Abstract
Purpose: :
This study aims to examine the morphological effects of low acute doses of methylmercury (MeHg) on the retina of the tropical fish Hoplias malabaricus (Thraira).
Methods: :
Four levels of MeHg intoxication were induced by intraperitoneal injection of doses of either 0.01, 0.05, 0.1 or 1.0 µg MeHg/g of body weight, followed by a fifteen day period of depuration. The retinas were dissected and fixed in 4% paraformaldehyde for 3 h. ON bipolar cells in the b sublamina of the inner plexiform layer (IPL) immunoreactive to protein Kinase Cα (irPKCα) were labeled and GCL cells were Nissl stained. Cell counts were performed in retina whole mounts for quantitative analysis of ON bipolar and ganglion cell layer (GCL) cell densities. These analyses were carried out in 3 or 4 retinas for each dose tested and in the control retinas. Sample retinal fields were photographed throughout the retina at intervals of 1 mm, with a digital camera attached to a microscope using Axio Vision software coupled to a computer. ON bipolar and GCL cells within the fields were counted with the help of the NIH Scion Image 2.0 software. The average density (mm2) of both types of cells was estimated for each retina and the data from each of the four MeHg-intoxicated groups were compared with the control group values (Student t-test).
Results: :
Thraira irPKCα ON bipolar cells showed the characteristic morphological aspect of this cell type both in retinas of control and exposed fish. The total estimated average cell densities in control fish were 1780,672 ± 608,230 for ON bipolar cells and 5247,214 ± 2539,142 for GCL cells. The density of ON bipolar cells did not show a significant difference in the acute low doses tested. Nissl stained cells (nuclei) of the GCL of exposed fish also showed no significant cell loss in estimated average density. However, there is a tendency in the decrease of the number of cells in both cells types analyzed, which can be seen in the isodensity maps.
Conclusions: :
low acute doses of MeHg/g do not decrease cell densities of either ON bipolar cells or cells in the GCL, compared to controls. There were no significant decreases in cell density (counts) for either cell type in any of the retinal regions, for any of the MeHg doses tested. This work supports previous findings (Tanan et al. 2006) that cell responses were still present, although decreased, at the same dose range but they were completely absent at higher doses.
Keywords: retina • bipolar cells • ganglion cells