8-[H-3]HYDROXY-2-(DI-N-PROPYLAMINO) TETRALIN BINDING-SITES IN GOLDFISH RETINA

The binding sites of 8-[H-3]hydroxy-2-(di-n-propylamino)tetralin ([H-3 ]DPAT) were characterized in the retina of goldfish in order to evalua te the selectivity of the ligand for serotonin(1A) (5HT(1A)) receptors . Specificity of the binding was performed in the presence of serotone rgic and dopaminergic agonists and antagonists. Buspirone, spiroxatrin e and 5-methoxy-N,N-dimethyltryptamine were potent inhibitors, followe d by propranolol, citalopram, imipramine and desipramine. Serotonin wa s not a potent inhibitor, and its interaction with the binding sites o f [H-3]DPAT was complex. Nomifensine displayed an important inhibition , however, other dopamine uptake blockers, such as bupropion and GBR-1 2909, were less potent. Haloperidol was also a good inhibitor, but the D-1 receptor agonist, SKF-38393, the D-2 receptor antagonist, sulpiri de, and dopamine did not inhibit the binding. GppNHp inhibited the bin ding in the micromolar range. The analysis of saturation experiments b y isotopic dilution, using buspirone to determine nonspecific binding, revealed two sites. The number of binding sites defined by buspirone were higher than the ones defined by nomifensine. The specific binding , using buspirone for definition, was reduced by the intraocular injec tion of 6-hydroxydopamine. This investigation demonstrates that [H-3]D PAT labels 5HT(1A) receptors in goldfish retina, but also interacts wi th a non-5HT receptor site. These receptors seem to be localized in do paminergic neurons.