Central excitation in the fruit fly (Drosophila melanogaster).

The probability of proboscis extension to a water posttest is increased by prior sucrose stimulation. This phenomenon, termed the central excitatory state (CES), first described in Phormia regina, has now been characterized in Drosophila melanogaster. Drosophila's CES (a) decays over time and (b) is a function of sucrose concentration. THe test for CES also measures water responsiveness, a component of proboscis extension operationally independent of CES. Control experiments confirmed that CES-dependent proboscis extension is not an artifact due to restimulation of sucrose residues and that the neural junctures involved are centrally located.