Immunocytochemical reactivity of rod and cone visual pigments in the sturgeon retina

Microspectrophotometry and immunocytochemistry with several antivisual pigment antibodies were used to study visual cells of the Siberian sturgeon, Acipenser baeri Brandt. The retina contained rods and three morphological types of cones: large cones with oil drops, small cones with oil drops, and cone-like cells without oil drops. Rods and cone-like drop-free cells were found to possess porphyropsin-549, while the large oil drop-bearing cones contained red-sensitive (P613), green-sensitive (P542), and blue-sensitive (P462) visual pigments. The immunocytochemical staining pattern with three antibodies to visual pigment proteins also revealed one visual pigment in rods and three visual pigments in cones. Rods were labeled with all three antibodies, while the majority of large cones (type I), presumably the red-sensitive ones, were negative with the polyclonal serum AO against bovine opsin. A less-frequently occurring large cone type (type II) was stained by all three antibodies including mAb COS-1 specific to middle-to-long-wave visual pigments in birds and mammals, and is thought to be green-sensitive. An even less-frequent large cone type (type III, probably the blue-sensitive one) did not bind COS-1. The small cones with oil droplets showed immunoreactivities similar to either type II or type III cones. The oil drop-free small photoreceptor exhibited a staining pattern identical with that of rods. These results indicate that the immunocytochemical approach can be used to reveal photoreceptor-specific neural connections in the sturgeon retina.