Nicotine stimulation on extracellular glutamate levels in the nucleus accumbens of ethanol-withdrawn rats in vivo

Investigating Behavioral and Neuronal Changes in Adolescent Mice Following Prenatal Exposure to Electronic Cigarette (E-Cigarette) Vapor Containing Nicotine

A substantial percentage of pregnant smokers stop using traditional cigarettes and switch to alternative nicotine-related products such as e-cigarettes. Prenatal exposure to tobacco increases the risk of psychiatric disorders in children. Adolescence is a complex phase in which higher cognitive and emotional processes undergo maturation and refinement. In this study, we examined the behavioral and molecular effects of first-trimester prenatal exposure to e-cigarettes. Adult female mice were divided into normal air, vehicle, and 2.5%-nicotine-exposed groups. Our analyses indicated that the adolescents in the 2.5%-nicotine-exposed group exhibited a significant lack of normal digging behavior, elevated initial sucrose intake, and reduced recognition memory. Importantly, we identified a substantial level of nicotine self-administration in the 2.5%-nicotine-exposed group. At a molecular level, the mRNAs of metabotropic glutamate receptors and transporters in the nucleus accumbens were not altered. This previously undescribed work indicates that prenatal exposure to e-cigarettes might increase the risk of nicotine addiction during adolescence, reduce cognitive capacity, and alter normal adolescent behavior. The outcome will aid in translating research and assist healthcare practitioners in tackling addiction and mental issues caused by toxicological exposure. Further, it will inform relevant policymaking, such as recommended taxation, labeling e-cigarette devices with more detailed neurotoxic effects, and preventing their sale to pregnant women and adolescents.

Medication overuse headache and substance use disorder: A comparison based on basic research and neuroimaging

It has yet to be determined whether medication overuse headache (MOH) is an independent disorder or a combination of primary headache and substance addiction. To further explore the causes of MOH, we compared MOH with substance use disorder (SUD) in terms of the brain regions involved to draw more targeted conclusions. In this review, we selected alcohol use disorder (AUD) as a representative SUD and compared MOH and AUD from two aspects of neuroimaging and basic research. We found that in neuroimaging studies, there were many overlaps between AUD and MOH in the reward circuit, but the extensive cerebral cortex damage in AUD was more serious than that in MOH. This difference was considered to reflect the sensitivity of the cortex structure to alcohol damage. In future research, we will focus on the central amygdala (CeA), prefrontal cortex (PFC), orbital-frontal cortex (OFC), hippocampus, and other brain regions for interventions, which may have unexpected benefits for addiction and headache symptoms in MOH patients.

The Homer1 family of proteins at the crossroad of dopamine-glutamate signaling: An emerging molecular "Lego" in the pathophysiology of psychiatric disorders. A systematic review and translational insight

Once considered only scaffolding proteins at glutamatergic postsynaptic density (PSD), Homer1 proteins are increasingly emerging as multimodal adaptors that integrate different signal transduction pathways within PSD, involved in motor and cognitive functions, with putative implications in psychiatric disorders. Regulation of type I metabotropic glutamate receptor trafficking, modulation of calcium signaling, tuning of long-term potentiation, organization of dendritic spines' growth, as well as meta- and homeostatic plasticity control are only a few of the multiple endocellular and synaptic functions that have been linked to Homer1. Findings from preclinical studies, as well as genetic studies conducted in humans, suggest that both constitutive (Homer1b/c) and inducible (Homer1a) isoforms of Homer1 play a role in the neurobiology of several psychiatric disorders, including psychosis, mood disorders, neurodevelopmental disorders, and addiction. On this background, Homer1 has been proposed as a putative novel target in psychopharmacological treatments. The aim of this review is to summarize and systematize the growing body of evidence on Homer proteins, highlighting the role of Homer1 in the pathophysiology and therapy of mental diseases.

Genetic variation in alcoholism and opioid addiction susceptibility and treatment: a pharmacogenomic approach

<abstract> <p>Alcohol and opioid abuse have pervasive and detrimental consequences from the individual to societal level. The extent of genetic contribution to alcoholism has been studied for decades, yielding speculative and often inconsistent results since the previous discovery of two pharmacokinetic variants strongly protective against alcoholism. The neurobiology of addiction involves innumerate genes with combinatorial and epistatic interactions, creating a difficult landscape for concrete conclusions. In contrast, pharmacogenomic variation in the treatment of alcoholism yields more immediate clinical utility, while also emphasizing pathways crucial to the progression of addiction. An improved understanding of genetic predisposition to alcohol abuse has inherent significance for opioid addiction and treatment, as the two drugs induce the same reward pathway. This review outlines current knowledge, treatments, and research regarding genetic predisposition to alcoholism, focusing on pharmacodynamic variation within the dopaminergic system and shared implications for opioid abuse. Multifaceted and highly polygenic, the phenotype of addiction seems to grow more complex as new research extends the scope of its impact on the brain, body, and progeny.</p> </abstract>

Role of glutamatergic system and mesocorticolimbic circuits in alcohol dependence

Emerging evidence demonstrates that alcohol dependence is associated with dysregulation of several neurotransmitters. Alterations in dopamine, glutamate and gamma-aminobutyric acid release are linked to chronic alcohol exposure. The effects of alcohol on the glutamatergic system in the mesocorticolimbic areas have been investigated extensively. Several studies have demonstrated dysregulation in the glutamatergic systems in animal models exposed to alcohol. Alcohol exposure can lead to an increase in extracellular glutamate concentrations in mesocorticolimbic brain regions. In addition, alcohol exposure affects the expression and functions of several glutamate receptors and glutamate transporters in these brain regions. In this review, we discussed the effects of alcohol exposure on glutamate receptors, glutamate transporters and glutamate homeostasis in each area of the mesocorticolimbic system. In addition, we discussed the genetic aspect of alcohol associated with glutamate and reward circuitry. We also discussed the potential therapeutic role of glutamate receptors and glutamate transporters in each brain region for the treatment of alcohol dependence. Finally, we provided some limitations on targeting the glutamatergic system for potential therapeutic options for the treatment alcohol use disorders.

Peri-adolescent drinking of ethanol and/or nicotine modulates astroglial glutamate transporters and metabotropic glutamate receptor-1 in female alcohol-preferring rats

Impairment in glutamate neurotransmission mediates the development of dependence upon nicotine (NIC) and ethanol (EtOH). Previous work indicates that continuous access to EtOH or phasic exposure to NIC reduces expression of the glutamate transporter-1 (GLT-1) and cystine/glutamate antiporter (xCT) but not the glutamate/aspartate transporter (GLAST). Additionally, metabotropic glutamate receptors (mGluRs) expression was affected following exposure to EtOH or NIC. However, little is known about the effects of EtOH and NIC co-consumption on GLT-1, xCT, GLAST, and mGluR1 expression. In this study, peri-adolescent female alcohol preferring (P) rats were given binge-like access to water, sucrose (SUC), SUC-NIC, EtOH, or EtOH-NIC for four weeks. The present study determined the effects of these reinforcers on GLT-1, xCT, GLAST, and mGluR1 expression in the nucleus accumbens (NAc), hippocampus (HIP) and prefrontal cortex (PFC). GLT-1 and xCT expression were decreased in the NAc following both SUC-NIC and EtOH-NIC. In addition, only xCT expression was downregulated in the HIP in both of these latter groups. Also, glutathione peroxidase (GPx) activity in the HIP was reduced following SUC, SUC-NIC, EtOH, and EtOH-NIC consumption. Similar to previous work, GLAST expression was not altered in any brain region by any of the reinforcers. However, mGluR1 expression was increased in the NAc in the SUC-NIC, EtOH, and EtOH-NIC groups. These results indicate that peri-adolescent binge-like drinking of EtOH or SUC with or without NIC may exert differential effects on astroglial glutamate transporters and receptors. Our data further parallel some of the previous findings observed in adult rats.

Influence of Volatile Anesthesia on the Release of Glutamate and other Amino Acids in the Nucleus Accumbens in a Rat Model of Alcohol Withdrawal: A Pilot Study

Background

Alcohol withdrawal syndrome is a potentially life-threatening condition, which can occur when patients with alcohol use disorders undergo general anesthesia. Excitatory amino acids, such as glutamate, act as neurotransmitters and are known to play a key role in alcohol withdrawal syndrome. To understand this process better, we investigated the influence of isoflurane, sevoflurane, and desflurane anesthesia on the profile of excitatory and inhibitory amino acids in the nucleus accumbens (NAcc) of alcohol-withdrawn rats (AWR).

Methods

Eighty Wistar rats were randomized into two groups of 40, pair-fed with alcoholic or non-alcoholic nutrition. Nutrition was withdrawn and microdialysis was performed to measure the activity of amino acids in the NAcc. The onset time of the withdrawal syndrome was first determined in an experiment with 20 rats. Sixty rats then received isoflurane, sevoflurane, or desflurane anesthesia for three hours during the withdrawal period, followed by one hour of elimination. Amino acid concentrations were measured using chromatography and results were compared to baseline levels measured prior to induction of anesthesia.

Results

Glutamate release increased in the alcohol group at five hours after the last alcohol intake (p = 0.002). After 140 min, desflurane anesthesia led to a lower release of glutamate (p < 0.001) and aspartate (p = 0.0007) in AWR compared to controls. GABA release under and after desflurane anesthesia was also significantly lower in AWR than controls (p = 0.023). Over the course of isoflurane anesthesia, arginine release decreased in AWR compared to controls (p < 0.001), and aspartate release increased after induction relative to controls (p_20min = 0.015 and p_40min = 0.006). However, amino acid levels did not differ between the groups as a result of sevoflurane anesthesia.

Conclusions

Each of three volatile anesthetics we studied showed different effects on excitatory and inhibitory amino acid concentrations. Under desflurane anesthesia, both glutamate and aspartate showed a tendency to be lower in AWR than controls over the whole timecourse. The inhibitory amino acid arginine increased in AWR compared to controls, whereas GABA levels decreased. However, there were no significant differences in amino acid concentrations under or after sevoflurane anesthesia. Under isoflurane, aspartate release increased in AWR following induction, and from 40 min to 140 min arginine release in controls was elevated. The precise mechanisms through which each of the volatile anesthetics affected amino acid concentrations are still unclear and further experimental research is required to draw reliable conclusions.

Interactions between nicotine and drugs of abuse: a review of preclinical findings

Polysubstance abuse is common among substance-use disorder patients, and nicotine is one of the most commonly co-used substances. Epidemiological and clinical laboratory studies suggest that nicotine, when combined with other drugs of abuse, increases intake of one or both substances. This review focuses on the preclinical literature regarding nicotine's interaction with alcohol, stimulants (i.e., cocaine, amphetamines), opioids (i.e., morphine, heroin), and Δ⁹-tetrahydrocannabinol (THC). The current understanding of how these various classes of abused drugs may interact with nicotine on behavioral, physiological, and pharmacological indices that may be important in maintaining co-use of one or both substances in human populations are highlighted. Suggestions as to future areas of research and gaps in knowledge are offered.

Role of astrocytic glutamate transporter in alcohol use disorder

Alcohol use disorder (AUD) is one of the most widespread neuropsychiatric conditions, having a significant health and socioeconomic impact. According to the 2014 World Health Organization global status report on alcohol and health, the harmful use of alcohol is responsible for 5.9% of all deaths worldwide. Additionally, 5.1% of the global burden of disease and injury is ascribed to alcohol (measured in disability adjusted life years, or disability adjusted life years). Although the neurobiological basis of AUD is highly complex, the corticostriatal circuit contributes significantly to the development of addictive behaviors. In-depth investigation into the changes of the neurotransmitters in this circuit, dopamine, gamma-aminobutyricacid, and glutamate, and their corresponding neuronal receptors in AUD and other addictions enable us to understand the molecular basis of AUD. However, these discoveries have also revealed a dearth of knowledge regarding contributions from non-neuronal sources. Astrocytes, though intimately involved in synaptic function, had until recently been noticeably overlooked in their potential role in AUD. One major function of the astrocyte is protecting neurons from excitotoxicity by removing glutamate from the synapse via excitatory amino acid transporter type 2. The importance of this key transporter in addiction, as well as ethanol withdrawal, has recently become evident, though its regulation is still under investigation. Historically, pharmacotherapy for AUD has been focused on altering the activity of neuronal glutamate receptors. However, recent clinical evidence has supported the animal-based findings, showing that regulating glutamate homeostasis contributes to successful management of recovery from AUD.

Targeting glutamate homeostasis for potential treatment of nicotine dependence

Several studies demonstrated that impairment in glutamatergic neurotransmission is linked to drug dependence and drug-seeking behavior. Increased extracellular glutamate concentration in mesocorticolimbic regions has been observed in animals developing nicotine dependence. Changes in glutamate release might be associated with stimulatory effect of nicotinic acetylcholine receptors (nAChRs) via nicotine exposure. We and others have shown increased extracellular glutamate concentration, which was associated with down regulation of the major glutamate transporter, glutamate transporter 1 (GLT-1), in brain reward regions of animals exposed to drug abuse, including nicotine and ethanol. Importantly, studies from our laboratory and others showed that upregulation of GLT-1 expression in the mesocorticolimbic brain regions may have potential therapeutic effects in drug dependence. In this review article, we discussed the effect of antagonizing presynaptic nAChRs in glutamate release, the upregulatory effect in GLT-1 expression and the role of glutamate receptors antagonists in the treatment of nicotine dependence.

Effects of ethanol exposure and withdrawal on dendritic morphology and spine density in the nucleus accumbens core and shell

Exposure to drugs of abuse can result in profound structural modifications on neurons in circuits involved in addiction that may contribute to drug dependence, withdrawal and related processes. Structural alterations on medium spiny neurons (MSNs) of the nucleus accumbens (NAc) have been observed following exposure to and withdrawal from a variety of drugs; however, relatively little is known about the effects of alcohol exposure and withdrawal on structural alterations of NAc MSNs. In the present study male rats were chronically exposed to vaporized ethanol for 10 days and underwent 1 or 7 days of withdrawal after which the brains were processed for Golgi-Cox staining and analysis of dendritic length, branching and spine density. MSNs of the NAc shell and core underwent different patterns of changes following ethanol exposure and withdrawal. At 1 day of withdrawal there were modest reductions in the dendritic length and branching of MSNs in both the core and the shell compared to control animals exposed only to air. At 7 days of withdrawal the length and branching of shell MSNs was reduced, whereas the length and branching of core MSNs were increased relative to the shell. The density of mature spines was increased in the core at 1 day of withdrawal, whereas the density of less mature spines was increased in both regions at 7 days of withdrawal. Collectively, these observations indicate that MSNs of the NAc core and shell undergo distinct patterns of structural modifications following ethanol exposure and withdrawal suggesting that modifications in dendritic structure in these regions may contribute differentially to ethanol withdrawal.

Effects of the beta-lactam antibiotic ceftriaxone on nicotine withdrawal and nicotine-induced reinstatement of preference in mice

RATIONALE

Several studies suggest that repeated nicotine administration causes alterations in glutaminergic transmission that may play an important role in developing and maintaining nicotine addiction. Chronic nicotine administration in rats decreases the expression of the glutamate transporter-1 (GLT-1) and cysteine-glutamate exchanger (system xC-) in the nucleus accumbens. We hypothesized that ceftriaxone, a GLT-1 and system xC- activator, would decrease murine behavioral aspects of nicotine dependence.

OBJECTIVE

This study aimed to investigate the effect of repeated ceftriaxone administration on the behavioral effects of nicotine using mouse models of conditioned reward and withdrawal.

METHOD

Using male ICR mice, the ability of repeated ceftriaxone injections to modulate the development and reinstatement of a nicotine-conditioned place preference (CPP) was evaluated. Additionally, nicotine withdrawal-associated signs were assessed. These included both physical (somatic signs and hyperalgesia) and affective (anxiety-related behaviors) withdrawal signs in mice. Finally, the effects of ceftriaxone on nicotine-induced antinociception and hypothermia after acute nicotine injection were measured.

RESULT

Ceftriaxone had no effect on the development of nicotine preference but significantly attenuated nicotine-induced reinstatement of CPP. Furthermore, ceftriaxone reversed all nicotine withdrawal signs measured in mice.

CONCLUSION

Altogether, these findings show that a β-lactam antibiotic reduces nicotine withdrawal and nicotine-seeking behavior. Our results suggest that the documented efficacy of ceftriaxone against cocaine and morphine dependence-related behaviors effects extends to nicotine.

Ethanol-induced alterations of amino acids measured by in vivo microdialysis in rats: a meta-analysis

PURPOSE

In recent years in vivo microdialysis has become an important method in research studies investigating the alterations of neurotransmitters in the extracellular fluid of the brain. Based on the major involvement of glutamate and γ-aminobutyric acid (GABA) in mediating a variety of alcohol effects in the mammalian brain, numerous microdialysis studies have focused on the dynamical behavior of these systems in response to alcohol.

METHODS

Here we performed multiple meta-analyses on published datasets from the rat brain: (i) we studied basal extracellular concentrations of glutamate and GABA in brain regions that belong to a neurocircuitry involved in neuropsychiatric diseases, especially in alcoholism (Noori et al., Addict Biol 17:827-864, 2012); (ii) we examined the effect of acute ethanol administration on glutamate and GABA levels within this network and (iii) we studied alcohol withdrawal-induced alterations in glutamate and GABA levels within this neurocircuitry.

RESULTS

For extraction of basal concentrations of these neurotransmitters, datasets of 6932 rats were analyzed and the absolute basal glutamate and GABA levels were estimated for 18 different brain sites. In response to different doses of acute ethanol administration, datasets of 529 rats were analyzed and a non-linear dose response (glutamate and GABA release) relationship was observed in several brain sites. Specifically, glutamate in the nucleus accumbens shows a decreasing logarithmic dose response curve. Finally, regression analysis of 11 published reports employing brain microdialysis experiments in 104 alcohol-dependent rats reveals very consistent augmented extracellular glutamate and GABA levels in various brain sites that correlate with the intensity of the withdrawal response were identified.

CONCLUSIONS

In summary, our results provide standardized basal values for future experimental and in silico studies on neurotransmitter release in the rat brain and may be helpful to understand the effect of ethanol on neurotransmitter release. Furthermore, this study illustrates the benefit of meta-analyses using the generalization of a wide range of preclinical data.

Involvement of metabotropic glutamate receptor 5 in brain reward deficits associated with cocaine and nicotine withdrawal and somatic signs of nicotine withdrawal

RATIONALE

The involvement of metabotropic glutamate 5 (mGlu5) receptors has been suggested in the reinforcing effects of psychostimulants. However, little is known about the role of these receptors in psychostimulant withdrawal.

OBJECTIVES

The role of mGlu5 receptors was assessed in the anhedonic and somatic aspects of psychostimulant withdrawal.

METHODS

Anhedonia was assessed with the discrete-trial current-intensity intracranial self-stimulation (ICSS) procedure after the termination of cocaine (180 mg kg(-1) day(-1), salt, 3 days, i.p.) or nicotine (40 mg kg(-1) day(-1), base, 28 days, s.c.) administration via osmotic minipumps in mGlu5 receptor knockout (mGluR5(-/-)) and wild-type (mGluR5(+/+)) mice. Somatic signs were assessed during nicotine withdrawal. The effects of the nicotinic acetylcholine receptor antagonist mecamylamine on ICSS thresholds were assessed during chronic nicotine administration.

RESULTS

Nicotine-treated mGluR5(+/+) and mGluR5(-/-) mice demonstrated similar threshold elevations during mecamylamine-precipitated withdrawal compared with their saline-treated counterparts. During spontaneous nicotine and cocaine withdrawal, thresholds in drug-withdrawing mGluR5(+/+), but not mGluR5(-/-), mice were elevated up to 72 h of nicotine/cocaine withdrawal and then returned to baseline, indicating attenuation of withdrawal-induced anhedonia in mGluR5(-/-) mice. Nicotine-withdrawing mGluR5(+/+), but not mGluR5(-/-), mice showed increases in somatic signs compared with saline-treated counterparts.

CONCLUSIONS

mGlu5 receptor null mutation attenuates the anhedonic and somatic effects of psychostimulant withdrawal. This attenuated withdrawal in mGluR5(-/-) mice may result from the lack of drug-induced adaptations in mGlu5 receptor function that may occur in mGluR5(+/+) mice with chronic drug administration. Thus, these results suggest the involvement of mGlu5 receptors in psychostimulant dependence and the mediation of the anhedonic and somatic signs of psychostimulant withdrawal.

Homers regulate drug-induced neuroplasticity: implications for addiction

Drug addiction is a chronic, relapsing disorder, characterized by an uncontrollable motivation to seek and use drugs. Converging clinical and preclinical observations implicate pathologies within the corticolimbic glutamate system in the genetic predisposition to, and the development of, an addicted phenotype. Such observations pose cellular factors regulating glutamate transmission as likely molecular candidates in the etiology of addiction. Members of the Homer family of proteins regulate signal transduction through, and the trafficking of, glutamate receptors, as well as maintain and regulate extracellular glutamate levels in corticolimbic brain regions. This review summarizes the existing data implicating the Homer family of protein in acute behavioral and neurochemical sensitivity to drugs of abuse, the development of drug-induced neuroplasticity, as well as other behavioral and cognitive pathologies associated with an addicted state.

Glutamatergic substrates of drug addiction and alcoholism

The past two decades have witnessed a dramatic accumulation of evidence indicating that the excitatory amino acid glutamate plays an important role in drug addiction and alcoholism. The purpose of this review is to summarize findings on glutamatergic substrates of addiction, surveying data from both human and animal studies. The effects of various drugs of abuse on glutamatergic neurotransmission are discussed, as are the effects of pharmacological or genetic manipulation of various components of glutamate transmission on drug reinforcement, conditioned reward, extinction, and relapse-like behavior. In addition, glutamatergic agents that are currently in use or are undergoing testing in clinical trials for the treatment of addiction are discussed, including acamprosate, N-acetylcysteine, modafinil, topiramate, lamotrigine, gabapentin and memantine. All drugs of abuse appear to modulate glutamatergic transmission, albeit by different mechanisms, and this modulation of glutamate transmission is believed to result in long-lasting neuroplastic changes in the brain that may contribute to the perseveration of drug-seeking behavior and drug-associated memories. In general, attenuation of glutamatergic transmission reduces drug reward, reinforcement, and relapse-like behavior. On the other hand, potentiation of glutamatergic transmission appears to facilitate the extinction of drug-seeking behavior. However, attempts at identifying genetic polymorphisms in components of glutamate transmission in humans have yielded only a limited number of candidate genes that may serve as risk factors for the development of addiction. Nonetheless, manipulation of glutamatergic neurotransmission appears to be a promising avenue of research in developing improved therapeutic agents for the treatment of drug addiction and alcoholism.