Effect of acute and chronic administration of methamphetamine on calcium-calmodulin dependent protein kinase II activity in the rat brain

D1R/PP2A/p-CaMKIIα signaling in the caudate putamen is involved in acute methamphetamine-induced hyperlocomotion

Drug addiction is underscored by the transition from experimental use to dependent use of addictive drugs. Acute use of methamphetamine (METH) causes a range of clinical symptoms, including hyperlocomotion. Dopamine D1 receptor (D1R)-mediated negative regulation of phosphorylated calcium/calmodulin-dependent protein kinase IIα (p-CaMKIIα, threonine [Thr] 286) is involved in the acute effects induced by single METH administration. Protein phosphatase 2A (PP2A) is a potential bridge that links D1R and p-CaMKIIα (Thr 286) after acute METH administration. However, the mechanisms underlying hyperlocomotion induced by single METH administration remain unclear. In this study, SCH23390 (a D1R inhibitor) and LB100 (a PP2A inhibitor) were administered to examine the involvement of D1R and PP2A signaling in acute METH-induced hyperlocomotion in mice. The protein levels of methylated PP2A-C (m-PP2A-C, leucine [Leu] 309), phosphorylated PP2A-C (p-PP2A-C, tyrosine [Tyr] 307), PP2A-C, p-CaMKIIα (Thr 286), and CaMKIIα in the prefrontal cortex (PFc), nucleus accumbens (NAc), and caudate putamen (CPu) were measured. Administration of 0.5 mg/kg SCH23390 reversed the acute METH-induced increase in protein levels of m-PP2A-C (Leu 309) and the decrease in protein levels of p-PP2A-C (Tyr 307) in the CPu, but not in the PFC and NAc. Moreover, prior administration of 0.1 mg/kg LB100 attenuated hyperlocomotion induced by single METH administration and reversed the decrease in protein levels of p-CaMKII (Thr 286) in the PFC, NAc, and CPu. Collectively, these results indicate that the D1R/PP2A/p-CaMKIIα signaling cascade in the CPu may be involved in hyperlocomotion after a single administration of METH.

Methamphetamine Activates Trace Amine Associated Receptor 1 to Regulate Astrocyte Excitatory Amino Acid Transporter-2 via Differential CREB Phosphorylation During HIV-Associated Neurocognitive Disorders

Methamphetamine (METH) use, referred to as methamphetamine use disorder (MUD), results in neurocognitive decline, a characteristic shared with HIV-associated neurocognitive disorders (HAND). MUD exacerbates HAND partly through glutamate dysregulation. Astrocyte excitatory amino acid transporter (EAAT)-2 is responsible for >90% of glutamate uptake from the synaptic environment and is significantly decreased with METH and HIV-1. Our previous work demonstrated astrocyte trace amine associated receptor (TAAR) 1 to be involved in EAAT-2 regulation. Astrocyte EAAT-2 is regulated at the transcriptional level by cAMP responsive element binding (CREB) protein and NF-κB, transcription factors activated by cAMP, calcium and IL-1β. Second messengers, cAMP and calcium, are triggered by TAAR1 activation, which is upregulated by IL-1β METH-mediated increases in these second messengers and signal transduction pathways have not been shown to directly decrease astrocyte EAAT-2. We propose CREB activation serves as a master regulator of EAAT-2 transcription, downstream of METH-induced TAAR1 activation. To investigate the temporal order of events culminating in CREB activation, genetically encoded calcium indicators, GCaMP6s, were used to visualize METH-induced calcium signaling in primary human astrocytes. RNA interference and pharmacological inhibitors targeting or blocking cAMP-dependent protein kinase A and calcium/calmodulin kinase II confirmed METH-induced regulation of EAAT-2 and resultant glutamate clearance. Furthermore, we investigated METH-mediated CREB phosphorylation at both serine 133 and 142, the co-activator and co-repressor forms, respectively. Overall, this work revealed METH-induced differential CREB phosphorylation is a critical regulator for EAAT-2 function and may thus serve as a mechanistic target for the attenuation of METH-induced excitotoxicity in the context of HAND.

Methamphetamine augment HIV-1 Tat mediated memory deficits by altering the expression of synaptic proteins and neurotrophic factors

Methamphetamine (METH) abuse is common among individuals infected with HIV-1 and has been shown to affect HIV replication and pathogenesis. These HIV-1 infected individuals also exhibit greater neuronal injury and higher cognitive decline. HIV-1 proteins, specifically gp120 and HIV-1 Tat, have been earlier shown to affect neurocognition. HIV-1 Tat, a viral protein released early during HIV-1 replication, contributes to HIV-associated neurotoxicity through various mechanisms including production of pro-inflammatory cytokines, reactive oxygen species and dysregulation of neuroplasticity. However, the combined effect of METH and HIV-1 Tat on neurocognition and its potential effect on neuroplasticity mechanisms remains largely unknown. Therefore, the present study was undertaken to investigate the combined effect of METH and HIV-1 Tat on behavior and on the expression of neuroplasticity markers by utilizing Doxycycline (DOX)-inducible HIV-1 Tat (1-86) transgenic mice. Expression of Tat in various brain regions of these mice was confirmed by RT-PCR. The mice were administered with an escalating dose of METH (0.1 mg/kg to 6 mg/kg, i.p) over a 7-day period, followed by 6 mg/kg, i.p METH twice a day for four weeks. After three weeks of METH administration, Y maze and Morris water maze assays were performed to determine the effect of Tat and METH on working and spatial memory, respectively. Compared with controls, working memory was significantly decreased in Tat mice that were administered METH. Moreover, significant deficits in spatial memory were also observed in Tat-Tg mice that were administered METH. A significant reduction in the protein expressions of synapsin 1, synaptophysin, Arg3.1, PSD-95, and BDNF in different brain regions were also observed. Expression levels of Calmodulin kinase II (CaMKII), a marker of synaptodendritic integrity, were also significantly decreased in HIV-1 Tat mice that were treated with METH. Together, this data suggests that METH enhances HIV-1 Tat-induced memory deficits by reducing the expression of pre- and postsynaptic proteins and neuroplasticity markers, thus providing novel insights into the molecular mechanisms behind neurocognitive impairments in HIV-infected amphetamine users.

Involvement of calcium/calmodulin-dependent protein kinase II in methamphetamine-induced neural damage

Methamphetamine (METH), an illicit drug, is widely abused in many parts of the world. Mounting evidence shows that METH exposure contributes to neurotoxicity, particularly for the monoaminergic neurons. However, to date, only a few studies have tried to unravel the mechanisms involved in METH-induced non-monoaminergic neural damage. Therefore, in the present study, we tried to explore the mechanisms for METH-induced neural damage in cortical neurons. Our results showed that METH significantly increased intracellular [Ca(2) (+) ]i in Ca(2) (+) -containing solution rather than Ca(2) (+) -free solution. Moreover, METH also upregulated calmodulin (CaM) expression and activated CaM-dependent protein kinase II (CaMKII). Significantly, METH-induced neural damage can be partially retarded by CaM antagonist W7 as well as CaMKII blocker KN93. In addition, L-type Ca(2) (+) channel was also proved to be involved in METH-induced cell damage, as nifedipine, the L-type Ca(2) (+) channel-specific inhibitor, markedly attenuated METH-induced neural damage. Collectively, our results suggest that Ca(2) (+) -CaM-CaMKII is involved in METH-mediated neurotoxicity, and it might suggest a potential target for the development of therapeutic strategies for METH abuse. Copyright © 2016 John Wiley & Sons, Ltd.

Regulatory effect of bee venom on methamphetamine-induced cellular activities in prefrontal cortex and nucleus accumbens in mice

Our previous studies demonstrated that subcutaneous injection of bee venom (BV) into the Zusanli (ST36) acupuncture point, namely BV acupuncture, dose-dependently prevents conditioned place preference (CPP) induced by repeated injection of methamphetamine (METH) in mice. To expand on our observations, the present study was designed to determine the suppressive mechanisms of BV acupuncture in the development of METH-induced CPP by evaluating the changes in expression of ΔFosB, phosphorylated extracellular signal-regulated kinase 1/2 (pERK), and phosphorylated calcium/calmodulin-dependent protein kinase type II (pCaMKII) in the prefrontal cortex (PFC) and nucleus accumbens (NAc) in mice. Pre-emptive treatment with BV at 30 min before repeated METH injection completely suppressed acquisition of CPP at the day 7 test session. METH-induced upregulation of ΔFosB and pERK in PFC and NAc was significantly reduced by BV pretreatment. Expression of pCaMKII was significantly elevated by METH in NAc and reduced in PFC. BV pretreatment reversed the changes of pCaMKII expression in PFC and NAc. These findings suggest that BV acupuncture may exert a suppressive effect on METH-induced addiction via regulation of signaling cascades of ΔFosB, ERK, and CaMKII in PFC and NAc.

Intra-nucleus accumbens administration of the calcium/calmodulin-dependent protein kinase II inhibitor KN93 induced antinociception in rats with mononeuropathy

The present study was conducted on rats with mononeuropathy induced by left common sciatic nerve ligation. Unilateral sciatic nerve loose ligation produced decreases of the hindpaw withdrawal latency (HWL) to noxious thermal and mechanical stimulation. Intra-nucleus accumbens (NAc) injection of 1μg, 3μg and 6μg of KN93, the calcium/calmodulin-dependent protein kinase II (CaMKII) inhibitor, dose-dependently increased the HWL in mononeuropathic rats. Furthermore, intra-NAc administration of morphine, the HWL to noxious thermal and mechanical stimulation increased markedly, and there were no significant differences between morphine group and KN93 group. The results demonstrated that intra-NAc injection of KN93 induced significant antinociceptive effects in rats with mononeuropathy, indicating CaMKII may play important roles in transmission of nociceptive information in the NAc of mononeuropathic rats.

Striatal signal transduction and drug addiction

Drug addiction is a severe neuropsychiatric disorder characterized by loss of control over motivated behavior. The need for effective treatments mandates a greater understanding of the causes and identification of new therapeutic targets for drug development. Drugs of abuse subjugate normal reward-related behavior to uncontrollable drug-seeking and -taking. Contributions of brain reward circuitry are being mapped with increasing precision. The role of synaptic plasticity in addiction and underlying molecular mechanisms contributing to the formation of the addicted state are being delineated. Thus we may now consider the role of striatal signal transduction in addiction from a more integrative neurobiological perspective. Drugs of abuse alter dopaminergic and glutamatergic neurotransmission in medium spiny neurons of the striatum. Dopamine receptors important for reward serve as principle targets of drugs abuse, which interact with glutamate receptor signaling critical for reward learning. Complex networks of intracellular signal transduction mechanisms underlying these receptors are strongly stimulated by addictive drugs. Through these mechanisms, repeated drug exposure alters functional and structural neuroplasticity, resulting in transition to the addicted biological state and behavioral outcomes that typify addiction. Ca²⁺ and cAMP represent key second messengers that initiate signaling cascades, which regulate synaptic strength and neuronal excitability. Protein phosphorylation and dephosphorylation are fundamental mechanisms underlying synaptic plasticity that are dysregulated by drugs of abuse. Increased understanding of the regulatory mechanisms by which protein kinases and phosphatases exert their effects during normal reward learning and the addiction process may lead to novel targets and pharmacotherapeutics with increased efficacy in promoting abstinence and decreased side effects, such as interference with natural reward, for drug addiction.

Protein kinases and addiction

Although drugs of abuse have different chemical structures and interact with different protein targets, all appear to usurp common neuronal systems that regulate reward and motivation. Addiction is a complex disease that is thought to involve drug-induced changes in synaptic plasticity due to alterations in cell signaling, gene transcription, and protein synthesis. Recent evidence suggests that drugs of abuse interact with and change a common network of signaling pathways that include a subset of specific protein kinases. The best studied of these kinases are reviewed here and include extracellular signal-regulated kinase, cAMP-dependent protein kinase, cyclin-dependent protein kinase 5, protein kinase C, calcium/calmodulin-dependent protein kinase II, and Fyn tyrosine kinase. These kinases have been implicated in various aspects of drug addiction including acute drug effects, drug self-administration, withdrawal, reinforcement, sensitization, and tolerance. Identifying protein kinase substrates and signaling pathways that contribute to the addicted state may provide novel approaches for new pharmacotherapies to treat drug addiction.