Olfactory and vomeronasal sensory inputs to the limbic system are essential for the initiation of mating behavior in male hamsters, but the neuroanatomical substrate for this chemosensory control of mating is unknown. This research is designed to determine the neuronal pathways which originate from olfactory terminal fields in the primary olfactory cortex, olfactory tubercle, entorhinal cortex, and anterolateral part of the corticomedial amygdala, and from the entirely segregated vomeronasal fields in the posteromedial part of the corticomedial amygdala and bed nucleus of the stria terminalis (BNST). Attention will also be directed toward elucidating the pattern of convergence of olfactory vomeronasal inputs with other afferents in the amygdala, frontal cortex, entorhinal cortex, and BNST. Efferent projections will be traced with autoradiography of transported proteins after injections or iontophoresis of tritiated amino acids, and with silver impregnation of degenerating terminals after destruction of cell bodies. The origins of afferent pathways to a brain area will be identified with injections or iontophoresis of horseradish peroxidase (HRP) which is localized histochemically after retrograde transport from neuron terminals back to their cell bodies. HRP will be used for identifying convergent inputs to a given region and also for refining information about efferent pathways. The significance of these central olfactory and vomeronasal areas will be studied in male hamsters with bilateral lesions of selected parts of the pathways.