CHARACTERIZATION OF MELATONIN RECEPTORS IN THE BRAIN OF 4 AVIAN SPECIES - DUCK, GOOSE, PIGEON, AND TURKEY

Melatonin receptor sites were characterized in the brains of four avia n species (duck, goose, pigeon, and turkey) by an in vitro binding tec hnique, using 2-[I-125]iodomelatonin as a labeled ligand. The specific binding of 2-[I-125]iodomelatonin to avian brain membranes was found to be stable, saturable, reversible, and of high affinity. Scatchard a nalysis revealed that 2-[I-125]iodomelatonin binds to a single class o f sites in brain membrane preparations of these species with high affi nity (affinity constants K-d between 153 and 289 pM) and low capacity (total number of binding sites B-max between 5.07 and 10.15 fmol/mg pr otein). Competition studies showed the following relative order of pot ency of indolic compounds to inhibit the specific 2-[I-125]iodomelaton in binding: melatonin >> N-acetyltryptamine> > N-acetyl-5-hydroxytrypt amine > 5-hydroxytryptamine >>> 5-methoxytryptamine. We conclude that the 2-[I-125]iodomelatonin-binding sites in brains of duck, goose, pig eon, and turkey have similar binding and pharmacological characteristi cs, and may represent ML-1 melatonin receptor sites. (C) 1996 Academic Press, Inc.