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Automatic quantitative analysis of experimental primary and secondary retinal neurodegeneration: implications for optic neuropathies

View Article: PubMed Central - PubMed

ABSTRACT

Secondary neurodegeneration is thought to play an important role in the pathology of neurodegenerative disease, which potential therapies may target. However, the quantitative assessment of the degree of secondary neurodegeneration is difficult. The present study describes a novel algorithm from which estimates of primary and secondary degeneration are computed using well-established rodent models of partial optic nerve transection (pONT) and ocular hypertension (OHT). Brn3-labelled retinal ganglion cells (RGCs) were identified in whole-retinal mounts from which RGC density, nearest neighbour distances and regularity indices were determined. The spatial distribution and rate of RGC loss were assessed and the percentage of primary and secondary degeneration in each non-overlapping segment was calculated. Mean RGC number (82 592±681) and RGC density (1695±23.3 RGC/mm2) in naïve eyes were comparable with previous studies, with an average decline in RGC density of 71±17 and 23±5% over the time course of pONT and OHT models, respectively. Spatial analysis revealed greatest RGC loss in the superior and central retina in pONT, but significant RGC loss in the inferior retina from 3 days post model induction. In comparison, there was no significant difference between superior and inferior retina after OHT induction, and RGC loss occurred mainly along the superior/inferior axis (~30%) versus the nasal–temporal axis (~15%). Intriguingly, a significant loss of RGCs was also observed in contralateral eyes in experimental OHT. In conclusion, a novel algorithm to automatically segment Brn3a-labelled retinal whole-mounts into non-overlapping segments is described, which enables automated spatial and temporal segmentation of RGCs, revealing heterogeneity in the spatial distribution of primary and secondary degenerative processes. This method provides an attractive means to rapidly determine the efficacy of neuroprotective therapies with implications for any neurodegenerative disorder affecting the retina.

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Retinal ganglion cell (RGC) survival after contralateral ocular hypertension (OHT) induction in the DA rat. Whole-retinal profile of (a) RGC density, (b) nearest neighbour distance (NND) and (c) regularity index demonstrating significant reducing in RGC populations when OHT was inducted in the opposite eye (Figure 4) over the course of this model with only minor degradation in the regularity of the retinal mosaic (one-way ANOVA with Dunnets’ post hoc test versus naïve controls). (d) Segmentation of RGC populations into a series of 15 non-overlapping concentric rings centred on the ONH suggest that greatest loss of RGC density occurs in the central versus the peripheral retina over the course of the OHT model (red) when compared with naïve controls (black). These observations are reflected in the change in NND and RI. Data are presented as means±S.E.
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fig5: Retinal ganglion cell (RGC) survival after contralateral ocular hypertension (OHT) induction in the DA rat. Whole-retinal profile of (a) RGC density, (b) nearest neighbour distance (NND) and (c) regularity index demonstrating significant reducing in RGC populations when OHT was inducted in the opposite eye (Figure 4) over the course of this model with only minor degradation in the regularity of the retinal mosaic (one-way ANOVA with Dunnets’ post hoc test versus naïve controls). (d) Segmentation of RGC populations into a series of 15 non-overlapping concentric rings centred on the ONH suggest that greatest loss of RGC density occurs in the central versus the peripheral retina over the course of the OHT model (red) when compared with naïve controls (black). These observations are reflected in the change in NND and RI. Data are presented as means±S.E.

Mentions: Analysis of contralateral untreated eyes from OHT cohorts was next performed (Figure 5). A significant decline in RGC density (Figure 5a) was observed from 7 days post OHT induction (P<0.001) (in an IOP related relationship), but to a lesser extent than eyes which were subject to elevated IOP (average RGC density loss 84 days post OHT induction 23±5% versus 14±6% for OHT and contralateral eyes, respectively, Table 1). Average NND increased from 7 days but only reached significance (P<0.01) versus naïve controls 56 days post OHT inductions (14.42±0.18 versus 15.44±0.37, P<0.01; Figure 5b). A similar trend was observed in RI (2.86±0.03 versus 2.51±0.18, P<0.05; Figure 5c), suggesting preservation of RGC retinal mosaic. Further segmentation of retinal whole-mounts into 15 concentric rings (Figure 5d) reveals that loss of RGC density and NND occurs primarily in the central retinal and that despite significant loss of RGCs, RI remains largely unaffected, indicating preservation of the retinal mosaic.


Automatic quantitative analysis of experimental primary and secondary retinal neurodegeneration: implications for optic neuropathies
Retinal ganglion cell (RGC) survival after contralateral ocular hypertension (OHT) induction in the DA rat. Whole-retinal profile of (a) RGC density, (b) nearest neighbour distance (NND) and (c) regularity index demonstrating significant reducing in RGC populations when OHT was inducted in the opposite eye (Figure 4) over the course of this model with only minor degradation in the regularity of the retinal mosaic (one-way ANOVA with Dunnets’ post hoc test versus naïve controls). (d) Segmentation of RGC populations into a series of 15 non-overlapping concentric rings centred on the ONH suggest that greatest loss of RGC density occurs in the central versus the peripheral retina over the course of the OHT model (red) when compared with naïve controls (black). These observations are reflected in the change in NND and RI. Data are presented as means±S.E.
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Related In: Results  -  Collection

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fig5: Retinal ganglion cell (RGC) survival after contralateral ocular hypertension (OHT) induction in the DA rat. Whole-retinal profile of (a) RGC density, (b) nearest neighbour distance (NND) and (c) regularity index demonstrating significant reducing in RGC populations when OHT was inducted in the opposite eye (Figure 4) over the course of this model with only minor degradation in the regularity of the retinal mosaic (one-way ANOVA with Dunnets’ post hoc test versus naïve controls). (d) Segmentation of RGC populations into a series of 15 non-overlapping concentric rings centred on the ONH suggest that greatest loss of RGC density occurs in the central versus the peripheral retina over the course of the OHT model (red) when compared with naïve controls (black). These observations are reflected in the change in NND and RI. Data are presented as means±S.E.
Mentions: Analysis of contralateral untreated eyes from OHT cohorts was next performed (Figure 5). A significant decline in RGC density (Figure 5a) was observed from 7 days post OHT induction (P<0.001) (in an IOP related relationship), but to a lesser extent than eyes which were subject to elevated IOP (average RGC density loss 84 days post OHT induction 23±5% versus 14±6% for OHT and contralateral eyes, respectively, Table 1). Average NND increased from 7 days but only reached significance (P<0.01) versus naïve controls 56 days post OHT inductions (14.42±0.18 versus 15.44±0.37, P<0.01; Figure 5b). A similar trend was observed in RI (2.86±0.03 versus 2.51±0.18, P<0.05; Figure 5c), suggesting preservation of RGC retinal mosaic. Further segmentation of retinal whole-mounts into 15 concentric rings (Figure 5d) reveals that loss of RGC density and NND occurs primarily in the central retinal and that despite significant loss of RGCs, RI remains largely unaffected, indicating preservation of the retinal mosaic.

View Article: PubMed Central - PubMed

ABSTRACT

Secondary neurodegeneration is thought to play an important role in the pathology of neurodegenerative disease, which potential therapies may target. However, the quantitative assessment of the degree of secondary neurodegeneration is difficult. The present study describes a novel algorithm from which estimates of primary and secondary degeneration are computed using well-established rodent models of partial optic nerve transection (pONT) and ocular hypertension (OHT). Brn3-labelled retinal ganglion cells (RGCs) were identified in whole-retinal mounts from which RGC density, nearest neighbour distances and regularity indices were determined. The spatial distribution and rate of RGC loss were assessed and the percentage of primary and secondary degeneration in each non-overlapping segment was calculated. Mean RGC number (82&thinsp;592&plusmn;681) and RGC density (1695&plusmn;23.3 RGC/mm2) in na&iuml;ve eyes were comparable with previous studies, with an average decline in RGC density of 71&plusmn;17 and 23&plusmn;5% over the time course of pONT and OHT models, respectively. Spatial analysis revealed greatest RGC loss in the superior and central retina in pONT, but significant RGC loss in the inferior retina from 3 days post model induction. In comparison, there was no significant difference between superior and inferior retina after OHT induction, and RGC loss occurred mainly along the superior/inferior axis (~30%) versus the nasal&ndash;temporal axis (~15%). Intriguingly, a significant loss of RGCs was also observed in contralateral eyes in experimental OHT. In conclusion, a novel algorithm to automatically segment Brn3a-labelled retinal whole-mounts into non-overlapping segments is described, which enables automated spatial and temporal segmentation of RGCs, revealing heterogeneity in the spatial distribution of primary and secondary degenerative processes. This method provides an attractive means to rapidly determine the efficacy of neuroprotective therapies with implications for any neurodegenerative disorder affecting the retina.

No MeSH data available.


Related in: MedlinePlus