The significance of nitric oxide production in the brain after injury

Glutamate toxicity has been implicated in many aspects of brain injury including traumatic, ischemic, and hemorrhagic damage. We have used in vitro as well as in vivo methods to measure NO production and to examine the role of NO in glutamate toxicity. In building our recombinant system, we used human kidney embryonic cells, HEK 293, as host for transfection of nNOS and NMDA receptor proteins. Cells cotransfected with NMDA and nNOS were more resistant to glutamate toxicity. This resistance correlated with NO production as measured by citrulline assay. Meanwhile, the production of NO did not significantly change the response of the NMDA receptor as seen by calcium studies. Moreover, in vivo, NO production was directly correlated with brain tissue oxygen tension in subarachnoid hemorrhage patients. These data and others point toward the importance of NO production in the response of brain to injury.

Iron overload, oxidative stress, and axonal dystrophy in brain disorders

Hallervorden-Spatz syndrome is an autosomal-recessive brain disorder with signs of extrapyramidal dysfunction and mental deterioration, which associate with iron accumulation in globus pallidus and substantia nigra pars reticulata. Studies of oxidant stress in parkinsonian animal models suggest a linkage of iron overload to axonal dystrophy. Redox cycling of iron complexes (i.e., ferrous citrate and hemoglobin) increases hydroxyl radicals, lipid peroxidation, axonal dystrophy, and necrotic or apoptotic cell death. An increase of oxidative stress in the basal ganglia because of redox cycling of iron complexes leads to dopamine overflow and psychomotor dysfunction. Iron overload-induced axonal dystrophy has been demonstrated consistently using in vitro and in vivo models with a prominent feature of lipid peroxidation. This iron-induced oxidative stress is often accentuated by ascorbate and oxidized glutathione, although it is suppressed by the following antioxidants: S-nitrosoglutathione or nitric oxide, MnSOD mimics, manganese, U-78517F, Trolox, and deferoxamine. Preconditioning induction of stress proteins (i.e., hemeoxygenase-1 and neuronal nitric oxide synthase) and hypothermia therapy suppress the generation of toxic reactive oxygen, lipid, and thiol species evoked by bioactive iron complexes in the brain. Finally, combined antioxidative therapeutics and gene induction procedures may prove to be useful for slowing progressive neurodegeneration caused by iron overload in the brain.

Preconditioning regulation of bcl-2 and p66shc by human NOS1 enhances tolerance to oxidative stress

Preconditioning stress induced by a transient ischemia may increase brain tolerance to oxidative stress, and the underlying neuroprotective mechanisms are not well understood. In a series of experiments, we found that endogenous nitric oxide (NO), S-nitrosoglutathione (GSNO), and antioxidants blocked serum deprivation-induced oxidative stress and apoptosis in human neuroblastoma cells. Similar to nuclear redox factor-1 (Ref-1), mRNA of human neuronal nitric oxide synthase (hNOS1) was maximally up-regulated within 2 h after oxidative stress and down-regulated by NO/GSNO and hydroxyl radical (OH) scavenger. A brief preconditioning stress induced by serum deprivation for 2 h caused a delayed increase in the expression of hNOS1 protein and the associated formation of NO and cGMP, which in turn decreased OH generation and stress-related cell death. In addition to inhibiting caspase-3 through a dithiothreitol-sensitive S-nitrosylation process, preconditioning stress concomitantly up-regulated the expression of the anti-apoptotic bcl-2 protein and down-regulated the p66shc adaptor protein. This beneficial cytoprotective process of preconditioning stress is mediated by newly synthesized NO because it can be suppressed by the inhibition of hNOS1 and guanylyl cyclase. Therefore, the constitutive isoform of hNOS1 is dynamically redox-regulated to meet both functional and compensatory demands of NO for gene regulation, antioxidant defense, and tolerance to oxidative stress.

Effects of atypical antioxidative agents, S-nitrosoglutathione and manganese, on brain lipid peroxidation induced by iron leaking from tissue disruption

A fluorescent assay of brain lipid peroxidation was used for screening new antioxidants for the prevention of neurodegeneration caused by free radicals. Incubation of rat brain homogenates led to a temperature-dependent increase in production of fluorescent adducts of peroxidized polyunsaturated fatty acids; it was inhibited completely by lowering the incubation temperature to 4 degrees C. This tissue disruption-induced brain lipid peroxidation at 37 degrees C was blocked by deferoxamine (IC50 = 0.3 microM) and EDTA; it was augmented by adding submicromolar iron and hemoglobin. Ferrous ion's pro-oxidative activities were five times more potent than ferric ion. Micromolar manganese completely inhibited lipid peroxidation, confirming earlier unexpected in vivo reports. Trolox and vitamin C suppressed brain lipid peroxidation with IC50 values of 20 and 500 microM, respectively. U-78517F was approximately 20 times more potent than Trolox. 17 beta-Estradiol, hydralazine, S-nitrosoglutathione and 3-hydroxybenzylhydrazine were as potent as Trolox. Melatonin, glutathione, alpha-lipoic acid and l-deprenyl were about 20 times less potent than Trolox. Surprisingly, N-tert-butyl-alpha-phenylnitrone was a weak antioxidant. Furthermore, this procedure can also detect pro-oxidative side effects of vitamin C, oxidized glutathione, penicillamine and Angeli's salt. The present results obtained from this selective fluorescent assay are consistent with earlier reports that iron complexes promote while manganese inhibits brain lipid peroxidation caused by cell disruption. S-Nitrosoglutathione, melatonin, 17 beta-estradiol, and manganese have been successfully tested in cell/animal models for their potential neuroprotective effects. In conclusion, monitoring fluorescent adducts of peroxidizing polyunsaturated fatty acids in brain homogenates is a simple, quantitative method for studying iron-dependent brain lipid peroxidation and for screening of potential neuroprotective antioxidants in both in vitro and in vivo preparations.

Effect of MAO-B inhibitors on MPP+ toxicity in Vivo

l-Deprenyl (Selegiline), a selective and irreversible type B monoamine oxidase inhibitor, has been used as an adjunct to levodopa therapy in Parkinson's disease. Recently, it is proposed as a putative neuroprotective agent in delaying the progression of cell death based on its capability of reducing the oxidative stress derived from the MAO-B dependent metabolism of dopamine, and blocking the development of MPTP-parkinsonism. However, a variety of experimental models suggest that l-deprenyl provides neuroprotection through multiple modes of mechanism other than the inhibition of MAO-B. We have previously shown that l-deprenyl protects midbrain dopamine neurons from MPP+ toxicity by a novel antioxidant effect. In the present study we examined whether the protection against MPP+ toxicity is also shared by other reversible or irreversible MAO-B inhibitors including (+)-deprenyl, Ro16-6491 and pargyline. Our data show that non of these MAO-B inhibitors changes the dopamine loss in the striatum induced by intranigral injection of MPP+. Our result suggests that l-deprenyl may possess a unique neuroprotective action on nigral neuron against MPP+ toxicity independent of the MAO-B inhibition.

Neuroprotective properties of nitric oxide

The discoveries of physiological roles of nitric oxide (.NO) as the mediator of endothelium-derived relaxing factor (EDRF) action and the activator of guanylyl cyclase to increase cyclic guanosine monophosphate (cGMP), which lead to vasorelaxation in the cardiovascular system, have been awarded with the 1998 Nobel Prize of Medicine. The present review discusses putative beneficial effects of .NO in the central nervous system (CNS). In addition to its prominent roles of the regulation of cerebral blood flow and the modulation of cell to cell communication in the brain, recent in vitro and in vivo results indicated that .NO is a potent antioxidative agent. .NO terminates oxidant stress in the brain by (i) suppressing iron-induced generation of hydroxyl radicals (.OH) via the Fenton reaction, (ii) interrupting the chain reaction of lipid peroxidation, (iii) augmenting the antioxidative potency of reduced glutathione (GSH) and (iv) inhibiting cysteine proteases. It is apparent that .NO--a relative long half-life nitrogen-centered weak radical--scavenges those short-lived, highly reactive free radicals such as superoxide anion (O2.-), .OH, peroxyl lipid radicals (LOO.) and thiyl radicals (i.e., GS.), yielding reactive nitrogen species including nitrites, nitrates, S-nitrosoglutathione (GSNO) and peroxynitrite (ONOO-). GSNO is 100-fold more potent than GSH; it completely inhibits the weak peroxidative effect of ONOO-. Moreover, CO2 and .NO neutralize prooxidative effects of ONOO-. CO2 prevents protein oxidation but not 3-nitrotyrosine formation caused by ONOO-. Finally, neuroprotective effects of GSNO and .NO have been demonstrated in brain preparations in vivo. These novel neuroprotective properties of .NO and GSNO may have their physiological significance, since oxidative stress depletes GSH while increasing GS. and .NO formation in astroglial and endothelial cells, resulting in the generation of a more potent antioxidant GSNO and providing additional neuro-protection at microM concentrations. This putative GSNO pathway (GSH-->GS.-->GSNO-->.NO + GSSG-->GSH) may be an important part of endogenous antioxidative defense system, which could protect neurons and other brain cells against oxidative stress caused by oxidants, iron complexes, proteases and cytokines. In conclusion, .NO is a potent antioxidant against oxidative damage caused by reactive oxygen species, which are generated by Fenton reaction or other mechanisms in the brain via redox cycling of iron complexes.

Neuroprotective strategies in Parkinson's disease: protection against progressive nigral damage induced by free radicals

Brain undergoes neurodegeneration when excess free radicals overwhelm antioxidative defense systems during senescence, head trauma and/or neurotoxic insults. A site-specific accumulation of ferrous citrate-iron complexes in the substantia nigra dopaminergic neurons could lead to exaggerated dopamine turnover, dopamine auto-oxidation, free radical generation, and oxidant stress. Eventually, this iron-catalyzed dopamine auto-oxidation results in the accumulation of neuromelanin, a progressive loss of nigral neurons, and the development of Parkinson's disease when brain dopamine depletion is greater than 80%. Emerging evidence indicates that free radicals such as hydroxyl radicals ((.-)OH) and nitric oxide ((.-)NO) may play opposite role in cell and animal models of parkinsonism. (.-)OH is a cytotoxic oxidant whereas oNO is an atypical neuroprotective antioxidant. (.-)NO and S-nitrosoglutathione (GSNO) protect nigral neurons against oxidative stress caused by 1-methyl-4-phenylpyridinium (MPP(+)), dopamine, ferrous citrate, hemoglobin, sodium nitroprusside and peroxynitrite. MPP(+), the toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), increases the nigral uptake of iron complexes and dopamine overflow leading to the generation of (.-)OH, protein oxidation, lipid peroxidation, and associated retrograde degeneration. In addition to GSNO, MPP(+)-induced oxidative neurotoxicity can be prevented by antioxidants including selegiline, 7-nitroindazole, 17beta-estradiol, melatonin, alpha-phenyl-tert-butylnitrone and U78517F. Similar to selegiline, 7-nitroindazole is a MAO-B inhibitor, which blocks the bio-activation of MPTP and oxidative stress. Freshly prepared but not light exposed, (.-)NO-exhausted GSNO is about 100 times more potent than the classic antioxidant glutathione. Via S-nitrosylation, GSNO also inhibits proteolysis and cytotoxicity caused by caspases and HIV-1 protease. Furthermore, in addition to protection against serum deprivation stress, the induction of neuronal NOS1 in human cells increases tolerance to MPP(+)-induced neuro-toxicity since newly synthesized (.-)NO prevents apoptosis possibly through up-regulation of bcl-2 and down regulation of p66(shc). In conclusion, reactive oxygen species are unavoidable by-products of iron-catalyzed dopamine auto-oxidation, which can initiate lipid peroxidation, protein oxidation, DNA damage, and nigral loss, all of which can be prevented by endogenous and exogenous (.-)NO. Natural and man-made antioxidants can be employed as part of preventative or neuroprotective treatments in Parkinson's disease and perhaps dementia complexes as well. For achieving neuroprotection and neuro-rescue in early clinical parkinsonian stages, a cocktail therapy of multiple neuroprotective agents may be more effective than the current treatment with extremely high doses of a single antioxidative agent.

The redox pathway of S-nitrosoglutathione, glutathione and nitric oxide in cell to neuron communications

Recent results demonstrated that S-nitrosoglutathione (GSNO) and nitric oxide (*NO) protect brain dopamine neurons from hydroxyl radical (*OH)-induced oxidative stress in vivo because they are potent antioxidants. GSNO and *NO terminate oxidant stress in the brain by (i) inhibiting iron-stimulated hydroxyl radicals formation or the Fenton reaction, (ii) terminating lipid peroxidation, (iii) augmenting the antioxidative potency of glutathione (GSH), (iv) mediating neuroprotective action of brain-derived neurotrophin (BDNF), and (v) inhibiting cysteinyl proteases. In fact, GSNO--S-nitrosylated GSH--is approximately 100 times more potent than the classical antioxidant GSH. In addition, S-nitrosylation of cysteine residues by GSNO inactivates caspase-3 and HIV-1 protease, and prevents apoptosis and neurotoxicity. GSNO-induced antiplatelet aggregation is also mediated by S-nitrosylation of clotting factor XIII. Thus the elucidation of chemical reactions involved in this GSNO pathway (GSH GS* + *NO-->[GSNO]-->GSSG + *NO-->GSH) is necessary for understanding the biology of *NO, especially its beneficial antioxidative and neuroprotective effects in the CNS. GSNO is most likely generated in the endothelial and astroglial cells during oxidative stress because these cells contain mM GSH and nitric oxide synthase. Furthermore, the transfer of GSH and *NO to neurons via this GSNO pathway may facilitate cell to neuron communications, including not only the activation of guanylyl cyclase, but also the nitrosylation of iron complexes, iron containing enzymes, and cysteinyl proteases. GSNO annihilates free radicals and promotes neuroprotection via its c-GMP-independent nitrosylation actions. This putative pathway of GSNO/GSH/*NO may provide new molecular insights for the redox cycling of GSH and GSSG in the CNS.

Hemoglobin and iron-evoked oxidative stress in the brain: protection by bile pigments, manganese and S-nitrosoglutathione

In the present in vitro and in vivo study we investigated the pro-oxidant effects of hemoglobin, as well as the antioxidant effects of its metabolites, in the brain. Incubation of rat brain homogenates with hemoglobin (0-10 microM) but not hemin induced lipid peroxidation up to 24 h (EC50 = 1.2 microM). Hemoglobin's effects were similar to ferrous ion (EC50 = 1.7 microM) and were blocked by the chelating agent deferoxamine (IC50 0.5 microM) and a nitric oxide-releasing compound S-nitrosoglutathione (IC50 = 40 microM). However, metabolites of hemoglobin - biliverdin and bilirubin - inhibited brain lipid peroxidation induced by cell disruption and hemoglobin (biliverdin IC50 = 12-30 and bilirubin IC50 = 75-170 microM). Biliverdin's antioxidative effects in spontaneous and iron-evoked lipid peroxidation were further augmented by manganese (2 microM) since manganese is an antioxidative transition metal and conjugates with bile pigments. Intrastriatal infusion of hemoglobin (0-24 nmol) produced slight, but significant 20-22% decreases in striatal dopamine levels. Whereas, intrastriatal infusion of ferrous citrate (0-24 nmol) dose-dependently induced a greater 66% depletion of striatal dopamine which was preceded by an acute increase of lipid peroxidation. In conclusion, contrary to the in vitro results hemoglobin is far less neurotoxic than ferrous ions in the brain. It is speculated that hemoglobin may be partially detoxified by heme oxygenase and biliverdin reductase to its antioxidative metabolites in the brain. However, in head trauma and stroke, massive bleeding could significantly produce iron-mediated oxidative stress and neurodegeneration which could be minimized by endogenous antioxidants such as biliverdin, bilirubin, manganese and S-nitrosoglutathione.

Kynostatin and 17beta-estradiol prevent the apoptotic death of human neuroblastoma cells exposed to HIV-1 protease

A significant number of adult male patients with acquired immunodeficiency syndrome develop cerebral atrophy and progressive brain disorders such as dementia complex and neuropsychiatric problems. Upon entering the brain via activated macrophages or microglias, the human immunodeficiency type 1 virus (HIV-1) may produce cytotoxic factors such as HIV-1 envelope protein (gp120) and protease. Owing to significant proteolysis of nonviral proteins, the protease derived from HIV-1 may be detrimental to brain cells and neurons. Our results revealed that HIV-1 protease, at nanomolar concentrations, was as potent as gp120 in causing neurotoxicity in human neuroblastoma neurotypic SH-SY5Y cells. As shown by the Oncor ApopTag staining procedure, HIV-1 protease significantly increased the number of apoptotic cells over the serum-free controls. Moreover, HIV-1 protease-induced neurotoxicity was blocked by a selective protease inhibitor, kynostatin (KNI-272). Antioxidants such as 17beta-estradiol, melatonin, and S-nitrosoglutathione also prevented protease-induced neurotoxicity. These findings indicate that oxidative proteolysis may mediate HIV-1 protease-induced apoptosis and the degeneration of neurons and other brain cells. Centrally active protease inhibitors and antioxidants may play an important role in preventing cerebral atrophy and associated dementia complex caused by HIV-1.

Implications for atypical antioxidative properties of manganese in iron-induced brain lipid peroxidation and copper-dependent low density lipoprotein conjugation

Our group recently observed that manganese prevents oxidative brain injury in the iron-induced parkinsonian animal model. It has also been suggested that manganese retards while copper promotes the development of atherosclerosis. In this report, we provide further evidence to support a controversial notion that manganese is an atypical antioxidant. Among transition metals, Cu2+ and Fe2+ (0.1 to 125 microM), but not Mn2+, converted hydrogen peroxide to reactive hydroxyl radicals via the Fenton reaction at pH 7.4. Iron's pro-oxidative rate is relatively slow, but it is accelerated further by ascorbate (50 microM) in 37 degrees C Dulbecco's phosphate buffered saline. Moreover, Mn2+ (0-80 microM) concentration dependently retarded diene conjugation of human low density lipoproteins stimulated by 5 microM Cu2+. This new result is consistent with our recent finding that Mn2+ (0 to 20 microM) does not initiate brain lipid peroxidation while it inhibits iron-induced peroxidation of polyunsaturated fatty acids. These unexpected manganese results are somewhat at odds with a prominent theory that manganese is a prooxidative transition metal. Furthermore, iron and copper induced free radical generation and lipid peroxidation are suppressed by lowering the incubation temperature; this suggests that hypothermia may decrease the oxidative stress and damage in vivo. In conclusion, normal dietary intake of manganese may protect cells and neurons from oxidant stress through the inhibition of propagation of lipid peroxidation caused by hydroxyl radicals generated by pro-oxidative transition metals such as iron and copper. Potential therapeutical uses of manganese, manganese SOD mimetics and hypothermia for protecting brain neurons and vascular endothelial cells against oxidative stress and damage have been successfully demonstrated in both animal models and clinical trials.

Delta opioid peptide [D-Ala2,D-leu5]enkephalin blocks the long-term loss of dopamine transporters induced by multiple administrations of methamphetamine: involvement of opioid receptors and reactive oxygen species

Delta opioid peptide [D-Ala2,D-leu5]enkephalin (DADLE) can prolong organ preservation and increases myocardial tolerance to ischemia. Our study examined the protective property of DADLE against methamphetamine- (METH) induced dopaminergic terminal damage in the central nervous system. Because the neurotoxicity of METH involves reactive oxygen species, we also examined if DADLE might be an antioxidative agent in vitro. DADLE at 2 and 4 mg/kg (i.p.), given 30 min before each METH administration (5 or 10 mg/kg, i.p., four injections in a day at 2-hr intervals), dose-dependently blocked the METH-induced long-term dopamine transporter loss. The opioid antagonist naltrexone blocked this action of DADLE in both aspects of striata but tends not to affect the effects of DADLE in the nucleus accumbens. DADLE did not alter changes in body temperature induced by METH. The reduction of striatal dopaminergic content and tyrosine hydroxylase activity caused by METH, however, were not blocked by DADLE. In vitro, DADLE was approximately equipotent to glutathione in inhibiting both superoxide anion formation induced by xanthine oxidase and hydroxyl radical formation evoked by ferrous/citrate complex. DADLE was only slightly less potent than glutathione in inhibiting the iron/ascorbate-induced brain lipid peroxidation. These results suggest that DADLE can protect the terminal membranes of dopaminergic neurons against METH-induced insult but not the loss of dopaminergic content and tyrosine hydroxylase activity and that this action of DADLE might involve opioid receptors as well as the sequestration of free radical.

Manganese: a transition metal protects nigrostriatal neurons from oxidative stress in the iron-induced animal model of parkinsonism

It has been suggested that transition metals such as iron and manganese produce oxidative injury to the dopaminergic nigrostriatal system. which may play a critical role in the pathogenesis of Parkinson's disease. Intranigral infusion of ferrous citrate (0 to 8.4 nmol, i.n.) acutely increased lipid peroxidation in the substantia nigra and dopamine turnover in the caudate nucleus. Subsequently, it caused a severe depletion of dopamine levels in the rat caudate nucleus. In contrast to iron's pro-oxidant effect, manganese (up to 30 nmol, i.n.) causes neither lipid peroxidation nor nigral injury/dopamine depletion. Manganese (1.05 to 4.2 nmol, i.n.) dose-dependently protected nigral neurons from iron-induced oxidative injury and dopamine depletion. Manganese also suppressed acute increase in dopamine turnover and contralateral turning behaviour induced by iron. In brain homogenates manganese (0 to 10 microM) concentration-dependently inhibited propagation of lipid peroxidation caused by iron (0 to 5 microM). Without the contribution of manganese-superoxide dismutase manganese was still effective in sodium azide and/or heat-pretreated brain homogenates. Surprisingly, iron but not manganese, catalysed the Fenton reaction or the conversion of hydrogen peroxide to hydroxyl radicals. The results indicate that iron and manganese are two transition metals mediating opposite effects in the nigrostriatal system, as pro-oxidant and antioxidant, respectively. In conclusion, intranigral infusion of iron, but not manganese, provides an animal model for studying the pathophysiological role of oxidant and oxidative stress in nigrostriatal degeneration and Parkinsonism. The present results further suggest that the atypical antioxidative properties of manganese may protect substantia nigra compacta neurons from iron-induced oxidative stress.

Neuroprotection by nitric oxide against hydroxyl radical-induced nigral neurotoxicity

We investigated the effects of nitric oxide on an in vitro and in vivo generation of hydroxyl radicals, and in vivo neurotoxicity caused by intranigral infusion of ferrous citrate in rats. The formation of hydroxyl radicals in vitro, without exogenous hydrogen peroxide, was dose-dependent. Some nitric oxide donors (e.g. sodium nitroprusside) stimulated, while others (nitroglycerin, diethylamine/nitric oxide, nitric oxide in Ringer's solution) suppressed hydroxyl radical generation in vitro. A significant increase in extra-cellular hydroxyl radicals was detected in a brain microdialysis study. Intranigral infusion of ferrous citrate caused long-lasting lipid peroxidation and dopamine depletion in the ipsilateral nigral region and striatum, respectively. Sub-acute dopamine depletion in the striatum was positively correlated with acute lipid peroxidation in substantia nigra. Intranigral administration of nitric oxide did not affect striatal dopamine. Interestingly, nitric oxide in Ringer's protected nigral neurones against the oxidative injury. The results demonstrate that a regional increase in the levels of iron can result in hydroxyl radical generation and lipid peroxidation leading to neurotoxicity. It also demonstrates that exogenous nitric oxide can act as hydroxyl radical scavenger and protect neurones from oxidative injury.

Apparent role of hydroxyl radicals in oxidative brain injury induced by sodium nitroprusside

Sodium nitroprusside (disodium nitroferricyanide) has been suggested to cause cytotoxicity through either the release of cyanide and/or nitric oxide. The present study investigated a possible mechanism that after a brief release of nitric oxide, iron moiety of breakdown products of sodium nitroprusside could cause a long lasting oxidative stress, such as hydroxyl radical generation, lipid peroxidation and cytotoxicity. Intranigral administration of sodium nitroprusside (0-16.8 nmol) to rats induced an acute increase in lipid peroxidation in the substantia nigra and a chronic dopamine depletion in the caudate nucleus. Photodegraded (nitric oxide-exhausted) sodium nitroprusside, however, still produced lipid peroxidation and neurotoxicity in the midbrain. Moreover, non-iron containing nitric oxide-donor compounds, such as S-nitroso-N-acetylpenicillamine, did not cause oxidative brain injury in vivo suggesting that nitric oxide may not mediate neurotoxicity induced by sodium nitroprusside. Additional in vitro studies demonstrated that both freshly prepared (nitric oxide donor) and photodegraded (nitric oxide-exhausted) sodium nitroprusside generated hydroxyl radicals in the presence of ascorbate and also increased lipid peroxidation in brain homogenates. These pro-oxidative effects of sodium nitroprusside were blocked by nitric oxide, S-nitroso-N-acetylpenicillamine, oxyhemoglobin, and deferoxamine (iron chelator). The present results suggest that iron moiety, rather than nitric oxide, may mediate the pro-oxidative properties of sodium nitroprusside. With this new information in mind, the misuse of sodium nitroprusside as a selective nitric oxide donor in both basic and clinical uses should be urgently addressed.

Neuroprotection by S-nitrosoglutathione of brain dopamine neurons from oxidative stress

The proposed anti- and pro-oxidant effects of nitric oxide (NO) derivatives, such as S-nitrosoglutathione (GSNO) and peroxynitrite, were investigated in the rat nigrostriatal dopaminergic system. Intranigral infusion of freshly prepared GSNO (0-16.8 nmol, i.n.) prevented iron-induced (4.2 nmol, i.n.) oxidative stress and nigral injury, reflected by a decrease in striatal dopamine levels. This neuroprotective effect of GSNO was verified by ex vivo imaging of brain dopamine uptake sites using 125I-labeled RTI-55. In addition, in vitro data indicate that GSNO concentration-dependently inhibited iron-evoked hydroxyl radical generation and brain lipid peroxidation. In this iron-induced oxidant stress model, GSNO was approximately 100-fold more potent than the antioxidant glutathione (GSH). Light-exposed, NO-exhausted GSNO produced neither antioxidative nor neuroprotective effects, which indicates that NO may mediate at least part of GSNO's effects. Moreover, GSNO completely (and GSH only partially) inhibited the weak pro-oxidant effect of peroxynitrite, which produced little injury to nigral neurons in vivo. This study provides relevant in vivo evidence suggesting that nanomol GSNO can protect brain dopamine neurons from iron-induced oxidative stress and degeneration. In conclusion, S-nitrosylation of GSH by NO and oxygen may be part of the antioxidative cellular defense system.

Suppression of hydroxyl radical formation and protection of nigral neurons by l-deprenyl (selegiline)

The present study clearly demonstrated that l-deprenyl confers a substantial protective effect against MPP+ in the substantia nigra zona compacta in vivo. 32.39. The protection provided by l-deprenyl may not depend on its inhibition of type B monoamine oxidase. A unique antioxidant property of l-deprenyl by suppression of cycotoxic. OH formation and associated oxidative damage induced by MPP+ in the A9 melanized nigral neurons may contribute to the protection against MPP+ toxicity in the nigrostriatal system. The likelihood that l-deprenyl may confer neuroprotection against MPP+ toxicity through antioxidant effect is further strongly supported by our recent data that U-78517F (2-methlaminochromans) a potent inhibitor of ironcatalyzed lipid peroxidation, and DMSO an effective. OH scavenger also protect nigral neurons against MPP(+)-induced severe oxidative injury in the substantia nigra. This putative antioxidant effect of deprenyl may explore another mechanism which may in part contribute to its overt neuroprotection against several toxins, including 6-OHDA, DSP-4, and MPTP, and the possible clinical effects on slowing the neuronal degeneration in early Parkinson's disease, Alzheimer's disorder and even senescent changes.

S-nitrosothiols and nitric oxide, but not sodium nitroprusside, protect nigrostriatal dopamine neurons against iron-induced oxidative stress in vivo

Intranigral infusion of ferrous citrate (4.2 nmol) induced an acute lipid peroxidation in the substantia nigra and a chronic dopamine depletion in the striatum of rat nigrostriatal system. Coinfusion of 8.4 nmol nitric oxide donors such as S-nitrosoglutathione (GSNO) and S-nitroso-N-acetylpenicillamine (SNAP) or nitric oxide (approximately 2 nmol) protected nigrostriatal neurons against iron-induced lipid peroxidation and associated oxidative injury. However, sodium nitroprusside (SNP, 8.4 nmol) augmented dopamine depletion caused by ferrous citrate because SNP is a ferricyanide complex. The present in vivo results indicate that nitric oxide and S-nitrosothiols are antioxidants which can protect brain dopamine neurons against oxidant stress/damage.

Peroxidation of brain lipids in vitro: nitric oxide versus hydroxyl radicals

The pro-oxidant effects of hydroxyl radical (.OH, ferrous ammonium sulfate/Fe2+) or nitric oxide (NO., S-nitroso-N-acetylpenicillamine/SNAP) generating compounds were studied in rat brain homogenate preparations. Submicromolar concentrations of Fe2+, but not SNAP (up to 100 microM), increased the formation of fluorescent products of malondialdehyde in cortical homogenates. In fact, iron-catalyzed brain lipid peroxidation was inhibited by SNAP (100 microM), but not by light-exposed SNAP or its degradation product penicillamine (100 microM). This study provides relevant evidence to suggest that submicromolar concentrations of Fe2+ can potentiate lipid peroxidation in disrupted brain tissue. NO. released from SNAP did not stimulate, but rather inhibited brain lipid peroxidation. These results support the hypothesis that NO., as opposed to .OH radicals, is not a pro-oxidant but rather an antioxidant.

Novel protective effect of manganese against ferrous citrate-induced lipid peroxidation and nigrostriatal neurodegeneration in vivo

Earlier studies intranigrally infusing high doses of manganese (50-250 nmol) revealed a reversible oxidative injury to nigrostriatal dopaminergic neurons. In fact, intranigral infusion of lower dose manganese (4.2 nmol) in the present study did not significantly alter dopamine levels in rat striatum. Moreover, manganese completely suppressed both acute lipid peroxidation in substantia nigra and chronic degeneration of the nigrostriatal neurons induced by intranigral infusion of ferrous citrate (4.2 nmol). These in vivo data indicate that low dose manganese is a potent antioxidant which may activate antioxidative defense mechanisms to protect brain neurons against oxidative stress induced by iron complexes.

Effects of fetal brain grafting on adult behavioral masculinization and defeminization in neonatally androgenized female rats

Treatment of neonatal female rats with androgen results not only in decreased female sexual behavior but also in enhanced male sexual behavior examined in adulthood. The effects of grafting fetal preoptic area (POA) neurons into the POA, and fetal hypothalamic (HPT) neurons into the ventromedial hypothalamus (VMH), were tested in neonatally androgen-sterilized rats (ASR). The rats were injected subcutaneously with 80 micrograms testosterone propionate within the 24 hours after birth to see if sexual behavior could be normalized by fetal brain grafts. In repeated tests on ASR grafted with fetal HPT into the VMH, the lordotic response was seen to increase to the level seen in non-ASR controls, while the increase in mounting behavior in ASR was suppressed following grafting of fetal POA or cerebral cortex into the POA. These results suggest that there are dysfunctions of POA and VMH in ASR, and that the dysfunctions revealed by sexual behavior can be overcome by fetal POA or HPT grafting.

Neuronal protective and rescue effects of deprenyl against MPP+ dopaminergic toxicity

Intranigral infusion of 1-Methyl-4-phenylpyridinium ion (MPP+, 2.1-16.8 nmol) dose-dependently injured nigral neurons as reflected by reduced dopamine levels in the ipsilateral striatum four days after the infusion of this toxic metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP). Coadministration of deprenyl (4.2 nmol) with MPP+ into the substantia nigra protected against MPP(+)-induced moderate (20-50%) but not severe (over 70%) nigral injury as reflected in striatal dopamine reductions. However, supplementary treatment with deprenyl (0.25 mg/kg, s.c., twice daily for 4 days) after intranigral infusion of MPP+ significantly rescued nigral neurons from more severe damage caused by a higher MPP+ does (8.4 nmol) manifested by a lesser striatal dopamine decrease (-31%) compared to the non-deprenyl treated group (-70%). Thus, in addition to the blockade of bioactivation of MPTP, deprenyl can protect and/or rescue nigral neurons from MPP(+)-induced dopaminergic neurotoxicity. These in vivo data add further evidence to suggest that deprenyl, a putative and clinically unproven neuroprotective agent, may be of value in slowing the progressive nigral degeneration in "early" Parkinson's disease, but may prove to be less so in its terminal stages.

Ferrous-citrate complex and nigral degeneration: evidence for free-radical formation and lipid peroxidation

Increased nigral iron content in the parkinsonian brain is now well documented and is implicated in the pathogenesis of this movement disorder. Free iron in the pigmented DA-containing neurons catalyze DA autoxidation and Fenton reaction to produce cytotoxic .OH, initiating lipid peroxidation and consequent cell damage. The present results clearly demonstrate that a regional increase in the levels of the "labile iron pool" can result in the degeneration of dopaminergic nigral neurons as reflected by a significant inhibition in the expression of tyrosine hydroxylase mRNA and DA depletion. Iron-complex-induced damage of dopaminergic neurons in the substantia nigra, might have resulted from a sequence of cytotoxic events including the .OH generation and lipid peroxidation as demonstrated in this study. This free-radical-induced oxidative nigral injury may be a reliable free-radical model for studying parkinsonism and may be relevant to idiopathic Parkinson's disease. This apparent nigral injury stimulated by Fe(2+)-citrate is more severe than that produced by ferric iron and its citrate complex. Moreover, these data indicate that Fe(2+)-citrate is as potent as MPP+ in causing oxidative injury to the substantia nigral neurons. However, the nigral toxicity of MPTP and its congeners are not progressive, while Fe(2+)-citrate complex may produce a progressive degeneration of the nigrostriatal neurons which is similar to the progression of ideopathic Parkinson's disease. Thus, this unique Fe(2+)-citrate complex animal model could be used for studying neuroprotective treatments for retarding or halting the progressive nigrostriatal degeneration caused by free radicals in the iron-rich basal ganglia.

Antioxidant mechanism and protection of nigral neurons against MPP+ toxicity by deprenyl (selegiline)

The current research has demonstrated that MPP+ can induce lipid peroxidation in the nigrostriatal system of rat in vivo. Antioxidant agent U-78517F and .OH scavenger DMSO may protect against MPP+ toxicity through the inhibition of .OH radical-mediated oxidative injury in the substantia nigra. These findings indicate that the cytotoxic hydroxyl radical generated from dopamine oxidation in the iron-rich basal ganglia may contribute to the mechanism underlying the selective A9 melanized nigral degeneration in MPTP-Parkinsonism and possibly in idiopathic Parkinson's disease. In addition, the present studies also clearly demonstrate that deprenyl can substantially protect dopaminergic neurons against MPP+ toxicity in the substantia nigra zona compacta in vivo. The neuroprotective effect provided by deprenyl may not be the consequence of its inhibition of MAO-B activity or prevention of the uptake of MPP+ by dopaminergic neurons. A unique antioxidant property of deprenyl by suppressing .OH formation and associated oxidative injury induced by MPP+ may contribute to the apparent neuroprotective action. In perspective, this putative antioxidant effect of deprenyl may provide another mechanism to its overt neuroprotective effects against oxygen radical-mediated oxidative injury in some neurotoxic chemicals, such as 6-OHDA and DSP-4, and probably in Alzheimer's disease and senescent changes. Finally, based on the present data, a possible neuroprotective therapeutic window of deprenyl in the treatment of early Parkinson's disease has been proposed. It is suggested that deprenyl should be introduced as early as possible in de novo Parkinsonian patients to achieve its full neuroprotective effect on nigral degeneration. Moreover, a combination of early detection of individuals at risk of developing Parkinson's disease and early intervention of deprenyl and/or other centrally active antioxidants to these patients may provide a new preventive therapeutic strategy in the future, in addition to the current conventional levodopa treatment of Parkinson's disease.

In vivo generation of hydroxyl radicals and MPTP-induced dopaminergic toxicity in the basal ganglia

The in vivo generation of .OH free radicals in specific brain regions can be measured by intracerebral microdialysis perfusion of salicylate, avoiding many of the pitfalls inherent in systemic administration of salicylate. Direct infusion of salicylate into the brain can minimize the hepatic hydroxylation of salicylate and its contribution to brain levels of 2,5-DHBA. Levels of 2,5-DHBA detected in the brain dialysate may reflect the .OH adduct plus some enzymatic hydroxylation of salicylate in the brain. After minimizing the contribution of enzyme and/or blood-borne 2,5-DHBA, the present data demonstrate the validity of the use of 2,3-DHBA and apparently 2,5-DHBA as indices of .OH formation in the brain. Therefore, intracranial microdialysis of salicylic acid and measurement of 2,3-DHBA appears to be a useful .OH trapping procedure for monitoring the time course of .OH generation in the extracellular fluid of the brain. These results indicate that nonenzymatic and/or enzymatic oxidation of the dopamine released by MPTP analogues in the extracellular fluid may play a key role in the generation of .OH free radicals in the iron-rich basal ganglia. Moreover, a site-specific generation of cytotoxic .OH free radicals and quinone/semiquinone radicals in the striatum may cause the observed lipid peroxidation, calcium overload, and retrograde degeneration of nigrostriatal neurons. This free-radical-induced nigral injury can be suppressed by antioxidants (i.e., U-78517F, DMSO, and deprenyl) and possibly hypothermia as well. In the future, this in vivo detection of .OH generation may be useful in answering some of the fundamental questions concerning the relevance of oxidants and antioxidants in neurodegenerative disorders during aging. It could also pave the way for the research and development of novel neuroprotective antioxidants and strategies for the early or preventive treatment of neurodegenerative disorders, such as Parkinson's disease (Wu et al., this issue), amyotrophic lateral sclerosis, head trauma, and possibly Alzheimer's cognitive dysfunction as well. In conclusion, this in vivo free-radical trapping procedure provides evidence to support a current working hypothesis that a site-specific formation of cytotoxic .OH free radicals in the basal ganglia may be one of the neurotoxic mechanisms underlying nigrostriatal degeneration and Parkinsonism caused by the dopaminergic neurotoxin MPTP. Addendum added in proof: The controversy concerning possible neurotoxic and/or neuroprotective roles of NO. in cell cultures was discussed and debated at the symposium (Wink et al., this issue; Dawson et al., this issue; Lipton et al., this issue).(ABSTRACT TRUNCATED AT 400 WORDS)

Platelet [3H]paroxetine binding, 5-HT-stimulated Ca2+ response, and 5-HT content in winter seasonal affective disorder

The present study was designed to evaluate cellular serotonergic functions in winter seasonal affective disorder (SAD) using serotonin (5-HT)-stimulated Ca2+ response as an integrated measure of 5-HT2 receptor function in platelets, [3H]paroxetine binding to characterize the platelet 5-HT transporter and 5-HT content as an index of the platelet storage capacity for this neurotransmitter amine. Purified density-dependent subpopulations of platelets in untreated and light-treated SAD patients and matched controls were investigated in order to control for possible variations in platelet turnover. We found no differences between SAD patients and controls on any of the measures, nor between light therapy conditions in SAD patients, although we found a higher Bmax of [3H]paroxetine binding and 5-HT content in heavy platelets compared to light platelets. Although the validity of platelet serotonergic measures as a model for brain serotonergic systems still remains to be elucidated, we found no evidence of platelet serotonergic abnormalities in our sample of SAD patients.

[125I]CGP 42112 reveals a non-angiotensin II binding site in 1-methyl-4-phenylpyridine (MPP+)-induced brain injury

1. Intracerebral injection of the oxidative metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenylpyridine (MPP+), into the substantia nigra of adult rats resulted in a lesion at the injection site. 2. Using autoradiography, we localized specific [125I]CGP 42112 binding that was not recognized by angiotensin II or angiotensin II AT1 or AT2 receptor-selective ligands. 3. Our results suggest that [125I]CGP 42112 may be binding to activated microglia that appear at the lesion site.

Suppression of hydroxyl radical formation by MAO inhibitors: a novel possible neuroprotective mechanism in dopaminergic neurotoxicity

Prior studies concluded that 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP, a toxin causing parkinsonism) and its analogues are bioactivated by monoamine oxidase (MAO) to toxic pyridinium metabolites. Recently, a dissociation between the neuroprotective effects of deprenyl and its MAO inhibiting effects has been proposed. Furthermore, we have demonstrated that pyridinium metabolites of MPTP stimulate dopamine efflux and the formation of cytotoxic hydroxyl free radicals (.OH) in the striatum. Therefore, we investigated possible neuroprotective mechanisms of propargyl MAO inhibitors by studying their effects on the formation of oxygen free radicals produced by dopamine autoxidation. Our recent in vivo results indicate that deprenyl and clorgyline given systemically suppressed the generation of .OH that followed administration of 2'-methyl-MPTP. Combined deprenyl and clorgyline pretreatment are needed to block dopamine neurotoxicity elicited by 2'-methyl-MPTP. The present in vitro studies reveal that propargyl MAO inhibitors suppress non-enzymatic dopamine autoxidation and associated free radical production. Thus, .OH generation evoked by MPTP analogues may be due mainly to a burst increase in iron-catalyzed autoxidation of released dopamine in the basal ganglia where high levels of iron and oxygen are present. Our present in vitro and prior in vivo results suggest that a novel antioxidant property of propargyl MAO inhibitors may contribute to protection against nigral lesions elicited by dopamine autoxidation following the administration of MPTP analogues.

Apparent antioxidant effect of l-deprenyl on hydroxyl radical formation and nigral injury elicited by MPP+ in vivo

Using a modified microdialysis procedure, we confirmed that intrastriatal administration of 1-methyl-4-phenylpyridinium ion (MPP+) induced a sustained overflow of dopamine accompanied by increased formation of hydroxyl free radicals (.OH) as reflected by salicylate hydroxylation. Pretreatment with l-deprenyl (selegiline 60 pmol, intrastriatal perfusion) significantly decreased the .OH formation elicited by MPP+ (75 nmol). There was a small decrease of dopamine efflux and an insignificant change of the ratio of 3,4-dihydroxyphenylacetic acid (DOPAC)/dopamine following l-deprenyl pretreatment. These in vivo findings support prior in vitro data that an unique antioxidant property of l-deprenyl may be independent of its inhibition of type B monoamine oxidase. In addition, intranigral co-administration of l-deprenyl (4.2 nmol) with MPP+ (4.2 nmol) completely protected nigral neurons from probable oxidative injuries induced by MPP+ (4.2 nmol), as reflected by a near 50% loss of striatal dopamine ipsilateral to the side of infusion of drug into the substantia nigra. This apparent neuroprotective effect of l-deprenyl on midbrain nigral neurons was also confirmed by histological findings. The present in vivo data clearly demonstrate that l-deprenyl can protect nigral neurons against dopamine neurotoxicity produced by MPP+, as suggested by an earlier in vitro study. Thus, l-deprenyl can preserve the function of MPP(+)-damaged nigral neurons perhaps by its apparent antioxidant property in addition to its blockade of the bioactivation of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) to toxic pyridinium metabolites by type B monoamine oxidase.

Intracranial microdialysis of salicylic acid to detect hydroxyl radical generation through dopamine autooxidation in the caudate nucleus: effects of MPP+

Ringer's solution containing salicylic acid (5 nmol/microliters/min) was infused directly through an intracranial microdialysis probe to detect the generation of hydroxyl radicals (.OH) reflected by the formation of dihydroxybenzoic acids (DHBA) in the caudate nucleus of anesthetized rats. Brain dialysate was assayed for dopamine, 2,3-, and 2,5-DHBA by a high-pressure liquid chromatography-electrochemical (HPLC-EC) procedure. 1-Methyl-4-phenylpyridinium ions (MPP+, 0 to 150 nmol) increased dose-dependently the release of dopamine and the formation of DHBA. A positive linear correlation between the release of dopamine and the formation of 2,3- or 2,5-DHBA was observed (R2 = .98). The present results demonstrate the validity of the use of not only 2,3-DHBA but also 2,5-DHBA as an in vivo index of oxidative damage generated by reactive .OH radicals. In conclusion, the present study demonstrates a novel use of intracranial microdialysis of salicylic acid to assess the oxidative damage elicited by .OH in living brain.

In vivo release of dopamine by perfusion of 1-methyl-4-phenylpyridinium ion in the striatum with a microdialysis technique

We examined the effects of 1-methyl-4-phenylpyridinium ion (MPP+) on the release of DA in rat striatum by the in vivo microdialysis technique. For this study, we made a suitable microdialysis probe from a 22-G needle, microliter pipette tip, silica tube and polyethylene tube. Such a repairable microdialysis probe can be easily made from readily available and inexpensive materials. DA release, as determined by the 3-methoxytyramine level, was dose-dependently increased by MPP+ (1-10 mM). Only the presence of a 1 mM concentration of MPP+ in the dialysate significantly decreased the level of the DA metabolite DOPAC, while administration of higher MPP+ concentrations resulted in no significant change.

Enhanced hydroxyl radical generation by 2'-methyl analog of MPTP: suppression by clorgyline and deprenyl

Sodium salicylate was infused through a microdialysis probe placed in the striatum of anesthetized rats in order to assay the formation of hydroxyl radical (.OH) in the extracellular fluid in vivo. In addition to causing sustained dopamine release, intrastriatal infusion of the 2'-methyl analog of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (2'CH3-MPTP) increased the formation of 2,3-dihydroxybenzoic acid (2,3-DHBA), the nonenzymatic .OH adduct of salicylate in the brain dialysate. Inhibition of monoamine oxidase (MAO) by clorgyline and deprenyl completely blocked the formation of 2,3-DHBA and the sustained dopamine overflow induced by 2'-CH3-MPTP. The results indicate that the enhanced formation of cytotoxic .OH by 2'-CH3-MPTP is suppressed by MAO inhibitors. These data support the hypothesis that the protective effect of MAO inhibitors on the neurotoxicity induced by MPTP analogues may be due not only to the inhibition of MPTP metabolism by MAO but also the blockade of the formation of .OH free radicals. An enhanced generation of cytotoxic .OH free radicals in the striatum which in turn leads to oxidant damage may be relevant to the development of parkinsonism-like changes in animals produced by MPTP analogues.

In vivo trapping of hydroxyl free radicals in the striatum utilizing intracranial microdialysis perfusion of salicylate: effects of MPTP, MPDP+, and MPP+

Increased formation of hydroxyl free radicals (.OH) reflected by .OH adduct of salicylate in brain dialysate was demonstrated during the sustained (more than 2 hours) dopamine overflow elicited by 75 nmol of 1-methyl-4-phenyldihydropyridine (MPDP+) and 1-methyl-4-phenylpyridinium (MPP+) in the rat striatum. Owing to its weak dopamine releasing action, 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) did not significantly increase the .OH formation. This data suggests that sustained elevation of dopamine in the extracellular fluid elicited by MPTP analogues can be auto-oxidized, which in turn leads (possibly by indirect mechanisms) to the formation of cytotoxic .OH free radicals near the nigrostriatal terminals.

Visualization of interleukin-2-like molecules in MPP(+)-lesioned rat brain

The tissue distribution of interleukin-2 (IL-2) in normal and 1-methyl-4-phenyl-pyridinium (MPP+)-lesioned brains of rats was investigated. Intrastriatal administration of MPP+ caused visible damage in the vicinity of the injected region two weeks after injection. Autoradiography of the tissue section with anti-IL-2 antibodies plus trace amounts of radiolabeled IL-2 showed that the antibodies treatment elicited a selective radiolabeling of the brain tissues localized at the MPP(+)-lesioned region but not at normal cryo-sliced sections. Addition of radiolabeled IL-2 alone or normal rabbit immunoglobulins did not show any labeling effect. These autoradiographic imaging results suggest that there is an accumulation of cells bearing IL-2-like molecules at the MPP(+)-induced lesion sites.

Effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine in the dog: effect of pargyline pretreatment

Adult beagle dogs of either sex were injected with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-HCl (2.5 mg/kg, i.v.) alone or after pretreatment with pargyline (5.0 mg/kg, s.c., twice), with pargyline alone, or were uninjected. Groups were killed 2 h, 3 weeks, or 3 months after injection, and several brain areas were assayed for biogenic amines and their synthetic and degradative enzymes. MPTP caused a massive and permanent loss of striatal dopamine, tyrosine hydroxylase, and 3,4-dihydroxyphenylalanine decarboxylase activities and the loss of cells within the substantia nigra pars compacta. Dopamine and norepinephrine also were depleted to various degrees in cortex, olfactory bulb, and hypothalamus; however, dopamine beta-hydroxylase activity in cortex was normal. There was no cell loss in the ventral tegmental area or locus ceruleus. The activities of monoamine oxidase (MAO)-A and MAO-B in cortex and caudate were not affected by MPTP. Despite a permanent loss of the nigrostriatal system, the dogs exhibited only a transient hypokinesia lasting 1-2 weeks. Pargyline pretreatment prevented the loss of striatal dopamine and cells from the substantia nigra, but did not prevent a prolonged but reversible decrease in the concentration of dopamine metabolites. It is argued that this apparent inhibition of MAO is due not to suicide inactivation of the enzyme by MPTP, but to reversible inhibition by accumulation of the pyridinium metabolite, 1-methyl-4-phenylpyridinium, selectivity in aminergic terminals.

Effects of MPP+ on the release of serotonin and 5-hydroxyindoleacetic acid from rat striatum in vivo

A procedure utilizing brain dialysis was employed to investigate the effects of 1-methyl-4-phenylpyridinium ion (MPP+), the major metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), on the in vivo release of 5-hydroxytryptamine (5-HT) from the rat striatum. MPP+ (10(-5)-10(-2) M) was administered through the microdialysis probe and dialysates were collected and assayed for monoamines and their metabolites by a high performance liquid chromatography coupled with an electrochemical detector (HPLC-EC). In addition to a dopamine (DA) releasing action, MPP+ caused a cumulatively dose-dependent increase in the release of 5-HT while concomitantly producing a decrease in the efflux of 5-hydroxyindoleacetic acid (5-HIAA). This MPP+-induced increase in the 5-HT release, may play an important role in the acute 5-HT syndrome seen in animals after MPTP.

Quality control procedure for 6-[18F]fluoro-L-DOPA: a presynaptic PET imaging ligand for brain dopamine neurons

The goal of the current study was to establish a quality control procedure for clinical use of 6-[18F]fluoro-L-DOPA (6-[18F]-DOPA) as a selective presynaptic positron emission tomographic (PET) imaging ligand for brain dopamine neurons. A high performance liquid chromatographic procedure using a 5-mu C-18 reverse phase column and ion-pairing mobile phase was used for the quantification of 6-[18F]-DOPA. The radiochemical purity of 6-[18F]-DOPA was measured by 18F radioactivity in HPLC fractions while the chemical purity was determined by an amperometric electrochemical detector with a sensitivity of 25 pg. Quality control of eight consecutive batches of highly purified 6-[18F]-DOPA sample used in a pre-clinical trial revealed that the chemical and/or radiochemical purity of the PET imaging ligand, 6-[18F]-DOPA was greater than 97 +/- 0.5% with a specific activity of 365 +/- 31 mCi/mmol. The knowledge and assurance of radiochemical purity of PET ligands are essential for the interpretation of clinical PET imaging results. The assurance of such quality control would enable comparisons of 6-[18F]-DOPA/PET data obtained from various medical centers using different radiopharmaceutical procedures.

Biogenic Amine and Corticotrophin-Releasing Factor Concentrations in Hypothalamic Paraventricular Nucleus and Biogenic Amine Levels in the Median Eminence of Normal Dogs, Chronic Dexamethasone-Treated Dogs, and Dogs with Naturally-Occurring Pituitary-Dependent Hyperadrenocorticism (Canine Cushing's Disease)

Abstract We measured dopamine, norepinephrine, serotonin and epinephrine concentrations in the paraventricular nucleus and median eminence, and corticotrophin-releasing factor levels in the paraventricular nucleus. Tissue was isolated by micropunch technique from hypothalami of normal dogs, dogs treated for one week with dexamethasone (1 mg/kg/day) and dogs with spontaneous pituitary-dependent hyperadrenocorticism. Concentrations of corticotrophin-releasing factor and most of the neurotransmitters were found to be similar between our three groups of dogs. However, we found the mean dopamine concentration in the median eminence tissue to be significantly decreased in dogs with Cushing's disease and in steroid-treated dogs. Epinephrine levels were elevated in the hypothalamic paraventricular nucleus of steroid-treated dogs.

Blockade of in vivo binding of 125I-labeled 3-iodobenzamide (IBZM) to dopamine receptors by D2 antagonist and agonist

The in vivo binding of [125I]3-iodobenzamide (IBZM), a substituted benzamide, to DA receptor binding sites in the caudate nucleus, nucleus accumbens, and olfactory tubercle was investigated by using ex vivo autoradiography. The in vivo binding of IBZM seems to be selective to D2 dopamine receptors, since the binding was blocked by pretreatment of animals with D2 agonist LY-171555 or antagonist YM-09151-2. Furthermore, in vitro binding assays in striatal membranes confirmed that IBZM binding was highly selective to D2 sites. Thus, IBZM, when labeled with 123I (T1/2: 13h; 159 kev), could be a potential ligand for imaging D2 dopamine receptors by single photon emission computerized tomography procedures.

Neurotoxic damage to the nigrostriatal system in rats following intranigral administration of MPDP+ and MPP+

Unilateral intranigral administration of the oxidative metabolites of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP), 1-methyl-4-phenyl-dihydropyridine (MPDP+) or 1-methyl-4-phenylpyridine (MPP+) produced dose-dependently a depletion of dopamine in the ipsilateral striatum of rats two weeks following treatment. d-Amphetamine and apomorphine induced circling toward the lesioned side in these unilaterally treated animals. No contralateral circling behavior was observed after challenging with apomorphine. This dopamine lesioning effect of MPP+ was not blocked by pretreatment of animals with a dopamine uptake blocker, GBR 12909. Furthermore, MPP+ increased the 45Ca accumulation into cells at the site of injection and produced "nonspecific" cell membrane and/or cytotoxic damage seen by histological procedures. These results indicate that MPDP+ and MPP+ produced localized cytotoxic damage to nigrostriatal neurons, caused a decrease in striatal dopamine, and disrupted the nigrostriatal system's functioning following intranigral administration to rats. It is postulated that the cationic surfactant properties of MPDP+ and MPP+ might contribute to its neurotoxic effects.

In vitro binding properties and autoradiographic imaging of 3-iodobenzamide ([125I]-IBZM): a potential imaging ligand for D-2 dopamine receptors in SPECT

The in vitro binding properties of the [125I] labeled benzamide (S(-)-N-[(1-ethyl-2-pyrrolidinyl)-methyl]-2-hydroxy-3-iodo-6-methoxy- benzamide, IBZM) were determined in bovine and mouse caudate membrane homogenates and by autoradiography of mouse brain slices. [125I]-IBZM binding is saturable and reversible with a Bmax of 373 +/- 51 fmol/mg protein and a Kd of 3.1 +/- 0.62 nM (mean +/- SD, Scatchard analyses) and 0.56 nM as calculated by association and dissociation time constants. In competition experiments, Ki values for the D-2 antagonists YM-09151-2 and spiperone are 4 orders of magnitude lower than the Ki value for the D-1 antagonist SCH-23390 and S(-)-IBZM is ten-fold more potent than R(+)-IBZM. [125I]-IBZM has a low affinity for serotonin S-2 and for alpha receptors. Therefore, it is a highly selective ligand for dopamine D-2 receptors. Autoradiographic images of brain sections incubated with [125I]-IBZM show the dopamine D-2 receptors of the striatum, nucleus accumbens and olfactory tubercle with a high ratio of specific to nonspecific binding. Thus, S(-)-IBZM, when labeled with [123I], may be useful for in vivo imaging of dopamine D-2 receptors by single photon emission computerized tomography (SPECT).

Localization of cholecystokinin receptors in relation to the nigrostriatal and mesolimbic dopaminergic pathways

The anatomical distribution of cholecystokinin (CCK)-dopamine (DA) neurons suggests that CCK could modulate dopaminergic activity. To further investigate that hypothesis, the cellular localization of CCK receptors was ascertained in relation to mesolimbic and nigrostriatal DA pathways after a series of chemical lesions induced with ibotenic acid and 6-hydroxydopamine. The results suggest that CCK receptors are not localized on dopaminergic neurons of the nigrostriatal and mesolimbic pathways.

MPP+ (1-methyl-4-phenylpyridine) is a neurotoxin to dopamine-, norepinephrine- and serotonin-containing neurons

1-Methyl-4-phenylpyridine (MPP+) is an oxidative metabolite of 1-methyl-4-phenyl-1,2,3,6-tetrahydroxypyridine (MPTP). MPP+ produced local cell death when injected directly into substantia nigra compacta, locus coeruleus, or dorsal and median raphe nuclei of rats. Corresponding significant decreases in dopamine, serotonin and norepinephrine levels were observed in the terminal areas. These observations indicate that MPP+ is a non-selective neurotoxin which causes lesions not only in dopaminergic neurons but also in noradrenergic and serotonergic systems following intracranial administration. Selective lesioning of these monoaminergic systems could only be achieved by a stereotaxic injection of MPP+ into specific brain regions containing monoamine neurons.

Biochemical changes in tissue catecholamines and serotonin in duodenal ulceration caused by cysteamine or propionitrile in the rat

Previous structure-activity and pharmacologic studies with duodenal ulcerogens cysteamine and propionitrile implicating catecholamines in the pathogenesis of duodenal ulceration have now been followed up by dose- and time-response biochemical investigations to assess the importance of monoamines in the development of duodenal ulcers. The concentrations of norepinephrine (noradrenaline), dopamine, serotonin and their metabolites were measured in total brain, brain regions, stomach, duodenum, pancreas and adrenals in the rat. Turnover of catecholamines was determined in rats pretreated with the inhibitor of tyrosine hydroxylase alpha-methyl-p-tyrosine. The duodenal ulcerogens caused a dose- and time-dependent depletion of norepinephrine in virtually all the tissues examined. The effect was maximal 4 or 7 hr after cysteamine or propionitrile, and norepinephrine levels returned to normal in 24 hr. Dopamine changes were selective and often biphasic, e.g., elevation in adrenals, biphasic in brain cortex, hippocampus and midbrain, but uniformly decreasing in glandular stomach and duodenum. In the median eminence dopamine levels decreased by 181 and 324% at 15 and 30 min, respectively, after cysteamine, but neither dopamine nor 3,4-dihydroxyphenylacetic acid was modified in the periventricular nucleus. Serotonin levels were relatively stable, revealing slight elevations or no changes in most of the tissues. The turnover of norepinephrine was accelerated by both chemicals in virtually all brain regions, but dopamine turnover was affected only in a few areas, e.g., in the corpus striatum and medulla oblongata cysteamine decreased dopamine turnover, whereas propionitrile first (at 1 hr) accelerated then (at 8 hr) significantly suppressed it.(ABSTRACT TRUNCATED AT 250 WORDS)

Hemiparkinsonism in monkeys after unilateral internal carotid artery infusion of 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)

Infusion of MPTP (0.2-0.8 mg/kg) into the right internal carotid artery of monkeys produces toxin-induced injury to the right nigrostriatal pathway with sparing of other dopaminergic neurones on the infused side and with negligible or little injury to the opposite, untreated side. There are contralateral limb dystonic postures, rigidity, and bradykinesia, but the animals are able to eat and maintain health without drug treatment. Spontaneous motor activity is attended by circling towards the injured side, whereas treatment with L-DOPA/-carbidopa or apomorphine stimulates circling towards the intact side. Dopamine and dopamine metabolite levels are normal in the left caudate and putamen, but markedly depressed on the right (MPTP-treated) side. This animal hemiparkinsonian model will be useful in studies of volitional movement control, drug treatments of Parkinson's disease, and functional efficacy of brain tissue implants.