EFFECTS OF PINEALECTOMY AND CONSTANT LIGHT EXPOSURE ON DAY-NIGHT CHANGES OF MELATONIN BINDING-SITES IN THE GOLDFISH BRAIN

Effects of pinealectomy and constant light exposure on day-night changes of melatonin binding sites in the goldfish brain were examined. The density and affinity of binding sites were higher at mid-day than at mid-night in sham-pinealectomized goldfish under light-dark cycles. The rhythms disappeared after pinealectomy, or constant light exposure both of which abolish plasma melatonin rhythms. The effects of pinealectomy and constant light exposure were not additive. These results indicate that diel changes of melatonin binding sites in the goldfish brain are regulated by endogenous melatonin of pineal origin.