Senior Honors Projects, 2010-current

Preferred Name - First Author

Christopher Dillingham

Date of Award

Spring 2016

Document Type

Dissertation/Thesis

Degree Name

Bachelor of Science (BS)

Department

Department of Biology

Advisor(s)

Mark L. Gabriele

Abstract

Processing of sound requires precise coordination of various levels of the auditory system. Auditory reflexes and orientation behaviors require interactions with other systems and modalities, emphasizing the importance of highly organized integrative circuits. The inferior colliculus (IC) is a unique midbrain structure in that it exhibits aspects that are specifically arranged for processing auditory cues, as well as regions that handle multisensory inputs and thereby exhibit an entirely different organization. While the central nucleus of the IC (CNIC) is primarily auditory and arranged tonotopically, the lateral cortex (LCIC) is multimodal and exhibits a unique array of modular and extramodular fields. The present study demonstrates the postnatal presence of LCIC modular zones through immunocytochemical and histochemical approaches that stain for the neurochemical markers glutamic acid decarboxylase (GAD), acetycholinesterase (AChE), cytochrome oxidase (CO), and nicotinamide adenine dinucleotide phosphate-diphorase (NADPH-d). Results are congruent with previous findings in adult models of rat and mouse (Chernock et al., 2004; Lesicko and Llano, 2015) and reveal a distinct pattern of discontinuous modules that span midrostrocaudal LCIC Layer 2. LCIC modules are present at birth (postnatal day 0), and remain distinct through the latest stage studied, P20. Distinct modular entities are most obvious in the coronal plane at midrostrocauldal levels of the LCIC, as adjacent modules exhibit cross-bridges caudally and merge in rostral extremes of the LCIC. Alignment of various stains in serial reconstruction experiments suggest each of these markers highlight the same LCIC modular set. Morphological similarities of neurochemcial modular staining with converging projection patterns from both auditory and somatosensory centers as well as guidance expression patterns of Eph/eprhin guidance molecules in nascent LCIC indicate a functional and 8 developmental significance of this architecture. The present study is the first to provide several markers of the developing LCIC modular field architecture. Proper understanding of LCIC modularity may serve a role in development of therapeutic treatments of somatic tinnitus that seemingly involve multimodal LCIC circuits.

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