Abstract
Purpose: :
Previous research has demonstrated that laser photocoagulation treatment of the monkey retina affords protection against retinal ganglion cell (RGC) loss induced by experimental glaucoma. Interestingly, protection only occurred in areas overlying laser spots. The underlying mechanism is unknown, but it is conceivable that the laser acted as a preconditioning stimulus, inducing endogenous production of survival factors. The purpose of the current study was to examine whether a conventional, continuous wave, photocoagulator laser (CW; 532nm, 0.1s pulse duration) and a novel, non-thermal laser (2RT; 532nm, 3ns pulse duration), which causes drastically reduced damage to photoreceptors, improve RGC survival in rats after optic nerve (ON) crush in areas overlying the laser spots.
Methods: :
Pigmented rats were randomly assigned to one of three groups: sham, CW, 2RT. Treatment consisted of 25 laser spots administered to the mid-central retina of the right eye. The left eye served as a control. Laser settings were at visible lesion threshold for the CW laser and at below visible lesion threshold for the 2RT laser. Experiment 1: rats were lasered 24 hours before optic nerve crush, then killed 7 days later. Experiment 2: rats were lasered 7 days before optic nerve crush, then killed 7 days later. Wholemounts retinas were prepared and double labeling immunofluorescence performed. Nestin labelling allowed visualization of laser spots. Brn3a labelling identified viable RGCs. Photomicrographs of Brn3a labelling were taken in areas overlying nestin-positive laser spots. Quantification of Brn3a RGCs was then performed and expressed relative to the control eye.
Results: :
Both the CW and 2RT lasers induced local glial cell activation, as evidenced by robust upregulation of the intermediate filament nestin. In sham rats, 33.2% ± 3.0 RGCs remained 7 days after ON crush. Neither the CW nor the 2RT lasers augmented Brn3a-positive RGC survival in areas overlying laser spots following ON crush. This was the case irrespective of whether lasering occurred 24 hours before ON crush, or if lasering occurred 7 days before ON crush.
Conclusions: :
Despite causing activation of glial cells, treatment of the rat retina with medical lasers failed to induce an endogenous, preconditioning response sufficiently efficacious to enhance RGC survival after ON crush, as delineated by immunolabelling for Brn3a.
Keywords: laser • ganglion cells • neuroprotection