Fig. S10.

Diagram summarizing the meso-diencephalic DA projections to the striatum and MLR in lampreys, salamanders, and rats. The findings from the present study and from our previous study in lampreys (22) are highlighted in red. In lampreys, DA neurons are located in the diencephalon. Some send ascending projections to the striatum and others send descending projections to the MLR (22). Occasional neurons were found to project to both structures, but were very rare (one or two cells per animal) and are thus not illustrated here. In salamanders, the ascending dopaminergic projections to the striatum originate mostly from the mesencephalon and to some extent from the diencephalon (15 and present study), whereas the descending projections to the MLR mostly originate from the diencephalon (present study). No DA neurons were found to project to both the striatum and MLR in salamanders. In rats, diencephalic and mesencephalic DA neurons are known to project to the striatum as confirmed here. Our data now show that many mesencephalic DA neurons project to the MLR and virtually all of them also send an ascending projection to the striatum.