NMDA receptor signaling is required for proper synapse formation, maintenance, plasticity and function. Dysregulation of the NMDA receptor has been implicated in pathophysiology of schizophrenia, which has an adult onset of symptoms. NMDA receptor deficient mice were utilized to assess the developmental consequences of NMDA receptor hypofunction. Locomotor activity was elevated throughout development; however, deficits in social interaction and working memory only manifest in adulthood and did not progress with age. Age-dependent deficits in neuron synapse biology were also detected; postsynaptic spine number was normal in juveniles, decreased post-adolescence, and progressively declined in adulthood. To investigate possible molecular mechanisms underlying the observed changes in spine number, protein levels of RhoGTPases and their downstream effectors were examined. Significant changes in Rac1 and downstream effectors were detected at different developmental stages. These studies provide clarification of the temporal sequence of events and mechanisms by which NMDA receptor dysfunction affects neurodevelopment.

No description available.

No description available.

L-glutamate is the predominant excitatory amino acid neurotransmitter inthe mammalian central nervous system. Prior aging studies have focusedprimarily on dopaminergic circuitry of the striatum, and data obtained studyingglutamate regulation in the striatum have been largely equivocal. Thesediscrepancies are due in large part to the limitations of microdialysis; while it isextremely sensitive to minute concentrations of analyte, it is lacking in terms ofthe temporal resolution necessary to study a neurotransmitter with rapid releaseand clearance kinetics such as glutamate. In order to address this matter, ourlaboratory has designed a ceramic-based multisite microelectrode with thecapability to detect and analyze fluctuations in extracellular glutamateconcentrations on a sub-second basis. These microelectrodes were utilized tostudy the phasic release and uptake dynamics of potassium-evoked glutamate inthe striatum of young (6 month), late-middle aged (18 month) and aged (24month) Fischer 344 rats. Our results showed a reduced glutamate clearancerate and an attenuated response to potassium depolarization in the corticostriatalprojections of aged animals in comparison to other age groups. In addition,average maximal glutamate release amplitudes were decreased in the striatumof aged animals. Pressure ejection of exogenous glutamate solution furtherconfirmed the decreased glutamate clearance ability of the aged striatum. Thesepotassium and exogenous glutamate data also highlighted a markeddorsoventral gradient in the striatum in terms of glutamate release and clearanceability. We further explored this phenomenon of age-related decreased glutamateuptake by coupling our in vivo technology with classical immunoblotting andbiotinylation techniques in order to investigate glutamate transporter regulation.Decreased glutamate clearance in the aged rats cannot be attributed to areduction in steady-state total transporter protein levels. Rather, our resultsindicate that reduced plasma membrane surface trafficking of GLAST in the agedstriatum may be partially responsible for this effect. Finally, we modified ourmicroelectrodes to study basal glutamate levels in the striatum of the aging,freely moving rat. This approach allowed us to study extracellular glutamateregulation free from the potential confounding variable of anesthesia. Our resultsdemonstrate that there is no significant alteration in basal glutamate levels inaging in the brain regions investigated. More importantly, this study validated theefficacy of the utilization of ceramic-based multisite microelectrodes for the studyof alterations in glutamate neurotransmission in the aging, freely moving rat, andit lays the foundation for future work correlating such changes with age associatedimpairments in motor function.

Epileptogenesis is the complex process of the brain developing epileptic acitivity. Due to the role of glutamate and the hippocampus in synaptic plasticity a dysregulation in glutamate neurotransmission and hippocampal dysfunction are implicated in the process of epileptogenesis. However, the exact causal factors that promote epileptogenesis are unknown. We study presynaptic proteins that regulate glutamate neurotransmission and their role in epileptogenesis. The presynaptic protein, tomosyn, is believed to be a negative regulator of glutamate neurotransmission; however, no one has studied the effects of this protein on glutamate transmission in vivo. Furthermore, evidence suggests that mice lacking tomosyn have a kindling phenotype. Thus, in vivo glutamate recordings in mice lacking tomosyn have the potential to elucidate the exact role of tomosyn in glutamate neurotransmission and its potential relationship to epileptogenesis. Here we used biosensors to measure glutamate in the dentate gyrus (DG), CA3, and CA1 of the hippocampus in tomosyn wild-type (Tom+/+), heterozygous (Tom+/-), and knock out (Tom-/-) mice. We found that, in the DG, that glutamate release increases as tomosyn expression decreases across genotype. This suggests that tomosyn dysregulation in the DG leads to an increase in glutamate release, which may explain why these mice have an epileptogenic phenotype.

I studied how glutamate receptor-mediated responses, spatial arrangements, intrinsic properties and molecular specificity of cells serve cortical functions. I tested whether two somatosensory submodalities in the primary somatosensory (SI) cortex can be distinguished by glutamate receptor involvement in vivo. Low-threshold responses evoked by innocuous stimuli had a short-duration and long-duration component. The short-duration responses were mostly mediated by AMPA/kainate receptors and the long-duration responses involved the additional recruitment of NMDA receptors. High-threshold responses evoked by noxious stimuli were unimodal and mediated by both AMPA/kainate and NMDA receptors throughout the entire response. During noxious stimulus trials, an increase in baseline activity in SI cortical cells was observed. I attribute the changes in baseline activity to cells in the medial thalamic nuclei, which project to the SI cortex and are involved in the affective-motivational aspects of nociceptive signalling. To gain insight into the influence of synaptic organisation of a well-defined cortical area, I studied in vitro whether the intrinsic properties of two anatomically well-defined nonpyramidal cells in the hippocampus can provide clues into the modulation of neuronal signalling. During a depolarising current pulse, O-LM and O-Bi cells were distinguished by their accommodation of action potentials depending on the early or late part of the response. Also, during a hyperpolarising current pulse, O-LM cells displayed a prominent voltage 'sag' as compared to O-Bi cells. Both cell types contain somatostatin and I showed that O-LM cells express the metabotropic glutamate receptor type 1α. Although O-LM and O-Bi cells have a similar somatodendritic position their different axonal arbours imply that they are involved in the feedback modulation of the entorhinal and CA3 glutamatergic influences, respectively. I also found that contrary to previous reports not only somatostatin but also vasoactive intestinal polypeptide containing cells express mGluR1α, which might facilitate their oscillatory responses. To relate the action potential discharge of specific cortical cell classes to behaviourally relevant network activity, I also sought to identify hippocampal cells following in vivo recording. Novel information was provided for both the temporal and anatomical properties of cells not recorded previously. In particular, a putative interneuron targeting nonpyramidal cell and backprojection cell was recorded in relation to theta field events. A novel nonpyramidal projection cell was recorded in relation to sharp wave field events. A remarkable specificity was found in the dendritic and axonal patterns of these cells. The results show that distinct types of glutamate receptors are differentially involved in cortical function. The intrinsic properties and expression of mGluR1α in particular is highly specific in distinct nonpyramidal cell classes.

Thesis (Ph.D.)--University of Tennessee Health Science Center, 2007. / Title from title page screen (viewed on June 20, 2008). Research advisor: Jeffery D.Steketee, Ph.D. Document formatted into pages (xi, 89 p. : ill.). Vita. Abstract. Includes bibliographical references (p. 71-89).

Thesis (M. Sc.)--Carleton University, 2008. / Includes bibliographical references (p. 116-125). Also available in electronic format on the Internet.

Thesis (doctoral)--Freie Universität Berlin, 1979.

Universiẗat, Diss., 2002--Bielefeld.