Genetic studies of daily variations of first-step enzymes of monoamines metabolism in the brain of inbred strains of mice and hybrids. II. Daily variations of tyrosine hydroxylase activity in the locus coeruleus.

Daily variations of tyrosine hydroxylase (TH) activity in the locus coeruleus of 3 inbred strains of mice (BALB/c; C57BL6; C57Br) and the F1 hybrids obtained from BALB/c and C57BL/6 are discussed. Precise characteristics of the circadian rhythms were observed in each strain. They were found significantly different in two genetically pure parents (BALB/c and C57BL6). In their two F1 hybrids the daily variation of TH activity was similar to that observed in one of the parents (C57BL6). This strongly suggests selective and genetically controlled mechanisms of regulation responsible for the daily variation of TH activity in the locus coeruleus of mice.