REPRODUCTIVE CAPACITY AND BEHAVIOURAL OESTRUS IN THE RAT BEARING HYPOTHALAMIC IMPLANTS OF SEX STEROIDS

Abstract

Neural implants of the sex steroids, estrogen, progesterone and testosterone in the female rat indicate that only estrogen will inhibit pregnancy in 100% of an experimental class. The most sensitive locus was the arcuate-mammillary nuclear regions of the hypothalamus. Although, progesterone in no way in hibits pregnancy and testosterone does so only very weakly both of these hormones appear to interfere with the normal process of parturition resulting in prolonged labor and death of mothers and fetuses. The mating behavior of the intact rat was altered only after estrogen implants. Large implants resulted in constant mating behavior and no pregnancies. Small implants in the mating center resulted in single matings from which pregnancies ensued and further mating did not occur. Thus in the intact rat the response of the mating center to estrogen was different than in the castrate animal, indicating the modifying influences of other hormones or nervous reflexes in the operational control of this brain region.