Involvement of µ-Opioid Receptor in Methamphetamine-Induced Behavioral Sensitization

Differences in clinical features and gut microbiota between individuals with methamphetamine casual use and methamphetamine use disorder

Background

The transition from methamphetamine (MA) casual use (MCU) to compulsive use is enigmatic as some MA users can remain in casual use, but some cannot. There is a knowledge gap if gut microbiota (GM) play a role in differing MCU from MA use disorder (MUD). We aimed to investigate the clinical features and GM differences between individuals with MCU and MUD.

Method

We recruited two groups of MA users -MCU and MUD - and matched them according to age and body mass index (n=21 in each group). Participants were accessed using the Semi-Structured Assessment for Drug Dependence and Alcoholism, and their fecal samples were undergone 16S ribosomal DNA sequencing. We compared the hosts' clinical features and GM diversity, composition, and structure (represented by enterotypes) between the two groups. We have identified differential microbes between the two groups and performed network analyses connecting GM and the clinical traits.

Result

Compared with the casual users, individuals with MUD had higher incidences of MA-induced neuropsychiatric symptoms (e.g., paranoia, depression) and withdrawal symptoms (e.g., fatigue, drowsiness, and increased appetite), as well as stronger cravings for and intentions to use MA, and increased MA tolerance. The GM diversity showed no significant differences between the two groups, but four genera (Halomonas, Clostridium, Devosia, and Dorea) were enriched in the individuals with MUD (p<0.05). Three distinct enterotypes were identified in all MA users, and Ruminococcus-driven enterotype 2 was dominant in individuals with MUD compared to the MCU (61.90% vs. 28.60%, p=0.03). Network analysis shows that Devosia is the hub genus (hub index = 0.75), which is not only related to the counts of the MUD diagnostic criteria (ρ=0.40; p=0.01) but also to the clinical features of MA users such as reduced social activities (ρ=0.54; p<0.01). Devosia is also associated with the increased intention to use MA (ρ=0.48; p<0.01), increased MA tolerance (ρ=0.38; p=0.01), craving for MA (ρ=0.37; p=0.01), and MA-induced withdrawal symptoms (p<0.05).

Conclusion

Our findings suggest that Ruminococcus-driven enterotype 2 and the genera Devosia might be two influential factors that differentiate MA casual use from MUD, but further studies are warranted.

Goofballing of Opioid and Methamphetamine: The Science Behind the Deadly Cocktail

Globally, millions of people suffer from various substance use disorders (SUD), including mono-and polydrug use of opioids and methamphetamine. Brain regions such as the cingulate cortex, infralimbic cortex, dorsal striatum, nucleus accumbens, basolateral and central amygdala have been shown to play important roles in addiction-related behavioral changes. Clinical and pre-clinical studies have characterized these brain regions and their corresponding neurochemical changes in numerous phases of drug dependence such as acute drug use, intoxication, craving, withdrawal, and relapse. At present, many studies have reported the individual effects of opioids and methamphetamine. However, little is known about their combined effects. Co-use of these drugs produces effects greater than either drug alone, where one decreases the side effects of the other, and the combination produces a prolonged intoxication period or a more desirable intoxication effect. An increasing number of studies have associated polydrug abuse with poorer treatment outcomes, drug-related deaths, and more severe psychopathologies. To date, the pharmacological treatment efficacy for polydrug abuse is vague, and still at the experimental stage. This present review discusses the human and animal behavioral, neuroanatomical, and neurochemical changes underlying both morphine and methamphetamine dependence separately, as well as its combination. This narrative review also delineates the recent advances in the pharmacotherapy of mono- and poly drug-use of opioids and methamphetamine at clinical and preclinical stages.

An up-converting phosphor technology-based lateral flow assay for point-of-collection detection of morphine and methamphetamine in saliva

Morphine (Mop) and methamphetamine (Met) are highly addictive drugs worldwide. Point-of-collection testing (POCT) for drug-of-abuse screening is important in abuse/rehabilitation clinics and law-enforcement agencies. We established an up-converting phosphor technology-based lateral flow assay (UPT-LFA) as a point-of-collection testing (POCT) method, namely Mop-UPT-LFA and Met-UPT-LFA, for the detection of morphine and methamphetamine without complicated sample pre-treatment, respectively, in saliva. The sensitivities of the Mop-UPT-LFA and the Met-UPT-LFA were 5 and 10 ng mL-1 with accurate quantitation of 5-100 ng mL-1 and 10-250 ng mL-1 for morphine and methamphetamine, respectively, for a detection time of 15 min. In reference to the detection limits of 20 and 25 ng mL-1 for morphine and methamphetamine, respectively, in the Driving Under the Influence of Drugs, Alcohol and Medicines (DRUID) program of the European Union, the percentage test/control (T/C) ratio of the UPT-LFA between 2 and 15 min reached 101% and 86%, and the UPT-LFA produced accurate qualitative results in 2 min for 100 simulated-saliva samples with the exception of a few weakly positive samples. The sample and sample treating buffer were mixed and added to the test strip, and the test was conducted 15 min later. Although we found no significant difference between the UPT-LFA quantitative test and the liquid chromatography tandem mass spectrometry (LC-MS) test, compared with the latter, the UPT-LFA was substantially faster and had higher detection efficiency. The UPT-LFA showed more accurate qualitative results than the LC-MS for 50 simulated-saliva samples. The ease of operation, high sensitivity, and accuracy of the UPT-LFA make it a valid candidate POCT method for drug-of-abuse screening.

Methamphetamine potentiates HIV-1 gp120-mediated autophagy via Beclin-1 and Atg5/7 as a pro-survival response in astrocytes

Methamphetamine (METH), a commonly used controlled substance, is known to exacerbate neuropathological dysfunction in HIV-infected individuals. The neuropathological manifestation results from cell death or dysfunction in the central nervous system (CNS) wherein autophagy is expected to have an important role. Autophagy is generally considered protective during deprivation/stress. However, excessive autophagy can be destructive, leading to autophagic cell death. This study was designed to investigate if METH and HIV-1 gp120 interact to induce autophagy in SVGA astrocytes, and whether autophagy is epiphenomenal or it has a role in METH- and gp120-induced cytotoxicity. We found that METH and gp120 IIIb caused an increase in LC3II level in astrocytes in a dose- and time-dependent manner, and the level of LC3II was further increased when the cells were treated with METH and gp120 IIIb in combination. Next, we sought to explore the mechanism by which METH and gp120 induce the autophagic response. We found that METH induces autophagy via opioid and metabotropic glutamate receptor type 5 (mGluR5) receptors. Other than that, signaling proteins Akt, mammalian target of rapamycin (mTOR), Beclin-1, Atg5 and Atg7 were involved in METH and gp120-mediated autophagy. In addition, long-term treatment of METH and gp120 IIIb resulted in cell death, which was exacerbated by inhibition of autophagy. This suggests that autophagy functions as a protective response against apoptosis caused by METH and gp120. This study is novel and clinically relevant because METH abuse among HIV-infected populations is highly prevalent and is known to cause exacerbated neuroAIDS.

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.

Development of sensitization to methamphetamine in offspring prenatally exposed to morphine, methadone and buprenorphine

Heroin use among young women of reproductive age has drawn much attention around the world. However, there is lack of information on the long-term effects of prenatal exposure to opioids on their offspring. Our previous study demonstrated that prenatally buprenorphine-exposed offspring showed a marked change in the cross-tolerance to morphine compared with other groups. In the current study, this animal model was used to study effects of methamphetamine (METH)-induced behavioral sensitization in the offspring at their adulthood. The results showed no differences in either basal or acute METH-induced locomotor activity in any of the groups of animals tested. When male offspring received METH injections of 2 mg/kg, i.p., once a day for 5 days, behavioral sensitization was induced, as determined by motor activity. Furthermore, the distance and rate of development (slope) of locomotor activity and conditioned place preference induced by METH were significantly increased in the prenatally buprenorphine-exposed animals compared with those in other groups. The dopamine D1 R in the nucleus accumbens of the prenatally buprenorphine-exposed offspring had lower mRNA expression; but no significant changes in the μ-, κ-opioid, nociceptin, D2 R and D3 R receptors were noted. Furthermore, significant alterations were observed in the basal level of cAMP and the D1 R agonist enhanced adenylyl cyclase activity in the prenatally buprenorphine-exposed group. Overall, the study demonstrates that D1 R and its downregulated cAMP signals are involved in enhancing METH-induced behavioral sensitization in prenatally buprenorphine-exposed offspring. The study reveals that prenatal exposure to buprenorphine caused long-term effects on offspring and affected the dopaminergic system-related reward mechanism.

Effect of prenatal methadone on reinstated behavioral sensitization induced by methamphetamine in adolescent rats

It has been known that methadone maintenance treatment is the standard treatment of choice for pregnant opiate addicts. However, there are few data on newborn outcomes especially in the cross talk with other addictive agents. The present study was to investigate the effect of prenatal exposure to methadone on methamphetamine (METH)-induced behavioral sensitization as an indicator of drug addiction in later life. Pregnant rats received saline or methadone (7 mg/kg, s.c.) twice daily from E3 to E20. To induce behavioral sensitization, offspring (5 weeks old) were treated with METH (1mg/kg, i.p.) or saline once daily for 5 consecutive days. Ninety-six hours (day 9) after the 5th treatment with METH or saline, animals received a single dose of METH (1mg/kg, i.p.) or saline to induce the reinstated behavioral sensitization. Prenatal methadone treatment enhanced the level of development of locomotor behavioral sensitization to METH administration in adolescent rats. Prenatal methadone treatment also enhanced the reinstated locomotor behavioral sensitization in adolescent rats after the administration had ceased for 96 h. These results indicate that prenatal methadone exposure produces a persistent lesion in the dopaminergic system, as indicated by enhanced METH-induced locomotor behavioral sensitization (before drug abstinence) and reinstated locomotor behavioral sensitization (after short term drug abstinence) in adolescent rats. These findings show that prenatal methadone exposure may enhance susceptibility to the development of drug addiction in later life. This could provide a reference for drug usage such as methamphetamine in their offspring of pregnant woman who are treating with methadone.

Inter-individual diversity and intra-individual stability of amphetamine-induced sensitization of frequency-modulated 50-kHz vocalization in Sprague-Dawley rats

RATIONALE

Propensity for drug dependence shows great diversity that is related to intrinsic neurobiological factors. This diversity is important both for the understanding of these traits and for the development of therapies.

OBJECTIVES

The goals of the study were (1) to define, using ultrasonic vocalization characteristics, inter-individual differences in rats' propensity for sensitization to amphetamine, (2) to test whether possible resistance to this effect could be overcome with repetitive treatment, and (3) to seek useful predictors of the propensity.

METHODS

Rats were subject to tests meant to characterize their anxiety, pain sensitivity, and responses to novelty and natural rewards. Then they were subject to the so-called two-injection protocol of sensitization (using amphetamine) followed by 2 weeks of daily amphetamine treatment, 2-week withdrawal, and final amphetamine challenge. The development and outcome of sensitization were monitored by measuring 50-kHz vocalization.

RESULTS

The two-injection protocol yielded three patterns of changes in the frequency-modulated 50-kHz vocalization response to amphetamine. These patterns persisted after completion of the extended drug treatment. Rats with lower sensitivity to pain or with longer latency of their vocalization response to the first drug exposure showed an increased propensity for ultrasonic vocalization sensitization.

CONCLUSION

Vulnerability to sensitization of frequency-modulated 50-kHz vocalization response of Sprague-Dawley rats to amphetamine, which supposedly reflects rats' propensity for amphetamine dependence, shows large inter-individual diversity. Resistance to this effect, which is evident in a majority of the rats, cannot be overcome even with prolonged intermittent drug treatment under the conditions (novelty) that promote sensitization.