title: Electron microscopic analysis of S-antigen- and serotonin-immunoreactive neural and sensory elements in the photosensory pineal organ of the salmon.
abstract: Photoreceptor cells in the pineal complex of poikilothermic vertebrates are regarded as homologous with the neuroendocrine pinealocytes in the mammalian pineal organ. They possess an indolamine metabolism, and they contain a number of substances that are immunochemically similar to photo-transduction-related proteins otherwise found in photoreceptors of the lateral eye retina. Using correlative light and electron microscopic pre-embedding immunocytochemistry, we have identified photosensory and neural elements that are immunoreactive with specific antisera against serotonin (5-hydroxy-tryptamine) and the 48 kDa soluble protein S-antigen (arrestin). One type of serotonin-immunoreactive (5HTir) photoreceptor cell was identified. This was characterized by a short basal pole, into which an immunonegative (post-synaptic?) element protruded. Two types of S-antigen-immunoreactive (SAir) photoreceptor cells were observed, one characterized by a short basal pole, similar to that of the 5HTir photoreceptors and the other characterized by a long, extensively branching basal pole. In addition, two types of neurons bearing no morphological specializations typical of photoreceptor cells were SAir: bipolar neurons and multipolar neurons. These were often situated dorsally in the pineal organ. The results indicate an emergence of multiple lines of photoreceptor-derived "pinealocytes" either early in phylogeny, or independently in different taxa. The results are discussed in relation to current theories of pineal evolution.
authors.affiliation: Department of Zoology, University of Lund, Sweden.
authors.forename: P
authors.initials: P
authors.lastname: Ekström
authors.forename: H
authors.initials: H
authors.lastname: Meissl
mesh_terms: D000818:Animals; D000941:Antigens / Q000378:metabolism*; D019393:Arrestin; D005136:Eye Proteins / Q000378:metabolism*; D005260:Female; D007150:Immunohistochemistry; D008029:Lighting; D008297:Male; D008854:Microscopy, Electron; D008970:Molecular Weight; D009475:Neurons, Afferent / Q000378:metabolism* / Q000648:ultrastructure; D010870:Pineal Gland / Q000378:metabolism* / Q000648:ultrastructure; D012474:Salmon / Q000033:anatomy & histology / Q000378:metabolism*; D011984:Sensory Receptor Cells / Q000378:metabolism* / Q000648:ultrastructure; D012701:Serotonin / Q000378:metabolism*
chemical_list: D000941:Antigens; D019393:Arrestin; D005136:Eye Proteins; D012701:Serotonin