Background: Ocular hypertension is a major risk factor for glaucoma, a neurodegenerative disease characterized by an irreversible decrease in ganglion cells and their axons. Macroglial and microglial cells appear to play an important role in the pathogenic mechanisms of the disease. Here, we study the effects of laser-induced ocular hypertension (OHT) in the macroglia, microglia and retinal ganglion cells (RGCs) of eyes with OHT (OHT-eyes) and contralateral eyes two weeks after lasering. Methods: Two groups of adult Swiss mice were used: age-matched control (naïve, n = 9); and lasered (n = 9). In the lasered animals, both OHT-eyes and contralateral eyes were analyzed. Retinal whole-mounts were immunostained with antibodies against glial fibrillary acid protein (GFAP), neurofilament of 200kD (NF-200), ionized calcium binding adaptor molecule (Iba-1) and major histocompatibility complex class II molecule (MHC-II). The GFAP-labeled retinal area (GFAP-RA), the intensity of GFAP immunoreaction (GFAP-IR), and the number of astrocytes and NF-200 + RGCs were quantified. Results: In comparison with naïve: i) astrocytes were more robust in contralateral eyes. In OHT-eyes, the astrocyte population was not homogeneous, given that astrocytes displaying only primary processes coexisted with astrocytes in which primary and secondary processes could be recognized, the former having less intense GFAP-IR (P < 0.001); ii) GFAP-RA was increased in contralateral (P <0.05) and decreased in OHT-eyes (P <0.001); iii) the mean intensity of GFAP-IR was higher in OHT-eyes (P < 0.01), and the percentage of the retinal area occupied by GFAP+ cells with higher intensity levels was increased in contralateral (P = 0.05) and in OHT-eyes (P < 0.01); iv) both in contralateral and in OHT-eyes, GFAP was upregulated in Müller cells and microglia was activated; v) MHC-II was upregulated on macroglia and microglia. In microglia, it was similarly expressed in contralateral and OHT-eyes. By contrast, in macroglia, MHC-II upregulation was observed mainly in astrocytes in contralateral eyes and in Müller cells in OHT-eyes; vi) NF-200+RGCs (degenerated cells) appeared in OHT-eyes with a trend for the GFAP-RA to decrease and for the NF-200+RGC number to increase from the center to the periphery (r = −0.45). Conclusion: The use of the contralateral eye as an internal control in experimental induction of unilateral IOP should be reconsidered. The gliotic behavior in contralateral eyes could be related to the immune response. The absence of NF-200+RGCs (sign of RGC degeneration) leads us to postulate that the MHC-II upregulation in contralateral eyes could favor neuroprotection.

Glaucomatous optic neuropathy, a leading cause of blindness, can progress despite control of intraocular pressure - currently the main risk factor and target for treatment. Glaucoma progression shares mechanisms with neurodegenerative disease, including microglia activation. In the present model of ocular hypertension (OHT), we have recently described morphological signs of retinal microglia activation and MHC-II upregulation in both the untreated contralateral eyes and OHT eyes. By using immunostaining, we sought to analyze and quantify additional signs of microglia activation and differences depending on the retinal layer.

Glaucoma, the second most common cause of blindness, is characterized by a progressive loss of retinal ganglion cells and their axons, with a concomitant loss of the visual field. Although the exact pathogenesis of glaucoma is not completely understood, a critical risk factor is the elevation, above normal values, of the intraocular pressure. Consequently, deciphering the anatomical and functional changes occurring in the rodent retina as a result of ocular hypertension has potential value, as it may help elucidate the pathology of retinal ganglion cell degeneration induced by glaucoma in humans. This paper predominantly reviews the cumulative information from our laboratory's previous, recent and ongoing studies, and discusses the deleterious anatomical and functional effects of ocular hypertension on retinal ganglion cells (RGCs) in adult rodents. In adult rats and mice, perilimbar and episcleral vein photocauterization induces ocular hypertension, which in turn results in devastating damage of the RGC population. In wide triangular sectors, preferentially located in the dorsal retina, RGCs lose their retrograde axonal transport, first by a functional impairment and after by mechanical causes. This axonal damage affects up to 80% of the RGC population, and eventually causes their death, with somal and intra-retinal axonal degeneration that resembles that observed after optic nerve crush. Importantly, while ocular hypertension affects the RGC population, it spares non-RGC neurons located in the ganglion cell layer of the retina. In addition, functional and morphological studies show permanent alterations of the inner and outer retinal layers, indicating that further to a crush-like injury of axon bundles in the optic nerve head there may by additional insults to the retina, perhaps of ischemic nature.

Glaucoma, one of the leading causes of blindness worldwide, affects primarily retinal ganglion cells (RGCs) and their axons. The pathophysiology of gl aucoma is not fully understood, but it is currently believed that damage to RGC axons at the optic nerve head plays a major role. Rodent models to study glaucoma include those that mimic either ocular hypertension or optic nerve injury. Here we review the anatomical loss of the general population of RGCs (that express Brn3a; Brn3a+RGCs) and of the intrinsically photosensitive RGCs (that express melanopsin; m+RGCs) after chronic (LP-OHT) or acute (A-OHT) ocular hypertension and after complete intraorbital optic nerve transection (ONT) or crush (ONC). Our studies show that all of these insults trigger RGC death. Compared to Brn3a+RGCs, m+RGCs are more resilient to ONT, ONC and A-OHT but not to LP-OHT. There are differences in the course of RGC loss both between these RGC types and among injuries. An important difference between the damage caused by ocular hypertension or opti nerve injury appears in the outer retina. Both axotomy and LP-OHT induce selective loss of RGCs but LP-OHT also induces a protracted loss of cone photoreceptors. This review outlines our current understanding of the anatomical changes occurring in rodent models of glaucoma and discusses the advantages of each one and their translational value.

Purpose: We compared the time-course and magnitude of retinal nerve fiber layer (RNFL) thinning with that of retinal ganglion cell (RGC) loss after intraorbital optic nerve transection (IONT) in adult rats. Methods: At 3, 7, 12, or 21 days, or 1, 2, or 4 months after ONT, the retinas were imaged with spectral-domain optical coherence tomography (SD-OCT) using the circular-peripapillary scan and volume scan raster pattern (61 horizontal sections equally spaced) both centered in the optic nerve. In all sections, the RNFL and retinal thickness were measured to obtain the total values of the peripapillary scan and the values of three concentric sectors (400, 1200, and 2400 μm in diameter) from the volume scan. After SD-OCT, retinas were dissected and immunoreacted for Brn3a and neurofilaments (pNFH) to identify RGCs and their intraretinal axons, respectively. Total numbers of RGCs were quantified. Results: Thinning of the RNFL was first observed at 12 days in peripapillary scan (10% decrease) and progressed up to 4 months (72% decrease). The volume scan showed transient RNFL swelling in central and medial sectors at 3, 7, and 12 days followed by progressive significant thinning first observed at 21 days (central sector, 30%; medial sector, 40%) and 12 days (peripheral sector, 15%), respectively. Following IONT, Brn3a⁺ RGCs decreased to approximately 80%, 52%, 17%, 9%, 5%, 3%, and 2% at 3, 7, 12, 21 days, and at 1, 2, and 4 months, respectively. Retinal ganglion cell axon immunodetection decreased from 12 days onwards. Conclusions: After IONT, RGC death is more severe and precedes thinning of the RNFL.