Dual localization of neuropeptide FF receptors in the rat dorsal horn

Abstract

Although neuropeptide FF (NPFF) is generally considered an anti-opioid, its intrathecal administration produces analgesia. In the present study, the stable analog 1DMe ([D.Tyr(1), (NMe)Phe(3)]neuropeptide FF) was used in quantitative autoradiographic experiments in combination with surgical and chemical lesions to precisely localize NPFF receptors in the rat spinal cord. Ligation of lumbar dorsal spinal roots revealed the presence of NPFF receptors in dorsal root fibers and it induced a significant accumulation of [(125)I]1DMe-specific binding on the side peripheral to the ligature, demonstrating that a population of NPFF receptors is synthesized in dorsal root ganglia and migrates anterogradely towards primary afferent nerve endings. Complete mid-thoracic spinal cord transection failed to modify the [(125)I]1DMe labeling density in the dorsal horn, indicating that NPFF receptors are not located on the descending fiber terminals. In contrast, unilateral microinjections of kainic acid into the dorsal horn dramatically reduced [(125)I]1DMe-specific binding in the superficial layers, revealing localization of a population of NPFF receptors on the spinal intrinsic neurons. NPFF receptor binding was not modified during the development of spinal opioid tolerance. The pre- and postsynaptic localization of spinal NPFF receptors provide further support for heterogeneity in the pain modulation by NPFF and related agonists.

Discovery of Novel Regulatory Peptides by Reverse Pharmacology: Spotlight on Chemerin and the RF-amide Peptides Metastin and QRFP

“…NPFF2 is more ligand selective than NPFF1 [55]. RT-PCR, in situ hybridization and autoradiographic studies revealed the localization of both receptors in CNS areas implicated in pain transmission consistent with the supposed physiological role of NPFF peptides [44,46,[56][57][58][59][60][61]. The presence of two peptidergic systems of neurotransmission, mediated via two receptors (NPFF1 and NPFF2) stimulated by four or more peptides generated from pro-NPFFa and pro-NPFFb, respectively, may explain the complex pharmacological effects of NPFF-like peptides.…”

Modulatory role of neuropeptide FF system in nociception and opiate analgesia

“…In contrast, the NPFF R2 mRNA is relatively abundant in DRG and trigeminal ganglia (Bonini et al, 2000) though the highest levels are in the spinal cord. In the rat, ligation of lumbar dorsal spinal roots induced a significant accumulation of NPFF binding sites on the side peripheral to the ligature suggesting the axonal transport of NPFF binding sites, synthesized in DRG, towards primary afferent endings (Gouarderes et al, 2000). This migration of NPFF binding sites (receptor protein) was further supported by the finding of relatively dense NPFF binding sites in the spinal trigeminal tract (Allard et al, 1992;Dupouy and Zajac, 1996) where NPFF receptor mRNA was not detected (Liu et al, 2001).…”

Modulatory roles of the NPFF system in pain mechanisms at the spinal level

“…However, it is possible that NPFF, which shows no affinity for opioid receptors, may modify opioid receptor activity through some as yet undetermined mechanism. NPFF binding sites in primary afferent nerve terminals have been demonstrated using receptor binding autoradiography [21,22]. NPFF-R2 transcripts are expressed in both spinal cord (dorsal cord) and dorsal root ganglia (DRG) as revealed by the cloning of NPFF-R2 from the RNA extracted from DRG (unpublished result).…”