Protective effects of the β3-adrenoceptor agonist CL316243 against N-methyl-D-aspartate-induced retinal neurotoxicity.

We have previously reported that β(3)-adrenoceptor agonists dilate retinal blood vessels, but their effects on retinal neurons have been unclear. In this study, we examined the action of the β(3)-adrenoceptor agonist CL316243 against retinal damage induced by intravitreal injection of N-methyl-D-aspartate (NMDA) in rats. CL316243 was injected into the vitreous cavity before, with, or after intravitreal NMDA injection. Seven days after NMDA injection, cell loss in the ganglion cell layer (GCL) and thinning of the inner plexiform layer were observed. The reduction in the number of cells in the GCL was diminished by injection of CL316243 at 15, 30, 60, or 120 min after NMDA injection, whereas no significant protective effect was observed when CL316243 was administered 240 min after NMDA injection. Neither preinjection of CL316243 30 min before NMDA nor simultaneous injection of CL316243 with NMDA exerted any protective effect. The β(3)-adrenoceptor antagonist L748337 almost completely abolished the protection conferred by CL316243 injection 120 min after NMDA injection. The number of parvalbumin-positive amacrine cells was decreased in eyes examined 1 day after NMDA treatment, but this was prevented by CL316243 injection at 120 min after NMDA injection. These results suggest that CL316243 exerts protective effects against NMDA-induced damage by stimulation of β(3)-adrenoceptors. β(3)-adrenoceptor agonists may be effective candidates for the treatment of retinal diseases associated with glutamate-induced excitotoxicity, including glaucoma and diabetic retinopathy.