Semester

Spring

Date of Graduation

2019

Document Type

Thesis

Degree Type

MS

College

Eberly College of Arts and Sciences

Department

Biology

Committee Chair

Gary Marsat

Committee Co-Chair

Andrew Dacks

Committee Member

Andrew Dacks

Committee Member

Sarah Farris

Abstract

Apteronotid weakly electric fish heavily rely on their electrosensory system for behaviors like spatial navigation, communication and prey capture. Since the behaviorally important information about their environment is contained in the spatial and temporal modulations of the electrosensory signal, efficient mechanisms to process this information with great fidelity are of the utmost importance. Efficient sensory processing often involves having multiple parallel processing streams so that each stream can specialize to treat signals with different properties. This strategy requires the response properties and neural dynamic to be adjusted in each pathway to implement different neural coding strategies. One of the neural coding strategies employed by the primary electrosensory area is to use bursts of spikes in response to specific temporal features of the signal - a coding strategy described as feature-extraction. Burst generation relies on dendritic voltage-gated sodium channels (Nav channels) expressed on pyramidal cell apical dendrites to support the active backpropagation of somatic spikes and the generation of depolarizing after-potentials. The presence and role of these Nav channels is well documented but variation in their expression across processing stream has not been investigated. Considering that many of the other ion channels expressed in these cells show differences across pathways, we hypothesize that Nav expression varies across the 3 electrosensory lateral line segments (lateral, centro-lateral and centro-medial segments; LS, CLS, CMS respectively) representing different processing streams. We used immunocytochemistry and confocal imaging of hindbrain slices to quantify differences in density and distribution of Nav channels in the apical dendrites of pyramidal cells. The dendritic Nav channel distribution follows a mediolateral gradient with lateral segment of the ELL exhibiting the highest density. We also found that dendritic Nav channel densities remain fairly constant across the proximal and distal locations of the apical dendrites across maps with CMS showing slightly higher Nav density in distal regions. We argue that the differences we observed may contribute to shaping the response properties and the specialization of each processing stream thereby contributing to the efficiency of the sensory system.

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