Date on Master's Thesis/Doctoral Dissertation

12-2025

Document Type

Doctoral Dissertation

Degree Name

Ph. D.

Department

Anatomical Sciences and Neurobiology

Degree Program

Anatomical Sciences and Neurobiology, PhD

Committee Chair

Bickford, Martha

Committee Member

Lundy, Robert

Committee Member

Krimm, Robin

Committee Member

McGee, Aaron

Committee Member

Fox, Michael

Author's Keywords

Saccade; eye movement; superior colliculus; motor cortex; sensory circuits; motor circuits

Abstract

Integration of sensorimotor information in the visual system has always been an intriguing topic to scientists, yet the subcortical sensory and motor circuits that are essential components of this process have remained elusive. In these studies, we used a blend of classical and contemporary techniques such as viral tracing, immunohistochemistry, optogenetics in-vitro whole cell electrophysiology, and electron microscopy in mice to characterize sensory and motor circuits of the superior colliculus (SC), a conserved visuomotor structure with connections with a wide variety of brain structures, including the thalamus. We focused on two SC cell types: visually responsive widefield vertical (WFV) cells that project to the pulvinar nucleus and premotor cells that project to the thalamus as well as the brainstem (via the predorsal bundle, PDB). Quantitative comparison of WFV projections to the pulvinar revealed that ipsilateral tectopulvinar terminals are significantly larger than contralateral tectopulvinar terminals as well as the overall population of terminals in the pulvinar nucleus. We also found that the Ntsr1-GN209 mouse line labels a subset of WFV cells that innervate the pulvinar with smaller terminals than the overall population of tectopulvinar terminals. However, we could not identify subtypes of WFV cells based on their projection patterns. Ultrastructural analysis of WFV dendrites revealed that 33% of their synaptic inputs are of retinal origin and that both retinal and non-retinal terminals target the distal dendritic tufts of WFV cells. To examine thalamic regions innervated by PDB cells, we focused on the centrolateral (CL) nucleus, utilizing the Pitx2-Cre line to examine PDB projections and the Rbp4-Cre line to label inputs that originate from layer 5 neurons in the motor cortex (M1). We found widespread overlap of ascending premotor SC and descending M1 projections to the CL. Ultrastructural analysis revealed that Pitx2 projections, and their dendritic partners in the CL are larger than their layer 5 M1 counterparts. Functional analysis showed that both terminal types converge on individual CL neurons, and their responses are depressed during high frequency photoactivation. Finally, we found that tectorecipient CL neurons display multipolar dendrites that vary in orientation, and project to M1 and the striatum.

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