Type of Document	Dissertation
Author	Halberstadt, Adam Lee
URN	etd-08072006-142347
Title	Antomical characterization of serotonergic and nonserotonergic projections from the dorsal raphe nucleus to the vestibular nuclei.
Degree	Doctor of Philosophy
Program	Neurobiology
School	School of Medicine
Advisory Committee	Advisor Name Title Susan R. Sesack Committee Chair Barry D. Waterhouse Committee Member Carey D. Balaban Committee Member Daniel J. Simons Committee Member David A. Lewis Committee Member Robert H. Schor Committee Member
Keywords	rat serotonin 5-HT anterograde tracing
Date of Defense	2006-07-06
Availability	unrestricted
Abstract Preclinical and clinical evidence indicates that the serotonergic system regulates processing in the vestibular nuclei and in pathways linking balance function with emotional responses and affect. Previous studies conducted in this laboratory demonstrated that the serotonergic innervation of the vestibular nuclei is derived largely from the dorsal raphe nucleus (DRN), and revealed that the DRN also sends a nonserotonergic projection to the vestibular nuclei. The purpose of these experiments was to characterize the organization of the serotonergic and nonserotonergic components of the DRN projection to the vestibular nuclei. In Chapter 3, we describe retrograde tracing experiments that examined whether DRN cells send collateralized projections to the vestibular nuclei and central amygdaloid nucleus (CeA), regions involved in the clinical linkage between disorders of balance control and anxiety, and concluded that a subset of the serotonergic and nonserotonergic projections to the vestibular nuclei also project to CeA. Chapter 4 describes experiments with the anterograde tracer biotinylated dextran amine (BDA) that identified the terminal distribution of DRN projections within the vestibular nuclei. This study revealed that DRN projections descending in the ventricular plexus and the medial longitudinal fasciculus terminate within distinct vestibular terminal fields. In Chapter 5, BDA was used in combination with the serotonergic neurotoxin 5,7-dihydroxytryptamine (5,7-DHT) to selectively anterogradely trace nonserotonergic DRN projections to the vestibular nuclei. These experiments demonstrated that nonserotonergic DRN projections descend exclusively within the ventricular plexus and terminate primarily within the periventricular aspect of the vestibular nuclei. The purpose of the experiments in Chapter 6 was to map the distribution of serotonergic DRN terminals within the vestibular nuclei; 5,7-DHT was injected directly into DRN and silver staining was used to visualize the resulting pattern of terminal degeneration. It appears that projections from serotonergic DRN neurons terminate within both medial and lateral regions of the vestibular nuclei. Based on these findings, we conclude that major differences exist in the course of descent and termination patterns of serotonergic and nonserotonergic DRN projections to the vestibular nuclei, indicating that serotonergic and nonserotonergic cells give rise to distinct DRN projection systems that may selectively modulate processing within specific functional domains of the vestibular nuclei.
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