Of particular interest were the three mutants in which conditioned aversion persisted, since this phenotype resembled what was observed when dopaminergic neurotransmission was blocked. The mutant with the most severe phenotype, 5-120, carries a P{GawB} (GAL4-containing P-element) insertion 125 bp 5’ of exon 1 of scabrous (sca)24 (Fig 7b). Quantitative RT-PCR showed that the 5-120 mutation significantly decreased sca expression to 55% that of wild-type controls (Fig 7c). Although sca5-120 mutants show conditioned aversion to ethanol when tested 30 min after training (Fig. 7c), they failed to switch from conditioned aversion to preference (Fig. 7d). sca5-120 mutants show normal sensitivity to acute ethanol exposure, place-memory performance, and olfactory-shock memory performance24, indicating that their failure to form associations between odorants and the rewarding effects of ethanol is not a result of a general inability to learn. sca5-120 mutants also showed normal olfactory acuity to the odorants used in this assay (Table 5), and did not show any gross morphological abnormalities of the mushroom body (Supplementary Fig. 6). An attempt to rescue the sca5-120 phenotype by over-expressing UAS-sca in sca5-120 mutant flies
