SLC6A3 and Menkes disease: One possibility is that A9 TH+ neurons projecting to MD may exhibit extensive axonal branching, analogous to the large arboreal pattern described for the dopaminergic projection to the rat striatum and thalamus25, 26; thus, the loss of a few A9 neurons projecting to MD would result in a marked decrease in DAT‐ir axon length density (Fig. 5E,F).