Genetic investigation of salt reception in Drosophila melanogaster

We have used mutants defective in gustatory behavior to investigate the neural basis of salt perception in the fruitfly Drosophila melanogaster. Salts elicit responses from two sensory neurons, L1 and L2, in each taste sensillum. Results from competition tests, selective proteoloysis, and mutant studies lead us to speculate that L1 possesses two sites (A and B) for the detection of monovalent ions. The A site accepts Na<SUP>+</SUP> ions alone, while the B site is less selective responding to Na<SUP>+</SUP>, K<SUP>+</SUP>, and Li<SUP>+</SUP>. The loss of the A-mediated response in the mutant gustE leads to a concomitant reduction in its behavioral attraction to NaCl. This suggests that the L1 neuron signals attraction to low concentrations of NaCl. This inference is supported by examining the kinetics of behavioral and electrophysiological responses in the wild type and in mutants that show enhanced attraction to salts