Neuroprotective effects of lycium barbarum polysaccharide on corticosterone-induced damage on retinal ganglion cells

Abstract

It has been known that light input can affect the emotions of a person. The depressive syndrome Seasonal Affective Disorder (SAD) is an effective example of the power of light in changing the mood of a person. Patients with SAD have recurring depressive episodes that follow seasonal changes, which is due to the changing daylight hours. This phenomenon suggests that there would be receptors in the retina that would not simply be responsible for vision, but also for the regulation of non-visual signals such as emotion.

In many animals, projections have been found from the retina to the dorsal raphe nucleus (DRN). This brain region is a serotonergic area and has been found to be involved in the occurrence of depression. As such, the cells in the retina which were found to have projections to the DRN have a high possibility to be involved in emotion regulation.

Retinal Ganglion Cells (RGCs) are classified into many types. A specific type known as an alpha cell is suspected to be the DRN-projecting subtype. This study uses Lycium Barbarum Polysaccharide (LBP) as a treatment in protecting the large RGCs from corticosterone (CORT) -induced damage. The aim is to observe if LBP will provide neuroprotection to large sized RGCs damaged by 40mg/kg or 50mg/kg CORT, and hence if LBP can be further investigated as a possible anti-depressant drug.

This study observed that although LBP did not reduce large cell deaths, it reduced cell atrophy of the RGCs under high dosage of CORT (50mg/kg). For the same number of cells counted, treatment groups with a high dose CORT injection found more cells over 300μm2 in area than cells under 300μm2. Also, it was found that the temporal quadrants were more sensitive to cell size change than the nasal quadrants, paving way for more in-depth research of the spatial sensitivity to CORT or to LBP.

The findings in this study indicate that LBP does indeed have a neuroprotective effect on large RGCs, although this effect is limited and as of yet seems conditional, as this study ignores the effect of CORT and LBP on other large cell properties such as the dendritic field size and the amount of synapses. Further studies are needed to determine the mechanism of the neuroprotective effect of LBP and to determine the exact site of action LBP works on.