Age-specific treatment effects of orexin/hypocretin-receptor antagonism on methamphetamine-seeking behavior

The estrous cycle has no effect on incubation of methamphetamine craving and associated Fos expression in dorsomedial striatum and anterior intralaminar nucleus of thalamus

Relapse is a major challenge in treating drug addiction, and drug seeking progressively increases after abstinence, a phenomenon termed "incubation of drug craving". Previous studies demonstrated both sex differences and an effect of estrous cycle in female rats in incubation of cocaine craving. In contrast, while incubation of methamphetamine craving is similar across sexes, whether estrous cycle plays a role in this incubation has yet to be fully addressed. Moreover, whether neural mechanisms underlying incubation of methamphetamine craving differ across estrous cycles is largely unknown. To address these gaps, we first compared methamphetamine self-administration, and methamphetamine seeking on both abstinence days 1 and 28 between male rats and female rats across the estrous cycle. Next, we examined neuronal activation associated with incubated methamphetamine seeking in dorsomedial striatum (DMS) and lateral portion of the anterior intralaminar nucleus of thalamus (AIT-L), two brain areas previously implicated in incubation of methamphetamine craving. We found no effect of sex or estrous cycle on methamphetamine self-administration and methamphetamine seeking on abstinence days 1 and 28. We also found no effect of sex or estrous cycle on the number of Fos-expressing cells in DMS or AIT-L following methamphetamine seeking test. Taken together, our results showed that methamphetamine self-administration and incubation of methamphetamine craving was not dependent on sex or estrous cycles under our experimental condition, and the role of DMS and AIT-L in incubation of methamphetamine craving may be similar across sexes and across estrous cycles in female rats.

Modeling methamphetamine use disorder in mammals: Sex differences in behavioral, biochemical, and transcriptional consequences

Methamphetamine (METH) is the most commonly misused amphetamine-type stimulant throughout the globe. METH is very rewarding, and its misuse can lead to a diagnosis of METH use disorder (MUD). Although METH use is observed in both sexes, there are, however, reported differences in the clinical manifestations of METH use and its consequences. These observations indicate the need for more research on the long-term sex-dependent consequences of METH taking in both preclinical and clinical settings. In effect, sex is a biological variable that can impact conclusions drawn from various basic and clinical studies. Thus, the present chapter provides a succinct review of the current state of the research on METH and its sex-associated consequences. In addition to behavioral and cognitive aspects of METH use, we discuss METH-induced changes in neurotransmitter systems and structures in the brain. Thus, the book chapter serves to highlight the significance of sex as a critical element that needs to be considered during discussions of novel therapeutic approaches to MUD.

GxE interaction effects of HCRTR2 single nucleotide polymorphism and adverse childhood experiences on methamphetamine use disorder

Background: Methamphetamine use disorder (MUD) is a worldwide health concern. The hypothalamic orexin system regulates stress response and addictive behaviors. The genetic variation in the hypocretin receptor 2 (HCRTR2), rs2653349, is associated with substance use disorder.Objectives: We explored the gene-environment (GxE) interaction of rs2653349 and adverse childhood experiences (ACEs) associated with MUD susceptibility.Methods: Four hundred and one individuals (336 males, 65 females) with MUD and 348 healthy controls (288 males, 60 females) completed a self-report questionnaire evaluating ACEs, encompassing childhood abuse and household dysfunction categories, and were genotyped for SNP rs2653349. Methamphetamine use variables were collected using the Diagnostic Interview for Genetic Studies. We used regression analyses to assess the GxE effect on MUD risk.Results: The MUD group had a comparable genotypic distribution for rs2653349 to the control group, albeit with a higher prevalence and number of types of ACEs, correlating with an increased MUD risk (p < .05). No significant genetic impact of rs2653349 on MUD risk was found. However, we observed a GxE interaction effect between the minor allele of rs2653349 and the number of childhood abuse or household dysfunction types, correlating with a reduced MUD risk (OR = -0.71, p = .04, Benjamini-Hochberg adjusted p = .08 and OR = -0.59, p = .045, Benjamini-Hochberg adjusted p = .09, respectively).Conclusion: HCRTR2 SNP rs2653349 has no significant impact on MUD risk, but ACEs may increase this risk. GxE results suggest that rs2653349 could offer protection against developing MUD in individuals experiencing multiple types of ACEs.

Blockade of the orexin-2 receptors within the ventral tegmental area facilitates the extinction and prevents the reinstatement of methamphetamine-seeking behavior

Repeated use of methamphetamine (METH) causes severe effects on the central nervous system, associated with an increased relapse rate. The orexinergic system is highly implicated in the reward circuitry and may be a promising target for treating psychostimulant dependency. The present study aimed to investigate the involvement of the orexin system, mainly the orexin-2 receptors (OX2R) in the ventral tegmental area (VTA) in the extinction and reinstatement of METH-seeking behavior using a conditioned place preference (CPP) paradigm. To this end, animals received METH (1 mg/kg; sc) for a 5-day conditioning period. Then, in the first set of experiments, different groups of rats were given intra-VTA TCS OX2 29 (1, 3, 10, or 30 nmol/0.3 μl DMSO) as an OX2R antagonist over a 10-day extinction period. In another experiment, after the extinction period, a different set of animals received a single dose of TCS OX2 29 (1, 3, 10, or 30 nmol) before the priming dose of METH (0.25 mg/kg; sc) on the reinstatement day. The results revealed that TCS OX2 29 (10 and 30 nmol) remarkably facilitated the extinction of rewarding properties of METH (P < 0.001 for both doses). Furthermore, TCS OX2 29 (3, 10, or 30 nmol) significantly suppressed the METH-induced reinstatement (3 nmol; P < 0.05, 10 nmol; P < 0.01, and 30 nmol; P < 0.001). In conclusion, the current study revealed that the orexinergic system, specifically the VTA OX2R, is involved in METH-seeking behaviors and that manipulation of this system can be considered a potential therapeutics in treating METH dependency.

The role of sex and drug use during adolescence in determining the risk for adverse consequences of amphetamines

Use of amphetamines during adolescence, a critical period of brain development and reorganization, may lead to particularly adverse outcomes that are long-lasting. Similarly, female users may be uniquely vulnerable to certain aspects of drug use. A recognition of the role of use during adolescence and sex on outcomes of amphetamine and methamphetamine exposure are of critical importance in understanding and treating substance use disorders. This chapter highlights what human research, which has been largely epidemiological, suggests about sex and age differences in drug use patterns and outcomes. We also discuss work in laboratory animals that has typically utilized rats or mice exposed to drugs in a non-contingent manner (i.e., involuntarily) or through volitional self-administration. Lastly, we draw attention to the fact that advancing our understanding of the effects of amphetamine and methamphetamine use, the development of problematic drug taking, and the mechanisms that contribute to relapse will require an emphasis on inclusion of age and sex as moderating factors in future studies.

Rethinking the Role of Orexin in the Regulation of REM Sleep and Appetite

Orexin plays a significant role in the modulation of REM sleep, as well as in the regulation of appetite and feeding. This review explores, first, the current evidence on the role of orexin in the modulation of sleep and wakefulness and highlights that orexin should be considered essentially as a neurotransmitter inhibiting REM sleep and, to a much lesser extent, a wake promoting agent. Subsequently, the relationship between orexin, REM sleep, and appetite regulation is examined in detail, shedding light on their interconnected nature in both physiological conditions and diseases (such as narcolepsy, sleep-related eating disorder, idiopathic hypersomnia, and night eating syndrome). Understanding the intricate relationship between orexin, REM sleep, and appetite regulation is vital for unraveling the complex mechanisms underlying sleep-wake patterns and metabolic control. Further research in this field is encouraged in order to pave the way for novel therapeutic approaches to sleep disorders and metabolic conditions associated with orexin dysregulation.

Adenosine receptor stimulation inhibits methamphetamine-associated cue seeking

BACKGROUND

Methamphetamine (METH) is a psychostimulant drug that remains a popular and threatening drug of abuse with high abuse liability. There is no established pharmacotherapy to treat METH dependence, but evidence suggests that stimulation of adenosine receptors reduces the reinforcing properties of METH and could be a potential pharmacological target. This study examines the effects of adenosine receptor subtype stimulation on METH seeking using both a cue-induced reinstatement and cue-craving model of relapse.

METHODS

Male and female rats were trained to self-administer METH during daily 2-h sessions. Cue-induced reinstatement of METH seeking was evaluated after extinction training. A systemic pretreatment of an adenosine A1 receptor (A1R) or A2A receptor (A2AR) agonist was administered prior to an extinction or cue session to evaluate the effects of adenosine receptor subtype stimulation on METH seeking. The effects of a systemic pretreatment of A1R or A2AR agonists were also evaluated in a cue-craving model where the cued-seeking test was conducted after 21 days of forced home-cage abstinence without extinction training.

RESULTS

Cue-induced reinstatement was reduced in both male and female rats that received A1R or A2AR agonist pretreatments. Similarly, an A1R or A2AR agonist pretreatment also inhibited cue craving in both male and female rats.

CONCLUSION

Stimulation of either adenosine A1R or A2AR subtypes inhibits METH-seeking behavior elicited by METH-associated cues. These effects may be attributed to the ability of A1R and A2AR stimulation to disrupt cue-induced dopamine and glutamate signaling throughout the brain.

Hypocretin/orexin system in the nucleus accumbens as a promising player in the extinction and reinstatement of methamphetamine-induced CPP

One of the main obstacles in treating psychostimulant addiction is relapse even after long-term abstinence. The nucleus accumbens (NAc) is located in the basal forebrain, responsible for regulating several behaviors, specifically reward-related effect of psychostimulants. In the current study, an unbiased place conditioning paradigm was performed to inquire the role of the hypocretin/orexin system in the NAc in the extinction and reinstatement of methamphetamine (Meth)-induced conditioned place preference (CPP). Similar to previous investigations, rats were conditioned with Meth (1 mg/kg; sc) for five consecutive days to elicit CPP. The rats underwent Meth conditioning protocol received SB334867 or TCS OX2 29, an orexin receptor 1 (OXr1) antagonist or orexin receptor 2 (OXr2) antagonist (0, 3, 10, and 30 nmol/0.5 μL DMSO %12) in the NAc during the extinction period to elucidate the role of OXrs on the extinction of Meth-induced CPP. Meanwhile, extinguished rats received SB334867 or TCS OX2 29 (0, 1, 3, 10, and 30 nmol/0.5 μL DMSO %12) in the NAc prior to an effective priming dose of Meth to evaluate the impact of OXr antagonists on the reinstatement of Meth-induced CPP. The current data pointed out intra-NAc microinjection of SB334867 or TCS OX2 29 blocked both extinction and reinstatement of Meth-induced CPP. In addition, the OXr1 antagonist was more potent than the OXr2 antagonist to suppress both extinction and reinstatement phases of Meth-induced CPP. Based on the current data, the OX system in the NAc is extensively implicated in the reward properties of Meth; therefore, modulation of this system has therapeutic potential in treating psychostimulant use disorders.

Sex-Dependent Alterations in the mRNA Expression of Enzymes Involved in Dopamine Synthesis and Breakdown After Methamphetamine Self-Administration

Sex differences have been reported in methamphetamine (METH) use disorder in humans and in animal models of METH exposure. Specifically, animals that self-administer METH show sex-related dissimilarities in dopamine (DA) metabolism. To better understand the molecular bases for the differences in DA metabolism, we measured the levels of mRNAs of enzymes that catalyze DA synthesis and breakdown in the prefrontal cortex (PFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and hippocampus (HIP) of rats that had self-administered METH. There were significant sex differences in control rats, with males having higher basal levels of Th in the PFC and dSTR, Ddc in the NAc, and MaoB in the HIP. In contrast, female controls showed higher basal levels of Comt in the HIP. Male and female METH SA rats also showed some distinct responses to the drug. Specifically, female METH rats exhibited increased expression of Ddc and MaoB, whereas male METH animals showed higher levels of Comt mRNA in the PFC compared to their respective controls. In the NAc, male METH rats displayed decreased Th and Ddc mRNA levels. Together, our results identified sex-dependent and region-specific changes in the mRNA expression of several enzymes involved in DA synthesis and breakdown in response to METH SA, with the majority of differences being observed in the mesocorticolimbic dopaminergic system. These findings are of significant translational importance providing further support for the inclusion of sex as an important variable when planning and evaluating therapeutic interventions against METH use disorder in human clinical studies.

Sex differences in methamphetamine use disorder perused from pre-clinical and clinical studies: Potential therapeutic impacts

Methamphetamine (METH) use, and misuse are associated with severe socioeconomic consequences. METH users develop tolerance, lose control over drug taking behaviors, and suffer frequent relapses even during treatment. The clinical course of METH use disorder is influenced by multifactorial METH-induced effects on the central and peripheral nervous systems. Although these METH-induced consequences are observed in humans of all ages, races, and sexes, sexual dimorphism in these outcomes have been observed in both pre-clinical and clinical settings. In this review, we have provided a detailed presentation of the sex differences reported in human and animal studies. We have therefore presented data that identified the influences of sex on METH pharmacokinetics, METH-induced changes in behaviors, cognitive processes, structural changes in the brain, and the effects of the drug on neurotransmitter systems and molecular mechanisms. Finally, we highlighted the potential significance of sex as a critical variable that should be considered when planning the development of new pharmacotherapeutic approaches against MEH use disorder in humans.

Sex-Specific Alterations in Dopamine Metabolism in the Brain after Methamphetamine Self-Administration

Methamphetamine (METH) use disorder affects both sexes, with sex differences occurring in behavioral, structural, and biochemical consequences. The molecular mechanisms underlying these differences are unclear. Herein, we used a rat model to identify potential sex differences in the effects of METH on brain dopaminergic systems. Rats were trained to self-administer METH for 20 days, and a cue-induced drug-seeking test was performed on withdrawal days 3 and 30. Dopamine and its metabolites were measured in the prefrontal cortex (PFC), nucleus accumbens (NAc), dorsal striatum (dSTR), and hippocampus (HIP). Irrespective of conditions, in comparison to females, male rats showed increased 3,4-dihydroxyphenylalanine (DOPA) in the PFC, dSTR, and HIP; increased cys-dopamine in NAc; and increased 3,4-dihydroxyphenylethanol (DOPET) and 3,4-dihydroxyphenylacetic acid (DOPAC) in dSTR. Males also showed METH-associated decreases in DA levels in the HIP but increases in the NAc. Female rats showed METH-associated decreases in DA, DOPAL, and DOPAC levels in the PFC but increases in DOPET and DOPAC levels in the HIP. Both sexes showed METH-associated decreases in NAc DA metabolites. Together, these data document sex differences in METH SA-induced changes in DA metabolism. These observations provide further support for using sex as an essential variable when discussing therapeutic approaches against METH use disorder in humans.

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.

Reviewing the role of the orexinergic system and stressors in modulating mood and reward-related behaviors

In this review study, we aimed to introduce the orexinergic system as an important signaling pathway involved in a variety of cognitive functions such as memory, motivation, and reward-related behaviors. This study focused on the role of orexinergic system in modulating reward-related behavior, with or without the presence of stressors. Cross-talk between the reward system and orexinergic signaling was also investigated, especially orexinergic signaling in the ventral tegmental area (VTA), the nucleus accumbens (NAc), and the hippocampus. Furthermore, we discussed the role of the orexinergic system in modulating mood states and mental illnesses such as depression, anxiety, panic, and posttraumatic stress disorder (PTSD). Here, we narrowed down our focus on the orexinergic signaling in three brain regions: the VTA, NAc, and the hippocampus (CA1 region and dentate gyrus) for their prominent role in reward-related behaviors and memory. It was concluded that the orexinergic system is critically involved in reward-related behavior and significantly alters stress responses and stress-related psychiatric and mood disorders.