The purpose of this proposal is to continue our investigation of the intrinsic neural organization of three nuclei in the medial hypothalamus. Specifically, we will focus our attention on the suprachiasmatic, paraventricular, and arcuate nuclei. We plan to use a combination of Golgi impregnations and immunocytochemistry to study the dendritic arbors, axonal ramifications, and synaptic communication between neurons resident in this part of the brain. Our first step will be to examine with computer-assistance the frequency and orientation of immunostained axons labeled with antibodies directed against peptides endodgenous to this part of the hypothalamus. Secondly, we will compare Golgi impregnated and immunocytochemically stained dendritic trees in different parts of each nucleus. Third, we will use double immunostaining at the ultrastructural level to determine what cells communicate with which other cells. Finally, we will use a combination of retrograde dye transport (fast blue) with immunocytochemistry to determine the location and specific peptide synthesized of cells which project to the neurohypophysis and median eminence. These studies are critical for our understanding the morphological substrates of hypothalamic function.