Daily variations of cerebral tyrosine in two inbred strains of mice and their F1 hybrids

The diurnal rhythms of endogenous cerebral tyrosine in 15 week-old mice from BALB/C/Orl and C57 BL/6/Orl strains and their reciprocal F1 hybrids, placed on a fixed 12/12 h dark-light schedule, were determined over a 24 h period in the fore-brain and hind-brain. Significant inter-strain differences in mean tyrosine levels were described in both structures. The main finding was that BALB/C exhibited a significant 24 h rhythm whereas a 12 h rhythm was found in C57/BL. In F1 hybrids, daily tyrosine rhythm appeared in both structures as a combination of the 2 parental ones. These findings support the suggestion that genetic factors may affect biological rhythms.