Inflammation enhances Y1 receptor signaling, neuropeptide Y-mediated inhibition of hyperalgesia, and substance P release from primary afferent neurons

Neuropeptide Y (NPY) is present in the superficial laminae of the dorsal horn and inhibits spinal nociceptive processing, but the mechanisms underlying its anti-hyperalgesic actions are unclear. We hypothesized that NPY acts at neuropeptide Y1 receptors in the dorsal horn to decrease nociception by inhibiting substance P (SP) release, and that these effects are enhanced by inflammation. To evaluate SP release, we used microdialysis and neurokinin 1 receptor (NK1R) internalization in rat. NPY decreased capsaicin-evoked SP-like immunoreactivity in the microdialysate of the dorsal horn. NPY also decreased non-noxious stimulus (paw brush)-evoked NK1R internalization (as well as mechanical hyperalgesia and mechanical and cold allodynia) after intraplantar injection of carrageenan. Similarly, in rat spinal cord slices with dorsal root attached, [Leu(31), Pro(34)]-NPY inhibited dorsal root stimulus-evoked NK1R internalization. In rat dorsal root ganglion neurons, Y1 receptors colocalized extensively with calcitonin gene-related peptide (CGRP). In dorsal horn neurons, Y1 receptors were extensively expressed and this may have masked the detection of terminal co-localization with CGRP or SP. To determine whether the pain inhibitory actions of Y1 receptors are enhanced by inflammation, we administered [Leu(31), Pro(34)]-NPY after intraplantar injection of complete Freund's adjuvant (CFA) in rat. We found that [Leu(31), Pro(34)]-NPY reduced paw clamp-induced NK1R internalization in CFA rats but not uninjured controls. To determine the contribution of increased Y1 receptor-G protein coupling, we measured [(35)S]GTPγS binding simulated by [Leu(31), Pro(34)]-NPY in mouse dorsal horn. CFA inflammation increased the affinity of Y1 receptor G-protein coupling. We conclude that Y1 receptors contribute to the anti-hyperalgesic effects of NPY by mediating the inhibition of SP release, and that Y1 receptor signaling in the dorsal horn is enhanced during inflammatory nociception.

Requirements for high affinity binding of glycine analogs to the glycine site of the NMDA receptor complex

Correlation of the isopotential contours of the optimized conformations of a series of alpha-amino acids, in their neutral and zwitterionic forms, with their potencies to inhibit [3H]glycine binding and to enhance [3H]10,11-dihydro-5-methyl-5H-dibenzo[a,d]cyclohepten-5,10-imine ([3H]MK-801) binding, leads to the following conclusions: (a) steric congestion at the amino group is detrimental to binding potency; (b) a zwitterionic amino acid is required for high affinity to the receptor; (c) a conformation in which the carboxylate group is at a 90 degrees dihedral angle to the ammonium nitrogen is preferred for high affinity; and (d) placing the carbon backbone of the zwitterionic alpha-amino acid, in its preferred conformation, above the plane defined by the ammonium nitrogen and the carboxylate oxygen atoms, and viewing the molecule along the nitrogen to carboxylate carbon axis, there is a space forbidden to the ligand (receptor-required-space) to the left.

High concentrations of glycine induce long-lasting changes in synaptic efficacy in rat hippocampal slices

Brief perfusion of adult rat hippocampal slices with high concentrations of glycine results in a slowly developing, long-lasting increase in synaptic responses in field CA1. Two observations indicated that the effect requires the activation of NMDA receptors by glycine. First, the glycine-induced potentiation is reduced by ketamine, an NMDA receptor channel blocker. Second, glycine potentiates the NMDA receptor-mediated epileptiform activity recorded in the presence of low magnesium concentration and picrotoxin. In slices prepared from rat pups (5-8 postnatal day), perfusion with glycine results in a slowly developing, long-lasting depression of EPSP amplitude. These results provide a new way of producing potentiation of synaptic efficacy and suggest new properties of NMDA receptors.

Malignant transformation by ras and other oncogenes produces common alterations in inositol phospholipid signaling pathways

The role of ras proteins in signal transduction was assessed by studying inositol phospholipid metabolism and inositol phospholipid-mediated cellular responsiveness to agonists in cells transformed by ras and other oncogenes. Specific alterations were observed in the inositol phospholipid cycle of ras-transformed fibroblasts, but similar changes were also produced by spontaneous transformation or transformation mediated by either membrane-associated oncogenes, such as src, met, or trk, or cytoplasmic oncogenes, mos and raf; the nuclear oncogenes fos and myc did not produce these changes. The alterations included (i) stimulation of phospholipase A2 activity as indicated by elevated levels of glycerophosphoinositol and nonesterified arachidonic acid and (ii) specific uncoupling between surface receptor-mediated stimulation by platelet-derived growth factor, bombesin, or serum and activation of intracellular phospholipase C. These findings suggest the existence of common biochemical pathways for transformation by cytoplasmic and membrane-associated oncogenes and are not consistent with the hypothesis that 21-kDa ras proteins (p21) are direct or distinct regulatory elements of phospholipase C or phospholipase A2 in inositol phospholipid signal transduction pathways.