Photoreceptor Organization and Rhythmic Phagocytosis in the Nile Rat Arvicanthis Ansorgei : A Novel Diurnal Rodent Model for the Study of Cone Pathophysiology

University of Strasbourg, Strasburg, Alsace, France
Investigative Ophthalmology &amp Visual Science (Impact Factor: 3.66). 08/2006; 47(7):3109-18. DOI: 10.1167/iovs.05-1397
Source: PubMed

ABSTRACT To characterize rod and cone distribution, organization, and phagocytosis in the diurnal mouse-like rodent Arvicanthis ansorgei.
Retinas of adult A. ansorgei were processed for histology, electron microscopy and immunohistochemistry using rod- and mouse cone-specific antibodies. For phagocytosis studies, retinas were sampled every 3 hours under a 12-hour light-dark cycle and processed for double-label immunohistochemistry. The number of phagosomes in the retinal pigmented epithelium were quantified with a morphometric system.
A. ansorgei retinas were composed of 33% cones and 67% rods, approximately 10 times more cones than mice and rats. Cones were arranged in two cell layers at the scleral surface, distributed uniformly across the entire retina. Cone arrestin was distributed throughout the dark-adapted cones, from outer segments to synapses, whereas short- and mid-wavelength cone opsins were restricted to outer segments. Short-wavelength cone density was mapped in wholemounted retinas, in a significantly higher number in the central region. Rhodopsin immunopositive (rod) phagosomes showed a small peak late in the dark phase, then a large burst 1 to 2 hours after light onset, after decreasing to low baseline levels by 12 AM. Mid-wavelength cone opsin immunopositive (cone) phagosomes were 10 times less numerous than rods, and demonstrated a broad peak 1 to 2 hours after light onset.
The diurnal rodent A. ansorgei possesses a large number of cones, organized in a strict anatomic array. Rod and cone outer segment phagocytosis and shedding can be monitored simultaneously and show similar profiles but different amplitudes. This species may constitute a valuable novel animal model for investigating cone pathophysiology.

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Available from: Cheryl M Craft, Jul 12, 2015
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    • "To better understand the differences between diurnal and nocturnal species, it seems essential to study the main circadian clock, located in the SCN of the hypothalamus but also the retina which represents an interface between the environment and the brain. Accordingly, cones – essential for daytime vision relevant for diurnal species – constitute 33% and 3% of the photoreceptors of A. ansorgei and nocturnal rats, respectively (Bobu et al., 2006, 2008; Jeon et al., 1998). By contrast, the SCN work in a close manner in diurnal and nocturnal species, but putative differences have been reviewed recently (Challet, 2007; Novak et al., 2008; Refinetti, 2008; Smale et al., 2008). "
    Dataset: HB2009-55
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    • "For example, in vertebrate rod and cone photoreceptors, outer segment phagocytosis, shedding, and renewal are continuous processes, but their rates are under circadian control. The circadian phase of the rhythmic shedding and renewal in both cones and rods is highly species dependent (Anderson et al. 1978, 1980; LaVail 1980; Besharse and Dunis 1983; Fisher et al. 1983; Reme et al. 1986; Bobu et al. 2006), while the photosensitive membrane undergoes daily turnover in the lateral eye of Limulus (Runyon et al. 2004). "
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    • "Finally, the monoclonal anti-rhodopsin rho4D2 (prepared using fresh bovine rod outer segments as the immunogen; Hicks and Molday, 1986) binds specifically to amino acids 2–39 of bovine rhodopsin N-terminal. This antibody has been shown previously to stain reactive bands of similar molecular weight in Western blots of rat and A. ansorgei retinas (Bobu et al., 2006). In both species it specifically labels rod outer segments (OS) and outlines rod cell bodies in the outer nuclear layer (ONL). "
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