Thesis (Ph.D.)--Brown University, 2005. / Vita. Thesis advisor: Leon N. Cooper. Includes bibliographical references (leaves 138-150). Also available online.

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Synaptic plasticity is the activity-dependent modification of the strength of synaptic transmission. It is important for learning and memory. One of the mechanisms mediating synaptic plasticity at glutamatergic synapses is regulation of the postsynaptic α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA)-type glutamate receptor (AMPAR), which governs excitatory synaptic transmission. Perineuronal heparan sulfates (HS) have been implicated in controlling the open-state of AMPARs. Earlier findings in our laboratory showed heparanase expression and secretion of proheparanase by hippocampal neurons. Recombinant proheparanase triggered neuronal co-internalization of HS-proteoglycans and AMPAR subunits; this led to decreases in basal synaptic strength and long term potention of synaptic transmission at Schaffer collateral synapses of the hippocampus. The findings suggested proheparanase acting as a negative regulator of synaptic plasticity but the underlying mechanism remained unclear. We hypothesized that neuronal secretion of proheparanase is localized toperi-synaptic regions such that proheparanase mediates clustering of peri-synaptic HS-proteoglycans and AMPARs for internalization of the protein cluster. To address this, protein kinase C-mediated secretion of proheparanase was enhanced by phorbol ester treatment of hippocampal slices. Synaptosome preparations from the treated slices indicated enrichment in proheparanase, suggesting that proheparanase was directed to synaptic terminals for localized secretion. With use of the hippocampal synaptosomes, pull-down experiments targeting syndecan-3and heparanase found AMPAR subunits, both GluR1 and GluR2/3, indicating that they formed clusters in the peri-synaptic area. Heparitinase pre-treated hippocampal neurons in culture led to lower levels of internalized AMPAR subunits, both GluR1 and GluR2/3,upon recombinant proheparanase treatment. This suggested that HS moieties were critical for proheparanase-mediated AMPAR internalization. Recombinant proheparanase treatment of the neuronal cultures also led to decreases in glutamate-induced calcium influx, in terms of both the number of responsive cells and the change in intracellular calcium level, consistent with proheparanase-mediated neuronal internalization of AMPARs. Taken together, these results support our hypothesis and highlight dependence on the HS moiety for proheparanase-mediated neuronal internalization of AMPARs. We further investigated if proheparanase action at synapses can be found in other brain regions. The finding of neuronal heparanase expression in vestibular nucleus (VN) microexplant culture led us to study the role of proheparanase in synaptic plasticity in the VN. PKC activation enhanced heparanase expression in VN microexplant cultures. Recombinant proheparanase also triggered the uptake of HS and led to decreases in glutamate-induced calcium influxin VN microexplant cultures. These results support that proheparanase plays a role in synaptic plasticity in the VN but the effect and mechanism of action of proheparanase in VN neurons remain to be elucidated. This study demonstrated that neuronal secretion of proheparanase at synaptic terminals regulates AMPAR internalization, resets peri-synaptic HS levels and lowers calcium dependent signaling in responsive cells. This work has revealed a novel role of neuronal proheparanase in synaptic plasticity. / published_or_final_version / Biochemistry / Master / Master of Philosophy

Thesis (Ph.D.)--University of Texas at Dallas, 2007. / Includes vita. Includes bibliographical references.

Thesis (Ph.D.) - James Cook University, 2006. / Typescript (photocopy) Bibliography: leaves 174-200.

published_or_final_version / Physiology / Doctoral / Doctor of Philosophy

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--Open University.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

The neuroplastic changes in the motor representations within the face primary motor cortex (Face-M1) due to jaw and tongue motor alterations following the unilateral extraction of maxillary molars teeth have not been explored. The present study used intracortical microstimulation (ICMS) and recordings of evoked electromyographic responses to compare jaw (anterior digastric) and tongue (genioglossus) motor representations within the histologically defined Face-M1 one week post intervention across naive rats (n=6), rats that underwent anesthesia, right maxillary molar extraction after soft tissue manipulation (n=6) and rats that underwent anesthesia and soft tissue manipulation without extraction (n = 7). A small but significant anterior increase in the representation of the jaw and tongue motor representations was observed (oneway ANOVA p < 0.01, Bonferroni p < 0.01) in the contralateral Face-M1 one week following unilateral extraction of maxillary molars in rats.