Attractivity of male rats induced by estradiol and progesterone.

From the present study it appears that castrated male rats can be made attractive to intact males by estradiol benzoate plus progesterone (EB + P). For the determination of attractivity a residential plus-maze was used in which the resident male could choose between the company of the experimental male and that of an ovariectomized female with or without EB + P. In one experiment the males were castrated in adulthood; these animals were less attractive than the ovariectomized females with a similar hormone treatment. In a second experiment it was found that males that had been castrated at birth were as attractive as the ovariectomized females, after treatment with EB + P. These findings indicate that the attractivity that can be induced by EP + P in gonadectomized adult rats is somewhat but not wholly reduced if androgen is present during the neonatal period.