9. An olfactory filter that is tuned to androgen-dependent pheromones and that facilitates the exploration/marking motivational mechanism; suppressed perinatally by androgen and activated in adulthood by estrogen.
Female muroid rodents respond specifically to the odors of conspecific males with an increase in exploration/marking behaviors. As in the case of the corresponding filter in males (site 8), it is apparently due to an interaction between an inborn olfactory filter tuned to androgen-dependent pheromones (figure 1, site 9), and the effects of conditioning or imprinting that activate or enhance the operation of the filter.
The increased exploration/marking by females in response to male odors occurs in many muroid rodent species. In the rat, adult females approach and investigate the odors of intact conspecific males more than those of castrated males or females (Brown, 1977; Carr et al, 1965). In the mouse, females are attracted to the odors of adult male preputial glands (Caroom and Bronson, 1971), locomote more in response to odors from intact males than odors from castrated males (Ropartz, 1970), and do more urine-marking in the presence of odors from intact males than odors from castrates (Maruniak et a1, 1975). In the hamster, the vaginal marking by proestrous females is greater in response to home cage odors of a male than to those of a female or a clean cage (Johnston, 1977a).
The facilitation of exploration/marking of muroid rodent females in the presence of male odors is usually dependent upon the presence of estrogen in the female. The enhanced approach, urine-marking, and sniffing of male odors by female rats is no longer seen after ovariectomy (Brown, 1977). Similarly, in the mouse, the differential attraction to male odors is enhanced following estrogen injections (Caroom and Bronson, 1971). However, in the case of the enhanced urine-marking by female mice in response to male odors, the behavior remains intact despite ovariectomy (:Maruniak et a1, 1915).
As far as I know there are no data that would indicate the location of the hypothesized olfactory filter in the female muroid rodent. Since the female's filter is parallel in many respects to that of the male which facilitates exploration/marking, one might begin the search by looking at the corticomedial amygdala. In females, there are estrogen-concentrating neurons in this structure, just as there are androgen-concentrating neurons in the male (Stumpf and Sar, 1976; Floody and Pfaff, 1974).
One would expect, given that this mechanism operates in females but not in males, that it is organized by gonadal hormones around the time of birth in the female. Most likely, its appearance in the male is suppressed by androgen at that period of development. As far as I know, however, the relevant studies to test this hypothesis have not been done,