Abstract
Abstract: :
Purpose: To quantify the effects of methyl mercury (MeHg) contamination on the number and distribution of amacrine cells and displaced amacrine cells in the fish retina. Methods: Experiments were performed on control and MeHg contaminated adult thrairas, Hoplias malabaricus, at two dose levels: 2µg/Kg and 6µg /Kg i.p. The retinas of both control and MeHg-treated fish were dissected out, fixed by immersion with 4% paraformaldehyde in 0.1 M phosphate buffer during 3 hs and processed with mouse anti-parvalbumin immunocytochemistry. Morphology and soma location in the inner nuclear layer (INL) were used to identify parvalbumin immunoreactive (PV-IR) amacrine cells in wholemount preparations. Total number, cell density and topography were estimated in confocal images (Zeiss LSM 3.98) obtained throughout the entire retina, using NIH Scion Image 2.0 and DeltaGraph 4.0 software Results: PV-IR was found in amacrine cells as well as in bipolar cells in the INL and in ganglion and displaced amacrine cells in the ganglion cell layer. Only amacrine cells and displaced amacrine cells were quantified. The mean density was lower in treated retinae (1,076/mm2 and 1,016/mm2 , respectively for the 2µg/Kg and 6µg /Kg MeHg doses) relative to control (1,300/mm2) (P <0.05, ANOVA test). Density of amacrine cells in the control retinas ranged from 2, 083/mm2 in the center to 743/mm2 in the periphery. The MeHg treated retinae, on the other hand, did not reach density values above 2,011 and 1,817/mm2 at the center and 680 and 466/mm2 at the periphery, for the lower and higher doses, respectively. However, the loss of displaced amacrine cells in control retina was more prominent: the mean density changed from 442/mm2 to < 200/mm2 and <150/mm2 respectively for MeHg contamination with 2 and 6 µg (P <0.001, T-test). Conclusions: MeHg lowers amacrine cell density in the INL throughout the entire retina in a dose-dependent way. We did not find regional selectivity for the cell losses.
Keywords: amacrine cells • retina: proximal(bipolar, amacrine, and gangli • immunohistochemistry