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Many nociceptive dorsal root ganglion (DRG) sensory neurons express the high affinity nerve growth factor (NGF) receptor TRKA, and respond to NGF. However, many do not express TRKA but are thought to respond to glial cell-derived neurotrophic factor (GDNF) and related molecules. We therefore cultured DRG neurons in the presence of GDNF, and looked at the expression of substance P and of the capsaicin receptor, VR1, two nociceptive properties already known to be NGF regulated. Using several different approaches we demonstrated that GDNF produced clear increases in expression of both properties, comparable in magnitude to increases seen with NGF. Following axotomy, aberrant expression of substance P in A fibres may be involved in the generation of neuropathic pain. Factors regulating substance P and other properties in the absence of retrogradely transported NGF may therefore be of significance in neuropathic pain states.

We have studied TNF-related apoptosis-inducing ligand (TRAIL) and its membrane-bound (R1-R4) and soluble receptors [osteoprotegerin (OPG)] in gestational membranes to assess their significance in preterm parturition and premature rupture of membranes (PROM). TRAIL was detected by ELISA in extracts of term choriodecidual (but not amnion) tissues and explant-conditioned media. Concentrations of OPG (determined using ELISA) in gestational membranes were 20- to 50-fold greater than those of TRAIL. Median OPG concentrations in amniotic fluid (AF) at 15-17 wk gestation were similar to those at term before and during labor, whereas levels in pregnancies sampled preterm were significantly elevated. OPG levels in AF from women with preterm PROM were similar to those from women in preterm labor. In contrast, in pooled AF samples (n = 23-33), TRAIL concentrations at term with and without labor were elevated compared with samples from preterm deliveries. TRAIL-R3 and -R4 decoy receptors were detected in term amnion and choriodecidual extracts by immunoblotting and were localized by immunohistochemistry to amnion epithelial cells and chorionic trophoblasts. TRAIL (100 ng/ml) had little or no effect on amnion or choriodecidual cell viability or apoptosis, although these tissues responded to TNF-alpha with increased prostaglandin E(2) production. Our findings suggest that OPG is abundant in gestational membranes and, in concert with TRAIL decoy receptors, may protect resident cells of the fetal membranes against the proapoptotic effects of TRAIL and other related ligands during pregnancy.

In recent years, it has been demonstrated that high circulating levels of the endogenous cannabinoid anandamide, resulting from low expression of its metabolizing enzyme fatty acid amide hydrolase (FAAH), may contribute to spontaneous miscarriage and poor outcome in women undergoing in vitro fertilization. The site of action of this compound, however, has not been determined. In this study, we examined the distribution of the cannabinoid receptors, CB1 and CB2, and the endocannabinoid-metabolizing enzyme FAAH in first trimester human placenta. Here, we show that FAAH is expressed throughout the human first trimester placenta, in extravillous trophoblast columns, villous cytotrophoblasts, syncytiotrophoblasts, and macrophages. Furthermore, FAAH mRNA levels appear to be regulated during gestation, with levels peaking at 11 wk before declining again. The immune system-associated cannabinoid CB2 receptors were localized only to placental macrophages. Interestingly, the cannabinoid receptor CB1 was not identified in first trimester placenta despite having previously been shown to be present in placental tissues at term. These findings suggest that the placenta may form a barrier preventing maternal-fetal transfer of anandamide and/or modulate local levels of anandamide by regulation of FAAH expression with gestation.

A new member of the G protein-coupled receptor superfamily has been isolated from an ovine genomic library with a probe generated by the application of the PCR technique, using cDNA synthesized on a mRNA template isolated from the ovine pars tuberalis. This genomic clone encodes a novel receptor of 325 amino acids with seven transmembrane domains. These domains share homology with other members of this family, but the best homology is with the recently cloned human MC-1 (50% in the transmembrane domains) and MC-3 (69% in the transmembrane domains) MSH receptors and the human ACTH (42% in the transmembrane domains) receptor. When this receptor was expressed in Cos7 cells, it was able to bind a potent analogue of alpha-MSH, [Nle4,D-Phe7]-alpha-MSH (NDP-MSH), with high affinity. This binding could be displaced by pro-opiomelanocortin-derived and related peptides, with the order of potency NDP-MSH > alpha-MSH = ACTH > beta-MSH and with no effect of gamma-MSH, delta-MSH or beta-endorphin. The expressed receptor was demonstrated to be functionally coupled to the adenylate cyclase second messenger pathway, with alpha-MSH, beta-MSH and ACTH stimulating cyclic AMP production. The amount of the mRNA for this receptor was found to be very low. The tissue distribution of this receptor could only be observed using the reverse transcription-PCR technique and the receptor was found to be present in a number of somatic tissues. These data indicate that this is a new and distinct member of the melanocortin receptor family.