NEURORECEPTOR MECHANISMS IN INSECT GUSTATION - A PHARMACOLOGICAL APPROACH

Taste chemoreception is essential for animals to select suitable foods . Gustatory sensilla concentrated on mouthparts, other external append ages, or the food canal are responsible for transduction of chemical s timuli into nerve signals that trigger behavioral acceptance or reject ion of a potential nutrient source. Insects have primary taste neurons containing both a dendrite and a direct axonal connection to the cent ral nervous system, whereas receptor cells and afferent neurons are se parated by a synapse in vertebrates. Taste receptor proteins have not been successfully purified or cloned from any animal to date. Our rece nt work with western corn rootworm beetles, Diabrotica virgifera virgi fera LeConte, implicates a gamma-aminobutyric acid (GABA)/glycine rece ptor in the perception of phago-stimulants and -deterrents. GABA stimu lates feeding in herbivorous members of four orders of insects. The me rits of this ligand-gated receptor model for chemoreception of 'sweet' , 'bitter' and other taste classes will be contrasted with those propo sed from vertebrate studies. Possibly one receptor gene family allows for insect perception of both food cues and potentially toxic non-host or environmental chemicals prior to their action at critical internal sites. Studies of taste receptors offer advantages over other insect neuroreceptors by their external location which simplifies ligand phar macodynamics and allows coupled use of behavioral and electrophysiolog ical methods to directly link receptor pharmacology with function.