Biological sexual maturation in rats: Interaction among genetic line, sex, age, and body weight

Abstract

Interaction among genetic line, sex, age and body weight was studied for biological sexual maturation in rats. In female rats vaginal opening, first estrus, and duration of estrus cycle were determined. In male rats first presence of sperm was determined. Age and body weight at vaginal opening, first estrus or first detection of sperm were determined. Differences among five genetic lines were found on all measures of sexual maturation. The random bred control rats differed from the selectively bred lines of rats on majority of the measures, thus suggesting the influence of selective breeding on sexual maturation. The Maudsley lines selected for open-field defecation and Roman lines selected for two-way active avoidance learning showed different patterns of sexual maturation. Age was found to be crucial for the sexual maturation of female rats, whereas body weight was more important for the sexual maturation of male rats. This study is the first to investigate systematically the biological sexual maturation in live male rats and related sex differences. Findings suggest an important genetic component, and effect of selective breeding on the biological sexual maturation of rats.