Fragile X Syndrome is the most common form of heritable cognitive disability. It is caused by a genetic mutation that leads to a lack of protein from the FMR1 gene. This protein (FMRP) is used to regulate the translation of many other proteins, thereby leading to a wide range of effects. Because the origin of this disease is based on the lack of a single protein, an animal model with construct validity can be used to investigate the potential effects leading to the symptoms of the disease. Many studies have investigated the synaptic plasticity differences of CA1 pyramidal neurons between a mouse model of fragile X syndrome (KO) and a wild type mouse (WT). This study investigates the differences in firing properties of a CA1 pyramidal neuron between the KO and WT. Specifically, contributions of two ion channels are investigated: the Ca2+ and voltage activated potassium channel (BK) and the potassium channel (M) inhibited by the muscarinic acetylcholine receptor. This study finds some differences that warrant further investigation, including differences in spike timing, spike width and the initial rate of rise of an action potential. However, several areas of investigation yield subtle or confounding results, which may indicate that the CA1 pyramidal neurons affected by the lack of FMRP may make up more than one population. / text

published_or_final_version / Biochemistry / Master / Master of Philosophy

Angelman syndrome (AS), a genetic disorder occurring in approximately one in every 15,000 births, is characterized by severe mental retardation, seizures, difficulty speaking and ataxia. The gene responsible for AS was discovered to be UBE3A and encodes an E6-AP ubiquitin ligase. A unique feature of this gene is that it undergoes maternal imprinting in a neuron-specific manner. In the majority of AS cases, there is a mutation or deletion in the maternally inherited UBE3A gene, although other cases are the result of uniparental disomy or mismethylation of the maternal gene. While most human disorders characterized by severe mental retardation involve abnormalities in brain structure, no gross anatomical changes are associated with AS. Although it was previously believed that UBE3A was imprinted in a brain region-specific manner, primarily in the hippocampus and cortex, recent evidence indicates that there is a widespread knockdown of Ube3a protein throughout the AS mouse brain. As a result, it became necessary to evaluate AS human brain samples to verify the relevance and accuracy of the AS mouse model. It was determined that Ube3a is deficient throughout all major brain regions in humans with AS. The remainder of this dissertation work was focused on determining if increased UBE3A expression in the AS mouse brain would be sufficient to rescue the AS phenotype. The results show that adeno-associated virus-mediated UBE3A delivery is not effective in the AS neonatal brain. In the adult AS mouse brain, however, it increased Ube3a in the hippocampus to near wild-type levels. This was sufficient to rescue the associative fear conditioning learning deficit in the AS mouse and improve learning and memory in the Morris water maze. These studies are the first to demonstrate that increased protein production in the adult AS mouse is sufficient to improve the AS phenotype, indicating that the symptoms of AS are not necessarily embryonic developmental.

No description available.

Levels of retinoic acid (RA), the active metabolite of vitamin A, are tightly regulated throughout vertebrate CNS development by RA synthesising and catabolising enzymes. However, increasing evidence suggests that similar regulatory mechanisms exist in the adult brain to maintain RA at the optimum level. The hippocampus is one of very few regions where neurons continue to be born. Furthermore, the hippocampus is one of the regions in which RA regulates function. RA is synthesised in the region of the hippocampus by the enzyme, retinaldehyde dehydrogenase 2 (RALDH2), expressed in the adjacent meninges. CYP26B1 has been previously shown to be present by in situ hybridisation in the CA4/3 region between the two blades of the dentate gyrus. We hypothesised that a gradient was set up between the source and sink of RA in the adult hippocampus. To test this, we disrupted the balance using exogenous RA and using inhibitors to its catabolising enzymes. A reporter mouse was used to detect RA signalling and significantly more lacZ expression was detected in the infrapyramidal blade (closest to the meninges) compared to the suprapyramidal blade. Furthermore, administration of RA equalised lacZ expression between the two blades. RA is a potent differentiation agent; however, its effects on cell proliferation are less clear. In order to examine the direct effects RA on cell proliferation, an organotypic hippocampal slice culture technique was optimised and it was found that RA inhibits cell proliferation specifically in the dentate gyrus in a dose dependent manner. Taken together, this thesis provides insight for the first time into a parallel regulatory mechanism in the adult hippocampus to the embryo where RA is tightly regulated by its synthesising and catabolising enzymes and this mechanism is involved in the regulation of cell proliferation in the adult dentate gyrus.

Alcohol consumption during pregnancy is detrimental to the developing nervous system of the unborn offspring. The hippocampus, one of the two brain regions where neurogenesis persists into adulthood, is particularly sensitive to the teratogenic effects of alcohol. The present study examined the effects of alcohol exposure throughout all three trimester equivalents on the stages of adult neurogenesis. Prenatal and early postnatal alcohol exposure (PPAE) altered cell proliferation in adult but not adolescent animals and increased early neuronal differentiation without affecting cell survival in both age groups. The levels of brain-derived neurotrophic factor (BDNF) were not affected by PPAE in the dentate gyrus but were significantly decreased in the Cornu ammonis region of the hippocampus. These results might explain the functional deficits seen in this hippocampal sub-region. This study identified that voluntary wheel running increased cell proliferation, differentiation and survival as well as BDNF expression in both PPAE and control animals. / Graduate

No description available.

The mechanisms underlying the transition to seizure are still unresolved. Proposed mechanisms include excitatory GABAergic drive, loss of interneuron-mediated inhibition, and glutamatergic input potentiation. The objective of this thesis was to investigate the relative contributions of synchronized glutamatergic and GABAergic inputs and their functional roles during ictogenesis in the epileptic neonatal (postnatal days 6-12) mouse hippocampus, induced with 0.25mM Mg2+/5mM K+ perfusion. Simultaneous field and whole-cell patch-clamp recordings were obtained from CA3 stratum-oriens interneurons and pyramidal cells. The antagonists for GABAA and glutamate receptors abolished the preictal and ictal discharges, respectively, suggesting that the preictal state is mediated by the coherent discharges of GABAergic inhibitory interneurons, whereas the recurrent excitatory inputs are required for ictogenesis. Synaptic charge transfers underlying the synchronized discharges showed a dynamic change in the balance between the inputs: GABAergic currents markedly diminished by ictal onset whereas glutamatergic currents dominated at ictal onset and throughout the ictus.

The mechanisms underlying the transition to seizure are still unresolved. Proposed mechanisms include excitatory GABAergic drive, loss of interneuron-mediated inhibition, and glutamatergic input potentiation. The objective of this thesis was to investigate the relative contributions of synchronized glutamatergic and GABAergic inputs and their functional roles during ictogenesis in the epileptic neonatal (postnatal days 6-12) mouse hippocampus, induced with 0.25mM Mg2+/5mM K+ perfusion. Simultaneous field and whole-cell patch-clamp recordings were obtained from CA3 stratum-oriens interneurons and pyramidal cells. The antagonists for GABAA and glutamate receptors abolished the preictal and ictal discharges, respectively, suggesting that the preictal state is mediated by the coherent discharges of GABAergic inhibitory interneurons, whereas the recurrent excitatory inputs are required for ictogenesis. Synaptic charge transfers underlying the synchronized discharges showed a dynamic change in the balance between the inputs: GABAergic currents markedly diminished by ictal onset whereas glutamatergic currents dominated at ictal onset and throughout the ictus.

Recent anatomical investigations have revealed that the striatum is an intrinsically heterogeneous structure that forms multiple parallel circuits with different cortical areas. The present series of experiments investigated the possibility that such anatomical diversity may promote functional differences between subregions of the rat dorsal striatum. Using different versions of the water maze and radial arm maze tasks, evidence is presented showing that the medial and lateral subregions of the caudate-putamen make distinct contributions to behaviors guided by either ambient spatial or discrete cues. The findings support a multiple subsystems view of dorsal striatal function. Specifically, the lateral (sensorimotor-innervated) caudate-putamen may mediate the process of habit formation based on simple stimulus-response associations, whereas the medial (limbic-innervated) caudate-putamen may contribute to the cognitive/spatial control of behavior in competitive response situations. Further evidence is presented suggesting that the medial caudate-putamen is functionally related to the hippocampal system. Together, these structures may form a functional limbic circuit that mediates the serial processing of cognitive/spatial information.