Fig. 2. Loss of mesDA neurons in postnatal Ngn2 mutant mice. (A-M) In postnatal Ngn2 mutants, the number of Th-positive neurons was markedly reduced in both the SN and the VTA (A,B,D,E), and a population of Th-positive cells located close to the midbrain aqueduct was completely missing (F,G). Parallel sections stained for Vmat2 showed that no other cells present in the SN-VTA area displayed a DA phenotype (H,I). The Th-positive innervation of striatal and limbic forebrain areas was normal, although the target areas were reduced in size (L,M). The Ngn2 mutants were similar in size to wild-type mice at birth but showed a reduced weight gain postnatally (C), and the size of their brain was reduced by about 20% (J,K). Stars indicate the rostrocaudal levels used for cell counting. (N,O) Cell counts at P0 and P18 revealed a more than 50% loss of Th-positive neurons in the SN and VTA of the Ngn2 mutants. ^*P0.01 relative to wild type (N), and in wild type adn heterozygous (O) (Student's t-test). Scale bars: 500 µm.