Satellite glial cells in mouse spinal ganglia express connexin 43 throughout life

In spinal ganglia satellite cells that envelope each nerve cell body are connected to each other by gap junctions. These junctions form transmembrane channels that are implicated in intercellular communications and control the ions and small molecules passage. They may endow perineuronal satellite cells with the coordination necessary for the efficient performance of functions such as buffering of K+ in the perineuronal microenvironment, and neuroprotection. Our knowledge of gap junctions has increased considerably in recent years, in particular, studies on the central and the peripheral nervous systems have concurred to identify different types of connexin in the glial cells, such as astrocytes, oligodendrocytes, and Schwann cells, but little information is available on the connexins that form these junctions in spinal ganglia. In the present study we set out to determine whether the perineuronal satellite cells of mouse spinal ganglia express the connexins that are mainly present in neuroglial cells (i. e. Cx32 and Cx43). Using Reverse Transcriptase-PCR we demonstrated that in the spinal ganglia of young mice (3-months old) the Cx32 transcript is present at low levels, while the Cx43 transcript is present at high levels. By immunocytochemistry, we localized Cx32 to the Schwann cells of nerve fibers, but not to other parts of the ganglion. Double-immunofluorescence labeling showed Cx43 positivity in the perineuronal satellite cells, which were identified by their immunoreactivity to S100 protein and to glutamine synthetase. Cx43 immunostaining was present in satellite cells sur¬rounding all nerve cell bodies, irrespective of size. We also determined whether expression of Cx43 undergoes changes with age. To this aim digital confocal images from 3 age groups (3-months old, 8-months old, and 24-months old mice) were post-processed using ImageJ 1.36b image analysis software. Quantification of punctate signals of Cx43 associated with perineuronal satellite cells (as revealed by the S100 and glutamine synthetase labeling) was performed. It was found that the mean number of Cx43-immunoreactive puncta (per 500 µm2) is significantly lower in the perineuronal satellite cells of aged mice (1.18 ± 0.1) compared to young (2.88 ± 0.2) and adult (2.97 ± 0.18) animals. This latter finding is consistent with observations in non nervous tissues, and the hypothesis that a prominent decrease in Cx43 is a marker of senescence.