Imunolocalização de canais para sódio voltagem-dependentes em neurônios do núcleo coclear dorsal e do núcleo medial do corpo trapezoidal

Abstract

The present study aimed to characterize the expression of voltage-gated sodium channels in neurons of inferior auditory system, more specifically at dorsal cochlear nucleus (DCN) and medial nucleus of trapezoid body (MNTB) of thirty days rats. For this purpose, double-labeling immunofluorescence reactions were done in slices of 40 or 150 m of brain stem and documented using confocal microscopy. We have used an antibody that recognizes all the isoforms of sodium channels (PAN-Nav), specific antibodies against the isoforms of voltage-dependent sodium or calcium channels Nav1.1, Nav1.2 e Nav1.6 or Cav3.2, and also antibodies against the neuronal markers anti-Map-2 e anti-ankyrin-G. It was not observed anti-Nav1.1 or Nav1.2 labeled neurons from both nuclei evaluated, at least at densities normally detected through the immunofluorescence technique utilized. The Nav1.6 channels are highly expressed at axon initial segments (AIS) of cartwheel, fusiforms and giant cells of DCN. The cartwheel cells showed a mean somatic silhouette area of 181,5 ± 16,3 (n=8), the fusiforms of 423,9 ± 43,6 (n=8) and the giant cells of 1119,3 ± 123,4 µm2 (n=3), whereas the anti-Nav1.6 labeling along the AIS measured 17,6 ± 0,5; 22,5 ±1,8; 45,3 ± 1,5 µm, respectively. When compared, both the somatic silhouette area and the extension of anti-Nav1.6 at AIS, presented a statistically significant difference between the neuronal subpopulations of DCN. At cartwheel cells from DCN, the Cav3.2 calcium channel is observed in the soma and also in processes near the soma, although the colocalization of this channel with the Nav1.6 at AIS was not detected. At MNTB principal cells, the analysis of anti-Pan and anti-Nav1.6 along the AIS, also does not suggest the presence of other isoforms besides the Nav1.6. At this neuronal domain we observed the colocalizaion of anti-Nav1.6 e anti-ankyrin-G, where only the anti-Nav1.6 labeling increases with the distance along the AIS. Therefore, our data suggest that the high density of Nav1.6 isoform at AIS is a common finding of auditory neurons. However, the extension of its expression at the probable site of the action potential generation differs between neuronal populations of auditory neurons. Besides the Nav1.6, the cartwheel cells of DCN exhibited a somatic expression of Cav3.2 calcium channel and both voltage-gated ion channels may be involved with complex action potential characteristic of these neurons.