Reducing GABA synthesis in the APL neuron enhances olfactory learning. (a) The flies carrying the GH146-Gal4 driver and the UAS-Gad-RNAi transgene exhibited an enhanced performance index (P.I.) after olfactory conditioning using 1, 3, or 12 electric shock pulses presented within a 1 min exposure to the conditioned odor. The P.I. of the Gad knock down group was not significantly higher than one control group, GH146/+, after 12 shocks of training. This was due to a ceiling effect as the P.I.s approached 1.0. (b) Expression pattern of mCD8-GFP driven by GH146-Gal4 alone (top row) or by the GH146-Gal4, Cha-Gal80 combined driver (bottom row). Both front and back views of the brains are shown, together with higher magnification images of the areas marked by squares in both views, illustrating the mushroom body lobes or the mushroom body calyx and the lateral horn (LH). The APL neuron cell bodies are marked by the arrows in the first panel of row 1. The punctate arc of fluorescence that is posterior to the vertical lobes shown in the second panel of row 1 (marked by the empty arrow head) is from an antennal lobe projection neuron previously characterized,. Note the loss of APL and mushroom body neuropil fluorescence by the introduction of Cha-Gal80. (c) Knock down of Gad by the combined GH146-Gal4, Cha-Gal80 driver failed to enhance learning, while knock down by GH146-Gal4 alone reproduced the enhanced learning shown in (a). n = 6 for each group under each condition. Means ± s.e.m.; *P<0.05; **P<0.01 (Fisher's PLSD). Scale bars represent 20 μm.