α-Syn accumulation in dopaminergic neurons impairs visual response. (A) Steady-state visual evoked potential (SSVEP) was measured in flies raised in the dark and restrained in a Gilson pipette tip. The recording electrode was placed on the surface of the eye, with a reference electrode in the mouthparts. A full field blue light stimulus is provided from an LED. A pattern of 45 stimuli is provided, with different amounts of the 1F1 (12 Hz) and 2F1 (15 Hz) stimuli. (B) An example stimulus made up of 70% contrast at 1F1, and 30% contrast at 2F1 and its response. (C) The response (in B) is analysed by the Fast-Fourier Transform, revealing that the visual system responds to the supplied frequencies (1F1, 2F1) but also to their multiples (2F1, 2F2) and to the sums and differences (1F1 + 1F2; 1F2 − 1F1). Higher frequency harmonics are also seen, notably 2F1 + 2F2. (D) Genetic dissection60,61 shows that the majority of the 1F1 and 1F2 components come from the photoreceptors, the 2F1 and 2F2 come from the lamina neurons, and the 1F1 + 1F2, 1F1 + 1F2 and 1F2 − 1F1 from the medulla. (A−D) Modified after Afsari et al.60 and Petridi et al.37 (E) Flies expressing WT-α-Syn-EGFP under control of TH-Gal4 driver demonstrated a higher lamina neuron activity in the SSVEP, which is known to negatively correlate with levels of dopamine in the brain; *P = 0.03. (F) Photoreceptors of TH>WT-α-Syn-EGFP displayed no alteration in their response compared with control groups; ns—not significant P > 0.05, n = 6–11 flies/genotype. Mean ± SEM are shown, statistical analyses were performed using one-way ANOVA with Tukey’s multiple comparison post hoc test.
