Figure 6.

Shh is required for serotonergic RST axon pathfinding. (A) In E14.5 Shh^loxp/− hypomorphic mice, in which Shh expression was substantially downregulated, both axon length and the number of projecting serotonergic RST axons were greatly reduced compared to those in WT mice of the same age. Scale bar: 500 μm. White arrowheads indicate projecting serotonergic RST axons. (B) Quantification of the average length and density of serotonergic RST axons. Axon density was used as a measure of axon number. A significant reduction in the RST projection distance and density was observed in Shh^loxp/− hypomorphic mice. Axon lengths (mm) are presented as the mean ± S.E.M. WT: 12.878 ± 0.501; Shh^loxp/−: 1.236 ± 0.333. Axon densities are presented as the mean ± S.E.M. WT: 167.45 ± 10.247; Shh^loxp/−: 90.76 ± 5.489. Asterisks indicate values that differ significantly from those of the control groups (P < 0.05), and n indicates the total number of embryos quantified.