Systemic administration of D-amphetamine induced a delayed production of nitric oxide in the striatum of rats

The neurotoxic mechanisms of amphetamine: Step by step for striatal dopamine depletion

Amphetamine (AMPH) is a commonly abused psychostimulant that induces neuronal cell death/degeneration in humans and experimental animals. Although multiple neurotoxic mechanisms of AMPH have been intensively investigated, the interplay between these mechanisms has remained elusive. In this study, we used a rat model of AMPH-induced long-lasting striatal dopamine (DA) depletion and identified mechanisms of neurotoxicity, energy failure, excitotoxicity, and oxidative stress. Pretreatment with nicotinamide (NAM, a co-factor for the electron transport chain) blocked AMPH-induced free radical formation, energy failure, and striatal DA decrease. Also, MK-801 (a NMDA receptor antagonist) blocked AMPH-induced free radical formation and striatal DA but not energy failure decrease, indicating excitotoxicity may occur before free radical formation and after energy failure. Thus, these results show that during AMPH intoxication, energy failure, excitotoxicity, and free radical formation are orchestrated consecutively to mediate the depletion of striatal DA.

Protection from noise-induced temporary threshold shift by D-methionine is associated with preservation of ATPase activities

OBJECTIVE

The present study was designed to test whether noise-induced temporary threshold shift (TTS) could be attenuated by D-methionine and its possible relation to the biochemical changes of cochlear lateral walls such as ATPase activities and oxidative stress in guinea pigs.

DESIGN

Thirty-two normal-hearing male guinea pigs were randomly divided into saline-treated and D-methionine-treated (300 mg/kg) experimental groups. One hour after treatment, they were exposed to a continuous broadband white noise at 105 +/- 2 dB sound pressure level for 10 min, causing TTS. Each group was then divided into four subgroups based on the number of survival days after noise exposure (0, 1, 2, and 7 days). Each subgroup had four animals and eight ears included. By means of click-evoked auditory brain stem responses (ABR), auditory thresholds of guinea pigs were measured before noise exposure, immediately after noise exposure, and before killing. After animals were killed, cochlear lateral walls were immediately harvested and assayed for enzyme-specific activities of Na+, K+-ATPase and Ca2+-ATPase, lipid peroxidation, and nitric oxide.

RESULTS

A 15.31 +/- 3.80 dB threshold shift was found immediately after noise exposure in saline-pretreated guinea pigs. In contrast, ABR threshold shift was significantly attenuated to 4.06 +/- 2.35 dB in D-methionine-treated animals. Furthermore, D-methionine enhanced the restoration of ABR threshold to baseline level by 1 day. In addition, noise significantly decreased Na+, K+-ATPase, and Ca2+-ATPase activities and increased lipid peroxidation and nitric oxide levels of the cochlear lateral walls. D-methionine significantly protected against all of these changes.

CONCLUSIONS

Noise not only induced TTS but also inhibited ATPase activities as well as increased oxidative stress in guinea-pig cochlear lateral walls; all of these changes could be attenuated by d-methionine through its antioxidative property. These results suggest the potential usefulness of d-methionine in protecting from noise-induced ototoxicity.

Effects of methylprednisolone on nitric oxide formation and survival of facial motor neurons after axotomy

The aims of this study were to evaluate the effect of a high dose (160 mg/kg) of methylprednisolone sodium succinate (MPSS) on the formation of endogenous nitric oxide (NO) in the brainstem after facial nerve transection and to explore whether this effect has relevance to the survival of facial motor neurons. Guinea pig facial nerves were transected at the tympanic segment, and half were administered with MPSS, while the other half were given a vehicle of saline solution. Post operation NO formation in the brainstem at different time points was directly measured with a NO/ozone chemiluminescence technique. The surviving motor neurons were counted in histological coronal frozen sections of facial motor nuclei. The present results revealed that facial nerve transection induced a significant increase in NO formation in the brainstem by 1 week in both MPSS and saline treated groups and lasted to the end of the study (4 weeks). Compared to the saline treated group, it appeared that MPSS administration could delay the increase of nitric oxide synthase (NOS) expression and NO formation during the first 1 approximately 2 weeks after facial nerve transection. The survival rate of facial motor neurons was significantly higher in the MPSS treated group than in the saline treated group when examined at 3 or 4 weeks after facial nerve transection. These results indicate that a high dose of MPSS elicited a delayed increase of NO formation and thus may concomitantly enhance the survival time of motor neurons after facial nerve transection.

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.

Nitric oxide and MPP+-induced hydroxyl radical generation

Although neuroprotective effect of nitric oxide (NO) is discussed, NO has a role of pathogenesis of cellular injury. NO is synthesized from L-arginine by NO synthase (NOS). NO contributes to the extracellular potassium-ion concentration ([K(+)](o))-induced hydroxyl radical ((*)OH) generation. Cytotoxic free radicals such as peroxinitrite (ONOO(-)) and (*)OH may also be implicated in NO-mediated cell injury. NO activation was induced by K(+) depolarization. NO may react with superoxide anion (O(2) (-)) to form ONOO(-) and its decomposition generates (*)OH. 1-Methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) metabolite 1-methyl-4-phenylpyridinium ion (MPP(+)) involve toxicity induced by NO. Intraneuronal Ca(2+) triggered by MPP(+) may be detrimental to the functioning of dopaminergic nerve terminals in the striatum. Although the [K(+)](o)-induced depolarization enhances the formation of (*)OH product due to MPP(+), the (*)OH generation via NOS activation may be unrelated the dopamine (DA)-induced (*)OH generation. Depolarization enhances the MPP(+)-induced (*)OH formation via NOS activation. NOS inhibition is associated with a protective effect due to suppression of depolarization-induced (*)OH generation. ONOO(-) has been implicated as a causative factor under conditions in which DA neurons are damaged. These findings may be useful in elucidating the actual mechanism of free radical formation in the pathogenesis of neurodegenerative brain disorders, including Parkinson's disease and traumatic brain injuries.

Effects of alpha-phenyl-N-tert-butyl nitrone and N-acetylcysteine on hydroxyl radical formation and dopamine depletion in the rat striatum produced by d-amphetamine

Previous studies have shown that treatment with free radical scavengers attenuated the D-amphetamine (AMPH) neurotoxicity. But several of these agents also prevent AMPH-induced elevation of body temperature in the rat. Thus, further studies are needed to determine if blockade of the production of free radical or hypothermia are related to the neuroprotective mechanism of the free radical scavengers for AMPH neurotoxicity. In the present study, we examined the effects of the free radical scavengers alpha-phenyl-N-tert-butyl nitrone (PBN) and N-acetylcysteine (NAC) on long-term depletion of striatal dopamine (DA) and lipid peroxidation formation and on hyperthermia induced by AMPH. We also determined their effects on acute hydroxyl radical formation after direct intrastriatal infusion of AMPH. The results showed that both significantly attenuated long-term DA depletion and lipid peroxidation formation in the rat striatum at the dose range that did not block hyperthermia induced by AMPH. These agents also completely inhibited the production of hydroxyl radical after AMPH infusion into the striatum. Our results suggest that free radical scavengers such as PBN and NAC could protect against AMPH-induced oxidative stress and DAergic terminal toxicity via their free radical removing property independent of lowering the core body temperature of rats, and imply that supplement with antioxidants is a potential strategy in the treatment of AMPH neurotoxicity.

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.

Involvement of nitric oxide generation in noise-induced temporary threshold shift in guinea pigs

The present study explored the role of endogenous nitric oxide (NO) in the temporary threshold shift caused by acoustic trauma. Guinea pigs were exposed to broadband white noise at a level of 105+/-2dB sound pressure level (SPL) for 10min, causing a temporary threshold shift (TTS). The guinea pigs were divided into six groups (N-1 to N-6) according to survival days after noise exposure (0, 1, 2, 3, 7, 28days). Auditory brainstem responses (ABR) were recorded before noise exposure, immediately after noise exposure and before sacrifice. Immediately after animals were sacrificed, the stria vascularis and the spiral ligament of the lateral wall of each individual cochlea were harvest as a unit and prepared for assay of NO. There was a significant correlation (P<0.001) between the NO concentration and final ABR threshold in the noise exposure groups. But the return of ABR threshold to pre-noise-exposed level is early than that of NO concentration. An average 16.2dB threshold shift was found immediately after noise exposure. The threshold returned to the pre-noise-exposed level on the second post-exposure day. Comparing to unexposed control animals, the NO concentration increased nearly threefold immediately following noise exposure and decreased to twofold when the hearing threshold had returned to the pre-noise-exposed level. On the seventh post-exposure day the NO concentration was not different from that in unexposed control animals. Those findings indicate that endogenous NO is generated in the noise-induced temporal threshold shift and its concentration is correlated with the hearing loss.

Exposure to traffic exhausts and oxidative DNA damage

AIMS

To assess the relations between exposure to traffic exhausts and indicators of oxidative DNA damage among highway toll station workers.

METHODS

Cross-sectional study of 47 female highway toll station workers exposed to traffic exhausts and 27 female office workers as a reference group. Exposure assessment was based on average and cumulative traffic density and a biomarker of exposure, urinary 1-hydroxypyrene-glucuronide (1-OHPG). Urinary 8-hydroxydeoxyguanosine (8-OHdG) was used as a biomarker of oxidative DNA damage. Plasma nitric oxide (NO) was measured as an indicator of oxidative stress related to traffic exhaust exposure.

RESULTS

The mean concentration of urinary 8-OHdG was substantially higher among the exposed non-smokers (13.6 microg/g creatinine) compared with the reference non-smokers (7.3 microg/g creatinine; difference 6.3, 95% CI 3.0 to 9.6). The mean concentration of NO among the exposed (48.0 micromol/l) was also higher compared with the reference non-smokers (37.6 micromol/l; difference 10.4, 95% CI -0.4 to 21.2). In linear regression adjusting for confounding, a change in log(8-OHdG) was statistically significantly related to a unit change in log(1-OHPG) (beta = 0.372, 95% CI 0.081 to 0.663).

CONCLUSIONS

Results indicate that exposure to traffic exhausts increases oxidative DNA damage. Urinary 8-OHdG is a promising biomarker of traffic exhaust induced oxidative stress.

Comparative Effects of NO-Synthase Inhibitor and NMDA Antagonist on Generation of Nitric Oxide and Release of Amino Acids and Acetylcholine in the Rat Brain Elicited by Amphetamine Neurotoxicity

The aim of this study was to clarify the role of nitric oxide (NO) and lipid peroxidation (LPO) processes as well as the contribution of various neurotransmitters in pathophysiological mechanisms of neurotoxicity induced by amphetamine (AMPH). NO level was determined directly in brain tissues using electron paramagnetic resonance spectroscopy technique. The content of the products of lipid peroxidation (LPO) was measured spectrophotometrically as thiobarbituric acid reactive species (TBARS). The output of neurotransmitter amino acids (glutamate, aspartate, and GABA) and acetylcholine (ACH) was monitored in nucleus accumbens (NAc) by push-pull technique with HPLC detection. Repeated, systemic application of AMPH elevated striatal and cortical NO generation and LPO production. Moreover, administration of AMPH led to a marked and long-lasting increase of ACH release. Surprisingly, while glutamate output was not affected, aspartate release was enhanced 30 to 50 min after each AMPH injection. The release rate of GABA was also elevated. The selective NO-synthase inhibitor 7-nitroindazole (7-NI) was highly effective in abating the rise in the neurotransmitter release induced by the AMPH. The NOS inhibitor also abolished the increase of NO generation produced by AMPH, but did not influence the intensity of LPO elicited by the AMPH administration. Pretreatment with the noncompetitive NMDA receptor antagonist dizocilpine (MK-801) completely prevented increase of NO generation and TBARS formation induced by multiple doses of AMPH. Dizocilpine also abolished the effect of the psychostimulant drug on the release of neurotransmitters ACH, glutamate, aspartate, and GABA in the NAc. Our findings suggest a key role of NO in AMPH-induced transmitter release, but not in the formation of LPO products. It appears that AMPH enhances release of ACH and neurotransmitter amino acids through increased NO synthesis and induces neurotoxicity via NO and also by NO-independent LPO.

Enhanced P2Y1 receptor expression in the brain after sensitisation with d-amphetamine

RATIONALE AND OBJECTIVES

Many pathological and physiological processes are associated with the transcriptional induction of specific receptors. The aim of the present study was to examine whether the development of d-amphetamine (AMPH)-induced sensitisation is related to an altered P2Y(1) receptor expression.

METHODS

Rats, treated for 5 successive days with AMPH (1.5 mg/kg, i.p.), alone or after pre-treatment with the non-specific P2 receptor antagonist pyridoxal-phosphate-6-azophenyl-2,4-disulphonic acid (PPADS, 0.6 nmol, i.c.v.) and tested in an open field system with respect to locomotor response, were studied immunocytochemically 5 days after the last AMPH injection.

RESULTS

In the behaviourally sensitised animals, astrogliosis, characterised by hypertrophy, increase in glial fibrillary acidic protein (GFAP) immunoreactivity (IR) and astrocytic proliferation in striatal areas and the nucleus accumbens were observed. Quantification of the P2Y(1) receptor stained cells revealed an increase in the receptor expression after AMPH-induced sensitisation in the studied regions. Pre-treatment with PPADS prior to each AMPH administration prevented the development of sensitisation, astrogliosis and P2Y(1) receptor up-regulation. PPADS failed to alter the number of P2Y(1) receptor-labelled cells when given alone. Confocal laser scanning microscopy indicated the localisation of P2Y(1) receptors on GFAP-labelled astrocytes as well as on tubulin (betaIII)-labelled neurones, under control conditions and after AMPH administration.

CONCLUSION

The present results confirm the existence of P2Y(1) receptors on astrocytes and neurones as possible targets of endogenous ATP and in addition show their up-regulation as a consequence of P2Y(1) receptor-involvement in AMPH-induced sensitisation in vivo.

Nitric oxide-induced mitochondrial dysfunction: implications for neurodegeneration

Excessive generation of nitric oxide (NO) has been implicated in the pathogenesis of several neurodegenerative disorders. Damage to the mitochondrial electron transport chain has also been implicated in these disorders. NO and its toxic metabolite peroxynitrite (ONOO(-)) can inhibit the mitochondrial respiratory chain, leading to energy failure and ultimately cell death. There appears to be a differential susceptibility of brain cell types to NO/ONOO(-), which may be influenced by factors including cellular antioxidant status and the ability to maintain energy requirements in the face of marked respiratory chain damage. Although formation of NO/ONOO(-) following cytokine exposure does not affect astrocyte survival, these molecules may diffuse out and cause mitochondrial damage to neighboring NO/ONOO(-)-sensitive cells such as neurons. Evidence suggests that NO/ONOO(-) causes release of neuronal glutamate, leading to glutamate-induced activation of neuronal NO synthase and generation of further damaging species. While neurons appear able to recover from short-term exposure to NO/ONOO(-), extending the period of exposure results in persistent damage to the respiratory chain and cell death ensues. These findings have important implications for acute infection vs. chronic neuroinflammatory disease states. The evidence for NO/ONOO(-)-mediated mitochondrial damage in neurodegenerative disorders is reviewed and potential therapeutic strategies are discussed.

cDNA array analysis of gene expression profiles in the striata of wild-type and Cu/Zn superoxide dismutase transgenic mice treated with neurotoxic doses of amphetamine

Amphetamine (AMPH) is a drug of abuse that causes the degeneration of striatal dopamine terminals in mammals. Superoxide radicals seem to participate in AMPH-induced damage because its toxicity is attenuated in Cu/Zn superoxide dismutase transgenic (SOD-tg) mice. To provide a detailed analysis of molecular changes associated with AMPH toxicity, we used cDNA arrays consisting of 1176 genes to detect differential changes in gene expression in the striata of wild-type and SOD-tg mice treated with neurotoxic doses of the drug. We found 42 genes that showed >1.8-fold changes in at least two consecutive time points during the course of the study and were differentially affected by AMPH in the two genotypes. Specifically, more transcription factors and genes involved in responses to injury/inflammation were affected in wild-type mice after AMPH administration. Some of these stimulant-induced superoxide-dependent alterations in gene expression might affect neuronal functions and promote neuronal damage. Other changes might help to provide some degree of protection against AMPH toxicity. These results support the view that the use of global array analysis of gene expression will help to identify novel molecular mediators of AMPH-induced neurodegeneration.

Role of hydroxyl radical formation in neurotoxicity as revealed by in vivo free radical trapping

Reactive oxygen species have been implicated in dopaminergic toxicity caused by 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) and iron. Although MPTP produces a parkinsonian syndrome after its conversion to 1-methyl-4-phenylpyridine (MPP(+)) by type B monoamine oxidase (MAO-B) in the brain, the etiology of this disease remains obscure. MPP(+) is a highly potent dopaminbergic-releasing agents and dopamine (DA) autoxidation catalyzed by iron and oxidative stress may be involved in the pathogenesis of Parkinson's disease. Neuromelanine synthesis from DA produce highly reactive free radicals. Although the controversy possible neurotoxin and/or neuroprotective roles of nitric oxide (NO) was discussed, NO contributes to oxidative injury to brain neurons in vivo. An environmental estrogen-like chemical also related to MPP(+)-induced *OH generation. This review describes actual mechanism of the free radicals formation by dialysis studies of in vivo free radical trapping in the pathogenesis of neurodegenerative disorders, including in the Parkinson's disease, Alzheimer disease and traumatic brain injuries.

Neurochemical changes and neurotoxic effects of an acute treatment with sydnocarb, a novel psychostimulant: comparison with D-amphetamine

Sydnocarb [(phenylisopropyl)N-phenylcarbamoylsydnonimine; SYD] was introduced to clinical practice in Russia as a psychostimulant drug used for the treatment of asthenia and apathy, which accompany schizophrenia and manic depression. It has been described as a psychostimulant with addiction liability and toxicity less than amphetamine (AMPH). The precise cellular mechanisms by which sydnocarb elicits its psychostimulant effect are still unclear. At present its neurochemical and neurotoxic effects are compared to those of AMPH in the striatum, the main input structure of the basal ganglia. The expression of c-fos protein in striatal neurons was much more increased after a single injection of D-AMPH (5 mg/kg) than after an equimolar concentration of SYD (23.8 mg/kg) in both the anterior and the posterior part of the striatum. Using in situ hybridization on striatal slices, we observed that AMPH increased the striatal levels of preprodynorphin (PPDYN) mRNAs in both parts of the striatum, while SYD did not affect basal levels of PPDYN mRNAs. Furthermore, AMPH and SYD increased striatal preprotachykinin (PPT-A) and preproenkephalin (PPE) mRNA levels. The effects of AMPH and SYD on PPT-A-mRNA levels were similar. A differential effect of AMPH and SYD was observed only on the PPE-mRNA levels measured in the anterior striatum where SYD increased these levels more than AMPH. The acute neurotoxicity of these two psychostimulants was analyzed by measuring their effects on the parameters of oxidative stress, such as nitric oxide (NO) generation, as well as specific indices of lipid peroxidation (i.e., thiobarbituric acid reactive substances; TBARS), while, on the other hand, the alpha-tocopherol level was taken as an index of antioxidant defense processes. Measuring generation of NO directly by electron paramagnetic resonance, it was observed that AMPH shows a more pronounced increase in comparison to SYD, in the striatum and in cortex. TBARS levels in the striatum and cortex were significantly less enhanced than AMPH after a single injection of SYD. Similarly, the alpha-tocopherol level was decreased only by AMPH in the striatum, and neither AMPH nor SYD had any effect in the cortex. Results show that a single injection of a high dose of AMPH is able to induce several neurotoxic effects. The study also demonstrates that SYD has mild neurochemical effects as well as fewer neurotoxic properties than AMPH.

Dizocilpine inhibits amphetamine-induced formation of nitric oxide and amphetamine-induced release of amino acids and acetylcholine in the rat brain

Glutamate receptor activation participates in mediation of neurotoxic effects in the striatum induced by the psychomotor stimulant amphetamine. The effects of the non-competitive NMDA receptor antagonist dizocilpine (MK-801) on amphetamine-induced toxicity and formation of nitric oxide (NO) in both striatum and cortex and on induced transmitter release in the nucleus accumbens were investigated. Repeated, systemic application of amphetamine elevated striatal and cortical lipid peroxidation and NO production. Moreover, amphetamine caused an immediate release of acetylcholine and aspartate and a delayed release of GABA in the nucleus accumbens. Surprisingly, glutamate release was not affected. Dizocilpine abolished the amphetamine-induced lipid peroxidation and NO production in striatum and cortex and diminished the elevation of neurotransmitter release. These findings suggest that amphetamine evokes neurotoxic effects in both striatal and cortical brain areas that are prevented by inhibiting NMDA receptor activation. The amphetamine-induced acetylcholine, aspartate and GABA release in the nucleus accumbens is also mediated through NMDA receptor-dependent mechanisms. Interestingly, the enhanced aspartate release might contribute to NMDA receptor activation in the nucleus accumbens, while glutamate does not seem to mediate amphetamine-evoked transmitter release in this striatal brain area.

Amphetamine-induced toxicity in dopamine terminals in CD-1 and C57BL/6J mice: complex roles for oxygen-based species and temperature regulation

In order to examine differential strain susceptibility to neurotoxic effects of amphetamine and to assess the potential role of superoxide radicals in amphetamine-induced dopaminergic damage, the drug was injected to mice with different levels of copper/zinc superoxide dismutase (Cu/Zn SOD) enzyme. Administration of amphetamine (10 mg/kg, i.p., given every 2 h, a total of four times) to wild-type CD-1 and C57BL/6J mice caused significant decreases in dopamine and 3,4-dihydroxyphenylacetic acid levels, in [(125)I]RTI-121-labeled dopamine transporters as well as a significant depletion in the concentration of dopamine transporter and vesicular monoamine transporter 2 proteins. The amphetamine-induced toxic effects were less prominent in CD-1 mice, which have much higher levels of Cu/Zn SOD activity (0.69 units/mg of protein) in their striata than C57BL/6J animals (0.007 units/mg of protein). Transgenic mice on CD-1 and C57BL/6J background, which had striatal levels of Cu/Zn SOD 2.57 and 1.67 units/mg of protein, respectively, showed significant protection against all the toxic effects of amphetamine. The attenuation of toxicity observed in transgenic mice was not caused by differences in amphetamine accumulation in wild-type and mutant animals. However, CD-1-SOD transgenic mice showed marked hypothermia to amphetamine whereas C57-SOD transgenic mice did not show a consistent thermic response to the drug. The data obtained demonstrate distinctions in the neurotoxic profile of amphetamine in CD-1 and C57BL/6J mice, which show some differences in Cu/Zn SOD activity and in their thermic responses to amphetamine administration. Thus, these observations provide evidence for possible complex interactions between thermoregulation and free radical load in the long-term neurotoxic effects of this illicit drug of abuse.

Nitric oxide and depolarization induce hydroxyl radical generation

Nitric oxide (NO) contributes to the extracellular potassium-ion concentration ([K+]o)-induced hydroxyl radical (*OH) generation. Cytotoxic free radicals such as peroxinitrite (ONOO-) and *OH may also be implicated in NO-mediated cell injury. NO is synthesized from L-arginine by NO synthase (NOS). NOS activation was induced by K+ depolarization. Oxidative modification of low-density lipoprotein (LDL) is thought to contribute to the production of oxygen derived-free radicals. However, LDL oxidation may be related to noradrenaline-induced *OH generation, but LDL oxidation may be unrelated to *OH generation via NOS activation. Abnormal levels of extracellular free dopamine (DA) and/or intraneuronal Ca2+ triggered by 1-methyl-4-phenylpyridinium ion (MPP+) may be detrimental to the functioning of dopaminergic nerve terminals in the striatum. Although [K+]o-induced depolarization enhances the formation of *OH product due to MPP+, the *OH generation via NOS activation may be unrelated to the DA-induced *OH generation. Depolarization enhances the formation of *OH products via NOS activation.

Investigation of extracellular L-citrulline concentration in the striatum during alcohol withdrawal in rats

In this study, changes in striatal extracellular L-citrulline concentrations were investigated hourly for 5 h following alcohol withdrawal in chronic alcohol feeding Wistar rats. Alcohol (7.2% ethyl alcohol, v/v) was given to rats as modified liquid diet for 20 days. Signs of alcohol withdrawal appeared from the 1st h of alcohol withdrawal and the total alcohol withdrawal scores remained higher during the course of experiments. The mean of basal levels of L-citrulline in the microdialysis samples collected in conscious rat model from the striatum of control and alcoholized rats were found to be 1.28 +/- 0.48 microM and 0.35 +/- 0.08 microM, respectively. L-citrulline levels in the striatum of alcoholized rats increased by 4 folds significantly within 1 h following alcohol withdrawal. The increased striatal L-citrulline concentration was blocked by NG-nitro-L-arginine methyl ester (L-NAME; 60 mg/kg), a nitric oxide synthase inhibitor, pretreatment. Our results indicate an increased L-citrulline level in the rat striatum during early alcohol withdrawal and this situation may be related to an increased nitric oxide production.

An analysis of excitatory amino acids, nitric oxide, and prostaglandin E2 in the cerebrospinal fluid of pregnant women: the effect on labor pain

It is still unclear which neurotransmitters are involved in labor pain. We measured the concentrations of excitatory amino acids, nitric oxide, and prostaglandin E2 in the cerebrospinal fluid (CSF) of pregnant women, particularly in those with labor pain. The patients included in the study consisted of women who underwent cesarean delivery either with labor pain (Labor Pain group, n = 40) or without labor pain (Nonlabor Pain group, n = 58). All patients received spinal anesthesia (intrathecal injection of 10-12 mg of bupivacaine) for the operation, and 2 mL of CSF was collected before bupivacaine injection. Concentrations of aspartate and glutamate (0.50 +/- 0.06 microM and 0.79 +/- 0.10 microM, respectively) were significantly larger in the Labor Pain group than in the Nonlabor Pain group (0.35 +/- 0.03 microM and 0.54 +/- 0.04 microM, P < 0.05). There were no significant differences in the concentrations of nitric oxide and prostaglandin E2 between the groups. A positive correlation was found between CSF concentrations of excitatory amino acids and labor pain.

IMPLICATIONS

The excitatory amino acids, aspartate and glutamate, play a role in labor pain. N-methyl-D-aspartate receptor antagonists may be useful for labor pain and postlabor uterine contraction pain relief.

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

Neuronal nitric oxide synthase (nNOS) is normally expressed in one population of intrinsic interneurons of the striatum. Production of nitric oxide in the nNOS-containing neurons is sensitive to dopamine stimulation. Using quantitative in situ hybridization, the present study investigated the alteration in basal nNOS mRNA expression in striatal nNOS-containing neurons of mice treated with the psychostimulant amphetamine or a full D1 dopamine receptor agonist, SKF-82958. A single systemic injection of amphetamine induced a dose-related change in striatal nNOS mRNA expression. Whereas amphetamine at 4 mg/kg decreased basal levels of nNOS mRNA in both the dorsal (caudoputamen) and ventral (nucleus accumbens) striatum, the drug at a higher dose (12 mg/kg) increased nNOS expression in the two regions. Similarly, an acute systemic injection of SKF-82958 decreased and increased nNOS mRNA levels in the dorsal and ventral striatum at 2 and 4 mg/kg, respectively. These data indicate that constitutive nNOS expression in nitric oxide-producing neurons of the mouse striatum is regulated by dopaminergic transmission. Altered nNOS expression may result in changes in nitric oxide synthesis and thus contribute to biological actions of dopamine stimulants.

Involvement of nitric oxide in morphine-induced c-Fos expression in the rat striatum

Induction of expression of immediate-early gene c-Fos in the striatum is a common effect of many drugs of abuse, including morphine. Previous studies have shown that the morphine-mediated c-Fos response is attenuated by antagonists of the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor. Other evidence suggests that the NDMA receptor may be coupled to the enzyme neuronal nitric oxide synthase (nNOS). NMDA receptor-mediated increases in intracellular calcium can activate nNOS, which catalyzes the formation of the signaling molecule nitric oxide. Because activation of NMDA receptors mediates morphine-induced c-Fos expression, we tested the hypothesis that activation of nNOS is involved in this cascade. Male rats were injected with the nNOS-selective inhibitor 7-nitroindazole (7-NI) or vehicle 30 min prior to injection of morphine sulfate or vehicle. Two hours later they were perfused with fixative and the brains removed for immunocytochemical analysis for c-Fos. Morphine induced c-Fos expression in the striatum, cerebral cortex, and midline/intralaminar nuclei of thalamus. Expression in the striatum, but not thalamus or cortex, was significantly blocked by 7-NI. Double-label immunocytochemistry revealed no co-localization of c-Fos and nNOS in any brain region. These results support a role for nNOS in the neural circuits activated by morphine.

Formation of hydroxy radicals by environmental estrogen-like chemicals in rat striatum

We investigated effects of environmental estrogen-like chemicals, para-nonylphenol and bisphenol A, on hydroxy radical formation in the striatum of adult rats, using an in vivo microdialysis system. Para-nonylphenol significantly stimulated hydroxy radical formation in the striatum. Bisphenol A also increased hydroxy radical formation, albeit effect being slight. The formation of hydroxy radicals induced by para-nonylphenol was dose-dependently inhibited by tamoxifen, which suggests that the effect of this chemical was an estrogenic action via estrogen receptors. The results of the present study are the first demonstration on hydroxy radical formation induced by environmental estrogen-like chemicals and suggest that the in vivo microdialysis may be useful for evaluating toxic effects of environmental chemicals on nervous tissues.