title: Gamma-atrial natriuretic peptide 1-25 is found in bipolar cells in turtle and rat retinas.
abstract: Immunocytochemistry was used to reveal a population of bipolar cells that contain gamma-atrial natriuretic peptide 1-25 (gamma-ANP) in turtle retina. This same antibody was also used in rat retina as a comparative control. The retinas were examined by both conventional light microscopy and confocal microscopy with double-labeling to determine whether protein kinase C-alpha-like immunoreactivity (PKC-alpha-LI) was colocalized with the gamma-ANP-LI. Some thick sections of turtle retina immunostained with only the gamma-ANP antibody were also examined by electron microscopy. In rat, a subpopulation of bipolar cells with axons terminating close to the ganglion cell layer was labeled. Double-labeling experiments indicated that the gamma-ANP-LI and PKC-alpha-LI were colocalized in rat retina, and thus all the bipolar cells with gamma-ANP-LI were rod bipolar cells. In turtle, the gamma-ANP antibody labeled certain bipolar cells that were characterized by bistratified axon terminals arborizing on the borders of strata S2/3 and S3/4 in the inner plexiform layer (IPL). Double labeling with PKC-alpha antibody indicated that bipolar cells with gamma-ANP-LI were not the same bipolar cell types with PKC-alpha-LI. Thus, gamma-ANP-LI appears to be a new marker for a distinct type of bipolar cell in turtle retina. At the ultrastructural level, the gamma-ANP-LI was visible throughout the cytoplasm of the bipolar cells from dendrites to axon terminals. In the outer plexiform layer (OPL), labeled dendrites contacted photoreceptor pedicles almost exclusively at narrow-cleft basal junctions, but infrequently formed the central element at a photoreceptor ribbon synapse. In the IPL, axon terminals with gamma-ANP-LI made ribbon synapses onto a combination of amacrine and ganglion cells. Since narrow-cleft basal junctions and photoreceptor ribbon-related junctions are known to be associated with ON-center bipolar cells in turtle, and since the axon terminals of bipolars with gamma-ANP-LI stratify primarily in the ON-strata of the IPL, we suggest that these cells are likely to be ON-center cells. It is possible that the gamma-ANP may be involved in regulating the activity of Na+/K+ ATPase or in the modulation of cGMP levels.
authors.affiliation: Neurobiology Department, University of Oldenburg, Germany.
authors.forename: S
authors.initials: S
authors.lastname: Haverkamp
authors.forename: H
authors.initials: H
authors.lastname: Kolb
authors.forename: T A
authors.initials: TA
authors.lastname: Blute
authors.forename: L
authors.initials: L
authors.lastname: Cao
authors.forename: W D
authors.initials: WD
authors.lastname: Eldred
mesh_terms: D000818:Animals; D009320:Atrial Natriuretic Factor / Q000378:metabolism*; D007150:Immunohistochemistry; D007527:Isoenzymes / Q000378:metabolism; D008854:Microscopy, Electron; D010446:Peptide Fragments / Q000378:metabolism*; D011493:Protein Kinase C / Q000378:metabolism; D051571:Protein Kinase C-alpha; D051381:Rats / Q000378:metabolism*; D020318:Rats, Long-Evans; D012160:Retina / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D014426:Turtles / Q000378:metabolism*
chemical_list: D007527:Isoenzymes; D010446:Peptide Fragments; D009320:Atrial Natriuretic Factor; D011493:Protein Kinase C; D051571:Protein Kinase C-alpha