Characterization of photoreceptor degeneration in the rhodopsin P23H transgenic rat line 2 using optical coherence tomography

Abstract

PurposeTo characterize the optical coherence tomography (OCT) appearances of photoreceptor degeneration in the rhodopsin P23H transgenic rat (line 2) in relation to the histological, ultrastructural, and electroretinography (ERG) findings.Materials and methodsHomozygous rhodopsin P23H transgenic albino rats (line 2, very-slow degeneration model) were employed. Using OCT (Micron IV®; Phoenix Research Labs, Pleasanton, CA, USA), the natural course of photoreceptor degeneration was recorded from postnatal day (P) 15 to P 287. The OCT images were qualitatively observed by comparing them to histological and ultrastructural findings at P 62 and P 169. In addition, each retinal layer was quantitatively analyzed longitudinally during degeneration, compared it to that observed in wild type Sprague-Dawley (SD) rats. The relationships between the ERG (full-field combined rod-cone response, 3.0 cds/m2 stimulation) findings and OCT images were also analyzed.ResultsIn the qualitative study, the two layers presumably corresponding to the photoreceptor inner segment ellipsoid zone (EZ) and interdigitation zone (IZ) were identified in the P23H rat until PN day 32. However, the photoreceptor inner and outer segment (IS/OS) layer became diffusely hyperreflective on OCT after P 46, and the EZ and IZ zones could no longer be identified on OCT. In contrast, in the SD rats, the EZ and IZ were clearly distinguished until at least P 247. The ultrastructural study showed partial disarrangements of the photoreceptor outer segment discs in the P23H rats at P 62, although a light-microscopic histological study detected almost no abnormality in the outer segment. In the quantitative study, the outer retinal layer including the outer plexiform layer (OPL) and the outer nuclear layer (ONL) became significantly thinner in the P23H rats than in the SD rats after P 71. The thickness of the IS/OS layer was maintained in the P23H rats until P 130, and it became statistically thinner than in the SD rats at P 237. The longitudinal attenuation in the amplitude of the a- and b-waves of ERG was significantly correlated with the thickness of the combined OPL and ONL but not with that of the IS/OS layer.ConclusionOCT showed the degenerated photoreceptor IS/OS layer in rhodopsin P23H transgenic rats (line 2) as a diffuse hyperreflective zone, even in the early stage, with the partially disarranged and destabilized OS discs recognizable by ultrastructural assessment but not by a histological study. The amplitude of the a- and b-waves mainly depends on the thickness of the OPL and ONL layer rather than the thickness of the photoreceptor IS/OS layer in P23H rats.

Epigallocatechin Gallate Slows Retinal Degeneration, Reduces Oxidative Damage, and Modifies Circadian Rhythms in P23H Rats

“…The administration of EGCG to SD × LE rats was intended to verify the long-term effect of this compound on healthy individuals. The loss of visual function evaluated with VA and CS by optomotor in P23H over six months is supported by numerous studies conducted in this animal model [6,39,41,56]. Rhodopsin mutation is responsible for the apoptosis of rod and cone photoreceptors, triggering general disorganization and remodeling of the whole retina with the subsequent visual field and VA losses, ending in blindness in the final stage [57,58].…”

“…These animals are characterized by primary rod photoreceptor degeneration, as in human RP, which continues until the complete loss and disorganization of retinal tissue. The slower progression of the disease in these animals allows the administration of long-term treatments compared to other retinal animal models [5,6]. In addition, this mutation triggers molecular and morphological changes in the inner retina, which is involved in circadian mechanisms [7].…”

A spectral-domain optical coherence tomographic analysis of Rdh5-/- mice retina

“…SD-OCT and fundus photography were performed by the methods as described in detail previously, using a Micron 1 IV, Image-Guided 830 nm OCT (Phoenix Retinal Imaging System, Phoenix Research Labs, Pleasanton, CA, USA) [22,23,25,27]. In brief, SD-OCT and fundus photography were carried out at 6 points of time from postnatal-month (PM) 1 to PM6 for both Rdh5 -/and C57BL/6J mice.…”

“…The inner retinal layer A consisted of the retinal nerve fiber layer (NFL), the ganglion cell layer (GCL), the inner plexiform layer (IPL) and the inner nuclear layer (INL); the outer retinal layer B consisted of the outer plexiform layer (OPL) and the outer nuclear layer (ONL); the photoreceptor segments layer C consisted of the photoreceptor inner segment (IS) and outer segment (OS) layers; and combined RPE and the choroid layer (D) (S1 Fig). As previously reported [23,25,27], we measured the thickness of layers A, B, C and D using the InSight 1 software program (Phoenix Research Labs). The borderline between each layer was automatically identified by the software program using the SD-OCT images and was manually modified by the researchers when necessary.…”

“…Although SD-OCT is a noninvasive technology that allows us to investigate the morphological characteristics of various retinal diseases [20,21], it is impossible to directly evaluate the pathological features. In contrast, animal models associated with known gene mutations provide strong evidence that facilitate our understanding of the relationship between the SD-OCT findings and the pathological background [22][23][24][25][26][27][28][29][30][31][32]. However, to our knowledge, no study has assessed the relationship between SD-OCT findings and the origin of the structural changes in Rdh5 -/mice.…”