The Tokay gecko is ideal for studies of the neural substrates of auditory communication in reptiles. Audition is very acute in the Tokay, rivaling the auditory sensitivity of some animals. Vocalization is well developed in the Family Gekkonidae. The reptilian brain may provide a model system for studying the neural mechanisms of auditory communication, which are not amenable to investigation in the more elaborated mammalian brain. Lizards are modern descendants of the reptilian lineage from which mammals evolved. Information gained from these studies may provide insights into the organization of mammalian systems of auditory communication. The proposed research will elucidate the ascending auditory pathways and the vocalization pathways. The torus semicircularis has been demonstrated, electrophysiologically, to contain a central nucleus involved in audition and a peripheral nucleus involved in vocalization. Selective silver techniques as well as the anterograde axonal transport of tritiated amino acids and retrograde transport of horseradish peroxidase will be used to identify the efferent and afferent connections of these nuclei. Investigations will be extended to diencephalic and telencephalic regions involved in audition and vocalization. Analyses of Golgi-impregnated material will be undertaken to identify possible sites of interactions between audition and vocalization. Such interactions underlie symbolic communication.