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

Exploring the potential link between ΔFosB and N-acetylcysteine in craving/relapse dynamics: can N-acetylcysteine stand out as a possible treatment candidate?

From a neuroscientific point of view, one of the unique archetypes of substance use disorders is its road to relapse, in which the reward system plays a crucial role. Studies on the neurobiology of substance use disorders have highlighted the central role of a protein belonging to the Fos family of transcription factors, ΔFosB. Relying on the roles ΔFosB plays in the pathophysiology of substance use disorders, we endeavour to present some evidence demonstrating that N-acetylcysteine, a low-cost and well-tolerated over-the-counter medicine, may influence the downstream pathway of ΔFosB, thereby serving as a treatment strategy to mitigate the risk of relapse in cases of substance use.

Effects of methylphenidate on mitochondrial dynamics and bioenergetics in the prefrontal cortex of juvenile rats are sex-dependent

Methylphenidate (MPH) is a central nervous system stimulant drug and a first order prescription in the treatment of Attention Deficit Hyperactivity Disorder (ADHD). Although MPH biochemistry in neurodevelopment is not completely understood, studies showed it alters energy metabolism in rat brains. ADHD prevalence during neurodevelopment is related to males and the investigation has been mainly done in these subjects, therefore, little is known about MPH action in females and, consequently, about sexual dimorphism. In the present study we evaluated markers of mitochondrial dynamics (DRP1 and MFN2, fission and fusion, respectively), biogenesis (mtTFA) and bioenergetics (respiratory chain complexes) in prefrontal cortex of male and female juvenile rats submitted to exposure to MPH to better understand MPH effect during postnatal neurodevelopment. ATP and oxidative stress levels were also evaluated. Wistar rats received intraperitoneal injection of MPH (2.0 mg/kg) or control (saline), once a day, from 15th to 45th day of age. Results showed that MPH increased DRP1 and decreased MFN2, as well as increased mtTFA in prefrontal cortex of male rats. In female, MPH decreased NRF1 and increased Parkin, which are mitochondrial regulatory proteins. Respiratory chain complexes (complex I, SDH, complexes III and IV), ATP production and oxidative stress parameters were altered and shown to be sex-dependent. Taken together, results suggest that chronic MPH exposure at an early age in healthy animals changes mitochondrial dynamics, biogenesis and bioenergetics differently depending on the sex of the subjects.

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.

Modeling Methamphetamine Use Disorder and Relapse in Animals: Short- and Long-term Epigenetic, Transcriptional., and Biochemical Consequences in the Rat Brain

Methamphetamine use disorder (MUD) is a neuropsychiatric disorder characterized by binge drug taking episodes, intervals of abstinence, and relapses to drug use even during treatment. MUD has been modeled in rodents and investigators are attempting to identify its molecular bases. Preclinical experiments have shown that different schedules of methamphetamine self-administration can cause diverse transcriptional changes in the dorsal striatum of Sprague-Dawley rats. In the present review, we present data on differentially expressed genes (DEGs) identified in the rat striatum following methamphetamine intake. These include genes involved in transcription regulation, potassium channel function, and neuroinflammation. We then use the striatal data to discuss the potential significance of the molecular changes induced by methamphetamine by reviewing concordant or discordant data from the literature. This review identified potential molecular targets for pharmacological interventions. Nevertheless, there is a need for more research on methamphetamine-induced transcriptional consequences in various brain regions. These data should provide a more detailed neuroanatomical map of methamphetamine-induced changes and should better inform therapeutic interventions against MUD.

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.

Persistent Neuroadaptations in the Nucleus Accumbens Core Accompany Incubation of Methamphetamine Craving in Male and Female Rats

Relapse is a major problem in treating methamphetamine use disorder. "Incubation of craving" during abstinence is a rat model for persistence of vulnerability to craving and relapse. While methamphetamine incubation has previously been demonstrated in male and female rats, it has not been demonstrated after withdrawal periods greater than 51 d and most mechanistic work used males. Here, we address both gaps. First, although methamphetamine intake was higher in males during self-administration training (6 h/d × 10 d), incubation was similar in males and females, with "incubated" craving persisting through withdrawal day (WD)100. Second, using whole-cell patch-clamp recordings in medium spiny neurons (MSNs) of the nucleus accumbens (NAc) core, we assessed synaptic levels of calcium-permeable AMPA receptors (CP-AMPARs), as their elevation is required for expression of incubation in males. In both sexes, compared with saline-self-administering controls, CP-AMPAR levels were significantly higher in methamphetamine rats across withdrawal, although this was less pronounced in WD100-135 rats than WD15-35 or WD40-75 methamphetamine rats. We also examined membrane properties and NMDA receptor (NMDAR) transmission. In saline controls, MSNs from males exhibited lower excitability than females. This difference was eliminated after incubation because of increased excitability of MSNs from males. NMDAR transmission did not differ between sexes and was not altered after incubation. In conclusion, incubation persists for longer than previously described and equally persistent CP-AMPAR plasticity in NAc core occurs in both sexes. Thus, abstinence-related synaptic plasticity in NAc is similar in males and females although other methamphetamine-related behaviors and neuroadaptations show differences.

Compulsive methamphetamine self-administration in the presence of adverse consequences is associated with increased hippocampal mRNA expression of cellular adhesion molecules

Methamphetamine (METH) is a popular but harmful psychostimulant. METH use disorder (MUD) is characterized by compulsive and continued use despite adverse life consequences. METH users experience impairments in learning and memory functions that are thought to be secondary to METH-induced abnormalities in the hippocampus. Recent studies have reported that about 50% of METH users develop MUD, suggesting that there may be differential molecular effects of METH between the brains of individuals who met criteria for addiction and those who did not after being exposed to the drug. The present study aimed at identifying potential transcriptional differences between compulsive and non-compulsive METH self-administering male rats by measuring global gene expression changes in the hippocampus using RNA sequencing. Herein, we used a model of METH self-administration (SA) accompanied by contingent foot-shock punishment. This approach led to the separation of animals into shock-resistant rats (compulsive) that continued to take METH and shock-sensitive rats (non-compulsive) that suppressed their METH intake in the presence of punished METH taking. Rats were euthanized 2 h after the last METH SA plus foot-shock session. Their hippocampi were immediately removed, frozen, and used later for RNA sequencing and qRT-PCR analyses. RNA sequencing analyses revealed differential expression of mRNAs encoding cell adhesion molecules (CAMs) between the two rat phenotypes. qRT-PCR analyses showed significant higher levels of Cdh1, Glycam1, and Mpzl2 mRNAs in the compulsive rats in comparison to non-compulsive rats. The present results implicate altered CAM expression in the hippocampus in the behavioral manifestations of continuous compulsive METH taking in the presence of adverse consequences. Our results raise the novel possibility that altered CAM expression might play a role in compulsive METH taking and the cognitive impairments observed in MUD patients.

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.