Conditioned suppression in the rat as a behavioral assay for conspecific odor

Abstract

The influence of the information about the environment obtained through the olfactory system of mammalian species is an increasingly investigated phenomenon and is most often interpreted in a pheromone framework. Such investigations emphasize the conditions under which the pheromone is emitted, its mechanisms of production and release, the type of behavioral and or physiological change elicited in conspecific organisms as well as the actual chemical description of the substance. While the ultimate goal of the present study was the chemical description of conspecific odor of nonreward, perhaps a stress odor possessing pheromonal properties, the immediate goal was the development of an apparatus and behavioral task that would allow greater stimulus control and more reliable behavioral measurement of conspecific odors. An olfactometer was developed in the present study that suited practical constraints imposed by the nature of the odors studied, namely, those of rewarded, nonrewarded and neutral rats and rat urine. A conditioned suppression procedure that also suited constraints imposed by the nature of the stimuli was used as a behavioral assay. The results of a series of training and testing sessions in two experiments revealed that the design of the olfactometer and the conditioned suppression procedure allowed stimulus control and response measurement sensitive enough to train and measure a discrimination between conspecific nonreward odor and a no odor condition. Further tests showed that response suppression generalized to presentations of all conspecific odors used in the present experiments, including reward, neutral and urine odor. Subsequent experimentation attempted unsuccessfully to obtain differential behavioral sensitivity to odors of nonrewarded and rewarded conspecifics in the conditioned suppression procedure. Nonetheless, additional training showed that the conditioned suppression procedure was sensitive to a discrimination between nonreward odor and the perhaps more salient, odor of rat food pellets and that the experimental subjects could discriminate in a different procedure the odor of nonrewarded and rewarded donor rats. In the absence of extensive training procedures or the performance of naive experimental subjects trained from the outset to discriminate two conspecific odors, the present results do not show that the methods employed in these experiments provide an inadequate behavioral assay of conspecific odor. Rather, the results point to research aimed at further refining the methodology before the ultimate goal of chemically describing conspecific odors can be attained.