Nicotine and endogenous opioids: Neurochemical and pharmacological evidence

Heavy Versus Light Smoking: Its Association With Opioid Use, Chronic Pain, and Mental Health

INTRODUCTION

There is much concern that substance use treatment programs are rarely integrated with smoking cessation programs. Here, the first national statistics are presented on the connection between heavy vs. light smoking and the opioid epidemic.

METHODS

Using the 2013-2021 Medical Expenditure Panel Survey linked to the National Health Interview Survey, N=81,400 adults-years, logit regressions estimate the impact of heavy vs. light smoking on opioid use, chronic pain, work limitations due to pain, and poor mental health. Analyses were conducted from October 2023 to May 2024.

RESULTS

Only 37 percent of the population has ever smoked, but they used 69% of the nation's annual prescription opioids. Adults who smoked more than 5 cigarettes a day composed 12% of the population but used about the same number of opioids as the 63% of the population who never smoked. Adults who formerly smoked used 16% fewer opioids than adults who currently smoke (p<0.01). The percent with chronic pain during the year varied from 12.2% for adults who never smoked to 14.2% for light smoking, to 16.5% for those smoking more than a pack a day (p<0.01). Severe work limitations due to pain varied from 7.3% for adults who never smoked to 16.9% for those smoking more than a pack a day (p<0.01). Adults smoking more than a pack a day were twice as likely to report fair or poor mental health compared to those who never smoked (29.2% vs 13.6%) (p<0.01).

CONCLUSIONS

As nations deal with the opioid epidemic, integrating smoking cessation programs into substance abuse treatment programs appears prudent.

Elevating levels of the endocannabinoid 2-arachidonoylglycerol blunts opioid reward but not analgesia

Converging findings have established that the endocannabinoid (eCB) system serves as a possible target for the development of new treatments as a complement to opioid-based treatments. Here, we show in male and female mice that enhancing levels of the eCB, 2-arachidonoylglycerol (2-AG), through pharmacological inhibition of its catabolic enzyme, monoacylglycerol lipase (MAGL), either systemically or in the ventral tegmental area (VTA) with JZL184, leads to a substantial attenuation of the rewarding effects of opioids in mice using conditioned place preference and self-administration paradigms, without altering their analgesic properties. These effects are driven by cannabinoid receptor 1 (CB1R) within the VTA, as VTA CB1R conditional knockout counteracts JZL184's effects. Using fiber photometry with fluorescent sensors for calcium and dopamine (DA), we find that enhancing 2-AG levels diminishes opioid reward-related nucleus accumbens (NAc) activity and DA neurotransmission. Together, these findings reveal that 2-AG diminishes the rewarding properties of opioids and provides a potential adjunctive therapeutic strategy for opioid-related analgesic treatments.

The association between smoking, chronic pain, and prescription opioid use: 2013-2021

It is known that smoking is associated with greater chronic pain. However, little is known about the magnitude of this relationship and its association with prescription opioid use. We examine the association between smoking status and three sets of outcomes: (1) starting and discontinuing opioids, (2) intensity of opioid use, and (3) opioid use and pain outcomes after quitting smoking. We use multinomial logit on adults in the nationally representative 2013-2021 Medical Expenditure Panel Survey linked to the National Health Interview Survey (N = 36,796). Smoking adults made up 16% of the population but used 30% of all opioid prescriptions and 40% of all annual Morphine Milligram Equivalents (MMEs). The 1% of the population that smoked and had severe work limitations due to pain used 20% of all MMEs. Smoking adults were 24% more likely than never-smoking adults to have chronic pain. Among those with pain, smoking adults had 46% higher relative risk of starting opioids compared to never-smoking adults (p < .01), and smoking adults had 6.6 times higher relative risk of continuing opioids the next year compared to never-smoking adults (p < .01). Those smoking and using opioids had 95% higher odds of using a prescribed dosage of 50 MME or more than never-smoking adults. A year after quitting smoking, opioid use declined by 20% and pain declined by 7% compared to those continuing to smoke, with no difference from never-smoking adults after 12 years. Integrating smoking cessation into pain management programs could be highly beneficial to adults with chronic pain. PERSPECTIVE: Rarely are smoking cessation and pain management programs integrated together. We show that such integration would be highly beneficial by estimating a strong association between smoking cessation and reduced chronic pain, work limitations, and prescription opioid use.

Elevating levels of the endocannabinoid 2-arachidonoylglycerol blunts opioid reward but not analgesia

Converging findings have established that the endocannabinoid (eCB) system serves as a possible target for the development of new treatments for pain as a complement to opioid-based treatments. Here we show in male and female mice that enhancing levels of the eCB, 2-arachidonoylglycerol (2-AG), through pharmacological inhibition of its catabolic enzyme, monoacylglycerol lipase (MAGL), either systemically or in the ventral tegmental area (VTA) with JZL184, leads to a substantial attenuation of the rewarding effects of opioids in male and female mice using conditioned place preference and self-administration paradigms, without altering their analgesic properties. These effects are driven by CB1 receptors (CB1Rs) within the VTA as VTA CB1R conditional knockout, counteracts JZL184's effects. Conversely, pharmacologically enhancing the levels of the other eCB, anandamide (AEA), by inhibition of fatty acid amide hydrolase (FAAH) has no effect on opioid reward or analgesia. Using fiber photometry with fluorescent sensors for calcium and dopamine (DA), we find that enhancing 2-AG levels diminishes opioid reward-related nucleus accumbens (NAc) activity and DA neurotransmission. Together these findings reveal that 2-AG counteracts the rewarding properties of opioids and provides a potential adjunctive therapeutic strategy for opioid-related analgesic treatments.

Class A and C GPCR Dimers in Neurodegenerative Diseases

Neurodegenerative diseases affect over 30 million people worldwide with an ascending trend. Most individuals suffering from these irreversible brain damages belong to the elderly population, with onset between 50 and 60 years. Although the pathophysiology of such diseases is partially known, it remains unclear upon which point a disease turns degenerative. Moreover, current therapeutics can treat some of the symptoms but often have severe side effects and become less effective in long-term treatment. For many neurodegenerative diseases, the involvement of G proteincoupled receptors (GPCRs), which are key players of neuronal transmission and plasticity, has become clearer and holds great promise in elucidating their biological mechanism. With this review, we introduce and summarize class A and class C GPCRs, known to form heterodimers or oligomers to increase their signalling repertoire. Additionally, the examples discussed here were shown to display relevant alterations in brain signalling and had already been associated with the pathophysiology of certain neurodegenerative diseases. Lastly, we classified the heterodimers into two categories of crosstalk, positive or negative, for which there is known evidence.

Genetic deletion or pharmacological blockade of nociceptin/orphanin FQ receptors in the ventral tegmental area attenuates nicotine-motivated behaviour

BACKGROUND AND PURPOSE

The nociceptin/orphanin FQ (N/OFQ)-nociceptin opioid-like peptide (NOP) receptor system is widely distributed in the brain and pharmacological activation of this system revealed therapeutic potential in animal models of substance use disorder. Studies also showed that genetic deletion or pharmacological blockade of NOP receptors confer resistance to the development of alcohol abuse. Here, we have used a genetic and pharmacological approach to evaluate the therapeutic potential of NOP antagonism in smoking cessation.

EXPERIMENTAL APPROACH

Constitutive NOP receptor knockout rats (NOP-/- ) and their wild-type counterparts (NOP+/+ ) were tested over a range of behaviours to characterize their motivation for nicotine. We next explored the effects of systemic administration of the NOP receptor antagonist LY2817412 (1.0 & 3.0 mg·kg-1 ) on nicotine self-administration. NOP receptor blockade was further evaluated at the brain circuitry level, by microinjecting LY2817412 (3.0 & 6.0 μg·μl-1 ) into the ventral tegmental area (VTA), nucleus accumbens (NAc) and central amygdala (CeA).

KEY RESULTS

Genetic NOP receptor deletion resulted in decreased nicotine intake, decreased motivation to self-administer and attenuation of cue-induced nicotine reinstatement. LY2817412 reduced nicotine intake in NOP+/+ but not in NOP-/- rats, confirming that its effect is mediated by inhibition of NOP transmission. Finally, injection of LY2817412 into the VTA but not into the NAc or CeA decreased nicotine self-administration.

CONCLUSIONS AND IMPLICATIONS

These findings indicate that inhibition of NOP transmission attenuates the motivation for nicotine through mechanisms involving the VTA and suggest that NOP receptor antagonism may represent a potential treatment for smoking cessation.

Dopamine receptors in the anterior cingulate cortex implicate in nicotine enhanced morphine analgesia

RATIONALE

It is well known that the anterior cingulate cortex (ACC) plays an important role in acute pain perception.

OBJECTIVES

In the present study, we aimed to investigate the possible involvement of the ACC dopamine D1 and D2 receptors in nicotine plus morphine-induced analgesia.

METHODS

The ACC's of adult male Wistar rats were bilaterally cannulated by stereotaxic instrument and the tail-flick test was used to measure the thermal pain threshold.

RESULTS

The results indicated that subcutaneous (s.c.) injection of nicotine (0.3 mg/kg) potentiated the analgesic response of intraperitoneal (i.p.) administration of morphine (3 mg/kg). Systemic administration of the same doses of nicotine or morphine alone had no effect on tail-flick latency. Intra-ACC administration of apomorphine (0.3-0.9 μg/rat), the non-selective D1/D2 receptors agonist, plus ineffective doses of nicotine (0.1 mg/kg, s.c.) plus morphine (3 mg/kg, i.p) induced analgesia in rats. In addition, the analgesia induced with co-administration of nicotine and morphine was inhibited via intra-ACC administration of SCH23390 (0.5-1 μg/rat) or sulpiride (0.5-2 μg/rat), the selective antagonists of D1 or D2 receptors, respectively. The intra-ACC microinjection of the same doses of drugs alone had no effect on tail-flick latency. Cubic interpolation analysis also confirmed that activation or inactivation of the ACC D1 and D2 receptors by different doses of drugs can modulate the nicotine-morphine analgesic response.

CONCLUSIONS

The findings suggest that the ACC has an important role in acute thermal pain perception and modulates the analgesia induced by nicotine plus morphine via dopaminergic receptors.

Memory enhancing effects of nicotine, cocaine, and their conditioned stimuli; effects of beta-adrenergic and dopamine D2 receptor antagonists

BACKGROUND

There is evidence that post-training exposure to nicotine, cocaine, and their conditioned stimuli (CS), enhance memory consolidation in rats. The present study assessed the effects of blocking noradrenergic and dopaminergic receptors on nicotine and cocaine unconditioned and conditioned memory modulation.

METHODS

Males Sprague-Dawley rats tested on the spontaneous object recognition task received post-sample exposure to 0.4 mg/kg nicotine, 20 mg/kg cocaine, or their CSs, in combination with 5-10 mg/kg propranolol (PRO; beta-adrenergic antagonist) or 0.2-0.6 mg/kg pimozide (PIM; dopamine D2 receptor antagonist). The CSs were established by confining rats in a chamber (the CS +) after injections of 0.4 mg/kg nicotine, or 20 mg/kg cocaine, for 2 h and in another chamber (the CS -) after injections of vehicle, repeated over 10 days (5 drug/CS + and 5 vehicle/CS - pairings in total). Object memory was tested 72 h post sample in drug-free animals.

RESULTS

Co-administration of PRO or PIM blocked the memory-enhancing effects of post-training injections of nicotine, cocaine, and, importantly, exposure to their CSs.

CONCLUSIONS

These data suggest that nicotine, cocaine as well as their conditioned stimuli share actions on overlapping noradrenergic and dopaminergic systems to modulate memory consolidation.

Blunted opioid regulation of the HPA stress response during nicotine withdrawal: therapeutic implications

Endogenous opioids regulate pain, drug reward, and stress responses. We have previously shown reduced hypothalamic-pituitary-adrenal (HPA) responses to psychological stress and to opioid blockade among dependent smokers. In this study, we examined the extent to which biologically confirmed nicotine withdrawal alters endogenous opioid regulation of HPA axis functioning during rest and in response to acute stress. Smokers were randomly assigned to one of two conditions; 24 h withdrawal from all nicotine-containing products (n = 62) or smoking ad libitum (n = 44). A nonsmoking comparison group (n = 43) was also included. Participants (85 males and 64 females) completed two acute stress sessions during which a placebo or 50 mg of naltrexone (opioid antagonist) were administered using a double-blind design. Blood and saliva samples (assayed for cortisol and adrenocorticotropic hormone, i.e. ACTH) and mood measures were obtained during a resting absorption period, after acute stress (public speaking, mental arithmetic, and cold pressor tasks), and during an extended recovery period. Results indicated that opioid blockade (naltrexone) was associated with increased ACTH and cortisol responses to stress, and tobacco withdrawal was associated with blunted hormonal responses. A pattern of sex differences also emerged, with women exhibiting reduced ACTH responses to stress and higher ACTH and plasma cortisol responses to opioid blockade. These results indicated that compared to ad libitum smoking, nicotine withdrawal is associated with blunted opioid modulation of the HPA axis. Sex may modulate these effects. Blunted endogenous opioid regulation may underlie an incentive process that reinforces smoking behavior and may warrant therapeutic attention.

Altered mRNA Levels of Stress-Related Peptides in Mouse Hippocampus and Caudate-Putamen in Withdrawal after Long-Term Intermittent Exposure to Tobacco Smoke or Electronic Cigarette Vapour

Nicotine addiction is a severe public health problem. The aim of this study was to investigate the alterations in key neurotransmissions after 60 days of withdrawal from seven weeks of intermittent cigarette smoke, e-cigarette vapours, or an e-cigarette vehicle. In the nicotine withdrawal groups, increased depressive and anxiety/obsessive–compulsive-like behaviours were demonstrated in the tail suspension, sucrose preference and marble burying tests. Cognitive impairments were detected in the spatial object recognition test. A significant increase in Corticotropin-releasing factor (Crf) and Crf1 mRNA levels was observed, specifically after cigarette withdrawal in the caudate-putamen nucleus (CPu). The nociceptin precursor levels were reduced by cigarette (80%) and e-cigarette (50%) withdrawal in the CPu. The delta opioid receptor showed a significant reduction in the hippocampus driven by the exposure to an e-cigarette solubilisation vehicle, while the mRNA levels doubled in the CPu of mice that had been exposed to e-cigarettes. Withdrawal after exposure to e-cigarette vapour induced a 35% Bdnf mRNA decrease in the hippocampus, whereas Bdnf was augmented by 118% by cigarette withdrawal in the CPu. This study shows that long-term withdrawal-induced affective and cognitive symptoms associated to lasting molecular alterations in peptidergic signalling may determine the impaired neuroplasticity in the hippocampal and striatal circuitry.

Increased Expression of Plasma miRNA-320a and let-7b-5p in Heroin-Dependent Patients and Its Clinical Significance

Heroin use disorder is a chronic and relapsing disease that induces persistent changes in the brain. The diagnoses of heroin use disorders are mainly based on subjective reports and no valid biomarkers available. Recent researches have revealed that circulating miRNAs are useful non-invasive biomarkers for diagnosing brain diseases such as Alzheimer's disease, multiple sclerosis, schizophrenia, and bipolar disorder. However, studies on circulating miRNAs for the diagnosis of heroin use disorders are rarely reported. In this study, we investigated the differential expression of plasma miRNAs in 57 heroin-dependent patients. Based on literature research and microarray analysis, two candidate miRNAs, miR-320a and let-7b-5p, were selected and analyzed by quantitative real-time RT-PCR. The results showed miR-320a and let-7b were significantly upregulated in plasma of the heroin-dependent patients compared to that in healthy controls. The area under curves (AUCs) of receiver operating characteristic (ROC) curves of miR-320a and let-7b-5p were 0.748 and 0.758, respectively. The sensitivities of miR-320a and let-7b-5p were 71.9 and 70.2%, while the specificities of miR-320a and let-7b-5p were 76.1 and 78.3%, respectively. The combination of these two miRNAs predicted heron dependence with an AUC of 0.782 (95% CI 0.687-0.876), with 73.7% sensitivity and 82.6% specificity. Our findings suggest a potential use for circulating miRNAs as biomarkers for the diagnosis of heroin abuse.

Nicotine and Opioids: a Call for Co-treatment as the Standard of Care

The U.S. is in the midst of an opioid epidemic. At the same time, tobacco use remains the leading cause of preventable death and disability. While the shared biological underpinnings of nicotine and opioid addiction are well established, clinical implications for co-treatment of these two substance use disorders has not been emphasized in the literature, nor have researchers, clinicians, and policy makers adequately outlined pathways for incorporating co-treatment into existing clinical workflows. The current brief review characterizes the metabolic and neural mechanisms which mediate co-use of nicotine and opioids, and then outlines clinical and policy implications for concurrently addressing these two deadly epidemics. Screening, assessment, medication-assisted treatment (MAT), and tobacco-free policy are discussed. The evidence suggests that clinical care and policies that facilitate co-treatment are an expedient means of delivering healthcare to individuals that result in better health for the population while also meeting patients' substance abuse disorder recovery goals.

Quit ratios for cigarette smoking among individuals with opioid misuse and opioid use disorder in the United States

BACKGROUND

The prevalence of cigarette smoking is more than two times higher among individuals with versus without opioid misuse and/or opioid use disorders (OUD). Overall, smoking cessation has increased over time although it is unknown whether it has similarly increased for those with opioid misuse or OUD. The current study examined cigarette quit ratios from 2002 to 2018 among US individuals with and without opioid misuse or OUD.

METHODS

Data came from the National Survey on Drug Use and Health, a yearly cross-sectional survey of US civilians 12 years or older. Annual quit ratios (i.e., proportion of former smokers among lifetime-smokers) were estimated from 2002 to 2018. Logistic regression tested time trends in quit ratios by opioid misuse/OUD.

RESULTS

Past-month smoking prevalence was much higher for persons with versus without opioid misuse (64.6 % versus 25.7 %) and OUD (73.3 % versus 26.0 %). In 2018, quit ratios for individuals with opioid misuse (18.0 %) or OUD (10.0 %) were less than half of those without opioid misuse (48.3 %) or OUD (48.1 %). After adjusting for background characteristics, the quit ratio did not change over time among individuals with opioid misuse or OUD in contrast to an increase in quit ratios for those without opioid misuse or OUD. For those without opioid misuse or OUD, males had higher quit ratios than females.

CONCLUSIONS

Cigarette quit ratios remain dramatically lower among those with opioid misuse or OUD. Public health and clinical attention are needed to increase cessation and reduce smoking consequences for individuals with opioid misuse and OUD.

Achieving Smoking Cessation Among Persons with Opioid Use Disorder

While prevalence of tobacco use in the US general population is declining, prevalence among those with opioid use disorder (OUD) remains high and results in excessive tobacco-related disease and premature mortality. Among smokers with OUD, tobacco cessation rates are negligible without treatment. However, both low-intensity behavioral interventions and more intensive motivational interventions yield negligible cessation rates. While contingency management has potent short-term cessation effects, effects are not maintained at post-intervention follow-up. Evidence-based smoking cessation pharmacotherapies, such as nicotine replacement therapy, bupropion, and varenicline, result in very modest cessation rates among smokers with OUD. Intensification of pharmacotherapy, such as high-dose and combination nicotine replacement therapy or extended medication treatment, has failed to improve cessation outcomes compared with standard treatment regimens. Targeting the unique challenges faced by smokers with OUD, including nicotine-opioid interactions and poor medication adherence, has potential to improve cessation outcomes, but further research is needed to optimize intervention efficacy among smokers with OUD.

Activation of PPARγ Attenuates the Expression of Physical and Affective Nicotine Withdrawal Symptoms through Mechanisms Involving Amygdala and Hippocampus Neurotransmission

An isoform of peroxisome proliferator-activated receptors (PPARs), PPARγ, is the receptor for the thiazolidinedione class of anti-diabetic medications including pioglitazone. Neuroanatomical data indicate PPARγ localization in brain areas involved in drug addiction. Preclinical and clinical data have shown that pioglitazone reduces alcohol and opioid self-administration, relapse to drug seeking, and plays a role in emotional responses. Here, we investigated the behavioral effect of PPARγ manipulation on nicotine withdrawal in male Wistar rats and in male mice with neuron-specific PPARγ deletion (PPARγ^(-/-)) and their littermate wild-type (PPARγ^(+/+)) controls. Real-time quantitative RT-PCR and RNAscope in situ hybridization assays were used for assessing the levels of expression and cell-type localization of PPARγ during nicotine withdrawal. Brain site-specific microinjections of the PPARγ agonist pioglitazone were performed to explore the role of this system on nicotine withdrawal at a neurocircuitry level. Results showed that activation of PPARγ by pioglitazone abolished the expression of somatic and affective nicotine withdrawal signs in rats and in (PPARγ^(+/+)) mice. This effect was blocked by the PPARγ antagonist GW9662. During early withdrawal and protracted abstinence, the expression of PPARγ increased in GABAergic and glutamatergic cells of the amygdala and hippocampus, respectively. Hippocampal microinjections of pioglitazone reduced the expression of the physical signs of withdrawal, whereas excessive anxiety associated with protracted abstinence was prevented by pioglitazone microinjection into the amygdala. Our results demonstrate the implication of the neuronal PPARγ in nicotine withdrawal and indicates that activation of PPARγ may offer an interesting strategy for smoking cessation.SIGNIFICANCE STATEMENT Smoking cessation leads the occurrence of physical and affective withdrawal symptoms representing a major burden to quit tobacco use. Here, we show that activation of PPARγ prevents the expression of both somatic and affective signs of nicotine withdrawal. At molecular levels results show that PPARγ expression increases in GABAergic cells in the hippocampus and in GABA- and glutamate-positive cells in the basolateral amygdala. Hippocampal microinjections of pioglitazone reduce the insurgence of the physical withdrawal signs, whereas anxiety linked to protracted abstinence is attenuated by pioglitazone injected into the amygdala. Our results demonstrate the implication of neuronal PPARγ in nicotine withdrawal and suggest that PPARγ agonism may represent a promising treatment to aid smoking cessation.

Acute and chronic modulation of striatal endocannabinoid-mediated plasticity by nicotine

The endocannabinoid (eCB) system modulates several phenomena related to addictive behaviors, and drug‐induced changes in eCB signaling have been postulated to be important mediators of physiological and pathological reward‐related synaptic plasticity. Here, we studied eCB‐mediated long‐term depression (eCB‐LTD) in the dorsolateral striatum, a brain region critical for acquisition of habitual and automatic behavior. We report that nicotine differentially affects ex vivo eCB signaling depending on previous exposure in vivo. In the nicotine‐naïve brain, nicotine facilitates eCB‐signaling and LTD, whereas tolerance develops to this facilitating effect after subchronic exposure in vivo. In the end, a progressive impairment of eCB‐induced LTD is established after protracted withdrawal from nicotine. Endocannabinoid‐LTD is reinstated 6 months after the last drug injection, but a brief period of nicotine re‐exposure is sufficient to yet again impair eCB‐signaling. LTD induced by the cannabinoid 1 receptor agonist WIN55,212‐2 is not affected, suggesting that nicotine modulates eCB production or release. Nicotine‐induced facilitation of eCB‐LTD is occluded by the dopamine D2 receptor agonist quinpirole, and by the muscarinic acetylcholine receptor antagonist scopolamine. In addition, the same compounds restore eCB‐LTD during protracted withdrawal. Nicotine may thus modulate eCB‐signaling by affecting dopaminergic and cholinergic neurotransmission in a long‐lasting manner. Overall, the data presented here suggest that nicotine facilitates eCB‐LTD in the initial phase, which putatively could promote neurophysiological and behavioral adaptations to the drug. Protracted withdrawal, however, impairs eCB‐LTD, which may influence or affect the ability to maintain cessation.

ALDH1A1 regulates postsynaptic μ-opioid receptor expression in dorsal striatal projection neurons and mitigates dyskinesia through transsynaptic retinoic acid signaling

Aldehyde dehydrogenase 1A1 (ALDH1A1), a retinoic acid (RA) synthase, is selectively expressed by the nigrostriatal dopaminergic (nDA) neurons that preferentially degenerate in Parkinson’s disease (PD). ALDH1A1–positive axons mainly project to the dorsal striatum. However, whether ALDH1A1 and its products regulate the activity of postsynaptic striatal neurons is unclear. Here we show that μ–type opioid receptor (MOR1) levels were severely decreased in the dorsal striatum of postnatal and adult Aldh1a1 knockout mice, whereas dietary supplement of RA restores its expression. Furthermore, RA treatment also upregulates striatal MOR1 levels and signaling and alleviates L-DOPA–induced dyskinetic movements in pituitary homeobox 3 (Pitx3)–deficient mice that lack of ALDH1A1–expressing nDA neurons. Therefore, our findings demonstrate that ALDH1A1–synthesized RA is required for postsynaptic MOR1 expression in the postnatal and adult dorsal striatum, supporting potential therapeutic benefits of RA supplementation in moderating L-DOPA–induced dyskinesia.

Nicotinic Cholinergic System in the Hypothalamus Modulates the Activity of the Hypothalamic Neuropeptides During the Stress Response

BACKGROUND

The hypothalamus harbors high levels of cholinergic neurons and axon terminals. Nicotinic acetylcholine receptors, which play an important role in cholinergic neurotransmission, are expressed abundantly in the hypothalamus. Accumulating evidence reveals a regulatory role for nicotine in the regulation of the stress responses. The present review will discuss the hypothalamic neuropeptides and their interaction with the nicotinic cholinergic system. The anatomical distribution of the cholinergic neurons, axon terminals and nicotinic receptors in discrete hypothalamic nuclei will be described. The effect of nicotinic cholinergic neurotransmission and nicotine exposure on hypothalamic-pituitaryadrenal (HPA) axis regulation at the hypothalamic level will be analyzed in view of the different neuropeptides involved.

METHODS

Published research related to nicotinic cholinergic regulation of the HPA axis activity at the hypothalamic level is reviewed.

RESULTS

The nicotinic cholinergic system is one of the major modulators of the HPA axis activity. There is substantial evidence supporting the regulation of hypothalamic neuropeptides by nicotinic acetylcholine receptors. However, most of the studies showing the nicotinic regulation of hypothalamic neuropeptides have employed systemic administration of nicotine. Additionally, we know little about the nicotinic receptor distribution on neuropeptide-synthesizing neurons in the hypothalamus and the physiological responses they trigger in these neurons.

CONCLUSION

Disturbed functioning of the HPA axis and hypothalamic neuropeptides results in pathologies such as depression, anxiety disorders and obesity, which are common and significant health problems. A better understanding of the nicotinic regulation of hypothalamic neuropeptides will aid in drug development and provide means to cope with these diseases. Considering that nicotine is also an abused substance, a better understanding of the role of the nicotinic cholinergic system on the HPA axis will aid in developing improved therapeutic strategies for smoking cessation.

Differentially expressed gene (DEG) based protein-protein interaction (PPI) network identifies a spectrum of gene interactome, transcriptome and correlated miRNA in nondisjunction Down syndrome

Down syndrome, a genetic disorder of known attribution reveals several types of brain abnormalities resulting in mental retardation, inadequacy in speech and memory. In this study, we have presented a consolidative network approach to comprehend the intricacy of the associated genes of Down syndrome. In this analysis, the differentially expressed genes (DEG's) were identified and the central networks were constructed as upregulated and downregulated. Subsequently, GNB5, CDC42, SPTAN1, GNG2, GNAZ, PRKACB, SST, CD44, FGF2, PHLPP1, APP, and FYN were identified as the candidate hub genes by using topological parameters. Later, Fpclass a PPI tool identified WASP gene, a co-expression interacting partner with highest network topology. Moreover, an enhanced enrichment pathway namely Opioid signaling was obtained using ClueGo, depicting the roles of the hub genes in signaling and neuronal mechanisms. The transcriptional regulatory factors and the common miRNA connected to them were identified by using MatInspector and miRTarbase. Later, a regulatory network constructed showed that PLAG, T2FB, CREB, NEUR, and GATA were the most commonly connected transcriptional factors and hsa-miR-122-5p was the most prominent miRNA. In a nutshell, these hub genes and the enriched pathway could help understand at a molecular level and eventually used as therapeutic targets for Down syndrome.

Marijuana and Prescription Pain Reliever Use among Cigarette Smokers

Due to marijuana's analgesic effects and its growing national legal status, it is likely that marijuana's rising prevalence will impact prescription pain reliever (PPR) use. The present study investigates the relationship between marijuana and PPR use among U.S. adult current cigarette smokers. Data were analyzed from the Tobacco and Attitudes Beliefs Survey II, with 348 current cigarette smokers, aged 24-88. Logistic regression was used to examine the likelihood of current (past 30 days) PPR use by marijuana use (never, ever, and current) among cigarette smokers. Among PPR users (N = 76), we also investigated whether marijuana use frequency predicted current PPR use. Compared to never marijuana users, participants were more likely to report past 30-day PPR use if they have ever used marijuana (AOR: 2.58, 95% CI: 1.51-4.43) or have used marijuana in the past 30 days (AOR: 3.38, CI: 1.76-6.49). No significant relationship was found between marijuana use frequency and PPR use. Thus, in this sample of adult cigarette smokers, past and current marijuana users were two to three times more likely to report PPR use than never marijuana users. These findings can help inform policymakers and healthcare providers in their fight against the opioid epidemic.

From genes to treatments: a systematic review of the pharmacogenetics in smoking cessation

Smoking cessation treatment outcomes may be heavily influenced by genetic variations among smokers. Therefore, identifying specific variants that affect response to different pharmacotherapies is of major interest to the field. In the current study, we systematically review all studies published in or after the year 1990 which examined one or more gene-drug interactions for smoking cessation treatment. Out of 644 citations, 46 articles met the inclusion criteria for the systematic review. We summarize evidence on several genetic polymorphisms (CHRNA5-A3-B4, CYP2A6, DBH, CHRNA4, COMT, DRD2, DRD4 and CYP2B6) and their potential moderating pharamacotherarpy effects on patient cessation efficacy rates. These findings are promising and call for further research to demonstrate the effectiveness of genetic testing in personalizing treatment decision-making and improving outcome.

Association study of DRD2 A2/A1, DRD3 Ser9Gly, DβH -1021C>T, OPRM1 A118G and GRIK1 rs2832407C>A polymorphisms with alcohol dependence

BACKGROUND

The reinforcing effects of alcohol are mediated through complex interactions between multiple neurochemical systems. Genes of dopaminergic (DRD2, DRD3 and DβH), opioid (OPRM1) and glutaminergic (GRIK1) systems mediate the dependent behavior via different mechanisms; however, they all target the serotonergic and dopaminergic pathways in the ventral tegmental area.

METHODS

In the present study, DRD2 A2/A1, DRD3 Ser9Gly, DβH -1021C>T, OPRM1 A118G and GRIK1 rs2832407C>A polymorphisms and their interactions were analyzed in 72 alcohol-dependent patients and 74 controls of Greek-Cypriot origin, using the PCR-RFLP method.

RESULTS

No differences were found in the genotype or allele distribution of DRD2 A2/A1, DRD3 Ser9Gly, DβH -1021C>T, OPRM1 A118G and GRIK1 rs2832407C>A between alcohol-dependent patients and controls. Additionally, we did not find any gene×gene interactions in association with alcohol dependence in the studied population.

CONCLUSIONS

Alcohol dependence is a complex interaction of genetic and environmental factors. In the present study, we have shown that DRD2 A2/A1, DRD3 Ser9Gly, DβH -1021C>T, OPRM1 A118G and GRIK1 rs2832407C>A are not associated with this dependent behavior alone or in interaction.

Effects of pharmacological manipulation of the kappa opioid receptors on the aversive effects of nicotine

Nicotine, an addictive component of tobacco smoke, produces both rewarding and aversive effects. Increasing the aversive effects of nicotine may help in promoting smoking cessation. However, neural targets mediating the aversive effects of nicotine have not been fully identified. In this study, we evaluated the role of kappa opioid receptors (KORs) in the aversive effects of nicotine (0.4 mg/kg, base; s.c.) using the nicotine-induced conditioned taste aversion (CTA) model in Wistar rats. The KORs were activated using the selective KOR agonist (±)U-50,488H (0, 0.03, 0.15 & 0.3mg/kg; s.c.) and inhibited using the KOR antagonist nor-binaltorphimine (nor-BNI; 0, 15 & 30mg/kg; s.c.) in separate groups of rats using a between-subjects design. Pretreatment with the KOR agonist (±)U-50,488H (0.3mg/kg) significantly increased aversion for the nicotine-associated solution. Additionally, (±)U-50,488H (0.3mg/kg) on its own induced aversion to the flavored solution associated with it even in the absence of nicotine, suggesting that the KOR agonist induced increase in nicotine-induced aversion was an additive effect. Interestingly, administration of the KOR antagonist nor-BNI (30mg/kg) prior to conditioning with nicotine/saline, but not after conditioning with nicotine/saline, attenuated nicotine-induced aversive effects compared to saline controls. Taken together, these data suggest a role for KORs in the aversive effects of nicotine.

Pharmacotherapy for smoking cessation: effects by subgroup defined by genetically informed biomarkers

BACKGROUND

Smoking cessation therapies are not effective for all smokers, and researchers are interested in identifying those subgroups of individuals (e.g. based on genotype) who respond best to specific treatments.

OBJECTIVES

To assess whether quit rates vary by genetically informed biomarkers within pharmacotherapy treatment arms and as compared with placebo. To assess the effects of pharmacotherapies for smoking cessation in subgroups of smokers defined by genotype for identified genome-wide significant polymorphisms.

SEARCH METHODS

We searched the Cochrane Tobacco Addiction Group specialised register, clinical trial registries, and genetics databases for trials of pharmacotherapies for smoking cessation from inception until 16 August 2016.

SELECTION CRITERIA

We included randomised controlled trials (RCTs) that recruited adult smokers and reported pharmacogenomic analyses from trials of smoking cessation pharmacotherapies versus controls. Eligible trials included those with data on a priori genome-wide significant (P < 5 × 10-8) single-nucleotide polymorphisms (SNPs), replicated non-SNPs, and/or the nicotine metabolite ratio (NMR), hereafter collectively described as biomarkers.

DATA COLLECTION AND ANALYSIS

We used standard methodological procedures expected by Cochrane. The primary outcome was smoking abstinence at six months after treatment. The secondary outcome was abstinence at end of treatment (EOT). We conducted two types of meta-analyses- one in which we assessed smoking cessation of active treatment versus placebo within genotype groups, and another in which we compared smoking cessation across genotype groups within treatment arms. We carried out analyses separately in non-Hispanic whites (NHWs) and non-Hispanic blacks (NHBs). We assessed heterogeneity between genotype groups using T², I², and Cochrane Q statistics.

MAIN RESULTS

Analyses included 18 trials including 9017 participants, of whom 6924 were NHW and 2093 NHB participants. Data were available for the following biomarkers: nine SNPs (rs1051730 (CHRNA3); rs16969968, rs588765, and rs2036527 (CHRNA5); rs3733829 and rs7937 (in EGLN2, near CYP2A6); rs1329650 and rs1028936 (LOC100188947); and rs215605 (PDE1C)), two variable number tandem repeats (VNTRs; DRD4 and SLC6A4), and the NMR. Included data produced a total of 40 active versus placebo comparisons, 16 active versus active comparisons, and 64 between-genotype comparisons within treatment arms.For those meta-analyses showing statistically significant heterogeneity between genotype groups, we found the quality of evidence (GRADE) to be generally moderate. We downgraded quality most often because of imprecision or risk of bias due to potential selection bias in genotyping trial participants. Comparisons of relative treatment effects by genotypeFor six-month abstinence, we found statistically significant heterogeneity between genotypes (rs16969968) for nicotine replacement therapy (NRT) versus placebo at six months for NHB participants (P = 0.03; n = 2 trials), but not for other biomarkers or treatment comparisons. Six-month abstinence was increased in the active NRT group as compared to placebo among participants with a GG genotype (risk ratio (RR) 1.47, 95% confidence interval (CI) 1.07 to 2.03), but not in the combined group of participants with a GA or AA genotype (RR 0.43, 95% CI 0.15 to 1.26; ratio of risk ratios (RRR) GG vs GA or AA of 3.51, 95% CI 1.19 to 10.3). Comparisons of treatment effects between genotype groups within pharmacotherapy randomisation armsFor those receiving active NRT, treatment was more effective in achieving six-month abstinence among individuals with a slow NMR than among those with a normal NMR among NHW and NHB combined participants (normal NMR vs slow NMR: RR 0.54, 95% CI 0.37 to 0.78; n = 2 trials). We found no such differences in treatment effects between genotypes at six months for any of the other biomarkers among individuals who received pharmacotherapy or placebo.

AUTHORS' CONCLUSIONS

We did not identify widespread differential treatment effects of pharmacotherapy based on genotype. Some genotype groups within certain ethnic groups may benefit more from NRT or may benefit less from the combination of bupropion with NRT. The reader should interpret these results with caution because none of the statistically significant meta-analyses included more than two trials per genotype comparison, many confidence intervals were wide, and the quality of this evidence (GRADE) was generally moderate. Although we found evidence of superior NRT efficacy for NMR slow versus normal metabolisers, because of the lack of heterogeneity between NMR groups, we cannot conclude that NRT is more effective for slow metabolisers. Access to additional data from multiple trials is needed, particularly for comparisons of different pharmacotherapies.

Quantitative Mass Spectrometry Reveals Food Intake-Induced Neuropeptide Level Changes in Rat Brain: Functional Assessment of Selected Neuropeptides as Feeding Regulators

Endogenous neuropeptides are important signaling molecules that function as regulators of food intake and body weight. Previous work has shown that neuropeptide gene expression levels in a forebrain reward site, the nucleus accumbens (NAc), were changed by feeding. To directly monitor feeding-induced changes in neuropeptide expression levels within the NAc, we employed a combination of cryostat dissection, heat stabilization, neuropeptide extraction and label-free quantitative neuropeptidomics via a liquid chromatography-high resolution mass spectrometry platform. Using this methodology, we described the first neuropeptidome in NAc and discovered that feeding caused the expression level changes of multiple neuropeptides derived from different precursors, especially proSAAS-derived peptides such as Big LEN, PEN and little SAAS. We further investigated the regulatory functions of these neuropeptides derived from the ProSAAS family by performing an intra-NAc microinjection experiment using the identified ProSAAS neuropeptides, 'Big-LEN' and 'PEN'. Big LEN significantly increased rats' food and water intake, whereas both big LEN and PEN affected other behaviors including locomotion, drinking and grooming. In addition, we quantified the feeding-induced changes of peptides from hippocampus, hypothalamus and striatum to reveal the neuropeptide interplay among different anatomical regions. In summary, our study demonstrated neuropeptidomic changes in response to food intake in the rat NAc and other key brain regions. Importantly, the microinfusion of ProSAAS peptides into NAc revealed that they are behaviorally active in this brain site, suggesting the potential use of these peptides as therapeutics for eating disorders.

Endogenous opioid system: a promising target for future smoking cessation medications

BACKGROUND

Nicotine addiction continues to be a health challenge across the world. Despite several approved medications, smokers continue to relapse. Several human and animal studies have evaluated the role of the endogenous opioid system as a potential target for smoking cessation medications.

METHODS

In this review, studies that have elucidated the role of the mu (MORs), delta (DORs), and kappa (KORs) opioid receptors in nicotine reward, nicotine withdrawal, and reinstatement of nicotine seeking will be discussed. Additionally, the review will discuss discrepancies in the literature and therapeutic potential of the endogenous opioid system, and suggest studies to address gaps in knowledge with respect to the role of the opioid receptors in nicotine dependence.

RESULTS

Data available till date suggest that blockade of the MORs and DORs decreased the rewarding effects of nicotine, while activation of the MORs and DORs decreased nicotine withdrawal-induced aversive effects. In contrast, activation of the KORs decreased the rewarding effects of nicotine, while blockade of the KORs decreased nicotine withdrawal-induced aversive effects. Interestingly, blockade of the MORs and KORs attenuated reinstatement of nicotine seeking. In humans, MOR antagonists have shown benefits in select subpopulations of smokers and further investigation is required to realize their full therapeutic potential.

CONCLUSION

Future work must assess the influence of polymorphisms in opioid receptor-linked genes in nicotine dependence, which will help in both identifying individuals vulnerable to nicotine addiction and the development of opioid-based smoking cessation medications. Overall, the endogenous opioid system continues to be a promising target for future smoking cessation medications.

Opioid system in L-DOPA-induced dyskinesia

L-3, 4-Dihydroxyphenylalanine (L-DOPA)-induced dyskinesia (LID) is a major clinical complication in the treatment of Parkinson’s disease (PD). This debilitating side effect likely reflects aberrant compensatory responses for a combination of dopaminergic neuron denervation and repeated L-DOPA administration. Abnormal endogenous opioid signal transduction pathways in basal ganglia have been well documented in LID. Opioid receptors have been targeted to alleviate the dyskinesia. However, the exact role of this altered opioid activity is remains under active investigation. In the present review, we discuss the current understanding of opioid signal transduction in the basal ganglia and how the malfunction of opioid signaling contributes to the pathophysiology of LID. Further study of the opioid system in LID may lead to new therapeutic targets and improved treatment of PD patients.

OPRD1 Genetic Variation and Human Disease

The OPRD1 gene encodes the delta-opioid receptor, which has multiple functions including regulating reward pathways. The gene contains more than 2,000 verified genetic variants but only 2 currently have evidence for specific functions: rs1042114 disrupts maturation of the receptor and rs569356 affects OPRD1 expression. These polymorphisms and others in the gene have been found to be associated with human diseases. The most reproducible data are associations between opioid addiction and three variants in intron 1 (rs2236861, rs2236857, and rs3766951), which have been described in a number of independent populations. Several publications also point toward an association between anorexia and a haplotype block containing rs569356 and rs533123. Unfortunately the mechanisms underlying these two effects are currently unknown. In contrast, rs1042114 has been linked to Alzheimer's disease through an increasingly well-defined mechanism by which the variant allele reduces production of the beta-amyloid plaques associated with the disease. Additional studies of OPRD1 variants are necessary to replicate current findings and to delineate the functional roles of relevant polymorphisms.

Repeated nicotine exposure modulates prodynorphin and pronociceptin levels in the reward pathway

BACKGROUND

Nicotine dependence is maintained by neurobiological adaptations in the dopaminergic brain reward pathway with the contribution of opioidergic circuits. This study assessed the role of opioid peptides and receptors on the molecular changes associated with nicotine dependence. To this aim we analysed nicotine effects on opioid gene and receptor expression in the reward pathway in a nicotine sensitization model.

METHODS

Sprague-Dawley rats received nicotine administrations for five days and locomotor activity assessment showed the development of sensitization. The mRNA expression of prodynorphin (pdyn), pronociceptin (pnoc) and the respective receptors was measured by quantitative PCR in the ventral midbrain (VM), the nucleus accumbens (NAc), the caudate-putamen (CPu), the pre-frontal cortex (PFCx), and the hippocampus.

RESULTS

A significant positive effect of sensitization on pdyn mRNA levels was detected in the CPu. This effect was supported by a significant and selective correlation between the two parameters in this region. Moreover, chronic but not acute nicotine treatment significantly decreased pdyn mRNA levels in the NAc and increased expression in the PFCx. Pnoc mRNA was significantly increased in the VM and the PFCx after sub-chronic administration of nicotine, whereas no alterations were observed after acute treatment. No treatment associated changes were detected in κ-opioid receptor or nociceptin receptor mRNAs.

CONCLUSIONS

This experiment revealed an effect of nicotine administration that was distinguishable from the effect of nicotine sensitization. While several pnoc and pdyn changes were associated to nicotine administration, the only significant effect of sensitization was a significant increase in pdyn in the CPu.

Molecular Histochemistry Identifies Peptidomic Organization and Reorganization Along Striatal Projection Units

Matrix-assisted laser desorption ionization (MALDI) imaging mass spectrometry (IMS) (MALDI-IMS) provides a technical means for simultaneous analysis of precise anatomic localization and regulation of peptides. We explored the technical capability of matrix-assisted laser desorption ionization mass spectrometry for characterization of peptidomic regulation by an addictive substance along two distinct projection systems in the mouse striatum. The spatial expression patterns of substance P and proenkephalin, marker neuropeptides of two distinct striatal projection neurons, were negatively correlated at baseline. We detected 768 mass/charge (m/z) peaks whose expression levels were mostly negatively and positively correlated with expression levels of substance P and proenkephalin A (amino acids 218-228), respectively, within the dorsal striatum. After nicotine administration, there was a positive shift in correlation of mass/charge peak expression levels with substance P and proenkephalin A (218-228). Our exploratory analyses demonstrate the technical capacity of MALDI-IMS for comprehensive identification of peptidomic regulation patterns along histochemically distinguishable striatal projection pathways.

Neuroscience of nicotine for addiction medicine: novel targets for smoking cessation medications

Morbidity and mortality associated with tobacco smoking constitutes a significant burden on healthcare budgets all over the world. Therefore, promoting smoking cessation is an important goal of health professionals and policy makers throughout the world. Nicotine is a major psychoactive component in tobacco that is largely responsible for the widespread addiction to tobacco. A majority of the currently available FDA-approved smoking cessation medications act via neuronal nicotinic receptors. These medications are effective in approximately half of all the smokers, who want to quit and relapse among abstinent smokers continues to be high. In addition to relapse among abstinent smokers, unpleasant effects associated with nicotine withdrawal are a major motivational factor in continued tobacco smoking. Over the last two decades, animal studies have helped in identifying several neural substrates that are involved in nicotine-dependent behaviors including those associated with nicotine withdrawal and relapse to tobacco smoking. In this review, first the role of specific brain regions/circuits that are involved in nicotine dependence will be discussed. Next, the review will describe the role of specific nicotinic receptor subunits in nicotine dependence. Finally, the review will discuss the role of classical neurotransmitters (dopamine, serotonin, noradrenaline, glutamate, and γ-aminobutyric acid) as well as endogenous opioid and endocannabinoid signaling in nicotine dependence. The nicotinic and nonnicotinic neural substrates involved in nicotine-dependent behaviors can serve as possible targets for future smoking cessation medications.

Opioid Analgesics and Nicotine: More Than Blowing Smoke

Practitioners are highly likely to encounter patients with concurrent use of nicotine products and opioid analgesics. Smokers present with more severe and extended chronic pain outcomes and have a higher frequency of prescription opioid use. Current tobacco smoking is a strong predictor of risk for nonmedical use of prescription opioids. Opioid and nicotinic-cholinergic neurotransmitter systems interact in important ways to modulate opioid and nicotine effects: dopamine release induced by nicotine is dependent on facilitation by the opioid system, and the nicotinic-acetylcholine system modulates self-administration of several classes of abused drugs-including opioids. Nicotine can serve as a prime for the use of other drugs, which in the case of the opioid system may be bidirectional. Opioids and compounds in tobacco, including nicotine, are metabolized by the cytochrome P450 enzyme system, but the metabolism of opioids and tobacco products can be complicated. Accordingly, drug interactions are possible but not always clear. Because of these issues, asking about nicotine use in patients taking opioids for pain is recommended. When assessing patient tobacco use, practitioners should also obtain information on products other than cigarettes, such as cigars, pipes, smokeless tobacco, and electronic nicotine delivery systems (ENDS, or e-cigarettes). There are multiple forms of behavioral therapy and pharmacotherapy available to assist patients with smoking cessation, and opioid agonist maintenance and pain clinics represent underutilized opportunities for nicotine intervention programs.

Dopaminergic and cholinergic learning mechanisms in nicotine addiction

Nicotine addiction drives tobacco use by one billion people worldwide, causing nearly six million deaths a year. Nicotine binds to nicotinic acetylcholine receptors that are normally activated by the endogenous neurotransmitter acetylcholine. The widespread expression of nicotinic receptors throughout the nervous system accounts for the diverse physiological effects triggered by nicotine. A crucial influence of nicotine is on the synaptic mechanisms underlying learning that contribute to the addiction process. Here, we focus on the acquisition phase of smoking addiction and review animal model studies on how nicotine modifies dopaminergic and cholinergic signaling in key nodes of the reinforcement circuitry: ventral tegmental area, nucleus accumbens (NAc), amygdala, and hippocampus. Capitalizing on mechanisms that subserve natural rewards, nicotine activates midbrain dopamine neurons directly and indirectly, and nicotine causes dopamine release in very broad target areas throughout the brain, including the NAc, amygdala, and hippocampus. In addition, nicotine orchestrates local changes within those target structures, alters the release of virtually all major neurotransmitters, and primes the nervous system to the influence of other addictive drugs. Hence, understanding how nicotine affects the circuitry for synaptic plasticity and learning may aid in developing reasoned therapies to treat nicotine addiction.

The opioid receptors as targets for drug abuse medication

The endogenous opioid system is largely expressed in the brain, and both endogenous opioid peptides and receptors are present in areas associated with reward and motivation. It is well known that this endogenous system plays a key role in many aspects of addictive behaviours. The present review summarizes the modifications of the opioid system induced by chronic treatment with drugs of abuse reported in preclinical and clinical studies, as well as the action of opioid antagonists and agonists on the reinforcing effects of drugs of abuse, with therapeutic perspectives. We have focused on the effects of chronic psychostimulants, alcohol and nicotine exposure. Taken together, the changes in both opioid peptides and opioid receptors in different brain structures following acute or chronic exposure to these drugs of abuse clearly identify the opioid system as a potential target for the development of effective pharmacotherapy for the treatment of addiction and the prevention of relapse.

Neural correlates of adherence to extended-release naltrexone pharmacotherapy in heroin dependence

Injectable extended-release naltrexone (XRNTX) presents an effective therapeutic strategy for opioid addiction, however its utility could be hampered by poor adherence. To gain a better insight into this phenomenon, we utilized blood oxygenation level-dependent functional magnetic resonance imaging (fMRI) in conjunction with a validated cue-induced craving procedure to examine neural correlates of XRNTX adherence. We operationalized treatment adherence as the number of monthly XRNTX injections (range: 0-3) administered to a group of fully detoxified heroin-dependent subjects (n=32). Additional outcomes included urine toxicology screening and self-reported tobacco use. The presented heroin-related visual cues reliably elicited heroin craving in all tested subjects. Nine, five, three and 15 of the participants, respectively, received zero, one, two and three XRNTX injections, predicted by the individual baseline fMRI signal change in response to the cues in the medial prefrontal cortex, a brain region involved in inhibitory self-control and emotional appraisal. The incidence of opioid-positive urines during the XRNTX therapy was low and remained about half the pre-treatment rate after the XRNTX ended. During the treatment, cigarette smoking behaviors followed patterns of opioid use, while cocaine consumption was increased with reductions in opioid use. The present data support the hypothesis that medial prefrontal cortex functions are involved in adherence to opioid antagonist therapy. A potential role of concurrent non-opioid addictive substances consumption during the XRNTX pharmacotherapy warrants further investigation. Our findings set the stage for further bio-behavioral investigations of the mechanisms of relapse prevention in opioid dependence.

Varenicline for opioid withdrawal in patients with chronic pain: a randomized, single-blinded, placebo controlled pilot trial

BACKGROUND AND OBJECTIVES

The objectives of this randomized, single-blinded, placebo-controlled pilot trial were to investigate the effects of varenicline on opioid withdrawal among chronic pain patients undergoing opioid detoxification in an interdisciplinary pain program and the feasibility of varenicline use in this population.

METHODS

Twenty-one patients were recruited (varenicline=10, placebo=11), and 7 patients in the varenicline and 11 in the placebo group completed the study. Opioid withdrawal was quantified using the Clinical Opiate Withdrawal Scale, and varenicline-related adverse effects were assessed.

RESULTS

Opioid withdrawal scores tended to decrease over the course of opioid tapering in those receiving varenicline and increase in those receiving placebo. Varenicline was well-tolerated in this population, with no adverse drug effects (including nausea) observed and no effect on improvements in pain severity and depression.

CONCLUSIONS

This randomized pilot study provides preliminary data for future trials of varenicline in opioid-dependent adults with chronic pain undergoing medically directed opioid detoxification.

Pharmacogenetics of nicotine addiction: role of dopamine

The neurotransmitter dopamine (DA) plays a central role in addictive disorders, including nicotine addiction. Specific DA-related gene variants have been studied to identify responsiveness to treatment for nicotine addiction. Genetic variants in DRD2, DRD4, ANKK1, DAT1, COMT and DBH genes show some promise in informing personalized prescribing of smoking cessation pharmacotherapies. However, many trials studying these variants had small samples, used retrospective design or were composed of mainly self-identified Caucasian individuals. Furthermore, many of these studies lacked a comprehensive measurement of nicotine metabolism rate, did not assess the roles of sex or the menstrual cycle, and did not investigate the role of rare variants and/or epigenetic factors. Future work should be conducted addressing these limitations to more effectively utilize DA genetic information to unlock the potential of smoking cessation pharmacogenetics.

Translational Research on Nicotine Dependence

Nicotine dependence is a chronic, relapsing disorder with complex biological mechanisms underlying the motivational basis for this behavior. Although more than 70 % of current smokers express a desire to quit, most relapse within one year, underscoring the need for novel treatments. A key focus of translational research models addressing nicotine dependence has been on cross-validation of human and animal models in order to improve the predictive value of medication screening paradigms. In this chapter, we review several lines of research highlighting the utility of cross-validation models in elucidating the biological underpinnings of nicotine reward and reinforcement, identifying factors which may influence individual response to treatment, and facilitating rapid translation of findings to practice.

Mu Opioid Receptor Binding Correlates with Nicotine Dependence and Reward in Smokers

The rewarding effects of nicotine are associated with activation of nicotine receptors. However, there is increasing evidence that the endogenous opioid system is involved in nicotine's rewarding effects. We employed PET imaging with [¹¹C]carfentanil to test the hypotheses that acute cigarette smoking increases release of endogenous opioids in the human brain and that smokers have an upregulation of mu opioid receptors (MORs) when compared to nonsmokers. We found no significant changes in binding potential (BP_ND) of [¹¹C]carfentanil between the placebo and the active cigarette sessions, nor did we observe differences in MOR binding between smokers and nonsmokers. Interestingly, we showed that in smokers MOR availability in bilateral superior temporal cortices during the placebo condition was negatively correlated with scores on the Fagerström Test for Nicotine Dependence (FTND). Also in smokers, smoking-induced decreases in [¹¹C]carfentanil binding in frontal cortical regions were associated with self-reports of cigarette liking and wanting. Although we did not show differences between smokers and nonsmokers, the negative correlation with FTND corroborates the role of MORs in superior temporal cortices in nicotine addiction and provides preliminary evidence of a role of endogenous opioid signaling in frontal cortex in nicotine reward.

Vibrational circular dichroism and theoretical study of the conformational equilibrium in (-)-S-nicotine

We report an extensive study of the molecular and electronic structure of (-)-S-nicotine, to deduce the phenomenon that controls its conformational equilibrium and to solve its solution-state conformer population. Density functional theory, ab initio, and molecular mechanics calculations were used together with vibrational circular dichroism (VCD) and Fourier transform infrared spectroscopies. Calculations and experiments in solution show that the structure and the conformational energy profile of (-)-S-nicotine are not strongly dependent on the medium, thus suggesting that the conformational equilibrium is dominated by hyperconjugative interactions rather than repulsive electronic effects. The analysis of the first recorded VCD spectra of (-)-S-nicotine confirmed the presence of two main conformers at room temperature. Our results provide further evidence of the hypersensitivity of vibrational optical activity spectroscopies to the three-dimensional structure of chiral samples and prove their suitability for the elucidation of solution-state conformer distribution.

Nicotinic, glutamatergic and dopaminergic synaptic transmission and plasticity in the mesocorticolimbic system: focus on nicotine effects

Cigarette smoking is currently the leading cause of preventable deaths and disability throughout the world, being responsible for about five million premature deaths/year. Unfortunately, fewer than 10% of tobacco users who try to stop smoking actually manage to do so. The main addictive agent delivered by cigarette smoke is nicotine, which induces psychostimulation and reward, and reduces stress and anxiety. The use of new technologies (including optogenetics) and the development of mouse models characterised by cell-specific deletions of receptor subtype genes or the expression of gain-of-function nAChR subunits has greatly increased our understanding of the molecular mechanisms and neural substrates of nicotine addiction first revealed by classic electrophysiological, neurochemical and behavioural approaches. It is now becoming clear that various aspects of nicotine dependence are mediated by close interactions of the glutamatergic, dopaminergic and γ-aminobutyric acidergic systems in the mesocorticolimbic system. This review is divided into two parts. The first provides an updated overview of the circuitry of the ventral tegmental area, ventral striatum and prefrontal cortex, the neurotransmitter receptor subtypes expressed in these areas, and their physiological role in the mesocorticolimbic system. The second will focus on the molecular, functional and behavioural mechanisms involved in the acute and chronic effects of nicotine on the mesocorticolimbic system.

Brain region specific modulation of ethanol-induced depression of GABAergic neurons in the brain reward system by the nicotine receptor antagonist mecamylamine

The mechanisms underlying ethanol-induced activation of the mesolimbic dopamine system are not fully understood, but increased extracellular dopamine in the nucleus accumbens (nAc) has been shown to involve nicotinic acetylcholine receptors (nAChRs). Basal activity of dopaminergic neurons in the ventral tegmental area (VTA) is under the influence of GABAergic neurotransmission, and the aim of this study was to characterize the involvement of nAChRs in mediating acute ethanol effects on GABAergic activity in subregions of the brain reward system. Multi-electrode in vivo recordings were made in the VTA and nAc of awake and behaving C57BL6/J mice receiving intraperitoneal injections of saline or ethanol (2.0 g/kg), combined with, or without, pre-injection of the non-competitive nAChR antagonist mecamylamine (1.0 mg/kg). Ethanol significantly decreased the activity of quinpirole-insensitive slow-spiking and fast-spiking units in both the VTA and the nAc as compared to saline injection. Pre-treatment with mecamylamine inhibited the rate-inhibiting properties of ethanol in the VTA, but not in the nAc. The data presented here show that ethanol depresses the activity of quinpirole-insensitive, putative GABAergic neurons, in the mesolimbic dopamine system of mice, and that nAChRs contribute to this modulation. This finding, taken together with previous microdialysis studies, supports an involvement of GABAergic neurons and nAChRs in ethanol's interaction with the mesolimbic dopamine system.

Association of smoking with μ-opioid receptor availability before and during naltrexone blockade in alcohol-dependent subjects

Persons with a history of alcohol dependence are more likely to use tobacco and to meet criteria for nicotine dependence compared with social drinkers or non-drinkers. The high levels of comorbidity of nicotine and alcohol use and dependence are thought to be related to interactions between nicotinic, opioid and dopamine receptors in mesolimbic regions. The current study examined whether individual differences in regional μ-opioid receptor (MOR) availability were associated with tobacco use, nicotine dependence and level of nicotine craving in 25 alcohol-dependent (AD) subjects. AD subjects completed an inpatient protocol, which included medically supervised alcohol withdrawal, monitored alcohol abstinence, transdermal nicotine maintenance (21 mg/day) and Positron Emission Tomography (PET) imaging using the MOR agonist [(11) C]-carfentanil (CFN) before (basal scan) and during treatment with 50 mg/day naltrexone (naltrexone scan). Subjects who had higher scores on the Fagerström Nicotine Dependence Test had significantly lower basal scan binding potential (BPND ) across mesolimbic regions, including the amygdala, cingulate, globus pallidus, thalamus and insula. Likewise, the number of cigarettes per day was negatively associated with basal scan BPND in mesolimbic regions. Higher nicotine craving was significantly associated with lower BPND in amygdala, globus pallidus, putamen, thalamus and ventral striatum. Although blunted during naltrexone treatment, the negative association was maintained for nicotine dependence and cigarettes per day, but not for nicotine craving. These findings suggest that intensity of cigarette smoking and severity of nicotine dependence symptoms are systematically related to reduced BPND across multiple brain regions in AD subjects.

Altered neurochemical levels in the rat brain following chronic nicotine treatment

Converging evidence shows that neurochemical systems are crucial mediators of nicotine dependence. Our present study evaluates the effect of 3-month chronic nicotine treatment on the levels of multiple quaternary ammonium compounds as well as glutamate and gamma aminobutyric acid in the rat prefrontal cortex, dorsal striatum and hypothalamus. We observed a marked decrease of acetylcholine levels in the dorsal striatum (22.88%, p<0.01), reflecting the impact of chronic nicotine in local interneuron circuits. We found decreases of carnitine in the dorsal striatum and prefrontal cortex (19.44%, p<0.01; 13.58%, p<0.01, respectively), but robust enhancements of carnitine in the hypothalamus (26.59%, p<0.01), which may reflect the alterations in food and water intake during chronic nicotine treatment. Finally, we identified an increase of prefrontal cortex glutamate levels (8.05%, p<0.05), supporting previous studies suggesting enhanced prefrontal activity during chronic drug use. Our study shows that quaternary ammonium compounds are regulated in a highly brain region specific manner during chronic nicotine treatment, and provides novel insights into neurochemical regulation during nicotine use.