COMPARISON OF MELATONIN-BINDING SITES IN THE BRAIN OF 2 AMPHIBIANS - AN AUTORADIOGRAPHIC STUDY

Neuroanatomic comparison of the binding capability of 2-[I-125] iodome latonin in the crested newt Triturus carnifex Laur, and the green frog Rana esculenta, using quantitative autoradiographic techniques, revea led a heterogeneous distribution pattern. The highest and relatively h igh binding activities were shown to occur in the optic tracts and in the suprachiasmatic area of the hypothalamus and the optic tectum, res pectively, of both species. Low or no 2-[I-125] iodomelatonin binding values were obtained in the preoptic nucleus, the tuberal hypothalamus , the medulla oblongata, the septum and the dorsal pallium. A differen tial binding pattern was observed in the amygdaloid nucleus pars later alis, the striatum and the hindbrain of these amphibians. Indeed, nota bly high binding levels were shown to occur in the former two brain ar eas of the crested newt, whereas high levels were displayed in the lat ter brain region of the green frog. On the basis of elevated quantitie s of melatonin receptors in mesencephalic, hypothalamic and telencepha lic sites, it seems plausible to ascribe some important sensory functi ons to this receptor system in both species. The remarkably different binding activities in the brain of the two amphibians could be correla ted with the simpler cytoarchitectonic brain structure of urodeles and with species-specific variations.