Dose-related alteration in nitric oxide synthase mRNA expression induced by amphetamine and the full D1 dopamine receptor agonist SKF-82958 in mouse striatum

Role of nitric oxide in psychostimulant-induced neurotoxicity

In recent decades, consumption of psychostimulants has been significantly increased all over the world, while exact mechanisms of neurochemical effects of psychomotor stimulants remained unclear. It is assumed that the neuronal messenger nitric oxide (NO) may be involved in mechanisms of neurotoxicity evoked by psychomotor stimulants. However, possible participation of NO in various pathological states is supported mainly by indirect evidence because of its short half-life in tissues. Aim of this review is to describe the involvement of NO and the contribution of lipid peroxidation (LPO) and acetylcholine (ACH) release in neurotoxic effects of psychostimulant drugs. NO was directly determined in brain structures by electron paramagnetic resonance (EPR). Both NO generation and LPO products as well as release of ACH were increased in brain structures following four injections of amphetamine (AMPH). Pretreatment of rats with the non-selective inhibitor of NO-synthase (NOS) N-nitro-L-arginine or the neuronal NOS inhibitor 7-nitroindazole significantly reduced increase of NO generation as well as the rise of ACH release induced by AMPH. Both NOS inhibitors injected prior to AMPH had no effect on enhanced levels of LPO products. Administration of the noncompetitive NMDA receptor antagonist dizocilpine abolished increase of both NO content and concentration of LPO products induced by of the psychostimulant drug. Dizocilpine also eliminated the influence of AMPH on the ACH release. Moreover, the neurochemical and neurotoxic effects of the psychostimulant drug sydnocarb were compared with those of AMPH. Single injection of AMPH showed a more pronounced increase in NO and TBARS levels than after an equimolar concentration of sydnocarb. The findings demonstrate the crucial role of NO in the development of neurotoxicity elicited by psychostimulants and underline the key role of NOS in AMPH-induced neurotoxicity.

The neuropeptide F/nitric oxide pathway is essential for shaping locomotor plasticity underlying locust phase transition

Behavioral plasticity is widespread in swarming animals, but little is known about its underlying neural and molecular mechanisms. Here, we report that a neuropeptide F (NPF)/nitric oxide (NO) pathway plays a critical role in the locomotor plasticity of swarming migratory locusts. The transcripts encoding two related neuropeptides, NPF1a and NPF2, show reduced levels during crowding, and the transcript levels of NPF1a and NPF2 receptors significantly increase during locust isolation. Both NPF1a and NPF2 have suppressive effects on phase-related locomotor activity. A key downstream mediator for both NPFs is nitric oxide synthase (NOS), which regulates phase-related locomotor activity by controlling NO synthesis in the locust brain. Mechanistically, NPF1a and NPF2 modify NOS activity by separately suppressing its phosphorylation and by lowering its transcript level, effects that are mediated by their respective receptors. Our results uncover a hierarchical neurochemical mechanism underlying behavioral plasticity in the swarming locust and provide insights into the NPF/NO axis.

DOI:http://dx.doi.org/10.7554/eLife.22526.001

Migratory locusts are widespread throughout the Eastern Hemisphere, especially in Asia, Australia and Africa. Although usually solitary insects, locusts can also form swarms made up of millions of individuals, which can devastate crops. Swarming can be studied on a smaller scale in the laboratory by forcing locusts to crowd together. This causes the locusts to enter a so-called gregarious state in which they are more active and sociable, which in turn promotes swarming. Isolating individual locusts has the opposite effect, causing the insects to enter a solitary state in which they are less active.

Chemicals in the locust brain called neuropeptides control phase transitions between solitary and gregarious behavior. Neuropeptides bind to specific proteins called receptors in the outer membranes of neurons and initiate unique signaling cascades inside cells. However, exactly how neuropeptides regulate the changes in locust behavior that affect swarming was not clear.

Hou et al. now reveal the role that two related neuropeptides, NPF1a and NPF2, play in this process. Crowding causes the levels of NPF1a and NPF2 in the locust brain to decrease, whereas isolating individual locusts causes the levels of two NPF receptors to increase. Both neuropeptides reduce levels of a molecule called nitric oxide in the brain. NPF1a does this by reducing the activity of the enzyme that produces nitric oxide, whereas NPF2 reduces the production of this enzyme. The reduction in nitric oxide in turn makes the locusts less active.

Similar NPF neuropeptides had previously been shown to affect activity levels in other invertebrates, such as roundworms and fruit flies. This, combined with the results now presented by Hou et al., suggests that the NPF/nitric oxide pathway may regulate activity in insects in general. Future work should investigate this possibility, as well as whether the NPF/nitric oxide pathway controls changes in other insect behaviors such as feeding and mating.

DOI:http://dx.doi.org/10.7554/eLife.22526.002

Neuronal Nicotinic Receptors as New Targets for Amphetamine-Induced Oxidative Damage and Neurotoxicity

Amphetamine derivatives such as methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA, “ecstasy”) are widely abused drugs in a recreational context. This has led to concern because of the evidence that they are neurotoxic in animal models and cognitive impairments have been described in heavy abusers. The main targets of these drugs are plasmalemmal and vesicular monoamine transporters, leading to reverse transport and increased monoamine efflux to the synapse. As far as neurotoxicity is concerned, increased reactive oxygen species (ROS) production seems to be one of the main causes. Recent research has demonstrated that blockade of α7 nicotinic acetylcholine receptors (nAChR) inhibits METH- and MDMA-induced ROS production in striatal synaptosomes which is dependent on calcium and on NO-synthase activation. Moreover, α7 nAChR antagonists (methyllycaconitine and memantine) attenuated in vivo the neurotoxicity induced by METH and MDMA, and memantine prevented the cognitive impairment induced by these drugs. Radioligand binding experiments demonstrated that both drugs have affinity to α7 and heteromeric nAChR, with MDMA showing lower K_i values, while fluorescence calcium experiments indicated that MDMA behaves as a partial agonist on α7 and as an antagonist on heteromeric nAChR. Sustained Ca increase led to calpain and caspase-3 activation. In addition, modulatory effects of MDMA on α7 and heteromeric nAChR populations have been found.

Methamphetamine Dysregulates Redox Status in Primary Rat Astrocyte and Mesencephalic Neuronal Cultures

Astrocytes provide structural, metabolic and trophic support to neurons. They are directly involved in the regulation of neuronal transmission and synaptic activity and respond to the synaptic release and remove neurotransmitters from the extracellular fluid. The dysfunction of astrocytes has been implicated in multiple neurotoxicities, including those associated with drugs of abuse. Methamphetamine (METH) has long-lasting neurotoxic effects, yet little is known about the mechanisms that govern METH-induced neural dysfunction, and especially the astrocytic control over the extracellular milieu. The purpose of this study was to clarify the response of astrocytes and neurons treated with METH and determine their relative sensitivity to this drug of abuse. Confluent rat primary astrocyte and mesencephalic neuron cultures were treated for 24 hrs with 0, 0.1, 0.5 or 1 mM METH, and the initial rate of glutamate and glutamine uptake was measured over a 5 min period. Additional studies examined the effect of METH (24 hr exposure at similar concentrations) on oxidative endpoints, namely glutathione (GSH) levels, lactate dehydrogenase (LDH) release and isoprostane (IsoP) levels, considered to be the most accurate biomarker of lipid peroxidation. There was no effect of METH on the rates of glutamate and glutamine uptake, and these were indistinguishable from controls. However, METH concentration-dependently affected astrocytic and neuronal GSH levels, leading to a significant decrease in redox potential at all of the tested concentrations (p<0.05). METH also significantly enhanced astrocytic LDH release at the 0.5 and 1.0 mM exposures. Consistent with the changes in IsoPs, METH (0.5 and 1.0 mM) also increased the expression of nuclear factor erythroid 2-related factor 2 (Nrf2), a transcription factor with a key role in regulating oxidative stress responses. However, this Nrf2 increased in expression was observed only in astrocytes and no effect was noted in neurons. Taken together, this study establishes that METH affects both astrocyte and neuronal functions, and that oxidative stress is a proximate mechanism for METH's-induced neurotoxicity on both cell types. Furthermore, in response to oxidative stress astrocytes efficiently upregulated Nrf2 nuclear translocation and transcription. These effects were absent in neurons. Combined with their lower content of GSH, these characteristics may account for the greater sensitivity of neurons to METH-induce toxicity.

Involvement of nicotinic receptors in methamphetamine- and MDMA-induced neurotoxicity: pharmacological implications

During the last years, we have focused on the study of the neurotoxic effects of 3,4-methylenedioxymethamphetamine (MDMA) and methamphetamine (METH) on the central nervous system (CNS) and their pharmacological prevention methods. In the process of this research, we have used a semipurified synaptosomal preparation from striatum of mice or rats as a reliable in vitro model to study reactive oxygen species (ROS) production by these amphetamine derivatives, which is well-correlated with their dopaminergic injury in in vivo models. Using this preparation, we have demonstrated that blockade of alpha7 nicotinic receptors with methyllycaconitine (MLA) prevents ROS production induced by MDMA and METH. Consequently, in vivo, MLA significantly prevents MDMA- and METH-induced neurotoxicity at dopaminergic level (mouse striatum), without affecting hyperthermia induced by these amphetamines. Additionally, when neuroprotection was assayed with memantine (MEM), a dual antagonist of NMDA and alpha7 receptors, an effective neuroprotection was obtained also ahead of serotonergic injury induced by MDMA in rats. MEM also prevents MDMA effect on serotonin transporter functionality and METH effect on dopamine transporter (DAT), suggesting that behavioral effects of these psychostimulants can also be modulated by MEM. Finally, we have demonstrated that MEM prevents the impaired memory function induced by MDMA, and also, using binding studies with radioligands, we have characterized the interaction of these substances with nicotinic receptors. Studies at molecular level showed that both MDMA and METH displaced competitively the binding of radioligands with homomeric alpha7 and heteromeric nicotinic acetylcholine receptors (nAChRs), indicating that they can directly interact with them. In all the cases, MDMA displayed higher affinity than METH and it was higher for heteromeric than for alpha7 subtype. Pre-incubation of differentiated PC12 cells with MDMA or METH induces nAChR upregulation in a concentration- and time-dependent manner, as many nicotinic ligands do, supporting their functional interaction with nAChRs. Such interaction expands the pharmacological profile of amphetamines and can account for some of their effects.

Differential role of the nNOS gene in the development of behavioral sensitization to cocaine in adolescent and adult B6;129S mice

RATIONALE

Previous studies have suggested the involvement of neuronal nitric oxide synthase (nNOS) in the development of sensitization to psychostimulants. Ontogeny-dependent differences in the response to psychostimulants have been reported.

OBJECTIVE

The objectives were to investigate (a) the short- and long-term consequences of adolescent and adult cocaine exposure on behavioral sensitization and (b) the role of the nNOS gene in behavioral sensitization in adolescent and adult mice.

MATERIALS AND METHODS

Adolescent and adult wild type (WT) and nNOS knockout (KO) mice received saline or cocaine (20 mg/kg) for 5 days and then were challenged with cocaine (20 mg/kg) after a drug-free period of 10 or 30 days. Locomotor activity was recorded by infrared beam interruptions. nNOS immunoreactive (ir) neurons in the dorsal and ventral striatum were quantified 24 h after repeated administration of cocaine to adolescent and adult WT mice.

RESULTS

Repeated administration of cocaine to either WT or nNOS KO mice during adolescence resulted in locomotor sensitization, which persisted into adulthood. WT but not KO adult mice developed long-term sensitization to cocaine. Repeated cocaine administration resulted in a 96% increase in the expression of nNOS-ir neurons in the dorsal striatum of adult but not adolescent WT mice.

CONCLUSIONS

The nNOS gene is essential for the induction of behavioral sensitization to cocaine in adulthood but not in adolescence. The increased expression of nNOS-ir neurons in the dorsal striatum may underlie the induction of behavioral sensitization in adulthood. Thus, the NO-signaling pathway has an ontogeny-dependent role in the neuroplasticity underlying cocaine behavioral sensitization.

Dopamine D1 receptor-dependent regulation of extracellular citrulline level in the rat nucleus accumbens during conditioned fear response

Nucleus accumbens (N.Acc) contains a subclass of nitric oxide (NO)-generating interneurons that are presumably regulated by the dopamine input. Receptor mechanisms underlying dopamine-NO interaction in the N.Acc are poorly understood. In the current study, we used in vivo microdialysis combined with high-performance liquid chromatography to examine participation of dopamine D1 receptors in regulation of extracellular levels of citrulline (an NO co-product) in the medial N.Acc of Sprague-Dawley rats during both pharmacological challenge and a conditioned fear response. The intraaccumbal infusion of the D1 receptor agonist SKF-38393 (100-500 microM) increased dose-dependently the local dialysate citrulline levels. The SKF-38393-induced increase in extracellular citrulline was prevented by intraaccumbal infusions of 500 microM 7-nitroindazole, a neuronal NO synthase inhibitor. In behavioral microdialysis experiment, the accumbal levels of extracellular citrulline markedly increased in rats given a mild footshock paired with tone. The presentation of the tone previously paired with footshock (the conditioned fear response) produced a "conditioned" rise of extracellular citrulline levels in the N.Acc which was attenuated by intraaccumbal infusion of 100 microM SCH-23390, a dopamine D1 receptor antagonist, and prevented by intraaccumbal infusion of 500 microM 7-nitroindazole. The results suggest that in the N.Acc, the dopamine D1 receptors might regulate the neuronal NO synthase activity; this dopamine-dependent mechanism seems to participate in activation of the neuronal NO synthase and probably NO formation in this brain area during the conditioned fear response.

Methamphetamine-induced selective dopaminergic neurotoxicity is accompanied by an increase in striatal nitrate in the mouse

Exposure to high doses of methamphetamine (METH), a major drug of abuse, may cause neuronal damage. Previous studies have implicated the role of peroxynitrite, produced by nitric oxide (NO) and reactive oxygen species, in dopaminergic neurotoxicity produced by METH in mice. The present article was undertaken to investigate if a neurotoxic regimen of METH is associated with changes in tissue levels of nitrate and nitrite, which are the stable products of NO. Administration of METH (5 mg/kg x 3) to Swiss Webster mice resulted in marked depletion of dopamine (DA) and DA transporter (DAT) binding sites but no change in 5-hydroxytryptamine (5-HT) and 5-HT transporter (5-HTT) binding sites in the striatum, amygdala, frontal cortex, and hippocampus, suggesting that METH causes selective neurotoxicity to DA nerve terminals. The concentration of nitrate in the striatum was increased by about two-fold after METH administration; however, no changes in nitrate concentration were detected in other brain regions that endured dopaminergic neurotoxicity. These findings suggest that (a) a neurotoxic regimen of METH produces selective increase in NO in the striatum, which may generate toxic species such as peroxynitrite, and (b) toxins other than NO-related derivatives may mediate dopaminergic neurotoxicity in the amygdala and frontal cortex.

Multiple high doses of methamphetamine increase the number of preproneuropeptide Y mRNA-expressing neurons in the striatum of rat via a dopamine D1 receptor-dependent mechanism

Neuropeptide Y (NPY) is a neuropeptide that may be involved with emotional regulation and drug addiction and may act as a neuroprotective agent during toxic insults, such as is associated with multiple, high doses of methamphetamine (METH). The purpose of the present study was to elucidate the nature of METH-induced changes in the NPY system by examining the effect of multiple, high doses of METH on preproNPY (ppNPY) mRNA expression in the striatum and the role that dopamine (DA) D1 and D2 receptors might play in these changes. Rats were administered five injections of 10 mg/kg METH at 6-h intervals, along with the D1 receptor antagonist 7-chloro-8-hydoxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benazepine hydrochloride (SCH22390) or the D2 receptor antagonist eticlopride, and they were sacrificed 3 h after the last dose of METH. The number of neurons expressing ppNPY mRNA in striatum was examined using in situ hybridization histochemistry. An acute dose of METH as well as multiple, high doses of METH increased the number of neurons expressing ppNPY mRNA in all regions of striatum examined. There was no change in the number of prosomatostatin (pSOM) mRNA-containing neurons. The increase in the number of ppNPY mRNA-expressing neurons was abolished by pretreatment with SCH22390. Eticlopride alone increased the number of ppNPY mRNA-expressing neurons in striatum, and METH treatment did not further increase the number. These findings suggest that exposure to multiple, high doses of METH increases the number of neurons expressing detectable levels of ppNPY mRNA and that this phenomenon is dependent on DA D1-receptor activation.

Mechanisms of methamphetamine-induced dopaminergic neurotoxicity

Methamphetamine (METH) is a powerful stimulant of abuse with potent addictive and neurotoxic properties. More than 2.5 decades ago, METH-induced damage to dopaminergic neurons was described. Since then, numerous advancements have been made in the search for the underlying mechanisms whereby METH causes these persistent dopaminergic deficits. Although our understanding of these mechanisms remains incomplete, combinations of various complex processes have been described around a central theme involving reactive species, such as reactive oxygen and/or nitrogen species (ROS and RNS, respectively). For example, METH-induced hyperthermia, aberrant dopamine(DA), or glutamate transmission; or mitochondrial disruption leads to the generation of reactive species with neurotoxic consequences. This review will describe the current understanding of how high-dose METH administration leads to the production of these toxic reactive species and consequent permanent dopaminergic deficits.

Role of nitrergic system in behavioral and neurotoxic effects of amphetamine analogs

Several amphetamine analogs are potent psychostimulants and major drugs of abuse. In animal models, the psychomotor and reinforcing effects of amphetamine, methamphetamine (METH), 3,4-methylenedioxymethamphetamine (MDMA; Ecstasy), and methylphenidate (MPD; Ritalin) are thought to be dependent on increased extracellular levels of dopamine (DA) in mesocorticolimbic and mesostriatal pathways. However, amphetamine analogs that increase primarily serotonergic transmission, such as p-chloroamphetamine (PCA) and fenfluramine (FEN), have no potential for abuse. High doses of METH, MDMA, PCA, and FEN produce depletions of dopaminergic and serotonergic nerve terminal markers and are considered as potential neurotoxicants. The first part of this review briefly summarizes the behavioral and neurotoxic effects of amphetamines that have a different spectrum of activity on dopaminergic and serotonergic systems. The second part discusses evidence supporting involvement of the nitrergic system in dopamine-mediated effects of amphetamines. The nitrergic system in this context corresponds to nitric oxide (NO) produced from neuronal nitric oxide synthase (nNOS) that has roles in nonsynaptic interneuronal communication and excitotoxic neuronal injury. Increasing evidence now suggests cross talk between dopamine, glutamate, and NO. Results from our laboratory indicate that dopamine-dependent psychomotor, reinforcing, and neurotoxic effects of amphetamines are diminished by pharmacological blockade of nNOS or deletion of the nNOS gene. These findings, and evidence supporting the role of NO in synaptic plasticity and neurotoxic insults, suggest that NO functions as a neuronal messenger and a neurotoxicant subsequent to exposure to amphetamine-like psychostimulants.

Bimodal induction of dopamine-mediated striatal neurotoxicity is mediated through both activation of D1 dopamine receptors and autoxidation

Striatal neurodegeneration occurs through unknown mechanisms in certain neurodegenerative disorders characterized by increased and sustained synaptic levels of dopamine (DA). Treatment of rat primary striatal neurons with DA causes profound neurotoxicity, with increased production of free radicals and accelerated neuronal death. DA effects were partly reduced by the antioxidant sodium metabisulfite (SMBS), and the D1 DA receptor antagonist, SCH 23390, and were completely blocked upon co-treatment with SMBS and SCH 23390. Part of DA effects were mimicked by either H(2)O(2), or by the D1 agonist, SKF R-38393, indicating the existence of two distinct signaling pathways through which the neurotoxicity of DA is manifest. DA effects did not proceed through D2-like DA or beta-adrenergic receptor signaling pathways. The D1 receptor-mediated and the autoxidative pathways of DA neurotoxicity converge to cause activation and/or increased synthesis of neuronal and inducible, but not endothelial, nitric oxide synthase (NOS). The reduction of DA striatal neurotoxicity through blockade of D1 DA receptors, suggests novel therapeutic approaches in the management of striatal neurodegeneration.

Effect of UUO on D1aR expression reveals a link among dopamine, transforming growth factor-β, and nitric oxide

Interactions between transforming growth factor-β (TGF-β) and nitric oxide (NO) are important in the pathophysiology of unilateral ureteral obstruction (UUO). Dopamine (DA) is a vasoactive renal mediator active at the D1Areceptor (D1AR), which has not been studied in UUO; therefore, we examined the interactions among DA, TGF-β, and NO in UUO. In vivo, UUO was carried out in rats with or without concurrent treatment with 1D11, a monoclonal antibody to TGF-β, for 14 days. In vitro, NRK-52E cells (normal rat kidney tubules) were treated with DA, and NO and TGF-β release were examined. UUO resulted in a 70% decrease in the expression of renal D1AR, confirmed by both Western blot analysis and immunohistochemistry. 1D11 treatment restored expression to 60% of control values. DA treatment decreased NRK-52E release of TGF-β by 80%; conversely, DA significantly increased NO release from NRK-52E cells. These results suggest that DA modulates the release of cytokines, which are involved in the fibrotic and apoptotic sequelae of UUO, and that these effects are independent of DA's known vasoactive properties.