Culturas organotípicas de hipocampo como modelo para o estudo dos efeitos neurobiológicos da deficiência de tiamina: parâmetros morfológicos e níveis de BDNF

Abstract

Thiamine deficiency (TD) can lead to the loss of neurons in specific regions of the brain, generating a broad spectrum of diseases. One of the areas affected by this vitamin deficiency is the hippocampus, a region of the brain involved in cognitive processes such as learning and memory. Results of studies using animal models to evaluate the effects of DT on the hippocampus are contradictory, indicating several consequences, such as: only biochemical dysfunctions or neurodegeneration or deficit in the process of neurorregeneration. The organotypic hippocampal culture of hippocampus (OHC) is an adequate model to contribute to the solution of these apparent contradictions. Ex vivo tissue culture, maintaining the cytoarchitecture and the relationship between the different cell types, is one of the advantages of this model that allows certain types of manipulations that would be unfeasible in the experimental animal model. In the present study, we carried out (i) the standardization of the process of obtaining OHC, (ii) the establishment of OHC as a model for the study of TD, and (iii) the study of the effects of TD on levels of brain-derived neurotrophic factor (BDNF) by neurons and oligodendrocytes. The contribution of neurons and/or oligondendrocytes to the effects of TD on the production of BDNF is another issue that is still unclear. This neurotrophic factor has, among others, a role in the maintenance of existing neurons, in the growth and differentiation of new neurons and synapses. In the establishment of OHC for the study of TD, the exposure of the cultures to the Neurobasal medium without thiamine (TDNM) for 4, 7 and 10 days was determined. A significant decrease was observed in hippocampal areas such as dentate gyrus (DG, p=0.006) and CA1-CA3 region (p=0.004) in cultures exposed to TDN medium. However, an increase in total slice size (p=0.030) was observed, probably due to glial proliferation in order to protect the neuronal population. A significant decrease in the number of neurons was observed after exposure to TDN medium on the seventh day, in the DG (p=0.0007), in the CA1-CA3 region (p=0.0002) and in the total tissue (p=0.0002). On the tenth day of exposure a process of compensatory neurobiological reactions seems to occur, possibly generating stimulation of the neurogenesis as a compensatory effect contrary to the insult. The number of oligodendrocytes did not change after exposure to TD, but there was a loss of correlation between the area and the oligodendrocity density in the CA1-CA3 region, indicating a greater susceptibility of this region to the effects of DT compared to DG. The data obtained show for the first time an increase in the neuronal production of BDNF on the tenth day in the deficient group, in the DG (p=0.001), in the CA1-CA3 region (p=0.006) and in the total tissue (p=0.030). After recovery from the deficiency, we observed a positive correlation between the number of neurons producing BDNF and the neuronal density in the deficient group (r=0.77; p=0.010), indicating that the production of BDNF seems to be oriented to re-population after the insult. Thus, this work represents the first study to establish OHC as a model for the study of the effects of TD, showing a significant loss of neurons in the hippocampus and an increase in production of BDNF as a possible compensatory effect of neurodegenerative biochemical changes induced by TD