Administration of minocycline reduces microglia and Caspase‐3 activation but does not mitigate retinal ganglion cell loss after ocular hypertension in mice

Purpose: To study the effect of minocycline administration on the evolution of retinal ganglion cell (RGC) loss, the number of microglial cells and the activation of the apoptotic signal Caspase‐3 after ocular hypertension (OHT) in mice. Methods: In left eyes of Swiss albino mice, OHT was induced by diode laser photocoagulation of the limbal and episcleral veins and the intraocular pressure (IOP) evolution was monitored with a TonoLab®. Mice received daily intraperitoneal injections of minocycline hydrochloride (45 mg/kg) diluted in saline starting the day before OHT induction until the day of sacrifice (4 or 15 days, n = 12–14 per group/time point). Control groups received saline injections. Retinas were divided into two groups. Retinas of the first group were double immunodetected against Brn3a and active Caspase‐3 to identify surviving (Brn3a+RGCs) and apoptotic (a‐Casp3+RGCs) RGCs. In the second group, RGCs were retrogradely traced with Fluorogold 7 days before OHT induction and retinas were immunodetected against Iba‐1. Total Brn3a+RGCs, a‐Casp3+RGCs, Iba‐1+cells and FG+microglial cells in the RGC layer were manually or automatically quantified, and the distributions were analysed by topographical maps. Results: IOP was significantly elevated 24 hours after OHT induction (33.2 ± 6.1 mmHg) and returned to baseline at 1 week (17.3 ± 5.3 mmHg). This evolution was not altered by minocycline administration. Although minocycline treatment was not successful in protecting Brn3a+RGCs at 4 (40 878 ± 4860 vs 43 526 ± 2714) nor at 15 (16 161 ± 12 650 vs 12 919 ± 6085) days after OHT, the numbers of a‐Casp3+RGCs, Iba‐1+cells and FG+microglial cells were significantly lower in the minocycline‐treated groups at both 4 (58.6%, 46.8% and 24.5%, respectively) and 15 (33.6%, 54.2% and 37.3%, respectively) days compared to the saline‐treated groups (100%). Conclusions: Minocycline treatment decreases the number of microglial cells and caspase‐3 activation but does not reduce RGC loss after OHT.