Morphine tolerance increases μ-noncompetative δ binding sites (original) (raw)
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European Journal of Pharmacology, 1989
A variety of data support the hypothesis of an opiate receptor complex composed of distinct, yet interacting/Z and 6 binding sites (termed /zcx and 6cx to indicate binding sites 'in the complex'), in addition to independent /Z and 6 binding sites, termed /znc~ and 6no ~, to indicate binding sites 'not in the complex'. Ligand binding studies using membranes and slide-mounted sections of rat brain support the hypothesis that the irreversible /z-antagonist fl-funaltrexamine (FNA) selectively alkylates the opiate receptor complex, altering the binding of ~ agonists to the/zcx binding site and the binding of [3 H][D.Ala2 D_Leu 5]enkephalin to the 8~x site. Previous studies demonstrated that the chronic administration of morphine to rats selectively 'upregulates' the opiate receptor complex. In contrast, the chronic administration of naltrexone upregulates several types of opioid receptors, including x, the 6no X binding site, and multiple binding sites labeled by ~ agonists. A prediction based upon these observations is that, using [3H][D-Alae,MePhe4,Gly-olS]enkephalin to label /Z binding sites, chronic morphine should upregulate only the ~cx binding site, whereas chronic naltrexone should additionally up-regulate the /Ln~ binding site. In this study we test and confirm this hypothesis, using sensitivity to FNA to define the ~ binding site. The implications of these data for models of the opioid receptors and the mechanism(s) of tolerance and dependence are discussed.
Peptides, 1998
peptide receptor studies. 9. Identification of a novel non--non-␦-like opioid peptide binding site in rat brain. PEPTIDES 19(6) 1079 -1090, 1998. Quantitative binding studies resolved two high-affinity [ 3 H][D-Ala 2 ,D-Leu 5 ]enkephalin binding sites in rat brain membranes depleted of binding sites by pretreatment with the irreversible agent BIT. -The two binding sites had lower (␦ ncx-2 , Ki ϭ 96.6 nM) and higher (␦ ncx-1 , Ki ϭ 1.55 nM) affinity for DPDPE. The ligand-selectivity profile of the ␦ ncx-1 site was that of a classic ␦ binding site. The ligand-selectivity profile of the ␦ ncx-2 site was neitheror ␦-like. The Ki values of selected agents for the ␦ ncx-2 site were: [pCl]DPDPE (3.9 nM), DPLPE (140 nM), and DAMGO (2.6 nM). Under these assay conditions, [ 3 H][D-Ala 2 ,D-Leu 5 ]enkephalin binding to the cells expressing the cloned receptor is very low and pretreatment of cell membranes with BIT almost completely inhibits [ 3 H]DAMGO and [ 3 H][D-Ala 2 ,D-Leu 5 ]enkephalin binding. Intracerebroventricular administration of antisense DNA to the cloned delta receptor selectively decreased [ 3 H][D-Ala 2 ,D-Leu 5 ]enkephalin binding to the ␦ ncx-1 site. Administration of buprenorphine to rats 24 h prior to preparation of membranes differentially affected , ␦ ncx-1 , and ␦ ncx-2 binding sites. Viewed collectively, these studies have identified a novel non--non-␦-like binding site in rat brain.
Reassessment of opioid binding sites in the rat brain
Neuropeptides, 1986
Opioid binding sites have been characterized pharmacologically in membranes from different areas of the rat brain. Delta,mu and sites belonging to the kappa family (Kl,K2,K3) have been detected.Delta sites were more abundant in cortex and striatum,mu sites in striatum and hypothalamus,while kappa binding site concentration was higher in deeper enkephalic structures (brainstem,cerebellum,hypothalamus) and the pituitary gland. A distinct distribution of each subtype of the kappa site was found: kappa 1 sites were higher in the spinal cord,kappa 2 sites in the brainstem and kappa 3 sites in cerebellum. The distribution of delta and kappa sites in the central nervous system was correlated with the distribution of proenkephalin-A derived peptides and precursors, suggesting that these peptides could be their endogenous ligands.
Journal of Pharmacology and Experimental Therapeutics, 2002
Prolonged exposure to opioid agonists can induce adaptive changes resulting in tolerance and dependence. Here, rats were rendered tolerant by subcutaneous injections of increasing doses of morphine from 10 to 60 mg/kg for 3, 5, or 10 consecutive days. Binding parameters of the μ-opioid receptor in subcellular fractions were measured with [ 3 H]DAMGO ([D-Ala 2 ,N-Me-Phe 4 ,Gly 5 -ol]enkephalin). Although the density of surface μ-sites did not change after the 5-day morphine treatment, up-regulation of synaptic plasma membrane binding was detected after the 10-day drug administration. In contrast, the number of μ-binding sites in a light vesicle or microsomal fraction (MI) was elevated by 68 and 30% after 5 and 10 days of morphine exposure, respectively. The upregulated MI μ-sites displayed enhanced coupling to G proteins compared with those detected in saline-treated controls. Pertussis toxin catalyzed ADP ribosylation, and Western blotting with specific antisera was used to quantitate chronic morphine-induced changes in levels of various G protein μ-subunits. Morphine treatment of 5 days and longer induced significant increases in levels of Gα o , Gα i1 , and Gα i2 in MI fractions that are part of an adaptation process. Up-regulation of intracellular μ-sites may be the result of post-translational changes and in part de novo synthesis. The results provide the first evidence that distinct regulation of intracellular μ-opioid receptor G protein coupling and G protein levels may accompany the development of morphine tolerance.
Neuropeptides, 1984
Opioid receptor binding, including the mu, delta, and kappa receptor subtypes, was compared in morphine-injected and control rats. Brain tissues were homogenized and centrifuged either one or two times prior to receptor binding assay. In brain membranes from morphine-injected rats centrifuged once, there was a decrease in mu, but not delta or kappa, binding compared to controls, perhaps indicating occupation of these sites by morphine. By contrast, homogenates from morphine-injected rats centrifuged twice manifested an increase in mu, but not delta or kappa, binding sites. These results suggest that pharmacological stimulation of central opioid receptors with morphine causes a rapid, selective increase in the number of available mu binding sites.
Chronic opioid antagonist treatment: assessment of receptor upregulation
European Journal of Pharmacology, 1989
Changes in specific brain opioid binding and opioid pharmacodynamics were determined in mice treated with the opioid antagonist naltrexone (subcutaneously implanted pellets) for 8 days. Chronic opioid antagonist treatment increased the number of binding sites (upregulation) for [3H]naloxone (+ 55%) and [3H][D-Ala2,D-LeuS]enkephalin (+41%) but did not alter the affinity of the ligands, as determined in saturation studies. Displacement studies of [3H]naloxone by morphine also indicated that there was no change in morphine's affinity. In vivo estimation of naloxone affinity (pA2), agreed with the in vitro results indicating that chronic naltrexone treatment did not alter naloxone affinity. Chronic naltrexone treatment (0.5, 1.0, 15.0 mg pellets) increased the analgesic potency of morphine (supersensitivity) in a dose-dependent manner, up to a maximal increase in relative potency of 1.8. However, in mice tested with the naltrexone pellets still implanted, the 15 mg naltrexone pellet was able to shift the dose-response function for morphine analgesia more than 300-fold. The lowest dose naltrexone pellet (0.5 mg), produced significant antagonism of morphine analgesia, but did not produce significant supersensitivity. Thus, supersensitivity and upregulation are not proportional to the degree of antagonism of opioid effects; and supersensitivity in the mouse is related to increased binding sites and not to changes in receptor affinity as determined by in vivo and in vitro methods.
A role for heterodimerization of µ and opiate receptors in enhancing morphine analgesia
Proceedings of The National Academy of Sciences, 2004
Opiates such as morphine are the choice analgesic in the treatment of chronic pain. However their long-term use is limited because of the development of tolerance and dependence. Due to its importance in therapy, different strategies have been considered for making opiates such as morphine more effective, while curbing its liability to be abused. One such strategy has been to use a combination of drugs to improve the effectiveness of morphine. In particular, ␦ opioid receptor ligands have been useful in enhancing morphine's potency. The underlying molecular basis for these observations is not understood. We propose the modulation of receptor function by physical association between and ␦ opioid receptors as a potential mechanism. In support of this hypothesis, we show that -␦ interacting complexes exist in live cells and native membranes and that the occupancy of ␦ receptors (by antagonists) is sufficient to enhance opioid receptor binding and signaling activity. Furthermore, ␦ receptor antagonists enhance morphine-mediated intrathecal analgesia. Thus, heterodimeric associations between -␦ opioid receptors can be used as a model for the development of novel combination therapies for the treatment of chronic pain and other pathologies.
Opiate withdrawal intensity correlates with the presence of DSLET high-affinity binding
Pharmacology Biochemistry and Behavior, 1994
YUKHANANOV, R. YU., P. M. KLODT, A. D. IL'INA, S. V. ZAITSEV AND A. I. MAISKY. Opiate withdrawal intensity correlates with the presence of DSLET high-affinity binding. PHARMACOL BIOCHEM BEHAV 49(4) [1109][1110][1111][1112] 1994.-The goal of this study was to compare the characteristics of #-and 6-opioid receptors in the cortex of DBA/2 and C57BL/6 mice, which differ in sensitivity to the long-and short-term effects of morphine. The characteristics of t~-opiate receptors were not different in the cortex of both strains. Both high-and low-affinity binding sites of DSLET, a specific ligand of 6-opiate receptors, were present in the cortex of C57BL/6 mice, whereas the high-affinity binding sites were not found in the cortex of DBA/2 mice. The absence of high-affinity DSLET binding sites, which are similar to the 62 type of opioid receptors, may explain the less intensive naloxone-precipitated withdrawal reaction of DBA/2 as compared with C57BL/6 mice.