Neuropeptide FF Analog Research Articles

Subcutaneous injection of an analog of neuropeptide FF prevents naloxone-precipitated morphine abstinence syndrome

There is evidence that neuropeptide FF (NPFF) has antiopiate activity and may play a role in opiate dependence and subsequent abstinence syndrome. A fragment of NPFF was modified at the C-terminal in an effort to convert it to an NPFF antagonist. It was also dansylated at the N-terminal in an effort to render it more lipophilic and increase its penetration of the blood-brain barrier. Third ventricle administration of the resulting compound, dansyl-PQRamide (0.75 μg and 1 μg), dose-dependently antagonized the quasi-morphine abstinence activity of NPFF (10 μg) in opiate-naive rats. Subcutaneous injection of dansyl-PQRamide (13 mg/kg) in chronically morphine-infused rats attenuated opiate dependence as indicated by prevention of naloxone-precipitated abstinence syndrome. Dansyl-PQRamide displaced radiolabelled ligand from NPFF receptors in a concentration-dependent manner with a K i of 13 μM, and had a half-life over 300 times longer than NPFF under aminopeptidase digestion.

Modulation of neuropeptide FF release from rat spinal cord slices by glutamate. Involvement of NMDA receptors

This study examined the effects of glutamate receptor agonists on the release of neuropeptide FF-like immunoreactivity from rat spinal dorsal half slices. Glutamate (10 μM) only induced release in Mg 2+-free medium enriched with glycine (1 μM) and with slight depolarization (15 mM K +). This effect was abolished by the NMDA receptor antagonist, 2-amino-5-phosphonovalerate (100 μM), suggesting major participation of NMDA receptors. The quisqualate and metabotropic receptor agonists, α-amino-3-hydroxy-5-methylisoxazole-4-propionate (AMPA) and trans-1-hydroxy-5-methylisoxazole-4-propionate ( t-ACPD) respectively, had no effect at 10 μM. In contrast, NMDA dose dependently stimulated neuropeptide FF release, even in the presence of the Na + channel blocker, tetrodotoxin (1 μM), suggesting that NMDA receptors involved in the release of neuropeptide FF are mainly located on nerve terminals. The NMDA receptor antagonists, 2-amino-5-phosphonovalerate or (+)-5- methyl-10−11- dihydro-5 H-dibenzo [ a, d]cyclohepten-5,10-imine (MK-801) (100 μM), blocked the 10 μM NMDA effect. Furthermore, neuropeptide FF-like material inhibited binding of [ 125I]Y8Fa, a radioiodinated analog of neuropeptide FF, to spinal membranes, suggesting physiological relevance of NMDA-induced release. Taken together, these results suggest a relationship between neuropeptide FF and NMDA receptors in the spinal cord.

Structure-activity study of neuropeptide FF: contribution of N-terminal regions to affinity and activity.

Twenty neuropeptide FF (NPFF) analogs having various lengths were synthesized by solid-phase peptide synthesis to gain more information on the role of N-terminal residues for the NPFF receptor affinity. The affinities were evaluated in the rat spinal cord membrane preparations, and the biological activities were measured on morphine analgesia in the mouse tail-flick test. Shortening of the NPFF sequence from the N-terminal produced only a moderate decrease in affinity until NPFF (4-8) was reached. In the same way, NPFF(3-8) significantly decreased morphine analgesia, while NPFF(4-8) had no significant effect at a dose of 22 nmol. The introduction in the N-terminal part of NPFF of a D-enantiomer at positions 2 and 1 or the presence of an N-methyl group on position 3 did not modify affinity and activity. Substitution of proline5 by the D-isomer decreased the affinity of NPFF analogs whatever their length, and [Tyr1,D-Pro5]NPFF(1-8) was 2.5-fold less potent than [Tyr1]NPFF(1-8) in reversing morphine-induced analgesia. In contrast, the presence of a glycine residue in position 5 did not influence the affinity toward NPFF receptors. Data provide evidence that the N-terminal segment of neuropeptide FF is responsible for high-affinity binding.

Subcutaneous injection of an analog of neuropeptide FF precipitates morphine abstinence syndrome

Neuropeptide FF (NPFF) has been shown to exert various antiopiate actions, including precipitation of opiate abstinence syndrome by third ventricle injection in morphine dependent rats. In the present study, dansyl-Pro-Gln-Arg-Phe-amide, a lipophilic analog of NPFF, was injected into morphine dependent rats and appropriate sham controls at a dose of 9 mg/kg s.c. Comparison groups were injected with ethanol/water vehicle alone. The NPFF analog precipitated a vigorous opiate abstinence syndrome in morphine dependent rats, but not in sham controls.

Analog of neuropeptide FF attenuates morphine tolerance

Previous studies suggest that neuropeptide FF (NPFF) plays a role in opiate dependence and subsequent abstinence syndrome. Endogeneous NPFF also appears to play a role in opiate tolerance since third ventricle injection of IgG from NPFF antiserum selectively restores morphine sensitivity in morphine-tolerant rats. The NPFF analog, desaminoYFLFQPQRamide (daY8Ra) has previously antagonized behavioral effects of NPFF and has attenuated morphine dependence. The present study assessed whether daY8Ra could similarly attenuate morphine tolerance. Third ventricle (i.c.v.) injection of daY8Ra restored the analgesic response to i.c.v. morphine in morphine-tolerant rats (radiant heat tail flick test). Saline injection failed to produce this effect. In opiate-naive rats, however, the same treatment with daY8Ra did not affect the analgesic response to i.c.v. morphine. Thus, daY8Ra appears to selectively restore morphine sensitivity in opiate-tolerant animals. These results further support the hypothesis that endogenous NPFF contributes to opiate tolerance.