L-Tyrosine-3-hydroxylase regulation in the brain: genetic aspects.

L-tyrosine-3-hydroxylase (TH) is the first and rate limiting enzyme in the biosynthetic pathway of catecholamine neurotransmitters (dopamine, noradrenaline, adrenaline). Implication of dopamine (DA) in various psychopathological phenomena, such as schizophrenia, has considerably contributed to the intensity of investigation of basic biochemical regulation of TH by activation and induction. Here we consider a third, constitutional (genotypic) aspect of regulation and present evidence that differences in mesencephalic (TH/SN), striatal (TH/CS), and hypothalamic (TH/HT) TH activity between virtually isogeneic strains of mice can be explained by segregating genetic factors. Biometrical genetic analysis of progenitor strains and their crosses indicated significant additive gene effects for TH/SN, TH/CS, and TH/HT, whereas dominance effects were statistically non-significant. A monogenic model of inheritance for TH/SN and TH/CS could not be rejected, while more than one gene was indicated for TH/HT. Significant positive phenotypic correlations were found in genetically segregating populations among mesencephalic, striatal and hypothalamic TH activities. This would suggest that some common genetic factors (or linked genes) are involved in the genetic variation of all three traits. A genetic selection experiment to elucidate the cellular and biochemical mechanisms underlying these variations is in progress.