133 research outputs found

    Investigating energy homeostasis using in vivo imaging techniques

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    Obesity is a major growing cause of death with no effective long-term treatment apart from surgical procedures such as Roux-en-Y gastric bypass (RYGB). The sustained weight loss following surgery is thought to be due in part to the increased levels of circulating anorexigenic gut hormones such as peptide YY3-36 (PYY3-36). Peripheral administration of PYY3-36 suppresses appetite in rodents and man and represents a potential therapy for obesity however its effects on feeding are transient. Here I have characterized a long-lasting PYY3-36 analogue; PYY3-36 latrotoxin (PYY3-36 (LT)) which demonstrated greater longevity than PYY3-36 in acute feeding studies and that produced a 10% reduction in bodyweight following once daily peripheral administration in a one month chronic feeding study performed on diet induced obese mice. Manganese enhanced MRI (MEMRI) has been used previously to assess the effects of nutritional status and gut hormones on brainstem and hypothalamic neuronal activity in vivo. I revealed through the MEMRI technique that the anorexigenic hormone pancreatic polypeptide (PP) modulates hypothalamic neuronal activity in fasted mice. Following this work, I performed more in-depth MEMRI experiments that revealed differential temporal effects of PYY3-36 and PYY3-36 (LT) on hypothalamic neuronal activity in fasted mice after treatment that corresponded to the effects seen with these peptides in feeding stuides. I also performed pharmacological MEMRI studies with the food additive monosodium glutamate (MSG) and confirmed its excitatory effect on neurons of the arcuate nucleus of the hypothalamus (ARC) following peripheral administration to mice. Roux-en-Y gastric bypass has been shown to increase energy expenditure possibly via a brown adipose tissue (BAT) mediated mechanism. I performed positron emission tomography-computed tomography (PET-CT) experiments on a rodent model of RYGB. I observed no differences in the activity of BAT of RYGB animals compared to shamoperated controls, indicating means other than increased BAT activity account for the weight loss seen in this bariatric model. The work in this thesis demonstrates that long-lasting PYY3-36 analogues represent a viable obesity therapy. Furthermore, I have further developed both MEMRI and PET-CT techniques for the study of energy balance

    Alkoholin palkitseviin ominaisuuksiin ja amfetamiinin myrkkyvaikutuksiin liittyvien hermostollisten järjestelmien funktionaalinen kuvantaminen

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    Alcohol addiction is one of the most prevalent brain disorders in the world. A major hurdle for reducing alcohol-related harms and developing effective treatments is the poor understanding of neural processes responsible for the development of dependence and addiction. Alcohol has been shown to affect various neurotransmitter systems; however, the mesolimbic dopamine (DA) system, which projects from the ventral tegmental area (VTA) to the nucleus accumbens (NAc), has been thought to play a key role in producing the reinforcing effects of alcohol. The VTA region has also been suggested to be the anatomical site for the interaction of the dopaminergic system with the opioidergic and γ-aminobutyric acid (GABA) systems. Here, manganese-enhanced magnetic resonance imaging (MEMRI) and behavioral tests were used to study drug-induced alterations in brain activity of the alcohol-preferring AA (Alko Alcohol) and heterogeneous Wistar rats. MEMRI is based on the ability of paramagnetic Mn2+ ions to accumulate in excitable neurons, thus enhancing the T1-weighted signal in activated brain regions. Mn2+ ions can also be transported anterogradely and retrogradely in neurons, released to the synaptic cleft, and taken up by other neurons. These properties allow MEMRI to measure long-term changes in brain activity, as well as map neural pathways involved in acute and long-term drug actions, including drug reward and toxicity. The AA rats exposed to alcohol compared to water controls displayed a widespread and persistent activation in brain regions that have been previously linked with alcohol reinforcement. Similarly, activity in neural pathways originating in the NAc and projecting caudally to the midbrain was enhanced in alcohol drinking rats. Moreover, this alcohol-induced activation was blocked by systemic naltrexone (NLX) administration. Comparison of naïve AA and Wistar rats revealed a lowered basal activity in the caudal linear nucleus (CLi) of AA rats, which was restored by voluntary alcohol drinking. The intra-CLi γ-aminobutyric acid type A receptor (GABAA) agonist muscimol produced a dose-dependent increase in alcohol drinking, blocked by co-administration of the GABAA antagonist bicuculline, suggesting that the CLi GABAergic system is involved in the regulation of alcohol reward. MEMRI was also employed for assessing stimulant-induced toxicity. Methamphetamine and mephedron displayed disparate effects on brain activity, as methamphetamine produced widespread decreases in activity, whereas mephedron increased activity in limited brain areas. Taken together, the use of MEMRI for mapping alcohol- and stimulant-induced alterations in functional brain activity revealed networks and specific pathways that have potential for guiding further translational efforts to develop medications for drug abuse disorders, as well as for evaluating drug-induced toxicity.Alkoholismi on maailman yleisimpiä aivosairauksia. Alkoholin aiheuttamien haittojen vähentämistä ja tehokkaiden hoitomuotojen kehittämistä haittaa se, että päihderiippuvuuden kehittymiseen vaikuttavat aivojen toiminnan muutokset ymmärretään yhä huonosti. Alkoholin vaikutukset syntyvät monien hermoston välittäjäaineiden toiminnan kautta, ja etenkin nk. mesolimbisellä dopamiinijärjestelmällä on arveltu olevan keskeinen rooli alkoholin tuottamassa mielihyvässä. Töissämme käytettiin mangaanitehosteista magneettiresonanssikuvantamista (MRI) selvitettäessä alkoholin ja stimulanttien vaikutuksia alkoholiin mieltyneiden AA-rottien ja normaalien Wistar-rottien aivoissa. Kyseinen kuvantamismenetelmä perustuu siihen, että magneettisia ominaisuuksia omaavat mangaani-ionit kulkeutuvat hermopäätteiden kalsiumkanavien kautta hermosoluihin niiden aktivoituessa. Mangaani-ioneja sisältävien hermosolujen muodostamat radat ja aivoalueet tuottavat mitattavissa olevan signaalin. Mangaani voi myös siirtyä synapsiraon ylitse viereiseen hermosoluun ja tuottaa siten MRI-kuvan aktiivisista hermoverkoista. Viikkoja kestänyt alkoholin juominen johti aivojen aktiivisuusmuutoksiin sellaisilla aivojen alueilla, joiden on aikaisemmin oletettu liittyvän alkoholin positiivisiin vaikutuksiin. Selvitettäessä tarkemmin yksittäisten hermoratojen merkitystä havaittiin, että etuaivojen accumbens-tumakkeen keskiaivoihin lähettävä rata aktivoitui alkoholin juomisen seurauksena, kun taas alkoholismin hoidossa käytettävä lääkeaine, naltreksoni, vähensi alkoholin aiheuttamaa aktivaatiota. Verrattaessa alkoholiin mieltyneitä rottia tavalliseen rottakantaan löydettiin keskiaivoista tumake (kaudaalinen lineaaritumake), jonka aktiivisuus oli ennen alkoholin juomista tavallista alhaisempi, mutta jota alkoholi aktivoi. Kun tähän tumakkeeseen annettiin ainetta, joka salpasi gamma-aminovoihapon (GABA) vastaanottokohdat, alkoholin kulutus lisääntyi huomattavasti. Tämä löydös viittasi keskiaivojen GABA-järjestelmän merkitykseen alkoholin kulutuksen säätelyssä. Kaikkiaan kehittämämme mangaanitehosteinen magneettiresonanssikuvantaminen tuotti uutta tietoa alkoholin juomista säätelevistä hermoradoista ja yksittäisistä aivojen alueista. Tätä tietoa voidaan käyttää hyväksi, kun suunnitellaan ja testataan alkoholismin hoitoon tarkoitettuja lääkeaineita

    Dissecting the neuronal basis of threat responding in mice

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    Environmental threats demand adaptive defensive responses of an organism that ensure its survival. Extreme stressors, however, can unbalance stress homeostasis and lead to long-term changes that impair appropriate defensive behaviors and emotional responses. In my thesis, I assessed (1) the interaction of two stress-related neuromodulatory systems, (2) the effects of a traumatic incident on brain volume and hyperarousal, and (3) sonic vocalization as a defensive behavior in mice, and discussed the topics in three independent studies.In the first study, I evaluated the interaction of two regulatory systems with respect to fear, anxiety, and trauma-related behaviors. Although the endocannabinoid and the corticotropin-releasing factor (CRF) systems are well described in modulating stressrelatedresponses, the direct interaction of both systems remained poorly understood. The generation of a new conditional knockout mouse line that selectively lacked the expression of the cannabinoid type 1 (CB1) receptor in CRF-positive neurons presented no differences in various tests of fear and anxiety-related behaviors under basal conditions or after a traumatic event. Also stress hormone levels were unaffected. However, male knockout animals exhibited a significantly increased acoustic startle response thus suggesting a specific involvement of CB1-CRF interactions in controlling arousal.In the second study, I assessed the consequences of a traumatic experience on behavior and grey matter volume in mice. Whole-brain deformation-based morphometry (DBM) by means of magnetic resonance imaging (MRI) after incubation of a traumatic incident showed changes in the dorsal hippocampus and the reticular nucleus. Using the severity of hyperarousal as regressor for cross-sectional volumetric differences between traumatized mice and controls revealed a negative correlation with the dorsal hippocampus. Further, longitudinal analysis including volumetric measurements before and after the traumatic incident showed that volume reductions in the globus pallidus reflect trauma-related changes in hyperarousal severity.In the third study, I characterized sonic vocalization as a defensive behavior in mice. Mice bred for high anxiety-related behavior (HAB) were found to have a high disposition to emit audible squeaks when taken by the tail which was not the case for any of the other five mouse lines tested. The calls emitted had a fundamental frequency of 3.8 kHz and were shown to be sensitive to anxiolytic but not panicolytic compounds. Manganese-enhanced MRI (MEMRI) scans pointed towards an increased tonic activity, among others, in the periaqueductal grey (PAG). Inhibition of the dorsal PAG by muscimol not only completely abolished sonic vocalization, but also reduced anxiety-like behavior. This suggests that sonic vocalization of mice is related to anxiety and controlled by the PAG. To explore the ecological relevance of defensive vocalization, I performed playback experiments with conspecifics and putative predators. Squeaks turned out to be aversive to HAB mice but became appetitive to both mice and rats when a stimulus mouse was present during playback.Collectively, the results of this thesis provide novel insights into fear and anxiety-related behaviors and shine light onto their mechanistic basis and ecological relevance

    The startle response as a measure in mouse models of mood disorders

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    Ein großer Teil der Fragestellungen in den Neurowissenschaften beschäftigt sich mit dem Thema, wie das Säugerhirn Verhalten auslöst und steuert. Die Schreckreaktion ist ein relativ einfaches Verhalten, welches bei Säugetieren ohne großen Aufwand ausgelöst werden kann und variabel auf eine Vielfalt von experimentellen Behandlungen reagiert. Das Ziel der vorliegenden Arbeit war es, Schreckreaktions-Messungen am Max-Planck- Institut für Psychiatrie in München (MPI-P) zu etablieren. Vor dem Hintergrund aktueller Fragestellungen sollten die Experimente zu einsatzbereiten Messmethoden und Verhaltensparadigmen führen. In der vorliegenden Arbeit gelang es nicht, das Paradigma der furchtpotenzierten Schreckreaktion (FPS) zuverlässig in einem häufig am MPI-P eingesetzten Mausstamm anzuwenden. Das FPS maskierende Phänomen, daß die Präsentation eines unkonditionierten Tons bereits zu einer deutlich verstärkten Schreckreaktion in diesen Mäusen führt ("tone enhanced startle", TES) wurde dann charakterisiert und im Folgenden als ergänzendes Paradigma zur Messung und Abschätzung des Hörvermögens, der Stimulus Adaptation und der Aufmerksamkeit in Mäusen vorgeschlagen. Eine Literaturrecherche ergab, daß im Paradigma der Furchtkonditionierung ("fear conditioning", FC) und deren aktives Verlernen ("extinction of FC", ExFC) verwendete Stimulus-Parameter eine hohe Varianz zwischen verschiedenen Laboratorien aufweisen. Der im Verhalten ausgelesene Lernerfolg während einer FC wie auch einem ExFC hingen in den vorliegenden Experimenten wesentlich von der verwendeten Stimulusqualität ab (d.h. sinus-Ton oder weißes Rauschen). Im Umkehrschluß empfiehlt die vorliegende Arbeit einen überlegteren Umgang mit den eingetzten Stimulus-Parametern. Es zeigte sich, daß eine erhöhte Schreckreaktion (Übererregbarkeit) ohne weiteres in einem Tiermodell der Posttraumatischen Belastungsstörung ("posttraumatic stress disorder",PTSD) gemessen werden kann. Im Weiteren konnte gezeigt werden, daß verändertes Hippocampus-Volumen in diesen Tieren, gemessen über ultramikroskopische Aufnahmen und analog zu Hippocampusveränderungen in Patienten, unabhängig von anderen PTSD-ähnlichen Symptomen dieser Mäuse ist. In einem weiteren Abschnitt widmet sich die vorliegende Arbeit der laufenden Charakterisierung der Rolle von Dopaminrezeptoren (DR) in der Präpulsinhibition (PPI) und -Faszilitierung (PPF) der Schreckreaktion. Durch lokale injektion von DR-Antagonisten konnte gezeigt werden, daß die Blockade von DR1 wiederholbar PPI verstärkt, während die Rolle von DR2, getestet mit zwei verschiedenen Antagonisten, als ambivalent gedeutet werden muß. Basierend auf diesen Experimenten wurden optogenetische Methoden in die Schreckreaktionsmessung eingeführt. Transgenen Mäusen, die lichtsensitive Ionenkanäle in ihren neuronalen Zellmembranen bestimmter Zellpopulationen tragen, wurden Lichtblitze ins Gehirn appliziert. Auf diese Weise konnten PPI und PPF unabhängig voneinander manipuliert werden. Daraus folgend, und im Unterschied zur populären Summationshypothese der PPF, schlägt die vorliegende Arbeit einen eigenständigen, von der PPI unabhängigen PPF-Schaltkreis vor, der Pyramidenneuronen der präfrontalen Kortexschicht V beinhaltet. Die vorliegende Arbeit konnte erfolgreich verschiedene Protokolle und Verhaltensparadigmen der Schreckreaktionsmessung am MPI-P etablieren und zur sofortigen Nutzung zur Verfügung stellen. Es wurden nicht nur neue Techniken wie z.B. optogenetische Methoden in die Schreckreaktionsmessung eingeführt, die vorliegenden Experiemente leisten auch ihren Beitrag zur aktiven Forschung, in dem sie z.B. die große Bedeutung der Stimulus-Parameter für den Lernerfolg von Versuchstieren nachweisen.In neuroscience major efforts are focused on the question of how the mammalian brain generates and controls behaviour. The startle response is a relatively simple behaviour that can be easily elicited in mammals and is sensitive to a variety of experimental treatments. The aim of the present work was to establish startle response measures at the Max-Planck-Institute of Psychiatry (MPI-P), Munich, providing a set of readily applicable methods and paradigms, and contributing to questions in behavioural neuroscience. While the present thesis failed to robustly elicit fear potentiated startle (FPS) in a commonly used mouse strain at the MPI-P, strong unconditioned startle enhancement by acoustic stimulus presentation in that mouse strain was capitalised to propose tone enhanced startle (TES) as an additional paradigm to assess hearing capability, stimulus adaptation and attention in mice. A literature survey revealed considerably varying parameters used in fear conditioning (FC) and extinction of conditioned fear (ExFC). In the present work, FC, ExFC as well as FPS/TES highly depended on the stimulus quality (i.e. sine wave or white noise), demanding a more careful handling of stimulus parameters. Hyper-arousal was readily tested in a mouse model of posttraumatic stress disorder (PTSD). Additionally it was shown that altered hippocampal volume in these animals, assessed by ultramicroscopic measures and mimicking patient data, was independent of other symptoms present in this model. The present thesis contributes to the ongoing characterisation of the role of dopamine receptors (DR) in prepulse inhibition (PPI) and prepulse facilitation (PPF) of startle, manipulating PPI/F by injections of DR-antagonists into the prefrontal cortex of mice. It was found that blockade of DR1 reliably increases PPI, while the effect of DR2 was inconsistent, using to different DR2-antagonists. Based on this work, optogenetic methods were established. Applying intracerebral light flashes to transgenic mice carrying light sensitive ion channels on their neuronal cell membrane, PPI and PPF were manipulated independently, proposing the existence of a discrete PPF mediating pathway including prefrontal layer V pyramidal neurons, contrasting the popular summation hypothesis of PPF. The present work established and developed successfully different startle paradigms that are ready to use for animal characterisation and testing. Apart from combining startle measures with new techniques such as optogenetic methods, the present thesis points out the stimulus parameter dependence of animal learning, suggesting a fundamental discussion about fear conditioning and extinction learning protocols

    Manganese-Enhanced Magnetic Resonance Imaging: Overview and Central Nervous System Applications With a Focus on Neurodegeneration

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    Manganese-enhanced magnetic resonance imaging (MEMRI) rose to prominence in the 1990s as a sensitive approach to high contrast imaging. Following the discovery of manganese conductance through calcium-permeable channels, MEMRI applications expanded to include functional imaging in the central nervous system (CNS) and other body systems. MEMRI has since been employed in the investigation of physiology in many animal models and in humans. Here, we review historical perspectives that follow the evolution of applied MRI research into MEMRI with particular focus on its potential toxicity. Furthermore, we discuss the more current in vivo investigative uses of MEMRI in CNS investigations and the brief but decorated clinical usage of chelated manganese compound mangafodipir in humans

    Manganese-Enhanced Magnetic Resonance Imaging: Overview and Central Nervous System Applications With a Focus on Neurodegeneration

    Get PDF
    Manganese-enhanced magnetic resonance imaging (MEMRI) rose to prominence in the 1990s as a sensitive approach to high contrast imaging. Following the discovery of manganese conductance through calcium-permeable channels, MEMRI applications expanded to include functional imaging in the central nervous system (CNS) and other body systems. MEMRI has since been employed in the investigation of physiology in many animal models and in humans. Here, we review historical perspectives that follow the evolution of applied MRI research into MEMRI with particular focus on its potential toxicity. Furthermore, we discuss the more current in vivo investigative uses of MEMRI in CNS investigations and the brief but decorated clinical usage of chelated manganese compound mangafodipir in humans

    Manganese Enhanced MRI for Use in Studying Neurodegenerative Diseases

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    MRI has been extensively used in neurodegenerative disorders, such as Alzheimer’s disease (AD), frontal-temporal dementia (FTD), mild cognitive impairment (MCI), Parkinson’s disease (PD), Huntington’s disease (HD) and amyotrophic lateral sclerosis (ALS). MRI is important for monitoring the neurodegenerative components in other diseases such as epilepsy, stroke and multiple sclerosis (MS). Manganese enhanced MRI (MEMRI) has been used in many preclinical studies to image anatomy and cytoarchitecture, to obtain functional information in areas of the brain and to study neuronal connections. This is due to Mn2+ ability to enter excitable cells through voltage gated calcium channels and be actively transported in an anterograde manner along axons and across synapses. The broad range of information obtained from MEMRI has led to the use of Mn2+ in many animal models of neurodegeneration which has supplied important insight into brain degeneration in preclinical studies. Here we provide a brief review of MEMRI use in neurodegenerative diseases and in diseases with neurodegenerative components in animal studies and discuss the potential translation of MEMRI to clinical use in the future

    Underlying Mechanisms of Epilepsy

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    This book is a very provocative and interesting addition to the literature on Epilepsy. It offers a lot of appealing and stimulating work to offer food of thought to the readers from different disciplines. Around 5% of the total world population have seizures but only 0.9% is diagnosed with epilepsy, so it is very important to understand the differences between seizures and epilepsy, and also to identify the factors responsible for its etiology so as to have more effective therapeutic regime. In this book we have twenty chapters ranging from causes and underlying mechanisms to the treatment and side effects of epilepsy. This book contains a variety of chapters which will stimulate the readers to think about the complex interplay of epigenetics and epilepsy
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