Losses of immunoreactive parvalbumin amacrine and immunoreactive aprotein kinase C bipolar cells caused by methylmercury chloride intoxication in the retina of the tropical fish Hoplias malabaricus
Bonci, D.M.O.; Lima, S.M.A. de; Grötzner, S.R.; Oliveira Ribeiro, C.A.; Hamassaki, D.E.; Ventura, D.F.
To quantify the effects of methylmercury (MeHg) on amacrine and on ON-bipolar cells in the retina, experiments were performed in MeHg-exposed groups of adult trahiras (iHoplias malabaricus/i) at two dose levels (2 and 6 µg/g, iip/i). The retinas of test and control groups were processed by mouse anti-parvalbumin and rabbit anti-subspan style=font-family: Symbol;a/span/subprotein kinase C (subspan style=font-family: Symbol;a/span/subPKC) immunocytochemistry. Morphology and soma location in the inner nuclear layer were used to identify immunoreactive parvalbumin (PV-IR) and subspan style=font-family: Symbol;a/span/subPKC (subspan style=font-family: Symbol;a/span/subPKC-IR) in wholemount preparations. Cell density, topography and isodensity maps were estimated using confocal images. PV-IR was detected in amacrine cells in the inner nuclear layer and in displaced amacrine cells from the ganglion cell layer, and subspan style=font-family: Symbol;a/span/subPKC-IR was detected in ON-bipolar cells. The MeHg-treated group (6 µg/g) showed significant reduction of the ON-bipolar subspan style=font-family: Symbol;a/span/subPKC-IR cell density (mean density = 1306 ± 393 cells/mmsup2/sup) compared to control (1886 ± 892 cells/mmsup2/sup; P lt; 0.001). The mean densities found for amacrine PV-IR cells in MeHg-treated retinas were 1040 ± 56 cells/mmsup2/sup (2 µg/g) and 845 ± 82 cells/mmsup2/sup (6 µg/g), also lower than control (1312 ± 31 cells/mmsup2/sup; P lt; 0.05), differently from the data observed in displaced PV-IR amacrine cells. These results show that MeHg changed the PV-IR amacrine cell density in a dose-dependent way, and reduced the density of subspan style=font-family: Symbol;a/span/subKC-IR bipolar cells at the dose of 6 µg/g. Further studies are needed to identify the physiological impact of these findings on visual function.
Keywords: Methylmercury; Retina; Hoplias malabaricus; Amacrine cells; Displaced amacrine cells; ON-bipolar cells.