Genetic determination of hypothalamic tyrosine hydroxylase activity in mice.

Tyrosine hydroxylase (TH) activity data obtained from hypothalamic tissue samples of highly inbred mouse strains with known differences in their mesencephalic TH activity (BALB/cJ, C57BL/6ByJ, CXBI/ByJ), F1 hybrids and F2 generations were subjected to quantitative genetic analysis. No differences were observed between C57BL/6ByJ and CXBI/ByJ strains, but highly significant differences were found in hypothalamic TH activity between BALB/cJ and C57BL/6ByJ strains. Segregating genetic factors could not be detected in the replicate (C57BL/6ByJ X CXBI/ByJ) F2 generations, while the presence of segregating genetic units was indicated in the (C57BL/6ByJ X BALB/cJ)F2 population. Estimation of minimum number of genes and Elston's non-parametric one-locus test reveal that more genes are responsible for strain differences of TH activity in the hypothalamus compared to the dopaminergic areas of the mesotelencephalon. The results indicate that the heterogeneity of the catecholamine neuronal populations and terminal fields in the hypothalamus is reflected by the complex nature of the genetic control of TH activity in this brain region.