Proteomic analysis of methamphetamine-induced reinforcement processes within the mesolimbic dopamine system

Neurotoxic Methamphetamine Doses Alter CDCel-1 Levels and Its Interaction with Vesicular Monoamine Transporter-2 in Rat Striatum

In recent years, methamphetamine METH misuse in the US has been rapidly increasing and there is no FDA-approved pharmacotherapy for METH use disorder (MUD). In addition to being dependent on the drug, people with MUD develop a variety of neurological problems related to the toxicity of this drug. A variety of molecular mechanisms underlying METH neurotoxicity has been identified, including dysfunction of the neuroprotective protein parkin. However, it is not known whether parkin loss of function within striatal dopaminergic (DAergic) terminals translates into a decrease in DA storage capacity. This study examined the relationship between parkin, its substrate cell division cycle related-1 (CDCrel-1), and vesicular monoamine transporter-2 (VMAT2) in METH neurotoxicity in male Sprague Dawley rats. To also assess individual differences in response to METH's neurotoxic effects, a large group of rats was treated with binge METH or saline and sacrificed 1h or 24h later. This study is the first to show that binge METH alters the levels and subcellular localization of CDCrel-1 and that CDCrel-1 interacts with VMAT2 and increases its levels at the plasma membrane. Furthermore, we found wide individual differences in the responses of measured indices to METH. Proteomic analysis of VMAT-2-associated proteins revealed upregulation of several proteins involved in the exocytosis/endocytosis cycle. The results suggest that at 1h after METH binge, DAergic neurons are engaged in counteracting METH-induced toxic effects, including oxidative stress- and hyperthermia-induced inhibition of synaptic vesicle cycling, with the responses varying between individual rats. Studying CDCrel-1, VMAT2, and other proteins in large groups of outbred rats can help define individual genetic and molecular differences in responses to METH neurotoxicity which, in turn, will aid treating humans suffering from METH use disorder and its neurological consequences.

Targeting the cytoskeleton as a therapeutic approach to substance use disorders

Substance use disorders (SUD) are chronic relapsing disorders governed by continually shifting cycles of positive drug reward experiences and drug withdrawal-induced negative experiences. A large body of research points to plasticity within systems regulating emotional, motivational, and cognitive processes as drivers of continued compulsive pursuit and consumption of substances despite negative consequences. This plasticity is observed at all levels of analysis from molecules to networks, providing multiple avenues for intervention in SUD. The cytoskeleton and its regulatory proteins within neurons and glia are fundamental to the structural and functional integrity of brain processes and are potentially the major drivers of the morphological and behavioral plasticity associated with substance use. In this review, we discuss preclinical studies that provide support for targeting the brain cytoskeleton as a therapeutic approach to SUD. We focus on the interplay between actin cytoskeleton dynamics and exposure to cocaine, methamphetamine, alcohol, opioids, and nicotine and highlight preclinical studies pointing to a wide range of potential therapeutic targets, such as nonmuscle myosin II, Rac1, cofilin, prosapip 1, and drebrin. These studies broaden our understanding of substance-induced plasticity driving behaviors associated with SUD and provide new research directions for the development of SUD therapeutics.

Methamphetamine potentiates HIV-1 gp120-mediated autophagy via Beclin-1 and Atg5/7 as a pro-survival response in astrocytes

Methamphetamine (METH), a commonly used controlled substance, is known to exacerbate neuropathological dysfunction in HIV-infected individuals. The neuropathological manifestation results from cell death or dysfunction in the central nervous system (CNS) wherein autophagy is expected to have an important role. Autophagy is generally considered protective during deprivation/stress. However, excessive autophagy can be destructive, leading to autophagic cell death. This study was designed to investigate if METH and HIV-1 gp120 interact to induce autophagy in SVGA astrocytes, and whether autophagy is epiphenomenal or it has a role in METH- and gp120-induced cytotoxicity. We found that METH and gp120 IIIb caused an increase in LC3II level in astrocytes in a dose- and time-dependent manner, and the level of LC3II was further increased when the cells were treated with METH and gp120 IIIb in combination. Next, we sought to explore the mechanism by which METH and gp120 induce the autophagic response. We found that METH induces autophagy via opioid and metabotropic glutamate receptor type 5 (mGluR5) receptors. Other than that, signaling proteins Akt, mammalian target of rapamycin (mTOR), Beclin-1, Atg5 and Atg7 were involved in METH and gp120-mediated autophagy. In addition, long-term treatment of METH and gp120 IIIb resulted in cell death, which was exacerbated by inhibition of autophagy. This suggests that autophagy functions as a protective response against apoptosis caused by METH and gp120. This study is novel and clinically relevant because METH abuse among HIV-infected populations is highly prevalent and is known to cause exacerbated neuroAIDS.

Involvement of dorsal striatal α1-containing GABAA receptors in methamphetamine-associated rewarding memories

Rewarding memories induced by addictive drugs may contribute to persistent drug-seeking behaviors, which is an important contributing factor to drug addiction. However, the biological mechanisms underlying drug-associated rewarding memories have not yet been fully understood, especially the new synthetic drugs, such as amphetamine-type stimulants (ATS). In this study, using the rat-conditioned place preference (CPP) model, a classic animal model for the reward-associated effects of addictive drugs, we found that the expression level of GABAA α1 subunits was significantly decreased in the dorsal striatum (Dstr) after conditioned methamphetamine (METH) pairing, and no significant differences were observed in the other four rewarding memory-associated areas (medial prefrontal cortex (mPFC), nucleus accumbens (NAc), amygdala (Amy), and dorsal hippocampus (DH)). Intra-Dstr injection of either the GABAA receptor agonist muscimol or the specific α1GABAA receptor-preferring benzodiazepine (BDZ) agonist zolpidem significantly abolished METH CPP formation. Thus, this study extends previous findings by showing that GABAA receptors, particularly the α1-containing GABAA receptors, may be strongly implicated in METH-associated rewarding memories. This work provides us with a new perspective on the goal of treating ATS addiction.

Proteomics Analysis of Dorsal Striatum Reveals Changes in Synaptosomal Proteins following Methamphetamine Self-Administration in Rats

Methamphetamine is a widely abused, highly addictive drug. Regulation of synaptic proteins within the brain’s reward pathway modulates addiction behaviours, the progression of drug addiction and long-term changes in brain structure and function that result from drug use. Therefore, using large scale proteomics studies we aim to identify global protein expression changes within the dorsal striatum, a key brain region involved in the modulation of addiction. We performed LC-MS/MS analyses on rat striatal synaptosomes following 30 days of methamphetamine self-administration (2 hours/day) and 14 days abstinence. We identified a total of 84 differentially-expressed proteins with known roles in neuroprotection, neuroplasticity, cell cytoskeleton, energy regulation and synaptic vesicles. We identify significant expression changes in stress-induced phosphoprotein and tubulin polymerisation-promoting protein, which have not previously been associated with addiction. In addition, we confirm the role of amphiphysin and phosphatidylethanolamine binding protein in addiction. This approach has provided new insight into the effects of methamphetamine self-administration on synaptic protein expression in a key brain region associated with addiction, showing a large set of differentially-expressed proteins that persist into abstinence. The mass spectrometry proteomics data are available via ProteomeXchange with identifier PXD001443.

Mesocorticolimbic monoamine correlates of methamphetamine sensitization and motivation

Methamphetamine (MA) is a highly addictive psychomotor stimulant, with life-time prevalence rates of abuse ranging from 5–10% world-wide. Yet, a paucity of research exists regarding MA addiction vulnerability/resiliency and neurobiological mediators of the transition to addiction that might occur upon repeated low-dose MA exposure, more characteristic of early drug use. As stimulant-elicited neuroplasticity within dopamine neurons innervating the nucleus accumbens (NAC) and prefrontal cortex (PFC) is theorized as central for addiction-related behavioral anomalies, we used a multi-disciplinary research approach in mice to examine the interactions between sub-toxic MA dosing, motivation for MA and mesocorticolimbic monoamines. Biochemical studies of C57BL/6J (B6) mice revealed short- (1 day), as well as longer-term (21 days), changes in extracellular dopamine, DAT and/or D2 receptors during withdrawal from 10, once daily, 2 mg/kg MA injections. Follow-up biochemical studies conducted in mice selectively bred for high vs. low MA drinking (respectively, MAHDR vs. MALDR mice), provided novel support for anomalies in mesocorticolimbic dopamine as a correlate of genetic vulnerability to high MA intake. Finally, neuropharmacological targeting of NAC dopamine in MA-treated B6 mice demonstrated a bi-directional regulation of MA-induced place-conditioning. These results extend extant literature for MA neurotoxicity by demonstrating that even subchronic exposure to relatively low MA doses are sufficient to elicit relatively long-lasting changes in mesocorticolimbic dopamine and that drug-induced or idiopathic anomalies in mesocorticolimbic dopamine may underpin vulnerability/resiliency to MA addiction.

Comparative peptidomics analysis of neural adaptations in rats repeatedly exposed to amphetamine

Repeated exposure to amphetamine (AMPH) induces long-lasting behavioral changes, referred to as sensitization, that are accompanied by various neuroadaptations in the brain. To investigate the chemical changes that occur during behavioral sensitization, we applied a comparative proteomics approach to screen for neuropeptide changes in a rodent model of AMPH-induced sensitization. By measuring peptide profiles with matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and comparing signal intensities using principal component analysis and variance statistics, subsets of peptides are found with significant differences in the dorsal striatum, nucleus accumbens, and medial prefrontal cortex of AMPH-sensitized male Sprague-Dawley rats. These biomarker peptides, identified in follow-up analyses using liquid chromatography and tandem mass spectrometry, suggest that behavioral sensitization to AMPH is associated with complex chemical adaptations that regulate energy/metabolism, neurotransmission, apoptosis, neuroprotection, and neuritogenesis, as well as cytoskeleton integrity and neuronal morphology. Our data contribute to a growing number of reports showing that in addition to the mesolimbic dopamine system, which is the best known signaling pathway involved with reinforcing the effect of psychostimulants, concomitant chemical changes in other pathways and in neuronal organization may play a part in the overall effect of chronic AMPH exposure on behavior.

Effects of maternal separation and methamphetamine exposure on protein expression in the nucleus accumbens shell and core

Early life adversity has been suggested to predispose an individual to later drug abuse. The core and shell sub-regions of the nucleus accumbens are differentially affected by both stressors and methamphetamine. This study aimed to characterize and quantify methamphetamine-induced protein expression in the shell and core of the nucleus accumbens in animals exposed to maternal separation during early development. Isobaric tagging (iTRAQ) which enables simultaneous identification and quantification of peptides with tandem mass spectrometry (MS/MS) was used. We found that maternal separation altered more proteins involved in structure and redox regulation in the shell than in the core of the nucleus accumbens, and that maternal separation and methamphetamine had differential effects on signaling proteins in the shell and core. Compared to maternal separation or methamphetamine alone, the maternal separation/methamphetamine combination altered more proteins involved in energy metabolism, redox regulatory processes and neurotrophic proteins. Methamphetamine treatment of rats subjected to maternal separation caused a reduction of cytoskeletal proteins in the shell and altered cytoskeletal, signaling, energy metabolism and redox proteins in the core. Comparison of maternal separation/methamphetamine to methamphetamine alone resulted in decreased cytoskeletal proteins in both the shell and core and increased neurotrophic proteins in the core. This study confirms that both early life stress and methamphetamine differentially affect the shell and core of the nucleus accumbens and demonstrates that the combination of early life adversity and later methamphetamine use results in more proteins being affected in the nucleus accumbens than either treatment alone.

Dose-dependent changes in the locomotor responses to methamphetamine in BALB/c mice: low doses induce hypolocomotion

The overall goal of the present study was to determine the effects of different doses of (+)-methamphetamine (meth) on locomotor activity of Balb/C mice. Four experiments were designed to test a wide range of meth doses in BALB/c female mice. In Experiment 1, we examined locomotor activity induced by an acute administration of low doses of meth (0.01 and 0.03mg/kg) in a 90-min session. Experiment 2 was conducted to test higher meth doses (0.3-10mg/kg). In Experiment 3, separate sets of mice were pre-treated with various meth doses once or twice (one injection/week) prior to a locomotor challenge with a low meth dose. Finally, in Experiment 4, we tested whether locomotor activation would be affected by pretreatment with a low or moderate dose of meth one month prior to the low meth dose challenge. Results show that low doses of meth induce hypolocomotion whereas moderate to high doses induce hyperlocomotion. Prior exposure to either one moderate or high dose of meth or to two, low doses of meth attenuated the hypolocomotor effect of a low meth dose one week later. This effect was also attenuated in mice tested one month after administration of a moderate meth dose. These results show that low and high doses of meth can have opposing effects on locomotor activity. Further, prior exposure to the drug leads to tolerance, rather than sensitization, of the hypolocomotor response to low meth doses.

Baclofen facilitates the extinction of methamphetamine-induced conditioned place preference in rats

The powerful, long-lasting association between the rewarding effects of a drug and contextual cues associated with drug administration can be studied using conditioned place preference (CPP). The GABA(B) receptor agonist baclofen facilitates the extinction of morphine-induced CPP in mice. The current study extended this work by determining if baclofen could enhance the extinction of methamphetamine (Meth) CPP. CPP was established using a six-day conditioning protocol wherein Meth-pairings were alternated with saline-pairings. Rats were subsequently administered baclofen (2 mg/kg i.p. or vehicle) immediately after each daily forced extinction session, which consisted of a saline injection immediately prior to being placed into the previously Meth- or saline-paired chamber. One extinction training cycle, consisted of six once-daily forced extinction sessions, mimicking the alternating procedure established during conditioning, followed by a test for preference (Ext test). CPP persisted for at least four extinction cycles in vehicle-treated rats. In contrast, CPP was inhibited following a single extinction training cycle. These data indicate that Meth-induced CPP was resistant to extinction, but extinction training was rendered effective when the training was combined with baclofen. These findings converge with the prior demonstration of baclofen facilitating the extinction of morphine-induced CPP indicating that GABA(B) receptor actions are independent of the primary (unconditioned) stimulus (i.e., the opiate or the stimulant) and likely reflect mechanisms engaged by extinction learning processes per se. Thus, baclofen administered in conjunction with extinction training may be of value for addiction therapy regardless of the class of drug being abused.

Involvement of µ-Opioid Receptor in Methamphetamine-Induced Behavioral Sensitization

Methamphetamine is a potent addictive stimulant drug that activates certain systems in the brain. It is a member of the amphetamine family, but the effects of methamphetamine are much more potent, longer lasting, and more harmful to the central nervous system. Repeated administration of methamphetamine induces behavioral sensitization, which is considered to be related to compulsive drug-seeking behavior. Although the mechanism responsible for methamphetamine-induced behavioral sensitization remains unclear, it is believed that the mesolimbic dopaminergic system in the central nervous system plays a critical role in the development of behavioral sensitization. Our previous studies indicate that the involvement of the μ-opioid receptor system underlies the development of methamphetamine-induced behavioral sensitization. Understanding the mechanisms of behavioral sensitization that are regulated by the μ-opioid receptor system would be helpful in developing therapeutic programs against methamphetamine addiction. This review briefly discusses the neural circuitry and cellular mechanisms that are known to play a central role in methamphetamine-induced behavioral sensitization and outlines the role of the μ-opioid receptor system in the development of methamphetamine-induced sensitization.

Genes and pathways co-associated with the exposure to multiple drugs of abuse, including alcohol, amphetamine/methamphetamine, cocaine, marijuana, morphine, and/or nicotine: a review of proteomics analyses

Drug addiction is a chronic neuronal disease. In recent years, proteomics technology has been widely used to assess the protein expression in the brain tissues of both animals and humans exposed to addictive drugs. Through this approach, a large number of proteins potentially involved in the etiology of drug addictions have been identified, which provide a valuable resource to study protein function, biochemical pathways, and networks related to the molecular mechanisms underlying drug dependence. In this article, we summarize the recent application of proteomics to profiling protein expression patterns in animal or human brain tissues after the administration of alcohol, amphetamine/methamphetamine, cocaine, marijuana, morphine/heroin/butorphanol, or nicotine. From available reports, we compiled a list of 497 proteins associated with exposure to one or more addictive drugs, with 160 being related to exposure to at least two abused drugs. A number of biochemical pathways and biological processes appear to be enriched among these proteins, including synaptic transmission and signaling pathways related to neuronal functions. The data included in this work provide a summary and extension of the proteomics studies on drug addiction. Furthermore, the proteins and biological processes highlighted here may provide valuable insight into the cellular activities and biological processes in neurons in the development of drug addiction.

Proteomic analysis reveals differentially expressed proteins in the rat frontal cortex after methamphetamine treatment

Methamphetamine (MA) is an addictive psycho-stimulant and the illicit use of the drug is escalating. In the present study, we examined protein expression profiles in the rat frontal cortex exposed to a total of eight MA injections (1 mg/kg, intraperitoneal) using 2-DE based proteomics. We investigated protein changes occurring in both the cytosolic fraction and the membrane fraction. 2-DE analysis resulted in 62 cytosolic and 44 membrane protein spots that were differentially regulated in the frontal cortex of rats exposed to MA when compared to control animals. Of these spots, 47 cytosolic and 42 membrane proteins were identified respectively, using ESI-Quad-TOF, which included ubiquitin carboxyl-terminal hydrolase isozyme L1 (UCH-L1), beta-synuclein, 78 kDa glucose-regulated protein (GRP 78), gamma-enolase, dihydropyrimidase-related protein 2 (DRP 2), complexin 2 and synapsin II. These proteins are associated with protein degradation, redox regulation, energy metabolism, cellular growth, cytoskeletal modifications and synaptic function. Proteomic research may be useful in exploring the complex underlying molecular mechanisms of MA dependence.