Variabilidade dependente de localização do sinal de entrada e características dinâmica de motoneurônios: um estudo computacional

• Autor(a) principal: Fernandes, Evlyn de Jesus
• Data de Publicação: 2014
• Tipo de documento: Dissertação
• Idioma: por
• Título da fonte: Repositório Institucional da UFG
• dARK ID: ark:/38995/0013000006pm7
• Texto Completo: http://repositorio.bc.ufg.br/tede/handle/tede/4702
• topic: Correntes de cálcio; Correntes hiperpolarizantes; Modelagem matemática; Motoneurônio; Variabilidade dependente de localização da entrada sináptica; Calcium currents; Hyperpolarizing currents; Location-dependent variability; Mathematical modeling; Motoneuron; SISTEMAS DE COMPUTACAO::HARDWARE

Mathematical motoneurons models are widely used to help researchers to understand the behavior of the neuromuscular system. This study aims to analyze the currents involved in the temporal summation process and in the location-dependent variability of the synaptic input (LDV), using models of type S and type FF motoneurons. The temporal summation was defined as the percentual increase of soma’s depolarization for a train of synaptic inputs. LDV is the variability of discharge patterns in soma for the same input pattern applied in a distal or proximal dendrite. The models developed were parameterized to motoneurons of cats and validated according to protocols described in literature. The dendritic branch was simulated in an active manner, simulating the presence of calcium –L channels in dendrites. A hyperpolarizing current has been identified as the responsible for the decrease of temporal summation in hyppocampal’s neurons, therefore, we also simulated these channels in order to detect their influence on temporal summation. Temporal summation was evaluated applying synaptic currents of 20 Hz, and also applying excitatory post-synaptic currents–shaped (EPSC-shaped) inputs in the dendrite of the model with a pseudo-random distance between each peak. Results indicated that the presence of a hyperpolarizing current, which turns off during membrane depolarization, can counteract the temporal summation effects introduced by the calcium-L channels, minimizing the location-dependent variability for high input values. Minimizing the effects of variability is interesting because similar input pattern applied in a proximal or distal dendrite will cause the same output in soma, standardizing the input/output relationship of the motorneuron. The hyperpolarizing current, however, greatly reduces the excitability of the cell so that it can lead to variability in the output if the distal or proximal input applied is very low, since the distal one will be unable to trigger an action potential. There may be an interaction between the calcium –L channels, the hyperpolarizing current channels and the monoamine levels which will modulate the input/output relationship of the motoneuron.