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P.K. Ahnelt, E.M. Anger, C. Schubert, E. Fernandez; Identification of Pedicles of Retinal S-cone Photoreceptors in a Non-primate Mammal, the Domestic Pig . Invest. Ophthalmol. Vis. Sci. 2003;44(13):2858.
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Purpose: To identify S-cone synaptic terminals in non-primate mammals as a prerequisite for identifying circuitry underlying the primarily dichromate system of mammalian retinal color vision. Methods: Retinas of domestic pigs were obtained from veterinary pathology or after experimental surgery. After fixation for 15min to several hrs in aldehydes and transfer into buffer the samples were cryosectioned or processed for resin embedding. Sections were incubated for polyclonal anti-S-opsin antibody JH 455 (donated by J.Nathans), PNA (Vector), PKC, rhodopsin and other markers to characterize the synaptic interfaces at the OPL and visualized by TRITC, Alexa conjugates or DAB-reaction. Results: In pig retina FITC-conjugated PNA is not only present at the cone outer segments but also at domains surrounding or on the synaptic surface of all cone pedicles. The majority of medium wavelength sensitive pedicle (ca. 90%, characterized by lack of JH 455) have polygonal spiny shapes. Several (4-8) punctate condensations of the fluorescent PNA marker are present predominantly along the outer rim of these pedicles. The minority of S-cone terminals could be identified by superposition of JH 455 AB/Alexa labeling extending from the intensely stained outer segments along the entire soma. S-cone pedicles show the irregular distribution characteristic for most mammalian S-cone subpopulations. The S-cone pedicle PNA domains are more roundish and somewhat smaller and PNA labeling is more diffusely distributed across their proximal surface. In many cases the distance to the surrounding pedicles is enlarged indicating the presence of more interspersed rod terminals. Conclusions: Similar to previous findings in primate and human retina (Ahnelt et al, 1990, 1994) S-cone synaptic terminals of the pig retina can be differentiated by morphological and immunocytochemical features. The differential PNA-affinity may be linked to specific properties of the S-cone pedicle membrane/extracellular matrix sheath complex similar to what has been reported for ground squirrel S-cone outer segments (Szél et al. 1993). The criteria will be useful to search for specific circuitries associated with the basally dichromatic design of mammalian color processing.
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