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

N-isopropylbenzylamine, a methamphetamine mimics, produces toxicity via increasing nitric oxide in vitro

N-isopropylbenzylamine, an isomer of methamphetamine, has been used to adulterate methamphetamine, and distributed as fake "Ice" methamphetamine by illicit manufacturers, leading to a world problem of N-isopropylbenzylamine exposure. Though it is unclear whether N-isopropylbenzylamine has addictive potential like methamphetamine, N-isopropylbenzylamine users reported side effects such as headaches and confusion. However, the pharmacological targets and cytotoxicity of this chemical remained unknown. In this study, in vitro toxicity of N-isopropylbenzylamine and its toxicity-related targets were investigated in SN4741, SH-SY5Y or PC12 cell lines that model neurons. The cell viability was analyzed by using MTT assay after incubation with N-isopropylbenzylamine for 24 h in cells. N-isopropylbenzylamine caused cell death with IC₅₀ values at around 1-3 mM in these cell lines. N-isopropylbenzylamine time- and concentration-dependently facilitated the expression of neuronal nitric oxide synthase (nNOS), and increased intracellular nitric oxide (NO) in SN4741 cells. Furthermore, 7-nitroindazole, a specific inhibitor of nNOS, significantly prevented N-isopropylbenzylamine-induced toxicity in vitro. These results suggested that N-isopropylbenzylamine-induced toxicity is at least partially related to the increased intracellular NO levels and the activated nNOS. Considering the circumstances that N-isopropylbenzylamine was used to adulterate and mimic methamphetamine, and the side effects associated with N-isopropylbenzylamine in abusers, our findings sounded an alarm for abuser and warn the dangerousness of N-isopropylbenzylamine for public health.

Neurotoxicity of MDMA: Main effects and mechanisms

Preclinical and clinical studies indicate that 3,4-methylenedioxymethamphetamine (MDMA; 'ecstasy'), in addition to having abuse potential, may elicit acute and persistent abnormalities of varying severity at the central level. Importantly, neurotoxic effects of MDMA have been demonstrated in experimental animals. Accordingly, central toxicity induced by MDMA may pose a serious harm for health, since MDMA is among the substances that are used for recreational purposes by young and adult people. This review provides a concise overview of recent findings from preclinical and clinical studies that evaluated the central effects of MDMA, and the mechanisms involved in the neurotoxicity induced by this amphetamine-related drug.

Disrupting the Interaction of nNOS with CAPON Prevents the Reinstatement of Morphine Conditioned Place Preference

Drug abuse is a dramatic challenge for the whole society because of high relapse rate. Environmental cues are crucial for the preference memory of drug abuse. Extinction therapy has been developed to inhibit the motivational effect of drug cues to prevent the reinstatement of morphine abuse. However, extinction therapy alone only forms a new kind of unstable inhibitory memory. We found that morphine conditioned place preference (CPP) extinction training increased the association of nitric oxide synthase (nNOS) with its carboxy-terminal PDZ ligand (CAPON) in the dorsal hippocampus (dHPC) significantly and blocking the morphine-induced nNOS-CAPON association using Tat-CAPON-12C during and after extinction training reversed morphine-induced hippocampal neuroplasticity defect and prevented the reinstatement and spontaneous recovery of morphine CPP. Moreover, in the hippocampal selective ERK2 knock-out or nNOS knockout mice, the effect of Tat-CAPON-12C on the reinstatement of morphine CPP and hippocampal neuroplasticity disappeared, suggesting ERK2 is necessary for the effects of Tat-CAPON-12C. Together, our findings suggest that nNOS-CAPON interaction in the dHPC may affect the consolidation of morphine CPP extinction and dissociating nNOS-CAPON prevents the reinstatement and spontaneous recovery of morphine CPP, possibly through ERK2-mediated neuroplasticity and extinction memory consolidation, offering a new target to prevent the reinstatement of drug abuse.

Increased iNOS and Nitrosative Stress in Dopaminergic Neurons of MDMA-Exposed Rats

Several mechanisms underlying 3,4-Methylenedioxy-N-methylamphetamine (MDMA) neurotoxicity have been proposed, including neurochemical alterations and excitotoxicity mediated by reactive oxygen species (ROS), nitric oxide (NO), and reactive nitrogen species (RNS). However, ROS, NO, and RNS sources in the brain are not fully known. We aimed to investigate possible alterations in the expression of the ROS producer NOX enzymes (NOX2, NOX1, and NOX4), NO generators (iNOS, eNOS, and nNOS), markers of oxidative (8-hydroxy-2′-deoxyguanosine, 8OHdG), and nitrosative (3-nitrotyrosine, NT) stress, as well as the colocalization between cells positive for the dopamine transporter (DT1) and cells expressing the neuronal nuclei (NeuN) marker, in the frontal cortex of rats receiving saline or MDMA, sacrificed 6 h, 16 h, or 24 h after its administration. MDMA did not affect NOX2, NOX1, and NOX4 immunoreactivity, whereas iNOS expression was enhanced. The number of NT-positive cells was increased in MDMA-exposed animals, whereas no differences were detected in 8OHdG expression among experimental groups. MDMA and NT markers colocalized with DT1 positive cells. DT1 immunostaining was found in NeuN-positive stained cells. Virtually no colocalization was observed with microglia and astrocytes. Moreover, MDMA immunostaining was not found in NOX2-positive cells. Our results suggest that iNOS-derived nitrosative stress, but not NOX enzymes, may have a crucial role in the pathogenesis of MDMA-induced neurotoxicity, highlighting the specificity of different enzymatic systems in the development of neuropathological alterations induced by the abuse of this psychoactive compound.

Potential Negative Effects of Dextromethorphan as an Add-On Therapy to Methylphenidate in Children With ADHD

Objectives: Methylphenidate (MPH) is highly effective in controlling the symptoms of attention-deficit/hyperactivity disorder (ADHD), but some children with ADHD either do not respond to, or do not tolerate, treatment. Dextromethorphan (DM) is a neuroprotective agent which has been used in the treatment of neuropsychiatric disorders. This clinical trial had examined the effect of DM on the use of MPH in the children with ADHD. Methods: This randomized double-blind clinical trial had evaluated 44 male outpatients, aged between 6 and 12 years, with a diagnosis of ADHD. The study subjects were randomly assigned into one of the two groups: receiving MPH alone (15-60 mg per day) or MPH plus DM (30-60 mg per day) for 8 weeks. Assessments, comprising the Chinese version of the Child Behavior Checklist (CBCL-C) scale and the Swanson, Nolan and Pelham Questionnaire (SNAP)-IV rating tests conducted by parents and the serum cytokines measured by microarray and enzyme-linked immunosorband assay (ELISA), were compared between groups at baseline and at 8 weeks after the medication was started. Results: There were a significant decrease at the mean scores of both CBCL-C and SNAP-IV scales after 8 weeks of treatment, but no significant differences between MPH and MPH+DM groups. Compared with the MPH-only group, the mean scores of some psychometric parameters reported on the CBCL-C and SNAP-IV scales regarding time effects as well as the attention problems on the CBCL-C scale regarding group effect were significantly higher in the DM+MPH group. Although there were no significant differences in the levels of various serum cytokines between groups, the subjects in the DM-MPH group had relatively fewer and lower levels of adverse effects. Significant interactions were found between the withdrawn/depression item reported on the CBCL-C scale and tumor necrosis factor α (ခTNF-α) (p = 0.027), as well as between thought problems item on the CBCL-C and TNF-α (p = 0.028) in subjects who had received DM+MPH treatment. Conclusion: Following the trial, DM+MPH was not superior to MPH alone for the treatment of children with ADHD, yet DM may potentially have negative effects on ADHD symptoms when combined with MPH. Clinical Trial Registration: Clinicaltrials.gov, trial number: NCT01787136.

Repeated Administration of 3,4-Methylenedioxymethamphetamine (MDMA) Elevates the Levels of Neuronal Nitric Oxide Synthase in the Nigrostriatal System: Possible Relevance to Neurotoxicity

Previous studies have consistently demonstrated that the amphetamine-related drug 3,4-methylenedioxymethamphetamine (MDMA) induces dopaminergic damage in the mouse brain, and that this effect is most marked in the nigrostriatal system. Moreover, it has been suggested that the overproduction of nitric oxide (NO) may participate in the dopaminergic damage induced by MDMA. To further elucidate this issue, we evaluated the levels of the enzyme nitric oxide synthase (nNOS), which catalyzes the production of NO, in mice treated with regimens of MDMA that induce progressive and persistent neurotoxicity in the dopaminergic nigrostriatal system. Mice received 14, 28, or 36 administrations of MDMA (10 mg/kg i.p.), twice a day/twice a week, and were sacrificed at different time-points after treatment discontinuation. Thereafter, the number of nNOS-positive neurons was quantified by immunohistochemistry in the caudate-putamen (CPu) and substantia nigra pars compacta (SNc). MDMA elevated the numbers of nNOS-positive neurons in the CPu of mice that received 28 or 36 drug administrations. This effect was still detectable at 3 months after treatment discontinuation. Moreover, MDMA elevated the numbers of nNOS-positive neurons in the SNc. However, this effect occurred only in mice that received 28 drug administrations and were sacrificed 3 days after treatment discontinuation. These results are in line with the hypothesis that activation of the NO cascade participates in the toxic effects induced by MDMA in the dopaminergic nigrostriatal system. Moreover, they suggest that activation of the NO cascade induces toxic effects that are more marked in striatal terminals, compared with nigral neurons.

Selective Nitric Oxide Synthase Inhibitor 7-Nitroindazole Protects against Cocaine-Induced Oxidative Stress in Rat Brain

One of the mechanisms involved in the development of addiction, as well as in brain toxicity, is the oxidative stress. The aim of the current study was to investigate the effects of 7-nitroindazole (7-NI), a selective inhibitor of neuronal nitric oxide synthase (nNOS), on cocaine withdrawal and neurotoxicity in male Wistar rats. The animals were divided into four groups: control; group treated with cocaine (15 mg/kg⁻¹, i.p., 7 days); group treated with 7-NI (25 mg/kg⁻¹, i.p., 7 days); and a combination group (7-NI + cocaine). Cocaine repeated treatment resulted in development of physical dependence, judged by withdrawal symptoms (decreased locomotion, increased salivation and breathing rate), accompanied by an increased nNOS activity and oxidative stress. The latter was discerned by an increased formation of malondialdehyde (MDA), depletion of reduced glutathione (GSH) levels, and impairment of the enzymatic antioxidant defense system measured in whole brain. In synaptosomes, isolated from cocaine-treated rats, mitochondrial activity and GSH levels were also decreased. 7-NI administered along with cocaine not only attenuated the withdrawal, due to its nNOS inhibition, but also reversed both the GSH levels and antioxidant enzyme activities near control levels.

Methylphenidate treatment causes oxidative stress and alters energetic metabolism in an animal model of attention-deficit hyperactivity disorder

OBJECTIVES

To evaluate oxidative damage through the thiobarbituric acid-reactive species (TBARS) and protein carbonyl groups; antioxidant enzymatic system - superoxide dismutase (SOD) and catalase (CAT); and energetic metabolism in the brain of spontaneously hypertensive adult rats (SHR) after both acute and chronic treatment with methylphenidate hydrochloride (MPH).

METHODS

Adult (60 days old) SHRs were treated during 28 days (chronic treatment), or 1 day (acute treatment). The rats received one i.p. injection per day of either saline or MPH (2 mg/kg). Two hours after the last injection, oxidative damage parameters and energetic metabolism in the cerebellum, prefrontal cortex, hippocampus, striatum and cortex were evaluated.

RESULTS

We observed that both acute and/or chronic treatment increased TBARS and carbonyl groups, and decreased SOD and CAT activities in many of the brain structures evaluated. Regarding the energetic metabolism evaluation, the acute and chronic treatment altered the energetic metabolism in many of the brain structures evaluated.

CONCLUSION

We observed that both acute and chronic use of methylphenidate hydrochloride (MPH) in adult spontaneously hypertensive rats (SHRs) was associated with increased oxidative stress and energetic metabolism alterations. These data also reinforce the importance of the SHR animal model in further studies regarding MPH.

Psychostimulants and brain dysfunction: a review of the relevant neurotoxic effects

Psychostimulants abuse is a major public concern because is associated with serious health complications, including devastating consequences on the central nervous system (CNS). The neurotoxic effects of these drugs have been extensively studied. Nevertheless, numerous questions and uncertainties remain in our understanding of these toxic events. Thus, the purpose of the present manuscript is to review cellular and molecular mechanisms that might be responsible for brain dysfunction induced by psychostimulants. Topics reviewed include some classical aspects of neurotoxicity, such as monoaminergic system and mitochondrial dysfunction, oxidative stress, excitotoxicity and hyperthermia. Moreover, recent literature has suggested new phenomena regarding the toxic effects of psychostimulants. Thus, we also reviewed the impact of these drugs on neuroinflammatory response, blood-brain barrier (BBB) function and neurogenesis. Assessing the relative importance of these mechanisms on psychostimulants-induced brain dysfunction presents an exciting challenge for future research efforts. This article is part of the Special Issue entitled 'CNS Stimulants'.

Increased densities of nitric oxide synthase expressing neurons in the temporal cortex and the hypothalamic paraventricular nucleus of polytoxicomanic heroin overdose victims: possible implications for heroin neurotoxicity

Heroin is one of the most dangerous drugs of abuse, which may exert various neurotoxic actions on the brain (such as gray matter loss, neuronal apoptosis, mitochondrial dysfunction, synaptic defects, depression of adult neurogenensis, as well as development of spongiform leucoencephalopathy). Some of these toxic effects are probably mediated by the gas nitric oxide (NO). We studied by morphometric analysis the numerical density of neurons expressing neuronal nitric oxide synthase (nNOS) in cortical and hypothalamic areas of eight heroin overdose victims and nine matched controls. Heroin addicts showed significantly increased numerical densities of nNOS immunoreactive cells in the right temporal cortex and the left paraventricular nucleus. Remarkably, in heroin abusers, but not in controls, we observed not only immunostained interneurons, but also cortical pyramidal cells. Given that increased cellular expression of nNOS was accompanied by elevated NO generation in brains of heroin addicts, these elevated levels of NO might have contributed to some of the known toxic effects of heroin (for example, reduced adult neurogenesis, mitochondrial pathology or disturbances in synaptic functioning).

Computer-aided (in silico) approaches in the mode-of-action analysis and safety assessment of ostarine and 4-methylamphetamine

OBJECTIVE

This study exemplifies computer-aided (in silico) approaches in assessing the risks of new psychoactive substances emerging in the European Union. In this work, we (i) consider the potential of Ostarine exhibiting psychoactivity and (ii) anticipate potential activities and toxicities of 4-methylamphetamine.

METHOD

The approach, termed in silico target prediction, suggests potential protein targets modulated by compounds given their chemical structure. This is achieved by first establishing the associations between chemical structure and protein targets using data from the bioactivity database, ChEMBL, via the use of two different computational algorithms. On the basis of the associations, protein targets and consequently the mode of action of novel compounds were predicted.

RESULTS

For Ostarine, none of the targets anticipated are currently known to elicit psychoactivity. Furthermore, Ostarine is unlikely to cross the blood-brain barrier to reach relevant target sites on the basis of its physicochemical properties. For 4-methylamphetamine, toxicities were anticipated, that is, serotonin syndrome (based on the prediction of SERT) and other effects similar to related substances, that is, methamphetamine.

CONCLUSION

From the two case studies, we showed that in silico target prediction appears to have potential in assessing new psychoactive compounds where experimental data are scarce. The applicability domain of target predictions when applied to psychoactive compounds needs to be established in future work.

Up-regulation of protein tyrosine nitration in methamphetamine-induced neurotoxicity through DDAH/ADMA/NOS pathway

Protein tyrosine nitration is an important post-translational modification mediated by nitric oxide (NO) associated oxidative stress, occurring in a variety of neurodegenerative diseases. In our previous study, an elevated level of dimethylarginine dimethylaminohydrolase 1 (DDAH1) protein was observed in different brain regions of acute methamphetamine (METH) treated rats, indicating the possibility of an enhanced expression of protein nitration that is mediated by excess NO through the DDAH1/ADMA (Asymmetric Dimethylated l-arginine)/NOS (Nitric Oxide Synthase) pathway. In the present study, proteomic methods, including stable isotope labeling with amino acids in cell culture (SILAC) and two dimensional electrophoresis, were used to determine the relationship between protein nitration and METH induced neurotoxicity in acute METH treated rats and PC12 cells. We found that acute METH administration evokes a positive activation of DDAH1/ADMA/NOS pathway and results in an over-production of NO in different brain regions of rat and PC12 cells, whereas the whole signaling could be repressed by DDAH1 inhibitor N(ω)-(2-methoxyethyl)-arginine (l-257). In addition, enhanced expressions of 3 nitroproteins were identified in rat striatum and increased levels of 27 nitroproteins were observed in PC12 cells. These nitrated proteins are key factors for Cdk5 activation, cytoskeletal structure, ribosomes function, etc. l-257 also displayed significant protective effects against METH-induced protein nitration, apoptosis and cell death. The overall results illustrate that protein nitration plays a significant role in the acute METH induced neurotoxicity via the activation of DDAH1/ADMA/NOS pathway.

Methylphenidate induces lipid and protein damage in prefrontal cortex, but not in cerebellum, striatum and hippocampus of juvenile rats

The use of psychostimulant methylphenidate has increased in recent years for the treatment of attention-deficit hyperactivity disorder in children and adolescents. However, the behavioral and neurochemical changes promoted by its use are not yet fully understood, particularly when used for a prolonged period during stages of brain development. Thus, the aim of this study was to determine some parameters of oxidative stress in encephalic structures of juvenile rats subjected to chronic methylphenidate treatment. Wistar rats received intraperitoneal injections of methylphenidate (2.0 mg/kg) once a day, from the 15th to the 45th day of age or an equivalent volume of 0.9% saline solution (controls). Two hours after the last injection, animals were euthanized and the encephalic structures obtained for determination of oxidative stress parameters. Results showed that methylphenidate administration increased the activities of superoxide dismutase and catalase, but did not alter the levels of reactive species, thiobarbituric acid reactive substances levels and sulfhydryl group in cerebellum of rats. In striatum and hippocampus, the methylphenidate-treated rats presented a decrease in the levels of reactive species and thiobarbituric acid reactive substances, but did not present changes in the sulfhydryl groups levels. In prefrontal cortex, methylphenidate promoted an increase in reactive species formation, SOD/CAT ratio, and increased the lipid peroxidation and protein damage. These findings suggest that the encephalic structures respond differently to methylphenidate treatment, at least, when administered chronically to young rats. Notably, the prefrontal cortex of juvenile rats showed greater sensitivity to oxidative effects promoted by methylphenidate in relation to other encephalic structures analyzed.

Functional and structural brain changes associated with methamphetamine abuse

Methamphetamine (MA) is a potent psychostimulant drug whose abuse has become a global epidemic in recent years. Firstly, this review article briefly discusses the epidemiology and clinical pharmacology of methamphetamine dependence. Secondly, the article reviews relevant animal literature modeling methamphetamine dependence and discusses possible mechanisms of methamphetamine-induced neurotoxicity. Thirdly, it provides a critical review of functional and structural neuroimaging studies in human MA abusers; including positron emission tomography (PET) and functional and structural magnetic resonance imaging (MRI). The effect of abstinence from methamphetamine, both short- and long-term within the context of these studies is also reviewed.

Toward a theory of childhood learning disorders, hyperactivity, and aggression

Learning disorders are often associated with persistent hyperactivity and aggression and are part of a spectrum of neurodevelopmental disorders. A potential clue to understanding these linked phenomena is that physical exercise and passive forms of stimulation are calming, enhance cognitive functions and learning, and are recommended as complementary treatments for these problems. The theory is proposed that hyperactivity and aggression are intense stimulation-seeking behaviors (SSBs) driven by increased brain retinergic activity, and the stimulation thus obtained activates opposing nitrergic systems which inhibit retinergic activity, induce a state of calm, and enhance cognition and learning. In persons with cognitive deficits and associated behavioral disorders, the retinergic system may be chronically overactivated and the nitrergic system chronically underactivated due to environmental exposures occurring pre- and/or postnatally that affect retinoid metabolism or expression. For such individuals, the intensity of stimulation generated by SSB may be insufficient to activate the inhibitory nitrergic system. A multidisciplinary research program is needed to test the model and, in particular, to determine the extent to which applied physical treatments can activate the nitrergic system directly, providing the necessary level of intensity of sensory stimulation to substitute for that obtained in maladaptive and harmful ways by SSB, thereby reducing SSB and enhancing cognitive skills and performance.

Methylphenidate administration determines enduring changes in neuroglial network in rats

Repeated exposure to psychostimulant drugs induces complex molecular and structural modifications in discrete brain regions of the meso-cortico-limbic system. This structural remodeling is thought to underlie neurobehavioral adaptive responses. Administration to adolescent rats of methylphenidate (MPH), commonly used in attention deficit and hyperactivity disorder (ADHD), triggers alterations of reward-based behavior paralleled by persistent and plastic synaptic changes of neuronal and glial markers within key areas of the reward circuits. By immunohistochemistry, we observe a marked increase of glial fibrillary acidic protein (GFAP) and neuronal nitric oxide synthase (nNOS) expression and a down-regulation of glial glutamate transporter GLAST in dorso-lateral and ventro-medial striatum. Using electron microscopy, we find in the prefrontal cortex a significant reduction of the synaptic active zone length, paralleled by an increase of dendritic spines. We demonstrate that in limbic areas the MPH-induced reactive astrocytosis affects the glial glutamatergic uptake system that in turn could determine glutamate receptor sensitization. These processes could be sustained by NO production and synaptic rearrangement and contribute to MPH neuroglial induced rewiring.

Nitric oxide modulates dopaminergic regulation of prepulse inhibition in the basolateral amygdala

Systemic injection of the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (LNO) prevents the disruptive effect of amphetamine (Amph) on prepulse inhibition (PPI), a sensorimotor gating model in which the amplitude of the acoustic startle response (ASR) to a startling sound (pulse) is reduced when preceded immediately by a weaker stimulus (prepulse). Given that dopamine (DA) projections to the basolateral amygdala (BLA) are involved in the control of information processing, our aim was to investigate if intra-BLA administration of LNO would modify the disruption caused by the DA agonists, Amph, apomorphine (Apo) and quinpirole (QNP), on PPI. Male Wistar rats received bilateral intra-BLA microinjections (0.2 µL/min/side) of combined treatments (saline or LNO 11 µg followed by saline, QNP 3 µg, Apo 10 µg or Amph 30 µg). PPI was disrupted by intra-BLA Apo, QNP or Amph but not by LNO. Prior bilateral intra-BLA injection of LNO prevented the Apo- and QNP-induced disruption of PPI but did not affect that caused by Amph. APO- or QNP-induced increases in ASR to prepulse + pulse were also restored by LNO. Since local inhibition of NO formation affected the effects of direct, but not indirect, DA agonists, the results suggest that this modulation is not occurring at the level of DA release but may involve complex interactions with other neurotransmitter systems.

Cerebral microglia mediate sleep/wake and neuroinflammatory effects of methamphetamine

Methamphetamine and modafinil exert their wake-promoting effects by elevating monoaminergic tone. The severity of hypersomnolence that occurs subsequent to induced wakefulness differs between these two agents. Microglia detects and modulates CNS reactions to agents such as D-methamphetamine that induce cellular stress. We therefore hypothesized that changes in the sleep/wake cycle that occur subsequent to administration of D-methamphetamine are modulated by cerebral microglia. In CD11b-herpes thymidine kinase transgenic mice (CD11b-TK(mt-30)), activation of the inducible transgene by intracerebroventricular (icv) ganciclovir results in toxicity to CD11b-positive cells (i.e. microglia), thereby reducing cerebral microglial cell counts. CD11b-TK(mt-30)and wild type mice were subjected to chronic icv ganciclovir or vehicle administration with subcutaneous mini-osmotic pumps. D-methamphetamine (1 and 2 mg/kg), modafinil (30 and 100 mg/kg) and vehicle were administered intraperitoneally to these animals. In CD11b-TK(mt-30) mice, but not wild type, icv infusion of ganciclovir reduced the duration of wake produced by D-methamphetamine at 2 mg/kg by nearly 1h. Nitric oxide synthase (NOS) activity, studied ex vivo, and NOS expression were elevated in CD11b-positive cerebral microglia from wild type mice acutely exposed to d-methamphetamine. Additionally, CD11b-positive microglia, but not other cerebral cell populations, exhibited changes in sleep-regulatory cytokine expression in response to d-METH. Finally, CD11b-positive microglia exposed to d-methamphetamine in vitro exhibited increased NOS activity relative to pharmacologically-naïve cells. CD11b-positive microglia from the brains of neuronal NOS (nNOS)-knockout mice failed to exhibit this effect. We propose that the effects of D-METH on sleep/wake cycles are mediated in part by actions on microglia, including possibly nNOS activity and cytokine synthesis.

Minocycline attenuates subjective rewarding effects of dextroamphetamine in humans

RATIONALE

Minocycline, a tetracycline antibiotic, interacts with brain glutamate and dopamine neurotransmission. In preclinical studies, minocycline attenuated amphetamine-induced acute dopamine release and subsequent behavioral sensitization. The goal of this study was to determine minocycline's effects on the acute physiological, behavioral, and subjective responses to dextroamphetamine (DAMP) in healthy volunteers.

METHODS

Ten healthy volunteers participated in an outpatient double-blind, placebo-controlled, crossover study. Subjects had a 5-day treatment period with either minocycline (200 mg/day) or placebo and then were crossed over for 5 days of the other treatment. After 2 days of taking the study medication, on days 3 and 4, subjects were randomly assigned to double-blind acute challenge with either 20 mg/70 kg DAMP or placebo DAMP (randomly labeled as drug A or B) and then crossed over to the other challenge. On day 5 (experimental session 3), subjects had the opportunity to self-administer either placebo or DAMP capsules by working on a progressive ratio computer task.

RESULTS

Minocycline attenuated DAMP-induced subjective rewarding effects but did not change DAMP choice behavior. Minocycline treatment speeded reaction times on a Go No-Go task and reduced plasma cortisol levels.

CONCLUSIONS

These findings warrant further studies examining the potential use of minocycline for stimulant addiction.

Red wine but not ethanol at low doses can protect against the toxicity of methamphetamine

The goal of this study was twofold: (a) to search for possible interactive effects between two common drugs of abuse, ethanol and methamphetamine. b) To inquire whether any effects of ethanol could be replicated using an equivalent amount of ethanol in the form of red wine. Adult male C57/6N mice received 2% ethanol for 8 weeks in drinking water or red wine diluted to yield the same ethanol content. On the 9th week animals received multiple injections of methamphetamine (4 x 10 mg/kg, ip, every 2 h). They were then sacrificed 72 h after treatment. Methamphetamine produced a significant depletion of dopamine and DOPAC in the striatum. Treatment with both ethanol and methamphetamine led to a reduction of striatal dopamine and DOPAC that were both non-significantly greater than that observed with methamphetamine alone. Alcohol alone produced no changes in the striatal content of dopamine or its metabolite, DOPAC. These data suggest that low doses of alcohol potentiate methamphetamine-induced neurotoxicity in mice and that this combination may be especially detrimental to the brain. However, an equivalent dose of ethanol in the form of red wine actually partially protected against methamphetamine-induced depletion of dopamine and DOPAC in red wine treated mice. This implies the presence of other agents in red wine, which may mitigate the toxicity of methamphetamine.

Superoxide production after acute and chronic treatment with methylphenidate in young and adult rats

The prescription of methylphenidate (MPH) has dramatically increased in this decade for attention deficit hyperactivity disorder (ADHD) treatment. The action mechanism of MPH is not completely understood and studies have been demonstrated that MPH can lead to neurochemical adaptations. Superoxide radical anion is not very reactive per se. However, severe species derived from superoxide radical anion mediate most of its toxicity. In this study, the superoxide level in submitochondrial particles was evaluated in response to treatment with MPH in the age-dependent manner in rats. MPH was administrated acutely or chronically at doses of 1, 2 or 10 mg/kg i.p. The results showed that the acute administration of MPH in all doses in young rats increased the production of superoxide in the cerebellum and only in the high dose (10mg/kg) in the hippocampus, while chronic treatment had no effect. However, acute treatment in adult rats had no effect on production of superoxide, but chronic treatment decreased the production of superoxide in the cerebellum at the lower doses. Our data suggest that the MPH treatment can influence on production of superoxide in some brain areas, but this effect depends on age of animals and treatment regime with MPH.

Enhancement of endocannabinoid signaling by fatty acid amide hydrolase inhibition: a neuroprotective therapeutic modality

AIMS

This review posits that fatty acid amide hydrolase (FAAH) inhibition has therapeutic potential against neuropathological states including traumatic brain injury; Alzheimer's, Huntington's, and Parkinson's diseases; and stroke.

MAIN METHODS

This proposition is supported by data from numerous in vitro and in vivo experiments establishing metabolic and pharmacological contexts for the neuroprotective role of the endogenous cannabinoid ("endocannabinoid") system and selective FAAH inhibitors.

KEY FINDINGS

The systems biology of endocannabinoid signaling involves two main cannabinoid receptors, the principal endocannabinoid lipid mediators N-arachidonoylethanolamine ("anandamide") (AEA) and 2-arachidonoyl glycerol (2-AG), related metabolites, and the proteins involved in endocannabinoid biosynthesis, biotransformation, and transit. The endocannabinoid system is capable of activating distinct signaling pathways on-demand in response to pathogenic events or stimuli, thereby enhancing cell survival and promoting tissue repair. Accumulating data suggest that endocannabinoid system modulation at discrete targets is a promising pharmacotherapeutic strategy for treating various medical conditions. In particular, neuronal injury activates cannabinoid signaling in the central nervous system as an intrinsic neuroprotective response. Indirect potentiation of this salutary response through pharmacological inhibition of FAAH, an endocannabinoid-deactivating enzyme, and consequent activation of signaling pathways downstream from cannabinoid receptors have been shown to promote neuronal maintenance and function.

SIGNIFICANCE

This therapeutic modality has the potential to offer site- and event-specific neuroprotection under conditions where endocannabinoids are being produced as part of a physiological protective mechanism. In contrast, direct application of cannabinoid receptor agonists to the central nervous system may activate CB receptors indiscriminately and invite unwanted psychotrophic effects.

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.

Methamphetamine toxicity and messengers of death

Methamphetamine (METH) is an illicit psychostimulant that is widely abused in the world. Several lines of evidence suggest that chronic METH abuse leads to neurodegenerative changes in the human brain. These include damage to dopamine and serotonin axons, loss of gray matter accompanied by hypertrophy of the white matter and microgliosis in different brain areas. In the present review, we summarize data on the animal models of METH neurotoxicity which include degeneration of monoaminergic terminals and neuronal apoptosis. In addition, we discuss molecular and cellular bases of METH-induced neuropathologies. The accumulated evidence indicates that multiple events, including oxidative stress, excitotoxicity, hyperthermia, neuroinflammatory responses, mitochondrial dysfunction, and endoplasmic reticulum stress converge to mediate METH-induced terminal degeneration and neuronal apoptosis. When taken together, these findings suggest that pharmacological strategies geared towards the prevention and treatment of the deleterious effects of this drug will need to attack the various pathways that form the substrates of METH toxicity.

Methamphetamine preconditioning: differential protective effects on monoaminergic systems in the rat brain

Pretreatment with methamphetamine (METH) can attenuate toxicity due to acute METH challenges. The majority of previous reports have focused mainly on the effects of the drug on the striatal dopaminergic system. In the present study, we used a regimen that involves gradual increases in METH administration to rats in order to mimic progressively larger doses of the drug used by some human METH addicts. We found that this METH preconditioning was associated with complete protection against dopamine depletion caused by a METH challenge (5 mg/kg x 6 injections given 1 h apart) in the striatum and cortex. In contrast, there was no preconditioning-mediated protection against METH-induced serotonin depletion in the striatum and hippocampus, with some protection being observed in the cortex. There was also no protection against METH-induced norepinephrine (NE) depletion in the hippocampus. These results indicate that, in contrast to the present dogmas, there might be differences in the mechanisms involved in METH toxicity on monoaminergic systems in the rodent brain. Thus, chronic injections of METH might activate programs that protect against dopamine toxicity without influencing drug-induced pathological changes in serotoninergic systems. Further studies will need to evaluate the cellular and molecular bases for these differential responses.

Molecular bases of methamphetamine-induced neurodegeneration

Methamphetamine (METH) is a highly addictive psychostimulant drug, whose abuse has reached epidemic proportions worldwide. The addiction to METH is a major public concern because its chronic abuse is associated with serious health complications including deficits in attention, memory, and executive functions in humans. These neuropsychiatric complications might, in part, be related to drug-induced neurotoxic effects, which include damage to dopaminergic and serotonergic terminals, neuronal apoptosis, as well as activated astroglial and microglial cells in the brain. Thus, the purpose of the present paper is to review cellular and molecular mechanisms that might be responsible for METH neurotoxicity. These include oxidative stress, activation of transcription factors, DNA damage, excitotoxicity, blood-brain barrier breakdown, microglial activation, and various apoptotic pathways. Several approaches that allow protection against METH-induced neurotoxic effects are also discussed. Better understanding of the cellular and molecular mechanisms involved in METH toxicity should help to generate modern therapeutic approaches to prevent or attenuate the long-term consequences of psychostimulant use disorders in humans.

Pharmacological and neurotoxicological actions mediated by bupropion and diethylpropion

The antiappetite agent diethylpropion (DEP), and the antidepressant and antismoking aid compound bupropion (BP), not only share the same structural motif but also present similar mechanisms of action in the CNS. For example, both drugs induce the release as well as inhibit the reuptake of neurotransmitters such as a dopamine (DA) and norepinephrine (NE). In general, they produce mild side effects, including reversible psychomotor alterations mostly in geriatric patients (by BP), or moderate changes in neurotransmitter contents linked to oxidative damage (by DEP). Therefore, attention must be paid during any therapeutic use of these agents. Regarding the interaction of BP with the DA transporter, residues S359, located in the middle of TM7, and A279, located close to the extracellular end of TM5, contribute to the binding and blockade of translocation mediated by BP, respectively. Additional mechanisms of action have also been determined for each compound. For example, BP is a noncompetitive antagonist (NCA) of several nicotinic acetylcholine receptors (AChRs). Based on this evidence, the dual antidepressant and antinicotinic activity of BP is currently considered to be mediated by its stimulatory action on DA and NE systems as well as its inhibitory action on AChRs. Considering the results obtained in the archetypical mouse muscle AChR, a sequential mechanism can be hypothesized to explain the inhibitory action of BP on neuronal AChRs: (1) BP first binds to AChRs in the resting state, decreasing the probability of ion channel opening, (2) the remnant fraction of open ion channels is subsequently decreased by accelerating the desensitization process, and finally (3) BP interacts with a binding domain located between the serine (position 9') and valine (position 13') rings that is shared with the NCA phencyclidine and other tricyclic antidepressants. The homologous location in the alpha3beta4 AChR is between the serine and valine/phenylalanine rings. This new evidence opens a window for further investigation using AChRs as targets for the action of safer antidepressants and novel antiaddictive compounds.

Acrylamide: a dietary carcinogen formed in vivo?

Acrylamide, a chemical formed during heating of human foods, reacts with N-terminal valine in hemoglobin (Hb) and forms stable reaction products (adducts). These adducts to N-terminal valine in Hb have been used to estimate daily intake of acrylamide. Daily intake of acrylamide estimated from Hb adduct levels was higher than daily intake estimated from dietary questionnaires, possibly indicating other sources of exposures. Therefore, in this study the possible endogenous formation of acrylamide was investigated by treating mice with FeSO 4, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine-hydrochloric acid (MPTP), or methamphetamine (METH). Acrylamide Hb adducts were determined, and a significant increase ( p < 0.05) in acrylamide Hb adduct levels was observed 24 h following treatment with FeSO 4 and 72 h following treatment with MPTP or METH. The results of this study show that acrylamide Hb adduct levels are increased in mice treated with compounds known to induce free radicals, thus suggesting the endogenous production of acrylamide.

Effect of adolescent exposure to MDMA and cocaine on acquisition and reinstatement of morphine-induce CPP

It is well known that an elevated percentage of ecstasy users also consume cocaine. Recently, it has been reported that a high frequency of heroin smokers first consumed heroin under the effects of ecstasy with the hope of reducing the stimulant effects of the latter drug. The aim of the present study was to evaluate the effect of exposure to MDMA and cocaine during adolescence on morphine-induced conditioned place preference (CPP) and reinstatement in adulthood. In the first experiment, adolescent mice were exposed to six injections of MDMA and three weeks later their response to the reinforcing properties of 40 mg/kg of morphine was evaluated using the CPP paradigm. All the treatment groups developed the same magnitude of morphine-induced preference and, after CPP was extinguished, it was restored in all the groups with a priming dose of 10 mg/kg of morphine. Only mice that had been treated with 10 or 20 mg/kg of MDMA had their morphine-induced preference reinstated after receiving only 5 mg/kg of morphine. In the second experiment, adolescent mice were similarly treated with six administrations of cocaine (25 mg/kg) or cocaine plus MDMA (5, 10 or 20 mg/kg), and their response to morphine-induce CPP was evaluated three weeks later. Similarly to the first experiment, all the groups developed a preference for the morphine-paired compartment, but this preference was not reinstated with a priming dose of 10 mg/kg of morphine following extinction, as was the case among the control animals. These results lead us to hypothesize that periadolescent MDMA exposure alters responsiveness to the rewarding properties of morphine, highlighting MDMA as a gateway drug whose use may increase the likelihood of dependence on other drugs.

Interactions of HIV and methamphetamine: cellular and molecular mechanisms of toxicity potentiation

Methamphetamine (METH) is a highly addictive psychostimulant drug, whose abuse has reached epidemic proportions worldwide. METH use is disproportionally represented among populations at high risks for developing HIV infection or who are already infected with the virus. Psychostimulant abuse has been reported to exacerbate the cognitive deficits and neurodegenerative abnormalities observed in HIV-positive patients. Thus, the purpose of the present paper is to review the clinical and basic observations that METH potentiates the adverse effects of HIV infection. An additional purpose is to provide a synthesis of the cellular and molecular mechanisms that might be responsible for the increased toxicity observed in co-morbid patients. The reviewed data indicate that METH and HIV proteins, including gp120, gp41, Tat, Vpr and Nef, converge on various caspase-dependent death pathways to cause neuronal apoptosis. The role of reactive microgliosis in METH- and in HIV-induced toxicity is also discussed.

Biological treatments for amfetamine dependence : recent progress

Amfetamine abuse has grown into a worldwide epidemic. Methamfetamine, a derivative of amfetamine made from readily accessible chemicals, has plagued the US since the 1960s, with an alarming recent surge in the numbers of those meeting the criteria for amfetamine abuse and dependence. We review this problem using a computerised literature search (PubMed 1964-2007) to summarise knowledge from animal and human studies about treatments for amfetamine dependence, while exploring the potential of pharmacogenetics to help uncover new treatment targets. Several promising therapeutic targets have come from animal models of reward, drug-taking behaviour and withdrawal. Although preclinical and selected clinical results have been promising, clinical studies have yielded inconsistent results. To improve these outcomes, pharmacogenetic studies may be used to identify candidate alleles that predict therapeutic response. Exciting preclinical findings and a steady progression of clinical results offer hope for the development of a treatment for amfetamine dependence.

Neurotoxicity of substituted amphetamines: Molecular and cellular mechanisms

The amphetamines, including amphetamine (AMPH), methamphetamine (METH) and 3,4-methylenedioxymethamphetamine (MDMA), are among abused drugs in the US and throughout the world. Their abuse is associated with severe neurologic and psychiatric adverse events including the development of psychotic states. These neuropsychiatric complications might, in part, be related to drug-induced neurotoxic effects, which include damage to dopaminergic and serotonergic terminals, neuronal apoptosis, as well as activated astroglial and microglial cells in the brain. The purpose of the present review is to summarize the toxic effects of AMPH, METH and MDMA. The paper also presents some of the factors that are thought to underlie this toxicity. These include oxidative stress, hyperthermia, excitotoxicity and various apoptotic pathways. Better understanding of the cellular and molecular mechanisms involved in their toxicity should help to generate modern therapeutic approaches to prevent or attenuate the long-term consequences of amphetamine use disorders in humans.

A rapid oxidation and persistent decrease in the vesicular monoamine transporter 2 after methamphetamine

Methamphetamine (METH) produces long-term decreases in markers of dopamine (DA) terminals in animals and humans. A decrease in the function of the vesicular monoamine transporter 2 (VMAT2) has been associated with damage to striatal DA terminals caused by METH; however, a possible mechanism for this decrease in VMAT2 function has not been defined. The current study showed that METH caused a rapid decrease to 68% of controls in VMAT2 protein immunoreactivity of the vesicular fraction from striatal synaptosomes within 1 h after a repeated high-dose administration regimen of METH. This decrease was associated with a 75% increase in nitrosylation of VMAT2 protein in the synaptosomal fraction as measured by nitrosocysteine immunoreactivity of VMAT2 protein. The rapid decreases in VMAT2 persisted when evaluated 7 days later and were illustrated by decreases in VMAT2 immunoreactivity and DA content of the vesicular fraction to 34% and 51% of control values, respectively. The decreases were blocked or attenuated by prior injections of the neuronal nitric oxide synthase inhibitor, S-methyl-l-thiocitrulline. These studies demonstrate that METH causes a rapid neuronal nitric oxide synthase-dependent oxidation of VMAT2 and long-term decreases in VMAT2 protein and function. The results also suggest that surviving DA terminals after METH exposure may have a compromised capacity to buffer cytosolic DA concentrations and DA-derived oxidative stress.

Impairment in consolidation of learned place preference following dopaminergic neurotoxicity in mice is ameliorated by N-acetylcysteine but not D1 and D2 dopamine receptor agonists

Some of the major concerns related to methamphetamine (METH) abuse are the neuronal damage inflicted at dopamine (DA) nerve terminals and the cognitive deficits observed in human METH abusers. We have shown that a high dose of METH selectively depleted dopaminergic markers in striatum, frontal cortex and amygdala of Swiss Webster mice, and impaired learned place preference. In this study, we investigated whether deficits in consolidation of place learning, as a consequence of METH neurotoxicity, underlie the underperformance of cocaine conditioned place preference (CPP). Administration of METH (5 mg/kg x 3) to Swiss Webster mice decreased striatal tyrosine hydroxylase (TH) immunoreactive neurons and significantly increased glial fibrillary acidic protein (GFAP) expression, confirming the neurotoxic potential of METH in mice. This treatment significantly attenuated the establishment of cocaine (15 mg/kg) CPP compared to control. To investigate whether manipulation of the consolidation phase improves learned place preference, mice were trained by cocaine and received daily post-training injections of DA receptor agonists or N-acetylcysteine (NAC). As memory consolidation occurs shortly after training, drugs were administered either immediately or 2 h post-training. Immediate post-training administration of the D1 DA receptor agonist SKF38393 (5, 10, and 20 mg/kg) or the D2 DA receptor agonist quinpirole (0.25, 0.5, and 1.0 mg/kg) did not improve the establishment of CPP following METH neurotoxicity. However, immediate but not delayed NAC administration (50 and 100 mg/kg) enhanced cocaine CPP following METH neurotoxicity and had no effect on control CPP. The levels of the reduced form of glutathione (GSH) in striatum, amygdala, hippocampus and frontal cortex were significantly lower in METH-treated mice compared to control during the period of CPP training. Acute and repeated administration of NAC to METH-treated mice restored the decreased brain GSH but had no effect on controls. Results suggest that METH-induced dopaminergic neurotoxicity is associated with impairment of consolidation of learned place preference, and that this impairment is improved by immediate post-training administration of the glutathione precursor NAC and not by D1 or D2 DA receptor agonists. Restoration of brain glutathione levels immediately post-training may facilitate the consolidation process.

The serotonin releaser fenfluramine alters the auditory responses of inferior colliculus neurons

Local direct application of the neuromodulator serotonin strongly influences auditory response properties of neurons in the inferior colliculus (IC), but endogenous stores of serotonin may be released in a distinct spatial or temporal pattern. To explore this issue, the serotonin releaser fenfluramine was iontophoretically applied to extracellularly recorded neurons in the IC of the Mexican free-tailed bat (Tadarida brasiliensis). Fenfluramine mimicked the effects of serotonin on spike count and first spike latency in most neurons, and its effects could be blocked by co-application of serotonin receptor antagonists, consistent with fenfluramine-evoked serotonin release. Responses to fenfluramine did not vary during single applications or across multiple applications, suggesting that fenfluramine did not deplete serotonin stores. A predicted gradient in the effects of fenfluramine with serotonin fiber density was not observed, but neurons with fenfluramine-evoked increases in latency occurred at relatively greater recording depths compared to other neurons with similar characteristic frequencies. These findings support the conclusion that there may be spatial differences in the effects of exogenous and endogenous sources of serotonin, but that other factors such as the identities and locations of serotonin receptors are also likely to play a role in determining the dynamics of serotonergic effects.

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.

Modulation of parathion toxicity by glucose feeding: Is nitric oxide involved?

Glucose feeding can markedly exacerbate the toxicity of the anticholinesterase insecticide, parathion. We determined the effects of parathion on brain nitric oxide and its possible role in potentiation of toxicity by glucose feeding. Adult rats were given water or 15% glucose in water for 3 days and challenged with vehicle or parathion (18 mg/kg, s.c.) on day 4. Functional signs, plasma glucose and brain cholinesterase, citrulline (an indicator of nitric oxide production) and high-energy phosphates (HEPs) were measured 1-3 days after parathion. Glucose feeding exacerbated cholinergic toxicity. Parathion increased plasma glucose (15-33%) and decreased cortical cholinesterase activity (81-90%), with no significant differences between water and glucose treatment groups. In contrast, parathion increased brain regional citrulline (40-47%) and decreased HEPs (18-40%) in rats drinking water, with significantly greater changes in glucose-fed rats (248-363% increase and 31-61% decrease, respectively). We then studied the effects of inhibiting neuronal nitric oxide synthase (nNOS) by 7-nitroindazole (7NI, 30 mg/kg, i.p. x4) on parathion toxicity and its modulation by glucose feeding. Co-exposure to parathion and 7NI led to a marked increase in cholinergic signs of toxicity and lethality, regardless of glucose intake. Thus, glucose feeding enhanced the accumulation of brain nitric oxide following parathion exposure, but inhibition of nitric oxide synthesis was ineffective at counteracting increased parathion toxicity associated with glucose feeding. Evidence is therefore presented to suggest that nitric oxide may play both toxic and protective roles in cholinergic toxicity, and its precise contribution to modulation by glucose feeding requires further investigation.