初級運動皮質直接負責運動控制。大量關於帕金森式癥(PD)的有效治療手段的研究已經證明，初級運動皮質在病理情況下的功能改變，直接與患者運動障礙相關。本論文的研究重點在於探索初級運動皮質在深部腦刺激治療帕金森氏症的運動障礙的過程中發揮的作用及其與運動學習功能障礙的聯繫。 / 丘腦底核深部腦刺激(STN-DBS) 已被廣泛應用於治療帕金森式症。雖然該項治療手段能顯著地改善患者的運動功能障礙，但其確切的治療機制仍未明確。理論上來說，丘腦底核深部腦刺激能夠直接啟動丘腦底核內部和其周圍很大範圍的神經組織，包括丘腦底核內部本身的神經元胞體，以及與其相連接的輸入輸出核團的神經元軸突。在丘腦底核眾多輸入核團之中，一個重要的神經輸入來自於初級運動皮質(MI)第五層的離皮質神經元(CxFn)，電刺激引起的逆行皮質啟動作用被提出，用於解釋丘腦底核深部腦刺激的治療機制。 / 為了研究逆行皮質啟動效應究竟如何在丘腦底核深部腦刺激的過程之中帶來治療效果，我們採用多通道神經電生理信號記錄系統在自由活動的單側帕金森大鼠的初級運動皮質進行鋒電位元和局部場電位元信號的記錄。實驗結果證明，當對丘腦底核進行高頻電刺激，在運動皮質第五層的離皮質神經元能成功記錄到保持固定延時的逆行鋒電位。由於增加刺激頻率會引起逆行鋒電位被成功記錄到的百分比下降，因此當深部腦刺激的頻率選擇在125Hz時，逆行鋒電位的放電頻率達到最高，而此刺激頻率正好與行為學實驗中帶來最佳治療效果的刺激頻率一致。於此同時，逆行皮質啟動作用還伴隨著初級運動皮質離皮質神經元的自發放電頻率增加、同步性爆發式放電減少等電生理信號特點。場電位分析的結果進一步表明，丘腦底核深部腦刺激減弱了病理情況下出現的beta波頻譜能量增高以及鋒電位-場電位相干性增強。更重要的是，我們發現只有逆行鋒電位被成功誘發，離皮質神經元的發放電機率才能被調節。這點有力地表明由電刺激隨機誘發的逆行鋒電位傳導至初級運動皮質，直接幹預並抑制了離皮質神經元在病理情況下的同步性爆發式放電活動，從而緩解了帕金森氏症的運動障礙。 / 另外，初級運動皮質並不僅僅是一個靜態的運動控制中樞，更為重要的功能在於它參與著與運動學習和運動記憶相關的動態資訊編碼。帕金森氏症患者普遍存在皮質可塑性減弱以及運動技能學習障礙。由於初級運動皮質分層結構的存在，層內神經元之間的突觸連接為神經可塑性提供了很好的結構基礎。因此，我們在初級運動皮質誘發在體長時程增強(LTP)，旨在研究與運動技能學習相關的皮質神經可塑性的動態變化過程，以及探索中腦多巴胺能投射系統對皮質神經可塑性的影響。 / 一方面，我們採用間斷性高頻刺激誘發在體長時程增強，證實六羥多巴損毀後皮質的長時程增強水準顯著下降。另一方面，我們設計前肢抓食的行為學範式用來評價動物在運動技能學習的不同階段皮質可塑性發生的動態變化。實驗結果表明，直接損毀皮質的多巴胺能輸入，模型組大鼠與假實驗組大鼠的行為表現在初期的技能獲取階段並無明顯差異，而只在後期的技能鞏固階段模型組大鼠表現出技能鞏固障礙。更為有趣的是，兩組行為學變化趨勢與各自的在體長時程增強的變化趨勢有很高的一致性。本研究表明多巴胺對初級運動皮質的支配在運動記憶的鞏固過程中起著關鍵作用。在帕金森氏症的病理情況下，多巴胺耗竭將影響皮質的突觸可塑性，從而造成帕金森患者在運動技能的鞏固階段表現出障礙。 / The primary motor cortex (MI) controls movement directly, but is an under-investigated brain region in the pathogenesis and treatment of Parkinsonian motor disability, when compared with the basal ganglia circuitry. In this study, the roles of MI in underlying the therapeutic action of surgical deep brain stimulation and motor learning impairment were investigated. / Deep brain stimulation of the subthalamic nucleus (STN-DBS) is now a recognized therapeutic option for Parkinson’s disease (PD). Although this surgical strategy provides behavioral benefits remarkably, its exact mechanism is still a matter of controversy. In principle, STN-DBS can directly activate a wide range of neuronal elements within the STN and surrounding areas. As the corticofugal neurons (CxFn) in the layer V motor cortex provide a major input to the STN, we hypothesized that the stimulation evoked antidromic cortical activation is involved in the therapeutic mechanism of STN-DBS. In the first series of experiments, we performed simultaneous recordings of multi-unit neuronal activities and local field potentials (LFPs) in MI in freely moving hemi-parkinsonian rats. By identifying stimulation evoked antidromic spike, which occurred at a fixed, short latency, CxFn located in the layer V MI were identified. Increasing stimulation frequency also increased failure rate of activation, resulting in a peak frequency of stochastic antidromic spikes at 125Hz STN-DBS, which was correlated with the optimal therapeutic efficacy observed in behavioral tests. Meanwhile, this antidromic effect was accompanied by the rectification of pathological neuronal activities including increased spontaneous firing rate, reduced burst discharge and synchrony among the CxFn. Field potential analysis revealed that STN-DBS alleviated the dominance of pathological beta band oscillation and spike-field coherence in the MI. More importantly, it was found that the firing probability of CxFn could only be modified following the occurrence of antidromic spikes, suggesting that direct interference of stochastic antidromic spikes with pathological neuronal activities underlies the beneficial effect of STN-DBS. / The MI is not simply a static motor control structure. It also contains a dynamic substrate that participates in motor learning or stores motor memory. In PD patients, loss of cortical plasticity and impaired motor learning is a common feature. As the intrinsic horizontal neuronal connections in MI are a strong candidate of cellular correlate for activity-dependent plasticity, in the second series of experiments, we developed in vivo long-term potentiation (LTP) technique in the MI to investigate the dynamics of cortical plasticity during motor skill learning and the role of the innervation by mesocortical dopamine input. Local depletion of dopamine in the primary motor cortex resulted in reduced performance in the forelimb reaching for food learning task. Although the performance of the PD rats in the initial learning phase was comparable to that of the sham-operated group, as training continued, these animals exhibited deficit in consolidating the motor skill. These deficits closely paralleled the impairment in training-enhanced synaptic connections in layer V neurons, and the in vivo LTP of evoked field excitatory postsynaptic potentials induced by intermittent high frequency stimulation. In addition, progressive recruitment of task-specific neurons was suppressed. Our study therefore revealed that dopamine depletion confined to the MI could lead to impairment in cortical synaptic plasticity which may preferentially affect the consolidation, but not the acquisition, of motor skills. These findings shed light on the cellular mechanisms of motor skill learning and could explain the decreased ability of PD patients in learning new motor skills. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Detailed summary in vernacular field only. / Li, Qian. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2013. / Includes bibliographical references (leaves 168-190). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts also in Chinese. / CHAPTER 1 --- p.1 / General Introduction --- p.1 / Chapter 1.1 --- Anatomical organization of the basal ganglia --- p.1 / Chapter 1.1.1 --- Overview of the basal ganglia circuit --- p.1 / Chapter 1.1.2 --- Cortico-basal ganglia-cortical circuit --- p.1 / Chapter 1.1.2.1 --- Direct and indirect pathway --- p.2 / Chapter 1.1.2.2 --- Hyperdirect pathway --- p.2 / Chapter 1.1.2.3 --- The midbrain dopamine system --- p.2 / Chapter 1.2 --- Striatum --- p.3 / Chapter 1.2.1 --- Cell types in the striatum. --- p.3 / Chapter 1.2.2 --- The Cortico-striatal system --- p.4 / Chapter 1.3 --- Subthalamic Nucleus --- p.5 / Chapter 1.3.1 --- Neuronal property of the STN. --- p.5 / Chapter 1.3.2 --- Electrophysiological property of the STN --- p.6 / Chapter 1.3.3 --- Cortico-subthalamic system --- p.7 / Chapter 1.3.4 --- Functional significance of the cortico-subthalamic and corticostriatal system. --- p.8 / Chapter 1.4 --- Parkinson’s disease --- p.9 / Chapter 1.4.1 --- Pathogenesis of PD --- p.9 / Chapter 1.4.2 --- Genetic risk factors of PD --- p.10 / Chapter 1.4.3 --- Progressive motor symptoms of PD --- p.11 / Chapter 1.4.4 --- Non-motor symptoms of PD --- p.13 / Chapter 1.4.5 --- Pathological neuronal rhythms in the basal ganglia of PD. --- p.16 / Chapter 1.5 --- Experimental studies of PD. --- p.18 / Chapter 1.5.1 --- Animal modeling of PD. --- p.18 / Chapter 1.5.2 --- Motor deficits evaluation in rodent models of PD --- p.21 / Chapter 1.5.3 --- Non-motor symptoms evaluation in experimental models of PD --- p.24 / Chapter 1.6 --- Deep Brain Stimulation --- p.27 / Chapter 1.6.1 --- DBS in alleviating Parkinsonian motor symptoms --- p.28 / Chapter 1.6.2 --- DBS in alleviating Parkinsonian non-motor symptoms --- p.29 / Chapter 1.6.3 --- Investigation of the STN-DBS mechanism. --- p.31 / Chapter 1.6.3.1 --- Local inhibitory effect within the STN --- p.32 / Chapter 1.6.3.2 --- Excitatory effect at output nuclei --- p.33 / Chapter 1.6.3.3 --- The de-coupling of soma and axons at system level --- p.34 / Chapter 1.6.3.4 --- Effects of DBS on abnormal rate or pattern --- p.35 / Chapter 1.6.3.5 --- Antidromic propagation of DBS effect towards cortex --- p.37 / Chapter 1.7 --- Objective --- p.38 / Chapter 1.8 --- Figures --- p.41 / CHAPTER 2 --- p.47 / General Methods --- p.47 / Chapter 2.1 --- Animals --- p.47 / Chapter 2.2 --- Stereotaxic surgery --- p.47 / Chapter 2.2.1 --- Preoperative preparation --- p.47 / Chapter 2.2.2 --- Anesthesia and craniotomy --- p.48 / Chapter 2.2.3 --- Induction of hemi-Parkinsonian rat model --- p.48 / Chapter 2.2.4 --- Electrode implantation techniques. --- p.49 / Chapter 2.3 --- Behavioral assessment. --- p.50 / Chapter 2.3.1 --- Apomorphine-induced contralateral rotation. --- p.50 / Chapter 2.3.2 --- Open field test --- p.50 / Chapter 2.4 --- STN-DBS protocol --- p.50 / Chapter 2.5 --- Electrophysiological data acquisition --- p.51 / Chapter 2.6 --- Data analysis --- p.52 / Chapter 2.6.1 --- Statistical analysis of behavioral data --- p.52 / Chapter 2.6.2 --- Electrophysiological data --- p.52 / Chapter 2.6.2.1 --- Stimulation artifact removal --- p.52 / Chapter 2.6.2.2 --- Multi-unit spike sorting --- p.53 / Chapter 2.6.2.3 --- Electrophysiological identification of pyramidal neuron and interneuron. --- p.54 / Chapter 2.6.2.4 --- Identification of antidromic cortical activation --- p.54 / Chapter 2.6.2.5 --- Discharge pattern classification --- p.54 / Chapter 2.6.2.6 --- Synchrony level evaluation --- p.55 / Chapter 2.6.2.7 --- Oscillatory rhythm characterization --- p.55 / Chapter 2.6.2.8 --- Coherence Level Measurement --- p.56 / Chapter 2.7 --- Histological verification --- p.56 / Chapter 2.8 --- Figures --- p.58 / CHAPTER 3 --- p.60 / Alleviation of Parkinsonian Motor Symptoms during Deep Brain Stimulation in Hemi-Parkinsonian Rats --- p.60 / Chapter 3.1 --- Introduction --- p.60 / Chapter 3.2 --- Materials & Methods --- p.61 / Chapter 3.2.1 --- Animals --- p.61 / Chapter 3.2.2 --- Chemicals --- p.61 / Chapter 3.2.3 --- Equipment --- p.61 / Chapter 3.3 --- Results --- p.62 / Chapter 3.3.1 --- Time course of the Apomorphine induced rotation behavior --- p.62 / Chapter 3.3.2 --- Dose-dependence of the Apomorphine induced rotation --- p.62 / Chapter 3.3.3 --- Acute behavioral response to STN-DBS. --- p.63 / Chapter 3.3.4 --- The dependence of STN-DBS effect on stimulation paradigm. --- p.64 / Chapter 3.3.5 --- Acute effects of STN-DBS on APO induced rotation. --- p.64 / Chapter 3.3.6 --- Long-term effects of STN-DBS on APO induced rotation --- p.64 / Chapter 3.3.7 --- Histological confirmation of the stimulation electrodes localization --- p.65 / Chapter 3.3.8 --- Loss of DA neurons in the SNc --- p.65 / Chapter 3.3.9 --- Reductions of the DA axon terminals in the striatum --- p.65 / Chapter 3.3.10 --- Chronic STN-DBS failed to rescue nigrostsriatal and striatal DA --- p.66 / Chapter 3.4 --- Discussion --- p.66 / Chapter 3.4.1 --- Neurotoxic mechanism of 6-OHDA --- p.66 / Chapter 3.4.2 --- Time course of dopamine degeneration induced by 6-OHDA --- p.66 / Chapter 3.4.3 --- Failure in observing worsened motor symptoms during low frequency STN-DBS. --- p.67 / Chapter 3.4.4 --- Experimental DBS based on rat model: does it mimic human case? --- p.67 / Chapter 3.4.5 --- Technical issues about STN-DBS --- p.69 / Chapter 3.5 --- Figures --- p.72 / CHAPTER 4 --- p.82 / Direct involvement of the Corticofugal Neurons in Motor Cortex during Therapeutic Deep Brain Stimulation --- p.82 / Chapter 4.1 --- Introduction --- p.82 / Chapter 4.2 --- Materials --- p.83 / Chapter 4.2.1 --- Animals --- p.83 / Chapter 4.2.2 --- Chemicals --- p.83 / Chapter 4.2.3 --- Equipment --- p.83 / Chapter 4.3 --- Results --- p.84 / Chapter 4.3.1 --- Identification of CxFn based on antidromic effect --- p.84 / Chapter 4.3.2 --- Antidromic spikes frequency correlates with therapeutic effect of STN-DBS. --- p.84 / Chapter 4.3.3 --- Pathological changes of neuronal firing rate in MI --- p.85 / Chapter 4.3.4 --- Only high frequency STN-DBS normalizes neuronal firing rate in MI --- p.86 / Chapter 4.3.5 --- Pathological changes of neuronal discharge pattern in MI --- p.88 / Chapter 4.3.6 --- Pathological synchrony of MI neuronal population, especially during burst discharge --- p.89 / Chapter 4.3.7 --- High frequency STN-DBS successfully suppresses synchronized burst discharge in MI --- p.89 / Chapter 4.3.8 --- Pathological β-band oscillatory activity in MI-LFPs induced by 6-OHDA lesion --- p.90 / Chapter 4.3.9 --- High frequency STN-DBS alleviates the β-band oscillation in MI-LFPs --- p.90 / Chapter 4.3.10 --- Synchronized bursting discharge correlates with oscillatory activity --- p.91 / Chapter 4.3.11 --- Pathological increased spike-LFP coherence level induced by 6-OHDA lesion --- p.92 / Chapter 4.3.12 --- High frequency STN-DBS modulated the spike-LFP coherence properties --- p.92 / Chapter 4.3.13 --- Antidromic spikes directly modulate the firing probability of CxFn --- p.93 / Chapter 4.3.14 --- Antidromic spikes modulate the firing probability of INs and non-CxFn nearby. --- p.94 / Chapter 4.3.15 --- The efficiency of antidromic cortical modulation depends on DBS frequency --- p.94 / Chapter 4.3.16 --- Orthodromic vs. antidromic effect: which one is responsible for the beneficial effect of DBS? --- p.95 / Chapter 4.3.17 --- Histology --- p.96 / Chapter 4.4 --- Discussion --- p.96 / Chapter 4.4.1 --- Origin of pathogenic rhythm in basal ganglia circuit --- p.96 / Chapter 4.4.2 --- Suppression of oscillatory synchronization equals to therapeutic effects of DBS? --- p.97 / Chapter 4.4.3 --- Beneficial effect of DBS corresponds to the topographic distribution of cortico-subthalamic projection. --- p.98 / Chapter 4.4.4 --- What is the reason for a stochastic pattern of antidromic activation effect? --- p.99 / Chapter 4.4.5 --- Desynchronization of pathological oscillatory rhythm by antidromic activation --- p.100 / Chapter 4.4.6 --- Antidromic vs. orthodromic: which is the cause of the beneficial effects of DBS? --- p.101 / Chapter 4.4.7 --- Wide propagation of antidromic effect by cortical horizontal circuits --- p.102 / Chapter 4.4.8 --- Significance of antidromic cortical activation in during STN-DBS --- p.102 / Chapter 4.4.9 --- Implication of antidromic activation effect on pathogenesis and treatment of PD --- p.104 / Chapter 4.5 --- Figures --- p.105 / CHAPTER 5 --- p.132 / Impaired Synaptic Plasticity in the Primary Motor Cortex after Dopamine Depletion: Potential Role in Motor Memory Consolidation --- p.132 / Chapter 5.1 --- Introduction --- p.132 / Chapter 5.1.1 --- Characteristics of motor learning --- p.132 / Chapter 5.1.2 --- Motor learning related cortical plasticity. --- p.133 / Chapter 5.1.3 --- Dopaminergic signals in the primary motor cortex --- p.134 / Chapter 5.1.4 --- Impaired cortical plasticity in PD --- p.135 / Chapter 5.1.5 --- Objective --- p.136 / Chapter 5.2 --- Materials --- p.136 / Chapter 5.2.1 --- Animals --- p.136 / Chapter 5.2.2 --- Chemicals --- p.136 / Chapter 5.2.3 --- Equipment --- p.136 / Chapter 5.3 --- Methods --- p.136 / Chapter 5.3.1 --- Functional mapping of the forelimb territory in MI --- p.136 / Chapter 5.3.2 --- Stereotaxic surgery --- p.137 / Chapter 5.3.3 --- Forelimb-reaching Task. --- p.137 / Chapter 5.3.4 --- In-vivo LTP Induction. --- p.138 / Chapter 5.4 --- Results --- p.139 / Chapter 5.4.1 --- Functional mapping of rat forelimb territory. --- p.139 / Chapter 5.4.2 --- Morphologies of evoked field potential response --- p.139 / Chapter 5.4.3 --- LTP of the early, monosynaptic plasticity within horizontal layer V MI --- p.140 / Chapter 5.4.4 --- LTP of the late, polysynaptic plasticity within horizontal layer V MI --- p.140 / Chapter 5.4.5 --- Impaired synaptic plasticity in MI after dopamine depletion --- p.140 / Chapter 5.4.6 --- Learning curve of forelimb-reaching task --- p.140 / Chapter 5.4.7 --- Physiologically enhanced cortical plasticity during motor learning --- p.141 / Chapter 5.4.8 --- Dynamic modulation of cortical neuronal activities during motor skill learning. --- p.142 / Chapter 5.4.9 --- Statistical analysis of ‘task related’ neuron’s modulation pattern. --- p.143 / Chapter 5.4.10 --- Loss of dopamine modulation in the MI --- p.144 / Chapter 5.5 --- Discussion --- p.144 / Chapter 5.5.1 --- Distinguishing between monosynaptic and polysynaptic transmission --- p.144 / Chapter 5.5.2 --- Artificially vs physiologically induced cortical plasticity. --- p.145 / Chapter 5.5.3 --- Cortical synaptic plasticity interprets motor learning dynamics --- p.146 / Chapter 5.5.4 --- Balance between neuronal recruitment and withdrawal in the consolidation stage --- p.147 / Chapter 5.5.5 --- Dopamine’s involvement in mediating the cortical synaptic plasticity. --- p.148 / Chapter 5.6 --- Figures --- p.150 / Conclusion --- p.162 / Abbreviations --- p.165 / References --- p.168

Introdução. A estimulação do córtex motor (ECM) tem sido utilizada para o tratamento de pacientes com síndromes neuropáticas dolorosas crônicas e resistentes a tratamentos farmacológicos convencionais. O córtex motor primário pode ser a estrutura mais rostral do neuroeixo relacionada ao sistema de modulação da dor, e a ECM provoca ativação neuronal na substância cinzenta periaquedutal (PAG). A PAG é um dos principais centros do sistema descendente supressor de dor e recebe aferências de diferentes regiões do encéfalo. Esse estudo investiga o efeito da estimulação do córtex motor sobre a liberação de neurotransmissores na PAG em modelo de dor neuropática, com o objetivo de investigar os mecanismos neuroquímicos responsáveis pelo feito terapêutico. Métodos. No primeiro experimento, ratos Wistar machos foram aleatoriamente divididos em três grupos. No primeiro grupo, os animais foram submetidos à indução de dor neuropática através da constrição crônica do nervo ciático, no segundo grupo, os animais foram submetidos apenas à exposição do nervo ciático e no terceiro grupo, nenhuma intervenção para indução de dor neuropática foi realizada. Todos os animais foram submetidos a implante unilateral epidural de eletródios de estimulação sobre a área do córtex motor correspondente a pata posterior e implante de cânula guia direcionada à PAG utilizando coordenadas estereotáxicas. Os animais foram avaliados no teste de hiperalgesia mecânica e uma sonda de microdiálise foi introduzida em direção a PAG. As amotras de microdiálise foram coletadas e a análise dos neurotransmissores foi feita em um sistema de cromatografia líquida de alta eficiência (HPLC). No segundo experimento, ratos Wistar machos com dor neuropática induzida na pata posterior foram submetidos a implante estereotáxico de cânula guia direcionada à PAG, e foi realizada micro-injeção de antagonista de glicina e/ou GABA na PAG, previamente a ECM, para avaliar a influência desses antagonistas no efeito analgésico induzido pela estimulação cortical. Resultados. Animais submetidos à indução de dor neuropática apresentaram reversão da hiperalgesia mecânica após ECM. A estimulação cortical induziu um aumento significativo nos níveis de glicina durante (aumento de 153%) e após MCS (134%). A concentração de GABA aumentou 145% durante a estimulação epidural. Os níveis de glutamato não mostraram alteração no microdialisado da PAG após ECM. Houve uma correlação estatisticamente significativa entre o posicionamento da sonda de microdiálise nas colunas lateral e dorsolateral da PAG e o aumento na liberação do neurotransmissor glicina nos animais do grupo CCI. A administração de antagonista de glicina na PAG reverteu o efeito antinociceptivo da estimulação cortical. A micro-injeção de antagonista de GABA na PAG reverteu parcialmente o efeito da ECM. Conclusões. Nossos resultados sugerem que os neutransmissores glicina e GABA, liberados na PAG durante ECM, contribuem para o efeito antinociceptivo da via analgésica descendente. Os resultados desse projeto poderão contribuir para a elucidação dos mecanismos do efeito antinociceptivo da ECM / Introduction. Motor cortex stimulation (MCS) has been used for the treatment of patients with chronic neuropathic pain syndromes that are resistant to conventional pharmacological treatment. The motor cortex may be the most rostral structure in the neuroaxis responsible for pain modulation, and MCS increase the neuronal activation of periaqueductal gray (PAG). The PAG is one of the main subcortical centers of the descending pain suppressor system, and receives inputs from several brain areas. This study investigates the effects of MCS on the release of neurotransmitters in the PAG in neuropathic pain model, in order to investigate the possible neurochemical mechanisms responsible for this effect. Methods. In the first experiment, Wistar male rats were randomly subdivided into three surgical groups. In the first group, induction of neuropathic pain was performed through chronic constriction injury of the right sciatic nerve, in the second group, the animals were submitted just to exposure of the sciatic nerve and in the third group, no intervention for induction of neuropathic pain was performed. All the rats underwent implantation of unilateral epidural electrodes on the motor area corresponding to the right hind paw. The animals were evaluated for mechanical hyperalgesia test and a microdialysis guide cannula was stereotaxically implanted into the PAG. The microdialysate samples were collected and the neurotransmitters analysis was performed by a high- performance (HPLC). In the second experiment, animals with induced neuropathic pain in the hind paw were submitted to a stereotaxic implantation of a guidewire directed to PAG, and a microinjection of glycine and/or GABA antagonist in the PAG before the ECM was performed, to evaluate the influence of these antagonists on the analgesic effect induced by the cortical stimulation. Results. Animals subjected to induction of neuropathic pain showed reversal of mechanical hyperalgesia after motor cortex stimulation. Cortical stimulation induced a significant increase in glycine levels during (153 % increase) and after MCS (134%). The GABA concentration increases 145 % during transdural stimulation. Glutamate levels showed no change in PAG microdialysate after MCS. There was a statistically significant correlation between the positioning of the microdialysis probe in the lateral and dorsolateral columns of the PAG and the increase in the release of the neurotransmitter glycine in the animals of the CCI group. Administration of glycine antagonist in PAG reversed the antinociceptive effect of cortical stimulation. Microinjection of GABA antagonist in PAG partially reversed the effect of MCS. Conclusions. Our results suggest that the neurotransmitters glycine and GABA, released in PAG during MCS, contribute to descending antinociceptive actions. The results of this project will contribute for the elucidation of the mechanisms of the antinociceptive effect of MCS, a phenomenon that has not been fully understood currently

Introdução. Nos últimos a função motora vem sendo associada com a atenuação sensitiva e de dor, logo antes, durante e apos a contração muscular. No entanto as vias anatômicas e funcionais deste fenômeno não são conhecidas. O objetivo deste estudo é o de criar um modelo animal e investigar o efeito da estimulação subliminar do córtex motor (ECM) no limiar nociceptivo e na atividade neuronal subcortical. Método. O limiar nociceptivo foi avaliado por teste plantar e reflexo de retirada da cauda antes e após o implante dos eletródios epidurais sobre o córtex motor da pata posterior orientado por mapa funcional na mesma cepa de ratos. Os mesmos testes foram repetidos antes, durante e após a ECM. Antagonismo sistêmico do por naloxona foi incluído neste protocolo para investigar a relação com mediação opióide. O registro neuronal multiunitário do núcleo centro mediano (CM) e ventral posterolateral (VPL) do tálamo e da substância periaqüeductal (SPM) foi realizado antes, durante e após ECM ipso e contralateral. Resultados. O implante per se não causou alterações no limiar nociceptivo. ECM induziu significativa antinocicepção seletiva na pata contralateral mas não na ipsolateral. Este efeito não mais foi observado 15 minutos após o término da estimulação. Nenhuma alteração motora e comportamental foi observada nos testes de campo aberto. A mesma estimulação no córtex sensitivo e parietal posterior não causou quaisquer alterações de limiar nociceptivo. Administração sistêmica de naloxone reverteu completamente o efeito antes observado com a ECM. O registro neuronal multiunitário evidenciou diminuição na atividade do CM durante e após a ECM contra e ipsolateral. O ritmo de disparos neuronais no VPL também mostrou diminuição apenas com a ECM ipsolateral. No entanto os neurônios da SPM aumentaram significativamente a freqüência de disparos com ECM ipsolateral e não com a contralateral. Conclusão. A ECM subliminar está relacionada consistentemente com a atenuação sensitiva durante o comportamento, provavelmente mediado por inibição talâmica e ativação da SPM. / Background. The motor function has been associated to sensory and pain attenuation, before during and shortly after the muscle activity. How ever the anatomical and functional basis of this phenomenon is not yet defined. The present study was designed to set an animal model and investigate the effect of subthreshold electrical stimulation of motor cortex (MCS) on pain threshold and neuron activity of thalamus and periaqüedutal gray. Method. Nociceptive thresholds of hind paws and the tail flick reflex were evaluated before and after surgical placement of epidural electrodes; before during and after electrical stimulation of motor cortex. Opioid antagonism was also included in this protocol in order to define neurotransmitter mediation of this process. Multiunit recording of thalamic median center (CM) and ventral posterolateral nuclei (VPL) and lateral periaqüedutal gray (SPM) were performed before and after electrical stimulation of ipso and contralateral motor cortex. Results. The procedure itself did not induce any threshold changes. MCS induced selective antinociception of contralateral paw, but no changes were detected in the nociceptive threshold of the ipsolateral side. This effect disappeared completely 15 minutes after the stimulation was ceased. No behavioral or motor impairment were observed during and after the stimulation session in the open field test. The same stimulation on sensory and posterior parietal cortex did not elicit any changes in behavioral and nociceptive tests. Systemic administration of naloxone completely reversed the previous observed antinociceptive effect. Multiunit recording evidenced decrease in spontaneous neuron firing in CM with short recovery time during ipso and contralateral MCS. Neuron activity in VPL was also significantly decreased during ipsolateral MCS but not with contralateral stimulation. How ever, neuron firing in SPM was significantly increased during and long after ipsolateral MCS but not with contralateral stimulation. Conclusion. Subthreshold MCS is consistently related to sensory attenuation during behavior, probably through thalamic inhibition and SPM activation.

Introdução. Nos últimos a função motora vem sendo associada com a atenuação sensitiva e de dor, logo antes, durante e apos a contração muscular. No entanto as vias anatômicas e funcionais deste fenômeno não são conhecidas. O objetivo deste estudo é o de criar um modelo animal e investigar o efeito da estimulação subliminar do córtex motor (ECM) no limiar nociceptivo e na atividade neuronal subcortical. Método. O limiar nociceptivo foi avaliado por teste plantar e reflexo de retirada da cauda antes e após o implante dos eletródios epidurais sobre o córtex motor da pata posterior orientado por mapa funcional na mesma cepa de ratos. Os mesmos testes foram repetidos antes, durante e após a ECM. Antagonismo sistêmico do por naloxona foi incluído neste protocolo para investigar a relação com mediação opióide. O registro neuronal multiunitário do núcleo centro mediano (CM) e ventral posterolateral (VPL) do tálamo e da substância periaqüeductal (SPM) foi realizado antes, durante e após ECM ipso e contralateral. Resultados. O implante per se não causou alterações no limiar nociceptivo. ECM induziu significativa antinocicepção seletiva na pata contralateral mas não na ipsolateral. Este efeito não mais foi observado 15 minutos após o término da estimulação. Nenhuma alteração motora e comportamental foi observada nos testes de campo aberto. A mesma estimulação no córtex sensitivo e parietal posterior não causou quaisquer alterações de limiar nociceptivo. Administração sistêmica de naloxone reverteu completamente o efeito antes observado com a ECM. O registro neuronal multiunitário evidenciou diminuição na atividade do CM durante e após a ECM contra e ipsolateral. O ritmo de disparos neuronais no VPL também mostrou diminuição apenas com a ECM ipsolateral. No entanto os neurônios da SPM aumentaram significativamente a freqüência de disparos com ECM ipsolateral e não com a contralateral. Conclusão. A ECM subliminar está relacionada consistentemente com a atenuação sensitiva durante o comportamento, provavelmente mediado por inibição talâmica e ativação da SPM. / Background. The motor function has been associated to sensory and pain attenuation, before during and shortly after the muscle activity. How ever the anatomical and functional basis of this phenomenon is not yet defined. The present study was designed to set an animal model and investigate the effect of subthreshold electrical stimulation of motor cortex (MCS) on pain threshold and neuron activity of thalamus and periaqüedutal gray. Method. Nociceptive thresholds of hind paws and the tail flick reflex were evaluated before and after surgical placement of epidural electrodes; before during and after electrical stimulation of motor cortex. Opioid antagonism was also included in this protocol in order to define neurotransmitter mediation of this process. Multiunit recording of thalamic median center (CM) and ventral posterolateral nuclei (VPL) and lateral periaqüedutal gray (SPM) were performed before and after electrical stimulation of ipso and contralateral motor cortex. Results. The procedure itself did not induce any threshold changes. MCS induced selective antinociception of contralateral paw, but no changes were detected in the nociceptive threshold of the ipsolateral side. This effect disappeared completely 15 minutes after the stimulation was ceased. No behavioral or motor impairment were observed during and after the stimulation session in the open field test. The same stimulation on sensory and posterior parietal cortex did not elicit any changes in behavioral and nociceptive tests. Systemic administration of naloxone completely reversed the previous observed antinociceptive effect. Multiunit recording evidenced decrease in spontaneous neuron firing in CM with short recovery time during ipso and contralateral MCS. Neuron activity in VPL was also significantly decreased during ipsolateral MCS but not with contralateral stimulation. How ever, neuron firing in SPM was significantly increased during and long after ipsolateral MCS but not with contralateral stimulation. Conclusion. Subthreshold MCS is consistently related to sensory attenuation during behavior, probably through thalamic inhibition and SPM activation.

Introdução. A estimulação do córtex motor (ECM) tem sido utilizada para o tratamento de pacientes com síndromes neuropáticas dolorosas crônicas e resistentes a tratamentos farmacológicos convencionais. O córtex motor primário pode ser a estrutura mais rostral do neuroeixo relacionada ao sistema de modulação da dor, e a ECM provoca ativação neuronal na substância cinzenta periaquedutal (PAG). A PAG é um dos principais centros do sistema descendente supressor de dor e recebe aferências de diferentes regiões do encéfalo. Esse estudo investiga o efeito da estimulação do córtex motor sobre a liberação de neurotransmissores na PAG em modelo de dor neuropática, com o objetivo de investigar os mecanismos neuroquímicos responsáveis pelo feito terapêutico. Métodos. No primeiro experimento, ratos Wistar machos foram aleatoriamente divididos em três grupos. No primeiro grupo, os animais foram submetidos à indução de dor neuropática através da constrição crônica do nervo ciático, no segundo grupo, os animais foram submetidos apenas à exposição do nervo ciático e no terceiro grupo, nenhuma intervenção para indução de dor neuropática foi realizada. Todos os animais foram submetidos a implante unilateral epidural de eletródios de estimulação sobre a área do córtex motor correspondente a pata posterior e implante de cânula guia direcionada à PAG utilizando coordenadas estereotáxicas. Os animais foram avaliados no teste de hiperalgesia mecânica e uma sonda de microdiálise foi introduzida em direção a PAG. As amotras de microdiálise foram coletadas e a análise dos neurotransmissores foi feita em um sistema de cromatografia líquida de alta eficiência (HPLC). No segundo experimento, ratos Wistar machos com dor neuropática induzida na pata posterior foram submetidos a implante estereotáxico de cânula guia direcionada à PAG, e foi realizada micro-injeção de antagonista de glicina e/ou GABA na PAG, previamente a ECM, para avaliar a influência desses antagonistas no efeito analgésico induzido pela estimulação cortical. Resultados. Animais submetidos à indução de dor neuropática apresentaram reversão da hiperalgesia mecânica após ECM. A estimulação cortical induziu um aumento significativo nos níveis de glicina durante (aumento de 153%) e após MCS (134%). A concentração de GABA aumentou 145% durante a estimulação epidural. Os níveis de glutamato não mostraram alteração no microdialisado da PAG após ECM. Houve uma correlação estatisticamente significativa entre o posicionamento da sonda de microdiálise nas colunas lateral e dorsolateral da PAG e o aumento na liberação do neurotransmissor glicina nos animais do grupo CCI. A administração de antagonista de glicina na PAG reverteu o efeito antinociceptivo da estimulação cortical. A micro-injeção de antagonista de GABA na PAG reverteu parcialmente o efeito da ECM. Conclusões. Nossos resultados sugerem que os neutransmissores glicina e GABA, liberados na PAG durante ECM, contribuem para o efeito antinociceptivo da via analgésica descendente. Os resultados desse projeto poderão contribuir para a elucidação dos mecanismos do efeito antinociceptivo da ECM / Introduction. Motor cortex stimulation (MCS) has been used for the treatment of patients with chronic neuropathic pain syndromes that are resistant to conventional pharmacological treatment. The motor cortex may be the most rostral structure in the neuroaxis responsible for pain modulation, and MCS increase the neuronal activation of periaqueductal gray (PAG). The PAG is one of the main subcortical centers of the descending pain suppressor system, and receives inputs from several brain areas. This study investigates the effects of MCS on the release of neurotransmitters in the PAG in neuropathic pain model, in order to investigate the possible neurochemical mechanisms responsible for this effect. Methods. In the first experiment, Wistar male rats were randomly subdivided into three surgical groups. In the first group, induction of neuropathic pain was performed through chronic constriction injury of the right sciatic nerve, in the second group, the animals were submitted just to exposure of the sciatic nerve and in the third group, no intervention for induction of neuropathic pain was performed. All the rats underwent implantation of unilateral epidural electrodes on the motor area corresponding to the right hind paw. The animals were evaluated for mechanical hyperalgesia test and a microdialysis guide cannula was stereotaxically implanted into the PAG. The microdialysate samples were collected and the neurotransmitters analysis was performed by a high- performance (HPLC). In the second experiment, animals with induced neuropathic pain in the hind paw were submitted to a stereotaxic implantation of a guidewire directed to PAG, and a microinjection of glycine and/or GABA antagonist in the PAG before the ECM was performed, to evaluate the influence of these antagonists on the analgesic effect induced by the cortical stimulation. Results. Animals subjected to induction of neuropathic pain showed reversal of mechanical hyperalgesia after motor cortex stimulation. Cortical stimulation induced a significant increase in glycine levels during (153 % increase) and after MCS (134%). The GABA concentration increases 145 % during transdural stimulation. Glutamate levels showed no change in PAG microdialysate after MCS. There was a statistically significant correlation between the positioning of the microdialysis probe in the lateral and dorsolateral columns of the PAG and the increase in the release of the neurotransmitter glycine in the animals of the CCI group. Administration of glycine antagonist in PAG reversed the antinociceptive effect of cortical stimulation. Microinjection of GABA antagonist in PAG partially reversed the effect of MCS. Conclusions. Our results suggest that the neurotransmitters glycine and GABA, released in PAG during MCS, contribute to descending antinociceptive actions. The results of this project will contribute for the elucidation of the mechanisms of the antinociceptive effect of MCS, a phenomenon that has not been fully understood currently