Reductions in frontocortical cytokine levels are associated with long-lasting alterations in reward valuation after methamphetamine

Methamphetamine and the Synthetic Cathinone 3,4-Methylenedioxypyrovalerone (MDPV) Produce Persistent Effects on Prefrontal and Striatal Microglial Morphology and Neuroimmune Signaling Following Repeated Binge-like Intake in Male and Female Rats

Psychostimulants alter cellular morphology and activate neuroimmune signaling in a number of brain regions, yet few prior studies have investigated their persistence beyond acute abstinence or following high levels of voluntary drug intake. In this study, we examined the effects of the repeated binge-like self-administration (96 h/week for 3 weeks) of methamphetamine (METH) and 21 days of abstinence in female and male rats on changes in cell density, morphology, and cytokine levels in two addiction-related brain regions-the prefrontal cortex (PFC) and dorsal striatum (DStr). We also examined the effects of similar patterns of intake of the cocaine-like synthetic cathinone derivative 3,4-methylenedioxypyrovalerone (MDPV) or saline as a control. Robust levels of METH and MDPV intake (~500-1000 infusions per 96 h period) were observed in both sexes. We observed no changes in astrocyte or neuron density in either region, but decreases in dendritic spine densities were observed in PFC pyramidal and DStr medium spiny neurons. The microglial cell density was decreased in the PFC of METH self-administering animals, accompanied by evidence of microglial apoptosis. Changes in microglial morphology (e.g., decreased territorial volume and ramification and increased cell soma volume) were also observed, indicative of an inflammatory-like state. Multiplex analyses of PFC and DStr cytokine content revealed elevated levels of various interleukins and chemokines only in METH self-administering animals, with region- and sex-dependent effects. Our findings suggest that voluntary binge-like METH or MDPV intake induces similar cellular perturbations in the brain, but they are divergent neuroimmune responses that persist beyond the initial abstinence phase.

Cognitive functioning of adolescents using Methamphetamine: The impact of inflammatory and oxidative processes

BACKGROUND

Methamphetamine is a substance that causes neurotoxicity and its use is increasing in recent years. Literature highlights cognitive impairment resulting from Methamphetamine use. The aim of the present study is to evaluate the relationship between cognitive impairment and inflammatory processes in adolescents with Methamphetamine use disorder.

METHODS

The study included 69 adolescents aged 15-19 years, comprising 37 participants with Methamphetamine Use Disorder and 32 healthy controls. Central Nervous System Vital Signs was used to detect cognitive impairment. Childhood Trauma Questionnaire-33 and The Children's Depression Inventory scales were used. In addition, venous blood was collected from the volunteers. Biochemical parameters (IL-1beta, IL-6, TNF-a, BDNF, FAM19A5, TAS, TOS) were analyzed.

RESULTS

Our study showed that (I) IL-6 and TNF-a levels of Methamphetamine users were lower than the healthy group; (II) BDNF levels of Methamphetamine users were higher than the healthy group; (III) mean Neurocognitive Index in cognitive tests of Methamphetamine using adolescents was negatively correlated with duration of Methamphetamine use and BDNF levels.

CONCLUSIONS

Our study suggests that Methamphetamine use may have a negative effect on cognitive functions.

The Utility of Methylphenidate for Fatigue in Long-Term Neurological Conditions: A Meta-analytical Review

OBJECTIVE

Fatigue is a chronic and debilitating symptom of many long-term neurological conditions (LTNCs). Although methylphenidate provides some promise in alleviating fatigue in other clinical groups, little work has explored its potential utility within LTNCs. The current systematic review and meta-analysis evaluates the utility of methylphenidate for symptoms of fatigue in LTNCs.

METHODS

Five databases (PsycINFO, MEDLINE, Embase, Scopus, and Cochrane Library) were searched for relevant articles from their inception to February 2022. A purpose-developed evaluation tool was used to assess each study's research quality (QuEST:F).

RESULTS

Of the 1698 articles identified, 11 articles were included within this review (n = 370). Meta-analytical findings reported an overall significant benefit of methylphenidate for symptoms of fatigue across a mixed neurological sample ( g = -0.44; 95% confidence interval, -0.77 to -0.11). Subgroup analyses identified a significantly greater benefit ( P < 0.001) of methylphenidate for fatigue in LTNCs with static pathogenic trajectories (eg, traumatic brain injury) (number needed to treat = 2.5) compared with progressive conditions (eg, multiple sclerosis) (number needed to treat = 40.2).

CONCLUSIONS

Methylphenidate may pose an effective intervention for the treatment of fatigue in a number of LTNCs. Nonetheless, given the quality of the current evidence base, there exists a clear need for further robust assessment of the utility of methylphenidate-with a focus on subgroup-specific variability.

The impact of psychostimulants on central and peripheral neuro-immune regulation: a scoping review of cytokine profiles and their implications for addiction

It is now well-accepted that psychostimulants act on glial cells causing neuroinflammation and adding to the neurotoxic effects of such substances. Neuroinflammation can be described as an inflammatory response, within the CNS, mediated through several cytokines, reactive oxygen species, chemokines and other inflammatory markers. These inflammatory players, in particular cytokines, play important roles. Several studies have demonstrated that psychostimulants impact on cytokine production and release, both centrally and at the peripheral level. Nevertheless, the available data is often contradictory. Because understanding how cytokines are modulated by psychoactive substances seems crucial to perspective successful therapeutic interventions, here, we conducted a scoping review of the available literature. We have focused on how different psychostimulants impact on the cytokine profile. Publications were grouped according to the substance addressed (methamphetamine, cocaine, methylphenidate, MDMA or other amphetamines), the type of exposure and period of evaluation (acute, short- or long-term exposure, withdrawal, and reinstatement). Studies were further divided in those addressing central cytokines, circulating (peripheral) levels, or both. Our analysis showed that the classical pro-inflammatory cytokines TNF-α, IL-6, and IL-1β were those more investigated. The majority of studies have reported increased levels of these cytokines in the central nervous system after acute or repeated drug. However, studies investigating cytokine levels during withdrawal or reinstatement have shown higher variability in their findings. Although we have identified fewer studies addressing circulating cytokines in humans, the available data suggest that the results may be more robust in animal models than in patients with problematic drug use. As a major conclusion, an extensive use of arrays for relevant cytokines should be considered to better determine which cytokines, upon the classical ones, may be involved in the progression from episodic use to the development of addiction. A concerted effort is still necessary to address the link between peripheral and central immune players, including from a longitudinal perspective. Until there, the identification of new biomarkers and therapeutic targets to envision personalized immune-based therapeutics will continue to be unlikely.

Role of Microglia in Psychostimulant Addiction

The use of psychostimulant drugs can modify brain function by inducing changes in the reward system, mainly due to alterations in dopaminergic and glutamatergic transmissions in the mesocorticolimbic pathway. However, the etiopathogenesis of addiction is a much more complex process. Previous data have suggested that microglia and other immune cells are involved in events associated with neuroplasticity and memory, which are phenomena that also occur in addiction. Nevertheless, how dependent is the development of addiction on the activity of these cells? Although the mechanisms are not known, some pathways may be involved. Recent data have shown psychoactive substances may act directly on immune cells, alter their functions and induce various inflammatory mediators that modulate synaptic activity. These could, in turn, be involved in the pathological alterations that occur in substance use disorder. Here, we extensively review the studies demonstrating how cocaine and amphetamines modulate microglial number, morphology, and function. We also describe the effect of these substances in the production of inflammatory mediators and a possible involvement of some molecular signaling pathways, such as the toll-like receptor 4. Although the literature in this field is scarce, this review compiles the knowledge on the neuroimmune axis that is involved in the pathogenesis of addiction, and suggests some pharmacological targets for the development of pharmacotherapy.

Partial MHC/neuroantigen peptide constructs attenuate methamphetamine-seeking and brain chemokine (C-C motif) ligand 2 levels in rats

There are no medications that target the neurotoxic effects or reduce the use of methamphetamine. Recombinant T-cell receptor ligand (RTL) 1000 [a partial major histocompatibility complex (pMHC) class II construct with a tethered myelin peptide], addresses the neuroimmune effects of methamphetamine addiction by competitively inhibiting the disease-promoting activity of macrophage migration inhibitory factor to CD74, a key pathway involved in several chronic inflammatory conditions, including substance use disorders. We previously reported that RTL constructs improve learning and memory impairments and central nervous system (CNS) inflammation induced by methamphetamine in mouse models. The present study in Lewis rats evaluated the effects of RTL1000 on maintenance of self-administration and cue-induced reinstatement using operant behavioral methods. Post-mortem brain and serum samples were evaluated for the levels of inflammatory factors. Rats treated with RTL1000 displayed significantly fewer presses on the active lever as compared to rats treated with vehicle during the initial extinction session, indicating more rapid extinction in the presence of RTL1000. Immunoblotting of rat brain sections revealed reduced levels of the pro-inflammatory chemokine (C-C motif) ligand 2 (CCL2) in the frontal cortex of rats treated with RTL1000, as compared to vehicle. Post hoc analysis identified a positive association between the levels of CCL2 detected in the frontal cortex and the number of lever presses during the first extinction session. Taken together, results suggest that RTL1000 may block downstream inflammatory effects of methamphetamine exposure and facilitate reduced drug seeking-potentially offering a new strategy for the treatment of methamphetamine-induced CNS injury and neuropsychiatric impairments.

Mammary tumors suppress aging-induced neuroinflammation in female Balb/c mice

Neuroinflammation confers changes in brain function (i.e., behavior) that are hypothesized to be adaptive in the short-term, but detrimental (e.g., depression, anxiety) if they persist. Both peripheral tumor growth (outside of the brain) and natural aging independently cause neuroinflammation in rodents, which is corroborated by clinical studies. Mammary tumor effects on neuroinflammation and behavior, however, are typically studied in young rodents, whereas most breast cancer patients are middle-aged. Therefore, the existing literature likely underestimates the resulting neuroinflammation that may occur in clinical cancer populations. The present study tested the hypothesis that aging exacerbates mammary tumor-induced neuroinflammation in female mice. Aging (16 months and ovariectomized) increased body and spleen masses, whereas tumors grew faster and increased spleen mass in young mice (12 weeks) only. Tumors (IL-6, IL-10, TNFα, MCP-1, CXCL1, IP-10) and aging (IL-10, IFNγ) independently increased circulating inflammatory markers, although these variables were only significantly additive in one case (TNFα). In contrast to our prediction, the interaction between tumors and aging resulted in reduced mRNA and protein expression of select inflammatory markers in the hippocampus of tumor-bearing aged mice relative to aged controls. These results indicate that tumors reduce inflammatory activation in the brains of aged mice, a deficit that is likely disadvantageous. Further understanding of how aging and cancer interact to affect brain function is necessary to provide clinically-relevant results and identify mechanisms underlying persistent behavioral issues hampering adult cancer patients.

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Tumors grew more slowly in aged mice.

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Tumors and aging independently increased circulating inflammatory markers.

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Tumors reduced mRNA and protein expression of inflammatory markers in the hippocampus in aged mice.

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Reduced inflammatory activation in the brains of aged mice is likely not adaptive.

Rodent Models of Adaptive Value Learning and Decision-Making

Real-world decisions are rarely as straightforward as choosing between clearly "good" vs. "bad" options. More often, options must be evaluated carefully because they differ in relative value. For example, we typically learn about (and make decisions between) options in comparison, where one outcome may be more costly or risky than the other. Several neuropsychiatric conditions are characterized by atypical evaluation of effort and risk costs, including major depression, schizophrenia, autism, obsessive-compulsive disorder, and substance use disorders. Aberrant value learning and decision-making have long been considered a cognitive-behavioral endophenotype of these disorders and can be modeled in rodents. This chapter presents two general methodological domains that the experimenter can manipulate in animal decision-making tasks: risk and effort. Here, we present detailed methods of rodent tasks frequently employed within these domains: probabilistic reversal learning (PRL) and effort choice. These tasks recruit regions within rodent frontal cortex, the amygdala, and the striatum, and performance is heavily modulated by dopamine, making these assays highly valid measures in the study of behavioral and substance addictions, in particular.

Differential effect of the DRD3 genotype on inflammatory cytokine responses during abstinence in amphetamine-dependent women

Amphetamine exposure impacts on innate and adaptive immunity and DRD3 may modulate the effect of amphetamine on the immune response. We assessed the immune-cytokine markers in 72 female patients with amphetamine dependence (AD) at baseline and after 4-week drug abstinence and in 51 healthy women. Multiplex magnetic bead assay was used to measure the plasma cytokine expression level simultaneously in all participants and DRD3 rs6280 polymorphism was genotyped in patients. We demonstrated an increase of the T helper 1 (Th1) cytokines (IL-2), Th2 cytokines (IL-4, IL-5, IL-6 and IL-10) and other cytokines (IL-1β) in the entire AD cohort. A similar cytokine pattern, along with a significantly decreased IL-8 and IL-10 levels was observed after 4-week abstinence. Among AD patients with DRD3 rs6280 TT genotype, the cytokine expression profile was consistent with total AD cohort at baseline and revealed a significant down-regulated plasma level of the Th1, Th2, and other cytokines except for IL-6 after 4-week abstinence. In AD group with DRD3 rs6280 C allele carrier, we found IL-2 level was significantly higher than healthy controls at baseline and remained higher, accompanied with a borderline increase in IL-4, IL-6 and IL-1β levels after 4-week abstinence. Our results suggest that chronic use of amphetamine increased both pro- and anti-inflammatory cytokines in AD patients, indicating the immune imbalance that may persist for 4 weeks or more. Besides, DRD3 rs6280 TT genotype may be associated with favorable recovery in general inflammatory cytokines during period of abstinence.

Persistent effect of withdrawal from intravenous methamphetamine self-administration on brain activation and behavioral economic indices involving an effort cost

Exposure to drugs of abuse produces maladaptive changes in cost-benefit decision-making, including the evaluation of time and risk. Studies probing the effects of drug exposure on such evaluations have primarily used experimenter-administered drug regimens. Similarly, while much is known about the neural bases of effort, there have been relatively fewer investigations of the effects of drug experience on effort-based choices. We recently reported that experimenter-administered methamphetamine (meth) resulted in steeper discounting of effort for food rewards in rats, when assessed in protracted withdrawal. Here, we studied rats that underwent withdrawal from weeks of meth intravenous self-administration that later could freely select between a high effort, preferred option (progressive ratio lever pressing for sucrose pellets) versus a low effort, less preferred option (freely-available lab chow). We found decreased effort for the preferred reward and changes in a behavioral economic index demonstrating an increased sensitivity to effort in meth-experienced rats. Critically, the decreased effort for the preferred option was only present in the context of a competing option, not when it was the only option. We also confirmed rats preferred sucrose pellets over chow when both were freely available. These long-lasting changes were accompanied by decreased c-Fos activation in ventral striatum and basolateral amygdala, regions known to be important in effort-based choices. Taken together with our previous observations, these results suggest a robust and enduring effect of meth on value-based decision-making, and point to the underlying neural mechanisms that support the evaluation of an effort cost.

Chronic ethanol consumption: role of TLR3/TRIF-dependent signaling

Chronic ethanol consumption stimulates neuroimmune signaling in the brain, and Toll-like receptor (TLR) activation plays a key role in ethanol-induced inflammation. However, it is unknown which of the TLR signaling pathways, the myeloid differentiation primary response gene 88 (MyD88) dependent or the TIR-domain-containing adapter-inducing interferon-β (TRIF) dependent, is activated in response to chronic ethanol. We used voluntary (every-other-day) chronic ethanol consumption in adult C57BL/6J mice and measured expression of TLRs and their signaling molecules immediately following consumption and 24 hours after removing alcohol. We focused on the prefrontal cortex where neuroimmune changes are the most robust and also investigated the nucleus accumbens and amygdala. Tlr mRNA and components of the TRIF-dependent pathway (mRNA and protein) were increased in the prefrontal cortex 24 hours after ethanol and Cxcl10 expression increased 0 hour after ethanol. Expression of Tlr3 and TRIF-related components increased in the nucleus accumbens, but slightly decreased in the amygdala. In addition, we demonstrate that the IKKε/TBK1 inhibitor Amlexanox decreases immune activation of TRIF-dependent pathway in the brain and reduces ethanol consumption, suggesting the TRIF-dependent pathway regulates drinking. Our results support the importance of TLR3 and the TRIF-dependent pathway in ethanol-induced neuroimmune signaling and suggest that this pathway could be a target in the treatment of alcohol use disorders.

Steep effort discounting of a preferred reward over a freely-available option in prolonged methamphetamine withdrawal in male rats

RATIONALE

Drug addiction can be described as aberrant allocation of effort toward acquiring drug, despite associated costs. It is unclear if this behavioral pattern results from an overvaluation of reward or to an altered sensitivity to costs.

OBJECTIVE

Present experiments assessed reward sensitivity and effortful choice in rats following 1 week of withdrawal from methamphetamine (mAMPH).

METHODS

Rats were treated with either saline or an escalating dose mAMPH regimen, then tested after a week without the drug. In experiment 1, rats were given a free choice between water and various concentrations of sucrose solution to assess general reward sensitivity. In experiment 2, rats were presented with a choice between lever-pressing for sucrose pellets on a progressive ratio schedule or consuming freely-available chow.

RESULTS

In experiment 1, we found no differences in sucrose preference between mAMPH- and saline-pretreated rats. In experiment 2, when selecting between two options, mAMPH-pretreated rats engaged in less lever-pressing for sucrose pellets (p < 0.01) and switched from this preferred reward to the chow sooner than saline-pretreated rats (p < 0.05). This effect was not consistent with general reward devaluation or loss of motivation.

CONCLUSIONS

These findings demonstrate that mAMPH exposure and withdrawal lead to steeper discounting of reward value by effort, an effect that is consistent with the effect of mAMPH on discounting by delay, and which may reflect an underlying shared mechanism.

Rigid patterns of effortful choice behavior after acute stress in rats

Physical effort is a common cost of acquiring rewards, and decreased effort is a feature of many neuropsychiatric disorders. Stress affects performance on several tests of cognition and decision making in both humans and nonhumans. Only a few recent reports show impairing effects of stress in operant tasks involving effort and cognitive flexibility. Brain regions affected by stress, such as the medial prefrontal cortex and amygdala, are also implicated in mediating effortful choices. Here, we assessed effort-based decision making after an acute stress procedure known to induce persistent impairment in shuttle escape and elevated plasma corticosterone. In these animals, we also probed levels of polysialyted neural cell adhesion molecule (PSA-NCAM), a marker of structural plasticity, in medial frontal cortex and amygdala. We found that animals that consistently worked for high magnitude rewards continued to do so, even after acute shock stress. We also found that PSA-NCAM was increased in both regions after effortful choice experience but not after shock stress alone. These findings are discussed with reference to the existing broad literature on cognitive effects of stress and in the context of how acute stress may bias effortful decisions to a rigid pattern of responding.

Methamphetamine blocks exercise effects on Bdnf and Drd2 gene expression in frontal cortex and striatum

Exposure to drugs of abuse can produce many neurobiological changes which may lead to increased valuation of rewards and decreased sensitivity to their costs. Many of these behavioral alterations are associated with activity of D2-expressing medium spiny neurons in the striatum. Additionally, Bdnf in the striatum has been shown to play a role in flexible reward-seeking behavior. Given that voluntary aerobic exercise can affect the expression of these proteins in healthy subjects, and that exercise has shown promise as an anti-addictive therapy, we set out to quantify changes in D2 and Bdnf expression in methamphetamine-exposed rats given access to running wheels. Sixty-four rats were treated for two weeks with an escalating dose of methamphetamine or saline, then either sacrificed, housed in standard cages, or given free access to a running wheel for 6 weeks prior to sacrifice. Rats treated with methamphetamine ran significantly greater distances than saline-treated rats, suggesting an augmentation in the reinforcement value of voluntary wheel running. Transcription of Drd2 and Bdnf was assessed via RT-qPCR. Protein expression levels of D2 and phosphorylation of the TrkB receptor were measured via western blot. Drd2 and Bdnf mRNA levels were impacted independently by exercise and methamphetamine, but exposure to methamphetamine prior to the initiation of exercise blocked the exercise-induced changes seen in rats treated with saline. Expression levels of both proteins were elevated immediately after methamphetamine, but returned to baseline after six weeks, regardless of exercise status.

The basolateral amygdala in reward learning and addiction

Sophisticated behavioral paradigms partnered with the emergence of increasingly selective techniques to target the basolateral amygdala (BLA) have resulted in an enhanced understanding of the role of this nucleus in learning and using reward information. Due to the wide variety of behavioral approaches many questions remain on the circumscribed role of BLA in appetitive behavior. In this review, we integrate conclusions of BLA function in reward-related behavior using traditional interference techniques (lesion, pharmacological inactivation) with those using newer methodological approaches in experimental animals that allow in vivo manipulation of cell type-specific populations and neural recordings. Secondly, from a review of appetitive behavioral tasks in rodents and monkeys and recent computational models of reward procurement, we derive evidence for BLA as a neural integrator of reward value, history, and cost parameters. Taken together, BLA codes specific and temporally dynamic outcome representations in a distributed network to orchestrate adaptive responses. We provide evidence that experiences with opiates and psychostimulants alter these outcome representations in BLA, resulting in long-term modified action.

Distinct patterns of outcome valuation and amygdala-prefrontal cortex synaptic remodeling in adolescence and adulthood

Adolescent behavior is typified by increased risk-taking, reward- and novelty-seeking, as well as an augmented need for social and environmental stimulation. This behavioral phenotype may result from alterations in outcome valuation or reward learning. In the present set of experiments, we directly compared adult and adolescent animals on tasks measuring both of these processes. Additionally, we examined developmental differences in dopamine D1-like receptor (D1R), dopamine D2-like receptor (D2R), and polysialylated neural cell adhesion molecule (PSA-NCAM) expression in animals that were trained on an effortful reward valuation task, given that these proteins play an important role in the functional development of the amygdala-prefrontocortical (PFC) circuit and mesocorticolimbic dopamine system. We found that adolescent animals were not different from adults in appetitive associative learning, but exhibited distinct pattern of responses to differences in outcome values, which was paralleled by an enhanced motivation to invest effort to obtain larger rewards. There were no differences in D2 receptor expression, but D1 receptor expression was significantly reduced in the striatum of animals that had experiences with reward learning during adolescence compared to animals that went through the same experiences in adulthood. We observed increased levels of PSA-NCAM expression in both PFC and amygdala of late adolescents compared to adults that were previously trained on an effortful reward valuation task. PSA-NCAM levels in PFC were strongly and positively associated with high effort/reward (HER) choices in adolescents, but not in adult animals. Increased levels of PSA-NCAM expression in adolescents may index increased structural plasticity and represent a neural correlate of a reward sensitive endophenotype.

The dopamine imbalance hypothesis of fatigue in multiple sclerosis and other neurological disorders

Fatigue is one of the most pervasive symptoms of multiple sclerosis (MS), and has engendered hundreds of investigations on the topic. While there is a growing literature using various methods to study fatigue, a unified theory of fatigue in MS is yet to emerge. In the current review, we synthesize findings from neuroimaging, pharmacological, neuropsychological, and immunological studies of fatigue in MS, which point to a specific hypothesis of fatigue in MS: the dopamine imbalance hypothesis. The communication between the striatum and prefrontal cortex is reliant on dopamine, a modulatory neurotransmitter. Neuroimaging findings suggest that fatigue results from the disruption of communication between these regions. Supporting the dopamine imbalance hypothesis, structural and functional neuroimaging studies show abnormalities in the frontal and striatal regions that are heavily innervated by dopamine neurons. Further, dopaminergic psychostimulant medication has been shown to alleviate fatigue in individuals with traumatic brain injury, chronic fatigue syndrome, and in cancer patients, also indicating that dopamine might play an important role in fatigue perception. This paper reviews the structural and functional neuroimaging evidence as well as pharmacological studies that suggest that dopamine plays a critical role in the phenomenon of fatigue. We conclude with how specific aspects of the dopamine imbalance hypothesis can be tested in future research.