Fear and anxiety disorders are potentially crippling conditions that often stem from past experience of trauma and chronic stress. One clear feature of these disorders is the failure to use proximate spatial and contextual information presented in the environment to regulate reflexive physiological threat responses. The central nervous system networks that govern spatial navigation and contextual learning and memory are a series of complex circuitries in which the hippocampus is integrally involved. Deficits in hippocampal function have been linked to severe anterograde and mild retrograde amnesia of semantic and episodic memory, and specific deficits in contextual processing. These deficits manifest as failure to distinguish between the details of contexts that help predict for danger or safety and can thus lead to the overexpression of threat responses that compose the behavioral symptoms of fear disorders. The dentate gyrus (DG) is a subdivision of the hippocampus that serves as the first filter of excitatory flow through the hippocampus. The DG is hypothesized to function in “pattern separation” or the dissociation of similar inputs into dissimilar outputs. Failure in this domain leads to generalization between contexts, a common feature of pathology. Pituitary adenylate cyclase activating polypeptide (PACAP) and the PAC1 receptor are associated with multiple behavioral disorders such as post-traumatic stress disorder, schizophrenia, and bipolar disorder. Mutations in the PAC1 receptor gene are associated with hypervigilance, and modified amygdalar and hippocampal activity. These results are mirrored by rodent studies where central PACAP infusion causes anxiety-like behavior, pain hypersensitivity, anorexia, and reinstatement of drug-seeking. PAC1 receptor transcript is found in high abundance in granule cells of the dentate gyrus and potentiation of DG synapses is impaired in PAC1 knockout mice. PACAP is known to have effects of long-duration, such as those in injury repair, growth, and development, but it also can affect ion channel physiology to control neuronal excitability through several parallel intracellular signaling cascades including those dependent on adenylyl cyclase, phospholipase C, and extracellular signal regulated kinase. Accumulated evidence suggests that recruitment of extracellular signal regulated kinase can be through either adenylyl cyclase-, phospholipase C-, or a receptor endocytosis-dependent mechanism. The experiments described in this dissertation address the role of PACAP in the DG in regulating expression of fear behavior, the effects of PACAP on the excitability of DG granule cells, and the signaling pathways and ion channels responsible for these effects. We found that PACAP infused into the DG amplifies expression of fear to a context but does not affect fear acquisition. Electrophysiology studies demonstrate that treating DG neurons with PACAP increases their excitability, and that parallel signaling mechanisms recruit extracellular signal regulated kinase to drive this excitability. Furthermore, these effects on excitability are attenuated by blocking a persistent inward sodium current. This work represents novel regulation of the DG and its impacts on behavior and identifies a current that likely participates in modulating granule cell excitability in multiple domains. In aggregate, this research traces the path from ligand, to receptor and intracellular signaling, to neurophysiology in order to propose a comprehensive description of behavioral regulation by these processes.

New neurons continue to be added to the dentate gyrus (DG) throughout adulthood and enhancing neurogenesis in this region holds therapeutic potential. However, the molecular mechanisms underlying DG neurogenesis remain elusive. Since developmental and adult neurogenesis often share the same signaling pathways, understanding how the DG develops is crucial to understanding adult neurogenesis. This study aims to determine the role of the retinoblastoma (Rb) protein in DG development and to determine if modulation of this pathway holds potential for enhancing neurogenesis in an adult system. A FoxG1 driven Cre is used to delete Rb in the developing forebrain and the resulting effects are analyzed in in vitro and in vivo mouse models. We show that Rb deletion enhances DG neurogenesis by specifically increasing proliferation of immature neurons. Overall this study suggests that Rb pathway modulation could hold potential for enhancing neurogenesis in the adult.

In functional magnetic resonance imaging (fMRI) studies, inter-subject anatomical variability of the human brain has been a major challenge in finding reliable functional/anatomical correspondences. Assessment of brain-behavior relations involves a series of geometrical/statistical operations on brain images to minimize such inter-subject variability, so that group maps of brain activity relative to brain anatomy can be developed. Various methods of image registration, segmentation, and analysis have been proposed for mapping functional activity on to anatomical atlases of the brain. The two most common techniques that have been widely accepted and used by neuroimaging scientists are volume-based (VB) analysis using group registration methods and region-of-interest (ROI)-based methods using automated segmentation algorithms or macro/microanatomical probabilistic atlases for labeling. Nevertheless, the analysis results based on these techniques are significantly affected by the accuracy of the selected segmentation and/or registration methods. Furthermore, conventional fMRI data analysis techniques (VB, and ROI-based methods) mainly rely on the assumption that brain processes are common and universal among individual humans; however, besides anatomical differences, there also exist cognitive and behavioral variability among individuals due to differential engagement of brain networks even when performing an identical cognitive task. In this thesis, I have assessed the impact of anatomy-based alignment techniques (VB, and ROI-based methods) on sensitivity of fMRI data group analysis. I evaluated the effect of the type of inter-subject registration used and related factors on sensitivity of group-level fMRI data analysis. Furthermore, I have also assessed the goodness of fit of probabilistic maps by proposing an evidence-based framework for evaluation of probabilistic maps. As a test model, I have selected the human auditory cortex. Auditory cortex is an interesting yet challenging case with substantial inter-individual functional/anatomical variability. For the sake of ROI-based method of analysis, I have proposed a novel approach for automatic segmentation of Heschl's gyrus, which is the landmark for primary auditory cortex. Finally, in order to assess the impact of inter-subject variability in anatomy on functional organization, I analyze data from an fMRI study, which demonstrates that the degree to which anatomical registration compensates for functional variability depends on the brain region activated. / Thesis (Ph.D, Computing) -- Queen's University, 2010-04-29 07:07:55.77

Stem/progenitor cells are present in the adult brain; they undergo constantproliferation and differentiate into mature neurons in certain brain areas, a phenomenoncalled neurogenesis. This study investigated the effects of GDNF, a potent trophic factorof dopaminergic neurons, on neurogenesis in the brain. Nestin and 5-Bromo-2'-deoxyuridine (BrdU) were used as stem/progenitor cells markers.First, we observed extensive bilateral increases of stem/progenitor cells in thedentate gyrus and substantia nigra after continuous infusion of GDNF into the normal ratbrain. However, none of the BrdU+ cells showed neuronal features in the substantia nigraas characterized by immunocytochemical procedures. Next, we identified themorphology of BrdU+ cells after infusing the marker into the brain. While the proceduresincreased the BrdU labeling, neurogenesis was not observed in the basal ganglia. Underelectron microscope, the BrdU+ cells either were undifferentiated or showedcharacteristics of astrocytes. This observation is consistent with suggestions thatastrocytes serve as multipotent progenitors. Later, we repeated GDNF intrastriatalinfusion one month after a severe 6-hydroxydopamine (6-OHDA) lesion. The number ofBrdU+ cells was significantly higher in the GDNF recipients in the ipsilateral substantianigra and both sides of the dentate gyrus. However, no neurogenesis was observed. Inaddition, motor functions were not improved by GDNF treatment. Thus, we measured theeffects of GDNF administration directly into the substantia nigra six hours before apartial 6-OHDA lesion. HPLC measurements of dopamine and its metabolites showed asignificant increase of tissue level in the substantia nigra and striatum, respectively.Despite this, no newly generated dopaminergic neurons was detected in the basal ganglia.Taken together, our studies investigated the effects of GDNF on adultstem/progenitor cells in normal and lesioned rat brain. For the first time, we demonstratedthat GDNF promoted their proliferation in the dentate gyrus, suggesting it has a role inneurogenesis and the function of learning and memory. In each scenario, GDNFpromoted stem/progenitor cell proliferation, but failed to induce neurogenesis in thesubstantia nigra. We believed that the local microenvironment in the substantia nigra mayprevent the stem/progenitor cells to mature into functional neurons.

New neurons continue to be added to the dentate gyrus (DG) throughout adulthood and enhancing neurogenesis in this region holds therapeutic potential. However, the molecular mechanisms underlying DG neurogenesis remain elusive. Since developmental and adult neurogenesis often share the same signaling pathways, understanding how the DG develops is crucial to understanding adult neurogenesis. This study aims to determine the role of the retinoblastoma (Rb) protein in DG development and to determine if modulation of this pathway holds potential for enhancing neurogenesis in an adult system. A FoxG1 driven Cre is used to delete Rb in the developing forebrain and the resulting effects are analyzed in in vitro and in vivo mouse models. We show that Rb deletion enhances DG neurogenesis by specifically increasing proliferation of immature neurons. Overall this study suggests that Rb pathway modulation could hold potential for enhancing neurogenesis in the adult.

Developmental ethanol exposure causes both structural and functional changes in the brain that can result in cognitive and behavioral abnormalities. The hippocampal formation, an area of the brain strongly linked with learning and memory, is particularly vulnerable to the teratogenic effects of ethanol. Research in this thesis focused on uncovering the effects of developmental ethanol exposure on hippocampal function in adulthood, particularly synaptic plasticity (a putative neurobiological mechanism of learning and memory). The first experiment sought to determine the temporal vulnerability of hippocampal synaptic plasticity as a function of exposure to ethanol during a single trimester. Ethanol exposure during the 1st or 3rd trimester equivalent resulted in minor changes in synaptic plasticity in adult offspring. In contrast, ethanol exposure during the 2nd trimester equivalent resulted in a pronounced decrease in long-term potentiation (LTP), indicating that the timing of exposure determines the severity of the deficit. The second experiment was aimed at determining the effects of prenatal ethanol exposure (1st and 2nd trimester equivalent combined) on bidirectional synaptic plasticity. Prenatal ethanol exposure resulted in a profound reduction in LTP but did not affect long-term depression. These findings show that prenatal ethanol exposure creates an imbalance in bidirectional synaptic plasticity. The third experiment sought to determine if prenatal ethanol exposure alters the affect of acute ethanol exposure in adulthood on synaptic plasticity. Acute exposure to ethanol in adulthood attenuated LTP in control offspring. Conversely, the magnitude of LTP was not affected by acute ethanol application in prenatal ethanol offspring. These results suggest that prenatal ethanol exposure alters the physiological response to ethanol in adulthood. Together, the results from the experiments undertaken in this thesis demonstrate long-lasting alterations in synaptic plasticity as the result of developmental ethanol exposure. Furthermore, these results allude to a malfunction of neural circuits within the hippocampal formation, perhaps relating to the learning and memory deficits observed in individuals with fetal alcohol spectrum disorders. / Graduate

Cognitive aging is a biological process characterized by physical changes in the brain and subsequent alterations in cognitive function. While neurodegenerative diseases result in extensive neuronal death and anatomical abnormalities, normal aging has subtle changes resulting in a range of cognitive abilities. Early studies of cognitive aging focused on changes in the neuronal population, but evidence has demonstrated that forebrain neurons are largely preserved with age. Furthermore, the proliferation of new neurons in the adult brain has generated great speculation regarding the role and contribution of new neurons to cognitive function. Conversely, both imaging and ultrastructural analyses have shown that age-related alterations in white matter and myelin are good predictors of cognitive impairment, suggesting that alterations in connectivity between brain regions may result in cognitive decline. In this dissertation, a rhesus monkey model of normal aging was used to assess the contribution of adult-neurogenesis and oligodendrogenesis to cognitive function. First, cell proliferation and adult neurogenesis were assessed in the subgranular zone of the hippocampal dentate gyrus. Aged animals demonstrated a decline in proliferating cells and neurogenesis but only limited correlations with behavioral impairment. Immature neurons were also identified in temporal lobe cortices, but results indicate these immature cortical neurons are most likely not adult-generated. Moreover, despite an age-related decline in numbers, they persist throughout the lifespan and many differentiate into Calretinin neurons. Further investigation of white matter alterations used immunohistochemistry and diffusion spectrum imaging to correlate oligodendrocyte numbers with white matter connectivity. In the corpus callosum and cingulum bundle, there were no correlations with age, but cognitive impairment was associated with increased oligodendrocyte number and decreased white matter connectivity. These correlations were only present in the anterior aspect of the cingulum bundle, not the posterior cingulum suggesting differential oligodendrocyte responses along the anterior-posterior axis of the brain. Together, these data demonstrate an age-related decline in adult neurogenesis may be only a small contributor to cognitive impairment. Additionally, a reserve pool of immature neurons continues to differentiate in the temporal cortex potentially contributing to local plasticity. Furthermore, cognitive impairment rather than aging has a stronger correlation with oligodendrocytes alterations and connectivity.

The current study explored the relationship between middle frontal gyrus (MFG) volume and working memory in children with Attention-Deficit/Hyperactivity Disorder (ADHD) and dyslexia (RD). it was hypothesized that there would be group differences in middle frontal gyrus volume and working memory performance, and that there would be a relationship between middle frontal gyrus volume and working memory performance. Results indicated that there was a trend of smaller left hemisphere middle frontal gyrus volumes in the RD groups compared to the non-RD groups. In addition, when total brain volume, Passage Comprehension and Attention Problems were included as covariates, Sequences, a verbal working memory task, significantly predicted left MFG volume. Finally, when exploratory analyses were conducted, Passage Comprehension significantly predicted both left and right MFG volumes when both Reading Fluency and Letter Word Identification were also included in the model as predictors. Little research has been conducted on the relationship between MFG volumes and RD and ADHD groups. Significant findings and trends reported here related to RD groups and reading-related tasks indicate that further research exploring the relationship between complex working memory tasks like Passage Comprehension and MFG volumes is warranted.

New neurons continue to be added to the dentate gyrus (DG) throughout adulthood and enhancing neurogenesis in this region holds therapeutic potential. However, the molecular mechanisms underlying DG neurogenesis remain elusive. Since developmental and adult neurogenesis often share the same signaling pathways, understanding how the DG develops is crucial to understanding adult neurogenesis. This study aims to determine the role of the retinoblastoma (Rb) protein in DG development and to determine if modulation of this pathway holds potential for enhancing neurogenesis in an adult system. A FoxG1 driven Cre is used to delete Rb in the developing forebrain and the resulting effects are analyzed in in vitro and in vivo mouse models. We show that Rb deletion enhances DG neurogenesis by specifically increasing proliferation of immature neurons. Overall this study suggests that Rb pathway modulation could hold potential for enhancing neurogenesis in the adult.

This study served as a pilot study of cingulate gyrus surface areas and their relation to intelligence in individuals with hydrocephalus. Surface areas of the corpus callosum and cingulate gyrus regions were compared between individuals with early hydrocephalus (n = 9) and controls (n = 7). Subsequently, the surface areas were correlated with full-scale intelligence scores and the verbal and nonverbal discrepancy scores. Corpus collosum surface areas were significantly smaller in participants with hydrocephalus. These areas also robustly correlated with full-scale intelligence scores. Although the cingulate gyrus did not differ significantly between the groups, the cingulate gyrus regions were increasingly divergent the more posterior the region. Additionally, the caudal anterior and the posterior cingulate gyrus regions had only moderate positive correlations with full-scale intelligence scores. Although the participants with hydrocephalus had a significantly lower mean performance IQ compared to verbal IQ, the discrepancy scores did not correlate significantly with any of the regions of interest.