Mh. Makman et B. Dvorkin, PRESENCE OF NOCICEPTIN (ORPHANIN FQ) RECEPTORS IN RAT RETINA - COMPARISON WITH RECEPTORS IN STRIATUM, European journal of pharmacology, 338(2), 1997, pp. 171-176
Nociceptin (orphanin FQ), a heptadecapeptide with some sequence homolo
gy to dynorphin A, has been proposed as an endogenous ligand for a pre
viously cloned orphan receptor with significant homology to opioid rec
eptors. Utilizing [I-125][Tyr(14)]nociceptin as ligand, saturable and
high affinity nociceptin binding sites were detected and characterized
in rat retina and striatum. For retina, B-max = 34.0 +/- 4.5 fmol/mg
and K-d = 32.4 +/- 2.7 pM; for striaturn, B-max = 51.6 +/- 7.7 fmol/mg
and K-d = 98.6 +/- 11.3 pM. In competition studies, nociceptin bound
with picomolar affinity, dynorphin A with nanomolar affinity, naloxone
and dynorphan A-(1-8) with micromolar affinity, while [des-Tyr(1)]dyn
orphin (dynorphin A-(2-17)), several other opioids, morphine and benzo
morphans failed to compete for binding at 1-10 mu M. Gpp(NH)p plus NaC
l markedly decreased binding, consistent with involvement of a G prote
in-linked receptor. It is concluded that rat retina contains nocicepti
n receptors similar in concentration to those present in striatum. Pro
perties of both the retinal and the striatal receptors are similar to
those previously found for rat hypothalamus. (C) 1997 Elsevier Science
B.V.