Dissertations and Theses
Date of Award
2023
Document Type
Thesis
Department
Biology
First Advisor
Jonathan Levitt
Second Advisor
Hysell Oviedo
Third Advisor
Jay Edelman
Keywords
visual cortex, ultrastructure, neuroscience, cortical layers, mammalian, ferret, layer 4, layer 3
Abstract
The goal of this study was to determine differences in distinctive layers of mammalian primary visual cortex through analysis of their ultrastructural characteristics. Characterizing brain circuitry using 3-dimensional reconstruction of electron microscopy images, and subsequent ultrastructural analysis of axonal populations provides us with a better understanding of the connectivity of the neural circuits. By quantifying ultrastructural differences in axonal processes such as synaptic densities, types of synapses and their post-synaptic densities (PSDs), mitochondrial volumes, synaptic vesicle aggregates, dendritic targets, and bouton volumes, we aimed to understand whether differences in anatomical specializations among different cortical layers could underlie differences in function of cells in those layers. We used focused ion beam scanning electron microscopy (FIBSEM) to analyze layers 3 and 4 of the ferret primary visual cortex neuropil. We analyzed FIBSEM images using AMIRA software, which allowed accurate evaluation of neuronal tissues by generating 3-dimensional reconstructions of axonal processes and their targets from serial individual EM images of brain tissue. We used these reconstructions to identify and quantify various neuronal circuit elements. In lower and upper layer 4, half the population of boutons had volumes larger than 0.4 μm3
; while the majority of the boutons observed in layer 3 were smaller; however, this layer contained the largest measured boutons in this study. We found in all layers, most PSDs had an asymmetric profile, with fewer being perforated or symmetric. Boutons in lower layer 4 had 1 to 4 synapses, upper layer 4 and layer 3 had up to 3 synapses per bouton. Furthermore, all layers contained more boutons with single asymmetric synapses and mitochondria; however, layer 4 had more boutons that produced multiple asymmetric synapses than layer 3. In all layers, as bouton volume increased, mitochondrial volume increased, leading to a roughly constant proportion of bouton volume occupied by mitochondria. No trend was seen between synaptic area and bouton volume. In upper layer 4 and layer 3 volume occupied by vesicles docked near the presynaptic membrane increased as bouton volume increased. These findings create a more detailed description of visual cortex circuitry. This will contribute to understanding neural correlates of normal function in the brain, providing a basis to examine how connectivity is altered in aberrant populations, and a better comprehension of the etiology of neurological diseases.
Recommended Citation
Sawh, Anjelique, "Ultrastructural correlates of axons and synapses belonging to different circuits in ferret primary visual cortex" (2023). CUNY Academic Works.
https://academicworks.cuny.edu/cc_etds_theses/1114