Retinal aging in the diurnal Chilean rodent (Octodon degus): histological, ultrastructural and neurochemical alterations of the vertical information processing pathway

Abstract

The retina is sensitive to age-dependent degeneration. To find suitable animal models to understand and map this process has particular importance. The degu (Octodon degus) is a diurnal rodent with dichromatic color vision. Its retinal structure is similar to that in humans in many respects, therefore, it is well suited to study retinal aging. Histological, cell type-specific and ultrastructural alterations were examined in 6-, 12- and 36-months old degus. The characteristic layers of the retina were present at all ages, but slightly loosened tissue structure could be observed in 36-month-old animals both at light and electron microscopic levels. Elevated Glial fibrillary acidic protein (GFAP) expression was observed in Müller glial cells in aging retinas. The number of rod bipolar cells and the ganglion cells was reduced in the aging specimens, while that of cone bipolar cells remained unchanged. Other age-related differences were detected at ultrastructural level: alteration of the retinal pigment epithelium and degenerated photoreceptor cells were evident. Ribbon synapses were sparse and often differed in morphology from those in the young animals. These results support our hypothesis that (i) the rod pathway seems to be more sensitive than the cone pathway to age-related cell loss; (ii) structural changes in the basement membrane of pigment epithelial cells can be one of the early signs of degenerative processes; (iii) the loss of synaptic proteins especially from those of the ribbon synapses are characteristic; and (iv) the degu retina may be a suitable model for studying retinal aging.

Aging changes in the retina of male albino rat: a histological, ultrastructural and immunohistochemical study

“…Electro-dense deposits were noticed especially in the inner collagenous layer, starting from the 12 months group. This was also reported by Szabadfi et al [34] who clarified that aged Bruch's membrane displays an increase in phospholipids, triglycerides, fatty acids and free cholesterol content which called advanced glycation end products.…”

“…Significant thinning of the retina was also observed by Nadal-Nicolás et al [27]. On the contrary, Szabadfi et al [34] found increased OLM--ILM distance and IPL thickness in 36-month-old degu rat retinae. The authors explained their findings by the loose retinal structure observed in aging retinae.…”

“…However, the senile group presented mild increase in the ONL thickness compared with group III, although the difference was statistically non-significant. This increase in thickness may be explained by the loosened structure that may occur in senile retinae Szabadfi et al [34].…”

Evidence of Synaptic and Neurochemical Remodeling in the Retina of Aging Degus

“…Degus have been described as a novel AD-like animal model (Inestrosa et al, 2005;van Groen et al, 2011;Ardiles et al, 2012Ardiles et al, , 2013Castro-Fuentes and Socas-Pérez, 2013;Tarragon et al, 2013;Vega-Zuniga et al, 2013;Acosta et al, 2014;Du et al, 2015;Inestrosa et al, 2015;Szabadfi et al, 2015;Altimiras et al, 2017;Cisternas et al, 2018). However, investigators have also found that degus housed and bred under different conditions may result in different levels of AD-protein accumulation.…”

“…Elevated levels of amyloid beta (Aβ) proteins and the associated cell damage have been described in the aging eye and opened up the possibility of Aβ being a key constituent of age-related ocular pathologies (Hinton et al, 1986;Dutescu et al, 2009;Koronyo-Hamaoui et al, 2011;Koronyo et al, 2017). Several investigations using the Octodon degus (degus) have confirmed a role for Aβ peptides in diseases, including increased Aβ peptides and phosphorylated tau levels in the adult retina (Acosta et al, 2014;Du et al, 2015) or altered retinal structure with age (Szabadfi et al, 2015).…”