Odor-guided behavior in mammals.

The odor-guided behaviors selected for presentation in this paper encompass the major areas of animal behavior, and illustrate the important principal that complex relations exist between odor-guided behaviors, hormonal state, and experiential factors. Clearly, experiences with odors at several life stages results in profound influences upon later behaviors, including those related to eating, mating, fighting, and nesting. Interestingly, only brief social encounters are needed in rats to induce such phenomena as ultrasonic calling to conspecific estrous females or their odors, preferences for estrous over non-estrous odors, and the short-term modification of feeding behaviors. Although the mechanisms behind these intriguing phenomena are poorly understood, it is noteworthy that rats can learn relatively complex concepts on the basis of odors, rivaling even the ability of our own species to learn analogous tasks by visual cues. Despite the fact that close relationships can be demonstrated between odor-guided behaviors and variables such as endocrine state and sexual experience, caution is warranted in assuming that simple causal relations exist between such variables. In normally cycling women, for example, the correlation between olfactory sensitivity and plasma levels of estradiol during the menstrual cycle is relatively high; however, attenuation of the cyclical estradiol fluctuations by oral contraceptives does not eliminate the olfactory fluctuations, suggesting the relation is not causal. In house mice, social experience can override hormonal factors in their odor-guided urine marking and submissive behaviors. Thus, even though androgen titer usually correlates with such measures, a mouse made subordinant in a social encounter will not exhibit scent marking even when its circulating testosterone is maintained at a high level by a silastic implant. Further reason for caution comes from studies that suggest olfactory input influences the endocrine systems of sexually experienced and sexually inexperienced animals in different ways. For example, in sexually experienced male rats, anosmia decreases testosterone and estradiol levels and increases corticosterone levels, whereas in sexually inexperienced ones it has no significant influence on the levels of these steroids. Taken together, such observations suggest that the causal bases of a number of the odor-guided behaviors described in this paper are complex.(ABSTRACT TRUNCATED AT 400 WORDS)