Increased absolute light sensitivity in Himalayan mice with cold-induced ocular pigmentation.
Controversy over the relationship between ocular pigmentation and absolute dark-adapted light sensitivity has persisted for over two decades. Previous electrophysiological experiments in hypopigmented mammals (mice, rats, rabbits) show increased thresholds in the dark-adapted state proportional to the deficit in ocular melanin. Animals with the least amount of ocular melanin have the most elevated thresholds. Dark-adapted thresholds in hypopigmented mice show similar threshold elevations in behavioral tests. The present study extends these findings to show that a specific increase in ocular pigmentation results in the converse effect, lowered absolute dark-adapted thresholds. The increase in ocular melanin was accomplished by keeping Himalayan mice in the cold (4 degrees C) for 6 weeks. Himalayan mice (C57BL/6J cH/cH) were compared to black mice (C57BL/6J (+/+)) and albino mice (C57BL/6J c2J/c2J) after 6 weeks at either 4 degrees C or 20 degrees C in 12-h cycling light (<1 cd/m2). The Himalayan mice that were kept in the cold exhibited a 44% increase in ocular melanin compared to Himalayan mice kept at room temperature. Cold rearing did not effect ocular melanin or visual thresholds in control animals (black mice = 10(-5.9) cd/m2 and albino mice = 10(-4.4) cd/m2). In contrast, the Himalayan mice maintained at 4 degrees C had thresholds of 10(-5.7) cd/m2 compared to 10(-5.1) cd/m2 for Himalayan mice kept at 20 degrees C. This represents compelling evidence of a direct relationship between ocular melanin concentration and absolute dark-adapted light sensitivity.
Biology Department, Boston College, Chestnut Hill, MA 02167, USA.
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Balkema
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MacDonald
D000818:Animals; D003080:Cold Temperature; D015350:Contrast Sensitivity / Q000502:physiology*; D003623:Dark Adaptation / Q000502:physiology*; D016015:Logistic Models; D008543:Melanins / Q000502:physiology; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D012168:Retinal Pigments / Q000502:physiology*; D012684:Sensory Thresholds / Q000502:physiology
D008543:Melanins; D012168:Retinal Pigments