Synthetic cathinone MDPV enhances reward function through purinergic P2X7 receptor-dependent pathway and increases P2X7 gene expression in nucleus accumbens

Transcriptional characterization of cocaine withdrawal versus extinction within nucleus accumbens

Substance use disorder is characterized by a maladaptive imbalance wherein drug seeking persists despite negative consequences or drug unavailability. This imbalance correlates with neurobiological alterations some of which are amplified during forced abstinence, thereby compromising the capacity of extinction-based approaches to prevent relapse. Cocaine use disorder (CUD) exemplifies this phenomenon in which neurobiological modifications hijack brain reward regions such as the nucleus accumbens (NAc) to manifest craving and withdrawal-like symptoms. While increasing evidence links transcriptional changes in the NAc to specific phases of addiction, genome-wide changes in gene expression during withdrawal vs. extinction (WD/Ext) have not been examined in a context- and NAc-subregion-specific manner. Here, we used cocaine self-administration (SA) in rats combined with RNA-sequencing (RNA-seq) of NAc subregions (core and shell) to transcriptionally profile the impact of experiencing withdrawal in the home cage or in the previous drug context or experiencing extinction training. As expected, home-cage withdrawal maintained drug seeking in the previous drug context, whereas extinction training reduced it. By contrast, withdrawal involving repetitive exposure to the previous drug context increased drug-seeking behavior. Bioinformatic analyses of RNA-seq data revealed gene expression patterns, networks, motifs, and biological functions specific to these behavioral conditions and NAc subregions. Comparing transcriptomic analysis of the NAc of patients with CUD highlighted conserved gene signatures, especially with rats that were repetitively exposed to the previous drug context. Collectively, these behavioral and transcriptional correlates of several withdrawal-extinction settings reveal fundamental and translational information about potential molecular mechanisms to attenuate drug-associated memories.

The pharmacology and neurotoxicology of synthetic cathinones

The synthetic cathinones are man-made compounds derived from the naturally occurring drug cathinone, which is found in the khat plant. The drugs in this pharmacological class that will be the focus of this chapter include mephedrone, MDPV, methcathinone and methylone. These drugs are colloquially known as "bath salts". This misnomer suggests that these drugs are used for health improvement or that they have legitimate medical uses. The synthetic cathinones are dangerous drugs with powerful pharmacological effects that include high abuse potential, hyperthermia and hyperlocomotion. These drugs also share many of the pharmacological effects of the amphetamine class of drugs including methamphetamine, amphetamine and MDMA and therefore have high potential to cause damage to the central nervous system. The synthetic cathinones are frequently taken in combination with other psychoactive drugs such as alcohol, marijuana and the amphetamine-like stimulants, creating a situation where heightened pharmacological and neurotoxicological effects are likely to occur. Despite the structural features shared by the synthetic cathinones and amphetamine-like stimulants, including their actions at monoamine transporters and receptors, the effects of the synthetic cathinones do not always match those of the amphetamines. In particular, the synthetic cathinones are far less neurotoxic than their amphetamine counterparts, they produce a weaker hyperthermia, and they cause less glial activation. This chapter will briefly review the pharmacology and neurotoxicology of selected synthetic cathinones with the aim of delineating key areas of agreement and disagreement in the literature particularly as it relates to neurotoxicological outcomes.

P2X7 receptor antagonist A-438079 alleviates oxidative stress of lung in LPS-induced septic rats

Sepsis is a deadly systemic inflammatory response of the body against infection resulting in immune response, cell differentiation and organ damage. Endotoxemia is one of the causes of sepsis-related acute respiratory distress and respiratory burst is an important generator of oxidants. Inflammation may be aggravated by overexpression of ATP-gated purinergic receptors (i.e., P2X7R) following cell damage. We aimed to evaluate the effects of P2X7R antagonist A-438079 on lung oxidative status and the receptor expression in endotoxemia of sepsis. Rats were subjected to sepsis by E. coli lipopolysaccharide (LPS) and treated with 15 mg/kg A-438079. The increase in circulatory IL-1β and IL-8 concentrations in LPS group confirmed the systemic inflammatory response to endotoxemia compared with Control groups (p < 0.001). Besides, there was an increase in P2X7R expression in lung tissue after LPS administration. Compared with Control groups, there were significant increases in the values of malondialdehyde (MDA), glutathione (GSH), superoxide dismutase (SOD) and catalase (CAT) (p < 0.001), and myeloperoxidase (MPO) (p < 0.05) in lung tissue of LPS group. P2X7R expression in lung and IL-1β level in blood did not increase in LPS + A-438079 group. A-438079 decreased the lung levels of MDA, GSH, CAT and SOD (p < 0.001), and MPO (p < 0.01) in septic rats. As a result, administration of pathogen-associated LPS led to increased P2X7R expression into lung tissue and elevated lipid peroxidation product MDA with regard to oxidative damage. The P2X7R antagonist A-438079 alleviated the oxidative stress of lung with a balance of tissue oxidant/antioxidant factors in experimental sepsis in rats.

Purinergic P2X7 receptor antagonist inhibits methamphetamine-induced reward, hyperlocomotion, and cortical IL-7A levels in mice: A role for P2X7/IL-17A crosstalk in methamphetamine behaviors?

P2X7 receptors are dysregulated during psychostimulant exposure. Furthermore, P2X7 receptors enhance endogenous systems (e.g., cytokines, dopamine, and glutamate) that facilitate psychostimulant addiction. Therefore, using mouse locomotor, conditioned place preference (CPP), and intracranial self-stimulation (ICSS) assays, we tested the hypothesis that methamphetamine (METH) reward and acute locomotor activation requires P2X7 receptor activity. We also investigated effects of P2X7 blockade on METH-induced changes in cytokine levels in brain reward regions. A438079 (5, 10, 50 mg/kg), a P2X7 antagonist, did not affect spontaneous locomotor activity but reduced hyperlocomotion caused by acute METH (1 mg/kg) exposure. A438079 (10 mg/kg) also prevented expression of METH CPP without causing aversive or rewarding effects. For ICSS experiments, METH (1 mg/kg) facilitated brain reward function as interpreted from reductions in baseline threshold. In the presence of A438079 (50 mg/kg), METH-induced facilitation of ICSS was reduced. Repeated METH exposure (1 mg/kg × 7 d) caused enhancement of IL-17A levels in the prefrontal cortex (PFC) that was normalized by A438070 (10 mg/kg × 7 d). The present data suggest that P2X7 receptor activity contributes to rewarding and locomotor-stimulant effects of METH through a potential mechanism involving IL-17A, which has recently been implicated in anxiety.

Interactions of neuroimmune signaling and glutamate plasticity in addiction

Chronic use of drugs of abuse affects neuroimmune signaling; however, there are still many open questions regarding the interactions between neuroimmune mechanisms and substance use disorders (SUDs). Further, chronic use of drugs of abuse can induce glutamatergic changes in the brain, but the relationship between the glutamate system and neuroimmune signaling in addiction is not well understood. Therefore, the purpose of this review is to bring into focus the role of neuroimmune signaling and its interactions with the glutamate system following chronic drug use, and how this may guide pharmacotherapeutic treatment strategies for SUDs. In this review, we first describe neuroimmune mechanisms that may be linked to aberrant glutamate signaling in addiction. We focus specifically on the nuclear factor-kappa B (NF-κB) pathway, a potentially important neuroimmune mechanism that may be a key player in driving drug-seeking behavior. We highlight the importance of astroglial-microglial crosstalk, and how this interacts with known glutamatergic dysregulations in addiction. Then, we describe the importance of studying non-neuronal cells with unprecedented precision because understanding structure-function relationships in these cells is critical in understanding their role in addiction neurobiology. Here we propose a working model of neuroimmune-glutamate interactions that underlie drug use motivation, which we argue may aid strategies for small molecule drug development to treat substance use disorders. Together, the synthesis of this review shows that interactions between glutamate and neuroimmune signaling may play an important and understudied role in addiction processes and may be critical in developing more efficacious pharmacotherapies to treat SUDs.

Salient brain entities labelled in P2rx7-EGFP reporter mouse embryos include the septum, roof plate glial specializations and circumventricular ependymal organs

The purinergic system is one of the oldest cell-to-cell communication mechanisms and exhibits relevant functions in the regulation of the central nervous system (CNS) development. Amongst the components of the purinergic system, the ionotropic P2X7 receptor (P2X7R) stands out as a potential regulator of brain pathology and physiology. Thus, P2X7R is known to regulate crucial aspects of neuronal cell biology, including axonal elongation, path-finding, synapse formation and neuroprotection. Moreover, P2X7R modulates neuroinflammation and is posed as a therapeutic target in inflammatory, oncogenic and degenerative disorders. However, the lack of reliable technical and pharmacological approaches to detect this receptor represents a major hurdle in its study. Here, we took advantage of the P2rx7-EGFP reporter mouse, which expresses enhanced green fluorescence protein (EGFP) immediately downstream of the P2rx7 proximal promoter, to conduct a detailed study of its distribution. We performed a comprehensive analysis of the pattern of P2X7R expression in the brain of E18.5 mouse embryos revealing interesting areas within the CNS. Particularly, strong labelling was found in the septum, as well as along the entire neural roof plate zone of the brain, except chorioidal roof areas, but including specialized circumventricular roof formations, such as the subfornical and subcommissural organs (SFO; SCO). Moreover, our results reveal what seems a novel circumventricular organ, named by us postarcuate organ (PArcO). Furthermore, this study sheds light on the ongoing debate regarding the specific presence of P2X7R in neurons and may be of interest for the elucidation of additional roles of P2X7R in the idiosyncratic histologic development of the CNS and related systemic functions.

ATP Signaling Controlling Dyskinesia Through P2X7 Receptors

Dopamine replacement therapy with L-3,4-dihydroxyphenylalanine (L-DOPA) is the only temporary therapy for Parkinson's disease (PD), but it triggers dyskinesia over time. Since dyskinesia is associated with increased neuronal firing that bolsters purinergic signaling, we now tested whether the selective and blood-brain barrier-permeable P2X7 receptor antagonist Brilliant Blue-G (BBG, 22.5-45 mg/kg ip) attenuated behavioral, neurochemical and biochemical alterations in rats turned hemiparkinsonian upon unilateral striatal injection of 6-hydroxydopamine (6-OHDA) and treated daily with L-DOPA (30 mg/kg by gavage) for 22 days. The blockade of P2X7 receptors decreased L-DOPA-induced dyskinesia and motor incoordination in hemiparkinsonian rats. In parallel, BBG treatment rebalanced the altered dopamine D1 and D2 receptor density and signaling as well as some neuroinflammation-associated parameters in the striatum and substantia nigra. These findings herald a hitherto unrecognized role for purinergic signaling in the etiopathology of dyskinesia and prompt P2X7 receptor antagonists as novel candidate anti-dyskinesia drugs.