[3H]raclopride and [3H]spiroperidol binding to retinal membranes of the teleost Eugerres plumieri: effect of light and dark adaptation.
Monoamine and metabolites were determined in the retina of the teleost Eugerres plumieri after dark and light adaptation. Dopamine, homovanillic acid and 3,4-dihydroxyphenylacetic acid increased after light exposure. The results indicate an increase in the turnover rate of dopamine due to light exposure. Dopamine D2 receptors were studied by determining the binding parameters of [3H]spiroperidol and [3H]raclopride to retinal membranes. The results were best fitted to a two-site model, where the high-affinity site may correspond to D2 receptors and the low-affinity site could be D4 receptors, which have been recently described in the retina, although further research is needed to confirm this suggestion. The number of sites labeled with [3H]spiroperidol was lower than with [3H]raclopride. This may indicate the existence of monomer and dimer conformations of D2-like receptors in the retina, as has been shown in the brain. Light exposure increased the number of sites labeled with both ligands. Since D2 receptors are known to modulate the production of melatonin, the augmentation in the capacity of these receptors could contribute to the reduction of melantonin during light exposure.
Obregón
F
F
Laboratorio de Neuroquimica, Instituto Venezolano de Investigaciones Cientificas, Caracas, Venezuela.
Urbina
M
M
Lima
L
L
D000221:Adaptation, Ocular / Q000502:physiology; D000818:Animals; D001665:Binding Sites; D003623:Dark Adaptation / Q000502:physiology; D004298:Dopamine / Q000378:metabolism; D018492:Dopamine Antagonists / Q000378:metabolism*; D005399:Fishes; D008566:Membranes / Q000378:metabolism; D020891:Raclopride; D012160:Retina / Q000378:metabolism*; D012457:Salicylamides / Q000378:metabolism*; D013134:Spiperone / Q000378:metabolism*; D014316:Tritium
D018492:Dopamine Antagonists; D012457:Salicylamides; D014316:Tritium; D020891:Raclopride; D013134:Spiperone; D004298:Dopamine