The experiments proposed examine the development of the central relays in the olfactory system: the olfactory bulb, anterior olfactory nucleus and primary olfactory cortex. The olfactory system has been chosen for several reasons: its function is quite important in young mammals and its clear laminar organization facilitates quantitative studies of early brain growth. The projects employ the gray, short-tailed opossum Monodelphis domestica. Monodelphis pups are born in a very immature state, and, as the species lacks a pouch, are quite accessible to early experimental manipulation. These features, coupled with the slow growth of the species, offer a mammalian preparation uniquely suited for examinations of early developmental interactions. Issues addressed include: A) How do glomeruli develop? Information is passed to the central nervous system in regions known as glomeruli, each of which are thought to receive specialized information about different aspects of stimuli. Therefore, the developmental segregation of inputs into glomeruli may organize information flow throughout the entire system. Data exists suggesting both peripheral and central factors are responsible for glomerular organization. We plan to test these ideas by examining sequences of development of both neurons and glia. B) What are the basic patterns of growth and maturation in the central olfactory projections? Surprisingly little is known about the development of cellular morphology for most of the major neuron classes in the olfactory system. We plan to examine the development of cell shape using several new techniques. C) How important is bulb development in the formation of higher order structures? The fact that the bulb is one of the most precocious regions of the forebrain to develop has been used to suggest that there is a "serial induction" in the system, with the periphery inducing the bulb and the bulb then acting to organize subsequent relays. We will test this notion by removing the olfactory' bulb during early life and examining the subsequent growth of the higher processing areas. D) How important is afferent activity in the formation of higher order structures? Early sensory manipulations have been demonstrated to have far-reaching effects on the development of the olfactory bulb. Monodelphis, due to its extreme immaturity at birth, offers an opportunity to examine the role of functional activation throughout the entire formative period of the system. Together, the studies will provide important information about normal processes of brain development and their control by both internal and external factors.