Functional and morphological effects of laser-induced ocular hypertension in retinas of adult albino Swiss mice

摘要

Purpose: To investigate the effects oflaser photocoagulation (LP)-induced ocular hypertension (OHT) on thesurvival and retrograde axonal transport of retinal ganglion cells(RGC), as well as on the function of retinal layers. Methods: Adult albino Swiss mice (35–45g) received laser photocoagulation of limbal and episcleral veins inthe left eye. Mice were sacrificed at 8, 17, 35, and 63 days.Intraocular pressure (IOP) in both eyes was measured with a Tono-Labbefore LP and at various days after LP. Flash electroretinogram (ERG)scotopic threshold response (STR) and a- and b-wave amplitudes wererecorded before LP and at various times after LP. RGCs were labeledwith 10% hydroxystilbamidine methanesulfonate (OHSt) applied to bothsuperior colliculi before sacrifice and in some mice, with dextrantetramethylrhodamine (DTMR) applied to the ocular stump of theintraorbitally transected optic nerve. Retinas were immunostained forRT97 or Brn3a. Retinas were prepared as whole-mounts and photographedunder a fluorescence microscope. Labeled RGCs were counted using imageanalysis software, and an isodensity contour plot was generated foreach retina. Results: IOP increased to twice itsbasal values by 24 h and was maintained until day 5, after which IOPgradually declined to reach basal values by 1 wk. Similar IOP increaseswere observed in all groups. The mean total number of OHSt+RGCs was 13,428±6,295 (n=12), 10,456±14,301 (n=13), 12,622±14,174(n=21), and 10,451±13,949 (n=13) for groups I, II, III, and IV,respectively; these values represented 28%, 23%, 26%, and 22% of thevalues found in their contralateral fellow retinas. The mean totalpopulation of Brn3a+ RGCs was 24,343±5,739 (n=12) and10,219±8,887 (n=9), respectively, for groups I and III; these valuesrepresented 49% and 20%, respectively, of the values found in theirfellow eyes. OHT retinas showed an absence of OHSt+ and DTMR+RGCs in both focal wedge-shaped and diffuse regions of the retina. By 1wk, there was a discrepancy between the total number of surviving OHSt+RGCs and Brn3a+ RGCs, suggesting that a large proportion ofRGCs had impaired retrograde axonal transport. In the retinal areaslacking backlabeled RGCs, neurofibrillar staining revealed aberrantexpression of RT97 within axons and RGC bodies characteristic ofaxotomy. Elevated IOP induced significant reductions in the registeredERG waves, including positive STR, a- and b-waves, that were observedby 24 h and remained throughout the period of study for the threegroups analyzed. Conclusions: LP of the perilimbal andepiscleral veins resulted in OHT leading to a lack of retrograde axonaltransport in approximately 75% of the original RGC population. Thislack did not progress further between 8 and 63 days, and it was bothfocal (in sectors with the apex located in the optic disc) and diffusewithin the retina. In addition, severe amplitude diminutions of the STRand a- and b-waves of the ERG appeared as early as 24 h after laseringand did not recover throughout the period of study, indicating thatincreased IOP results in severe damage to the innermost, inner nuclear,and outer nuclear layers of the retina.