EFFECT OF PINEALECTOMY AND THE LIGHT-DARK CYCLE ON 2-[I-125]IODOMELATONIN BINDING IN THE CHICK OPTIC TECTUM

1. These studies investigated the regulation of melatonin receptor sit es within the chick brain by the light/dark cycle and by endogenous me latonin using quantitative autoradiography. Saturation analyses perfor med in coronal brain sections of the optic tectum revealed a single cl ass of high-affinity binding sites. 2. For diurnal rhythm studies, chi cks were maintained on a 14:10 L:D cycle (light on 0400) and sacrifice d at 4-h intervals. No significant variation was observed in either th e affinity (K(D) = 67.8-76.4 pM) or the density (B(MAX) = 88.9-118.9 f mol/mg protein) of 2-[I-125]iodomelatonin binding sites as a function of time of day. 3. In pinealectomized or age-matched sham-operated chi cks, no changes were found in either the affinity (K(D) = 66.7-89.1 pM ) or the density (B(MAX) = 112.8-180.4 fmol/mg protein) of 2-[I-125]io domelatonin binding sites at either 1, 7, or 14 days following surgery . These data suggest that endogenous pineal melatonin may not play a r ole in the regulation of melatonin receptor site affinity or density i n the chick optic tectum.