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

Cocaine perturbs neurodevelopment and increases neuroinflammation in a prenatal cerebral organoid model

Prenatal exposure to cocaine causes abnormalities in foetal brain development, which are linked to later development of anxiety, depression and cognitive dysfunction. Previous studies in rodent models have indicated that prenatal cocaine exposure affects proliferation, differentiation and connectivity of neural cell types. Here, using cerebral organoids derived from the human iPSC cell line HPSI1213i-babk_2, we investigated cocaine-induced changes of the gene expression regulatory landscape at an early developmental time point, leveraging recent advances in single cell RNA-seq and single cell ATAC-seq. iPSC-cerebral organoids replicated well-established cocaine responses observed in vivo and provided additional information about the cell-type specific regulation of gene expression following cocaine exposure. Cocaine altered gene expression patterns, in part through epigenetic landscape remodelling, and revealed disordered neural plasticity mechanisms in the cerebral organoids. Perturbed neurodevelopmental cellular signalling and an inflammatory-like activation of astrocyte populations were also evident following cocaine exposure. The combination of altered neuroplasticity, neurodevelopment and neuroinflammatory signalling suggests cocaine exposure can mediate substantial disruption of normal development and maturation of the brain. These findings offer new insights into the cellular mechanism underlying the adverse effects of cocaine exposure on neurodevelopment and point to the possible pathomechanisms of later neuropsychiatric disturbances.

Morphine self-administration decreases intrinsic excitability of accumbal medium spiny neurons and suppresses the innate immune system in male Wistar rats

INTRODUCTION

Morphine alleviates severe pain but is addictive and associated with weakened immune system. Interestingly, the immunosuppressive effects have been linked to central circuits including the nucleus accumbens shell (NAc), suggesting that there might be a direct link between reward processing in the NAc and weakened immune system. The overall aim with this study was to assess the impact displayed by morphine self-administration on neuroplasticity in the NAc shell and circulating white blood cells.

METHODS

Wistar rats received morphine injections over ten days, and locomotor activity was monitored. Next, morphine self-administration, and relapse drinking after forced abstinence, were assessed. Lastly, electrophysiological recordings were conducted in the NAc ex vivo to define neurophysiological adaptations, and hematological analysis were conducted in parallel.

RESULTS

While ten days of morphine injections were not sufficient to affect morphine self-administration, behavioral sensitization to the locomotor stimulatory properties of morphine was observed and further correlated with the amount of morphine consumed following forced abstinence. Electrophysiological slice recordings demonstrated no effect on excitatory neurotransmission, but the intrinsic excitability of NAc neurons was significantly depressed compared to water drinking controls. In addition, hematological analysis demonstrated a significant decline in the number of white blood cells, especially monocytes and neutrophils, while erythrocytes were not affected. The amount of circulating white blood cells further correlated with morphine intake, but not with neurophysiological parameters.

CONCLUSION

The data presented here demonstrates that morphine self-administration produces accumbal neuroplasticity and biological transformations that could contribute to the addictive and immunosuppressive properties of morphine.

Characterization of serum and brain cytokine levels following prolonged binge-like methamphetamine self-administration and cued methamphetamine seeking

Methamphetamine (METH) use is associated with peripheral and brain inflammation that can contribute to METH-associated toxicity and heightened cue reactivity. However, the persistence of these phenomena, especially with regards to changes in brain proinflammatory cytokine levels, is not yet clear. In this study, we determined the effects of repeated binge-like METH self-administration (96-h/week for 3 weeks) followed by cued drug seeking for up to 60 days into abstinence in male and female rats. Serum cytokine levels were assessed prior to cued drug seeking tests on days 21 and 60 of abstinence, and cytokine levels in the prefrontal cortex (PFC) and dorsal striatum (DStr) were assessed on the day following that last cued seeking test. We observed robust levels of METH intake in both sexes as well as a gradual increase in magnitude of METH seeking across abstinence that did not differ between sexes. Magnitude of METH seeking on days 10 and 60 were positively correlated with prior total drug intake. Sex- and region-dependent changes in various chemokines and interleukins were observed in the PFC and DStr, as were sex- and time-dependent changes in serum cytokine levels, with the largest number of cytokines altered on day 60 in male animals. Serum levels of IL-6 were positively correlated with brain levels of this cytokine, but serum levels of this and other cytokines did not correlate with the magnitude of METH seeking. These findings suggest that binge-like METH intake produces persistent yet divergent central and peripheral immune responses that extend well into abstinence.

Impact of Substance Use Disorder on Tryptophan Metabolism Through the Kynurenine Pathway: A Narrative Review

Background/Objectives: Substance use disorder is a crisis impacting many people in the United States. This review aimed to identify the effect addictive substances have on the kynurenine pathway. Tryptophan is an essential amino acid metabolized by the serotonin and kynurenine pathways. The metabolites of these pathways play a role in the biological reward system. Addictive substances have been shown to cause imbalances in the ratios of these metabolites. With current treatment and therapeutic options being suboptimal, identifying biochemical mechanisms that are impacted during the use of addictive substances can provide alternative options for treatment or drug discovery. Methods: A systematic literature search was conducted to identify studies evaluating the relationship between substance use disorder and tryptophan metabolism through the kynurenine pathway. A total of 32 articles meeting eligibility criteria were used to review the relationship between the kynurenine pathway, tryptophan breakdown, and addictive substances. Results: The use of addictive substances dysregulates tryptophan metabolism and kynurenine metabolite concentrations. This imbalance directly affects the dopamine reward system and is thought to promote continued substance use. Conclusions: Further studies are needed to fully evaluate the metabolites of the kynurenine pathway, along with other options for treatment to repair the metabolite imbalance. Several possible therapeutics have been identified; drugs that restore homeostasis, such as Ro 61-8048 and natural products like Tinospora cordifolia or Decaisnea insignis, are promising options for the treatment of substance use disorder.

Role of Glial Cells in Neuronal Function, Mood Disorders, and Drug Addiction

Mood disorders and substance use disorder (SUD) are of immense medical and social concern. Although significant progress on neuronal involvement in mood and reward circuitries has been achieved, it is only relatively recently that the role of glia in these disorders has attracted attention. Detailed understanding of the glial functions in these devastating diseases could offer novel interventions. Here, following a brief review of circuitries involved in mood regulation and reward perception, the specific contributions of neurotrophic factors, neuroinflammation, and gut microbiota to these diseases are highlighted. In this context, the role of specific glial cells (e.g., microglia, astroglia, oligodendrocytes, and synantocytes) on phenotypic manifestation of mood disorders or SUD are emphasized. In addition, use of this knowledge in the potential development of novel therapeutics is touched upon.

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.

Methylone is a rapid-acting neuroplastogen with less off-target activity than MDMA

Background

Post-traumatic stress disorder (PTSD) is a highly prevalent psychiatric disorder that can become chronic and debilitating when left untreated. Available pharmacotherapies are limited, take weeks to show modest benefit and remain ineffective for up to 40% of patients. Methylone is currently in clinical development for the treatment of PTSD. Preclinical studies show rapid, robust and long-lasting antidepressant-like and anxiolytic effects. The mechanism of action underlying these effects is not yet fully understood. This study investigated the downstream gene expression changes and signaling pathways affected by methylone in key brain areas linked to PTSD and MDD. It also sought to determine whether neuroplasticity-related genes were involved. We compared effects of methylone with MDMA to explore similarities and differences in their brain effects because MDMA-assisted psychotherapy has recently shown benefit in clinical trials for PTSD and methylone is a structural analog of MDMA.

Methods

Monoamine binding, uptake and release studies were performed and a high-throughput-screen evaluated agonist/antagonist activities at 168 GPCRs in vitro. We used RNA sequencing (RNA-seq) to probe drug-induced gene expression changes in the amygdala and frontal cortex, two brain areas responsible for emotional learning that are affected by PTSD and MDD. Rats were treated with methylone or MDMA (both 10 mg/kg, IP), and their responses were compared with controls. We performed functional enrichment analysis to identify which pathways were regulated by methylone and/or MDMA. We confirmed changes in gene expression using immunohistochemistry.

Results

Methylone, a monoamine uptake inhibitor and releaser, demonstrated no off-target effects at 168 GPCRs, unlike MDMA, which showed activity at 5HT2A and 5HT2C receptors. RNA-seq results revealed significant regulation of myelin-related genes in the amygdala, confirmed by immunohistochemistry. In the frontal cortex, methylone significantly upregulated genes implicated in neuroplasticity.

Conclusion

Results suggest that (1) methylone is a rapid-acting neuroplastogen that affects key brain substrates for PTSD and MDD and that (2) methylone appears to exhibit higher specificity and fewer off-target effects than MDMA. Together, these results are consistent with the reported clinical experiences of methylone and MDMA and bolster the potential use of methylone in the treatment of PTSD and, potentially, other neuropsychiatric disorders.

Immunotherapeutic treatment of inflammation in mice exposed to methamphetamine

Introduction

Currently, there are no FDA-approved medications to treat methamphetamine addiction, including the inflammatory, neurotoxic, and adverse neuropsychiatric effects. We have shown that partial (p)MHC class II constructs (i.e., Recombinant T-cell receptor Ligand - RTL1000), comprised of the extracellular α1 and β1 domains of MHC class II molecules linked covalently to myelin oligodendrocyte glycoprotein (MOG)-35-55 peptide, can address the neuroimmune effects of methamphetamine addiction through its ability to bind to and down-regulate CD74 expression, block macrophage migration inhibitory factor (MIF) signaling, and reduce levels of pro-inflammatory chemokine ligand 2 (CCL2). The present study evaluated the effects of our third-generation pMHC II construct, DRmQ, on cognitive function and concentration of inflammatory cytokines in the frontal cortex, a region critical for cognitive functions such as memory, impulse control, and problem solving.

Methods

Female and male C57BL/6J mice were exposed to methamphetamine (or saline) via subcutaneous (s.c.) injections administered four times per day every other day for 14 days. Following methamphetamine exposure, mice received immunotherapy (DRmQ or ibudilast) or vehicle s.c. injections daily for five days. Cognitive function was assessed using the novel object recognition test (NORT). To evaluate the effects of immunotherapy on inflammation in the frontal cortex, multiplex immunoassays were conducted. ANOVA was used to compare exploration times on the NORT and immune factor concentrations.

Results

Post hoc analysis revealed increased novel object exploration time in MA-DRmQ treated mice, as compared to MA-VEH treated mice (non-significant trend). One-way ANOVA detected a significant difference across the groups in the concentration of macrophage inflammatory protein-2 (MIP-2) (p = 0.03). Post hoc tests indicated that mice treated with methamphetamine and DRmQ or ibudilast had significantly lower levels of MIP-2 in frontal cortex, as compared to mice treated with methamphetamine and vehicle (p > 0.05).

Discussion

By specifically targeting CD74, our DRQ constructs can block the signaling of MIF, inhibiting the downstream signaling and pro-inflammatory effects that contribute to and perpetuate methamphetamine addiction.