In this thesis, the consequences of Parkinson’s disease (PD) are studied using advanced approaches in neuroimaging, including structural as well as functional connectivity networks, examination of... Show moreIn this thesis, the consequences of Parkinson’s disease (PD) are studied using advanced approaches in neuroimaging, including structural as well as functional connectivity networks, examination of the role of aging in white matter degeneration in PD, and the use of machine learning classification models. Brain MRI features of PD patients are compared with healthy control subjects, and the relations between these features and patient characteristics, such as age, dopaminergic medication, motor and predominantly non-dopaminergic impairment, are described. Furthermore, brain features that may contribute to the differentiation of PD and Dementia with Lewy body dementia are described. Show less
During this research we wanted to gain more insight into the potential gene repertoire that is involved in the hippocampus when coping with stress and regulating learning and memory... Show more During this research we wanted to gain more insight into the potential gene repertoire that is involved in the hippocampus when coping with stress and regulating learning and memory processes. To investigate this further we aimed to answer the question:""What are the primary genomic binding sites of the by stress and thus cortisol stimulated protein receptors MR and GR in the hippocampus?" To answer this question, new methods have been applied to determine where exactly MR and GR bind to the DNA, to find out which genes are potentially involved during stress management. As a result we have identified thousands of GR-binding sites at the DNA of which we have analyzed a selection in further detail. One of the identified pathways that have been found to be sensitive for activated GR and corticosteroids is the mTOR pathway. This pathway is involved in neuronal plasticity, which is the fundament for resilience. We have found that expression of the mTOR protein is decreased after exposure to acute stress when the organism has a history of chronic stress. Our results indicate that the reduced resilience after experiencing chronic stress is likely to be mediated by mTOR. Show less
The results in this thesis showed for the first time doublecortin-like (DCL)-specific expression in the adult mouse brain. Besides the expected regions with the capacity to generate new neurons ... Show moreThe results in this thesis showed for the first time doublecortin-like (DCL)-specific expression in the adult mouse brain. Besides the expected regions with the capacity to generate new neurons (hippocampus and olfactory forebrain), DCL expression was found in three novel brain areas namely hypothalamic tanycytes, suprachiasmatic nucleus and Islands of Calleja. A state of the art conditional shRNA expressing mouse model was used to target DCL mRNA. The analysis of these DCL knockdown animals using qPCR and Western blot revealed strong reduction of DCL protein expression. Subsequent stereological analysis using BrdU and several stem cell and neuronal markers revealed increased progenitor proliferation, but impaired neurogenesis in the hippocampus. This impaired neurogenesis was associated, however, with an apparent normal spatial and contextual fear memory formation in circular hole board and in a contextual fear conditioning paradigm. Therefore, DCL-regulated adult neurogenesis seems not crucial for hippocampus-dependent learning. However, more subtle functions like pattern separation and context distinction might be regulated by DCL. DCL knockdown also increased D2 activity within the hypothalamus. Altogether, the DCL-KD mouse seems a good working model to study adult neurogenesis and the role of DCL in this process. Show less
Schizophrenia is heritable, but even in monozygotic twins differences in susceptibly exists. What is causing this difference in genetically identical individuals? The objective of this thesis was... Show moreSchizophrenia is heritable, but even in monozygotic twins differences in susceptibly exists. What is causing this difference in genetically identical individuals? The objective of this thesis was to identify novel susceptibility genes and pathways for psychosis in a psychostimulant mouse model which is considered a model for psychosis. Genome-wide analysis of transcripts in the hippocampal CA1, driving mesocortical dopaminergic activity, which has a prominent role in schizophrenia, revealed differential expression of target genes of Myocyte Enhancer Factor 2 (MEF2) and Glucocorticoid Receptor (GR). This suggest that this gene network is involved in sensitivity to amphetamine. In primary hippocampal neurons, knockdown of MEF2 reduced the expression of c-Jun and abolished its regulation by GR. Moreover, activation of MEF2 by neuronal depolarization was attenuated by glucocorticoids, suggesting a mutual feedback regulation of these transcription factors. Finally, in vivo MEF2 and GR appeared to be active in the induction phase of amphetamine sensitization. Overall, the findings suggest that in the hippocampus activation of GR can modulate the role of MEF2 target genes in induction of behavioral sensitization. This finding points to the hippocampus as an exciting target for further studies on the role of MEF2 and GR in the precipitation of psychosis susceptibility. Show less
Doublecortin (DCX) and DCX-domain containing Doublecortin-Like Kinase (DCLK) gene splice variants function during embryonic development, where they play a role in microtubule binding. Although a... Show moreDoublecortin (DCX) and DCX-domain containing Doublecortin-Like Kinase (DCLK) gene splice variants function during embryonic development, where they play a role in microtubule binding. Although a role for the DCLK gene during embryogenesis is clearly established, it encodes multiple, different transcripts, some of which are expressed in the adult brain or in response to neuronal activity. This suggests that the DCLK gene may have additional functions beyond neuronal development. Strikingly, the roles of two DCLK gene products, DCLK-short and CaMK-related peptide (CARP), remain largely elusive. Therefore, we have generated transgenic mice with over-expression of either CARP or a constitutively active form of DCLK-short, called _C-DCLK-short, in the brain. This has opened up the possibility to study the effect of over-expression of these DCLK transcripts in the brain during adulthood. To gain more insight in DCLK gene function in the adult brain we aimed to study and describe the phenotypes of these transgenic mice at different functional levels, such as the genetic, network and behavioural level. Show less
Pronounced ultradian and circadian rhythms in the hormones of the hypothalamic-pituitary-adrenal (HPA) axis (i.e. glucocorticoids), one of the body__s major neuroendocrine axes, were already... Show morePronounced ultradian and circadian rhythms in the hormones of the hypothalamic-pituitary-adrenal (HPA) axis (i.e. glucocorticoids), one of the body__s major neuroendocrine axes, were already demonstrated several decades ago. Until now, the clinical relevance of the pulsatile nature of glucocorticoids was poorly understood or sometimes even regarded as not important. Its evolutionary conservation across many species however implies biological significance. Indeed, glucocorticoids have been proven to be crucial for a plethora of bodily functions, e.g. emotion, cognition and the central mechanism underlying the adaptation to stress. Furthermore, disturbances in the characteristic temporal pattern of glucocorticoid exposure have often been described in stress-related pathology. However, the significance of glucocorticoids secretory patterns for physiology, stress responsiveness and nuclear receptor signalling is still largely unexplored and is accordingly addressed in this thesis. A new concept in the endocrinology of glucocorticoids has evolved from the data presented here showing that pulsatile release of glucocorticoids is a major determinant in __resilience__ of glucocorticoid signalling in neuronal cells and stress responsiveness. Moreover, we show that particularly the glucocorticoid receptor is affected after disrupting glucocorticoid pulsatility and could thus provide an excellent target for therapy to normalise the downstream effects of disturbances in glucocorticoid rhythms in stress-related disease. Show less
Glucocorticoid hormones exert modulatory effects on neural function in a delayed genomic fashion. The two receptor types that can bind glucocorticoids, the mineralocorticoid receptor (MR) and the... Show moreGlucocorticoid hormones exert modulatory effects on neural function in a delayed genomic fashion. The two receptor types that can bind glucocorticoids, the mineralocorticoid receptor (MR) and the glucocorticoid receptor (GR), are ligand-inducible transcription factors. Therefore, changes in gene expression most likely underlie glucocorticoid-mediated genomic effects on neural function. In this thesis, the central aim was to gain more insight into the transcriptional changes that mediate the effects of acutely activated GRs on neural function. Two different biological substrates i.e. ex vivo hippocampal slices and neuronal catecholaminergic PC12 cells, were used to measure the transcriptional response after GR-activation. Using microarrays, an interesting time-dependent pattern of gene transcription was observed, shifting from exclusively downregulated genes 1 hour after GR-activation to both up and downregulated genes 3 hours afterwards. This pattern suggests that the fast genomic effects of glucocorticoids may be realized via transrepression, preceding a later wave of transactivation. Additionally, many new candidate genes were found that could potentially underlie (part of) the effects glucocorticoids mediate on hippocampal and catecholaminergic neuronal function. Hence, these candidate genes can be used to formulate new hypotheses on how glucocorticoids affect neural function and future research should therefore focus on testing these hypotheses. Show less
