Figure 3. Connectivity of second-order nociceptive LNs is topographically arranged and consistent across larval development.

(A) Number of synaptic inputs onto LNs from mdIV terminals in the same segment. (B) Normalized dendritic synaptic input from mdIV terminals for each LN. (C) Fold-change in number of synapses and normalized synaptic inputs from mdIVs for each LN type. (D) Heatmap of normalized dendritic input from each mdIV terminal onto each LN for L1v (left) and L3v (right). Note that mdIV terminals are ordered clockwise from ventral left. (E) Normalized dendritic input from mdIVs onto LNs is strongly correlated across animals and developmental time points. Each data point corresponds to average normalized dendritic input from an mdIV type onto an LN type. (Pearson’s r = 0.77, p$<$0.001 to be different from zero). (F) Asymmetry between normalized mdIV synaptic input into left and right LNs, measured as coefficient of variation. Asymmetry in the L3v is significantly lower (p=0.006, paired two sided t-test). (G) Cartoon of the larval body wall viewed from posterior. The dendritic receptive field of each mdIV covers approximately 1/6 of the circumference of the animal. (H) Mean body wall orientation of mdIV input into each LN in the L1v (left) and L3v (right), computed as the average of unit vectors pointing at the center of each mdIV dendrite receptive field, weighted by number of synaptic inputs from that neuron. Arrow color corresponds to LN type. n.s. not significant; *p$<$0.05. **p$<$0.01. ***p$<$0.001.

Figure 3—figure supplement 1. Topographically structured feed-forward connectivity between mdIV-related LNs.

(A) Synaptic connectivity between LN cell types in the L1v (solid bars) and L3v (empty bars). Each bar plot depicts the number of synapses each cell of the post-synaptic cell type (rows) receives from all cells of the pre-synaptic cell type (columns). Cell types are labeled with spatial receptive fields from Figure 3H. Each cell type that was strongly connected in the L1v was again connected in the L3v. Strikingly, the dorsally oriented A09a targeted the dorsally oriented A02n and the ventrolaterally oriented A09c and A09l targeted the ventrolaterally oriented A10a, suggesting feed-forward topographic microcircuits. (B) Normalized synaptic connectivity between LNs. (C) Mean strength, measured as normalized synaptic inputs, for specific connections between cell types in the L1v and L3v. The number of data points is too small to make a statistical conclusion.