ABSTRACT
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 (Hoplias malabaricus) at two dose levels (2 and 6 µg/g, ip). The retinas of test and control groups were processed by mouse anti-parvalbumin and rabbit anti-alphaprotein kinase C (alphaPKC) immunocytochemistry. Morphology and soma location in the inner nuclear layer were used to identify immunoreactive parvalbumin (PV-IR) and alphaPKC (alphaPKC-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 alphaPKC-IR was detected in ON-bipolar cells. The MeHg-treated group (6 µg/g) showed significant reduction of the ON-bipolar alphaPKC-IR cell density (mean density = 1306 ± 393 cells/mm²) compared to control (1886 ± 892 cells/mm²; P < 0.001). The mean densities found for amacrine PV-IR cells in MeHg-treated retinas were 1040 ± 56 cells/mm² (2 µg/g) and 845 ± 82 cells/mm² (6 µg/g), also lower than control (1312 ± 31 cells/mm²; P < 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 alphaKC-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.
Subject(s)
Animals , Amacrine Cells/drug effects , Fishes/metabolism , Methylmercury Compounds/toxicity , Parvalbumins/drug effects , Protein Kinase C-alpha/drug effects , Retinal Bipolar Cells/drug effects , Amacrine Cells/metabolism , Parvalbumins/metabolism , Protein Kinase C-alpha/metabolism , Retinal Bipolar Cells/metabolismABSTRACT
The visual system is a potential target for methylmercury (MeHg) intoxication. Nevertheless, there are few studies about the cellular mechanisms of toxicity induced by MeHg in retinal cells. Various reports have indicated a critical role for nitric oxide synthase (NOS) activation in modulating MeHg neurotoxicity in cerebellar and cortical regions. The aim of the present study is to describe the effects of MeHg on cell viability and NOS activation in chick retinal cell cultures. For this purpose, primary cultures were prepared from 7-day-old chick embryos: retinas were aseptically dissected and dissociated and cells were grown at 37°C for 7-8 days. Cultures were exposed to MeHg (10 µM, 100 µM, and 1 mM) for 2, 4, and 6 h. Cell viability was measured by MTT method and NOS activity by monitoring the conversion of L-[H³]-arginine to L-[H³]-citrulline. The incubation of cultured retina cells with 10 and 100 µM MeHg promoted an increase of NOS activity compared to control (P < 0.05). Maximum values (P < 0.05) were reached after 4 h of MeHg incubation: increases of 81.6 ± 5.3 and 91.3 ± 3.7 percent, respectively (data are reported as mean ± SEM for 4 replicates). MeHg also promoted a concentration- and time-dependent decrease in cell viability, with the highest toxicity (a reduction of about 80 percent in cell viability) being observed at the concentration of 1 mM and after 4-6 h of incubation. The present study demonstrates for the first time the modulation of MeHg neurotoxicity in retinal cells by the nitrergic system.
Subject(s)
Animals , Chick Embryo , Methylmercury Compounds/toxicity , Nitric Oxide Synthase/metabolism , Retina/drug effects , Cells, Cultured , Cell Survival/drug effects , Retina/cytology , Time FactorsABSTRACT
The M-ganglion cell distribution was studied in the retinae of New World monkeys, the diurnal Cebus and the nocturnal Aotus. Retinal whole mounts were stained by the neurofibrillar method of Gros-Schultze. The M-ganglion cell distribution in the Cebus and Aotus is similar to that reported for Old World primates, such as the Macaca. The M-ganglion cell density peak occurs in the foveal slope and declines towards the periphery. There is a nasotemporal asymmetry: in the Cebus retina the M-ganglion cell density is 1.2-4.3 times higher in the nasal when compared to the temporal region at the equivalent eccentricities; in the Aotus, the nasotemporal asymmetry is smaller, 1.6-2.2 higher in the nasal region. We compared the M-ganglion cell density with previously published values for the density of the total population of ganglion cells and observed a larger proportion of M-ganglion cells in the Aotus, when compared with Cebus or Macaca