Estudo da Expressão do Canal para Sódio Dependente de Voltagem Nav1.6 nas Células Octopus e Multipolares do PVCN no Núcleo Coclear do Sistema Auditivo

Abstract

The present work aimed to evaluate which voltage-dependent sodium channel subunits are expressed in different neuronal subpopulations of the posterior ventral cochlear nucleus (PVCN). Immunofluorescence reactions of the type simple or dual labelling in parasagital slices of cochlear nucleus revealed the expression of Nav1.6 channel at the axon initial segments (AIS) in octopus or multipolar cells. Octopus cells, whose average silhouette área were 499 ± 9 μm2 presented na extension of Nav1.6 labelling at the AIS of 38,1 ± 2,6 μm, whereas multipolar cell these measurements were 271 ± 11 μm2 and 16,3 ± 2,5 μm, respectivelly. The definition that the structure labelled with the anti-Nav1.6 antibody corresponds to the AIS was based in the colocalization with anti-ankyrin-G labelling. The intensity of anti-Nav1.6 labelling increases with the distance from the soma. The lack of colocalization of anti-Nav1.6 and anti-MAP-2 labelling suggests the absence of this sodium channel at the dendrites. Similarly, the labeling of synaptic terminals with synaptic vesicle protein 2 antibody (anti-SV2) and colocalization analysis, showed that this channel is not expressed at synaptic terminals on PVCN neurons. The results suggest that Nav1.6 is present in PVCN neurons at pos natal day eight and that its expression follows the neuronal development being maintained after maturation. Our experimental results also revealed an intense Nav1.6 labeling at nodes of Ranvier and a weak somatic staining that apparently does not included the somatic membrane. At the AIS, the Nav1.1 and 1.2 subunits were not detected. The high density of Nav1.6 channel at the AIS suggests that this channel is responsible for the action potential generation at these cells. Nav1.2 labeling was observed at unmyelinated fibers. Overall, our data suggest that Nav1.6 is the main subunit expressed at multipolar and octopus cells of PVCN where it may be involved with the generation of action potentials at high frequency that is a characteristic of these cells.