Motivational Systems in Muroid Rodents

The motivating stimuli of unfamiliar conspecific odors is supplemented by additional stimuli that make males and females more likely to engage in patrol/marking activity if the odors are from an individual of the opposite sex. The data may be explained in terms of three hypothetical sensory analyzers corresponding exactly to those postulated for the motivating stimuli of offense: 1) A sensory analyzer tuned to odors of androgen-dependent pheromones, activated by androgens, and inhibiting the patrol/marking motivational mechanism; 2) a sensory analyzer tuned to estrogen-dependent pheromones, activated by androgens, and facilitating the patrol/marking motivational mechanism; and 3) a sensory analyzer tuned to odors of androgen-dependent pheromones, activated by estrogen, and facilitating the patrol/marking motivational mechanism.

The first supplementary analyzer can explain why males show less patrol/marking to stimuli from intact (than from castrated) males. The phenomenon was first described in male M musculus who spend less time in the part of an arena containing urine from other intact males [Jones and Nowell, 1973a], an effect that depends upon an androgen-dependent pheromone secreted by the coagulating gland into the urine of the other male [Jones and Nowell, 1973c]. Similarly, males of R norvegicus approach and sniff odors from intact males less than from castrated males [Brown, 1977], and male Me auratus approach and sniff castrated males in preference to intact males [Landauer et al, 1977]. Other motor patterns of patrol/marking may be affected as well. Male R norvegicus show significantly less urine-marking on areas which have the odors of intact males than on areas with the odors of castrated males [Brown, 1977].

The second supplementary analyzer can explain why males increase their . patrol/marking behaviors to stimuli from females and especially from estrous females. Thus, male rats approach and sniff the odors of intact conspecific estrous females more than the odors of anestrous females, males, or castrates [Lydell and Doty, 1972; Carr, 1974]. Although the effect is enhanced by previous sexual experience [Lydell and Doty, 1972; Stern, 1970], it has also been found under certain conditions in experienced males [Carr, 1974]. Male M musculus show a preference for estrous female odors over anestrous odors, but only after sexual experience [Hayashi and Kimura, 1974]. Urine-marking in male rats [Brown, 1977] and male laboratory mice [Maruniak et al, 1974] is maximal in response to estrous female odors, and ventral-rub marking by male gerbils is maximal in response to female odors, although the estrous state has not been studied as a variable [Daly, 1977]. In Mi ochrogaster, sexually experienced males show a preference for estrous female urine and inexperienced males prefer estrous vaginal odors [Richmond and Stehn, 1976]. In Me auratus, the male is maximally attracted by the vaginal secretions of the female that are secreted on the day before estrus [Gregory et al, 1974; Johnston, 1977b]. The mechanism of this last finding must be questioned, however, in view of a report that male hamsters do not prefer receptive over nonreceptive female odors in an olfactometer test [Landauer et al, 1978].

The third supplementary analyzer can explain why females increase their patrol/marking behaviors to stimuli from males. In R norvegicus, 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 M musculus, 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 to odors from castrated males [Ropartz, 1970], and urine-mark more in the presence of odors from intact males than odors from castrates [Maruniak et al, 1975a]. In Me auratus, 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].