Characterization of pericellular [125I]Tyr0 DTrp8 somatostatin binding sites in the rat arcuate nucleus by a newly developed method: quantitative high-resolution light microscopic radioautography.
In the present work we characterized the kinetic properties of [125I]somatostatin pericellular binding sites in the arcuate nucleus of the hypothalamus of the rat by quantitative high-resolution light microscopic radioautography. In order to determine whether these pericellular binding sites corresponded to functional receptors, their properties were compared with those of previously well-characterized [125I]somatostatin binding sites present on neuronal processes on the same sections in the stratum radiatum of the CA1 of the hippocampus. Radiolabelled sections were analysed by densitometry using a Biocom image analysis system coupled with a Leitz orthoplan microscope. The linear relationship between optical densities and radioactive standards allowed us to quantitate [125I]somatostatin-specific binding. Binding was time- and temperature-dependent, and saturable and specific in the arcuate nucleus as in the CA1 of the hippocampus. Saturation experiments indicated a single receptor population of binding sites with KD values of 0.2 +/- 0.1 nM in the arcuate nucleus and 0.6 +/- 0.4 nM in the CA1. In both structures, displacement curves obtained with somatostatin 14 and somatostatin 28 were monophasic, but shallow, while the somatostatin analogue SMS 201-995 induced a biphasic displacement, suggesting two populations of binding sites. In both regions binding was GTP-dependent. Desaturation procedures (in vivo by cysteamine and in vitro by preincubating with GTP) resulted in an increase in the number of measurable binding sites.(ABSTRACT TRUNCATED AT 250 WORDS)
U 159 INSERM, Paris, France.
J
J
Bertherat
A
A
Slama
C
C
Kordon
C
C
Videau
J
J
Epelbaum
D000818:Animals; D001111:Arcuate Nucleus of Hypothalamus / Q000378:metabolism*; D001345:Autoradiography / Q000379:methods; D003543:Cysteamine / Q000494:pharmacology; D006160:Guanosine Triphosphate / Q000494:pharmacology; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D051381:Rats; D011919:Rats, Inbred Strains; D017981:Receptors, Neurotransmitter / Q000187:drug effects / Q000378:metabolism*; D017481:Receptors, Somatostatin; D013004:Somatostatin / Q000031:analogs & derivatives* / Q000378:metabolism*
D007457:Iodine Radioisotopes; D017981:Receptors, Neurotransmitter; D017481:Receptors, Somatostatin; D013004:Somatostatin; C012088:somatostatin, N-Tyr(1)-; D003543:Cysteamine; D006160:Guanosine Triphosphate