Comparison of behavioural effects of NocII or NocIII, two related pronociceptin-derived peptides

Prepronociceptin contains, in addition to nociceptin, other potentially exc isable peptides which may have physiological significance. We have here con sidered NocII, a heptadecapeptide whose sequence lies immediately downstrea m of that of nociceptin in the precursor polypeptide, as well as NocIII whi ch corresponds to NoclI extended by a stretch of three arginine residues. W hen i.c.v.-administered in mice, NocII (10-10,000 ng) stimulated horizontal locomotor activity and decreased the latency to paw licking but neither to rearing nor escape jumping in the hot plate test (55 degrees C). When noci ceptin (100 ng) and NocII(100 ng) were simultaneously intracerebroventricul arly injected, each peptide produced its own effect without modifying the e ffect of the other. NocII was ineffective in the tail flick and writhing te sts. NocIII (NocII-Arg-Arg-Arg) was inactive in all tests, even when assaye d as long as 40 min following i.c.v. administration. The fact that NocII, b ut not its very close structural analogue NocIII, is biologically active in dicates that their may exist a specific receptor to NocII.