Efeitos da estriatotomia posterior estereotáxica unilateral no tremor induzido pela harmalina em ratos
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Data
2006
Autores
Vilela Filho, Osvaldo [UNIFESP]
Orientadores
Ferraz, Fernando Antonio Patriani [UNIFESP]
Tipo
Tese de doutorado
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Objetivos: Embora compreenda a mais prevalente desordem do movimento, a fisiopatologia do tremor essencial (TE) e ainda controversa. Conforme a hipotese mais aceita, trata-se de um tremor central causado por uma disfuncao do complexo olivar inferior, provavelmente secundario a uma hipofuncao do sistema GABAergico. Vilela Filho et al (2001), por outro lado, relataram o caso de uma paciente com TE da mao direita que foi completamente eliminado apos uma isquemia restrita ao putamen posterior contralateral e sugeriram que o TE poderia representar a manifestacao clinica da hiperatividade do putamen posterior. O presente estudo foi realizado para testar essa hipotese no mais frequentemente usado modelo animal de TE, o tremor induzido pela harmalina em ratos e, empregando-se o mapeamento fisiologico por estimulacao, melhor determinar a organizacao somatotopica do striatum no rato. Metodos: 54 ratos Wistar machos (peso=250-350g) foram aleatoriamente distribuidos em tres grupos: experimental-GE (n=26), controle cirurgico-GCC (n=18) e controle farmacologico-GCF (n=10). Animais do GE foram submetidos a estriatotomia posterior estereotaxica unilateral (coordenadas: 1.8mm posterior/4.6mm lateral/5.85mm inferior; eletrodo: 0.35mm em diametro externo e 1.0mm de ponta exposta; parametros da lesao eletrolitica: 5.0mA/6o/60Hz) apos estimulacao eletrica do alvo (parametros: 0.2, 0.5, 1.0 e 2.0mA/monopolar/6o/60Hz). Nos animais do GCC, o eletrodo foi introduzido no alvo e retirado, sem se proceder a estimulacao ou lesao. Animais do GCF serviram apenas como controles para os efeitos da harmalina, nao tendo sido operados. Todos os animais (7o dia pos-operatorio naqueles operados) receberam harmalina intraperitonial (20mg/kg/ml), tendo sido o tremor induzido filmado 45 e 110 minutos apos sua administracao. A intensidade do tremor apendicular foi avaliada, independentemente, por um observador ocegoo, enquanto a dos tremores axiais, bem como a latencia e duracao de todos os tremores, pelos pesquisadores. Apos o teste da harmalina, os animais do GE e GCC foram sacrificados e seus cerebros enviados para o exame histopatologico. Resultados: Conforme criterios estabelecidos, 13 animais foram excluidos do estudo. O tremor apendicular mostrou-se reduzido ipsolateralmente a cirurgia em 20/21 animais do GE e em 2/9 do GCC e assimetrico em 1/10 do GCF; tais diferencas foram estatisticamente significantes entre GE e GCC e GE e GCF, mas nao entre GCC e GCF. Curiosamente, a latencia e duracao dos tremores axiais foram menores no GCF que no GE e GCC. A percentagem de reducao media do tremor apendicular foi 43.70%±14.22, tendo sido maior nas patas anteriores que posteriores e apos a estriatotomia posterior direita que esquerda. Lesoes estriatais laterais proporcionaram melhores resultados que as mediais. Conclusoes: Esses resultados sao sugestivos de uma provavel participacao do striatum posterior no tremor induzido pela harmalina em ratos e reforcam a hipotese determinante da realizacao do presente estudo. Os resultados derivados do mapeamento fisiologico estriatal por estimulacao e da resposta do tremor a cirurgia, por sua vez, sugerem a seguinte organizacao somatotopica no striatum dorsal do rato: patas dianteiras (muito provavelmente superpostas), posteriores e ventrais; tronco e cauda, anteriores; e patas traseiras, em posicao intermediaria entre as duas anteriores, anterior e dorsalmente as patas dianteiras, situando-se a contralateral posteriormente a ipsolateral
Purposes: Although the most prevalent movement disorder, the pathophysiology of essential tremor (ET) remains controversial. The most accepted hypothesis is that it is a central tremor caused by a dysfunction of the inferior olivary complex, probably secondary to GABAergic system malfunctioning. Evidence for the involvement of the basal ganglia had never been presented. Vilela Filho et al (2001), though, reported a case of a patient with unilateral hand ET which was completely relieved after a stroke restricted to the contralateral posterior putamen and suggested that ET could be the clinical manifestation of posterior putamen hyperactivity. The present study was designed to evaluate this hypothesis in the most used model of ET, harmaline-induced tremor in rats, and, by stimulation mapping, to better determine the somatotopic organization of the rat striatum. Methods: 54 male Wistar rats, 250-350g, were randomly distributed in three groups: experimental-EG (n=26), surgical control-SCG (n=18), and pharmacological control-PCG (n=10) groups. EG animals underwent stereotactic unilateral posterior striatotomy (coordinates: 1.8 posterior/4.6 lateral/5.85mm inferior; electrode: 0.35mm in external diameter and 1.0mm exposed tip; electrolytic lesion parameters: 0.5mA/6”/60Hz) after target stimulation (parameters: 0.2, 0.5, 1.0, and 2.0mA/monopolar/6”/60Hz). SCG rats underwent electrode placement at the target and withdrawn without stimulation or lesioning (sham lesion). PCG served exclusively as controls for harmaline effects. All animals received (7th postoperative day in those of EG and SCG) IP harmaline (20mg/kg/ml) and the induced-tremor was video recorded 45` and 110` after the injection. Limb tremor intensity was independently evaluated by a blind observer, while axial tremors intensity, as well as latency and duration of both limb and axial tremors, were evaluated by the researchers. Animals of EG and SCG were killed after harmaline test and their brains sent to histopathology. Results: Obeying predetermined criteria, 13 animals were excluded from the study. Limb tremor was reduced ipsolaterally to the operation in 20/21 rats of EG and in 2/9 of SCG, and was asymmetric in 1/10 of PCG. Comparisons between EG x SCG and EG x PCG were statistically significant, but not between SCG x PCG. None of the rats presented tremor reduction contralateral to the operation. Curiously, latency and duration of axial tremors, but not of limb tremor, were lesser in PCG than in EG and SCG. The mean percentage of limb tremor reduction in animals of EG was 43.7%±14.22, being greater in anterior than in posterior paws, and after right than left striatotomy. Lateral lesions yielded better results than medial lesions. Conclusions: These results suggest that the posterior striatum is possibly involved with harmaline-induced tremor in rats and give support to our hypothesis, according to which hyperactivity of the posterior putamen may play a role in the genesis of ET. Data provided by stimulation mapping and tremor response to operation suggest the following somatotopic organization in the rat dorsal striatum: forepaws (probably overlapped), caudal and ventral; trunk and tail, rostral; and hind paws, in an intermediary position, dorsal and rostral to the forepaws, being the contralateral one caudal to the ipsolateral.
Purposes: Although the most prevalent movement disorder, the pathophysiology of essential tremor (ET) remains controversial. The most accepted hypothesis is that it is a central tremor caused by a dysfunction of the inferior olivary complex, probably secondary to GABAergic system malfunctioning. Evidence for the involvement of the basal ganglia had never been presented. Vilela Filho et al (2001), though, reported a case of a patient with unilateral hand ET which was completely relieved after a stroke restricted to the contralateral posterior putamen and suggested that ET could be the clinical manifestation of posterior putamen hyperactivity. The present study was designed to evaluate this hypothesis in the most used model of ET, harmaline-induced tremor in rats, and, by stimulation mapping, to better determine the somatotopic organization of the rat striatum. Methods: 54 male Wistar rats, 250-350g, were randomly distributed in three groups: experimental-EG (n=26), surgical control-SCG (n=18), and pharmacological control-PCG (n=10) groups. EG animals underwent stereotactic unilateral posterior striatotomy (coordinates: 1.8 posterior/4.6 lateral/5.85mm inferior; electrode: 0.35mm in external diameter and 1.0mm exposed tip; electrolytic lesion parameters: 0.5mA/6”/60Hz) after target stimulation (parameters: 0.2, 0.5, 1.0, and 2.0mA/monopolar/6”/60Hz). SCG rats underwent electrode placement at the target and withdrawn without stimulation or lesioning (sham lesion). PCG served exclusively as controls for harmaline effects. All animals received (7th postoperative day in those of EG and SCG) IP harmaline (20mg/kg/ml) and the induced-tremor was video recorded 45` and 110` after the injection. Limb tremor intensity was independently evaluated by a blind observer, while axial tremors intensity, as well as latency and duration of both limb and axial tremors, were evaluated by the researchers. Animals of EG and SCG were killed after harmaline test and their brains sent to histopathology. Results: Obeying predetermined criteria, 13 animals were excluded from the study. Limb tremor was reduced ipsolaterally to the operation in 20/21 rats of EG and in 2/9 of SCG, and was asymmetric in 1/10 of PCG. Comparisons between EG x SCG and EG x PCG were statistically significant, but not between SCG x PCG. None of the rats presented tremor reduction contralateral to the operation. Curiously, latency and duration of axial tremors, but not of limb tremor, were lesser in PCG than in EG and SCG. The mean percentage of limb tremor reduction in animals of EG was 43.7%±14.22, being greater in anterior than in posterior paws, and after right than left striatotomy. Lateral lesions yielded better results than medial lesions. Conclusions: These results suggest that the posterior striatum is possibly involved with harmaline-induced tremor in rats and give support to our hypothesis, according to which hyperactivity of the posterior putamen may play a role in the genesis of ET. Data provided by stimulation mapping and tremor response to operation suggest the following somatotopic organization in the rat dorsal striatum: forepaws (probably overlapped), caudal and ventral; trunk and tail, rostral; and hind paws, in an intermediary position, dorsal and rostral to the forepaws, being the contralateral one caudal to the ipsolateral.
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VILELA FILHO, Osvaldo. Efeitos da estriatotomia posterior estereotáxica unilateral no tremor induzido pela harmalina em ratos. 2006. 252 f. Tese (Doutorado em Ciências) - Escola Paulista de Medicina, Universidade Federal de São Paulo, São Paulo, 2006.