Genetic distortion of the balance between punishment and relief learning in Drosophila.

An experience with electric shock can support two opposing kinds of behavioral effects: Stimuli that precede shock during training are subsequently avoided as predictors for punishment, whereas stimuli that follow shock during training are later on approached, as they predict relief. We show here, for the fruit fly Drosophila, that upon the loss of white-function, the balance between these two kinds of learning is distorted in favor of punishment learning: white1118 mutants show stronger punishment learning and weaker relief learning, as compared to wild type flies. Thus, white1118 mutants establish, overall, more "negative" memories for the shock experience. This only concerns the mnemonic effects of the shock; the immediate, reflexive responsiveness to shock remains unaltered. Also, learning about reward is apparently unaffected, both in adult and larval Drosophila. Prompted by the proposed function of the White protein as the transporter for biogenic amine precursors, we probed the brains of white1118 mutants for the amounts of biogenic amines (octopamine, tyramine, dopamine, and serotonin) by using high-pressure liquid chromatography coupled to mass spectrometry. Using this method, we found, however, no difference between white1118 and wild type files for any of the probed amines. In any event, analyses of how the white1118 mutation affects the balance between punishment and relief learning should provide a study case of how heritable distortions of such balance can come about. Finally, the effects of the white1118 mutation should be considered as a source of confound when using white as the "marker gene" in behavior-genetic analyses of any sort.