N-acetylcysteine yields sex-specific efficacy for cue-induced reinstatement of nicotine seeking

Chronic N-acetyl cysteine treatment does not improve respiratory system performance in the mdx mouse model of Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is characterised by respiratory muscle injury, inflammation, fibrosis and weakness, ultimately culminating in respiratory failure. The dystrophin-deficient mouse model of DMD (mdx) shows evidence of respiratory muscle remodelling and dysfunction contributing to impaired respiratory system performance. The antioxidant N-acetylcysteine (NAC) has been shown to exert anti-inflammatory and anti-fibrotic effects leading to improved respiratory muscle performance in a range of animal models of muscle dysfunction, including mdx mice, following short-term administration (2 weeks). We sought to build on previous work by exploring the effects of chronic NAC administration (3 months) on respiratory system performance in mdx mice. One-month-old male mdx mice were randomised to receive normal drinking water (n = 30) or 1% NAC in the drinking water (n = 30) for 3 months. At 4 months of age, we assessed breathing in conscious mice by plethysmography followed by ex vivo assessment of diaphragm force-generating capacity. Additionally, diaphragm histology was performed. In separate studies, in anaesthetised mice, respiratory electromyogram (EMG) activity and inspiratory pressure across a range of behaviours were determined, including assessment of peak inspiratory pressure-generating capacity. NAC treatment did not affect force-generating capacity of the mdx diaphragm. Collagen content and immune cell infiltration were unchanged in mdx + NAC compared with mdx diaphragms. Additionally, there was no significant effect of NAC on breathing, ventilatory responsiveness, inspiratory EMG activity or inspiratory pressure across the range of behaviours from basal conditions to peak system performance. We conclude that chronic NAC treatment has no apparent beneficial effects on respiratory system performance in the mdx mouse model of DMD suggesting limited potential of NAC treatment alone for human DMD.

The importance of translationally evaluating steroid hormone contributions to substance use

Clinically, women appear to be more susceptible to certain aspects of substance use disorders (SUDs). The steroid hormones 17β-estradiol (E2) and progesterone (Pg) have been linked to women-specific drug behaviors. Here, we review clinical and preclinical studies investigating how cycling ovarian hormones affect nicotine-, cocaine-, and opioid-related behaviors. We also highlight gaps in the literature regarding how synthetic steroid hormone use may influence drug-related behaviors. In addition, we explore how E2 and Pg are known to interact in brain reward pathways and provide evidence of how these interactions may influence drug-related behaviors. The synthesis of this review demonstrates the critical need to study women-specific factors that may influence aspects of SUDs, which may play important roles in addiction processes in a sex-specific fashion. It is important to understand factors that impact women's health and may be key to moving the field forward toward more efficacious and individualized treatment strategies.

Relapse to cotinine seeking in rats: differential effects of sex

Relapse is a defining feature of smoking and a significant challenge in cessation management. Elucidation of novel factors underlying relapse may inform future treatments. Cotinine, the major metabolite of nicotine, has been shown to support intravenous self-administration in rats, implicating it as one potential factor contributing to nicotine reinforcement. However, it remains unknown whether cotinine would induce relapse-like behaviors. The current study investigated relapse to cotinine seeking in two relapse models, the reinstatement of drug seeking and incubation of drug craving models. In the reinstatement model, rats were trained to self-administer cotinine, underwent extinction of cotinine-associated responses, and were tested for cue-, drug-, or stress-induced reinstatement. Conditioned cues associated with cotinine self-administration, cotinine (1-2 mg/kg), or the pharmacological stressor yohimbine (1.25-2.5 mg/kg) induced reinstatement of cotinine seeking. Female rats displayed more pronounced cue-induced, but not drug- or stress-induced reinstatement than male rats. In the incubation of the craving model, rats were trained to self-administer cotinine and underwent forced withdrawal in home cages. Rats were tested for cue-induced cotinine-seeking on both withdrawal day 1 and withdrawal day 18. Rats exhibited greater cue-induced cotinine-seeking on withdrawal day 18 compared to withdrawal day 1, with no difference between male and female rats. These findings indicate that cotinine induces sex-specific relapse to drug seeking in rats, suggesting that cotinine may contribute to relapse.

Logical fallacies and misinterpretations that hinder progress in translational addiction neuroscience

Substance use disorders (SUDs) are heterogeneous and complex, making the development of translationally predictive rodent and nonhuman primate models to uncover their neurobehavioral underpinnings difficult. Neuroscience-focused outcomes have become highly prevalent, and with this, the notion that SUDs are disorders of the brain embraced as a dominant theoretical orientation to understand SUD etiology and treatment. These efforts, however, have led to few efficacious pharmacotherapies, and in some cases (as with cocaine or methamphetamine), no pharmacotherapies have translated from preclinical models for clinical use. In this theoretical commentary, we first describe the development of animal models of substance use behaviors from a historical perspective. We then define and discuss three logical fallacies including 1) circular explanation, 2) affirming the consequent, and 3) reification that can apply to developed models. We then provide three case examples in which conceptual or logical issues exist in common methods (i.e., behavioral economic demand, escalation, and reinstatement). Alternative strategies to refocus behavioral models are suggested for the field to better bridge the translational divide between animal models, the clinical condition of SUDs, and current and future regulatory pathways for intervention development.

Sex Differences in Opioid and Psychostimulant Craving and Relapse: A Critical Review

A widely held dogma in the preclinical addiction field is that females are more vulnerable than males to drug craving and relapse. Here, we first review clinical studies on sex differences in psychostimulant and opioid craving and relapse. Next, we review preclinical studies on sex differences in psychostimulant and opioid reinstatement of drug seeking after extinction of drug self-administration, and incubation of drug craving (time-dependent increase in drug seeking during abstinence). We also discuss ovarian hormones' role in relapse and craving in humans and animal models and speculate on brain mechanisms underlying their role in cocaine craving and relapse in rodent models. Finally, we discuss imaging studies on brain responses to cocaine cues and stress in men and women.The results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. However, this conclusion is tentative because most of the studies reviewed were correlational, not sufficiently powered, and not a priori designed to detect sex differences. Additionally, imaging studies suggest sex differences in brain responses to cocaine cues and stress. The results of the preclinical studies reviewed provide evidence for sex differences in stress-induced reinstatement and incubation of cocaine craving but not cue- or cocaine-induced reinstatement of cocaine seeking. These sex differences are modulated in part by ovarian hormones. In contrast, the available data do not support the notion of sex differences in craving and relapse/reinstatement for methamphetamine or opioids in rodent models. SIGNIFICANCE STATEMENT: This systematic review summarizes clinical and preclinical studies on sex differences in psychostimulant and opioid craving and relapse. Results of the clinical studies reviewed do not appear to support the notion that women are more vulnerable to psychostimulant and opioid craving and relapse. Results of preclinical studies reviewed provide evidence for sex differences in reinstatement and incubation of cocaine seeking but not for reinstatement or incubation of methamphetamine or opioid seeking.

The Potential of N-Acetyl-L-Cysteine (NAC) in the Treatment of Psychiatric Disorders

N-acetyl-L-cysteine (NAC) is a compound of increasing interest in the treatment of psychiatric disorders. Primarily through its antioxidant, anti-inflammatory, and glutamate modulation activity, NAC has been investigated in the treatment of neurodevelopmental disorders, schizophrenia spectrum disorders, bipolar-related disorders, depressive disorders, anxiety disorders, obsessive compulsive-related disorders, substance-use disorders, neurocognitive disorders, and chronic pain. Whilst there is ample preclinical evidence and theoretical justification for the use of NAC in the treatment of multiple psychiatric disorders, clinical trials in most disorders have yielded mixed results. However, most studies have been underpowered and perhaps too brief, with some evidence of benefit only after months of treatment with NAC. Currently NAC has the most evidence of having a beneficial effect as an adjuvant agent in the negative symptoms of schizophrenia, severe autism, depression, and obsessive compulsive and related disorders. Future research with well-powered studies that are of sufficient length will be critical to better understand the utility of NAC in the treatment of psychiatric disorders.

N-Acetylcysteine provides limited efficacy as treatment option for skin picking in Prader-Willi syndrome

Prader-Willi syndrome (PWS) is a rare neurodevelopmental disorder based on a loss of paternally expressed genes in chromosome region 15q11-13. In addition to typical characteristics such as hyperphagia, PWS is evidenced by a certain behavioral phenotype. Common indicators are repetitive behaviors, temper tantrums, and self-injurious behaviors such as skin- and/or rectal picking. N-Acetylcysteine (NAC) was previously described as a promising therapeutic option for skin picking in PWS. In this case series, we retrospectively investigated the effect of pharmacotherapy with NAC in 14 individuals with PWS suffering from skin- and/or rectal picking. Treatment success was determined using the Clinical Global Impression-Improvement scale (CGI-I). The Clinical Global Impression-Efficacy index (CGI-EI) was used to put treatment success and side effects into perspective. Six of fourteen patients, all of which were female, showed improvement in symptoms (dosage 1800-2400 mg/day), whereas six patients did not show any change during treatment. Moreover, two male patients treated for solitary rectal picking showed new onset of skin picking. Across all cases, a CGI-I of 3 (corresponding to minimal improvement) was seen after 3 months of treatment, with a CGI-EI of 1.6 (corresponding to moderate efficacy). NAC remains a reasonable therapeutic option in certain cases of skin picking in PWS but provides only limited efficacy compared to previous studies on the topic. There was a higher rate of adverse drug reactions than previously reported. The results particularly suggest caution in future treatment in individuals with solitary rectal picking and reduced efficacy when coadministered with neuroleptics.

Natural and synthetic estrogens specifically alter nicotine demand and cue-induced nicotine seeking in female rats

Women have more difficulty maintaining smoking cessation than men, and experience greater withdrawal symptomatology as well as higher prevalence of relapse. Further, currently available treatments for smoking cessation, such as the nicotine patch and varenicline, have been shown to be less effective in women. Fluctuations in ovarian hormones across the menstrual cycle can affect craving and smoking relapse propensity. In addition, many women who smoke use some form of oral contraceptives, which most often contain ethinyl estradiol (EE), a synthetic, orally bio-available estrogen that is currently prescribed to women chronically and has been shown to alter smoking reward in women. The current study examined the impact of 17β-estradiol (E2), the prominent endogenous form of the steroid hormone estrogen, as well as EE, on nicotine self-administration, demand, and reinstatement following ovariectomy (OVX) or sham surgery. OVX vehicle-treated female rats consumed less nicotine, had lower intensity of demand, and reinstated less compared to sham vehicle-treated female rats. OVX-E2 and OVX-EE treatment groups showed a rebound of nicotine intake later in training, and Q₀ levels of consumption were partially rescued in both groups. Further, E2 but not EE reversed the abolishment of reinstated nicotine seeking induced by OVX. Taken together, these results demonstrate that natural and synthetic estrogens play a critical role in mediating the neurobehavioral effects of nicotine, and future studies are essential for our understanding of how synthetic hormones contained within oral contraceptives interact with smoking.

Strain and sex matters: Differences in nicotine self-administration between outbred and recombinase-driver transgenic rat lines

Preclinical studies of nicotine self-administration provide important value for the field as they are highly rigorous, controlled, can be conducted quickly, and are generalizable to humans. Given the translational value of the nicotine self-administration model, and the relatively new guidelines of the National Institutes of Health to include sex as a biological variable, strain and sex differences in nicotine acquisition were examined here in two outbred rat strains. Sprague-Dawley (SD) and Long-Evans (LE; wildtype and cholinergic acetyltransferase cre-recombinase transgenic) rats of each sex were implanted with indwelling intravenous jugular catheters. Rats were trained to self-administer nicotine (0.02 mg/kg per infusion, paired with contingent light + tone stimuli). Acquisition criteria were set at a minimum active:inactive response ratio of 2:1 and a minimum of 10 infusions per session, both of which had to be met for a minimum of 10 sessions. Across 10 sessions, male SD rats self-administered significantly more nicotine than female SD rats (p < .05), indicating a sex difference in this strain. LE females self-administered more nicotine than SD females indicative of a strain difference between females (p < .05). SD males increased nicotine infusions across sessions compared to LE males and SD females (p < .05). No strain or sex differences were observed in the number of sessions to reach criteria. No differences between wildtype and transgenic LE rats were observed. These results demonstrate sex and strain differences in nicotine self-administration between SD and LE rats and may lend insight into development of other nicotine self-administration models, where sex and strain may impact acquisition. (PsycInfo Database Record (c) 2021 APA, all rights reserved).

Evaluating N-acetylcysteine for early and end-of-treatment abstinence in adult cigarette smokers

BACKGROUND

There is robust preclinical literature and preliminary clinical findings supporting the use of N-Acetylcysteine (NAC) to treat substance use disorders, including tobacco use disorder (TUD). However, randomized controlled trials have yielded mixed results and NAC's efficacy for TUD has not been established. The goals of this study were to assess the efficacy of NAC in promoting early and end-of-treatment abstinence and preventing relapse among adult smokers.

METHODS

This randomized, double-blinded clinical trial enrolled adult, daily smokers (N = 114; ages 23-64; 51 % female; 65 % White; 29 % Black/African American; 7% Hispanic/Latinx), who were randomized 1:1 to receive NAC (n = 59) or placebo (n = 55) (1200 mg b.i.d.) for eight weeks. Participants received brief cessation counseling and incentives for abstinence during the first three days of the quit attempt. Primary outcomes: (i) carbon monoxide (CO)-confirmed abstinence during the first three days of the quit attempt.

SECONDARY OUTCOMES

(ii) time to relapse; (iii) biologically confirmed abstinence at Week 8.

RESULTS

No differences were found between NAC and placebo groups on measures of early abstinence (3-day quit attempt; 11 % for NAC vs. 15 % for placebo; all p > 0.11), time to relapse (p = 0.19), and end-of-treatment abstinence (7% for NAC vs. 11 % for placebo; all p > 0.40].

CONCLUSIONS

Results indicate that NAC is a well-tolerated pharmacotherapy but is unlikely to be efficacious as a monotherapy for TUD in adults. Considered in the collective context of other research, NAC may potentially be more useful in a younger population, as a combination pharmacotherapy, or in the presence of more intensive psychosocial treatment.

Nicotine formulations impact reinforcement-related behaviors in a mouse model of vapor self-administration

BACKGROUND

Electronic nicotine delivery systems (ENDS) differ from combustible cigarettes given that nicotine-salt or nicotine-freebase may be used depending on the product. We have investigated how nicotine-salt and freebase formulations alter e-Vape® self-administration (EVSA) behavior and plasma cotinine levels in male and female mice.

METHODS

Adult C57/BL6 J mice were used in EVSA and assigned vaping e-liquids (50:50 PGVG, 6 mg/mL nicotine-freebase, or 6 mg/mL nicotine-salt). Mice were escalated on a fixed ratio 1 (FR1) schedule in daily 2 h sessions and then transitioned to a FR3 to examine reinforcement-related behaviors.

RESULTS

Here we observed that mice assigned nicotine-salt exhibited increased EVSA on a FR3 schedule compared to nicotine-freebase. Additionally, mice assigned nicotine-salt exhibited higher plasma cotinine concentrations following delivery-controlled passive-inhalation sessions.

CONCLUSIONS

These data provide evidence nicotine-salt formulations may contribute to greater reinforcement-related behavior and highlight the need for further investigations regarding nicotine formulation in ENDS.

N-acetylcysteine in substance use disorder: a lesson from preclinical and clinical research

Substance use disorder (SUD) is a chronic brain condition, with compulsive and uncontrollable drug-seeking that leads to long-lasting and harmful consequences. The factors contributing to the development of SUD, as well as its treatment settings, are not fully understood. Alterations in brain glutamate homeostasis in humans and animals implicate a key role of this neurotransmitter in SUD, while the modulation of glutamate transporters has been pointed as a new strategy to diminish the excitatory glutamatergic transmission observed after drugs of abuse. N-acetylcysteine (NAC), known as a safe mucolytic agent, is involved in the regulation of this system and may be taken into account as a novel pharmacotherapy for SUD. In this paper, we summarize the current knowledge on the ability of NAC to reduce drug-seeking behavior induced by psychostimulants, opioids, cannabinoids, nicotine, and alcohol in animals and humans. Preclinical studies showed a beneficial effect in animal models of SUD, while the clinical efficacy of NAC has not been fully established. In summary, NAC will be a small add-on to usual treatment and/or psychotherapy for SUD, however, further studies are required.

A Gender Perspective of Addictive Disorders

Purpose of Review

Substance use disorders (SUD) affect differentially women and men. Although the prevalence has been reported higher in men, those women with addictive disorders present a more vulnerable profile and are less likely to enter treatment than men. The aim of this paper is to present an overview of how sex and gender may influence epidemiology, clinical manifestations, social impact, and the neurobiological basis of these differences of women with SUD, based on human research.

Recent Findings

The differences in prevalence rates between genders are getting narrower; also, women tend to increase the amount of consumption more rapidly than men, showing an accelerated onset of the SUD (telescoping effect). In respect to clinical features, the most important differences are related to the risk of experience psychiatric comorbidity, the exposure to intimate partner violence, and the associated high risks in sexual and reproductive health; and those who are mothers and addicted to substances are at risk of losing the custody of children accumulating more adverse life events. Some of these differences can be based on neurobiological differences: pharmacokinetic response to substances, sensitivity to gonadal hormones, differences in neurobiological systems as glutamate, endocannabinoids, and genetic differences.

Summary

Specific research in women who use drugs is very scarce and treatments are not gender-sensitive oriented. For these reasons, it is important to guarantee access to the appropriate treatment of women who use drugs and a need for a gender perspective in the treatment and research of substance use disorders.

Administration of N-acetylcysteine Plus Acetylsalicylic Acid Markedly Inhibits Nicotine Reinstatement Following Chronic Oral Nicotine Intake in Female Rats

Background

Nicotine is the major addictive component of cigarette smoke and the prime culprit of the failure to quit smoking. Common elements perpetuating the use of addictive drugs are (i) cues associated with the setting in which drug was used and (ii) relapse/reinstatement mediated by an increased glutamatergic tone (iii) associated with drug-induced neuroinflammation and oxidative stress.

Aims

The present study assessed the effect of the coadministration of the antioxidant N-acetylcysteine (NAC) plus the anti-inflammatory acetylsalicylic acid (ASA) on oral nicotine reinstatement intake following a post-deprivation re-access in female rats that had chronically and voluntarily consumed a nicotine solution orally. The nicotine-induced oxidative stress and neuroinflammation in the hippocampus and its effects on the glutamate transporters GLT-1 and XCT mRNA levels in prefrontal cortex were also analyzed.

Results

The oral coadministration of NAC (40 mg/kg/day) and ASA (15 mg/kg/day) inhibited by 85% of the oral nicotine reinstatement intake compared to control (vehicle), showing an additive effect of both drugs. Acetylsalicylic acid and N-acetylcysteine normalized hippocampal oxidative stress and blunted the hippocampal neuroinflammation observed upon oral nicotine reinstatement. Nicotine downregulated GLT-1 and xCT gene expression in the prefrontal cortex, an effect reversed by N-acetylcysteine, while acetylsalicylic acid reversed the nicotine-induced downregulation of GLT-1 gene expression. The inhibitory effect of N-acetylcysteine on chronic nicotine intake was blocked by the administration of sulfasalazine, an inhibitor of the xCT transporter.

Conclusion

Nicotine reinstatement, following post-deprivation of chronic oral nicotine intake, downregulates the mRNA levels of GLT-1 and xCT transporters, an effect reversed by the coadministration of N-acetylcysteine and acetylsalicylic acid, leading to a marked inhibition of nicotine intake. The combination of these drugs may constitute a valuable adjunct in the treatment of nicotine-dependent behaviors.

Efficacy of N-acetylcysteine in the prevention of alcohol relapse-like drinking: Study in long-term ethanol-experienced male rats

Alcohol use disorders are chronic and highly relapsing disorders, thus alcoholic patients have a high rate of recidivism for drug use even after long periods of abstinence. The literature points to the potential usefulness of N-acetylcysteine (NAC) in the management of several substance use disorders probably due to its capacity to restore brain homeostasis of the glutamate system disrupted in addiction. However, there is little evidence in the case of alcohol. The aim of this study was to explore the potential anti-relapse efficacy of NAC using the alcohol deprivation effect (ADE) model in long-term experienced rats. Two experiments were performed in male Wistar rats to: (a) test the efficacy of NAC to prevent relapse and (b) discriminate the best administration schedule (intermittent vs. continuous) for NAC. In the first experiment, animals were implanted with mini-osmotic pumps delivering 0 or 1 mg/hr NAC during 14 days. In a second experiment, rats received 0, 60, or 100 mg/kg once daily by subcutaneous injection. The efficacy to prevent ADE was evaluated in both experiments. NAC subcutaneously administered, either by continuous infusion or by intermittent injections regimen, is able to block the ADE. The best results were obtained after using 60 mg/kg NAC dose. Our findings support the hypothesis that NAC may represent a valuable therapy in the management of alcohol relapse.

Accumbens neuroimmune signaling and dysregulation of astrocytic glutamate transport underlie conditioned nicotine-seeking behavior

Nicotine self-administration is associated with decreased expression of the glial glutamate transporter (GLT-1) and the cystine-glutamate exchange protein xCT within the nucleus accumbens core (NAcore). N-acetylcysteine (NAC) has been shown to restore these proteins in a rodent model of drug addiction and relapse. However, the specific molecular mechanisms driving its inhibitory effects on cue-induced nicotine reinstatement are unknown. Here, we confirm that extinction of nicotine-seeking behavior is associated with impaired NAcore GLT-1 function and expression and demonstrates that reinstatement of nicotine seeking rapidly enhances membrane fraction GLT-1 expression. Extinction and cue-induced reinstatement of nicotine seeking was also associated with increased tumor necrosis factor alpha (TNFα) and decreased glial fibrillary acidic protein (GFAP) expression in the NAcore. NAC treatment (100 mg/kg/day, i.p., for 5 d) inhibited cue-induced nicotine seeking and suppressed AMPA to NMDA current ratios, suggesting that NAC reduces NAcore postsynaptic excitability. In separate experiments, rats received NAC and an antisense vivo-morpholino to selectively suppress GLT-1 expression in the NAcore during extinction and were subsequently tested for cue-induced reinstatement of nicotine seeking. NAC treatment rescued NAcore GLT-1 expression and attenuated cue-induced nicotine seeking, which was blocked by GLT-1 antisense. NAC also reduced TNFα expression in the NAcore. Viral manipulation of the NF-κB pathway, which is downstream of TNFα, revealed that cue-induced nicotine seeking is regulated by NF-κB pathway signaling in the NAcore independent of GLT-1 expression. Ultimately, these results are the first to show that immunomodulatory mechanisms may regulate known nicotine-induced alterations in glutamatergic plasticity that mediate cue-induced nicotine-seeking behavior.

Potential of Glial Cell Modulators in the Management of Substance Use Disorders

The pervasive and devastating nature of substance use disorders underlies the need for the continued development of novel pharmacotherapies. We now know that glia play a much greater role in neuronal processes than once believed.  The various types of glial cells (e.g., astrocytes, microglial, oligodendrocytes) participate in numerous functions that are crucial to healthy central nervous system function. Drugs of abuse have been shown to interact with glia in ways that directly contribute to the pharmacodynamic effects responsible for their abuse potential. Through their effect upon glia, drugs of abuse also alter brain function resulting in behavioral changes associated with substance use disorders. Therefore, drug-induced changes in glia and inflammation within the central nervous system (neuroinflammation) have been investigated to treat various aspects of drug abuse and dependence. This article presents a brief overview of the effects of each of the major classes of addictive drugs on glia. Next, the paper reviews the pre-clinical and clinical studies assessing the effects that glial modulators have on abuse-related behavioral effects, such as pleasure, withdrawal, and motivation. There is a strong body of pre-clinical literature demonstrating the general effectiveness of several glia-modulating drugs in models of reward and relapse. Clinical studies have also yielded promising results, though not as robust. There is still much to disentangle regarding the integration between addictive drugs and glial cells. Improved understanding of the relationship between glia and the pathophysiology of drug abuse should allow for more precise exploration in the development and testing of glial-directed treatments for substance use disorders.

Direct administration of ifenprodil and citalopram into the nucleus accumbens inhibits cue-induced nicotine seeking and associated glutamatergic plasticity

Nicotine use disorder has been associated with glutamatergic alterations within the basal ganglia that might contribute to relapse. Specifically, initiation of cue-induced nicotine seeking produces rapid, transient synaptic potentiation (t-SP) in nucleus accumbens core (NAcore) medium spiny neurons (MSNs), defined as increases in spine head diameter and AMPA to NMDA current ratios (A/N). Ifenprodil, which inhibits nicotine reinstatement when administered systemically, antagonizes GluN2B-containing NMDA receptors, has affinity for serotonin receptors, and blocks serotonin transporters (SERT). The mechanisms underlying its therapeutic efficacy, however, remain unknown. Using pharmacological and genetic approaches, the current study examined the role of NAcore GluN2B receptors as well as SERT in mediating cue-induced nicotine seeking and associated MSN structure and physiology. Prior to reinstatement, rats received intra-NAcore injections of either ifenprodil, citalopram or artificial cerebral spinal fluid (15 min prior), or GluN2B or control siRNAs (3 consecutive days prior). Rats were sacrificed after a 15-min cue-induced reinstatement session for dendritic spine analysis, western blotting or whole-cell electrophysiology. Intra-NAcore ifenprodil blocked nicotine-seeking behavior and promoted a higher frequency of shorter spines on MSN dendrites. However, a decrease in membrane-bound GluN2B receptor expression did not prevent cue-induced nicotine seeking or associated MSN cell physiology. Interestingly, intra-NAcore citalopram, an SSRI, prevented cue-induced nicotine seeking. Together, these results indicate that the therapeutic effects of ifenprodil on cue-induced nicotine seeking may, in part, be due to its actions at SERT rather than GluN2B, which may be specific to nicotine-seeking as opposed to other drugs of abuse.

Neurobehavioral, testicular and erectile impairments of chronic ketamine administration: Pathogenesis and ameliorating effect of N-acetyl cysteine

Ketamine, a dissociative anesthetic, recently has spread as a recreational drug. Its abuse lead to neurobehavioral disturbance in addition to toxic effects on other body organs. To evaluate the toxic effects of chronic administration of low ketamine doses on the memory, testicles, and erection, explore its pathophysiology through oxidative stress mechanism and examine the ameliorating effect of N-acetyl cysteine (NAC). A total of 40 male albino rats were assigned to control, vehicle, ketamine only I.P. (10 mg/kg), and ketamine (10 mg/kg) + NAC (150 mg/kg) groups. Assessment of memory affection and erectile function by Passive Avoidance, Novel Object Recognition, and copulatory tests were performed. Estimation of malondialdehyde (MDA), catalase (CAT), and total antioxidant capacity (TAC) in serum and prefrontal & hippocampal homogenate, and luteinizing hormone (LH), testosterone in serum were done. Prefrontal cortex, hippocampus, and testes were collected for histopathology. Chronic ketamine administration induced significant memory deficits (P < 0.05), reduced erectile function (P < 0.05), severe hypospermatogenesis, increased MDA, reduced CAT, TAC levels in serum, and tissue homogenate (P < 0.05) and reduction of LH, and testosterone (P < 0.05). Treatment with NAC resulted in significant improvement of memory function, improved erectile function, and decrease in oxidative injury in both serum and tissue homogenates. Testosterone and LH levels exhibited significant difference between treatment groups and controls (P < 0.05). NAC reduced the deleterious histopathological changes. These data suggest that long-term ketamine affects short and long memory, induces erectile and testicular dysfunction through oxidative stress. Co-administration with NAC ameliorates these toxic effects.

Sex differences in the glutamate system: Implications for addiction

Clinical and preclinical research have identified sex differences in substance use and addiction-related behaviors. Historically, substance use disorders are more prevalent in men than women, though this gap is closing. Despite this difference, women appear to be more susceptible to the effects of many drugs and progress to substance abuse treatment more quickly than men. While the glutamate system is a key regulator of addiction-related behaviors, much of the work implicating glutamate signaling and glutamatergic circuits has been conducted in men and male rodents. An increasing number of studies have identified sex differences in drug-induced glutamate alterations as well as sex and estrous cycle differences in drug seeking behaviors. This review will describe sex differences in the glutamate system with an emphasis on implications for substance use disorders, highlighting the gaps in our current understanding of how innate and drug-induced alterations in the glutamate system may contribute to sex differences in addiction-related behaviors.

Economic demand analysis of within-session dose-reduction during nicotine self-administration

BACKGROUND

This study determined if a within-session dose-reduction design sufficiently captures elasticity of demand for nicotine in male and female rats using environmental enrichment to manipulate demand elasticity.

METHODS

Male and female Sprague-Dawley rats were trained to self-administer nicotine (60 μg/kg/infusion). In Experiment 1, rats began daily dose-reduction for nine sessions following acquisition. Rats then underwent a minimum of five within-session dose-reduction sessions where each dose was available for 10 min. In Experiment 2, rats were reared in isolated, social, or enriched housing followed by acquisition of nicotine self-administration. Rats then underwent within-session dose-reduction. Housing environments were then switched, followed by additional testing sessions. Consumption was calculated for each dose and exponential demand curves were fit.

RESULTS

No sex differences in acquisition of nicotine self-administration were detected for either experiment. In experiment 1, demand intensity (Q₀; estimated intake if nicotine were freely available), was higher with between- compared to within-session dose-reduction, although elasticity of demand (α; rate of decline in nicotine intake as a function of increasing unit price), was lower. In Experiment 2, animals reared in enrichment had fewer infusions during acquisition compared to animals in isolation. Enriched males had reduced demand intensity compared to both isolated and social males, whereas isolated females had reduced intensity compared to enriched females.

CONCLUSIONS

The within-session dose-reduction procedure for nicotine self-administration replicated effects of environmental enrichment on consumption behaviors. Additionally, this procedure captured differences in nicotine demand due to sex, laying important groundwork for future translational research on mechanisms of nicotine dependence.