Characterization and distribution of somatostatin binding sites in goldfish brain

Somatostatin (SRIF) binding sites were characterized in goldfish brain. Bin ding of I-125-[Tyr(11)]-SRIF-14 to a brain membrane preparation was found t o be saturable, reversible, and time, temperature-, and pH-dependent. Bindi ng was also displaceable by different forms of SRIF. Under optimal conditio ns (22 degrees C, pH 7.2), the equilibrium binding of I-125-[Tyr(11)]-SRIF- 14 to goldfish brain membranes was achieved after 60 min incubation. Analys is of saturable equilibrium binding revealed a one-site model fit with K-a of 1.3 nM. SRIF-14, mammalian SRIF-28, and salmon SRIF-25 displaced I-125-[ Tyr(11)]-SRIF-14 binding with similar affinity, whereas other neuropeptides , e.g., substance P, were unable to displace I-125-[Tyr(11)]- SRIF-14. Auto radiography studies demonstrated that I-125-[Tyr(11)]-SRIF-14 binding sites are found throughout the goldfish brain. A high density of I-125-[Tyr(11)] -SRIF-14 binding sites was found in the forebrain, including the nucleus pr eopticus, nucleus preopticus periventricularis, nucleus anterioris perivent ricularis, nucleus lateralis tuberis, nucleus dorsomedialis thalami, nucleu s dorsolateralis thalami, nucleus ventromedialis thalami, and nucleus diffu sus lobi inferioris. In midbrain, I-125-[Tyr(11)]- SRIF-14 binding sites we re found in the optic tectum. The facial and vagal lobes and the mesencepha lic-cerebellar tract were found to have a high density of binding sites. Th is study provides the first characterization and distribution of specific b inding sites for SRIF in a fish brain. (C) 2000 Academic Press.