Autoradiographic Characterization of Rat Spinal Neuropeptide FF Receptors by Using [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF

The binding properties of neuropeptide FF (NPFF) receptors were investigated in different laminae of the rat spinal cord by using quantitative autoradiography and [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF as radioligand. In the superficial layers, the specific binding of [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF was time-dependent, reversible, and saturable ( K D = 0.1 nM). Preincubation of spinal sections increased the maximal number of [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF binding sites. Bestatin, an inhibitor of aminopeptidases, increased significantly the apparent affinity of NPFF. Optimal binding of [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF was observed in the presence of 120 mM NaCl in all laminae of the spinal cord. No significant differences were noted in the salt dependence in laminae I–II, IV–V, and X, and the pharmacological profile of [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF binding was similar in each laminae. These results do not support the existence of NPFF receptors subtypes differentially localized in different area of the spinal cord. Our data reveal the effects of tissue treatments on binding characteristics of NPFF receptors and indicate that [ 125I][D.Tyr 1, (NMe)Phe 3]NPFF is a useful radioactive probe for the characterization of NPFF receptors in discrete brain areas.