Dissertations and Theses

Date of Award


Document Type




First Advisor

Jonathan Levitt

Second Advisor

Jay Edelman

Third Advisor

Hysell Oviedo


Ultrastructures, FIB/SEM, visual cortex


The purpose of this study was to analyze the size and ultrastructural characteristics of post-synaptic elements apposed to previously characterized pre-synaptic elements in layers 3 and 4 of the primary visual cortex (PVC). We are aiming to quantify a range of values for synaptic element morphologies as well as to correlate pre- and post-synaptic elements to find a set of rules that is prevalent in the visual cortex that can also be upheld in other mammals. We hypothesize that bigger pre-synaptic elements correlate to bigger synapses and bigger post-synaptic elements. We compared these two different layers because they receive synaptic inputs from different sources. Layer 4 is known to receive feedforward inputs from the thalamus, while layer 3 receives input from layer 4 as well as feedback inputs from higher cortical areas. We also analyzed the upper and lower regions of layer 4 independently because they receive different thalamic inputs. We used focused ion beam and scanning electron microscopy (FIB/SEM) to acquire and then analyze images of layer 3 and upper and lower layer 4 of the ferret primary visual cortex. In both layers there were more excitatory synapses on dendritic spines than on dendritic shafts. Presynaptic bouton volumes were much larger than their apposed post-synaptic targets in both layers. Layer 4 had the largest bouton volumes (specifically lower L4), presumably reflecting the large thalamic input to layer 4. Layer 3 had the largest post-synaptic targets. Synapse volumes (post-synaptic density) were similar in both layers but synapse surface area was bigger in layer 3. Bigger presynaptic boutons did not make bigger synapses (PSD); there was no correlation between pre-synaptic bouton size and PSD size. Larger pre-synaptic bouton volumes did not correlate with larger post-synaptic target volume or average cross-sectional area. Lastly, synapses in layer 3 occupied more surface area on post-synaptic targets than synapses in layer 4. Overall, these results suggest that morphological characteristics of elements in the PVC do not correlate with each other as well as there are differences between physical characteristics in layers of the same visual area.



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