The Expression Pattern of the Na(+) Sensor, Na(X) in the Hydromineral Homeostatic Network: A Comparative Study between the Rat and Mouse.

The Scn7a gene encodes for the specific sodium channel Na(X), which is considered a primary determinant of sodium sensing in the brain. Only partial data exist describing the Na(X) distribution pattern and the cell types that express Na(X) in both the rat and mouse brain. To generate a global view of the sodium detection mechanisms in the two rodent brains, we combined Na(X) immunofluorescence with fluorescent cell markers to map and identify the Na(X)-expressing cell populations throughout the network involved in hydromineral homeostasis. Here, we designed an anti-Na(X) antibody targeting the interdomain 2-3 region of the Na(X) channel's α-subunit. In both the rat and mouse, Na(X) immunostaining was colocalized with vimentin positive cells in the median eminence and with magnocellular neurons immunopositive for neurophysin associated with oxytocin or vasopressin in both the supraoptic and paraventricular nuclei. Na(X) immunostaining was also detected in neurons of the area postrema. In addition to this common Na(X) expression pattern, several differences in Na(X) immunostaining for certain structures and cell types were found between the rat and mouse. Na(X) was present in both NeuN and vimentin positive cells in the subfornical organ and the vascular organ of the lamina terminalis of the rat whereas Na(X) was only colocalized with vimentin positive cells in the mouse circumventricular organs. In addition, Na(X) immunostaining was specifically observed in NeuN immunopositive cells in the median preoptic nucleus of the rat. Overall, this study characterized the Na(X)-expressing cell types in the network controlling hydromineral homeostasis of the rat and mouse. Na(X) expression pattern was clearly different in the nuclei of the lamina terminalis of the rat and mouse, indicating that the mechanisms involved in systemic and central Na(+) sensing are specific to each rodent species.