Fig. 6. Synaptic gradients in VPNs emerge through spatial and spatially independent mechanisms.
a–h, LC4: spatial mechanism. a, Relationship between dendritic map and spatial arrangement of synapses in the glomerulus for LC4 (for 300 pairs of top 25 postsynaptic (postsyn.) partners); rs, Spearman’s rank correlation coefficient. Error bands, s.e.m. b, Location of DNp02 and DNp11 postsynaptic sites in the retinotopic LC4 glomerulus (green dashed outline); black line, separation plane; DKS, two-tailed Kolmogorov–Smirnov test. Scale bar, 5 μm. c, Confocal projections of LC4 glomeruli and DN dendrites. Scale bars, 5 μm. d, Normalized DN dendritic centroid position within the LC4 glomerulus (n = 12 brains each; one-way ANOVA, Dunnett’s test, versus LC4 glomerulus centroid, ****P < 0.0001). e,f, Single anterior and posterior LC4 neurons with labelled presynaptic sites colocalized with DNp02 and DNp11 dendrites, alongside their EM reconstructions (bodyID 1907587934 and 1249932198). Scale bars, 5 μm. g,h, Distance (dist.) between dendrites of DNp02 (g) and DNp11 (h) and presynaptic sites in anterior versus posterior LC4 (n = 8 and 10 brains, respectively; two-tailed unpaired Welch’s t-test, ***P < 0.001). i–m, LPLC2: non-spatial mechanism. i, Relationship of input and output centroids (as in a) for LPLC2. j, Location of PVLP071 and PVLP076 postsynaptic sites in the LPLC2 glomerulus (statistics as in a,b), which lacks retinotopy. Scale bar, 5 μm. k, Single ventral and dorsal LPLC2 neurons with labelled presynaptic (presyn.) sites colocalized with the GF dendrite. Scale bars, 5 μm. l, Distances between presynaptic sites of single dorsal versus ventral LPLC2 neurons and GF dendrites, measured along three cardinal axes (n = 5 brains each; two-tailed unpaired Welch’s t-test, NS, P > 0.05). m, GF depolarization responses from localized activation of dorsal versus ventral LPLC2 and LC4 neurons expressing the P2X2 receptor. Left: representative GF responses (n = 5, one fly); individual (lighter-coloured lines) and averaged (darker lines) responses. Right: comparison of normalized average GF responses (resp.) to dorsal versus ventral VPN activation (two-tailed paired t-test; error bars, s.e.m., *P ≤ 0.05, ****P < 0.0001). Responses were averaged during the late response peak; see Extended Data Fig. 12c for quantification of the early peak. n, individual flies tested. A, anterior; P, posterior; D, dorsal; V, ventral; L, lateral; M, medial. All box plots show median and interquartile range.