UC San Diego SearchMenu
2013 Research Showcase
NB Abstracts
Abstract Title : Assessing the Effect of PTEN/Nogo Deletions on Axon Regeneration After Spinal Cord Injury in Mice
Abstract : Spinal cord injury (SCI) is mainly characterized by damage to axonal tracts in the central nervous system (CNS), which often leads to a loss of locomotor function and permanent paralysis from the site of injury downward. The CNS, unlike the peripheral nervous system, does not show regeneration after injury. This lack of regeneration is believed to be the result of complex neuronal extrinsic and intrinsic mechanisms. Nogo, a myelin-derived axon growth inhibitor (extrinsic factor), has been previously shown to inhibit axon growth in vitro, and its deletion to promote axon sprouting (growth of uninjured axons) in the mice spinal cord. PTEN is a neuronal intrinsic molecule that negatively regulates the mTOR pathway. It has been demonstrated that deletion of PTEN in cortical neurons leads to the upregulation of the mTOR pathway and promotes significant sprouting and regeneration of corticospinal axons in mice. We examined the possibility that the removal of these two inhibitors of axon regeneration, Nogo and PTEN, in the CNS could lead to a further increase of axon regeneration and ultimately to functional recovery after SCI in mice. In order to examine axon regeneration (regrowth of injured axons) in the corticospinal tract (CST), we used the dorsal hemisection injury model. The behavioral assays used to quantify the amount of functional improvement after dorsal hemisection were the ladder rung, open field test, catwalk, and rotarod. Apart from functional improvement, we also assessed anatomical axonal growth by using a specific neuronal tracer to see if we could find correlations in functional recovery and anatomical axonal growth among the different genotypes. A correlation between this data would lead us to conclude whether functional recovery was a result of axon regeneration.
Abstract Title : Local dentate circuits support spatial working memory regardless of position along the longitudinal hippocampal axis
Abstract : The dentate gyrus (DG) is the initial site of information processing in the hippocampus. Previous studies have shown that the rostrodorsal DG (rdDG) is essential in the rat's ability to discriminate similar spatial locations. In addition, the DG has been shown to support spatial working memory (WM). However, the question of how the DG supports spatial WM remains unclear. Recent results in our lab have demonstrated that spatial WM performance in rats is not selectively supported by a specific region along the longitudinal axis of the DG (Piatti et al., SFN 2012). Rats with 60 80% volume reduction of the granule cell layer on the entire longitudinal axis due to selective lesions had impaired spatial WM on an eight-arm radial maze task. However, lesions with corresponding % volume reduction specific to the rdDG or the caudoventral DG (cvDG) did not impair spatial WM, suggesting a mechanism independent of the anatomical location of the DG could support WM. To further elucidate the mechanism responsible for WM in the DG, we investigated whether a compensatory activity of neurons existed in the remaining DG of the rdDG or cvDG lesion rats. Using immediate early gene c-fos to label active neurons in the DG granule cell layer, we quantified the number of active neurons for each group (control, rdDG lesion, and cvDG lesion) through stereological methods. The fraction of c-fos labeled granule neurons in the lesion groups did not change compared to control (n = 4 per group, n.s.). Thus, cvDG or rdDG alone could support WM without compensatory activity of granule neurons, which implies the local dentate circuits with the same level of sparsity in the remaining DG are functionally intact to support WM.
Abstract Title : The Role of Ubiquitin in Neurotransmitter Receptor Trafficking
Abstract : Ubiquitination is most commonly associated with protein turnover via the proteasome. However, ubiquitination of membrane proteins has emerged as a form of post-translational modification to regulate trafficking. Short-chain ubiquitination targets membrane proteins for internalization and subsequent endocytic sorting. Ubiquitinated proteins are either targeted to the lysosome for degradation, or they are deubiquitinated and recycled back to the membrane. Our lab studies how ubiquitination of neurotransmitter receptors controls their trafficking at the synapse. Because the loss of surface neurotransmitter receptors is observed in cell culture models of Alzheimer?s Disease (AD), we set out to investigate if an increase in ubiquitination of neurotransmitter receptors is involved in that mechanism. We treated cultured neurons with Aβ, a peptide important in the development of AD, and demonstrated loss of neurotransmitter receptors at the surface of the neuron. We, then, asked if Aβ treatment causes an increase in ubiquitinated neurotransmitter receptors. Our goal is to better understand the underlying mechanisms that contribute to the development of neurodegenerative diseases like AD.
Abstract Title : Muscle-specific excision of polyglutamine-expanded androgen receptor rescues survival and neuromuscular deficits in a mouse model of X-linked spinal & bulbar muscular atrophy
Abstract : X-linked spinal & bulbar muscular atrophy (SBMA) is a rare neuromuscular disorder characterized by adult onset proximal muscle weakness and lower motor neuron degeneration. SBMA patients display signs of androgen insensitivity, including gynecomastia, reduced fertility and testicular atrophy. SBMA is caused by a CAG repeat expansion (>36) in the Androgen Receptor (AR) gene. Pathological findings include extensive loss of motor neurons in the anterior horn of the spinal cord and brain stem motor nuclei, as well as accumulation of polyglutamine (polyQ) expanded AR in intranuclear inclusions. Muscle pathology is characterized by atrophic fibers, fiber type grouping and pyknotic and central nuclei. Despite major motor neuron loss, several studies suggest an important role for muscle polyQ-AR in SBMA pathogenesis, and work in other motor neuron disorders strongly suggests that non-neuronal cells help maintain neuronal function and can thus contribute to neurological disease. To better understand the role of cell versus non-cell autonomous degeneration in SBMA, we developed a new BAC transgenic mouse for SBMA featuring a floxed first exon to permit cell-type specific excision of the mutant human AR gene carrying 121CAG repeats (BAC fx121AR). Expression levels of the AR transgene were comparable to endogenous mouse AR levels in CNS, spinal cord and muscle. These mice develop a neuromuscular disease phenotype, including shortened survival, weight loss, grip strength deficits and reduced stride length. Pathology analysis revealed axonal disorganization and reduced axonal diameter in lumbar motor roots compared to non-transgenic littermates. Muscle histopathology showed generalized fiber atrophy as well as increased NADH staining, suggestive of muscle degeneration and fiber type grouping. To determine the contribution of muscle-specific expression of polyQ-AR, we crossed the BAC fx121AR mice to a human skeletal actin (HSA) promoter-Cre recombinase mouse. We confirmed skeletal-muscle specific excision of polyQ-AR in bigenic (fx121AR/HSACre ) mice, with polyQ-AR levels remaining unchanged in spinal cord. Muscle-specific excision in fx121AR/HSACre mice completely rescued the shortened survival observed in fx121AR mice, accompanied by significant improvement in all neuromuscular phenotypes. Muscle and lumbar root analysis also revealed significant rescue of observed pathologies, suggesting that expression of mutant polyQ-AR protein in muscle is mainly responsible for the systemic and neurological phenotypes observed in fx121 AR SBMA transgenic mice. Our results suggest that muscle targeting may be a viable option for SBMA therapy development.
Abstract Title : Kainate Impairs Pattern Separation and Affects Dentate Gyrus Function in Long Evans Rats
Abstract : The hippocampus is the brain region responsible for encoding episodic memory (the 'where, what, and when' of memories). Within the hippocampus, the dentate gyrus is the sub-region that specifically encodes pattern separation, the ability to distinguish or 'separate' very similar memories from one another. Previous research has shown that during epilepsy, one finds neuronal reorganization in the dentate gyrus that may impair pattern separation in epileptic patients. In this set of experiments, we attempt to induce epilepsy and dentate gyrus reorganization through subcutaneous injections of kainite in male Long Evans rats until they presented class IV or class V seizures for one hour. Rats were subsequently monitored for seizures in the months after the initial induction, and no class IV or class V seizures were recorded in most rats. Control and induced rats up to 6 months of age were trained on an 8 arm radial arm maze for up to 2 weeks in a pattern separation task. The task required rats to remember the location of a food reward and choose the correct arm when presented with a choice between adjacent, very similar arms. Rats induced with kainite injections showed a significant impairment compared to control rats. Histological analysis was then performed to measure corresponding neuronal reorganization in the groups and compared to the results of the behavior.
Abstract Title : The Role of the Basolateral Amygdala in Mediating Anticipatory Negative Contrast in Binge-like Intake
Abstract : The purpose of this project is to study the hedonic and rewarding mechanisms engaged during palatable food intake and binge-like eating in hopes of contributing to the understanding of binge eating disorders and obesity. Previous studies have shown that when given intermittent access to palatable food, rats develop binge-like hyperphagia of palatable food and undereating of standard chow that occurs from having predictably expected access to palatable food succeeding chow, termed anticipatory chow hypophagia. The binge model adopted involves a 2-hr food deprivation period, followed by 10-min access to chow, and succeeded sequentially by 10-min access to either palatable food (chocolate flavored diet) or chow. The rats were presented a 10-min cue prior to the first feeder to signal imminent access to food, and locomotor activity was monitored during the cue as a measure of food anticipatory behavior. Over several weeks, female Wistar rats developed binge-like intake of chocolate flavored food; however, their excessive intake of the chocolate flavored diet was compensated by significantly reducing both their home cage chow intake and their first feeder chow intake. Additionally, rats showed increased activity during the cue presentation, although this effect was not group specific. The goal of this study is to determine the role of the basolateral amygdala in these hedonic processes.
Abstract Title : Control of Neurogenesis by Fragile X Proteins Tyler J Wishard, Regina L Faulkner and Hollis T Cline The University of California, San Diego and The Scripps Research Institute, La Jolla, CA.
Abstract : Fragile X Syndrome (FXS) is the most common form of inherited intellectual disability. Loss of function of the fmr1 gene results in lack of Fragile X Mental Retardation Protein (FMRP), an RNA binding protein. Two homologs of FMR1, FXR1 and FXR2 are expressed in brain and may have functional redundancy in RNA binding, but little is known about their role in development. Recent studies suggest that neurogenesis, the generation of neurons from progenitor cells, is aberrant in FXS patients. We investigated whether Fragile X proteins affect neurogenesis, using Xenopus laevis tadpoles which express homologs of fmr1 and fxr1 genes. We knocked down FMR1 and FXR1 with antisense morpholinos and collected in vivo confocal time-lapse images of GFP-expressing radial glial progenitor cells and their progeny over three days. Animals treated with control morpholinos increase in the number of GFP-labeled cells between the first and third days of imaging, but FMR1 or FXR1P knockdown significantly decreased the total number of GFP-labeled cells generated over the imaging period. We identified neurons and glia based on their morphology and found that the average number of neurons and radial glia cells on days 2 and 3 is significantly reduced with FMR1 or FXR1 knockdown compared to controls, suggesting that proliferation and survival of neural progenitor cells is compromised by loss of Fragile X proteins. Interestingly, knockdown of FMRP increased the proportion of neural progeny compared to progenitors, suggesting that loss of FMRP induces rapid differentiation of neurons from progenitors, adding insight into mechanisms of FXS.