The Sweet, Sweet Smell of Diacetyl

Chemosensation in C. elegans Worms have a very simple chemosensory system composed of 32 neurons. Despite this simplicity, they are capable of detecting and appropriately responding to a Dallas, Texas 75235-9111 wide range of chemicals (Bargmann et al. Lucretius, one of the early Greek atomists, suggested have shown that chemoattraction to a number of mole-that all substances having odor gave off a vapor of tiny cules is mediated by three bilateral neuron pairs (Figure " atoms " ; different substances would release atoms of 1). The ASE neurons mediate attraction to water-soluble different size. He suggested that the nose distinguished molecules including sodium chloride, cyclic AMP, lysine, odors by having tiny pores of various sizes: odor was and biotin. Two other neuron pairs mediate chemoat-determined by which pores the atoms could pass traction to low concentrations of a variety of odorants. through. A recent paper from Cori Bargmann's group AWC mediates attraction to butanone, benzaldehyde, (Sengupta et al., 1996) has genetically defined the equiv-and alcohols, while AWA specifically mediates attraction alent of one of Lucretius's pores in an intact animal to diacetyl and pyrazine (Bargmann et al., 1993). Both system. These workers have correlated the loss of a AWC and AWA neurons can mediate attraction to thia-specific member of the seven transmembrane domain zoles. Single neurons can mediate responses to several receptor family with a specific olfactory deficit in the molecularly unrelated odorants; it is therefore likely that nematode Caenorhabditis elegans. worms express more than one odorant receptor per Chemosensation is a primary way organisms ranging olfactory neuron. Interestingly, pretreatment with one in complexity from bacteria to mammals perceive the odorant can specifically block responses to that odor-environment. Both vertebrate and invertebrate animals ant, but not to other odorants mediated by the same utilize olfaction to identify food, to avoid toxic or noxious neuron. Regulatory mechanisms must permit specific environments, and to recognize pheromonal cues. Un-desensitization of individual odorant signaling path-derstanding how odorants are detected, distinguished, ways, perhaps by phosphorylation of activated recep-and interpreted requires knowledge of the functional tors as occurs in homologous desensitization of the components. The recent discovery of a large family of ␤-adrenergic receptor (reviewed by Lefkowitz et al., genes encoding putative odorant receptors in the rat 1990). This could be important for the worm to follow a provided insight into how vertebrate olfactory systems concentration gradient—as the receptors desensitize, might recognize specific odors (Buck and …