Autoradiographic analysis of GABAA receptors in mu-opioid receptor knockout mice

High hepatitis C incidence in relation to prescription opioid injection and poly-drug use: Assessing barriers to hepatitis C prevention

BACKGROUND

Prescription opioid (PO) injection and poly-drug use have been associated with hepatitis C virus (HCV) infection among people who inject drugs (PWID). Poly-drug use is often a barrier to key HCV preventive programmes including opioid agonist treatment. The contribution of specific drug combinations to high HCV incidence in poly-drug users has not been assessed previously. Addressing this knowledge gap could enhance HCV treatment and prevention efforts. We examined the association between specific drugs and number of drugs used in addition to injected POs, and HCV seroconversion.

METHODS

PWID participating in a cohort study in Montréal (HEPCO), HCV-seronegative at baseline and followed between 2004 and 2013, were included. Data were collected by interview-administered questionnaires. Blood samples were tested for HCV new infections at each 3-6 month follow-up visit. Time-varying Cox regression models were utilized.

RESULTS

Of 356 participants (81.5% males; mean age: 34.7 years), 123 (34.6%) reported injected POs in the past month at baseline. In univariate analyses, recent use of the following drugs was associated with HCV seroconversion: injected POs, injected cocaine, injected heroin, non-injected tranquilisers, and smoked crack/cocaine. The relative excess risk of HCV seroconversion due to interaction (RER1_HR) was the highest for co-use of injected POs with the following substances: injected cocaine (RER1_HR=3.44), smoked crack/cocaine (RER1_HR=1.27), and non-injected tranquilisers (RER1_HR=0.8). In addition, a significant linear trend (p<0.001) towards higher risk was observed with increasing the number of these three drugs used in combination with injected POs.

CONCLUSION

Specific drugs and number of drugs used in addition to injected POs play a modulating role in the risk of HCV primary infection. Poly-drug use among people who inject POs has to be addressed in order to improve harm reduction programmes and reduce HCV transmission in this high-risk population.

Argon blocks the expression of locomotor sensitization to amphetamine through antagonism at the vesicular monoamine transporter-2 and mu-opioid receptor in the nucleus accumbens

We investigated the effects of the noble gas argon on the expression of locomotor sensitization to amphetamine and amphetamine-induced changes in dopamine release and mu-opioid neurotransmission in the nucleus accumbens. We found (1) argon blocked the increase in carrier-mediated dopamine release induced by amphetamine in brain slices, but, in contrast, potentiated the decrease in KCl-evoked dopamine release induced by amphetamine, thereby suggesting that argon inhibited the vesicular monoamine transporter-2; (2) argon blocked the expression of locomotor and mu-opioid neurotransmission sensitization induced by repeated amphetamine administration in a short-term model of sensitization in rats; (3) argon decreased the maximal number of binding sites and increased the dissociation constant of mu-receptors in membrane preparations, thereby indicating that argon is a mu-receptor antagonist; (4) argon blocked the expression of locomotor sensitization and context-dependent locomotor activity induced by repeated administration of amphetamine in a long-term model of sensitization. Taken together, these data indicate that argon could be of potential interest for treating drug addiction and dependence.

Argon prevents the development of locomotor sensitization to amphetamine and amphetamine-induced changes in mu opioid receptor in the nucleus accumbens

Systemic administration of γ-amino-butyric acid type A (GABA-A) and benzodiazepine receptor agonists has been reported to block the development of locomotor sensitization to amphetamine. Here, we investigated whether the non-anesthetic noble gas argon, shown to possess agonistic properties at these receptors, may block the acquisition of amphetamine-induced locomotor sensitization and mu opioid receptor activation in the nucleus accumbens. Rats were pretreated with saline solution or amphetamine (1 mg/kg) from day 1 to day 3 and then exposed, immediately after injection of amphetamine, to medicinal air or argon at 75 vol% (with the remainder being oxygen). After a 3-day period of withdrawal, rats were challenged with amphetamine on day 7. Rats pretreated with amphetamine and argon had lower locomotor activity (U = 5, P < 0.005) and mu opioid receptor activity in the nucleus accumbens (U = 0, P < 0.001) than rats pretreated with amphetamine and air. In contrast, argon had effect on locomotor and mu receptor activity neither in rats pretreated with saline and challenged with amphetamine (acute amphetamine) nor in rats pretreated and challenged with saline solution (controls). These results indicate that argon inhibits the development of both locomotor sensitization and mu opioid receptor activation induced by repeated administration of amphetamine.

Mu-opioid receptor knockout mice are more sensitive to chlordiazepoxide-induced anxiolytic behavior

We have previously demonstrated benzodiazepine binding in the cortex and hippocampus of mu-opioid receptor knockout (KO) mice. It is known that benzodiazepine receptors are involved in regulating anxiety-like behaviors. Thus, the present study was designed to examine whether there are changes in anxiety-like behavior in mice lacking mu-opioid receptors. To produce anxiolytic activity (less anxiety), the prototype benzodiazepine receptor agonist chlordiazepoxide (CDP, 5 mg/kg) was intraperitoneally administered in wild type (WT) and mu-opioid receptor KO mice. We found that compared to WT mice, mu-opioid receptor KO mice showed enhanced anxiolytic activity to CDP, including increased number of entries into open arm, increased percentage of the time spent in open arms, and decreased percentage of the time spent in enclosed arms in the elevated plus-maze test. We also assessed protein expression of the gamma-aminobutyric acid (GABA) synthetic enzyme (glutamic acid decarboxylase; GAD). Western blotting data indicated that neither the lack of mu-opioid receptors nor CDP treatment altered cortical or hippocampal GAD₆₅ or GAD₆₇ protein expression. These data indicate that compared with WT, mu-opioid receptor KO mice experienced less anxiety and exhibited enhanced anxiolytic activity to CDP treatment, and these effects were not dependent on GAD₆₅ or GAD₆₇ protein expression. Our previous and present data suggest that the anxiolytic activity displayed in mu-opioid receptor KO mice is associated with upregulation of the benzodiazepine receptor system.

Polydrug abuse: a review of opioid and benzodiazepine combination use

This paper reviews studies examining the pharmacological interactions and epidemiology of the combined use of opioids and benzodiazepines (BZDs). A search of English language publications from 1970 to 2012 was conducted using PubMed and PsycINFO(®). Our search found approximately 200 articles appropriate for inclusion in this paper. While numerous reports indicate that the co-abuse of opioids and BZDs is ubiquitous around the world, the reasons for the co-abuse of these medications are not entirely clear. Though the possibility remains that opioid abusers are using BZDs therapeutically to self-medicate anxiety, mania or insomnia, the data reviewed in this paper suggest that BZD use is primarily recreational. For example, co-users report seeking BZD prescriptions for the purpose of enhancing opioid intoxication or "high," and use doses that exceed the therapeutic range. Since there are few clinical studies investigating the pharmacological interaction and abuse liability of their combined use, this hypothesis has not been extensively evaluated in clinical settings. As such, our analysis encourages further systematic investigation of BZD abuse among opioid abusers. The co-abuse of BZDs and opioids is substantial and has negative consequences for general health, overdose lethality, and treatment outcome. Physicians should address this important and underappreciated problem with more cautious prescribing practices, and increased vigilance for abusive patterns of use.

Autoradiographic analysis of GABAA receptor binding in the neural anxiety network of postpartum and non-postpartum laboratory rats

Postpartum female rats exhibit a suppression of anxiety-related behaviors when compared to diestrous virgin females, pregnant females, and males. This blunted anxiety promotes optimal maternal care and involves elevated GABA neurotransmission, possibly including greater density of GABA(A) and benzodiazepine receptors in the postpartum brain. We here examined autoradiographic binding of [(3)H]muscimol to measure the total population of GABA(A) receptors and [(3)H]flunitrazepam to assess density of benzodiazepine sites in the medial prefrontal cortex, bed nucleus of the stria terminalis, amygdala, hippocampus, and periaqueductal gray of female rats sacrificed on day 7 postpartum, day 10 of pregnancy, or as diestrous virgins. A group of sexually naïve male rats was also included. We found that [(3)H]muscimol binding did not differ among groups in any site but that diestrous virgin females had greater [(3)H]flunitrazepam binding in the CA1 and dentate gyrus of the hippocampus compared to mid-pregnant females and males. Notably, postpartum and diestrous virgin females did not significantly differ in binding of either ligand in any site examined. This is the first study to evaluate the densities of GABA(A) and benzodiazepine binding sites simultaneously across three female reproductive states and sex with a focus on brain sites influencing anxiety-related behaviors. The results suggest that changes in other GABA(A) receptor characteristics such as subunit composition, or increased presynaptic GABA release during interactions with offspring, must instead play a greater role in the postpartum suppression of anxiety in laboratory rats.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.