Attempt to isolate with gas liquid chromatography chemical differences, between reward and frustrative nonreward odor emissions in the rat

Abstract

In a series of behavioral studies by Ludvigson and co-workers it became apparent that rats excrete odors following experimental reward and frustrative nonreward treatments. Through rigorous control procedures, it was demonstrated that rats will utilize these specific odor emissions to discriminate pending goal events, typically running fast in a straight alleyway in the presence of reward odor and slow in reaction to nonreward odor. The nature of the chemical message underlying this discrimination has remained unknown. It is not clear, for instance, whether distinctive chemical compounds are generated by these treatments, whether differential concentrations of animal scent are present or whether spatial distributions of odor result from the contrasting activity levels of animals on reward and nonreward trials. In an attempt to understand the chemical nature of animal odors arising from differential reinforcement, the technique of gas liquid chromatography was employed. A procedure which utilized headspace analysis of paper flooring in the alleyway, adsorption of its volatile substances on the porous polymer, Tenax GC, cold-trapping of these substances in a specialized pre-column and separation of compounds through 250' nickel capillary tubing was developed. These analyses revealed two peaks which eluted in significantly greater quantities on nonreward trials than on reward trials or with clean paper samples. Additional testing with animal urine and neutral subjects demonstrated a high degree of similarity among nonreward, urine and neutral subject chromatograms. Thus, on the basis of these preliminary data, which were the first attempts at such an isolation, it appears as though nonreward and neutral treatments result in urine excretion while reward treatments inhibit it or renders it highly inconsistent. Whether these stimuli comprise the key discriminative cues underlying the discrimination remains to be tested. However, the technique of headspace analysis of animal odors by gas liquid chromatography when used in combination with behavioral analysis, can provide a powerful tool for understanding odor communication in mammals. Several methodological issues pertaining to odor collection, the behavioral apparatus and chemical analyses of animal odor were identified and discussed.