Structural and physiological responses to prolonged constant lighting in the cone-rich retina of Arvicanthis ansorgei

• Published in: Experimental eye research Vol. 91; no. 6; pp. 793 - 799
• Main Authors: Mehdi, Madah Khawn -i- Muhammad, Hicks, David
• Format: Journal Article
• Language: English
• Published: England Elsevier Ltd 01.12.2010
• Subjects: Animal models; Animals; Blindness; Cell Count; circadian clock; Circadian Rhythm - radiation effects; Cones; Disease Models, Animal; Down-Regulation; Eye; Fluorescent Antibody Technique, Indirect; Illumination; immunohistochemistry; Light; Light effects; light treatment; Muridae; Opsins - metabolism; phagocytosis; Phagocytosis - radiation effects; Phagosomes; Phagosomes - physiology; Photoreceptors; Radiation Injuries, Experimental - metabolism; Radiation Injuries, Experimental - physiopathology; Retina; Retinal Cone Photoreceptor Cells - pathology; Retinal Cone Photoreceptor Cells - radiation effects; retinal degeneration; Retinal Degeneration - metabolism; Retinal Degeneration - physiopathology; Retinal Pigment Epithelium - metabolism; Retinal Pigment Epithelium - pathology; Retinal Rod Photoreceptor Cells - pathology; Retinal Rod Photoreceptor Cells - radiation effects; Rhythms; rods; photoreceptors; phagocytosis; cones; rods; immunohistochemistry; light treatment; circadian clock
• ISSN: 0014-4835; 1096-0007
• DOI: 10.1016/j.exer.2010.09.012

Cone photoreceptor death is a leading cause of blindness in industrialised countries. Despite this, there are few mammalian models available to study cone pathophysiology. The diurnal rodent Arvicanthis possesses a high cone percentage and ease of maintenance. We recently described the effect of ambient light conditions on cyclic disc shedding, and observed that 24 h of constant illumination (“LL”) completely disrupted the normal rhythmic process and increased cone shedding fourfold. The current study was undertaken to see whether protracted constant illumination (7 days LL) would further perturb cone (and rod) turnover, and possibly lead to photoreceptor degeneration. Whereas control (cyclic lighting) retinas exhibited a typical early morning burst in phagosomes, LL retinas exhibited only low uniform numbers of rod and cone phagosomes across 24 h, with no peak of shedding at any time. Morphometric and immunohistochemical analyses of Arvicanthis retinas after 7 days LL (300 lux) showed no structural changes compared to control retinas. ►Seven days of constant white light abolish rod and cone shedding rhythms in the diurnal rodent Arvicanthis ansorgei. ►Contrary to one day of constant light, there is significant down-regulation of rod and cone shedding (80 and 50% respectively). ►Seven days of constant light does not provoke any detectable photoreceptor degeneration or outer segment shortening.