Transmissão sináptica nos distúrbios do desenvolvimento cortical associado a epilepsia
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Data
2006
Autores
Calcagnotto, Maria Elisa [UNIFESP]
Orientadores
Mello, Luiz Eugenio Araujo de Moraes [UNIFESP]
Tipo
Tese de doutorado
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Ainda pouco se conhece sobre a transmissão sináptica nos distúrbios do desenvolvimento cortical (DDC) associados à epilepsia. Para estudar os aspectos funcionais das sinapses nos DDC foram utilizadas técnicas de patchclamp in vitro para examinar as correntes excitatórias e inibitórias póssinápticas
(CEPS e CIPS) em fatias de cérebro de modelos animais com DDC (os ratos expostos ao MAM in utero e camundongos Dlx1-/-) e de amostras de tecido cerebral displásico de pacientes com displasia cortical focal (DCF) submetidos ao tratamento cirúrgico para epilepsia refratária. Técnicas de imunohistoquímica foram realizadas para avaliar os aspectos morfológicos envolvidos associados às possíveis anormalidades funcionais. Por fim foi
realizado o transplante intracerebral de células precursoras neuronais (CPN) derivadas da eminência gangliônica medial (EGM) em camundongos recém nascidos para avaliar a capacidade destas células de modificar o circuito neural. Os resultados demonstraram que a função sináptica nas regiões de
malformação cerebral está alterada. Estas alterações são caracterizadas por: disfunção no componente NMDA da transmissão sináptica excitatória nas células heterotópicas dos animais expostos ao MAM in utero, atribuída em parte às modificações na composição e função das subunidades dos
receptores NMDA; redução na habilidade de recaptação de GABA das sinapses tanto da região heterotópica destes animais como nas áreas dispásicas dos pacientes com DCF; diminuição significativa do nível de inibição tanto nas áreas de DCF, associada a uma distribuição anômala dos interneurônios, como no córtex cerebral e hipocampo dos camundongos Dlx1-/- causada pela perda progressiva de interneurônios. Além disso, as CPN derivadas da EGM transplantadas foram capazes de migrar, se diferenciar em interneurônios maduros e de se integrar no
circuito neural pré-existente aumentando o nível global de inibição sináptica. Estes dados sugerem que algumas alterações na função sináptica nos DDC parecem contribuir para o processo de epileptogênese enquanto que outras parecem atuar como um mecanismo compensatório na tentativa de diminuir a hiperexcitabilidade. Estas anormalidades são comuns tanto para os modelos animais como para os pacientes com DDC. Além disso, os resultados referentes ao tranplante de CPN derivadas da EGM sugerem que esta técnica pode ter implicações importantes no desenvolvimento de novas estratégias terapêuticas em quadros neurológicos, como as epilepsias.
The synaptic function in disorders of cortical development (DCD) associated with epilepsy is still unknown. To study the synaptic transmission in DCD, the excitatory and inhibitory postsynaptic currents (EPSC and IPSC) were examined by patch-clamp techniques. These currents were recorded from hippocampal heterotopic cells of brain slices of rats exposed to methylazoxymethanol (MAM) in utero and from hippocampal and cortical cells of Dlx1-/- mice (two animal models of DCD), and from identified neurons in tissue slices obtained from patients with focal cortical dysplasia (FCD). Molecular approaches were also used to examine the morphological aspects associated with the functional abnormalities. Finally, postnatal mice received intracerebral transplants of neuronal precursors cells (NPC) from embryonic medial ganglionic eminence (MGE) to assess whether these cells were capable of modifying neuronal circuits and restore normal function. The results demonstrated that the synaptic function is altered in malformed brain. These alterations are characterized by: functional alteration in the NMDA-mediated component of the excitatory synaptic transmission in heterotopic cells (MAM) attributed, at least in part , to changes in composition and function of the NMDAR subunit.; reduced ability for GABA re-uptake at the synapses in the heterotopic region of MAM rats and in the dysplastic regions of FCD samples; significatly decreased level of inhibition in both, the dysplastic areas of FCD – associated with abnormalities in the interneuron distribution - and the cortical and hippocampal areas of Dlx1-/- mice – caused by a time-dependent reduction of a subset of cortical and hippocampal GABAergic interneurons. Additionally, MGE-derived NPC migrated across the brain parenchyma, integrated into local circuits, functioned as GABA-producing inhibitory cells and modified neural circuits increasing local inhibition These data suggest that some alterations in synaptic function on DCD play an essential contributory role to the process of epileptogenesis, while others perhaps act as compensatory mechanisms to suppress the hyperexcitability of the malformed brain. These abnormalities are common in both, the animal models and the patients with DCD associated with epilepsy. Moreover, the findings from transplanted MGE-derived cells suggest that this technique could have important implications for reparative cell therapies for brain disorders where increase in inhibition would be beneficial, such as epilepsy.
The synaptic function in disorders of cortical development (DCD) associated with epilepsy is still unknown. To study the synaptic transmission in DCD, the excitatory and inhibitory postsynaptic currents (EPSC and IPSC) were examined by patch-clamp techniques. These currents were recorded from hippocampal heterotopic cells of brain slices of rats exposed to methylazoxymethanol (MAM) in utero and from hippocampal and cortical cells of Dlx1-/- mice (two animal models of DCD), and from identified neurons in tissue slices obtained from patients with focal cortical dysplasia (FCD). Molecular approaches were also used to examine the morphological aspects associated with the functional abnormalities. Finally, postnatal mice received intracerebral transplants of neuronal precursors cells (NPC) from embryonic medial ganglionic eminence (MGE) to assess whether these cells were capable of modifying neuronal circuits and restore normal function. The results demonstrated that the synaptic function is altered in malformed brain. These alterations are characterized by: functional alteration in the NMDA-mediated component of the excitatory synaptic transmission in heterotopic cells (MAM) attributed, at least in part , to changes in composition and function of the NMDAR subunit.; reduced ability for GABA re-uptake at the synapses in the heterotopic region of MAM rats and in the dysplastic regions of FCD samples; significatly decreased level of inhibition in both, the dysplastic areas of FCD – associated with abnormalities in the interneuron distribution - and the cortical and hippocampal areas of Dlx1-/- mice – caused by a time-dependent reduction of a subset of cortical and hippocampal GABAergic interneurons. Additionally, MGE-derived NPC migrated across the brain parenchyma, integrated into local circuits, functioned as GABA-producing inhibitory cells and modified neural circuits increasing local inhibition These data suggest that some alterations in synaptic function on DCD play an essential contributory role to the process of epileptogenesis, while others perhaps act as compensatory mechanisms to suppress the hyperexcitability of the malformed brain. These abnormalities are common in both, the animal models and the patients with DCD associated with epilepsy. Moreover, the findings from transplanted MGE-derived cells suggest that this technique could have important implications for reparative cell therapies for brain disorders where increase in inhibition would be beneficial, such as epilepsy.
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Citação
CALCAGNOTTO, Maria Elisa. Transmissão sináptica nos distúbios do desenvolvimento cortical associados à epilepsia. 2006. 168 f. Tese (Doutorado em Ciências) – Escola Paulista de Medicina, Universidade Federal de São Paulo. São Paulo, 2006.