Postnatal growth rate and gonadal development in circadian tau mutant hamsters reared in constant dim red light

The role of the circadian clock in the reproductive development of Syrian h amsters (Mesocricetus auratus) was examined in wild type and circadian tau mutant hamsters reared from birth to 26 weeks of age under constant dim red light. Testis diameter and body weights were determined at weekly interval s in male hamsters from 4 weeks of age. In both genotypes, testicular devel opment, subsequent regression and recrudescence exhibited a similar time co urse. The age at which animals displayed reproductive photosensitivity, as exhibited by testicular regression, was unrelated to circadian genotype (me an +/- SEM: 54 +/- 3 days for wild type and 59 +/- 5 days for tau mutants). In contrast, our studies revealed a significant impact of the mutation on somatic growth, such that lau mutants weighed 18% less than wild types at t he end of the experiment. Our study reveals that the juvenile onset of repr oductive photoperiodism in Syrian hamsters is not timed by the circadian sy stem.