TH immunohistochemistry of adult wt (+/+) (A, C, and E) and ak/ak (−/−) (B, D, and F) ventral midbrain. Coronal sections through rostral (A and B), middle (C and D), and caudal (E and F) levels were stained. TH IR was strong in VTA, SN pars lateralis (SNpl), and A8 of both wt and mutant sections throughout the midbrain but absent in SNpc and SNr. ml, medial lemniscus.