ABSTRACT
Background Minocycline possesses neuroprotective effect in a variety of animal models and clinical trials of central nervous system,but whether it works on optic nerve injury remains unclear.Objective This study aimed to observe the protective effects of minocycline on retinal ganglion cells (RGCs) in the early stage of optic nerve crush and explore its mechanism.Methods One hundred and thirty-six clean C57BL/6J mice were randomly divided into normal control group,normal saline solution group and minocycline group.The optic nerve crush injury models were induced in the left eyes of the mice in the normal saline solution group and minocycline group by a cross-action forceps for 3 seconds.Minocycline was injected intraperitoneally in the minocycline group firstly 45 mg/kg(0.4 ml) and followed by 22.5 mg/kg per day after 24 hours until sacrifice of the animals,and the equivalent volume of normal saline solution was injected in the same way in the normal saline solution group.The mice were euthanized at 4,7,11,14 days postoperatively and the left eyeballs were collected.Retinal flat mounts and DAPI staining was used to observe and compare the change of RGCs density among different groups and various time points.Apoptosis of mice RGCs were assessed by TdT-mediated dUTP nick end labeling (TUNEL).Real-time polymerase chain reaction (real-time PCR) was used to detect the expression of CD11b mRNA in retinal microglials.Results DAPI staining in retinal flat mounts showed that the average RGCs density was (77.50±2.38)/0.01 mm2 and (70.00±2.94) /0.01 mm2 in the 4th and 7th day after modeling in the normal saline solution group,and those in the minocycline group were (88.75 ± 2.36) /0.01 mm2 and (81.00 ± 3.92)/0.01 mm2,with significant differences between the two groups (t4d =-6.708,P＜0.01 ;t7d =--4.491,P＜0.01).The apoptotic RGCs were (12±1)/mm and (4±1)/mm in the normal saline solution,which were significantly more than (4±1)/mm and (1±0)/mm in the minocycline group (t4 d =12.832,P＜0.01 ; t7d =3.455,P =0.026).However,no significant difference was found in apoptotic RGCs in postoperative 11 days and 14 days between the normal saline solution group and the minocycline group (P =0.708,0.777).The expressing levels of CD11 b mRNA in the retinal microglials were significantly higher in the 4th and 7th day in the normal saline solution group than those in the minocycline group (t4 d =8.312,P＜0.01 ;t7d=5.407,P＜0.01),but were not significantly different in the 11st and 14th day after modeling between the two groups (P=0.055,0.170).Conclusions Minocycline can play a neuroprotective effect on RGCs in the early stage of optic nerve crush in mice by inhibiting microglia activation and decreasing RGCs apoptosis.