Increased GABA-mediated neurotransmission, reported to occur in hepatic encephalopathy (HE), is associated with a decrease in the release of Met-enkephalin and the expression of its coding gene in the brain. Furthermore, patients with cirrhosis and a history of HE exhibit increased sensitivity to the neuroinhibitory effects of morphine. Thus, there is a rationale to study the status of the endogenous opioid system in HE. The aim of this study was to determine whether mu-opioid receptors in the brain are up-regulated in a well characterized model of HE. Binding parameters of mu-opioid receptors were derived by assaying the binding of the opiate agonist [3H]-tyr-D-Ala-Gly-N-Methyl-Phe-Gly-ol (DAMGO) to brain membranes from rats with precisely defined stages of HE and control animals. The mean density of mu-opioid receptor sites (Bmax) in rats with stage II, III, and IV HE was 15, 29, and 33% higher, respectively, than the corresponding control value (p<0.01). In addition, the affinity of mu opioid receptors for the agonist (1/Kd) also increased with progression of HE (mean for stage IV HE vs. corresponding control mean, p<0.01). In conclusion, in liver failure, increased density and affinity of central mu-opioid receptors in the brain may: (i) be the basis for the documented increased sensitivity to opiate agonists; and (ii) occur as a consequence of increased GABAergic tone reducing neuronal synthesis and release of opioid agonist peptides.
Download full-text PDF |
Source |
|---|---|
| http://dx.doi.org/10.1016/s0024-3205(02)01487-x | DOI Listing |
Publication Analysis
Top Keywords
Similar Publications
Evidence that flocking behavior is rewarded by singing, flock mates, and mu opioid receptors in the nucleus accumbens.
PLoS One
January 2025
Department of Integrative Biology, University of Wisconsin-Madison, Madison, Wisconsin, United States of America.
It has been proposed that social groups are maintained both by reward resulting from positive social interactions and by the reduction of a negative state that would otherwise be caused by social separation. European starlings, Sturnus vulgaris, develop strong conditioned place preferences for places associated with the production of song in flocks outside the breeding season (gregarious song) and singers are motivated to rejoin the flock following removal. This indicates that the act of singing in flocks is associated with a positive affective state and raises the possibility that reward induced by song in flocks may play a role in flock maintenance.
View Article and Find Full Text PDFBuprenorphine Pharmacodynamics: A Bridge to Understanding Buprenorphine Clinical Benefits.
Drugs
January 2025
Palliative Medicine, Geisinger Medical Center, Danville, PA, USA.
Buprenorphine is an agonist at the mu opioid receptor (MOR) and antagonist at the kappa (KOR) and delta (DOR) receptors and a nociceptin receptor (NOR) ligand. Buprenorphine has a relatively low intrinsic efficacy for G-proteins and a long brain and MOR dwell time. Buprenorphine ceiling on respiratory depression has theoretically been related multiple factors such as low intrinsic efficacy at MOR, binding to six-transmembrane MOR and interactions in MOR/NOR heterodimers.
View Article and Find Full Text PDFLarge library docking of tangible molecules has revealed potent ligands across many targets. While make-on-demand libraries now exceed 75 billion enumerated molecules, their synthetic routes are dominated by a few reaction types, reducing diversity and inevitably leaving many interesting bioactive-like chemotypes unexplored. Here, we investigate the large-scale enumeration and targeted docking of isoquinuclidines.
View Article and Find Full Text PDFNovel tertiary diarylethylamines as functionally selective agonists of the kappa opioid receptor.
Bioorg Med Chem Lett
January 2025
Contineum Therapeutics, 3565 General Atomics Court, Suite 200, San Diego, CA 92121, United States.
Novel kappa opioid receptor (KOR) agonists that preferentially activate G-protein signaling versus β-arrestin-2 recruitment are described. Starting from a literature-reported phenol-containing diphenethylamine KOR agonist, structure-activity relationship (SAR) studies revealed replacement of the phenol with various non-hydroxylated bicyclic heteroaromatics led to tertiary diarylethylamines which retained KOR agonist activity and improved metabolic stability in human liver microsomes. Further optimizations produced compound 39, a potent activator of G-protein signaling (GTPγS EC = 14 nM, 83 % E) that did not elicit a β-arrestin-2 recruitment functional response (E < 10 %).
View Article and Find Full Text PDFMu opioid receptors expressed in striatal D2 medium spiny neurons have divergent contributions to cocaine and morphine reward.
Neuroscience
January 2025
Interdisciplinary Neuroscience Program, The University of Texas at Austin, Austin, TX, USA; Waggoner Center for Alcohol & Addiction Research, The University of Texas at Austin, Austin, TX, USA; Department of Neuroscience, The University of Texas at Austin, Austin, TX, USA; Department of Neurology, Dell Medical School, The University of Texas at Austin, Austin, TX, USA. Electronic address:
While our understanding of the neurobiological mechanisms underlying cocaine and opiate reward has historically been dopamine-focused, evidence from genetic and pharmacological approaches indicates that µ-opioid receptors (MORs) in the striatum are important contributors. Within the striatum, MORs are expressed in both dopamine D1-receptor and D2-receptor expressing GABAergic medium spiny neurons (MSNs), as well as in interneurons and various afferents. Thus, it remains unclear how these distinct MOR populations regulate drug reward.
View Article and Find Full Text PDFWant AI Summaries of new PubMed Abstracts delivered to your In-box?
Enter search terms and have AI summaries delivered each week - change queries or unsubscribe any time!