(A) In situ hybridization experiments with the mdDA neuronal marker Th and the rostral mdDA subset marker Ahd2 in wild type and Chrna6−/− mice. The expression pattern indicated that during development there is no clear alteration in the morphology or number of mdDA neurons. (B) Schematic representation of the position of mdDA neurons and their projections in the adult brain (sagittal plane). The boxes A, B and C depict the areas shown in (C). Immunohistochemistry for Th in adult sagittal section in Chrna6+/+ and Chrna6−/− animals. In accordance to the absence of an early defect (A), the adult system does not seem to be affected in terms of neuronal field (mdDA, panels C), formation of the medial forebrain bundle (Axon bundles, panels B) and the target innervation in the striatum (Striatum, panels A). MF, mesencephalic flexure.