 carcinoma

The role of brain serotonin levels in Walker 256 tumor induced anorexia was investigated. Total and free plasma tryptophan, regional brain serotonin and 5-hydroxyindoleacetic acid were determined at night, and their relationship to nocturnal anorexia assessed by linear regression analysis. No significant difference in tryptophan, serotonin, or 5-hydroxyindoleacetic acid levels was detected between pair fed and tumor bearing rats exhibiting a 20% reduction of nighttime food intake. Tumor bearing rats with a 40% reduction in food intake had higher nighttime plasma free tryptophan and regional 5-hydroxyindoleacetic acid levels than their pair fed malnourished controls. These results indicate that increased plasma free tryptophan and elevated serotonin metabolism may not be the initial dysfunction responsible for nocturnal anorexia. However, it may contribute to the decreasing nocturnal food intake in severely anorexic tumor rats.

Naloxone reduction of stress-related feeding

The effects of the narcotic antagonist, naloxone, on various types of stress- related feeding in rats were examined. Tail pinch-induced eating of a palatable substance, and 3 hr daytime rat chow intake following acute 2-deoxy-D-glucose (2-DG, 400 mg/kg) administration or 24 hr food deprivation were significantly decreased by low doses (1 mg/kg) of naloxone. Night time food intake was likewise decreased by naloxone (4 mg/kg). In contrast, hyperphagia induced by insulin (10 U/kg) was not decreased by naloxone (0.06–16 mg/kg). These findings suggest that narcotic antagonists should be considered as possible anorexics selective for stress-induced eating, and that endogenous opiates may prove to be another significant factor involved in the control of food intake.