DEVELOPMENTAL APPEARANCE AND AGE-RELATED-CHANGES IN SPECIFIC 2-[I-125]IODOMELATONIN BINDING-SITES IN THE SUPRACHIASMATIC NUCLEI OF FEMALE SYRIAN-HAMSTERS

In Syrian hamsters, the circadian timing system is sensitive to melato nin during gestation but is not responsive in the adult. In order to f urther understand this developmental change in melatonin responsivenes s, in vitro autoradiography was used to assess the presence of specifi c 2-[I-125]iodomelatonin binding sites in the suprachiasmatic nuclei o f female hamsters of selected embryonic (E) and postnatal (PN) ages (e .g. E13, E14, E15, PN1, PN2, PN12, PN25, PN112-133). Specific 2-[I-125 ]iodomelatonin binding sites were seen in the Suprachiasmatic nuclei o f some of the E14 hamsters and all the perinatal hamsters (E15, PN1 an d PN2) but not in older hamsters. In contrast, specific 2-[I-l25]iodom elatonin binding sites were seen in the pars tuberalis of all hamsters (with the exception of one), regardless of age. The transient express ion of specific 2-[I-125]iodomelatonin binding sites in the suprachias matic nuclei suggests that melatonin may have some special functions r estricted to early development. The specific 2-[I-125]iodomelatonin bi nding sites in the embryonic suprachiasmatic nuclei may represent the substrate for maternal melatonin to set the phase of the developing ci rcadian timing system.