Different subtypes of tachykinin NK(1) receptor binding sites are present in the rat brain.
(2-[(125)I]iodohistidyl(1))Neurokinin A ([(125)I]NKA), which labels "septide-sensitive" but not classic NK(1) binding sites in peripheral tissues, was used to determine whether septide-sensitive binding sites are also present in the rat brain. Binding studies were performed in the presence of SR 48968 (NK(2) antagonist) and senktide (NK(3) agonist) because [(125)I]NKA also labels peripheral NK(2) binding sites and, as shown in this study, central NK(3) binding sites. [(125)I]NKA was found to label not only septide-sensitive binding sites but also a new subtype of NK(1) binding site distinct from classic NK(1) binding sites. Both subtypes of [(125)I]NKA binding sites were sensitive to tachykinin NK(1) antagonists and agonists but also to the endogenous tachykinins NKA, neuropeptide K (NPK), and neuropeptide gamma (NPgamma). However, compounds of the septide family such as substance P(6-11) [SP(6-11)] and propionyl-[Met(O(2))(11)]SP(7-11) and some NK(1) antagonists, GR 82334, RP 67580, and CP 96345, had a much lower affinity for the new NK(1)-sensitive sites than for the septide-sensitive sites. The hypothalamus and colliculi possess only this new subtype of NK(1) site, whereas both types of [(125)I]NKA binding sites were found in the amygdala and some other brain structures. These results not only explain the central effects of septide or SP(6-11), but also those of NKA, NPK, and NPgamma, which can be selectively blocked by NK(1) receptor antagonists.
Beaujouan
J C
JC
Chaire de Neuropharmacologie, INSERM U114, Paris, France. jean-c.beaujouan@college-de-france.fr
Saffroy
M
M
Torrens
Y
Y
Glowinski
J
J
D000679:Amygdala / Q000378:metabolism; D000818:Animals; D001665:Binding Sites; D001667:Binding, Competitive; D002462:Cell Membrane / Q000378:metabolism; D002540:Cerebral Cortex / Q000378:metabolism; D007457:Iodine Radioisotopes; D007700:Kinetics; D008297:Male; D015288:Neurokinin A / Q000031:analogs & derivatives / Q000378:metabolism* / Q000494:pharmacology; D020033:Protein Isoforms / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D017207:Rats, Sprague-Dawley; D018040:Receptors, Neurokinin-1 / Q000378:metabolism*; D013373:Substance P / Q000031:analogs & derivatives / Q000378:metabolism / Q000494:pharmacology; D015320:Tachykinins / Q000494:pharmacology
D007457:Iodine Radioisotopes; D020033:Protein Isoforms; D018040:Receptors, Neurokinin-1; D015320:Tachykinins; D013373:Substance P; D015288:Neurokinin A