How do inositol and glucose modulate feeding in Manduca sexta caterpillars?

Many species of caterpillar possess taste cells that respond exceptionally vigorously to the sugar alcohol myo-inositol, We examined the functional si gnificance of these inositol-sensitive taste cells in il Manduca sexta cate rpillars through an integrated series of electrophysiological and behaviora l studies. Neural recordings from all the gustatory chemosensilla revealed that M. sexta have only two pairs of inositol-sensitive taste cells, which respond strongly and selectively to myo-inositol, and two pairs of sugar-se nsitive taste cells, which respond relatively weakly to sugars (glucose and sucrose), Behavioral studies established that myo-inositol incites feeding and counteracts the inhibitory effects of aversive taste stimuli (e.g. caf feine) on feeding, but does not promote increased consumption once feeding has been initiated. In contrast, glucose and sucrose did not produce any ro bust effects on feeding. We failed to obtain any evidence of sensory inhibi tion between taste cells that responded to myoinositol and caffeine, indica ting that myo-inositol counteracts the inhibitory effects of caffeine on fe eding through a central gustatory mechanism. We conclude that sensory input from the inositol-sensitive taste cells, but not the sugar-sensitive taste cells, plays an important role in regulating feeding in M. sexta.