Developmental and circadian regulation of 2-[125I]iodomelatonin binding in chick brain

Abstract

The avian circadian system is composed of several oscillatory and photoreceptive components whose mutual interactions regulate the temporal pattern of a wide variety of biochemical, physiological, and behavioral events. The hormone melatonin is important in the regulation of the avian circadian system, therefore, the sites of melatonin action are of interest. The development of the melatonin analog, 2- [1211]iodomelatonin (IMEL), has allowed autoradiography to be utilized in studying melatonin binding sites. This dissertation focuses on the regulation of IMEL binding in the chick from the development of binding sites in the embryo to the regulation of binding sites on a daily basis. The main results are summarized as follows: I. IMEL binding is extensive in structures of the circadian, tectofugal, thalamofugal, and accessory optic pathways of the avian visual system. 2.IMEL binding is present in chick brain at embryo day 6 with the number of structures binding IMEL increasing until embryo day 18 at which time the post-hatch pattern of binding is present. 3.IMEL binding is rhythmic with a significant peak at ZTIO in a 12:12 light:dark cycle (LD). This rhythm continued in constant darkness (DD) with a peak at CTIO. 4.Scatchard analysis of the binding revealed that the rhythm is produced by an increase in total number of binding sites B(max) in daytime versus nighttime samples with no change in the binding affinities (KD). 5.Pinealectomy has little effect on the IMEL binding rhythm in LD. However, with the pineal gland removed, the system cannot maintain the binding rhythm in DD. 6.Lesions of the visual suprachiasmatic nuclei (VSCNX) abolish the binding rhythm in LD 12:12. This implies that the VSCN either control the IMEL binding rhythm or are major contributors in the pathway for producing the binding rhythms. 7. Also, VSCNX abolish the body temperature rhythm in chicks placed into constant conditions. This data supports the role of the VSCN as primary oscillators within the chick circadian system.