Characterization of neurokinin binding sites in rat brain membranes using highly selective ligands

Neurokinin binding sites are distributed throughout the central and peripheral nervous system and three neurokinin binding sites have been described until now. The endogenous tachykinins substance P, neurokinin A and eledoisin as well as the highly selective neurokinin ligands [Arg6, Sar9, Met(O2)11]SP6-11 and [Sar9, Met(O2)11]SP (for neurokinin-1), MEN 10,376 and [beta Ala8]NKA(4-10) (for neurokinin-2) and senktide and [MePhe7]NKB (for neurokinin-3) were used for displacement experiments. Neurokinin-1 and -3 binding sites were demonstrated in membrane preparations of rat striatum, frontal cortex, hypothalamus, hippocampus and amygdala by displacing [125I]-BH-substance P and [125I]-BH-eledoisin, respectively. The highly selective neurokinin-2 ligand MEN 10,376 was iodinated to measure neurokinin-2 binding sites, but no specific binding was found in membranes of all brain regions, the spinal cord, the stomach, the urinary bladder or the guinea-pig lung, probably due to loss of binding properties. We conclude that neurokinin-1 and neurokinin-3 binding sites are distributed in several brain regions of the rat brain and selective neurokinin ligands are important tools to characterize neurokinin binding sites.