Abstract

Glucose is the main source of energy for all living cells. In studies on mammals, an increase in blood glucose levels has been shown to inhibit feeding while a decrease in blood glucose enhances feeding. In order to determine if blood glucose levels might also affect ingestion in a mollusk, the common slug, Limax flavus, was used in the present study. Previous studies had shown that a fourteen-day fasting period produced the optimal food consumption in slugs. Also, following this deprivation period, blood glucose levels have fallen to approximately 25% of the level seen in freely feeding slugs. When 14-day fasted slugs were given an injection of 0.1M glucose to raise their blood glucose levels to that of fed slugs, they showed a feeding response similar to that of fed slugs. Slugs injected with mannitol, as a control for changes in blood osmolality, showed responses that were similar to other fasted slugs.

The glucose analog, 2-deoxy glucose (2-DG) , has been shown to stimulate feeding in non-deprived mammals by blocking glucose transport across the cell membrane, thus causing cellular glucoprivation. Tests were given to determine if 2-DG has an effect on the slug's feeding behavior. Various dosages of 2-DG (2.0, 1.0, 0.5 mg/g) were injected into fed slugs. These injections elevated blood glucose levels in a dose-dependent manner, indicating that cells in the slug were not absorbing glucose (i.e. glucoprivation). Following the injections, slugs displayed a dose-dependent increase in feeding, with the 2.0 mg/g dose increasing intake to that of a 14-day fasted slug. Control injections of distilled water had no effect on ingestion.

Taken together, these results indicate that blood glucose level exerts a regulatory influence on feeding behavior in slugs, and that this effect is at least as powerful as the effects seen in mammals.