TRPV1 channels are critical brain inflammation detectors and neuropathic pain biomarkers in mice

The capsaicin receptor TRPV1 has been widely characterized in the sensory system as a key component of pain and inflammation. A large amount of evidence shows that TRPV1 is also functional in the brain although its role is still debated. Here we report that TRPV1 is highly expressed in microglial cells rather than neurons of the anterior cingulate cortex and other brain areas. We found that stimulation of microglial TRPV1 controls cortical microglia activation per se and indirectly enhances glutamatergic transmission in neurons by promoting extracellular microglial microvesicles shedding. Conversely, in the cortex of mice suffering from neuropathic pain, TRPV1 is also present in neurons affecting their intrinsic electrical properties and synaptic strength. Altogether, these findings identify brain TRPV1 as potential detector of harmful stimuli and a key player of microglia to neuron communication

Interactions with pain-related systems - Towards new electrical treatments for chronic pain

Background. Persistent intolerable pain is still an unsolved issue with a huge socioeconomic impact. To develop appropriate treatments, it is crucial to understand the complex mechanisms underlying pain and how they change during sustained pain stimuli or during pathological conditions. In particular, it is essential to clarify how the endogenous analgesic centres which are present in the brain, such as periaqueductal grey (PAG) matter and dorsal raphe nuclei (DRN) in the brainstem, modulate pain by interfering with the nociceptive information. Deep brain stimulation of these areas can elicit potent analgesia. However, it has not been possible to exploit its full analgesic potential due to the insufficient stimulation specificity of the state-of-the-art probes.Aim. To address this challenge, we developed and implanted in rodents, a novel probe for high-definition brain stimulation (HDBS) based on the spread in 3D of ultra-flexible microelectrodes in PAG/DRN. The probe comprised 16 ultra-flexible microelectrodes embedded in a gelatine needle-like probe. The main aim was to elucidate whether stimulation of individually selected microelectrodes can selectively activate the anti-nociceptive pathways without activating networks that provoke side effects.Methodology. The selection of an appropriate microelectrode subset and stimulation intensity was done by monitoring the withdrawal reflexes elicited by CO2 laser stimuli and by simultaneous behavioural observations in awake freely moving animals. To evaluate the effect of HDBS in PAG/DRN on the nociceptive pathways related to pain perception, microelectrode recordings were made in cortical areas known to be involved in the sensory-discriminative and affective aspects of pain. Clinically relevant aspects such as potency, specificity, sustainability, reliability of HDBS as well as efficacy in conditions with hypersensitivity to nociceptive stimuli (hyperalgesia) were assessed by recording nociceptive-evoked cortical responses, withdrawal reflexes, gait and normal behaviours. To assess the presence of side effects, HDBS effect on intracortical spontaneous activity, brain states (ECoGs), behaviour in an open field, and the tactile input to cortex was also investigated. The tissue reactions to the implanted stimulation probe and the probe placement were evaluated using immunohistochemistry. In addition, we investigated whether tissue reactions related to probe implantation can be mitigated by incorporating PLGA-nanoparticles loaded with an anti-inflammatory drug, minocycline, and embedded into a gelatine vehicle.Results. For all the animals with verified placement within or nearby PAG/DRN, it was possible to individually select a microelectrode subset and stimulation intensity, which strongly inhibit nociceptive-evoked withdrawal reflexes without noticeable side effects. The selected microelectrode combinations also reduced nociceptive-evoked cortical responses (related to both discriminative and affective pain) in normal conditions and during hyperalgesia. The HDBS-induced analgesia could be sustained for at least 4 hours and did not provoke significant side effects on behaviour, spontaneous activity, and brain states and it had a minor effect on the tactile afferent pathway to the cortex. Histological analysis showed minimal tissue reactions and neuronal death around the stimulation implant. Minocycline containing PLGA nanoparticles significantly reduced glial reactions without signs of toxicity. Conclusions. These results show that granular and high-resolution PAG/DRN stimulation enables potent, specific, safe, and durable analgesia by blocking the nociceptive-evoked motor, sensory and affective responses without significant activation of pathways provoking adverse side effects. Therefore, HDBS in PAG/DRN holds great promise as an efficient treatment of intractable chronic pain disorders

Deep brain stimulation for disorders of consciousness and diminished motivation:A search for awakenings

This thesis deals with patients who are amongst the most severely affected after severe brain injury: those with permanent disorders of consciousness or diminished motivation. The research in this thesis is an attempt to improve consciousness and the general behavioral performance of these patients with the use of experimental interventions, including medication (such as zolpidem), and more invasive procedures, such as deep brain stimulation (DBS). The thesis contains extensive descriptions of the role of the intralaminar thalamus in the arousal regulation system, the importance of recognizing and treating secondary complications after brain injury, such as hydrocephalus, as well as a pathophysiological elaboration on akinetic mutism: a severe disorder of diminished motivation. Moreover, it describes the neurophysiological changes that accompany the paradoxical effects of zolpidem, a sleeping pill that temporarily induces ‘awakenings’ in some patients with severe brain injury. Further, it describes the first clinical and neurophysiological results of an N=6 trial of DBS in patients with a minimally conscious state and shows the importance of recognizing pathological changes from the brain’s ‘physiological baseline’ that seem to disturb normal brain functions. The thesis concludes with a description of the use of moral case deliberation in dealing with research dilemmas in patients with loss of autonomy after severe brain injury

Magneto-Electric Nanoparticles Cobalt Ferrite (CoFe2O4) -- Barium Titanate (BaTiO3) for Non-Invasive Neural Modulations

Indiana University-Purdue University Indianapolis (IUPUI)Non-invasive brain stimulation is valuable for studying neural circuits and treating various neurological disorders in human. However, current technologies of noninvasive brain stimulation usually have low spatial and temporal precision and poor brain penetration, which greatly limit their application. A new class of nanoparticles known as magneto-electric nanoparticles (MENs) is highly efficient in coupling an externally applied magnetics wave with generating local electric fields for neuronal activity modulation. Here, a new type of MENs was developed that consisted of CoFe2O4- BaTiO3 and had excellent magneto-electrical coupling properties. Calcium imaging technique was used to demonstrate their efficacy in evoking neuronal activity in organotyic and acute cortical slices that expressed GCaMP6 protein. For in vivo noninvasive delivery of MENs to brain, fluorescently labeled MENs were intravenously injected and attracted to pass through blood brain barrier to a targeted brain region by applying a focal magnet field. Magnetic wave (~450 G at 10 Hz) applied to mouse brain was able to activate cortical network activity, as revealed by in vivo two-photon and mesoscopic imaging of calcium signals at both cellular and global network levels. The effect was further confirmed by the increased number of c-Fos expressing cells after magnetic stimulation. Histological analysis indicated that neither brain delivery of MENs nor the subsequent magnetic stimulation caused any significant increases in the numbers of GFAP and IBA1 positive astrocytes and microglia in the brain. MENs stimulation also show high efficacy in short-term pain relieve when tested with a tibial nerve injury mouse model. The study demonstrates the feasibility of using MENs as a novel efficient and non-invasive technique of brain stimulation, which may have great potential for translation

Cortical mapping of the neuronal circuits modulating the muscle tone. Introduction to the electrophysiological treatment of the spastic hand

L'objectiu d'aquest estudi es investigar l'organització cortical junt amb la connectivitat còrtico-subcortical en subjectes sans, com a estudi preliminar. Els mapes corticals s'han fet per TMS navegada, i els punts motors obtinguts s'han exportant per estudi tractogràfic i anàlisi de las seves connexions. El coneixement precís de la localització de l'àrea cortical motora primària i les seves connexions es la base per ser utilitzada en estudis posteriors de la reorganització cortical i sub-cortical en pacients amb infart cerebral. Aquesta reorganització es deguda a la neuroplasticitat i pot ser influenciada per els efectes neuromoduladors de la estimulació cerebral no invasiva.The purpose of this study is to investigate the motor cortex organisation together with the cortico-subcortical connectivity in healthy subjects, as a preliminary study. Cortical maps have been performed by navigated TMS and the motor points have been exported to DTI to study their subcortical connectivity. The precise knowledge of localization of the primary motor cortex area and its connectivity is the base to be used in later studies of cortical and subcortical re-organisation in stroke patients. This re-organisation is due to the neuroplascity and can be influenced by the neuromodulation effects of the non-invasive cerebral stimulation therapy by TMS

Dissection of Affective Catecholamine Circuits Using Traditional and Wireless Optogenetics

Parsing the complexity of the mammalian brain has challenged neuroscientists for thousands of years. In the early 21st century, advances in materials science and neuroscience have enabled unprecedented control of neural circuitry. In particular, cell-type selective manipulations, such as those with optogenetics and chemogenetics, routinely provide answers to previously intractable neurobiological questions in the intact, behaving animal. In this two-part dissertation, I first introduce new minimally invasive, wireless technology to perturb neural activity in the ventral tegmental area dopaminergic system of freely moving animals. I report a series of novel devices for studying and perturbing intact neural systems through optogenetics, microfluidic pharmacology, and electrophysiology. Unlike optogenetic approaches that rely on rigid, glass fiber optics coupled to external light sources, these novel devices utilize flexible substrates to carry microscale, inorganic light emitting diodes (μ-ILEDs), multimodal sensors, and/or microfluidic channels into the brain. Each class of device can be wirelessly controlled, enabling studies in freely behaving mice and achieving previously untenable control of catecholamine neural circuitry. In the second part of this dissertation, I apply existing cell-type selective approaches to dissect the role of the locus coeruleus noradrenergic (LC-NE) system in anxiety-like and aversive behaviors. The LC-NE system is one of the first systems engaged following a stressful event. While LC-NE neurons are known to be activated by many different stressors, the underlying neural circuitry and the role of this activity in generating stress-induced anxiety has not been elucidated until now. I demonstrate that increased tonic activity of LC-NE neurons is both necessary and sufficient for stress-induced anxiety; a behavior which is driven by LC projections to the basolateral amygdala. Furthermore, this activity and behavior is elicited by corticotropin releasing hormone-containing afferent inputs into the LC from the central amygdala. These studies position the LC-NE system as a critical mediator of acute stress-induced anxiety and offer a potential intervention for preventing stress-related affective disorders. Together these two objectives provide a rich technological toolbox for neuroscientists and yield important knowledge of how small catecholamine structures with widespread forebrain innervation can selectively mediate higher order behaviors

Solenoidal Micromagnetic Stimulation Enables Activation of Axons With Specific Orientation

Electrical stimulation of the central and peripheral nervous systems - such as deep brain stimulation, spinal cord stimulation, and epidural cortical stimulation are common therapeutic options increasingly used to treat a large variety of neurological and psychiatric conditions. Despite their remarkable success, there are limitations which if overcome, could enhance outcomes and potentially reduce common side-effects. Micromagnetic stimulation (μMS) was introduced to address some of these limitations. One of the most remarkable properties is that μMS is theoretically capable of activating neurons with specific axonal orientations. Here, we used computational electromagnetic models of the μMS coils adjacent to neuronal tissue combined with axon cable models to investigate μMS orientation-specific properties. We found a 20-fold reduction in the stimulation threshold of the preferred axonal orientation compared to the orthogonal direction. We also studied the directional specificity of μMS coils by recording the responses evoked in the inferior colliculus of rodents when a pulsed magnetic stimulus was applied to the surface of the dorsal cochlear nucleus. The results confirmed that the neuronal responses were highly sensitive to changes in the μMS coil orientation. Accordingly, our results suggest that μMS has the potential of stimulating target nuclei in the brain without affecting the surrounding white matter tracts

Tinnitus – psychiatric comorbidity and treatment using transcranial magnetic stimulation (TMS)

Tinnitus is the perception of sound in the absence of any external noise. It severely impairs the quality of life in 1-2% of people. Tinnitus is frequently associated with depression, anxiety, and insomnia. The exact pathophysiology of tinnitus is still unclear. No curative therapy exists for chronic tinnitus, and treatment focuses on symptomatic relief. Repetitive transcranial magnetic stimulation (rTMS) is a non-invasive neuromodulation technique that is used for treating depression and neuropathic pain. The evidence of its efficacy for chronic tinnitus is still inconclusive, and the optimal treatment protocols are thus still obscure. This thesis aimed to further evaluate the use of rTMS for chronic tinnitus and investigate the psychiatric comorbidity of tinnitus patients. The first (open pilot) study utilized electric field (E-field) navigated rTMS for very severe chronic tinnitus with promising results. In the second (randomized placebo-controlled) study, the effects of 1-Hz E-field rTMS targeted according to the tinnitus pitch to the left auditory cortex were analyzed. Despite the significant improvements in tinnitus, active rTMS was not superior to the placebo, possibly due to large placebo-effect and wide inter-individual variation in treatment efficacy. The third study on parallel groups compared the effects of neuronavigated rTMS to nonnavigated rTMS (based on the 10-20 EEG localization system). Both groups benefitted from the treatment, but the method of coil localization was not a critical factor for treatment outcome. In the fourth study, current and lifetime DSM-IV diagnoses of Axis I (psychiatric disorders) and Axis II (personality disorders) were assessed in tinnitus patients using structured clinical interviews (SCID-I and -II). Tinnitus patients were prone to episodes of major depression, and they often had obsessive-compulsive personality features. Psychiatric disorders in this study seemed to be comorbid or predisposing conditions rather than the consequences of tinnitus.Tinnitus – psykiatrinen sairastavuus ja hoito transkraniaalisella magneettistimulaatiolla (TMS) Tinnituksen ääniaistimus syntyy ilman ulkoista äänilähdettä. Se heikentää vakavasti elämänlaatua 1-2%:lla ihmisistä. Tinnitus yhdistetään usein masennukseen, ahdistukseen ja unettomuuteen. Tinnituksen tarkka syntymekanismi on vielä epäselvä. Pitkäaikaiselle tinnitukselle ei ole parantavaa hoitoa, vaan hoidossa keskitytään oireiden lievittämiseen. Transkraniaalinen magneettistimulaatio sarjapulssein (rTMS) on kajoamaton aivojen toimintaa muokkaava menetelmä, jota käytetään masennuksen ja hermoperäisen kivun hoidossa. Sen teho pitkäaikaiseen tinnitukseen on vielä epävarmaa ja optimaaliset hoitoprotokollat ovat selvittämättä. Tämän väitöskirjan tavoitteena oli arvioida rTMS:n käyttöä pitkäaikaisen tinnituksen hoidossa ja lisäksi tutkia tinnituspotilaiden psykiatrista sairastavuutta. Ensimmäisessä osatyössä (avoin pilotti) käytettiin sähkökenttäohjattua (E-field) navigoivaa rTMS:a pitkäaikaiseen, erittäin vaikeaan tinnitukseen lupaavin tuloksin. Toisessa osatyössä (satunnaistettu lumekontrolloitu) arvioitiin tinnitusäänen korkeuden mukaan vasemmalle kuuloaivokuorelle suunnatun 1- Hz:n sähkökentän mukaan navigoidun rTMS:n vaikutuksia. Vaikka tinnitus helpottui merkittävästi, ei aktiivi-rTMS ollut lumehoitoa parempi, mahdollisesti johtuen suuresta lumevaikutuksesta ja laajasta yksilöiden välisestä vaihtelusta hoidon tehossa. Kolmannessa osatyössä verrattiin rinnakkaisryhmien välillä neuronavigoidun rTMS:n ja sokko rTMS:n (10-20 EEG-systeemiin perustuva paikannus) vaikutuksia. Molemmat ryhmät hyötyivät hoidosta, eikä kelan paikannusmenetelmä ollut ratkaiseva tekijä hoidon lopputuloksen kannalta. Neljännessä osatyössä nykyiset ja elämänaikaiset akselin I (psykiatriset häiriöt) ja akselin II (persoonallisuushäiriöt) DSM-IV diagnoosit määritettiin tinnituspotilailta käyttäen strukturoituja psykiatrisia haastatteluja (SCID-I ja -II). Tinnituspotilaat olivat alttiita vakaville masennusjaksoille ja heillä oli usein vaativan persoonallisuuden piirteitä. Psykiatriset häiriöt vaikuttivat olevan ennemmin samanaikaisia tai altistavia tiloja kuin tinnituksen seurauksena ilmaantuneita häiriöitä

Source reconstruction of the neural correlates of ongoing pain using magnetoencephalography

Pain is a pervasive, complex, and subjective phenomenon that can be described by many features and researched using many paradigms; chronic pain has a significant impact on the quality of life of patients experiencing it and constitutes a large burden on the National Health Service. Discovering neural biomarkers for ongoing pain and pain sensitivity has the potential to elucidate underlying mechanisms, evaluate therapy effectiveness, and identify regions of interest within the brain for further study or intervention; something that is possible with functional imaging of brain activity. Magnetoencephalography (MEG) is a non-invasive technique that records brain activity through magnetic fields unobstructed by tissue of the head. This thesis utilises modern source reconstruction of MEG data to explore brain activity that characterises tonic pain conditions, and explores the future of tonic pain research by evaluating the utility of the PATHWAY Contact Heat Evoked Potentials Stimulator (CHEPS) – a tool used both as an experimental pain stimulus, and a clinical evaluation method in chronic pain – in current and future MEG research. A systematic review of studies exploring the CHEPS and MEG, which highlights the paucity of the literature combining the two despite the potential benefits of each, is presented within. Study one investigates the brain activity changes resulting from paraesthesia-based Spinal Cord Stimulation for chronic pain: significant enhancements in synchrony for theta and delta frequency bands during SCS-on resting-state are demonstrated, and a significant reduction in Somatosensory Evoked Potential (SSEP) power spectra in the SCS-on condition – providing evidence that conventional SCS influences resting and ascending processing in the brain, but does not necessarily suppress the field strength of SSEPs. Study two compared the neural activity of participants with high and low pain sensitivity during the Cold Pressor Test, and identifies regions of interest for future study. Study three is a methodological chapter which attempts to mitigate the methodological challenges involved in utilising the PATHWAY CHEPS in MEG research: The thorough exploration of independent component analysis, signal space separation and beamforming parameters demonstrates that it is possible to suppress the artefacts generated by the non-fMRI compatible CHEPS’ thermode with the application of signal attenuation techniques, but only in an empty room dataset; the implications of this for future research are discussed