Endothelin receptors in the outer plexiform layer of the mouse retina

TORBIDONI V; IRIBARNE M; CASTAÑEDA M; SUBURO AM

Buenos Aires

Congreso; XVII International Congress of Eye Research (ICER); 2006

Internationational Society of Eye Research

Introduction: We have previously described the presence of endothelin-1 (ET-1) and its receptors, ET-A and ET-B, in different sites of the mouse retina, including the retinal pigment epithelium (RPE), the outer plexiform layer (OPL), the ganglion cell layer (GCL), astrocytes and vascular endothelia. After light-induced retinal degeneration, endothelinergic structures disappear from the OPL whereas ET-1 and ET-B increase in astrocytes. Besides, the inhibition of endothelinergic  receptors reduces gliosis and apoptosis, two characteristics of the light-induced photoreceptor degeneration. Purpose: Our purpose was to identify OPL structures bearing endothelinergic receptors and to evaluate changes induced by brief period of light stimulation. Methods: Male BALB-c mice were bred under a constant cycle of 12hours light/ 12hours dark. Basal illumination levels did not exceed 60 lux. Experimental animals were subjected to 1,500lux for 24hours. Retinal cryosections were double labeled with ET-A or ET-B sera and with antibodies against the synaptic protein SV2 (one marker of photoreceptor terminals) or a phosphorylated epitope of the 200kd neurofilament (clone RT97, one marker of horizontal cells). Results: Under basal illumination conditions, the OPL showed a layer of regularly distributed ET-A-immunofluorescent varicosities. A similar layer of varicosities was present after SV-2 labeling. But double immunofluorescence indicated that these immunoreactivities did not correspond to the same terminals. By contrast, ET-B and RT-97 immunofluorescences were completely colocalized. No changes in the distribution or density of ET-A and ET-B immunoreactivities could be detected in the OPL after 24hours of exposition to 1,500lux. However, this treatment slightly increased ET-B immunofluorescence in neighboring Müller cells. Conclusions: Our data supports the presence of endothelinergic regulatory mechanisms in the OPL. Photoreceptors and/or horizontal cells would probably release ET-1. Since they exhibited ET-B immunoreactivity, horizontal cells could accumulate ET-1 released by neighboring cells. After 1 day of continuous illumination ET-B increased in Müller probably reflecting a response to changes of endothelin levels. OPL cell processes bearing ET-A have still to be identified, but probably correspond to one of the bipolar cell subtypes.