Imunolocalização de canais para sódio voltagem-dependentes em neurônios dos núcleos ambíguo e dorsal motor do vago

Abstract

The nucleus ambiguus (NA) is a collection of neurons distributed ventrolaterally in the reticular formation of medulla that projects through special visceral efferent fibers to pharynx, larynx, esophagus or through general visceral efferent fibers to lung and heart. Dorsal motor nucleus of the vagus (DMV) contains autonomic neurons located dorsomedially in the medulla that send general visceral fibers mainly to abdominal viscera such as the stomach, liver, pancreas and intestines. The aim of this study was to evaluate the expression of voltage-gated sodium channels (Nav) and their subcellular location in neurons of different formations of NA and DMV. Wistar rats of 30 days were perfused transcardially and double or triple immunofluorescence staining was performed in 25 to 40 m coronal section of medulla. The identification of the NA formations was made through the analysis of immunofluorescence against choline acetyltransferase (ChAT). Experiments with retrograde tracer cholera toxin conjugated to Alexa Fluor 488 (CTb) applied to the lung parenchyma or the expression of neuronal injury marker ATF-3, after recurrent laryngeal nerve resection (RLN), were also used to identify neurons in the NA. Neurons in the loose formation (NAl, n=8), semi-compact (NAsc, n=8) and compact (NAc, n=168) had major diameter of 33 ± 1.6; 36 ± 0.4 and 22 ± 0.3 m, and somatic silhouette area (SSA) average of 462 ± 39.6; 503 ± 28.7 and 248 ± 7.3 m2 , respectively. Within NAc formation was observed extensive heterogeneity of neurons. The retrograde tracer CTb identified autonomic neurons in the NAc that showed anti-Nav1.7 staining at soma and presumed axon initial segments (AIS). Nav1.6 expression was observed in AIS of neurons within NAc, NAsc and NAl, and both NAL and NAc showed positive correlation between SSA and the extent of anti-Nav1.6 labeling along the AIS. Among the Nav1.6 positive neurons those that innervate the larynx are included, based on ATF-3 expression after resection of RLN. We also observed Nav1.2 staining in presumed dendrites of NAc neurons. At the neurons of the DMV an anti-Nav1.7 staining was observed at the soma and AIS. The results suggest that motoneurons of NA that innervate branchiomeric muscles use Nav1.6 channel isoform to generate the action potential whereas autonomic motoneurons seems to depend on the activity of Nav1.7 channels.