RUI: Development and Maturation of Olfactory Centers in the Lobster: Influences of Serotonin and Adult Neurogenesis

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Beltz0091092The primary goals of these studies are to understand how serotonin, nitric oxide and life-long neurogenesis contribute to the development and maintenance of the olfactory pathway, using in vivo and in vitro methods. The lobster Homarus americanus is used as the experimental system because of the presence of giant serotonergic neurons that innervate the olfactory areas from early embryonic development, and because neurogenesis in the olfactory pathway persists throughout the animal's life. Prior studies have shown that serotonin influences the proliferation of newborn olfactory interneurons and promotes the branching of olfactory projection neurons. Additionally, newborn projection neurons transiently take up serotonin within the first few hours after their birth. There are 4 specific aims of our current studies: 1. The functions that are mediated by the transient serotonin uptake into newborn olfactory projection neurons will be defined using pharmacological agents that block the serotonin transporter, while testing for effects on proliferation and outgrowth of the olfactory interneurons. 2. Preliminary studies in the lobster suggest that nitric oxide (NO) also may be important in the development and maintenance of the olfactory pathway. The NO system will be defined by examining the temporal and spatial regulation of NOS in the brain using immunocytochemical methods. Further, NO levels will be altered experimentally in order to test for effects on the rate of neurogenesis among olfactory interneurons. 3. An in vitro system will be established to test hypotheses emerging from our in vivo studies. The goal of this effort is to successfully culture olfactory interneurons in order to perform three major experiments: to co-culture olfactory projection neurons with the serotonergic dorsal giant neuron, to introduce serotonin into cultures of projection neurons in order to visualize effects on branching, and to have the potential to directly manipulate the NO/cGMP pathway and observe whether cultured projection neurons are NO sensitive. 4. One test for our hypotheses regarding the importance of neurogenesis in the development and maintenance of olfactory centers, is to look at these issues in crustacean species that have determinate growth and a defined lifespan. We will therefore ask whether there is persistent proliferation in the olfactory areas of these species before, and then after, a terminal molt. These studies are relevant to developmental mechanisms in higher organisms because there are many parallels between the organization of olfactory pathways and processing even in phylogenetically distant species. In addition, these studies are exploring basic mechanisms involved in the development and maintenance of neural circuits, which may be applicable in a spectrum of other systems.