enkephalin--ala(2)-mephe(4)-gly(5)- and Alcoholism

There is increasing evidence for a daily rhythm of µ-opioid receptor (MOR) efficacy and the development of alcohol dependence. Previous studies show that β-arrestin 2 (bArr2) has an impact on alcohol intake, at least partially mediated via modulation of MOR signaling, which in turn mediates the alcohol rewarding effects. Considering the interplay of circadian rhythms on MOR and alcohol dependence, we aimed to investigate bArr2 in alcohol dependence at different time points of the day/light cycle on the level of bArr2 mRNA (in situ hybridization), MOR availability (receptor autoradiography), and MOR signaling (Damgo-stimulated G-protein coupling) in the nucleus accumbens of alcohol-dependent and non-dependent Wistar rats. Using a microarray data set we found that bArr2, but not bArr1, shows a diurnal transcription pattern in the accumbens of naïve rats with higher expression levels during the active cycle. In 3-week abstinent rats, bArr2 is up-regulated in the accumbens at the beginning of the active cycle (ZT15), whereas no differences were found at the beginning of the inactive cycle (ZT3) compared with controls. This effect was accompanied by a specific down-regulation of MOR binding in the active cycle. Additionally, we detect a higher receptor coupling during the inactive cycle compared with the active cycle in alcohol-dependent animals. Together, we report daily rhythmicity for bArr2 expression linked to an inverse pattern of MOR, suggesting an involvement for bArr2 on circadian regulation of G-protein coupled receptors in alcohol dependence. The presented data may have implications for the development of novel bArr2-related treatment targets for alcoholism.

Topics: Alcoholism; Animals; beta-Arrestin 2; Circadian Rhythm; Down-Regulation; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Male; Microarray Analysis; Nucleus Accumbens; Rats; Rats, Wistar; Receptors, G-Protein-Coupled; Receptors, Opioid, mu; Reward

Using the drinking-in-the-dark (DID) model, we compared the effects of a novel mu-opioid receptor antagonist, GSK1521498, with naltrexone, a licensed treatment of alcohol dependence, on ethanol consumption in mice.. We test the ability of GSK1521498 to reduce alcohol consumption and compare its intrinsic efficacy to that of naltrexone by comparing the two drugs at doses matched for equivalent receptor occupancy.. Thirty-six C57BL/6J mice were tested in a DID procedure. In 2-day cycles, animals experienced one baseline, injection-free session, and one test session when they received two injections, one of test drug and one placebo. All animals received GSK1521498 (0, 0.1, 1 and 3 mg/kg, i.p., 30 min pre-treatment) and naltrexone (0, 0.1, 1 and 3 mg/kg, s.c. 10 min pre-treatment) in a cross-over design. Receptor occupancies following the same doses were determined ex vivo in separate groups by autoradiography, using [3H]DAMGO. Binding in the region of interest was measured integrally by computer-assisted microdensitometry and corrected for non-specific binding.. Both GSK1521498 and naltrexone dose-dependently decreased ethanol consumption. When drug doses were matched for 70-75% receptor occupancy, GSK1521498 3 mg/kg, i.p., caused a 2.5-fold greater reduction in alcohol consumption than naltrexone 0.1 mg/kg, s.c. Both GSK1521498 and naltrexone significantly reduced sucrose consumption at a dose of 1 mg/kg but not 0.1 mg/kg. In a test of conditioned taste aversion, GSK1521498 (3 mg/kg) reduced sucrose consumption 24 h following exposure to a conditioning injection.. Both opioid receptor antagonists reduced alcohol consumption but GK1521498 has higher intrinsic efficacy than naltrexone.

Topics: Alcohol Drinking; Alcoholism; Animals; Autoradiography; Behavior, Animal; Central Nervous System Depressants; Cross-Over Studies; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Ethanol; Indans; Male; Mice; Mice, Inbred C57BL; Naltrexone; Narcotic Antagonists; Radiopharmaceuticals; Receptors, Opioid, mu; Self Administration; Triazoles; Tritium

A series of substituted aryl amide derivatives of 6-naltrexamine, 3 designed to be metabolically stable were synthesized and used to characterize the structural requirements for their potency to binding and functional activity of human mu (mu), delta (delta) and kappa (kappa) opioid and nociceptin (NOP) receptors. Binding assays showed that 4-10 had subnanomolar K(i) values for mu and kappa opioid receptors. Functional assays for stimulation of [(35)S]GTPgammaS binding showed that several compounds acted as partial or inverse agonists and antagonists of the mu and delta, kappa opioid or NOP receptors. The compounds showed considerable stability in the presence of rat, mouse or human liver preparations and NADPH. The inhibitory activity on the functional activity of human cytochrome P450s was examined to determine any potential inhibition by 4-9. Only modest inhibition of CYP3A4, CYP2C9 and CYP2C19 was observed for a few of the analogs. As a representative example, radiolabeled 6 was examined in vivo and showed reasonable brain penetration. The inhibition of ethanol self-administration in rats trained to self-administer a 10% (w/v) ethanol solution, utilizing operant techniques showed 5-8 to have very potent efficacy (ED(50) values 19-50 microg/kg).

Topics: Alcohol Deterrents; Alcoholism; Animals; Humans; Liver; Male; Mice; Naltrexone; Nociceptin Receptor; Protein Binding; Rats; Rats, Wistar; Receptors, Opioid; Receptors, Opioid, delta; Receptors, Opioid, kappa; Receptors, Opioid, mu; Structure-Activity Relationship

Although ethanol addiction is believed to be mediated by the mesolimbic dopamine system, originating from the ventral tegmental area (VTA), how acute ethanol increases the activity of VTA dopaminergic (DA) neurons remains unclear.. Patch-clamp recordings of spontaneous firings of DA and GABAergic neurons in the VTA in acute midbrain slices from rats.. Ethanol (20-80 mM) excites DA neurons, and more potently depresses firing of local GABAergic neurons. The ethanol-induced excitation of DA neurons is considerably attenuated by DAMGO (Tyr-d-Ala-Gly-N-Me-Phe-Gly-ol enkephalin), a mu-opioid agonist that suppresses firing of GABAergic neurons, or by naloxone, a general opioid antagonist. The ongoing opioid-induced facilitation of DA cell firing (revealed by naloxone) is enhanced by ethanol, probably by an increase in opioid release or action.. Ethanol excites VTA DA neurons at least partly by increasing ongoing opioid-mediated suppression of local GABAergic inhibition. This indirect mechanism may contribute significantly to the positively reinforcing properties of ethanol.

Topics: Alcoholism; Animals; Brain; Dopamine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Ethanol; GABA Antagonists; gamma-Aminobutyric Acid; Humans; Neurons; Patch-Clamp Techniques; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Synaptic Transmission; Ventral Tegmental Area

Biochemical and pharmacological evidence suggest that the dopaminergic mesolimbic system plays a key role in mediating the reinforcing properties of alcohol and other drugs of abuse. Alcohol reinforcement and high alcohol drinking behavior have been postulated to be partially mediated by a neurobiological mechanism involving the alcohol-induced activation of the endogenous opioid system. The aim of this work was to study the effect of the in vivo acute administration of ethanol on mu (mu) opioid receptors in the rat dopaminergic meso-accumbens and mesocortical pathways by quantitative receptor autoradiography. [(3)H]DAMGO binding was significantly decreased in the ventral tegmental area (VTA) 30 min after ethanol administration. A small ethanol-induced reduction was observed in the shell region of the nucleus accumbens 1 h after exposure. In contrast, 2 h after ethanol administration, [(3)H]DAMGO binding was significantly increased in the frontal and prefrontal cortices. The observed changes correlated well with high ethanol plasma levels. Our results suggest that the reinforcing properties of ethanol may be partially mediated by mechanisms involving the ethanol-induced down- and up-regulation of mu receptors in the dopaminergic mesolimbic system. Mu receptors in the VTA and the frontal and prefrontal cortices may be involved in the in vivo acute responses to ethanol and could play a key role in modulating the dopaminergic activity of the mesocortical pathway in response to the drug. In contrast, the contribution of both mu and delta receptors in the nucleus accumbens might be relevant in these processes.

Topics: Alcoholism; Analgesics, Opioid; Animals; Autoradiography; Central Nervous System Depressants; Cerebral Cortex; Dopamine; Enkephalin, Ala(2)-MePhe(4)-Gly(5)-; Ethanol; Limbic System; Male; Neural Pathways; Nucleus Accumbens; Opioid Peptides; Radioligand Assay; Rats; Rats, Wistar; Receptors, Opioid, mu; Tritium; Ventral Tegmental Area