The main goals of this study are to 1) identify unique spatial patterns of neuronal activity in the olfactory bulb in response to odortypes expressed in urine and 2) clone and functionally characterize some of the olfactory receptors mediating odortype discrimination. Spatial distribution of urine-induced neuronal activity in the olfactory bulb will be determined by measuring increases in c-fos mRNA, a physiological marker of neuronal activity. Maps of neuronal activity elicited by urine odors will be constructed by imaging serial olfactory bulb c-fos in situ hybridized sections. Olfactory receptors win be cloned from the olfactory receptor neuron axons that project to the urine-responsive olfactory bulb glomeruli. Cloned olfactory receptors will be heterologously expressed using an expression vector cassette in HEK293 cells and tested for urine responsiveness by measuring increases in intracellular calcium. Elucidation of the molecular mechanisms responsible for individual odor signature discrimination will provide the foundation for further understanding human social interactions and will deepen our understanding of the strategies employed by neural systems in order to recognize and differentiate among complex sensory inputs.