Dopamine is a mediator of the stimulant properties of drugs of abuse, including ethanol, in mammals and in the fruit fly Drosophila. The neural substrates for the stimulant actions of ethanol in flies are not known. We show that a subset of dopamine neurons and their targets, through the action of the D1-like dopamine receptor DopR, promote locomotor activation in response to acute ethanol exposure. A bilateral pair of dopaminergic neurons in the fly brain mediates the enhanced locomotor activity induced by ethanol exposure, and promotes locomotion when directly activated. These neurons project to the central complex ellipsoid body, a structure implicated in regulating motor behaviors. Ellipsoid body neurons are required for ethanol-induced locomotor activity and they express DopR. Elimination of DopR blunts the locomotor activating effects of ethanol, and this behavior can be restored by selective expression of DopR in the ellipsoid body. These data tie the activity of defined dopamine neurons to D1-like DopR-expressing neurons to form a neural circuit that governs acute responding to ethanol.

The regular organization of the ommatidial lattice in the Drosophila eye originates in the precise regulation of the proneural gene atonal (ato), which is responsible for the specification of the ommatidial founder cells R8. Here we show that Rough eye (Roi), a dominant mutation manifested by severe roughening of the adult eye surface, causes defects in ommatidial assembly and ommatidial spacing. The ommatidial spacing defect can be ascribed to the irregular distribution of R8 cells caused by a disruption of the patterning of ato expression. Disruptions in the recruitment of other photoreceptors and excess Hedgehog production in differentiating cells may further contribute to the defects in ommatidial assembly. Our molecular characterization of the Roi locus demonstrates that it is a gain-of-function mutation of the bHLH gene amos that results from a chromosomal inversion. We show that Roi can rescue the retinal developmental defect of ato1 mutants and speculate that amos substitutes for some of ato's function in the eye or activates a residual function of the ato1 allele.