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The procerebrum of terrestrial molluscs is an important processing centre for olfaction. While the physiology of the procerebrum is relatively well characterized, the procerebrum's structure and organization has not been previously investigated in detail. The goal of this thesis is to better characterize the structural organization of the procerebrum and to understand how it compares with other olfactory systems. / The morphology of the procerebral neurons in the snail Helix aspersa was investigated through intracellular injections of biocytin. The population of cells is heterogeneous, but no formal categorization of neuronal types was possible. The main difference among cells lies in the placement of the cells' neurites. Furthermore, contradicting previous results, certain neurons were found to have neurite projections outside the procerebrum, travelling as far as the contralateral cerebral ganglion. / To investigate if differences in sites of arborization represent functional differences, the distribution of synaptic contacts on labelled cells was studied using serial sections and electron microscopy. Neurons with different sites of arborization have distinct patterns of synapse distribution. Cells with arborizations in the procerebrum but not in the internal mass have large varicosities specialized for output. Cells that arborize in the internal mass or outside the procerebrum have mostly input synapses proximal to the soma and mostly output synapses in the terminal region of the neurites. These latter cells appear to transmit information from the procerebral cell body mass to other brain regions. The implications of these data are, firstly, that the procerebrum directly distributes processed information throughout the nervous system. Secondly, the procerebral neuron population may be divisible into two subgroups: intrinsically arborizing interneurons and projection neurons. / These results suggest a novel mechanism by which compartmentalization could be achieved in the procerebrum. Compartmentalization is believed to be important for processing olfactory information, is present in most olfactory centres but has not previously been described in the molluscan olfactory system. I propose that varicosities on the local interneurons generate foci of activity in the procerebrum which, in turn, activate specific subsets of output neurons, similar to what happens in other olfactory systems.

The morphology of C3, a motoneuron mediating the tentacle withdrawal reflex, was investigated in the snail Helix aspersa by intracellular injections of the tracers Neurobiotin and biocytin. Axonal projections were identified in the optic nerve, the olfactory nerve, the internal peritentacular nerve, the external peritentacular nerve, the cerebral-pedal connective and the cerebral commissure. A rare characteristic of the cell was the multibranching of axons in the neuropil and the exiting of this bundle of fibres into the cerebral-pedal connective. Dendritic arborizations were observed branching from the cell body, the axon hillock and the dorsal main axon. In addition, tufts of dendrites were seen to branch from the ventral axon. Based on its morphology, C3 is probably a central component in the avoidance behaviour, receiving sensory input at extensive dendritic sites and sending axons to a number of key effector sites to co-ordinate the chain of reactions that constitutes the snail's avoidance behaviour.

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Traumatic brain injury (TBI) affects 1.4 million people a year in the United States alone and despite the fact that 96% of people survive a TBI, the health and socioeconomic consequences can be grave, partially due to the fact that very few clinical treatments are available to reduce the damage and subsequent dysfunction following TBI. To better understand the various mechanical, electrical, and chemical events during neural injury, and to elucidate specific cellular events and mechanisms that result in cell dysfunction and death, new high-throughput models are needed to recreate the environmental conditions during injury. This thesis project focuses on the creation of a novel and clinically relevant single-cell injury model of traumatic brain injury (TBI). The implementation of the model requires the development of a novel injury device that allows specialized micro-interfacing functionality with neural micro environments, which includes the induction of prescribed strains and strain rates onto neural tissue, such as groups of cells, individual cells, and cell processes. The device consists of a high-resolution micro-electro-mechanical-system (MEMS) microtweezer microactuator tool that is introducible into both biological and aqueous environments and can be proximally positioned to specific targets in neural tissue and neural culture systems. This microtweezer, which is constructed using traditional photolithography and micromachining processes, is controllable by a custom developed software-automated controller that incorporates a high precision linear actuator and utilizes a luer-based microtool docking interface. The injury studies will include examination of intracellular calcium concentration over the injury time course to evaluate neuronal plasma membrane permeability, which is a significant contributor to secondary injury cascades following initial mechanical insult. Mechanical strain and strain rate input tolerance criteria will also be used to determined thresholds for cellular dysfunction and death.

Dendritic spines are the major sites for receiving excitatory synaptic inputs and play important roles in neuronal signal transduction, memory storage and neuronal circuit organization. Structural plasticity of dendritic spines is correlated with functional plasticity, and is critical for learning and memory. Visualization of the changes of dendritic spines at the ultrastructural level that specifically correlated with their function changes in high throughput would shed light on detailed mechanisms of synaptic plasticity. Here we developed a correlative light and electron microscopy workflow which combines two-photon MNI-glutamate uncaging, pre-embedding immunolabeling, Automatic Tape-collecting Ultramicrotome sectioning and scanning electron microscopy imaging. This method bridges two different visualization platforms, directly linking ultrastructure and function at the level of individual synapses. With this method, we successfully relocated single dendritic spines that underwent long-term potentiation (LTP) induced by two-photon MNI-glutamate uncaging, and visualized their ultrastructures and AMPA receptors distribution at different phases of LTP in high throughput. / Includes bibliography. / Dissertation (Ph.D.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection