P2X7 receptor-mRNA and -protein in the mouse retina; changes during retinal degeneration in BALBCrds mice

A combined real-time PCR/immunohistochemistry study was carried out to investigate whether P2X7 receptors, known to induce apoptosis and necrosis, may be causally related to the process of retinal degeneration in BALBCrds mice. In the retinae of BALBCrds mice, P2X7 receptor-mRNA was the highest at an age of 20-40 days, and declined afterwards. At the same time, the P2X7 receptor-message was constantly low in the retina of control BALBC mice until postnatal day 100. The receptor-mRNA in total brain tissue of both strains of mice was comparable with that of BALBCrds retinae. Double immunofluorescence in combination with laser scanning microscopy was used to study the distribution of P2X7 receptor-immunoreactivity (IR) on neurons and different glial cell types of the retina. An exclusively neuronal localization of P2X7-IR in the ganglion cell layer was found by using either anti-neuronal nuclei or microtubule associated protein-2 as neuronal markers. There was a slight age-dependent decrease in the abundance of neuronal P2X7-IR both in BALBCrds or BALBC mice. P2X7-IR failed to co-localize with any of the non-neuronal markers used to stain microglial or Müller glial cells. No P2X7 receptor-IR was found in the retinal ganglion cell layer of P2X7−/− animals, when compared with the control littermates. Hence, we suggest that, in BALBCrds mice, an early up-regulation of neuronal P2X7 receptors may cause injury of retinal neurons and thereby functionally contribute to the retinal damage.