The proposed work consists of a cytological study of catecholamine- containing fibers and nuclei in the amphibian brain. A number of these have already been identified and shown to have cytological characteristics compatible with either secretory or sensory functions. These structures will be examined by fluorescence histochemical techniques coupled with electron microscopy and histological methods in order to establish their distribution and functional relation to other brain structures. Correlative physiological and pharmacological studies will also be undertaken to further clarify the functional roles of the structures examined, and embryological studies will be carried out in order to determine the time and place of origin of these catecholamine- containing elements and to correlate the development of their organelles ultrastructurally with the development of catecholamine fluorescence within them. Bibliographic references: McKenna, O.C. and J. Rosenbluth 1975 Golgi impregnation of a receptor cell in the toad hypothalamus. In Proc. Brain-Endocrine Interaction Symposium II The Ventricular System (D. Scott, ed.) Karger, Basel pp. 22-29; McKenna, O.C. and J. Rosenbluth 1975 Ontogenetic studies of a catecholamine-containing nucleus of the toad hypothalamus in relation to metamorphosis. Exp. Neurol. 46:496- 505.