Stimulation of P2X7 Receptor Kills Rat Retinal Ganglion Cells in vivo

Abstract

Purpose: : Stimulation of the P2X₇ receptor can lead to the death of many cell types. We have previously demonstrated that activation of the P2X₇ receptor can elevate intracellular calcium and kill rat retinal ganglion cells that have been isolated from the eye. However, the presence of glia and other cells in the intact eye may alter the lethal effects in vivo. We ask here whether stimulation of the P2X₇ receptor can kill retinal ganglion cells in vivo, and whether the NMDA receptor is involved as found in isolated cells.

Methods: : Compounds were injected into the nasal region of the vitreous chamber of Long Evans rats, PD 14-26. Ganglion cells were labeled by injecting aminostibamabine into the superior colliculus 2-3 days later. The effect on ganglion cell survival was determined by counting the number of fluorescence cells 2-3 days after the labeling. All animals were handled in accordance with the ARVO guidelines.

Results: : Intravitreal injection of the P2X₇ receptor agonist BzATP significantly reduced the number of ganglion cells as compared to animals injected with saline solution. Cell loss was localized to the injection point, consistent with limited diffusion in the restricted vitreal space. This death of retinal ganglion cells was prevented by coinjection of the specific P2X₇ antagonist brilliant blue G, confirming cell death was mediated by the P2X₇ receptor. The loss of ganglion cells following activation of the P2X₇ receptor was also prevented by the NMDA antagonist MK 801. In no case did intraocular pressure go up.

Conclusions: : Stimulation of the P2X₇ receptor can kill retinal ganglion cells in vivo. Activation of the NMDA receptor appears to be downstream of P2X₇ receptor activation, consistent with our findings in isolated ganglion cells. These observations suggest that situations leading to increased extracellular ATP, possibly including elevations in intraocular pressure, may lead to the loss of retinal ganglion cells in vivo.

Keywords: ganglion cells • receptors: pharmacology/physiology • adenosine