The role of acetylcholine in cocaine addiction

Glycine-induced activation of GPR158 increases the intrinsic excitability of medium spiny neurons in the nucleus accumbens

It has been recently established that GPR158, a class C orphan G protein-coupled receptor, serves as a metabotropic glycine receptor. GPR158 is highly expressed in the nucleus accumbens (NAc), a major input structure of the basal ganglia that integrates information from cortical and subcortical structures to mediate goal-directed behaviors. However, whether glycine modulates neuronal activity in the NAc through GPR158 activation has not been investigated yet. Using whole-cell patch-clamp recordings, we found that glycine-dependent activation of GPR158 increased the firing rate of NAc medium spiny neurons (MSNs) while it failed to significantly affect the excitability of cholinergic interneurons (CIN). In MSNs GPR158 activation reduced the latency to fire, increased the action potential half-width, and reduced action potential afterhyperpolarization, effects that are all consistent with negative modulation of potassium M-currents, that in the central nervous system are mainly carried out by Kv7/KCNQ-channels. Indeed, we found that the GPR158-induced increase in MSN excitability was associated with decreased M-current amplitude, and selective pharmacological inhibition of the M-current mimicked and occluded the effects of GPR158 activation. In addition, when the protein kinase A (PKA) or extracellular signal-regulated kinase (ERK) signaling was pharmacologically blocked, modulation of MSN excitability by GPR158 activation was suppressed. Moreover, GPR158 activation increased the phosphorylation of ERK and Kv7.2 serine residues. Collectively, our findings suggest that GPR158/PKA/ERK signaling controls MSN excitability via Kv7.2 modulation. Glycine-dependent activation of GPR158 may significantly affect MSN firing in vivo, thus potentially mediating specific aspects of goal-induced behaviors.

A non-adaptationist hypothesis of play behaviour

Play is a suite of apparently non-functional, pleasurable behaviours observed in human and non-human animals. Although the phenomenon has been studied extensively, no adaptationist behavioural theory of how play evolved can be supported by the available evidence. However, the advancement of the extended evolutionary synthesis and developments in systems biology offer alternative avenues for non-adaptationist physiological hypotheses. I therefore propose a hypothesis of play, based upon a complex ACh activity that is under agential control of the organism, whereby play initiates ACh-mediated feedforward and feedback processes which act to: (i) regulate metabolic processes; (ii) form new ACh receptors via ACh mRNA activity; (iii) mediate attention, memory consolidation and learning; and (iv) mediate social behaviours, reproduction and embryonic development. However, play occurs across taxa, but does not occur across all taxonomic groups or within all species of a taxonomic group. Thus, to support the validity of the proposed hypothesis, I further propose potential explanations for this anomaly, which include sampling and observer biases, altricial versus precocial juvenile development, and the influence of habitat niche and environmental conditions on behaviour. The proposed hypothesis thus offers new avenues for study in both the biological and social sciences, in addition to having potential applications in applied sciences, such as animal welfare and biomedical research. Crucially, it is hoped that this hypothesis will promote further study of a valid and behaviourally significant, yet currently enigmatic, biological phenomenon.

Preliminary investigation of the administration of biperiden to reduce relapses in individuals with cocaine/crack user disorder: A randomized controlled clinical trial

BACKGROUND

Several studies have demonstrated that ACh modulates the dopaminergic circuit in the nucleus accumbens, and its blockade appears to be associated with the inhibition of the reinforced effect or the increase in dopamine caused by cocaine use. The objective of this study was to evaluate the effect of biperiden (a muscarinic receptor antagonist with a relatively higher affinity for the M1 receptor) on crack/cocaine use relapse compared to a control group that received placebo.

METHODS

This study is a double-blind, randomized, placebo-controlled clinical trial. The intervention group received 2 mg of biperiden, 3 times a day, for a period of 3 months. The control group received identical placebo capsules, at the same frequency and over the same period. All participants were followed for a period of six months.

RESULTS

The sample comprised 128 people, with 61 in the control group and 67 in the biperiden group. Lower substance consumption was observed in the group that received biperiden treatment two (bT2 = -2.2 [-3.3; -1.0], p < 0.001) and six months (bT4 = -6, 2 [-8.6; -3.9], p < 0.001) after the beginning of the intervention. The biperiden group had a higher latency until a possible first day of consumption, in the same evaluation periods (bT2 = 0.26 [0.080; 0.44], p = 0.004; bT4 = 0.63 [0.32; 0.93], p < 0.001).

CONCLUSIONS

Despite the major limitations of the present study, the group that received biperiden reduced the number of days of cocaine/crack use and showed an increase in the latency time for relapse. More studies are needed to confirm the utility of this approach.

The hyperexcitability of laterodorsal tegmentum cholinergic neurons accompanies adverse behavioral and cognitive outcomes of prenatal stress

Exposure to prenatal stress (PS) leads to the offspring's vulnerability towards the development of cognitive and behavioral disorders. Laterodorsal tegmentum (LDT) is a part of the brainstem cholinergic system that is believed to play a pivotal role in the stress-associated progression of anxiety, memory impairment, and addictive behaviors. In this study, we aimed to investigate the electrophysiological alterations of LDT cholinergic neurons and its accompanied behavioral and cognitive outcomes in the offspring of mice exposed to physical or psychological PS. Swiss Webster mice were exposed to physical or psychological stress on the tenth day of gestation. Ex vivo investigations in LDT brain slices of adolescent male offspring were performed to evaluate the effects of two stressor types on the activity of cholinergic neurons. Open field test, elevated plus maze, passive avoidance test, and conditioned place preference were conducted to assess behavioral and cognitive alterations in the offspring. The offspring of both physical and psychological PS-exposed mice exhibited increased locomotor activity, anxiety-like behavior, memory impairment, and preference to morphine. In both early- and late-firing cholinergic neurons of the LDT, stressed groups demonstrated higher firing frequency, lower adaptation ratio, decreased action potential threshold, and therefore increased excitability compared to the control group. The findings of the present study suggest that the hyperexcitability of the cholinergic neurons of LDT might be involved in the development of PS-associated anxiety-like behaviors, drug seeking, and memory impairment.

TFOS Lifestyle: Impact of lifestyle challenges on the ocular surface

Many factors in the domains of mental, physical, and social health have been associated with various ocular surface diseases, with most of the focus centered on aspects of dry eye disease (DED). Regarding mental health factors, several cross-sectional studies have noted associations between depression and anxiety, and medications used to treat these disorders, and DED symptoms. Sleep disorders (both involving quality and quantity of sleep) have also been associated with DED symptoms. Under the domain of physical health, several factors have been linked to meibomian gland abnormalities, including obesity and face mask wear. Cross-sectional studies have also linked chronic pain conditions, specifically migraine, chronic pain syndrome and fibromyalgia, to DED, principally focusing on DED symptoms. A systematic review and meta-analysis reviewed available data and concluded that various chronic pain conditions increased the risk of DED (variably defined), with odds ratios ranging from 1.60 to 2.16. However, heterogeneity was noted, highlighting the need for additional studies examining the impact of chronic pain on DED signs and subtype (evaporative versus aqueous deficient). With respect to societal factors, tobacco use has been most closely linked to tear instability, cocaine to decreased corneal sensitivity, and alcohol to tear film disturbances and DED symptoms.

Nucleus accumbens in the pathogenesis of major depressive disorder: A brief review

Major depressive disorder (MDD) is the most prevalent mental disorder characterized by anhedonia, loss of motivation, avolition, behavioral despair and cognitive abnormalities. Despite substantial advancements in the pathophysiology of MDD in recent years, the pathogenesis of this disorder is not fully understood. Meanwhile,the treatment of MDD with currently available antidepressants is inadequate, highlighting the urgent need for clarifying the pathophysiology of MDD and developing novel therapeutics. Extensive studies have demonstrated the involvement of nuclei such as the prefrontal cortex (PFC), hippocampus (HIP), nucleus accumbens (NAc), hypothalamus, etc., in MDD. NAc,a region critical for reward and motivation,dysregulation of its activity seems to be a hallmark of this mood disorder. In this paper, we present a review of NAc related circuits, cellular and molecular mechanisms underlying MDD and share an analysis of the gaps in current research and possible future research directions.

Modulation of neuronal excitability by binge alcohol drinking

Drug use poses a serious threat to health systems throughout the world. The number of consumers rises every year being alcohol the drug of abuse most consumed causing 3 million deaths (5.3% of all deaths) worldwide and 132.6 million disability-adjusted life years. In this review, we present an up-to-date summary about what is known regarding the global impact of binge alcohol drinking on brains and how it affects the development of cognitive functions, as well as the various preclinical models used to probe its effects on the neurobiology of the brain. This will be followed by a detailed report on the state of our current knowledge of the molecular and cellular mechanisms underlying the effects of binge drinking on neuronal excitability and synaptic plasticity, with an emphasis on brain regions of the meso-cortico limbic neurocircuitry.

Chronic exposure to methadone induces activated microglia and astrocyte and cell death in the cerebellum of adult male rats

Methadone is a centrally-acting synthetic opioid analgesic widely used in the methadone maintenance therapy (MMT) programs throughout the world. Considering its neurotoxic effects particularly on the cerebellum, this study aims to address the behavioral and histological alterations in the cerebellar cortex associated with methadone administration. Twenty-four adult male albino rats were randomized into two groups of control and methadone treatment. Methadone was subcutaneously administered (2.5-10 mg/kg) once a day for two consecutive weeks. The functional and structural changes in the cerebellum were compared to the control group. Our data revealed that treating rats with methadone not only induced cerebellar atrophy, but also prompted the actuation of microgliosis, astrogliosis, and apoptotic biomarkers. We further demonstrated that treating rats with methadone increased complexity of astrocyte processes and decreased complexity of microglia processes. Our result showed that methadone impaired motor coordination and locomotor performance and neuromuscular activity. Additionally, relative gene expression of TNF-α, caspase-3 and RIPK3 increased significantly due to methadone. Our findings suggest that methadone administration has a neurodegenerative effect on the cerebellar cortex via dysregulation of microgliosis, astrogliosis, apoptosis, and neuro-inflammation.

Abnormal maternal behavior in mice lacking phospholipase Cβ1

Motherhood goes through preparation, onset and maintenance phases until the natural weaning. A variety of changes in hormonal/neurohormonal systems and brain circuits are involved in the maternal behavior. Hormones, neuropeptides, and neurotransmitters involved in maternal behavior act via G-protein-coupled receptors, many of which in turn activate plasma membrane enzymes including phospholipase C (PLC) β isoforms. In this study, we examined the effect of PLCβ1 knockout (KO) on maternal behavior. There was little difference between PLCβ1-KO and wild-type (WT) dams in the relative time spent in maternal behavior during the period between 24 h prepartum and 12 h postpartum (-24 h ∼ PPH 12). After PPH 18, however, PLCβ1-KO dams neglected their pups so that they all died in 2-3 days. In the pup retrieval test, latency was not different during the period within PPH 12, but after PPH 18, PLCβ1-KO dams could not finish pup retrieval in a given time. During both periods, FosB expression in the nucleus accumbens (NAcc) of PLCβ1-KO dams was significantly lower than WT, but not different in the medial preoptic area (mPOA). Given that mPOA activity is required for initiation of maternal behavior, and that NAcc is known to be involved in maternal motivation and maintenance of maternal behavior, our results suggest that PLCβ1 signaling is essential for transition from the onset to maintenance phase of maternal behavior.

A novel cholinergic projection from the lateral parabrachial nucleus and its role in methamphetamine-primed conditioned place preference

Drug relapse is a big clinical challenge in the treatment of addiction, but its neural circuit mechanism is far from being fully understood. Here, we identified a novel cholinergic pathway from choline acetyltransferase-positive neurons in the external lateral parabrachial nucleus (eLPB^ChAT) to the GABAergic neurons in the central nucleus of the amygdala (CeA^GABA) and explored its role in methamphetamine priming-induced reinstatement of conditioned place preference. The anatomical structure and functional innervation of the eLPB^ChAT–CeA^GABA pathway were investigated by various methods such as fluorescent micro-optical sectioning tomography, virus-based neural tracing, fibre photometry, patch-clamp and designer receptor exclusively activated by a designer drug. The role of the eLPB^ChAT–CeA^GABA pathway in methamphetamine relapse was assessed using methamphetamine priming-induced reinstatement of conditioned place preference behaviours in male mice. We found that the eLPB^ChAT neurons mainly projected to the central nucleus of the amygdala. A chemogenetic activation of the eLPB^ChAT neurons in vitro or in vivo triggered the excitabilities of the CeA^GABA neurons, which is at least in part mediated via the cholinergic receptor system. Most importantly, the chemogenetic activation of either the eLPB^ChAT neurons or the eLPB^ChAT neurons that project onto the central nucleus of the amygdala decreased the methamphetamine priming-induced reinstatement of conditioned place preference in mice. Our findings revealed a previously undiscovered cholinergic pathway of the eLPB^ChAT–CeA^GABA and showed that the activation of this pathway decreased the methamphetamine priming-induced reinstatement of conditioned place preference.

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Chronic escalating-dose and acute binge cocaine treatments change the hippocampal cholinergic muscarinic system on drug presence and after withdrawal

Cocaine addiction is a relapsing disorder with loss of control in limiting drug intake. Considering the involvement of acetylcholine in the neurobiology of the disease, our aim was to evaluate whether cocaine induces plastic changes in the hippocampal cholinergic muscarinic system. Male Swiss-Webster mice received saline or cocaine (ip) three times daily (60-min intervals) either acutely or in an escalating-dose binge paradigm for 14 days. Locomotor activity was measured in all treatment days. Dopaminergic and cholinergic muscarinic receptors (D₁R, D₂R, M₁-M_5, mAChRs), choline acetyltransferase (ChAT), vesicular acetylcholine transporter (VAChT) and acetylcholinesterase (AChE) were quantified in the hippocampus by immunoblotting one hour after the last injection (on drug) or after 14 days of abstinence (withdrawal). Escalating-dose group showed cocaine-induced locomotor sensitization from day 2. M₃ mAChR and ChAT significantly increased after the on-drug acute binge treatment. Escalating-dose on-drug group showed increased ChAT, M₁, M₅ mAChR and D₂R; and decreased D₁R. Acute-binge withdrawal group showed increased VAChT, M₂ mAChR, D₁R, and D₂R; and decreased M₁ mAChR. Escalating-dose withdrawal group presented increased D₁R and VAChT and decreased M₁ mAChR and D₂R. Locomotor activity was negatively correlated with M₁ mAChR and AChE in on-drug group and positively correlated with VAChT in withdrawal group. M₁ mAChR was positively correlated with M₂ mAChR and ChAT in on-drug group, whereas ChAT was positively correlated with M₅ mAChR in withdrawal group. The results indicate that cocaine induced an increase in the hippocampal cholinergic tone in the presence of the drug, whereas withdrawal causes a resetting in the system.

Varenicline for the Treatment of Cocaine Dependence

OBJECTIVES

Varenicline is a partial agonist at the α2β4 and α6β2 nAChR receptors and a full agonist at α7 receptors. Both α7 and α6β2 receptors are implicated in the neural reward circuitry activated by cocaine use. A preliminary clinical trial suggested that varenicline treatment reduced cocaine use. This trial was intended to replicate and extend the findings of the previous trial.

METHODS

This was a 12-week, double-blind, placebo-controlled clinical trial involving 156 subjects with DSM IV cocaine dependence. Subjects received up to 2 mg of varenicline or identical placebo daily along with weekly relapse prevention psychotherapy. The primary outcome measure was cocaine use measured by thrice-weekly urine drug screens. Additional outcome measures included end of study cocaine abstinence, cocaine craving, cocaine withdrawal symptom severity, cigarette use, and global improvement measure by the Clinical Global Improvement Scale.

RESULTS

End of study cocaine abstinence, measured by urine drug screens during the last 3 weeks of the trial, was not different between groups (8% in the varenicline treated subjects and versus 9% in placebo-treated subjects). Generalized estimating equations analysis of urine drug screen results showed no significant difference between groups in cocaine abstinence over the 12 weeks of the trial. There were no significant differences between the 2 groups in cocaine craving or cocaine withdrawal symptom severity. Varenicline was well-tolerated. There were no medication-associated serious adverse events.

CONCLUSIONS

Varenicline plus cognitive-behavioral therapy does not seem to be an efficacious treatment for cocaine dependence.

Cocaine-induced projection-specific and cell type-specific adaptations in the nucleus accumbens

Cocaine craving, seeking, and relapse are mediated, in part, by cocaine-induced adaptive changes in the brain reward circuits. The nucleus accumbens (NAc) integrates and prioritizes different emotional and motivational inputs to the reward system by processing convergent glutamatergic projections from the medial prefrontal cortex, basolateral amygdala, ventral hippocampus, and other limbic and paralimbic brain regions. Medium spiny neurons (MSNs) are the principal projection neurons in the NAc, which can be divided into two major subpopulations, namely dopamine receptor D1- versus D2-expressing MSNs, with complementing roles in reward-associated behaviors. After cocaine experience, NAc MSNs exhibit complex and differential adaptations dependent on cocaine regimen, withdrawal time, cell type, location (NAc core versus shell), and related input and output projections, or any combination of these factors. Detailed characterization of these cellular adaptations has been greatly facilitated by the recent development of optogenetic/chemogenetic techniques combined with transgenic tools. In this review, we discuss such cell type- and projection-specific adaptations induced by cocaine experience. Specifically, (1) D1 and D2 NAc MSNs frequently exhibit differential adaptations in spinogenesis, glutamatergic receptor trafficking, and intrinsic membrane excitability, (2) cocaine experience differentially changes the synaptic transmission at different afferent projections onto NAc MSNs, (3) cocaine-induced NAc adaptations exhibit output specificity, e.g., being different at NAc-ventral pallidum versus NAc-ventral tegmental area synapses, and (4) the input, output, subregion, and D1/D2 cell type may together determine cocaine-induced circuit plasticity in the NAc. In light of the projection- and cell-type specificity, we also briefly discuss ensemble and circuit mechanisms contributing to cocaine craving and relapse after drug withdrawal.

M1 muscarinic receptor activation decreases alcohol consumption via a reduction in consummatory behavior

Muscarinic acetylcholine receptors (mAChRs) have been shown to mediate alcohol consumption and seeking. Both M₄ and M₅ mAChRs have been highlighted as potential novel treatment targets for alcohol use disorders (AUD). Similarly, M₁ mAChRs are expressed throughout reward circuitry, and their signaling has been implicated in cocaine consumption. However, whether the same effects are seen for alcohol consumption, or whether natural reward intake is inadvertently impacted is still unknown. To determine the role of M₁ mAChRs in alcohol consumption, we tested operant self-administration of alcohol under both fixed ratio (FR3) and progressive ratio (PR3-4) schedules. Enhancing M₁ mAChR signaling (via the M₁ PAM-Agonist PF-06767832, 1 mg/kg, i.p.) reduced operant alcohol consumption on a fixed schedule but had no effect on motivation to acquire alcohol. To determine whether these actions were specific to alcohol, we examined the effects of M₁ enhancement on natural reward (sucrose) self-administration. Systemic administration of PF-06767832 (1 mg/kg, i.p.) also reduced operant sucrose self-administration, suggesting the actions of the M₁ receptor may be non-selective across drug and natural rewards. Finally, to understand whether this reduction extended to natural consummatory behaviors, we assessed home cage standard chow and water consumption. M₁ enhancement via systemic PF-06767832 administration reduced food and water consumption. Together our results suggest the M₁ PAM-agonist, PF-06767832, non-specifically reduces consummatory behaviors that are not associated with motivational strength for the reward. These data highlight the need to further characterize M₁ agonists, PAMs, and PAM-agonists, which may have varying degrees of utility in the treatment of neuropsychiatric disorders including AUD.

Effects of adolescent substance use disorders on central cholinergic function

Adolescence is a transitional period between childhood and adulthood, in which the individual undergoes significant cognitive, behavioral, physical, emotional, and social developmental changes. During this period, adolescents engage in experimentation and risky behaviors such as licit and illicit drug use. Adolescents' high vulnerability to abuse drugs and natural reinforcers leads to greater risk for developing substance use disorders (SUDs) during adulthood. Accumulating evidence indicates that the use and abuse of licit and illicit drugs during adolescence and emerging adulthood can disrupt the cholinergic system and its processes. This review will focus on the effects of peri-adolescent nicotine and/or alcohol use, or exposure, on the cholinergic system during adulthood from preclinical and clinical studies. This review further explores potential cholinergic agents and pharmacological manipulations to counteract peri-adolescent nicotine and/or alcohol abuse.

Addiction-related neuroadaptations following chronic nicotine exposure

The addiction-relevant molecular, cellular, and behavioral actions of nicotine are derived from its stimulatory effects on neuronal nicotinic acetylcholine receptors (nAChRs) in the central nervous system. nAChRs expressed by dopamine-containing neurons in the ventral midbrain, most notably in the ventral tegmental area (VTA), contribute to the reward-enhancing properties of nicotine that motivate the use of tobacco products. nAChRs are also expressed by neurons in brain circuits that regulate aversion. In particular, nAChRs expressed by neurons in the medial habenula (mHb) and the interpeduncular nucleus (IPn) to which the mHb almost exclusively projects regulate the "set-point" for nicotine aversion and control nicotine intake. Different nAChR subtypes are expressed in brain reward and aversion circuits and nicotine intake is titrated to maximally engage reward-enhancing nAChRs while minimizing the recruitment of aversion-promoting nAChRs. With repeated exposure to nicotine, reward- and aversion-related nAChRs and the brain circuits in which they are expressed undergo adaptations that influence whether tobacco use will transition from occasional to habitual. Genetic variation that influences the sensitivity of addiction-relevant brain circuits to the actions of nicotine also influence the propensity to develop habitual tobacco use. Here, we review some of the key advances in our understanding of the mechanisms by which nicotine acts on brain reward and aversion circuits and the adaptations that occur in these circuits that may drive addiction to nicotine-containing tobacco products.

Pharmacological evidence of a cholinergic contribution to elevated impulsivity and risky decision-making caused by adding win-paired cues to a rat gambling task

BACKGROUND

Pairing rewards with sensory stimulation, in the form of auditory and visual cues, increases risky decision-making in both rats and humans. Understanding the neurobiological basis of this effect could help explain why electronic gambling machines are so addictive, and inform treatment development for compulsive gambling and gaming. Numerous studies implicate the dopamine system in mediating the motivational influence of reward-paired cues; recent data suggest the cholinergic system also plays a critical role. Previous work also indicates that cholinergic drugs alter decision-making under uncertainty.

AIMS

We investigated whether the addition of reward-concurrent cues to the rat gambling task (crGT) altered the effects of peripherally administered cholinergic compounds.

METHODS

Muscarinic and nicotinic agonists and antagonists were administered to 16 male, Long-Evans rats trained on the crGT. Measures of optimal/risky decision-making and motor impulsivity were the main dependent variables of interest.

RESULTS

The muscarinic receptor antagonist scopolamine improved decision-making overall, decreasing selection of one of the risky options while increasing choice of the more advantageous options. The muscarinic agonist oxotremorine increased choice latency but did not significantly affect option preference. Neither the nicotinic antagonist mecamylamine nor the agonist nicotine affected choice patterns, but mecamylamine decreased premature responding, an index of motor impulsivity.

CONCLUSIONS

These results contrast sharply from those obtained previously using the uncued rGT, and suggest that the deleterious effects of win-paired cues on decision-making and impulse control may result from elevated cholinergic tone.

The duration of withdrawal affects the muscarinic signaling in the nucleus accumbens after chronic morphine exposure in neonatal rats

The infants experience withdrawal from opiates, and time-dependent adaptations in neuronal activity of nucleus accumbens (NAc) may be crucial for this process. A key adaptation is an increased release of acetylcholine. The present study investigates muscarinic acetylcholine receptors (mAChRs) functions in the NAc at short-term (SWT) and long-term (LWT) withdrawal time following chronic morphine exposure in neonatal rats. The inhibitory role of presynaptic mAChRs activation in spontaneous excitatory postsynaptic currents (sEPSCs) in medium spiny neurons was decreased at LWT but not at SWT. Whereas, the excitatory role of post/extrasynaptic mAChRs activation in membrane currents was reduced at LWT but enhanced at SWT. Furthermore, the inhibitory effect of acute morphine on post/extrasynaptic mAChRs-mediated inward currents was enhanced at SWT but not at LWT. These results suggest that withdrawal from morphine leads to downregulation of presynaptic and post/extrasynaptic mAChRs functions in the NAc, which may coregulate the development of withdrawal in neonates.NEW & NOTEWORTHY We investigated for the first time how the duration of withdrawal affects mAChRs functions in the nucleus accumbens in neonatal rats. Compared with short-term withdrawal time, rats showed downregulation of presynaptic and post/extrasynaptic mAChRs functions during long-term withdrawal time. Our finding introduces a new possible correlation between the mAChRs dysfunction in the nucleus accumbens and the development of withdrawal in neonates.

An acetylcholine-dopamine interaction in the nucleus accumbens and its involvement in ethanol's dopamine-releasing effect

Alcohol use disorder is a chronic, relapsing brain disorder causing substantial morbidity and mortality. Cholinergic interneurons (CIN) within the nucleus accumbens (nAc) have been suggested to exert a regulatory impact on dopamine (DA) neurotransmission locally, and defects in CIN have been implied in several psychiatric disorders. The aim of this study was to investigate the role of CIN in regulation of basal extracellular levels of DA and in modulation of nAc DA release following ethanol administration locally within the nAc of male Wistar rats. Using reversed in vivo microdialysis, the acetylcholinesterase inhibitor physostigmine was administered locally in the nAc followed by addition of either the muscarinic acetylcholine (ACh) receptor antagonist scopolamine or the nicotinic ACh receptor antagonist mecamylamine. Further, ethanol was locally perfused in the nAc following pretreatment with scopolamine and/or mecamylamine. Lastly, ethanol was administered locally into the nAc of animals with accumbal CIN‐ablation induced by anticholine acetyl transferase‐saporin. Physostigmine increased accumbal DA levels via activation of muscarinic ACh receptors. Neither scopolamine and/or mecamylamine nor CIN‐ablation altered basal DA levels, suggesting that extracellular DA levels are not tonically controlled by ACh in the nAc. In contrast, ethanol‐induced DA elevation was prevented following coadministration of scopolamine and mecamylamine and blunted in CIN‐ablated animals, suggesting involvement of CIN‐ACh in ethanol‐mediated DA signaling. The data presented in this study suggest that basal extracellular levels of DA within the nAc are not sustained by ACh, whereas accumbal CIN‐ACh is involved in mediating ethanol‐induced DA release.

Understanding the genetics and neurobiological pathways behind addiction (Review)

The hypothesis issued by modern medicine states that many diseases known to humans are genetically determined, influenced or not by environmental factors, which is applicable to most psychiatric disorders as well. This article focuses on two pending questions regarding addiction: Why do some individuals become addicted while others do not? along with Is it a learned behavior or is it genetically predefined? Recent data suggest that addiction is more than repeated exposure, it is the synchronicity between intrinsic factors (genotype, sex, age, preexisting addictive disorder, or other mental illness), extrinsic factors (childhood, level of education, socioeconomic status, social support, entourage, drug availability) and the nature of the addictive agent (pharmacokinetics, path of administration, psychoactive properties). The dopamine-mesolimbic motivation-reward-reinforcement cycle remains the most coherent physiological theory in addiction. While the common property of addictive substances is that they are dopamine-agonists, each class has individual mechanisms, pharmacokinetics and psychoactive potentials.

Effects of biperiden (cholinergic muscarinic m1/m4 receptor antagonist) on ethanol conditioned place preference in mice

BACKGROUND

Previous studies suggest that muscarinic cholinergic receptors might act upon the dopamine release in the mesolimbic system and alter drug-reinforcing values related to drug craving.

AIMS

We examined the effects of systemic biperiden administration, a muscarinic cholinergic (M1/M4) receptor antagonist, on ethanol (dose of 2 g/Kg) conditioned place preference (CPP), neuronal activation, dopamine and its metabolites levels in the nucleus accumbens.

METHODS

Thirty minutes before the ethanol-induced CPP test, mice received saline or biperiden at doses of 1.0, 5.0, or 10.0 mg/kg. The time spent in each compartment was recorded for 15 min. After the CPP protocol, animals were euthanized, and we investigated the activation of the nucleus accumbens by immunohistochemistry for Fos. We also quantified dopamine, homovanillic acid (HVA), and dihydroxyphenylacetic acid (DOPAC) levels in the nucleus accumbens by high-performance liquid chromatography (HPLC). Additionally, the rotarod was employed to evaluate the effects of biperiden on motor coordination.

RESULTS

Biperiden at different doses (1.0, 5.0, and 10.0 mg/kg) blocked the expression of ethanol-induced CPP. These biperiden doses increased the number of Fos-positive cells and the dopamine turnover in the nucleus accumbens. None of the doses affected the motor coordination evaluated by the rotarod.

CONCLUSIONS

Our results show that biperiden can modulate the effect of alcohol reward, and its mechanism of action may involve a change in dopamine and cholinergic mesolimbic neurotransmission.

Genetic Architecture and Molecular Neuropathology of Human Cocaine Addiction

We integrated genomic and bioinformatic analyses, using data from the largest genome-wide association study of cocaine dependence (CD; n = 6546; 82.37% with CD; 57.39% male) and the largest postmortem gene-expression sample of individuals with cocaine use disorder (CUD; n = 36; 51.35% with CUD; 100% male). Our genome-wide analyses identified one novel gene (NDUFB9) associated with the genetic predisposition to CD in African-Americans. The genetic architecture of CD was similar across ancestries. Individual genes associated with CD demonstrated modest overlap across European-Americans and African-Americans, but the genetic liability for CD converged on many similar tissue types (brain, heart, blood, liver) across ancestries. In a separate sample, we investigated the neuronal gene expression associated with CUD by using RNA sequencing of dorsal-lateral prefrontal cortex neurons. We identified 133 genes differentially expressed between CUD case patients and cocaine-free control subjects, including previously implicated candidates for cocaine use/addiction (FOSB, ARC, KCNJ9/GIRK3, NR4A2, JUNB, and MECP2). Differential expression analyses significantly correlated across European-Americans and African-Americans. While genes significantly associated with CD via genome-wide methods were not differentially expressed, two of these genes (NDUFB9 and C1qL2) were part of a robust gene coexpression network associated with CUD involved in neurotransmission (GABA, acetylcholine, serotonin, and dopamine) and drug addiction. We then used a "guilt-by-association" approach to unravel the biological relevance of NDUFB9 and C1qL2 in the context of CD. In sum, our study furthers the understanding of the genetic architecture and molecular neuropathology of human cocaine addiction and provides a framework for translating biological meaning into otherwise obscure genome-wide associations.SIGNIFICANCE STATEMENT Our study further clarifies the genetic and neurobiological contributions to cocaine addiction, provides a rapid approach for generating testable hypotheses for specific candidates identified by genome-wide research, and investigates the cross-ancestral biological contributions to cocaine use disorder/dependence for individuals of European-American and African-American ancestries.

Nanoscopic Visualization of Restricted Nonvolume Cholinergic and Monoaminergic Transmission with Genetically Encoded Sensors

How neuromodulatory transmitters diffuse into the extracellular space remains an unsolved fundamental biological question, despite wide acceptance of the volume transmission model. Here, we report development of a method combining genetically encoded fluorescent sensors with high-resolution imaging and analysis algorithms which permits the first direct visualization of neuromodulatory transmitter diffusion at various neuronal and non-neuronal cells. Our analysis reveals that acetylcholine and monoamines diffuse at individual release sites with a spread length constant of ∼0.75 μm. These transmitters employ varied numbers of release sites, and when spatially close-packed release sites coactivate they can spillover into larger subcellular areas. Our data indicate spatially restricted (i.e., nonvolume) neuromodulatory transmission to be a prominent intercellular communication mode, reshaping current thinking of control and precision of neuromodulation crucial for understanding behaviors and diseases.

Non-pharmacological factors that determine drug use and addiction

Based on their pharmacological properties, psychoactive drugs are supposed to take control of the natural reward system to finally drive compulsory drug seeking and consumption. However, psychoactive drugs are not used in an arbitrary way as pure pharmacological reinforcement would suggest, but rather in a highly specific manner depending on non-pharmacological factors. While pharmacological effects of psychoactive drugs are well studied, neurobiological mechanisms of non-pharmacological factors are less well understood. Here we review the emerging neurobiological mechanisms beyond pharmacological reinforcement which determine drug effects and use frequency. Important progress was made on the understanding of how the character of an environment and social stress determine drug self-administration. This is expanded by new evidence on how behavioral alternatives and opportunities for drug instrumentalization generate different patterns of drug choice. Emerging evidence suggests that the neurobiology of non-pharmacological factors strongly determines pharmacological and behavioral drug action and may, thus, give rise for an expanded system's approach of psychoactive drug use and addiction.

Cocaine potently blocks neuronal α3β4 nicotinic acetylcholine receptors in SH-SY5Y cells

Cocaine is one of the most abused illicit drugs worldwide. It is well known that the dopamine (DA) transporter is its major target; but cocaine also acts on other targets including nicotinic acetylcholine receptors (nAChRs). In this study, we investigated the effects of cocaine on a special subtype of neuronal nAChR, α3β4-nAChR expressed in native SH-SY5Y cells. α3β4-nAChR-mediated currents were recorded using whole-cell recordings. Drugs were applied using a computer-controlled U-tube drug perfusion system. We showed that bath application of nicotine induced inward currents in a concentration-dependent manner with an EC50 value of 20 µM. Pre-treatment with cocaine concentration-dependently inhibited nicotine-induced current with an IC50 of 1.5 μM. Kinetic analysis showed that cocaine accelerated α3β4-nAChR desensitization, which caused a reduction of the amplitude of nicotine-induced currents. Co-application of nicotine and cocaine (1.5 μM) depressed the maximum response on the nicotine concentration-response curve without changing the EC50 value, suggesting a non-competitive mechanism. The cocaine-induced inhibition of nicotine response exhibited both voltage- and use-dependence, suggesting an open-channel blocking mechanism. Furthermore, intracellular application of GDP-βS (via recording electrode) did not affect cocaine-induced inhibition, suggesting that cocaine did not alter receptor internalization. Moreover, intracellular application of cocaine (30 µM) failed to alter the nicotine response. Finally, cocaine (1.5 μM) was unable to inhibit the nicotine-induced inward current in heterologous expressed α6/α3β2β3-nAChRs and α4β2-nAChRs expressed in human SH-EP1 cells. Collectively, our results suggest that cocaine is a potent blocker for native α3β4-nAChRs expressed in SH-SY5Y cells.

The treatment of cocaine use disorder

Cocaine use continues to be a serious worldwide public health problem. Cocaine abuse is associated with substantial morbidity and mortality. Cocaine overdose deaths are increasing in the United States and, in certain populations, outnumber heroin and opiate overdose deaths. Psychosocial treatments remain the treatments of choice for cocaine use disorder (CUD), with standard approaches including contingency management and cognitive behavioral therapy. However, the effect sizes of these treatments are not large, and they are not effective for most patients. Consequently, investigators have sought to develop pharmacological agents to augment the efficacy of psychosocial treatments. Despite these efforts, no medications have yet been proven to be safe and effective for the treatment of CUD. The most promising pharmacological strategies for CUD treatment thus far include the use of dopamine agonists, such as long-acting amphetamine and modafinil or glutamatergic and GABAergic agents such as topiramate. Combination drugs may be especially promising.

Rivastigmine does not alter cocaine-induced subjective effects or self-administration

BACKGROUND

Acetylcholinergic (ACh) neurons interface with the mesolimbic dopamine pathway implicated in addiction, and acetylcholinesterase inhibitors (AChEis) have been shown to reduce the immediate effects of cocaine and amount used. Our study is the first to examine if the safe and low-interaction AChEi rivastigmine (riv) alters the subjective effects produced by cocaine administration.

METHODS

Cocaine-dependent subjects were randomized to daily placebo, riv 3 mg, or riv 6 mg, administered inpatient for 10 days. On day 1 (pre-dose) and day 9, subjects received both IV cocaine 40 mg or placebo in a randomized order with subsequent serial assessments of visual analog scale (VAS) subjective effects and pharmacokinetic measurements. On day 10 all participants received one baseline dose of cocaine 20 mg with assessment of subjective effects, and were then able to purchase additional doses at 15 min intervals with study earnings.

RESULTS

40 subjects were randomized to placebo (n = 16), riv 3 mg (n = 13), or riv 6 mg (n = 12). All subjects completed the study and there were no demographic differences between treatment groups. Pre- and post- treatment, there were no significant pharmacokinetic differences (blood levels of cocaine, BE, EME) following cocaine administration. In a two-way ANOVA, IV cocaine significantly increased positive VAS category ratings compared to placebo, but rivastigmine treatment at either dose had no significant effect on any VAS category ratings. Similarly, there was no significant rivastigmine effect on any category in the day 10 cocaine administration, and no effect on number of subsequent doses participants purchased.

CONCLUSION

Rivastigmine 3 or 6 mg had no significant effect on the subjective effects of cocaine after 9 days of treatment. This is an important finding as other drugs in the AChEi class (donepezil, Huperzine A) have produced significant results, but differ in their receptor specificity and PK parameters.

Association of status of acetylcholinesterase and ACHE gene 3' UTR variants (rs17228602, rs17228616) with drug addiction vulnerability in pakistani population

Substance addiction is a chronic, relapsing mental disorder Characterized by compulsive drug seeking, and loss of control over drug intake and relapse after prolonged abstinence. Genetics has been shown to contribute towards an individual's vulnerability to addiction. Acetylecholine (ACh), a cholinergic neurotransmitter hydrolyzed by acetylcholinesterase (AChE), is an essential neurotransmitter and neuromodulator in central and peripheral nervous system and has regulatory influence on numerous neuronal functions including addiction. The present study was carried out to investigate the role of acetylcholinesterase (AChE) in addiction through measurement of enzyme activity and to find potential association of ACHE gene 3'UTR variants rs17228602 and rs17228616 in heroin, hashish and poly drug addicts. Both SNPs are located within microRNA (miRNA) recognition sites with potential to affect miRNA/transcript interaction. A total of 122 addicts of heroin, hashish and polydrug were recruited from local rehabilitation centers to participate in this study. AChE activity was measured in blood by Ellman's method. SNP genotyping was performed by restriction fragment length polymorphism (PCR-RFLP) and Sanger sequencing. The AChE activity was found significantly higher (p ≤ 0.005) in addicted cohort (mean ± standard error of mean 0.020 ± 0.001 μmol/L/min; 95% confidence interval (CI) 0.018-0.022) in comparison to non-addicted healthy subjects (0.011 ± 0.001 μmol/L/min; 95% confidence interval CI 0.010-0.013). A statistically significant association of ACHE rs17228602 SNP with addiction vulnerability in dominant (DM: Odd's ratio OR = 2.095, 95% CI = 1.157-3.807 p = 0.009) and allelic genetic models (OR = 1.854 95% CI = 1.082-3.187, p = 0.016) was observed. However, no statistically significant association of rs17228616 SNP with substance abuse disorder was found. The data presented here shows that AChE could play significant role in substance addiction. Further studies with larger sample size and other variants of AChE are recommended to identify novel therapeutic approaches for cholinergic based treatment of addiction.

Cholinergic system in sleep regulation of emotion and motivation

Sleep profoundly regulates our emotional and motivational state of mind. Human brain imaging and animal model studies are providing initial insights on the underlying neural mechanisms. Here, we focus on the brain cholinergic system, including cholinergic neurons in the basal forebrain, ventral striatum, habenula, and brain stem. Although much is learned about cholinergic regulations of emotion and motivation, less is known on their interactions with sleep. Specifically, we present an anatomical framework that highlights cholinergic signaling in the integrated reward-arousal/sleep circuitry, and identify the knowledge gaps on the potential roles of cholinergic system in sleep-mediated regulation of emotion and motivation. Sleep impacts every aspect of brain functions. It not only restores cognitive control, but also retunes emotional and motivational regulation [1]. Sleep disturbance is a comorbidity and sometimes a predicting factor for various psychiatric diseases including major depressive disorder, anxiety, post-traumatic stress disorder, and drug addiction [2-9]. Although it is well recognized that sleep prominently shapes emotional and motivational regulation, the underlying neural mechanisms remain elusive. The brain cholinergic system is essential for a diverse variety of functions including cognition, learning and memory, sensory and motor processing, sleep and arousal, reward processing, and emotion regulation [10-14]. Although cholinergic functions in cognition, learning and memory, motor control, and sleep and arousal have been well established, its interaction with sleep in regulating emotion and motivation has not been extensively studied. Here we review current evidence on sleep-mediated regulation of emotion and motivation, and reveal knowledge gaps on potential contributions from the cholinergic system.

Quantitative Systems Pharmacological Analysis of Drugs of Abuse Reveals the Pleiotropy of Their Targets and the Effector Role of mTORC1

Existing treatments against drug addiction are often ineffective due to the complexity of the networks of protein-drug and protein-protein interactions (PPIs) that mediate the development of drug addiction and related neurobiological disorders. There is an urgent need for understanding the molecular mechanisms that underlie drug addiction toward designing novel preventive or therapeutic strategies. The rapidly accumulating data on addictive drugs and their targets as well as advances in machine learning methods and computing technology now present an opportunity to systematically mine existing data and draw inferences on potential new strategies. To this aim, we carried out a comprehensive analysis of cellular pathways implicated in a diverse set of 50 drugs of abuse using quantitative systems pharmacology methods. The analysis of the drug/ligand-target interactions compiled in DrugBank and STITCH databases revealed 142 known and 48 newly predicted targets, which have been further analyzed to identify the KEGG pathways enriched at different stages of drug addiction cycle, as well as those implicated in cell signaling and regulation events associated with drug abuse. Apart from synaptic neurotransmission pathways detected as upstream signaling modules that “sense” the early effects of drugs of abuse, pathways involved in neuroplasticity are distinguished as determinants of neuronal morphological changes. Notably, many signaling pathways converge on important targets such as mTORC1. The latter emerges as a universal effector of the persistent restructuring of neurons in response to continued use of drugs of abuse.

Making a case for constructive reductionism

Borsboom and colleagues argue that reductionism in psychopathology research has not provided the expected insights. Instead, they suggest a systems approach of interacting syndromes, which, however, falls short of a perspective for empirical testing. Here, a combination of both approaches is suggested: a reductionistic empirical approach allowing testability, synergistic with a constructivistic systems appraisal of syndrome networks – a constructive reductionism.

Cocaine Directly Inhibits α6-Containing Nicotinic Acetylcholine Receptors in Human SH-EP1 Cells and Mouse VTA DA Neurons

Alpha6-containing nicotinic acetylcholine receptors are primarily found in neurons of the midbrain dopaminergic (DA) system, suggesting these receptors are potentially involved in drug reward and dependence. Here, we report a novel effect that cocaine directly inhibits α6N/α3Cβ2β3-nAChR (α6*-nAChRs) function. Human α6*-nAChRs were heterologously expressed within cells of the SH-EP1 cell line for functional characterization. Mechanically dissociated DA neurons from mouse ventral tegmental area (VTA) were used as a model of presynaptic α6*-nAChR activation since this method preserves terminal boutons. Patch-clamp recordings in whole-cell configuration were used to measure α6*-nAChR function as well as evaluate the effects of cocaine. In SH-EP1 cells containing heterologously expressed human α6*-nAChRs, cocaine inhibits nicotine-induced inward currents in a concentration-dependent manner with an IC₅₀ value of 30 μM. Interestingly, in the presence of 30 μM cocaine, the maximal current response of the nicotine concentration-response curve is reduced without changing nicotine's EC₅₀ value, suggesting a noncompetitive mechanism. Furthermore, analysis of whole-cell current kinetics demonstrated that cocaine slows nAChR channel activation but accelerates whole-cell current decay time. Our findings demonstrate that cocaine-induced inhibition occurs solely with bath application, but not during intracellular administration, and this inhibition is not use-dependent. Additionally, in Xenopus oocytes, cocaine inhibits both α6N/α3Cβ2β3-nAChRs and α6M211L/α3ICβ2β3-nCAhRs similarly, suggesting that cocaine may not act on the α3 transmembrane domain of chimeric α6N/α3Cβ2β3-nAChR. In mechanically isolated VTA DA neurons, cocaine abolishes α6*-nAChR-mediated enhancement of spontaneous inhibitory postsynaptic currents (sIPSCs). Collectively, these studies provide the first evidence that cocaine directly inhibits the function of both heterologously and naturally expressed α6*-nAChRs. These findings suggest that α6*-nAChRs may provide a novel pharmacological target mediating the effects of cocaine and may underlie a novel mechanism of cocaine reward and dependence.

p11 in Cholinergic Interneurons of the Nucleus Accumbens Is Essential for Dopamine Responses to Rewarding Stimuli

A recent study showed that p11 expressed in cholinergic interneurons (CINs) of the nucleus accumbens (NAc) is a key regulator of depression-like behaviors. Dopaminergic neurons projecting to the NAc are responsible for reward-related behaviors, and their function is impaired in depression. The present study investigated the role of p11 in NAc CINs in dopamine responses to rewarding stimuli. The extracellular dopamine and acetylcholine (ACh) levels in the NAc were determined in freely moving male mice using in vivo microdialysis. Rewarding stimuli (cocaine, palatable food, and female mouse encounter) induced an increase in dopamine efflux in the NAc of wild-type (WT) mice. The dopamine responses were attenuated (cocaine) or abolished (food and female mouse encounter) in constitutive p11 knock-out (KO) mice. The dopamine response to cocaine was accompanied by an increase in ACh NAc efflux, whereas the attenuated dopamine response to cocaine in p11 KO mice was restored by activation of nicotinic or muscarinic ACh receptors in the NAc. Dopamine responses to rewarding stimuli and ACh release in the NAc were attenuated in mice with deletion of p11 from cholinergic neurons (ChAT-p11 cKO mice), whereas gene delivery of p11 to CINs restored the dopamine responses. Furthermore, chemogenetic studies revealed that p11 is required for activation of CINs in response to rewarding stimuli. Thus, p11 in NAc CINs plays a critical role in activating these neurons to mediate dopamine responses to rewarding stimuli. The dysregulation of mesolimbic dopamine system by dysfunction of p11 in NAc CINs may be involved in pathogenesis of depressive states.

A genetically encoded fluorescent acetylcholine indicator for in vitro and in vivo studies

The neurotransmitter acetylcholine (ACh) regulates a diverse array of physiological processes throughout the body. Despite its importance, cholinergic transmission in the majority of tissues and organs remains poorly understood owing primarily to the limitations of available ACh-monitoring techniques. We developed a family of ACh sensors (GACh) based on G-protein-coupled receptors that has the sensitivity, specificity, signal-to-noise ratio, kinetics and photostability suitable for monitoring ACh signals in vitro and in vivo. GACh sensors were validated with transfection, viral and/or transgenic expression in a dozen types of neuronal and non-neuronal cells prepared from multiple animal species. In all preparations, GACh sensors selectively responded to exogenous and/or endogenous ACh with robust fluorescence signals that were captured by epifluorescence, confocal, and/or two-photon microscopy. Moreover, analysis of endogenous ACh release revealed firing-pattern-dependent release and restricted volume transmission, resolving two long-standing questions about central cholinergic transmission. Thus, GACh sensors provide a user-friendly, broadly applicable tool for monitoring cholinergic transmission underlying diverse biological processes.

Varenicline treatment for methamphetamine dependence: A randomized, double-blind phase II clinical trial

BACKGROUND

Previous studies have suggested that varenicline, an α4β2 nicotinic receptor partial agonist, and α7 nicotinic receptor full agonist, may be effective for the treatment of methamphetamine (MA) dependence due to dopaminergic effects, relief of glutamatergic and cognitive dysfunction, and activation of nicotinic cholinergic systems. This study aimed to determine if varenicline (1 mg BID) resulted in reduced methamphetamine use compared to placebo among treatment-seeking MA-dependent volunteers.

METHODS

Treatment-seeking MA-dependent volunteers were randomized to varenicline 1 mg twice daily (n = 27) or placebo (n = 25) and cognitive behavioral therapy for 9 weeks. The primary outcomes were the proportion of participants achieving end-of-treatment-abstinence (EOTA, MA-negative urine specimens during weeks 8 and 9) and the treatment effectiveness score (TES, number of MA-negative urine specimens) for varenicline versus placebo.

RESULTS

There was no significant difference in EOTA between varenicline (15%, 4/27) and placebo (20%, 5/25; p = 0.9). There was some suggestion that urinary confirmed medication compliance corresponded with EOTA in the varenicline condition, though it did not reach statistical significance, OR = 1.57 for a 100 ng/ml increase in urine varenicline, p = 0.10, 95% CI (0.99, 3.02). There was no significant difference in mean TES in the varenicline condition (8.6) compared to the placebo condition (8.1), and treatment condition was not a statistically significant predictor of TES, IRR = 1.01, p = 0.9, 95% CI (0.39, 2.70).

CONCLUSIONS

The results of this study indicate that 1 mg varenicline BID was not an effective treatment for MA dependence among treatment-seeking MA-dependent volunteers.

Restoration of Kv7 Channel-Mediated Inhibition Reduces Cued-Reinstatement of Cocaine Seeking

Cocaine addicts display increased sensitivity to drug-associated cues, due in part to changes in the prelimbic prefrontal cortex (PL-PFC). The cellular mechanisms underlying cue-induced reinstatement of cocaine seeking remain unknown. Reinforcement learning for addictive drugs may produce persistent maladaptations in intrinsic excitability within sparse subsets of PFC pyramidal neurons. Using a model of relapse in male rats, we sampled >600 neurons to examine spike frequency adaptation (SFA) and afterhyperpolarizations (AHPs), two systems that attenuate low-frequency inputs to regulate neuronal synchronization. We observed that training to self-administer cocaine or nondrug (sucrose) reinforcers decreased SFA and AHPs in a subpopulation of PL-PFC neurons. Only with cocaine did the resulting hyperexcitability persist through extinction training and increase during reinstatement. In neurons with intact SFA, dopamine enhanced excitability by inhibiting Kv7 potassium channels that mediate SFA. However, dopamine effects were occluded in neurons from cocaine-experienced rats, where SFA and AHPs were reduced. Pharmacological stabilization of Kv7 channels with retigabine restored SFA and Kv7 channel function in neuroadapted cells. When microinjected bilaterally into the PL-PFC 10 min before reinstatement testing, retigabine reduced cue-induced reinstatement of cocaine seeking. Last, using cFos-GFP transgenic rats, we found that the loss of SFA correlated with the expression of cFos-GFP following both extinction and re-exposure to drug-associated cues. Together, these data suggest that cocaine self-administration desensitizes inhibitory Kv7 channels in a subpopulation of PL-PFC neurons. This subpopulation of neurons may represent a persistent neural ensemble responsible for driving drug seeking in response to cues.SIGNIFICANCE STATEMENT Long after the cessation of drug use, cues associated with cocaine still elicit drug-seeking behavior, in part by activation of the prelimbic prefrontal cortex (PL-PFC). The underlying cellular mechanisms governing these activated neurons remain unclear. Using a rat model of relapse to cocaine seeking, we identified a population of PL-PFC neurons that become hyperexcitable following chronic cocaine self-administration. These neurons show persistent loss of spike frequency adaptation, reduced afterhyperpolarizations, decreased sensitivity to dopamine, and reduced Kv7 channel-mediated inhibition. Stabilization of Kv7 channel function with retigabine normalized neuronal excitability, restored Kv7 channel currents, and reduced drug-seeking behavior when administered into the PL-PFC before reinstatement. These data highlight a persistent adaptation in a subset of PL-PFC neurons that may contribute to relapse vulnerability.

Valium without dependence? Individual GABAA receptor subtype contribution toward benzodiazepine addiction, tolerance, and therapeutic effects

Benzodiazepines are one of the most prescribed medications as first-line treatment of anxiety, insomnia, and epilepsy around the world. Over the past two decades, advances in the neuropharmacological understanding of gamma aminobutyric acid (GABA)_A receptors revealed distinct contributions from each subtype and produced effects. Recent findings have highlighted the importance of α₁ containing GABA_A receptors in the mechanisms of addiction and tolerance in benzodiazepine treatments. This has shown promise in the development of tranquilizers with minimal side effects such as cognitive impairment, dependence, and tolerance. A valium-like drug without its side effects, as repeatedly demonstrated in animals, is achievable.

Extracellular dopamine, acetylcholine, and activation of dopamine D1 and D2 receptors after selective breeding for cocaine self-administration in rats

RATIONALE

The low self-administration (LS)/Kgras (LS) and high self-administration (HS)/Kgras (HS) rat lines were generated by selective breeding for low- and high-intravenous cocaine self-administration, respectively, from a common outbred Wistar stock (Crl:WI). This trait has remained stable after 13 generations of breeding.

OBJECTIVE

The objective of the present study is to compare cocaine preference, neurotransmitter release, and dopamine receptor activation in LS and HS rats.

METHODS

Levels of dopamine, acetylcholine, and cocaine were measured in the nucleus accumbens (NA) shell of HS and LS rats by tandem mass spectrometry of microdialysates. Cocaine-induced locomotor activity and conditioned-place preference were compared between LS and HS rats.

RESULTS

HS rats displayed greater conditioned-place preference scores compared to LS and reduced basal extracellular concentrations of dopamine and acetylcholine. However, patterns of neurotransmitter release did not differ between strains. Low-dose cocaine increased locomotor activity in LS rats, but not in HS animals, while high-dose cocaine augmented activity only in HS rats. Either dose of cocaine increased immunoreactivity for c-Fos in the NA shell of both strains, with greater elevations observed in HS rats. Activation identified by cells expressing both c-Fos and dopamine receptors was generally greater in the HS strain, with a similar pattern for both D1 and D2 dopamine receptors.

CONCLUSIONS

Diminished levels of dopamine and acetylcholine in the NA shell, with enhanced cocaine-induced expression of D1 and D2 receptors, are associated with greater rewarding effects of cocaine in HS rats and an altered dose-effect relationship for cocaine-induced locomotor activity.

The role of the intrinsic cholinergic system of the striatum: What have we learned from TAN recordings in behaving animals?

Cholinergic interneurons provide rich local innervation of the striatum and play an important role in controlling behavior, as evidenced by the variety of movement and psychiatric disorders linked to disrupted striatal cholinergic transmission. Much progress has been made in recent years regarding our understanding of how these interneurons contribute to the processing of information in the striatum. In particular, investigation of the activity of presumed striatal cholinergic interneurons, identified as tonically active neurons or TANs in behaving animals, has pointed to their role in the signaling and learning of the motivational relevance of environmental stimuli. Although the bulk of this work has been conducted in monkeys, several studies have also been carried out in behaving rats, but information remains rather disparate across studies and it is still questionable whether rodent TANs correspond to TANs described in monkeys. Consequently, our current understanding of the function of cholinergic transmission in the striatum is challenged by the rapidly growing, but often confusing literature on the relationship between TAN activity and specific behaviors. As regards the precise nature of the information conveyed by the cholinergic TANs, a recent influential view emphasized that these local circuit neurons may play a special role in the processing of contextual information that is important for reinforcement learning and selection of appropriate actions. This review provides a summary of recent progress in TAN physiology from which it is proposed that striatal cholinergic interneurons are crucial elements for flexible switching of behaviors under changing environmental conditions.

Accumbal Cholinergic Interneurons Differentially Influence Motivation Related to Satiety Signaling

Satiety, rather than all or none, can instead be viewed as a cumulative decrease in the drive to eat that develops over the course of a meal. The nucleus accumbens (NAc) is known to play a critical role in this type of value reappraisal, but the underlying circuits that influence such processes are unclear. Although NAc cholinergic interneurons (CINs) comprise only a small proportion of NAc neurons, their local impact on reward-based processes provides a candidate cell population for investigating the neural underpinnings of satiety. The present research therefore aimed to determine the role of NAc-CINs in motivation for food reinforcers in relation to satiety signaling. Through bidirectional control of CIN activity in mice, we show that when motivated by food restriction, increasing CIN activity led to a reduction in palatable food consumption while reducing CIN excitability enhanced food intake. These activity-dependent changes developed only late in the session and were unlikely to be driven by the innate reinforcer strength, suggesting that CIN modulation was instead impacting the cumulative change in motivation underlying satiety signaling. We propose that on a circuit level, an overall increase in inhibitory tone onto NAc output neurons played a role in the behavioral results, as activating NAc-CINs led to an inhibition of medium spiny neurons that was dependent on nicotinic receptor activation. Our results reveal an important role for NAc-CINs in controlling motivation for food intake and additionally provide a circuit-level framework for investigating the endogenous cholinergic circuits that signal satiety.