The antagonistic properties of Tyr-d-Pro-Trp-Gly-NH(2) (d-Pro(2)-Tyr-W-MIF-1), a Tyr-Pro-Trp-Gly-NH(2)(Tyr-W-MIF-1) analog, on the antinociception induced by the mu-opioid receptor agonists Tyr-W-MIF-1, [d-Ala(2),N-Me-Phe(4),Gly(5)-ol]-enkephalin (DAMGO), Tyr-Pro-Trp-Phe-NH(2) (endomorphin-1), and Tyr-Pro-Phe-Phe-NH(2) (endomorphin-2) were studied in the mouse paw-withdrawal test. d-Pro(2)-Tyr-...

Opioid receptor subtypes may have site-specific effects and play different roles in modulating serotonergic neurotransmission in the mammalian central nervous system. To test this hypothesis, we used in vivo microdialysis to measure changes in extracellular serotonin (5-hydroxytryptamine; 5-HT) in response to local infusion of mu-, delta-, and kappa-opioid receptor ligands into the dorsal raphe...

The major objective of this paper is to characterize the mechanism by which morphine modulates lymphocyte function and if these effects are mediated through the mu-opioid receptor. We evaluated the in vitro effects of morphine on lymphocytes that were freshly isolated from lymph nodes from wild type (WT) and mu-opioid receptor knock-out (MORKO) mice. Results show that morphine inhibits Con A-in...

The influence of naloxone (NAL), a competitive antagonist of mu, kappa, delta and sigma receptors; D-Phe-Cys-Tyr-D-Trp-Orn-Thr-Pen-Thr-NH(2) (CTOP), selective antagonist of mu-opioid receptors; nor-binaltorphimine (NOR-BNI), a potent and higly selective kappa opioid receptor antagonist; naltrindole (NTI), a delta-opioid receptor antagonist and naltriben (NTB), a highly selective delta(2)-opioid...

The realization that the mu-opioid system plays a key role in the control of the process of neuroinflammation is a new concept that may lead to identification of novel therapies for this extremely widespread and intractable syndrome. Fever is the hallmark among the defense mechanisms evoked by the entry into the body of pathogens to initiate the innate immune responses. In an attempt to determi...

The rostral ventromedial medulla (RVM) forms part of a descending pathway that modulates nociceptive neurotransmission at the level of the spinal cord dorsal horn. However, the involvement of descending RVM systems in opioid analgesia are a matter of some debate. In the present study, patch-clamp recordings of RVM neurons were made from rats that had received retrograde tracer injections into t...

Dynorphin peptides act preferentially at kappa- as well as mu- and delta-opioid receptors. This study was conducted to determine whether dynorphin peptides act to lower dopaminergic tone in the tuberoinfundibular system, resulting in elevated serum prolactin levels and, if so, whether such an effect is mediated by the opioid receptors. Dose-related increases in serum prolactin levels were obser...

A previous study has implicated central mu opioid receptors in the preference for salt solutions. Because mu, kappa and delta receptors are all thought to play a role in food intake and/or the mediation of palatability, we performed a series of experiments to determine whether preferential agonists at kappa and delta receptors might also stimulate the intake of salt solutions. When injected cen...

Chronic opioid antagonist treatment up-regulates opioid receptors and produces functional supersensitivity. Although opioid antagonists vary from neutral to inverse, the role of antagonist efficacy in mediating the chronic effects of opioid antagonists is not known. In this study, the effects of two putative inverse agonists (naltrexone, naloxone) and a putative neutral antagonist (6beta-naltre...

Pharmacological approaches have defined the epsilon receptor as a beta-endorphin-preferring opioid receptor, described in rat vas deferens and in brain of several species. Only three opioid receptors-mu, delta and kappa-have been cloned and the existence of this additional subtype as a distinct protein remains controversial. Recently, the mouse brain epsilon receptor was detected in a G protein...