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Dissertation Defense: The development, cytoarchitecture, and circuitry of the ventral lateral geniculate nucleus

Graduate Student Dissertation Defense presented by the Fralin Biomedical Research Institute at VTC

Dissertation Defense: The development, cytoarchitecture, and circuitry of the ventral lateral geniculate nucleus 

Date: May 11, 2021
Time: 1:00 p.m.

About This Dissertation 

In the visual system, retinal axons convey visual information from the outside world to dozens of distinct retinorecipient brain regions. In rodents, two major areas that are densely innervated by this retinal input are the dorsal lateral geniculate nucleus (dLGN) and ventral lateral geniculate nucleus (vLGN), both of which reside in the thalamus. The dLGN is well-studied and known to be important for classical image‐forming vision. The vLGN, on the other hand, is associated with non‐image‐forming vision and its neurochemistry, cytoarchitecture, and retinothalamic connectivity all remain unresolved, raising fundamental questions of its role within the visual system. Sabbagh, mentored by Dr. Michael Fox, sought to shed light on these important questions by studying the cellular and extracellular landscape of the vLGN and map its connectivity with the retina. Using in situ hybridization, immunohistochemistry, electrophysiology, and genetic reporter lines, Sabbagh found that the two major laminae of vLGN, the retinorecipient externa`l vLGN (vLGNe) and the non‐retinorecipient internal vLGN (vLGNi) are composed of distinct types of neurons and have distinct extracellular landscapes. In vLGNe, the researchers discovered at least six transcriptionally distinct subtypes of inhibitory neurons that are distributed into distinct adjacent sublaminae. Using trans‐synaptic viral tracing and in vitro electrophysiology, we found that cells in each these sublaminae receive direct inputs from retina. Lastly, by genetically removing this visual input to the vLGN, Sabbagh found that the organization of these sublaminae is dramatically disrupted, suggesting a crucial role for sensory input in the cytoarchitectural maintenance of the vLGN. Taken together, these results not only identify novel subtypes of vLGN cells, but they also point to new means of organizing visual information into parallel pathways – by anatomically creating distinct sensory channels. This subtype-specific organization may be key to understanding how the vLGN receives, processes, and transmits light‐derived signals in the subcortical visual system.

 

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Ubadah Sabbagh

Ubadah Sabbagh

Graduate Student, Virginia Tech Translational Biology, Medicine, and Health

Graduate Research Assistant, Fox Lab, Fralin Biomedical Research Institute at VTC