The weaver gene continues to target late-generated dopaminergic neurons inmidbrain areas at P90

To determine if lethal action of the weaver gene is more intense in late-ge nerated dopaminergic neurons in midbrain areas on postnatal day (P) 90 [H-3 ] thymidine autoradiography and tyrosine hydroxylase immunohistochemistry w ere combined in the same tissue section in homozygous weaver mice and norma l controls. The experimental animals were the offspring of pregnant dams in jected with [H-3] thymidine on embryonic days (E) 11-12, E12-13, E13-14 and E14-15. Neurogenetic timetables of dopaminergic neurons were different bet ween wild type and homozygous weavers in all midbrain areas analyzed. A sub stantial number of late-generated neurons in the substantia nigra pars comp acta and in the ventral tegmental area are missing at P90, in these dopamin ergic areas the loss is greater than at P20 indicating that neuronal loss i s progressive. The greatest loss is in the substantia nigra pars compacta, confirming the report of Bayer et al. [Exp. Brain Res. 105 (1995) 200] at P 20, while in the retrorubral field and the interfascicular nucleus late-gen erated neuron loss was less severe. These results furnish more evidence tha t dopaminergic neuron loss in homozygous weaver midbrain is a phenomenon li nked to development. (C) 2000 Elsevier Science B.V. All rights reserved.