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Different vulnerability of rat retinal cells to methylmercury exposure
Y Goto1, J Shigematsu, S Tobimatsu
1Department of Clinical Neurophysiology, Graduate School of Medical Sciences, Kyushu University, Fukuoka, Japan. ygoto@neurophy.med.kyushu-u.ac.jp
Abstract:
We tested the hypothesis that methylmercury chloride (MMC) caused a selective vulnerability in rat retinal cells during the intact preparation. MMC was injected subcutaneously daily at 3 different doses (0.25, 0.70 or 1.50 mg/kg/day) for 30 days. The electroretinograms under dark- and light-adaptation were recorded before and at 10-day intervals during the treatment period. With the lowest dose of MMC, only the amplitude of the light-adapted (LA) 20 Hz response significantly decreased on Day 30. At the intermediate dose, amplitude reductions were observed on Day 20 for the LA 20 Hz response and dark-adapted (DA) a-wave, while reductions in the LA 2 Hz b-wave and DA b-wave were noted only on Day 30. At the highest dose, these changes occurred earlier during the course of treatment. However, the amplitude of the DA second positive oscillatory potentials and the implicit times of any response components remained unchanged at all dosages. These results suggest that the cones are more sensitive than the rods, bipolar cells and Müller cells to MMC. However, amacrine cells were found to be relatively insensitive. Therefore, each retinal cell was found to have a different vulnerability to MMC.
Insights
Methylmercury chloride (MMC) exposure differentially affects rat retinal cells. Cones show higher sensitivity to MMC toxicity than rods, bipolar cells, Müller cells, and amacrine cells.
Area of Science:
- Neuroscience
- Toxicology
- Ophthalmology
Background:
- Methylmercury chloride (MMC) is a known neurotoxin.
- Understanding its specific effects on retinal cells is crucial for assessing visual system vulnerability.
Purpose of the Study:
- To investigate the selective vulnerability of different rat retinal cell types to methylmercury chloride (MMC).
- To determine the dose-dependent and time-course effects of MMC on retinal function.
Main Methods:
- Subcutaneous injection of MMC at varying doses (0.25, 0.70, 1.50 mg/kg/day) in rats for 30 days.
- Recording of electroretinograms (ERGs) under dark- and light-adapted conditions at 10-day intervals.
- Analysis of ERG amplitude and implicit time changes to assess retinal cell function.
Main Results:
- MMC exposure led to dose-dependent reductions in ERG amplitudes, particularly affecting light-adapted 20 Hz responses and dark-adapted a-waves and b-waves.
- Cone-driven responses were more sensitive to MMC than rod-driven responses.
- Oscillatory potentials and implicit times remained largely unaffected, indicating cell-type specific toxicity.
Conclusions:
- Rat retinal cells exhibit differential vulnerability to methylmercury chloride (MMC).
- Cone cells are more susceptible to MMC toxicity compared to rods, bipolar cells, Müller cells, and amacrine cells.
- These findings highlight the specific impact of MMC on visual pathway function.