Senior Honors Projects, 2010-current

Date of Award

Spring 2015

Document Type

Dissertation/Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

Mark L. Gabriele

Abstract

A fully functional nervous system requires assimilation of sensory modalities to adequately interpret stimuli and determine appropriate motor responses. Two such regions responsible for multimodal integration are found in the auditory system, the cochlear nucleus (CN) and the inferior colliculus (IC). The lateral cortex of the IC (LCIC) in particular receives a diverse multimodal input array to discrete modular/extramodular zones. Staining for certain neurochemicals, including GAD, a marker for GABAergic neurons, reveal this compartmentalized LCIC organization. The present study utilizes fluorescent anterograde tracttracing techniques to determine the development of a somatosensory brainstem projection from the spinal trigeminal nucleus (Sp5), to multimodal aspects of the CN and LCIC. The results indicate somatosensory innervation of these structures parallels that of developing auditory afferents and that auditory-somatosensory convergence described in the adult in these areas is likely set prior to acoustic experience. Immunohistochemical GAD staining and expression studies for molecular guidance molecules (EphA4, ephrin-B2, ephrin-B3) reveal early LCIC modularity during the period of bimodal projection shaping. Such findings suggest an emergence of LCIC domains early in development that may in part be guided by Eph-ephrin protein interactions. Understanding the neuronal development of converging auditory and somatosensory maps is essential for understanding their presumed roles in suppression of self-generated sounds. Furthermore, a sound foundation for mechanisms guiding multimodal input array formation is necessary to improve noninvasive interactions that aim to reset maladaptive map plasticity underlying debilitating conditions like tinnitus.

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