Thesis (Ph.D.)--Boston University / PLEASE NOTE: Boston University Libraries did not receive an Authorization To Manage form for this thesis or dissertation. It is therefore not openly accessible, though it may be available by request. If you are the author or principal advisor of this work and would like to request open access for it, please contact us at open-help@bu.edu. Thank you. / The overall goal of this dissertation was to determine the role of the subthalamic nucleus (STN) in regulating the release of dopamine in the substantia nigra (SN). Experiments first established the existence of a direct connection between subthalamic neurons and SN dopaminergic cells. Further experiments showed that this connection triggers the dopamine release in the SN, and the mechanisms involved in this release were determined. Whole-cell current clamp recordings were performed in parasagittal brain slices obtained from 10 to 16 day-old rat pups. Electrical stimulations of the STN reliably triggered excitatory post-synaptic potentials (EPSPs) in dopaminergic neurons of the SN pars compacta (SNc). Pharmacological experiments with specific receptor antagonists indicated that this EPSP was mediated by NMDA, non-NMDA and metabotropic glutamate receptors. Stimulations of the subthalamic input triggered the release of dopamine. In a subset of neurons in the SN pars reticulata (SNr), repetitive stimulations of the STN produced a summating EPSP that was followed by an inhibitory postsynaptic potential (IPSP). A D2 receptor antagonist blocked this IPSP suggesting that it represents the D2 receptor-mediated response of the recorded cell to dopamine released upon stimulation of the STN. Pharmacological experiments using this assay indicated that NMDA, non-NMDA or metabotropic glutamate receptors were individually not required for dendritic release of dopamine; however, each contributed to this release. In dopaminergic neurons located in the SN pars compacta, the inhibitory effect of dopamine was revealed following block of L-type Ca channels, NMDA and non-NMDA glutamate receptors. These results indicated that dopaminergic neurons located both in the SNc and SNr respond to the dendritic release of dopamine triggered upon stimulations of the STN. Finally, a specific blocker of the dopamine transporter (GBR12935) blocked the IPSP reversibly in both SNr and SNc dopaminergic neurons. If release occurred by exocytosis, block of the transporter should increase extracellular levels of dopamine and produce an increase in the size of the recorded IPSP. Therefore, these results suggest that dopamine dendritic release triggered by activation of the subthalamic input was mediated by reversed transport of dopamine rather than by exocytosis. / 2031-01-01

Previous electrophysiological studies of the basal ganglia in Parkinson's disease (PD) patients have utilized linear analyses in time-or-frequency domains to characterize neuronal discharge patterns. However, these measures do not fully describe the non-linear features of discharge rates and oscillatory activities of basal ganglia neurons.In this original research, we investigate whether non-linear temporal organizations exist in the inter-spike interval series of neurons recorded in the globus pallidus or the subthalamic nucleus in PD patients undergoing surgery for the implantation of deep brain stimulating electrodes.Our data indicate that in approximately 80% of globus pallidus and subthalamic neurons, the raw inter-spike interval sequences have lower entropy values than those observed after shuffling of the original series. This is the first report establishing non-linear temporal organization as a common feature of neuronal discharge in the basal ganglia of PD patients.

京都大学 / 新制・論文博士 / 博士(医学) / 乙第13570号 / 論医博第2296号 / 新制||医||1069(附属図書館) / 京都大学大学院医学研究科医学専攻 / (主査)教授 花川 隆, 教授 渡邉 大, 教授 高橋 淳 / 学位規則第4条第2項該当 / Doctor of Medical Science / Kyoto University / DFAM

Background Parkinson’s disease (PD) is one of the most common neurodegenerative diseases in Europe. Besides motor dysfunction, PD is characterized by several non-motor and secondary motor features, such as weight change, sialorrhea, constipation and swallowing problems. Of these, swallowing is one of the most critical, as it is associated with aspiration pneumonia and consequently is the comorbidity with the highest mortality rate. Swallowing problems affect four of every five patients with PD, and even mild swallowing problems have notable psychosocial effects for patients and their caregivers. Consequently, it is essential to find treatment strategies for PD that may alleviate symptoms for patients with swallowing problems and their potential consequences. Deep Brain Stimulation (DBS) is a surgical treatment option for PD, which improves overall motor function and quality of life, but its effect on swallowing function is not clear. The purpose of this thesis was to contribute to the understanding of the effect of deep brain stimulation in the subthalamic nucleus (STN DBS) and the caudal zona incerta (cZI DBS) on pharyngeal swallowing function and on swallow-specific quality of life in patients with PD. The specific aims were to assess longitudinally the effect of STN DBS and cZI DBS on swallowing at 6 and 12 months postoperatively, in order to identify possible effects of the DBS on swallowing function. In addition, the effects of cZI DBS on ratings of swallowing-related non-motor and secondary motor features such as body weight changes, sialorrhea and speech problems were to be assessed. Methods Eleven PD patients with STN DBS (Paper I) and seventeen patients with cZI DBS (Paper II-IV) were included in this thesis. All patients were evaluated preoperatively and 6 and 12 months postoperatively. The effect of STN DBS and cZI DBS on swallowing was assessed with Fibreoptic-Endoscopic Evaluation of Swallowing (FEES) according to a predefined protocol including Penetration-Aspiration scale, Secretion Severity scale, preswallow spillage, pharyngeal residue, and pharyngeal clearance. Self-assessments were addressed using a visual analogue scale. The cZI DBS patients also completed the Swallowing Quality of Life (SWAL-QOL) questionnaire. Weight changes measured by Body Mass Index, and specific items from the Unified Parkinson’s Disease Rating Scale were also examined. Nine controls without PD were included in Paper IV, by answering the SWAL-QOL questionnaire. Results No clear effect of DBS on swallowing function or swallow-specific quality of life could be observed. There was no effect of DBS on the occurrence of aspiration, secretion, pharyngeal residue or clearance in the study groups with STN DBS or cZI DBS. Patients with STN DBS reported a subjective improvement in swallowing function with DBS stimulation turned on at 6 and 12 months after surgery. In patients with cZI DBS, the median body mass index was postoperatively increased with 1.1kg/m2 and the median increase in weight were +3.0 kg after 12 months with cZI DBS. The scores from the SWAL-QOL questionnaire were high overall in the group with cZI DBS, and the scores were unaffected by the cZI DBS surgery and stimulation. The SWAL-QOL total score was not significantly different between the PD patients and the controls, but the scores from the ‘burden’ and the ‘symptom’ subscales were worse in PD patients. Conclusions STN DBS or cZI DBS did not have a negative effect on swallowing function or ratings of swallow-specific ‘quality of life’ aspects in this cohort. Patients with STN DBS reported a self-perceived improvement in swallowing function when DBS was turned on. With regard to swallowing, patients with cZI DBS had an overall good quality of life throughout the conduct of the study and their swallow-specific quality of life was not negatively affected by cZI DBS. There seems to be no increased risk for aspiration or penetration due to surgery or stimulation for either the STN DBS or the cZI DBS groups. cZI DBS caused weight gain postoperatively. Since the sample sizes in these cohorts are small, the findings need to be confirmed in larger studies.

Parkinson's disease (PD) is characterized by debilitating impairments in motor control arising from pathophysiological alterations in basal ganglia circuitry and function. In this research thesis two main approaches, namely electrical recording and stimulation, are combined in order to better understand motor performance in Parkinson's disease and ways it might be improved. Three main types of motor behaviors are studied: discrete ballistic movement, repetitive movement, and motor adaptation. <ul><li>First, deep brain stimulation (DBS) of the subthalamic nucleus (STN) was shown to improve the velocity of discrete, ballistic movements in PD. The neural correlates of ballistic movements were then studied by recording from the STN of PD patients, revealing onset of beta-range desynchronization prior to, and gamma-range frequency synchronization during, performance of fast arm reaches. To determine a causal role for these oscillatory frequencies in motor behavior, the motor cortex of healthy humans was stimulated at either beta or gamma frequency during a 'go/no-go' grip force task. Beta stimulation resulted in slower force generation on 'go' trials but enhanced inhibition during 'no-go' trials, whereas gamma stimulation resulted in faster force generation on 'go' trials.</li> <li>Second, STN DBS resulted in improved repetitive tapping performance in PD patients through a reduction in variability. Recordings from the STN demonstrated that repetitive movement was accompanied by a substantial and persistent suppression of beta oscillatory activity.</li> <li>Third, Parkinson's patients were tested on a motor adaptation task, revealing intact learning but impaired retention of a visuomotor rotation. Application of direct current stimulation of the motor cortex resulted in enhanced adaptation during both learning and retention in PD patients and healthy controls.</li> <li>These results causally implicate the basal ganglia and oscillatory activity in motor control, provide insight into the neuronal mechanisms of motor performance and adaptation, and demonstrate promising new avenues for enhancing motor control in Parkinson's disease.</li></ul>

The basal ganglia (BG) is a complex set of heavily interconnected nuclei located in the central part of the brain that receives inputs from the several areas of the cortex and projects via the thalamus back to the prefrontal and motor cortical areas. Despite playing a significant part in multiple brain functions, the physiology of the BG and associated disorders like dystonia remain poorly understood. Dystonia is a devastating condition characterized by ineffective, twisting movements, prolonged co-contractions and contorted postures. Evidences suggest that it occurs due to abnormal discharge patterning in BG-thalamocortocal (BGTC) circuitry. The central purpose of this study was to understand the electrophysiology of BGTC circuitry and its role in motor control and dystonia. Toward this goal, an advanced multi-target multi-unit recording and analysis system was utilized, which allows simultaneous collection and analysis of multiple neuronal units from multiple brain nuclei. Over the cause of this work, neuronal data from the globus pallidus (GP), subthalamic nucleus (STN), entopenduncular nucleus (EP), pallidal receiving thalamus (VL) and motor cortex (MC) was collected from normal, lesioned and dystonic rats under awake, head restrained conditions. The results have shown that the neuronal population in BG nuclei (GP, STN and EP) were characterized by a dichotomy of firing patterns in normal rats which remains preserved in dystonic rats. Unlike normals, neurons in dystonic rat exhibit reduced mean firing rate, increased irregularity and burstiness at resting state. The chaotic changes that occurs in BG leads to inadequate hyperpolarization levels within the VL thalamic neurons resulting in a shift from the normal bursting mode to an abnormal tonic firing pattern. During movement, the dystonic EP generates abnormally synchronized and elongated burst duration which further corrupts the VL motor signals. It was finally concluded that the loss of specificity and temporal misalignment between motor neurons leads to corrupted signaling to the muscles resulting in dystonic behavior. Furthermore, this study reveals the importance of EP output in controlling firing modes occurring in the VL thalamus.

The subthalamic nucleus (STN), which is the most common target for deep brain stimulation for Parkinson's disease, is known to be crucially involved in motor control. Recent appreciation of the potential non-motor side effects of STN deep brain stimulation, however, has led to speculation that the importance of this nucleus may also relate to processes involved in decision- making, particularly during high conflict scenarios. This thesis concerns itself with investigating the STN's role in action selection during conflict. I begin by recording local field potentials directly from the STN of Parkinson's disease patients while they perform a flanker task that has been shown to elicit theta (4-8 Hz) band activity in areas of the prefrontal cortex involved in cognitive control. I report that like the prefrontal cortex, the STN demonstrates elevated theta activity during conflict. I then test whether STN theta activity is related to that of the prefrontal cortex by recording from both sites simultaneously while patients perform a novel task that temporally separates conflict from stimulus onset or movement. This reveals that theta activity indeed becomes synchronized during conflict, with cortical oscillations driving those of the STN. Thirdly, I investigate how STN oscillations may affect firing rate dynamics by intra-operatively recording local field potentials and single unit activity from patients performing the flanker task. I report that both theta and beta (15-30 Hz) oscillations entrain STN neurons, but only during conflict. Finally, I record cortical and STN activity while a fourth group of patients performs the flanker task. This experiment confirms that cortico-STN theta synchrony is elevated during conflict and may also relate to across-trial adaptations to conflict and errors. Taken together these studies shed light on the mechanisms by which cortical structures may influence the STN during conflict and why STN deep brain stimulation may result in impulsivity.

O óxido nítrico (NO) é uma molécula gasosa descrita recentemente, com implicações sobre uma vasta quantidade de processos fisiológicos, incluindo transmissão de sinais no sistema nervoso central (SNC). A sinalização nervosa mediada pelo NO ocorre por meios extrassinápticos, na chamada neurotransmissão por volume. Há evidências de que o NO seja um importante fator de modulação no controle da motricidade. A presença de neurônios que produzem NO já foi descrita em várias espécies, e estruturas ligadas ao controle do movimento como os núcleos da base (NNBB) contêm células nitrérgicas em quantidades variadas. Não se conhece os efeitos do processo de envelhecimento sobre a estrutura e função destes neurônios produtores de NO. O objetivo geral deste estudo foi investigar se o envelhecimento provoca alterações nos neurônios nitrérgicos presentes nos NNBB do encéfalo humano. Além disso, busca agregar mais conhecimento a aspectos morfológicos e de distribuição das células que compõem o sistema nitrérgico nos NNBB em humanos. As amostras de estriado (caudado e putâmen), globos pálidos (GP), núcleo subtalâmico (NST), substância negra (SN) e núcleo pedunculopontino (NPP) de 20 indivíduos sem doenças neurológicas e psiquiátricas foram submetidas à avaliação histológica em secções, coradas por técnicas que localizam neurônios que expressam NO, como a histoquímica para NADPH-diaforase (NADPHd) e à imunohistoquímica para sintase do NO neuronal (nNOS), e parâmetros de densidade neuronal e morfometria foram comparados entre indivíduos adultos jovens e idosos. Análises de densidade neuronal e morfometria entre subdivisões topográficas e funcionais também foram realizadas. Foi visto que o envelhecimento não provoca modificações na densidade neuronal e morfometria nitrérgica nos NNBB em humanos. Adicionalmente, o trabalho mostrou que: (I) as regiões mais posteriores do estriado se destacaram por apresentarem uma elevada densidade neuronal, associada a neurônios menores, em comparação com as regiões mais anteriores; (II) as porções do estriado ligadas ao córtex límbico apresentam maiores densidades neuronais; (III) o NST é uma região em que cerca de 90% de seus neurônios expressam NO, e suas características morfológicas sugerem que estas células coexpressem glutamato; (IV) o NPP é extensamente povoado por neurônios nitrérgicos, principalmente no nível do colículo inferior; (V) a presença de células NO-positivas é preponderante nas lâminas medulares de ambos GP, porém notamos maior concentração de células nitrérgicas no GPi; (VI) não foi detectada presença de neurônios quem contém NO na SN. Nossos resultados mostram que há uma presença maciça de neurônios que expressam NO em núcleos-chaves envolvidos com processamento motor corticobasal, como o NST, o estriado e o NPP, sugerindo que a neurotransmissão nitrérgica seja peça fundamental da fisiologia dos NNBB, portanto, com considerável potencial terapêutico nas doenças que afetam estas estruturas. / The nitric oxide (NO) is a gaseous molecule recently described, with a role on several physiologic processes, including signal transmission in central nervous system (CNS). The NO-mediated brain signaling occurs by extrasynaptic mode, called volume transmission. There are evidences supporting the NO as a major neurotransmitter involved on motor control modulation. The presence of NO neurons was described in many species, and movement-related structures, as the basal nuclei (BN), also contains variable densities of nitrergic cells. It is unknown the effect of aging over the structure and function of these NO neurons. The objective of the study is to investigate if the aging causes abnormalities on human BN nitrergic neurons. Furthermore, we aimed to explore distribution and morphologic features of these cells in BN. The samples of striatum (caudate and putamen), globus pallidum (GP), subthalamic nucleus (STN), substantia nigra (SN) and pedunculopontine nucleus (PPN) of 20 human brains from subjects without neurologic or psychiatric disases were processed for histologic analysis, stained by 2 techniques which localizes NO neurons: histochemistry for NADPH-diaphorase (NADPHd) and immunohistochemistry for neuronal NO synthase (nNOS); the neuronal density and morphometric parameters were compared between young adults and aged subjects. The neuronal density and morphometric analysis between striatal and subthalamic topographic / functional subdivisions were also performed. Our data showed that aging does not change the neuronal density or morphometric parameters of nitrergic neurons in human BN. Additionally, other results were found: (I) the most posterior regions of striatum have a higher neuronal density and smaller neurons than the most anterior regions of this nucleus; (II) the limbic cortex-associated areas of striatum have higher neuronal density than others functional subdivisions; (III) the STN is a region in which about 90% of its neurons expresses NO, and its morphologic features suggest these neurons coexpress glutamate; (IV) the PPN has a massive nitrergic neuronal density, mostly in the inferior colliculus level; (V) in GP, there is a marked presence of NO neurons in laminae medullaris, and the internal GP has more NO-positive cells than the external GP; (VI) nitrergic neurons were not detected in SN. Our results showed a remarkable presence of neurons expressing NO in nuclei essential for motor corticobasal processing (striatum, STN, PPN), suggesting that the nitrergic neurotransmission has a fundamental role in BN physiology, therefore, with great therapeutic potential in diseases involving these structures.

Background In advanced Parkinson’s disease (PD) the motor symptoms can be treated with deep brain stimulation (DBS). Subthalamic nucleus (STN) has been the most common target and caudal zona incerta (cZi) is a more recent target for stimulation. Stimulation in both of these targets has proved to be positive for the motor symptoms but there is no consensus about how DBS affects the speech and the articulation. Aim The aim of this study was to investigate how fricatives are realized within patients suffering from PD treated with DBS in STN or cZi. Method 9 patients stimulated in STN and 10 patients stimulated in cZi were recorded reading a shorter text.  The recordings were made preoperatively (Pre) and 12 months after surgery with the stimulation switched off (sOff) and on (sOn). From the recordings the fricatives were extracted and assessed in a blinded and randomized procedure. Results For the patients stimulated in cZi the target fricative /s/ had significant lower correct realizations in the sOn condition compared to the other two conditions. The other target fricatives in cZi showed the same pattern as well. For the STN group no unequivocal pattern could be seen. Conclusions The results suggest that stimulation in cZi may affect the patients’ articulation of fricatives and thereby their extended articulatory movements more negative than stimulation in STN.

Deep brain stimulation (DBS) has emerged as a potential intervention for treatment-resistant tardive dyskinesia (TD). Despite promising case reports, no consensus exists regarding optimal stimulation parameters, neuroanatomical target for DBS in TD, or mechanisms underlying its anti-dyskinetic effects. We used vacuous chewing movements (VCMs) in rats treated chronically with haloperidol (HAL) as a TD model to address some of these issues. We show that acute DBS applied to the subthalamic nucleus (STN) or the entopeduncular nucleus (EPN) suppresses VCMs without affecting locomotor activity. Using immediate early gene mapping with zif268 as an index of neuronal activity, we found that STN-DBS induced decreases in activity throughout the basal ganglia, whereas EPN-DBS increased activity in projection regions. While chemical inactivation of the STN or EPN with the GABAA agonist muscimol also suppressed VCMs, muscimol infusion did not mimic the changes in neuronal activity induced by DBS, suggesting that DBS is not equivalent to functional inactivation. We next examined the contribution of serotonin (5-HT) and dopamine (DA) to the anti-dyskinetic effects of DBS. Decreasing 5-HT transmission pharmacologically or with serotonergic lesions decreased VCMs. Using microdialysis and zif268 mapping, we determined that STN- but not EPN-DBS decreased 5-HT release and activity of raphe neurons. However, when the decrease in 5-HT induced by STN-DBS was prevented by pre-treating rats with fluoxetine or fenfluramine, we found that decreasing 5-HT is not necessary for the anti-dyskinetic effects of DBS. STN-DBS transiently increased striatal DA release in intact rats only, whereas EPN-DBS had no effect on DA release. Moreover, pharmacologically elevating DA levels did not suppress VCMs. Together these findings lead us to conclude that increased DA release does not contribute to the anti-dyskinetic effects of DBS. Finally, we compared depressive- and anxiety-like behaviours induced by chronic DBS of the EPN and STN, since adverse psychiatric effects of DBS have become a significant clinical concern. STN-DBS but not EPN-DBS induced depressive-like behaviour in a learned helplessness task. We established that the chronic HAL VCM model preparation may be used to explore mechanisms underlying anti-dyskinetic and psychiatric effects of DBS, and provided the first investigations into these mechanisms.