Investigations of a foregut receptor essential to taste threshold regulation in the blowfly

The involvement of the foregut in the regulation of taste threshold by the blowfly, Phormia regina, was investigated by behavioural techniques. The sensitivity of flies to sugar was measured as experimental meals moved through their foreguts at known rates. It was demonstrated that the duration of threshold elevation is determined by the duration of foregut stimulation. Injections of solutes into the blood which slow crop emptying and therefore prolong foregut stimulation also prolong the duration of threshold elevation. Similarly, large meal size and high sugar concentration prolong foregut stimulation and therefore threshold elevation. Fructose, glucose, sucrose, sorbose, mannose, and sorbitol produce the same behavioural effect when acting via the postulated foregut receptor, indicating that it is probably not a chemoreceptor. Because solutions which differ osmotically by a factor of 10 also produce the same behavioural effect, the foregut receptor does not appear to be sensitive to osmotic pressure. Solutions which distend the foregut to the same extent produce the same behavioural effect, suggesting that the essential element in the foregut is a stretch receptor. A homeostatic mechanism for the regulation of food intake, crop volume, and blood sugar is presented.