The present study investigated the effect of morphine sensitization on the impairment of spatial memory retrieval induced by acute morphine in adult male rats. Spatial memory was assessed by 2-day Morris water maze task which included training and test day. On the training day, rats were trained by a single training session of 8 trials. On the test day, a probe trial consisting of 60s free swim...

Delta and mu opioid receptors (DORs and MORs) are inhibitory G protein-coupled receptors that reportedly cooperatively regulate the transmission of pain messages by substance P and TRPV1-expressing pain fibers. Using a DOReGFP reporter mouse we now show that the DOR and MOR are, in fact, expressed by different subsets of primary afferents. The MOR is expressed in peptidergic pain fibers, the DO...

Received: December 20, 2016 Revised: February 14, 2017 Accepted: February 17, 2017 Abstract: Background: Pruritus is a very disturbing secondary effect that appears after epidural or intrathecal administration of opioid drugs, especially in the management of postoperative pain. It is induced by the activation of mu opioid receptors and it can often be even more unpleasant than the pain being tr...

The NOP receptor (nociceptin/orphanin FQ opioid peptide receptor) is the most recently discovered member of the opioid receptor family and, together with its endogenous ligand, N/OFQ, make up the fourth members of the opioid receptor and opioid peptide family. Because of its more recent discovery, an understanding of the cellular and behavioral actions induced by NOP receptor activation are les...

There is growing evidence that tonic activity of the opioid system may be important in the modulation of affective state. Naloxone produces a conditioned place aversion in rodents, an effect that is centrally mediated. Previous pharmacological data using antagonists with preferential actions at mu-, delta-, and kappa-opioid receptors indicate the importance of the mu-opioid receptor in mediatin...

Chronic infusion of morphine to guinea pigs produced selective changes in mu agonist binding properties in cerebrocortical membrane preparations. Employing the mu-selective opioid agonist [D-Ala2,MePhe4,Gly-ol5]enkephalin (DAMGO) in direct binding studies and in competition of labeled antagonist binding, we found that the major changes were a decrease in the number of sites with high affinity f...

In order to gain insight into a possible modulatory role for mu, delta, and kappa opioid receptors of the nigrostriatal dopaminergic pathway, we investigated the topographical organization of the receptors with respect to pre- and postsynaptic membranes. Dopaminergic terminals projecting from the substantia nigra to the corpus striatum were destroyed by unilateral injection of 6-hydroxydopamine...

The purpose of the present study was to analyze the effect of activation of mu-opioid receptors (mu-OR) on the immune response under blockade of postsynaptic D1and D2-receptors in mice of the C57BL/6J strain displaying either aggressive or depressive-like behaviors in the social conflict model. It is shown that activation of activation of mu-OR with a highly selective agonist DAGO (100 μg/kg) i...

The regulation of central mu-opioid receptors in women during the menstrual cycle was explored with positron emission tomography and the selective radiotracer [11C]carfentanil. Ten healthy women were studied twice, during their follicular and luteal phases. Plasma concentrations of estradiol, progesterone, testosterone, and beta-endorphin were determined immediately before scanning. LH pulsatil...

Opioid receptors are currently classified as mu, delta, and kappa types, but various subtypes have also been proposed. We have investigated whether subtypes exist by using [3H]bremazocine. [3H]Bremazocine binds to twice as many naloxone-sensitive sites as other nonselective opioid agonists, as shown in four membrane types that have very different ratios of mu, delta, and kappa receptor types. [...