Experimental treatment options in absence epilepsy

Contains fulltext : 182124.pdf (preprint version ) (Open Access)Background: The benign character of absence epilepsy compared to other genetic generalized epilepsy syndromes has often hampered the search for new treatment options. Absence epilepsy is most often treated with ethosuximide or valproic acid. However, both drugs are not always well tolerated or fail, and seizure freedom for a larger proportion of patients remains to be achieved. The availability of genuine animal models of epilepsy does allow to search for new treatment options not only for absence epilepsy perse but also for other genetic - previously called idiopathic - forms of epilepsy. The recent discovery of a highly excitable cortical zone in these models is considered as a new therapeutic target area. Methods: Here, we provide an overview regarding the search for new therapeutical options as has been investigated in the genetic rodent models (mainly WAG/Rij and GAERS) including drugs and whether antiepileptogenesis can be achieved, various types of electrical and optogenetical invasive stimulations, different types of non-invasive stimulation and finally whether absence seizures can be predicted and prevented. Results: Many factors determine either the cortical and or thalamic excitability or the interaction between cortex and thalamus and offer new possibilities for new anti-absence drugs, among others metabotropic glutamatergic positive and negative allosteric modulators. The inhibition of epileptogenesis by various drugs with its widespread consequences seems feasible, although its mechanisms remain obscure and seems different from the anti-absence action. Surgical intervention on the cortical zone initiating seizures, either with radiosurgery using synchrotron-generated microbeams, or ablation techniques might reduce spike-and-wave discharges in the rodent models. High frequency electrical subcortical or cortical stimulation might be a good way to abort ongoing spike-and-wave discharges. In addition, possibilities for prevention with real-time EEG analyses in combination with electrical stimulation could also be a way to fully control these seizures. Conclusion: Although it is obvious that some of these treatment possibilities will not be used for absence epilepsy and/or need to be further developed, all can be considered as proof of principle and provide clear directives for further developments

Neuromodulation in Experimetal Animal Models of Epilepsy

Epilepsy is the most common serious brain disorder affecting 0.5-1% of the general population. This neurological disorder consists of recurrent seizures, resulting from excessive, uncontrolled electrical activity in the brain. Despite the pharmacological development of new treatments, still one third of the epilepsy patients does not respond sufficiently to anti-epileptic drugs (AED) and are called refractory patients. Hence, there is a constant impetus to search for other treatment strategies like epilepsy surgery, vagus nerve stimulation and deep brain stimulation. Besides the ongoing research on the efficacy of anti-epileptic treatments in suppressing seizures (anti-seizure effect), we want to seek for therapies that can lead to plastic changes in the epileptic network and in this way have a modulating effect. The impact of such therapies cannot be overlooked, because they may slow down processes underlying epilepsy, might prevent or even cure epilepsy. Neuropharmacological therapy with levetiracetam (LEV) and vagus nerve stimulation (VNS) are two novel treatments for refractory epilepsy. Acute application of both treatment options can be very effective. LEV can act rapidly on seizures in both animals and humans. In addition, preclinical studies suggest that LEV may have anti-epileptogenic and neuroprotective effects, with the potential to slow or arrest disease progression. VNS as well can have an immediate effect on seizures in animals and patients with in addition a cumulative effect after prolonged treatment. Studies in man are hampered by the heterogeneity of patient populations (age, course of the epilepsy, type of epilepsy, AED regime and genetic background) and the difficulty to study therapy-related effects in a systematic way. Therefore, investigation was performed utilizing two models mimicking epilepsy in humans. They are both chronic models with seizures evolving from true, genetically-driven epileptogenesis. Genetic absence epilepsy rats from Strasbourg (GAERS) have inborn absence epilepsy and Fast rats have a genetically determined sensitivity for electrical amygdala kindling, which is an excellent model of temporal lobe epilepsy. Our findings support the hypothesis that these treatments can be considered as neuromodulatory: changes are induced in central nervous system function or organization as a result of influencing and initiating neurophysiological signals

Oscillatory and epileptiform activity in human and rodent cortical regions in vitro

Epilepsy is a chronic neurological disorder in which patients have spontaneous recurrent seizures. Approximately 50 million people worldwide live with epilepsy and of those ~30% fail to adequately respond to anti-epileptic drugs (AEDs), indicating a need for further research. In this study oscillatory and epileptiform activity was explored in the rodent piriform cortex (PC) in vitro, an underexplored brain region implicated in the development of epilepsy. PC gamma oscillations have been studied in both anaesthetised and awake rodents in vivo; however, to date they have not been reported in vitro. Extracellular field potential recordings were made in rodent PC brain slices prepared from 70-100g male Wistar rats in vitro. Application of kainic acid and carbachol reliably induced persistent gamma oscillations (30 – 40 Hz) in layer II of the PC. These oscillations were found to be pharmacologically similar to gamma oscillations previously found in other rodent brain regions in vitro, as they were dependent on GABAA receptors, AMPA receptors and gap junctions. Persistent oscillations were also induced and characterised for the first time in human neuronal tissue in vitro. Human brain slices were prepared from excised tissue from various brain regions (primarily temporal) from paediatric patients undergoing surgery to alleviate the symptoms of drug resistant epilepsy. As in the rodent PC, oscillations were induced by application of kainic acid and carbachol, however, these oscillations were found to be within the beta frequency range (12 – 30 Hz). Despite this difference in frequency band, these beta oscillations were pharmacologically similar to gamma oscillations found in the rodent PC. Seizure-like events (SLEs) were induced in brain slices prepared from 70-100g male Wistar rats via application of zero Mg2+ artificial cerebral spinal fluid (0[Mg]2+ aCSF). The properties of these SLEs were found to be similar between brain regions when recordings were performed in layer II of the anterior and posterior PC and lateral entorhinal cortex (LEC) and the stratum pyramidale of CA1. In the majority of recordings SLEs occurred in the PC before the LEC or CA1 and SLEs were displayed in the PC in a higher proportion of slices than the LEC. The sensitivity of these PC slices to 0[Mg]2+ aCSF was assessed at several stages (24 hours and 1 week (early latent), 4 weeks (mid latent) and 3 months+ (chronic period)) following the reduced intensity status epilepticus (SE) protocol for epilepsy induction compared to age-matched controls (AMCs). A decrease in excitability of the slices was observed in slices prepared from AMC animals with age, as the inter-event interval and latency to first SLE was observed to be longer in slices prepared from aged compared to young AMC animals. Slices prepared from SE animals maintained their youthful hyperexcitability with no difference in IEI or latency to first SLE observed in the early latent period compared to the chronic period. The pharmacoresistance (or sensitivity) of these SLEs to single and double AED challenge was evaluated. Differences in efficacy of the AEDs were found between SE and AMC in the mid-latent period; increased efficacy of Na+ channel modulating AEDs were found in slices prepared from SE compared to AMC animals. The proportion of slices that displayed pharmacoresistance of these SLEs to AEDs was found to be higher in slices prepared from young animals (early latent period and AMCs), and was similar to that found clinically in human patients. The pharmacoresistance of the SLEs to AEDs was lower in slices prepared from older animals (mid latent, chronic and AMCs) compared to young animals (early latent and AMCs). This age-dependent reduction in resistance likely reflects normal alterations in neuronal networks with ageing. SLEs induced in young control PC slices could be exploited as a new in vitro model of drug resistant epilepsy. Overall, oscillatory and epileptiform activity in the PC and human cortex in vitro could be further explored as tools to evaluate the efficacy and mechanism of action of newly developed AEDs, as well as to explore the networks involved in drug resistant epilepsy

Long-term potentiation in spinal nociceptive pathways as a novel target for pain therapy

Long-term potentiation (LTP) in nociceptive spinal pathways shares several features with hyperalgesia and has been proposed to be a cellular mechanism of pain amplification in acute and chronic pain states. Spinal LTP is typically induced by noxious input and has therefore been hypothesized to contribute to acute postoperative pain and to forms of chronic pain that develop from an initial painful event, peripheral inflammation or neuropathy. Under this assumption, preventing LTP induction may help to prevent the development of exaggerated postoperative pain and reversing established LTP may help to treat patients who have an LTP component to their chronic pain. Spinal LTP is also induced by abrupt opioid withdrawal, making it a possible mechanism of some forms of opioid-induced hyperalgesia. Here, we give an overview of targets for preventing LTP induction and modifying established LTP as identified in animal studies. We discuss which of the various symptoms of human experimental and clinical pain may be manifestations of spinal LTP, review the pharmacology of these possible human LTP manifestations and compare it to the pharmacology of spinal LTP in rodents

Emotional Experience and Awareness of Self: Functional MRI Studies of Depersonalization Disorder

This paper presents functional MRI work on emotional processing in depersonalization disorder (DPD). This relatively neglected disorder is hallmarked by a disturbing change in the quality of first-person experience, almost invariably encompassing a diminished sense of self and an alteration in emotional experience such that the sufferer feels less emotionally reactive, with emotions experienced as decreased or “damped down,” so that emotional life seems to lack spontaneity and subjective validity. Here we explored responses to emotive visual stimuli to examine the functional neuroanatomy of emotional processing in DPD before and after pharmacological treatment. We also employed concurrent skin conductance measurement as an index of autonomic arousal. In common with previous studies we demonstrated that in DPD, there is attenuated psychophysiological response to emotional material, reflected in altered patterns of (i) regional brain response, (ii) autonomic responses. By scanning participants before and after treatment we were able to build on previous findings by examining the changes in functional MRI response in patients whose symptoms had improved at time 2. The attenuation of emotional experience was associated with reduced activity of the insula, whereas clinical improvement in DPD symptoms was associated with increased insula activity. The insula is known to be implicated in interoceptive awareness and the generation of feeling states. In addition an area of right ventrolateral prefrontal cortex emerged as particularly implicated in what may be “top-down” inhibition of emotional responses. The relevance of these findings to the wider study of emotion, self-related processes, and interoception is discussed

Probing brain function with pharmacological MRI

Lo sviluppo di tecniche di risonanza magnetica funzionale (fMRI) ha rivoluzionato le ricerca neuroscientifica clinica, determinando la possibilit\ue0 di investigare le dinamiche spazio-temporali dell\u2019attivit\ue0 cerebrale in maniera non invasiva e con grande accuratezza. Sebbene la tecnica sia stata originariamente sviluppata in ambito clinico, essa ha il potenziale di poter essere utilizzata in ambito preclinico come efficace strumento investigativo e traslazionale. Tuttavia, l\u2019implementazione preclinica di questi metodi \ue8 complicata da una serie di costrizioni sperimentali, in primis l\u2019utilizzo di anestetici, che minano fortemente il potenziale traslazionale di queste tecniche. Il recente sviluppo di tecniche di "MRI farmacologico" (phMRI) offre la possibilit\ue0 di superare alcune delle limitazioni sperimentali correlate all\u2019implementazione di approcci fMRI classici in animali da laboratorio. La tecnica si basa sull'utilizzo di metodi fMRI per mappare alterazioni di attivit\ue0 cerebrale prodotte dalla somministrazione di sostanze psicoattive. Studi preliminari hanno evidenziato la capacit\ue0 di generare robusti e specifici segnali phMRI anche in condizioni di anestesia, ed ha dimostrato la possibilit\ue0 di stimolare selettivamente diversi sistemi di neurotrasmettitori. Sfruttando la conservazione di circuiti cerebrali tra specie, tecniche phMRI offrono quindi l\u2019opportunit\ue0 di ampliare in maniera significativa il repertorio di stimolazione neuronale a disposizione in ambito preclinico, consentendo di indagare selettivamente specifici aspetti della funzione cerebrale in diversi stati di precondizionamento neuronale. In tale contesto, le attivit\ue0 di ricerca di questa tesi sono state finalizzate ad ampliare il campo di applicazione di metodi phMRI preclinici in due diversi ambiti sperimentali: a) come modalit\ue0 di indagine traslazionale, qualora applicata a modelli di malattia clinicamente rilevanti, b) pi\uf9 in generale come piattaforma investigativa per l'indagine della funzione cerebrale e della sua topologia funzionale in contesti sperimentali diversi. In un primo gruppo di studi, tecniche phMRI sono state impiegate per mappare i circuiti neuronali attivati da antagonisti del recettore del glutammato NMDA nel cervello del ratto (Sezione 4.1). Tali composti, grazie alle loro propriet\ue0 psicotogeniche, sono ampiamente sfruttati come modelli sperimentali di schizofrenia in animali ed in volontari allo scopo di valutare e validare nuovi trattamenti per la malattia. I risultati di questa ricerca hanno evidenziato uno specifico circuito corticolimbo- talamico che risulta essere attivato da antagonisti NMDAR sia nell'uomo che in Riassunto XII specie precliniche, e che \ue8 risultato essere modulabile da meccanismi antipsicotici diversi (Sezione 4.2). Il potenziale traslazionale dei metodi phMRI \ue8 stato ulteriormente avvalorato da un secondo gruppo di studi, in cui un approccio multi-parametrico \u201cphMRI-based\u201d \ue8 stato impiegato per indagare molteplici aspetti della funzione cerebrale in un modello murino di dipendenza da cocaina. Questa linea di investigazione ha evidenziato multiple alterazioni della funzione cerebrale basale e reattiva nel cervello di roditori esposti alla cocaina strettamente connesse a quelle osservate in analoghi studi di imaging su pazienti cocaina-dipendenti (Sezione 4.2). In una terza linea d\u2019 investigazione, l'uso combinato di avanzate strategie di targeting neuro-genetico (pharmaco-genetic silencing) e phMRI si \ue8 dimostrato efficace nello stabilire correlazioni dirette tra cellule, circuito e comportamento in linee di topo geneticamente modificate. Questi studi hanno portato all\u2019identificazione di una nuova e circoscritta popolazione neuroni nell'amigdala, in grado di controllare qualitativamente la risposta comportamentale alla paura attraverso il reclutamento di circuiti colinergici corticali (Sezione 4.3) Infine, l'approccio phMRI si \ue8 dimostrato uno strumento potente e versatile per l\u2019implementazione di misure di connettivit\ue0 funzionale nel cervello di roditori. Questo aspetto ha permesso l\u2019esplorazione di nuovi approcci statistici per l\u2019analisi della topologia funzionale del cervello basati sulla rappresentazione di misure di connettivit\ue0 in termini di reti complesse (Sezione 4.4). Complessivamente, i risultati di questo lavoro avvalorano il potenziale traslazionale di metodi phMRI nell\u2019ambito di diverse aree delle neuroscienze e della psicofarmacologia. La combinazione di phMRI e tecniche di manipolazione genetica avanzate definisce una nuova, potente piattaforma tecnologica per lo studio delle basi circuitali del comportamento in animali da laboratorio.The development of functional Magnetic Resonance Imaging (fMRI) has heralded a revolution in neuroscience, providing clinicians with a method to non-invasively investigate the spatio-temporal patterns of neuro-functional activity. Although primarily developed for human investigations, there exists significant scope for the application of fMRI in pre-clinical species as a translational and investigational platform across different areas of neuroscience and psychiatry research. However, the realization of this potential is hampered by a number of experimental constraints which make the application of fMRI methods to animal models less than straightforward. As a result, most fMRI research in laboratory species has been reduced to the employment of basic somato-sensory stimulation paradigms, thus greatly limiting the translational potential of the technique. An interesting approach to overcome some of these limitations has been dubbed \u201cpharmacological MRI\u201d (phMRI) and relies on the use of fMRI to map patterns of brain activity induced by psychoactive drugs. The approach has demonstrated the ability to elicit reliable fMRI signals even under anaesthesia, and to enable selective stimulation of different neurotransmitter systems. Building upon the homology between brain circuits in humans and laboratory animals, phMRI techniques thus offer the opportunity of significantly expanding the stimulation repertoire available to preclinical fMRI research, by allowing to selectively probe specific aspects of brain function under different preconditioning states. Within this framework, the research presented herein was aimed to broaden the scope of application of preclinical phMRI both as a translational technique, when applied to clinically-relevant disease models, and more generally as a versatile platform for the pre-clinical investigation of brain activity and its functional topology as a function of behavioural, pharmacological or genetic preconditioning. In a first group of studies, we developed a phMRI assay to map the circuitry activated by NMDAR antagonists in the rat brain. These psychotogenic compounds are widely exploited to model schizophrenia symptoms and to provide experimental models that may prove useful in the development of novel treatments for the disorder. The results of this research highlighted a conserved cortico-limbo-thalamic circuit that is activated by NMDAR antagonists both in humans and preclinical species, which can be modulated by existing and novel antipsychotic drugs (Section 4.1). The translational potential of phMRI measurements was further corroborated by a second group of studies, where a multi-parametric phMRI-based approach was applied to investigate multiple facets of brain function in a rodent cocaine selfSummary X administration model, a behavioural paradigm of established construct-validity for research of drug addiction. This line of investigation revealed specific basal and reactive functional alterations in the brain of cocaine-exposed rodents closely related to those observed in analogous neuroimaging studies in humans (Section 4.2). In a third line of investigation, the combined use of advanced neuro-genetic targeting strategies (i.e. pharmacogenetic silencing) and phMRI has proven successful in establishing direct correlations between cells, circuit and complex behaviours in genetically engineered mouse lines. These studies (Section 4.3) have led to the identification of a novel cell population in the amygdala that controls the behavioural response to fear through the recruitment of cholinergic circuits. Finally, the phMRI approach has proven a powerful tool to explore functional connectivity in rodents, and to map a variety of different neurotransmitter pathways by performing measures of correlated responses in spatially remote brain areas. This has provided a useful playground to explore novel statistical methods of analysis of functional connectivity represented in terms of complex networks (Section 4.4). Collectively, the results of this work strongly corroborate the translational use of phMRI approaches, and pave the way to the integrated implementation of phMRI and advance genetic manipulation as a novel powerful platform for basic neurobiological research

EFFECTS OF NEUROMODULATION ON NEUROVASCULAR COUPLING

The communication between neurons within neural circuits relies on neurotransmitters (glutamate, γ-aminobutyric acid (GABA)) and neuromodulators (acetylcholine, dopamine, serotonin, etc.). However, despite sharing similar molecular elements, neurotransmitters and neuromodulators are distinct classes of molecules and mediate different aspects of neural activity and metabolism. Neurotransmitters on one hand are responsible for synaptic signal transmission (classical transmission) while neuromodulators exert their functions by mediating different postsynaptic events that result in changes to the balance between excitation and inhibition. Neuromodulation, while essential to nervous system function, has been significantly more difficult to study than neurotransmission. This is principally due to the fact that effects elicited by neuromodulators are usually of slow onset, long lasting, and are not simply excitation or inhibition. In contrast to the effects of neurotransmitters, neuromodulators enable neurons to be more flexible in their ability to encode different sorts of information (e.g. sensory information) on a variety of time scales. However, it is important to appreciate that one of the challenges in the study of neuromodulation is to understand the extent to which neuromodulators’ actions are coordinated at all levels of brain function. That is, from the cellular and metabolic level to network and cognitive control. Therefore, understanding the molecules that mediate brain networks interactions is essential to understanding the brain dynamic, and also helps to put the cellular and molecular processes in perspective. Functional magnetic resonance imaging (fMRI) is a technique that allows access to various cellular and metabolic aspects of network communication that are difficult to access when studying one neuron at the time. Its non-invasiveness nature allows the comparison of data and hypotheses of the primate brain to that of the human brain. Hence, understanding the effects of neuromodulation on local microcircuits is needed. Furthermore, given the massive projections of the neuromodulatory diffuse ascending systems, fMRI combined with pharmacological and neurophysiological methods may provide true insight into their organization and dynamics. However, little is known about how to interpret the effects of neuromodulation in fMRI and neurophysiological data, for instance, how to disentangle blood oxygenation level dependent (BOLD) signal changes relating to cognitive changes (presumably neuromodulatory influences) from stimulus-driven or perceptual effects. The purpose of this dissertation is to understand the causal relationship between neural activity and hemodynamic responses under the influence of neuromodulation. To this end we present the results of six studies. In the first study, we aimed to establish a mass-spectrometry-based technique to uncover the distribution of different metabolites, neurotransmitters and neuromodulators in the macaque brain. We simultaneously measured the concentrations of these biomolecules in brain and in blood. In a second study, we developed a multimodal approach consisting of fMRI (BOLD and cerebral blood flow or CBF), electrophysiological recording with a laminar probe and pharmacology to assess the effects of neuromodulation on neurovascular coupling. We developed a pharmacological injection delivery system using pressure-operated pumps to reliably apply drugs either systemically or intracortically in the NMR scanner. In our third study, we systemically injected lactate and pyruvate to explore whether the plasma concentration of either of these metabolites affects the BOLD responses. This is important given that both metabolites are in a metabolic equilibrium; if this equilibrium is disrupted, changes in the NAD and NADH concentrations would elicit changes in the CBF. In a fourth study, we explored the influence of dopaminergic (DAergic) neuromodulation in the BOLD, CBF and neurophysiological activity. Here we found that DAergic neuromodulation dissociated the BOLD responses from the underlying neural activity. Interestingly, the changes in the neural activity were tightly coupled to the effects seen in the CBF responses. In a subsequent study, we explored whether the effects of dopamine (DA) on the electrophysiological responses are cortical layer dependent and whether specific patterns of neural activity can be used to infer the effects of neuromodulation on the neural activity. This is important, given that different types of neural activity provide independent information about the amplitude and dynamics from BOLD responses, and studies have shown that these bands originate from different cortical layers. What this study revealed, is that local field potentials (LFPs) in the midrange frequencies can indeed provide indications about the sustained effects of neuromodulation on cortical sensory processing. Given the results from the previous study, in our sixth study, we aimed at understanding how different cortical layers may process incoming and outgoing information in the different LFP bands. These findings provide evidence that neuromodulation has profound effects on neurovascular coupling. By changing the excitation-inhibition balance of neural circuits, neuromodulators not only mediate the neural activity, but also adjust the metabolic demands. Therefore, understanding how the different types of neuromodulators affect the BOLD response is essential for an effective interpretation of fMRI-data, not only in tasks involving attentional and reward-related processes, but also for future diagnostic use of fMRI, since many psychiatric disorders are the result of alterations in neuromodulatory systems.Die Kommunikation zwischen den Neuronen innerhalb neuronalen Schaltkreise beruht auf Neurotransmitter (Glutamat, γ-Aminobuttersäure (GABA)) und Neuromodulatoren (Acetylcholin, Dopamin, Serotonin, etc.). Neurotransmitter und Neuromodulatoren sind jedoch unterschiedliche Klassen von Molekülen und verschiedenen Aspekte der neuronalen Aktivität und den Stoffwechsel vermitteln. Neurotransmitters sind einerseits verantwortlich für die synaptische Signalübertragung (klassische Übertragung), während ihre Funktionen ausüben, Neuromodulatoren durch verschiedene postsynaptischen Ereignisse zu vermitteln, die in Änderungen an der Balance zwischen Erregung und Hemmung führen. Neuromodulation , während wesentlich Funktion des Nervensystems hat sich als Neurotransmission wesentlich schwieriger gewesen, zu studieren. Dies ist hauptsächlich auf die Tatsache zurückzuführen, die durch Neuromodulatoren sind in der Regel von langsamen Beginn, langlebig, und sind nicht einfach Anregung oder Hemmung ausgelöst beeinflusst. Im Gegensatz zu den Wirkungen von Neurotransmittern, Neuromodulatoren ermöglichen Neuronen flexibler zu sein in ihrer Fähigkeit, verschiedene Arten von Informationen (beispielsweise sensorische Informationen) auf einer Vielzahl von Zeitskalen zu kodieren. Im Gegensatz zu den Wirkungen von Neurotransmittern, Neuromodulatoren ermöglichen Neuronen flexibler zu sein in ihrer Fähigkeit, verschiedene Arten von Informationen (beispielsweise sensorische Informationen) auf einer Vielzahl von Zeitskalen zu kodieren. Im Gegensatz zu den Wirkungen von Neurotransmittern, Neuromodulatoren ermöglichen Neuronen flexibler zu sein in ihrer Fähigkeit, verschiedene Arten von Informationen (beispielsweise sensorische Informationen) auf einer Vielzahl von Zeitskalen zu kodieren. Jedoch ist es wichtig, dass eine der Herausforderungen bei der Untersuchung von Neuromodulations zu schätzen ist, das Ausmaß, in dem Neuromodulatoren Aktionen koordiniert sind auf allen Ebenen der Gehirnfunktion zu verstehen. Das heißt, von der zellulären und metabolischen Ebene zu vernetzen und kognitive Kontrolle. Daher die Moleküle zu verstehen, die Gehirn Netzwerke Interaktionen vermitteln ist wesentlich für das Verständnis des Gehirns dynamisch, und hilft auch, die zellulären und molekularen Prozesse in Perspektive zu setzen. Funktionellen Kernspintomographie (fMRI) ist eine Technik, die Zugang zu verschiedenen zellulären und metabolischen Aspekte der Netzwerk-Kommunikation ermöglicht, die schwer zugänglich sind, wenn zu der Zeit eines Neurons zu studieren. Seine nicht-Invasivität Natur ermöglicht den Vergleich von Daten und Hypothesen des Primatengehirn zu der des menschlichen Gehirns. Somit wurde das Verständnis der Auswirkungen der Neuromodulation auf lokale Mikro benötigt. Darüber hinaus sind die massiven Projektionen der neuromodulatorischen diffuse Aufstiegsanlagen gegeben, kombiniert fMRI mit pharmakologischen und neurophysiologischen Methoden wahren Einblick in ihre Organisation und Dynamik liefern. Allerdings ist nur wenig darüber bekannt, wie die Auswirkungen der Neuromodulations in fMRI und neurophysiologische Daten zu interpretieren, zum Beispiel, wie Blutoxydation pegelabhängig (BOLD) Signaländerungen in Bezug auf kognitive Veränderungen (vermutlich neuromodulatorischen Einflüsse) von Stimulus-driven oder Wahrnehmungseffekte zu entwirren. Der Zweck dieser Arbeit ist es, die kausale Beziehung zwischen neuronaler Aktivität und hämodynamischen Reaktionen unter dem Einfluss der Neuromodulations zu verstehen. Zu diesem Zweck stellen wir die Ergebnisse von sechs Studien. In der ersten Studie wollten wir eine auf Massenspektrometrie basierende Technik einzurichten, um die Verteilung von verschiedenen Metaboliten, Neurotransmittern und Neuromodulatoren in Makakengehirn aufzudeckenWir maßen gleichzeitig die Konzentrationen dieser Biomoleküle im Gehirn und im Blut. In einer zweiten Studie entwickelten wir einen multimodalen Ansatz, bestehend aus fMRI (BOLD und zerebralen Blutflusses oder CBF), elektrophysiologische Aufzeichnung mit einer laminaren Sonde und Pharmakologie, die Auswirkungen der Neuromodulation auf neurovaskulären Kopplung zu beurteilen. Wir entwickelten eine pharmakologische Injektionsverabreichungssystem druckbetriebenen Pumpen mit zuverlässiger Medikamente gelten entweder systemisch oder intrakortikale im NMR-Scanner. In unserer dritten Studie injizierten wir systemisch Laktat und Pyruvat zu untersuchen, ob die Plasmakonzentration von entweder dieser Metaboliten die BOLD-Antworten beeinflusst. Dies ist wichtig, dass beide gegeben Metaboliten in einem Stoffwechselgleichgewicht sind; wenn dieses Gleichgewicht gestört ist, Veränderungen in den NAD und NADH-Konzentrationen würden Veränderungen in der CBF entlocken. In einer vierten Studie untersuchten wir den Einfluss von dopaminergen (DA-erge) -Neuromodulation im BOLD, CBF und neurophysiologische Aktivität. Hier fanden wir, dass DAerge -Neuromodulation die BOLD-Antworten von der zugrunde liegenden neuronalen Aktivität distanzierte. Interessanterweise waren verbunden, um die Veränderungen in der neuronalen Aktivität eng auf die in den CBF Reaktionen gesehen Wirkungen. In einer nachfolgenden Studie untersuchten wir, ob die Wirkungen von Dopamin (DA) auf die elektrophysiologischen Reaktionen sind Rindenschicht abhängig, und ob bestimmte Muster der neuronalen Aktivität verwendet werden kann, die Wirkungen von Neuromodulations auf die neurale Aktivität zu schließen. Dies ist wichtig, da verschiedene Arten von neuralen Aktivität liefern unabhängige Informationen über die Amplitude und die Dynamik von BOLD-Antworten, und Studien haben gezeigt, dass diese Bands aus verschiedenen kortikalen Schichten stammen. Was diese Studie ergab, dass lokale Feldpotentiale (LFP) in den mittleren Frequenzen in der Tat Hinweise über die nachhaltige Wirkung der Neuromodulation auf die kortikale sensorische Verarbeitung zur Verfügung stellen kann. In Anbetracht der Ergebnisse der früheren Studie, in unserer sechsten Studie wollten wir auf das Verständnis, wie die verschiedenen kortikalen Schichten verarbeiten kann ein- und ausgehenden Informationen in den verschiedenen LFP-Bands. Diese Ergebnisse belegen, dass -Neuromodulation profunde Auswirkungen auf die neurovaskulären Kopplung hat. Durch die Veränderung der Erregungs Hemmung Gleichgewicht neuronaler Schaltkreise vermitteln Neuromodulatoren nicht nur die neurale Aktivität, sondern auch die metabolischen Anforderungen anzupassen. Daher verstehen, wie die verschiedenen Arten von Neuromodulatoren beeinflussen die BOLD-Antwort für eine effektive Interpretation von fMRI-Daten notwendig ist, nicht nur in Aufgaben attentional und Belohnung bezogenen Prozessen mit, sondern auch für zukünftige diagnostische Verwendung von fMRI, da viele psychiatrische Störungen sind das Ergebnis von Veränderungen in neuromodulatorischen Systemen.La comunicación de las neuronas en los circuitos neuronales depende de los neurotransmisores (glutamato, acido γ-amino-butírico o GABA) y los neuromoduladores (acetilcolina, dopamina, serotonina, etc.). Sin embargo, tanto neurotransmisores como neuromoduladores son diferentes clases de moléculas y median diferentes aspectos de la actividad neuronal y del metabolismo, a pesar de compartir elementos moleculares muy similares. Los neurotransmisores, por una lado, son responsables de la transmisión sináptica de la información mientras que los neuromoduladores median diferentes eventos pos-sinápticos que resultan en cambios en el balance de la excitación e inhibición. La influencia de la neuromodulación es esencial para la función del sistema nerviosos, sin embargo es más difícil de estudiar que neurotransmisión. Esto se debe a que los efectos de los neuromoduladores suelen ser de un inicio lento, de larga duración, y no reflejan excitación o inhibición. En contraste a los efectos de los neurotransmisores, los neuromoduladores permiten que las neuronas sean más flexibles en su habilidad de codificar diferentes tipos de información (por ejemplo, información sensorial) en varias escalas temporales. Sin embargo, es importante darse cuenta que uno de objetivos primordiales en el estudio de neuromodulación es el de entender el grado en que la acción de los neuromoduladores está coordinada a todos los niveles de la función cerebral. Es decir, desde los aspectos celulares y metabólicos hasta los niveles de redes neuronales y control cognitivo. Por lo tanto, comprender los forma en la que diferentes moléculas median la interacción entre redes neuronal es esencial para el entendimiento de la dinámica cerebral, y también nos ayudara a comprender los procesos celulares y moleculares asociados a la percepción. La resonancia magnética funcional (fMRI, por sus siglas en inglés) es una técnica que permite acceder a varios aspectos celulares y metabólicos de la comunicación entre redes neuronales que suele ser de difícil acceso. Al mismo tiempo y debido que la fMRI es de naturaleza no invasiva, también permite comparar resultados e hipótesis entre humanos y primates. Por lo tanto, entender los efectos de la neuromodulación en la actividad de los circuitos neuronales es de alta relevancia. Dado que las proyecciones anatómicas de los sistemas de neuromoduladores, el uso de fMRI en combinación con farmacología y neurofisiología puede incrementar nuestro conocimiento sobre la estructura y dinámica de los sistemas de neuromoduladores. Sin embargo, poco se sabe sobre cómo interpretar los efectos de neuromodulation usando fMRI y neurofisiología, por ejemplo, como diferenciar los cambios en la señal BOLD que están relacionados a diferentes estados cognitivos (presumiblemente reflejando la influencia de neuromodulation). El propósito de esta disertación es la de comprender la relación causal que existe entre la actividad neural y la respuesta hemodinámica bajo la influencia de neuromodulación. Para tal fin presentamos los resultados de seis estudios que fueron producto de esta disertacion. En el primer estudio, desarrollamos una técnica basada en espectrometría de masa para detectar y medir la concentración de diferente metabolitos, neurotransmisores y neuromoduladores en el cerebro de primates. Dicha cuantificación se desarrollo simultáneamente tanto in sangre y cerebro. En un segundo estudio, utilizamos varias técnicas de fMRI (BOLD y flujo cerebral sanguíneo, CBF por sus siglas en ingles), registros electrofisiológicos con electrodos laminares y farmacología para acceder a los efectos de neuromodulation en el acople neurovascular. Para este fin, desarrollamos un sistema de inyecciones, basada en cambios de presión, para aplicar substancias sistémicamente o intracorticalmente dentro de un escáner de resonancia magnética. En nuestro tercer estudio, comparamos los efectos de lactato y piruvato para explorar como el desequilibrio metabólico de estas dos substancias afecta la respuesta BOLD. Esto es de gran importancia ya que ambas substancias metabólicas usualmente están en equilibrio. Sin embargo, cuando dicho equilibrio es interrumpido, los procesos metabólicos que acontecen en la mitocondria afectan las concentraciones de NAD y NADH causado cambios en el CBF. En un cuarto estudio, exploramos los efectos de las modulación dopaminergica (DAergic) en las señales BOLD, CBF y en la actividad neuronal. Encontramos que la modulación DAergic disocia las respuesta BOLD de la respuesta neuronal. Interesalmente, los cambios que observamos en la actividad de las neuronas estaba altamente acoplados a los efectos que observamos en la señal de CBF. En un estudio subsecuente, exploramos si los efectos de dopamina en la actividad neuronal es diferentes en las distintas capas de la corteza cerebral. Al mismo tiempo y ya que los neuromoduladores afectan la actividad de circuitos neuronales, exploramos si dichos efectos pueden usados como marcadores de la influencia de la neuromodulación . Esto es importante, ya que diferentes tipos de actividad neuronal brinda información sobre la amplitud y dinámica de la repuesta BOLD, y estudies han demostrado que estas bandas se originan de diferentes capas cortical. Este estudio revelo, que los potenciales de capo (LFPs, por sus siglas en ingles) en frecuencias intermedias puede ser indicativos sobre los efectos de neuromodulation en el procesamiento cortical. Dado los resultados en el estudio previo, en un sexto estudio, nos enfocamos a entender que tan diferentes las capas de la corteza procesan información entrante y saliente en diferentes frecuencias de los LFPs. Estos descubrimientos demuestran que los efectos de los neuromoduladores tiene una fuerte influencia en el acople neurovascular. Los neuromoduladores cambian el balance de excitación e inhibición de los circuitos neuronal, pero también median las demandas metabólicas. De esta manera, entender cómo interpretar los efectos de los neuromoduladores en la respuesta BOLD es esencial para una interpretación veraz y efectiva de los datos generados con fMRI. Estos resultados, no solo nos permiten comprender los procesos que están relacionados a la atención o de varios procesos cognitivos, sino que a su vez, nos permite comprender la señal de fMRI para su futuro uso en la medicina diagnostica, ya que muchas enfermedades psiquiátricas están asociadas a trastornos en el sistemas neuromoduladores