DISTRIBUTION OF NEUROPEPTIDE FF (FLFQPQRFAMIDE) RECEPTORS IN THE ADULT-RAT SPINAL-CORD - EFFECTS OF DORSAL RHIZOTOMY AND NEONATAL CAPSAICIN

By using quantitative autoradiography and highly selective iodinated l igands, we quantified modifications in neuropeptide FF binding sites i n the superficial layers (laminae I and II) of the cervical (C6-C8 seg ments) and lumbar (L3-L5 segments) enlargements in two models: (i) rat s neonatally treated with capsaicin; (ii) rat submitted 15 days before to unilateral dorsal rhizotomies. We comparatively analysed the distr ibution of mu-opioid binding sites in the same animals. We have shown that the [I-125]YLFQPQRFamide (neuropeptide FF sites) labelling is not significantly modified following selective damage of fine afferent fi bres by neonatal capsaicin treatment. In the cervical and lumbar enlar gements, capsaicin-treated/control binding ratios for [I-125]YLFQPQRFa mide were 0.90 and 0.86, respectively. For [I-125]FK-33-824 (mu sites) ratio values were 0.40 and 0.44, respectively. While unilateral dorsa l rhizotomy induced a drastic decrease in [I-125]FK-33-824 labelling i n the side ipsilateral to the lesion as compared to the intact side (y ielding ratios of 0.29 and 0.31 for cervical and lumbar levels, respec tively), [I-125]YLFQPQRFamide labelling was not significantly modified , yielding ratios of 0.98 and 0.91 for cervical and lumbar levels, res pectively. These data suggest that, in contrast with a majority of mu- opioid receptors, neuropeptide FF receptors are not located on fine pr imary afferent fibres carrying nociceptive information from the fore- or hindlimb in the rat. This preferential postsynaptic localization, t ogether with the reported ''morphine modulating'' action of this pepti de, support the proposal of a role for neuropeptide FF in intraspinal modulation of nociceptive input.