Longitudinal In Vivo Changes in Retinal Ganglion Cell Dendritic Morphology After Acute and Chronic Optic Nerve Injury

Abstract

PURPOSE.To characterize in vivo dendritic changes in retinal ganglion cells (RGCs) after acute (optic nerve transection, ONT) and chronic (experimental glaucoma, EG) optic nerve injury. METHODS.ONT and EG (microbead model) were carried out in Thy1-YFP mice in which the entire RGC dendritic arbor was imaged with confocal fluorescence scanning laser ophthalmoscopy over two weeks in the ONT group and over two and six months, respectively, in two (groups 1 and 2) EG groups. Sholl analysis was used to quantify dendritic structure with the parameters: area under the curve (AUC), radius of the dendritic field, peak number of intersections (PI), and distance to the PI (PD).RESULTS. Dendritic changes were observed after three days post-ONT with significant decreases in all parameters at two weeks. In group 1 EG mice, mean (SD) intraocular pressure (IOP) was 15.2 (1.1) and 9.8 (0.3) mmHg in the EG and untreated contralateral eyes, respectively, with a significant corresponding decrease in AUC, PI, and PD, but not radius. In group 2 mice, the respective IOP was 13.1 (1.0) and 8.8 (0.1) mmHg, peaking at two months before trending towards baseline. Over the first two months, AUC, PI, and PD decreased significantly, with no further subsequent changes. The rates of change of the parameters after ONT was 5 to 10 times faster than in EG. CONCLUSIONS.Rapid dendritic changes occurred after ONT, while changes in EG were slower and associated with level of IOP increase. The earliest alterations were loss of inner neurites without change in dendritic field.

Mechanisms of retinal ganglion cell injury following acute increases in intraocular pressure

“…RGC degeneration involves dendritic changes including a loss of arborization and a decrease in synapse number. Dendritic branching and complexity can be assessed using a Sholl analysis where concentric circles are placed at regular intervals around the soma of the RGC and intersections are counted ( 81 ). Additionally, synapse number can be assessed using pre- and post-synaptic markers (e.g., synapsin, PSD95), and individual RGCs can be assessed using Thy-1 YFP transgenic mice where less than 1% of RGCs express the YFP, allowing for visualization of the entire dendritic arbor ( 81 ).…”

“…Dendritic branching and complexity can be assessed using a Sholl analysis where concentric circles are placed at regular intervals around the soma of the RGC and intersections are counted ( 81 ). Additionally, synapse number can be assessed using pre- and post-synaptic markers (e.g., synapsin, PSD95), and individual RGCs can be assessed using Thy-1 YFP transgenic mice where less than 1% of RGCs express the YFP, allowing for visualization of the entire dendritic arbor ( 81 ). Alterations in dendritic morphology occur prior to soma loss following acute IOP elevation in mice ( 82 ) as they do after optic nerve transection and chronic IOP elevation ( 81 ).…”

“…Additionally, synapse number can be assessed using pre- and post-synaptic markers (e.g., synapsin, PSD95), and individual RGCs can be assessed using Thy-1 YFP transgenic mice where less than 1% of RGCs express the YFP, allowing for visualization of the entire dendritic arbor ( 81 ). Alterations in dendritic morphology occur prior to soma loss following acute IOP elevation in mice ( 82 ) as they do after optic nerve transection and chronic IOP elevation ( 81 ). In fact, dendritic morphological changes have been noted as soon as 90 minutes following acute elevation in IOP ( 82 ) ( Figure 1 ).…”