Dopamine D1-receptor immunolocalization in goldfish retina

Dopamine, a neuromodulator in the vertebrate retina, is involved in numerou s functions related to light adaptation. However, unlike in mammals, locali zation of retinal D1-dopamine receptors in nonmammalian vertebrates has bee n hampered due to a lack of antisera. To address this problem, an antiserum against the 18 C-terminal amino acids of the goldfish D1 receptor (gfD1r) was generated in chicken eggs and tested in retinae of goldfish and rat, an d rat caudate putamen, by using immunoblots and light microscopic immunocyt ochemistry. No labeling was observed in any tissue or immunoblots with prea bsorbed gfD1r antiserum. Immunoblot analysis of goldfish retina revealed a single band at about 101 kDa. The patterns of gfD1r immunoreactivity (gfD1r -IR), found in rat caudate putamen and rat retina were virtually identical to that previously reported with other D1-receptor ligands and antisera. In goldfish retina, gfD1r-IR was most intense over cell bodies in the ganglio n cell layer, amacrine cells in the proximal inner nuclear layer (INL), and bipolar cells in the distal INL. Weaker gfD1r-IR was observed over horizon tal cell bodies and both plexiform layers. Muller cells and axons of cone p hotoreceptors were labeled as well. Double labeling showed that all protein kinase C-immunoreactive bipolar cells (ON type) were gfD1r-IR on the soma, axon terminal, and dendrites. All glutamate decarboxylase-immunoreactive ( i.e., gamma-aminobutyric acid utilizing) amacrine cells and horizontal cell s were gfD1r-IR. Retinal Dir distribution is more extensive than dopamine n euron innervation, but is consistent with physiologic estimates of dopamine function, suggestive of both wiring and volume transmission of dopamine in the retina. The gfD1r antiserum displays cross-reactivity to dopamine rece ptors in a mammal and a nonmammal and should prove useful in future studies of dopaminergic systems. (C) 1999 Wiley-Liss, Inc.