Concentration-Dependent Inner Retina Layer Damage and Optic Nerve Degeneration in a NMDA Model

Abstract

The intravitreal injection of N-methyl-D-aspartate (NMDA), a glutamate analogue, is an established model for fast retinal ganglion cell (RGC) degeneration. Yet, NMDA does not cause specific RGC damage. Now, the effects on the whole retina were analyzed. Additionally, the related effects for the structure and apoptotic levels of the optic nerve were investigated. Therefore, different NMDA concentrations were intravitreally injected in rats (20, 40, or 80 nmol NMDA or PBS). At days 3 and 14, Brn-3a RGCs were degenerated. A damage of calretinin amacrine cells was also recognized at day 14. Only a slight damage was observed in regard to PKCα bipolar cells, while rhodopsin photoreceptors remained intact. A long-lasting retinal microglia response was observed from day 3 up to day 14. Furthermore, a partial degeneration of the optic nerve was noted. At day 3, the SMI-32 neurofilaments were just slightly affected, whereas the neurofilament structure was further degenerated at day 14. However, the luxol fast blue (LFB)-stained myelin structure remained intact from day 3 up to day 14. Interestingly, apoptotic mechanisms, like FasL and Fas co-localization as well as caspase 3 activation, were restricted to the optic nerve of the highest NMDA group at this late stage of degeneration. The degeneration of the optic nerve is probably only a side effect of neuronal degeneration of the inner retinal layers. The intact myelin structure might form a barrier against the direct influence of NMDA. In conclusion, this model is very suitable to test therapeutic agents, but it is important to analyze all inner retina layers and the optic nerve to determine their efficacy in this model more precisely.

Destructive Effect of Intravitreal Heat Shock Protein 27 Application on Retinal Ganglion Cells and Neurofilament

“…In contrast, the bipolar cells were not affected after the intravitreal HSP27 application. This finding is in accordance with intravitreal injected S100B or NMDA studies [34,50]. Furthermore, the immunization of HSP27 together with S100B did not impair PKCα + bipolar cells.…”

“…Likely, the degeneration of RGCs appears prior to the optic nerve damage. This was also described for the intravitreal injection of NMDA [50]. Currently, we cannot exclude that the degeneration starts in the optic nerve and subsequently leads to a retrograde retinal cell body damage at later points in time.…”

Multifarious Biologic Loaded Liposomes that Stimulate the Mammalian Target of Rapamycin Signaling Pathway Show Retina Neuroprotection after Retina Damage

“…71−73 NMDA has shown retinal toxicity at low concentrations ( e.g ., 20 nM) with the degree of inner retina damage corresponding to NMDA concentration. 74 NMDA affects other retina cell types and intravitreal administered NMDA also induces partial optic nerve damage, likely linked to the damage of the inner retina. A 20 mM NMDA injection is an extreme model of retina damage.…”

“…This confirmed that intravitreal NMDA injection at 20 mM concentration did not result in photoreceptor damage, which is consistent with previous observations. 74,75 …”

“…87 Additionally, the NMDA induced apoptotic environment in the host eye will have also induced tRGC apoptosis as NMDA induced toxic effects to retina cells has been shown to have a prolonged duration (up to 14 days). 74 The nonspecific ( i.e ., not associated with intact cells) green fluorescence observed in the whole retina tile scans is likely GFP debris from the tRGCs combined with tissue autofluorescence (Figure 6D). Transplant cell survival has been shown to be improved by injury and loss of host RGCs.…”