diprenorphine and Opioid-Related-Disorders

Although opioid receptor function in humans is clearly reduced during opioid dependence, what happens to the receptor in early abstinence is not understood.. This study sought to examine changes in opioid receptor availability in early abstinence from opioid dependence.. Ten people with opioid dependence who had completed in-patient detoxification and 20 healthy controls underwent [11C]-diprenorphine positron emission tomography. Clinical variables were assessed with structured questionnaires. Opioid receptor binding was characterised as the volume of distribution of [11C]-diprenorphine using a template of predefined brain volumes and an exploratory voxel-by-voxel analysis.. Compared with controls, participants with opioid dependence had increased [11C]-diprenorphine binding in the whole brain and in 15 of the 21 a priori regions studied.. This study suggests that opioid receptor binding is increased throughout the brain in early abstinence from dependent opioid use. These data complement the findings in cocaine and alcohol dependence.

Topics: Adult; Brain; Case-Control Studies; Diprenorphine; Female; Humans; Male; Middle Aged; Narcotic Antagonists; Opiate Alkaloids; Opioid-Related Disorders; Positron-Emission Tomography; Receptors, Opioid; Substance Withdrawal Syndrome

Substitute methadone prescribing is one of the main modes of treatment for opioid dependence with established evidence for improved health and social outcomes. However, the pharmacology underpinning the effects of methadone is little studied despite controversies about dosing in relation to outcome. We therefore examined the relationship between methadone dose and occupation of opioid receptors in brain using the positron emission tomography (PET) radioligand [(11)C]diprenorphine in humans and rats. Eight opioid-dependent subjects stable on their substitute methadone (18-90 mg daily) had an [(11)C]diprenorphine PET scan at predicted peak plasma levels of methadone. These were compared with eight healthy controls. No difference in [(11)C]diprenorphine binding was found between the groups, with no relationship between methadone dose and occupancy. Adult male Sprague-Dawley rats that had been given an acute i.v. injection of methadone hydrochloride (0.35, 0.5, 0.7, or 1.0 mg kg(-1)) before [(11)C]diprenorphine showed a dose-dependent increase in biodistribution but no reduction in [(11)C]diprenorphine binding. We suggest that the lack of a dose-dependent relationship between methadone dose, either given chronically in human or acutely in rat, and occupancy of opioid receptor measured with [(11)C]diprenorphine PET is related to efficacy of this opioid agonist at very low levels of opioid receptor occupancy. This has implications for understanding the actions of methadone in comparison with other opioid drugs such as partial agonists and antagonists.

Topics: Adult; Animals; Behavior, Addictive; Carbon Radioisotopes; Diprenorphine; Humans; Male; Methadone; Middle Aged; Opioid-Related Disorders; Rats; Rats, Sprague-Dawley; Receptors, Opioid; Time Factors

Topics: Animals; Aorta, Thoracic; Cocaine; Cyclic AMP; Electric Stimulation; Guinea Pigs; Humans; Ileum; In Vitro Techniques; Male; Mice; Muscle, Smooth; Opioid-Related Disorders; Rats; Receptors, Dopamine; Receptors, Opioid; Receptors, Serotonin; Substance-Related Disorders

At low (< nM) concentrations, mu, delta or kappa opioid peptides as well as morphine and other opioid alkaloids elicit dose-dependent excitatory prolongation of the calcium-dependent component of the action potential duration (APD) of many mouse sensory dorsal root ganglion (DRG) neurons, whereas application of the same opioids at higher (uM) concentrations results in inhibitory shortening of the APD. These bimodal opioid excitatory/inhibitory effects on DRG neurons are blocked by naloxone. In contrast to bimodally acting opioids, the opioid alkaloids, etorphine and dihydroetorphine (thebaine-oripavine derivatives) uniquely elicited only dose-dependent, naloxone-reversible inhibitory effects on sensory neurons in DRG-spinal cord explants, even at concentrations as low as 1 pM, and showed no excitatory effects at lower concentrations. These remarkably potent inhibitory opioid receptor agonists also act as antagonists at excitatory opioid receptors since pretreatment of DRG neurons with subthreshold concentrations (< pM) blocked excitatory APD prolongation by nM morphine (or other opioids) and unmasked inhibitory APD shortening which generally requires much higher concentrations. Furthermore, acute application of pM-nM etorphine to chronic microM morphine- or D-Ala2-D-Leu5 enkephalin (DADLE)-treated DRG neurons blocked the nM naloxone-precipitated APD prolongation that generally occurs in DRG cells sensitized by bimodally acting opioids. In the presence of pM etorphine, chronic treatment of DRG neurons with microM morphine or DADLE no longer resulted in development of tolerance/dependence effects, as previously observed after similar chronic opioid treatment in the presence of cholera toxin-B subunit. These in vitro studies may clarify the mechanisms underlying the potent analgesic effects of etorphine and dihydroetorphine in vivo and to guide the use of these and other excitatory opioid receptor antagonists in attenuating development of opiate dependence/addiction.

Topics: Analgesics; Animals; Cells, Cultured; Diprenorphine; Drug Tolerance; Electrophysiology; Enkephalin, Leucine-2-Alanine; Etorphine; Ganglia, Spinal; Mice; Morphine; Naloxone; Narcotic Antagonists; Narcotics; Neurons, Afferent; Opioid-Related Disorders

The ability of acute morphine injections to augment discriminative stimulus effects and rate-decreasing effects of opioid antagonists was examined in pigeons trained to discriminate among i.m. injections of morphine (5.6 mg/kg), saline and naltrexone (10.0 mg/kg). A single injection of 10.0 or 32.0 mg/kg of morphine 24 hr before naltrexone produced 3- and 10-fold decreases, respectively, in the dose of naltrexone required for complete generalization. When morphine (10.0-100.0 mg/kg) was administered 48 hr before naltrexone, pigeons were not more sensitive to naltrexone as a discriminative stimulus but continued to be more sensitive to the rate-decreasing effects of naltrexone. Conditions that produced the largest increase in sensitivity to the discriminative stimulus effects of naltrexone (32.0 mg/kg of morphine 24 hr before the session) also increased sensitivity to the discriminative stimulus effects and rate-decreasing effects of naloxone, but did not affect the discriminative stimulus effects of diprenorphine, nalorphine or morphine. Increases in sensitivity to the discriminative stimulus effects of naltrexone and naloxone after single injections of morphine approached in magnitude the increases reported previously in pigeons treated chronically (once/daily) with large doses of morphine. However, the lack of generalization to naltrexone after pretreatment with still larger doses of morphine, as well as the failure of nalorphine and diprenorphine to substitute for naltrexone as discriminative stimuli under conditions in which sensitivity to naltrexone was increased, support the view that naltrexone does not produce its discriminative stimulus effects in nondependent animals exclusively through an opioid antagonistic action. The results suggest that morphine induced, acute supersensitivity to the discriminative stimulus effects of naltrexone differs from the supersensitivity to antagonists observed during chronic morphine treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

Topics: Animals; Binding Sites; Columbidae; Diprenorphine; Discrimination Learning; Dose-Response Relationship, Drug; Generalization, Stimulus; Morphine; Nalorphine; Naloxone; Naltrexone; Opioid-Related Disorders