Odortypes, defined as genetically-determined individually-distinct body odors, are strongly represented in urine and are specified in large measure by known genes unique to the Major Histocompatibility Complex (MHC). Social perception of odortypes in mice influences mate choice and maintenance of early pregnancy. For example, there is a general preference to mate with animals possessing non-self MHC type. Odortypes are thus salient factors in maintaining genetic diversity within species. Our object is to ascertain presently unknown chemical and physical properties of odorants that mediate MHC-regulated expression. Urine of age-and sex-matched congenic mice with defined genetic differences limited to the MHC and test systems such as the specially-designed Y-maze, which have been the mainstay of odortype research, will facilitate our research. Due attention is paid to implications that the extraordinary range and specificity of odortypes may depend largely on their recognition as compound odors, i.e., on the distinction of differential proportions of similar sets of odorants. Parallel chemical fractions of urine samples from MHC congenic mice will be biologically tested for presence of differential odortypes. The simplest fractions that are distinguishable in the bioassay will be compared by liquid and gas phase chromatographic techniques to locate differences in chemical composition. These differences will be specified by chemical identification of the compounds involved. Then mixtures of authentic compounds will be tested for activity in the behavioral assay. The possible role of nonvolatile compounds, especially MHC encoded proteins in urine, will also be investigated in this research. Knowledge of the chemical makeup of the individual odors is critical for understanding how MHC genes control odortype production.
