N-nitro-L-arginine methyl ester influence on aluminium toxicity in the brain

We investigated the influence of a non-specific nitric oxide synthase (NOS) inhibitor, N-nitro-L-arginine methyl ester (L-NAME), on brain nitrite concentration and acetylcholine esterase activity in AlCl3-treated Wistar rats. Animals were killed 10 min, three hours, three days and 30 days after the treatment and hippocampus and basal forebrain were removed. The biochemical changes observed in neuronal tissues show the involvement of NO in the AlCl3 toxicity and cholinergic neurotransmission, and that L-NAME may have potential neuroprotective effects. Active avoidance learning was significantly impaired after AlCl3 application, while pretreatment with L-NAME prevented the behavioural deficits caused by AlCl3. We also applied immunohistochemical techniques to identify changes induced by AlCl3, L-NAME+AlCl3, as well as L-NAME injections after survival periods of three days and 30 days. Immunoreactivity of astrocytes and phagocytic microglia based on glial fibrillary acidic protein (GFAP) and a useful marker for rat macrophages (ED1), respectively, revealed a greater inflammatory response in AlCl3-injected animals compared to controls.     

Neuroprotective effect of Allium cepa L. in aluminium chloride induced neurotoxicity

The present study was envisaged to investigate the neuroprotective potential of Allium cepa (A. cepa) in aluminium chloride induced neurotoxicity. Aluminium chloride (50 mg/kg/day) was administered orally in mice supplemented with different doses of A. cepa hydroethanolic extract for a period of 60 days. Various behavioural, biochemical and histopathological parameters were estimated in aluminium exposed animals. Chronic aluminium administration resulted in significant motor incoordination and memory deficits, which were also endorsed biochemically as there was increased oxidative stress as well as elevated acetylcholinesterase (AChE) and aluminium levels in the brain. Supplementation with A. cepa in aluminium exposed animals significantly improved muscle coordination and memory deficits as well as reduced oxidative stress, AChE and decreased abnormal aluminium deposition in the brain. Histopathologically, there was marked deterioration visualized as decreased vacuolated cytoplasm as well as decreased pyramidal cells in the hippocampal area of mice brain which were found to be reversed with A. cepa supplementation. Administration of BADGE (PPARγ antagonist) in aluminium exposed animals reversed the neuroprotective potential of A. cepa as assessed with various behavioural, biochemical, neurochemical and histopathological estimations. In conclusion, finding of this study suggested significant neuroprotective potential of A. cepa in aluminium induced neurotoxicity. Further, the role of PPARγ receptor agonism has also been suggested as a putative neuroprotective mechanism of A. cepa, which needs further studies for confirmation.     

Chronic epigallocatechin-3-gallate ameliorates learning and memory deficits in diabetic rats via modulation of nitric oxide and oxidative stress

Due to anti-diabetic and antioxidant activity of green tea epigallocatechin gallate (EGCG) and the existence of evidence for its beneficial effect on cognition and memory, this research study was conducted to evaluate, for the first time, the efficacy of chronic EGCG on alleviation of learning and memory deficits in streptozotocin (STZ)-diabetic rats. Male Wistar rats were divided into control, diabetic, EGCG-treated-control and -diabetic groups. EGCG was administered at a dose of 20 and 40 mg/kg/day for 7 weeks. Learning and memory was evaluated using Y maze, passive avoidance, and radial 8-arm maze (RAM) tests. Oxidative stress markers and involvement of nitric oxide system were also evaluated. Alternation score of the diabetic rats in Y maze was lower than that of control and a significant impairment was observed in retention and recall in passive avoidance test (p < 0.01) and EGCG treatment (40 mg/kg) of diabetic rats significantly improved these parameters (p < 0.05). Also, diabetic animals exhibited fewer correct choices (p < 0.01) and more errors (p < 0.005) in the RAM task and EGCG (40 mg/kg) significantly ameliorated these changes (p < 0.05). Further, pretreatment with l-arginine as a substrate for nitric oxide synthase (NOS) and/or 7-nitroindazole as a neuronal NOS inhibitor attenuated and potentiated the beneficial effect of EGCG regarding learning and memory respectively. Meanwhile, increased levels of malondialdehyde (MDA) and nitrite in diabetic rats significantly reduced due to EGCG treatment (p < 0.05). In summary, chronic green tea EGCG dose-dependently could ameliorate learning and memory deficits in STZ-diabetic rats through attenuation of oxidative stress and modulation of NO.     

Repeated administration of the nitric oxide synthase inhibitor l-NAME differentially affects rats' recognition memory

Nitric oxide (NO) is sought to be an intracellular messenger in the central nervous system and its implication in learning and memory is well documented. Compounds that inhibit nitric oxide synthase (NOS), the key synthesizing enzyme, block cognition, though discrepant findings, in this context, have also been reported. The present study was designed to investigate in the rat (a) the effects of repeated treatment with the NOS inhibitor l-NAME (1, 3 and 10 mg/kg, i.p., for 5 consecutive days) on rats’ recognition memory and (b) whether or not at this treatment condition, l-NAME (1, 3 and 10 mg/kg, i.p., for 5 consecutive days), was able to counteract delay-dependent recognition memory deficits. For this aim, the novel object recognition task was selected. l-NAME (3, but not 1 or 10 mg/kg) disrupted rats’ performance in this recognition memory paradigm as compared to that expressed by their vehicle-treated cohorts. Subsequently, l-NAME (1 and 10, but not 3 mg/kg)-treated rats were capable to antagonize delay-dependent deficits, which instead were present in the vehicle-treated animals. These results indicate that repeated administration of this NOS inhibitor exerts a dual effect on rats’ recognition memory abilities suggesting a complex involvement of l-NAME in cognition.     

Protective effects of 7-nitroindazole on ketamine-induced neurotoxicity in rat forebrain culture

Ketamine, a non-competitive N-methyl-d-aspartate (NMDA) receptor antagonist, is used as a pediatric anesthetic for surgical procedures. Recent data suggest that anesthetic drugs may cause neurodegeneration during development. The purpose of this study was to determine the dose and temporal response of ketamine using newborn rat forebrain cultures and also to determine if co-administration of 7-nitroindazole, a nitric oxide synthase (NOS) inhibitor, could protect or reverse ketamine-induced cell death. Neural cells collected from the rat forebrain were incubated for 24h with 1, 10 or 20 microM ketamine alone or with ketamine plus 1, 5, 10 or 20 microM 7-nitroindazole. Ketamine (10 microM) caused an increase in DNA fragmentation and elevated immunoreactivity to nitrotyrosine, a marked reduction in the expression of the neuronal marker polysialic acid neural cell adhesion molecule (PSA-NCAM) and in mitochondrial metabolism, as well as an increased Bax/BCL-XL ratio. No significant effect was observed in the release of lactate dehydrogenase (LDH). Ketamine-induced neurotoxic effects were effectively blocked by 7-nitroindazole (10 microM). These data indicate a role for nitric oxide in the enhanced degeneration induced by ketamine in vitro and also suggest that blocking neuronal nitric oxide synthase (nNOS) may help reduce the risk of ketamine in pediatrics.     

Protective effect of 7-nitroindazole against DSP-4 induced noradrenaline depletion in mouse hippocampus

Summary. N-(2-chloroethyl)-N-ethyl-2-bromobenzylamine (DSP-4) is a selective noradrenaline (NA) uptake blocker, capable of inducing a long-lasting depletion of NA in some noradrenergic axon terminals originating from the locus coeruleus in rodents. Pretreatment with 7-nitroindazole, a fairly selective inhibitor of neuronal nitric oxide synthase in vivo, partially prevented DSP-4 induced NA depletion in mouse hippocampus measured seven days after the neurotoxic insult. Administration of L-arginine, the substrate of nitric oxide synthase, altered neither the NA depletion induced by DSP-4, nor the protective effect of 7-nitroindazole. Inhibition of nitric oxide synthesis by N(G)-nitro-L-arginine methyl ester did not attenuate the NA depleting effect of DSP-4. Thus, the contribution of neuronal nitric oxide synthase inhibition to the protective effect of 7-nitroindazole needs further studies. As 7-nitroindazole did not block NA uptake, this cannot play a part in the protective effect. The possible contribution of monoamine oxidase B enzyme inhibition by 7-nitroindazole to the protective effect is also discussed. Received July 3, 2000; accepted October 16, 2000     

Effects of electrolytic and 6-hydroxydopamine lesions of rat nigrostriatal pathway on nitric oxide synthase and nicotinamide adenine dinucleotide phosphate diaphorase

The aim of the present study was to assess degenerative changes in the nitric oxide (NO) system of basal ganglia in animals with experimentally induced Parkinson's disease. In one procedure, rats were stereotaxically injected with 6-hydroxydopamine (6-OHDA) in the right medial forebrain bundle; in a second procedure, electrodes were implanted in the right substantia nigra pars compacta (SNc). After 15 and 30 days animals were tested for rotational asymmetry induced by apomorphine. Apomorphine induced rotation in lesioned animals, towards the ipsilateral side after electrolytic lesion and towards contralateral side in 6-OHDA animals. Structural deficits in basal ganglia were quantified by nicotinamide adenine dinucleotide phosphate diaphorase (NADPH-d) histochemistry and by nitric oxide synthase (NOS) immunoreactivity. 6-OHDA and electrolytic lesions induced a significant decrease in the number of NADPH-d/NOS positive cells in the lesion ipsilateral to SNc, in contrast with cell number increase in the ipsilateral dorsal striatum. By contrast, 6-OHDA-treated animals showed a decrease in the number of NOS immunoreactive cells in the contralateral nucleus accumbens. We conclude that populations of NO-synthesizing neurons are differentially regulated in Parkinson's disease induced by different experimental procedures.     

一氧化氮合酶抑制剂对脊髓损伤后运动功能的影响

目的观察诱导型和神经型一氧化氮合酶(iNOS,nNOS)抑制剂对大鼠脊髓损伤(SCI)后运动功能的影响和机理。方法大鼠脊髓压迫伤后分别给予iNOS和nNOS抑制剂—氨基胍(AG)和7-硝基吲唑(7-NI)进行治疗,24h后用分光光度法测定组织中一氧化氮(NO)含量和一氧化氮合酶(NOS)活性,72h后用流式细胞仪检测神经细胞凋亡情况,4周后用电生理和动物行为学等指标评价运动功能的恢复情况。结果AG和7-NI均可以抑制组织中的NO含量,并使NOS活性下降,同时降低神经细胞的凋亡比率,对运动功能的恢复前者优于后者。结论脊髓损伤后应用NOS抑制剂可以使伤后运动功能得到改善,AG的作用似乎更明显,提示iNOS活性变化可能对脊髓损伤的恢复更具决定作用。     

Developmental effects of perinatal exposure to extremely weak 7 Hz magnetic fields and nitric oxide modulation in the Wistar albino rat

Prenatal exposure of pregnant dams to oscillating magnetic fields can cause behavioural deficits in their offspring which persist into adulthood. These changes are waveform-specific and may involve nitric oxide. To investigate the interaction between nitric oxide modulation and perinatal magnetic fields, dams were exposed from 2 days before to 14 days after birth to one of six magnetic field conditions (1, 5, 10, 50 or 500 nT or sham) and given either water, 1g/L nitric oxide precursor l-arginine or 0.5 g/L nitric oxide synthase inhibitor n-methylarginine. At weaning (22d), their offspring were placed in the open field for observation. Rats given 50 nT field or 500 nT field+water were hyperactive and showed increased rearing and bodyweight. These strong effects were attenuated or absent in groups given 50 or 500 nT field+n-methylarginine. Groups given sham field+l-arginine were behaviourally similar to animals given 50 or 500 nT field+water. Higher intensity fields showed robust behavioural and physiological effects. In general, these effects were counteracted by co-administration of nitric oxide synthase inhibitor n-methylarginine, which had little effect on its own. Shams given NO precursor l-arginine were highly similar to those given any higher intensity magnetic field. Results support a critical developmental role of NO and the involvement of NO in magnetic field effects.     

Counteraction by Nitric Oxide Synthase Inhibitor of Neurochemical Alterations of Dopaminergic System in 6-OHDA-Lesioned Rats Under l-DOPA Treatment

Nitric oxide synthase inhibitors reduce l-3, (Del-Bel et al., Cell Mol Neurobiol 25(2):371–392, 2005) 4-dihydroxyphenylalanine (l-DOPA)-induced abnormal motor effects subsequent to depletion of dopaminergic neurons in rodents and non-human primates. The present study used quantitative high-performance liquid chromatography to analyze, for the first time, dopamine metabolism in striatum of rats in order to elucidate the mechanism of action of the nitric oxide synthase inhibitors. Adult male Wistar rats received unilateral microinjection of saline (sham) or 6-hydroxydopamine (6-OHDA-lesioned) in the medial forebrain bundle. Past 3 weeks, rats were treated during 21 days with l-DOPA/benserazide (30 mg/kg/7.5 mg/kg, respectively, daily). On the 22nd day rats received an intraperitoneal (i.p.) injection of either vehicle or 7-nitroindazole, a preferential neuronal nitric oxide synthase inhibitor before l-DOPA. Abnormal involuntary movements and rotarod test were assessed as behavioral correlate of motor responses. Lesion intensity was evaluated through tyrosine hydroxylase immunohystochemical reaction. Dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC), and an extent of dopamine striatal tissue levels/dopamine metabolism were measured in the striatum. Lesion with 6-OHDA decreased dopamine, DOPAC, and DOPAC/dopamine ratio in the lesioned striatum. l-DOPA treatment induced abnormal involuntary movements and increased DOPAC/dopamine ratio (nearly five times) in the lesioned striatum. l-DOPA-induced dyskinesia was mitigated by 7-nitroindazole, which also decreased dopamine turnover, dopamine and DOPAC levels. Our results revealed an almost two times increase in dopamine content in the non-lesioned striatum of 6-OHDA-lesioned rats. Reduction of striatal DOPAC/dopamine ratio in dyskinetic rats may suggest an increase in the dopamine availability. Our data confirm contribution of nitrergic transmission in the pathogenesis of l-DOPA-induced dyskinesia with potential utilization of nitric oxide synthase inhibitors for treatment.     

Correlation between hippocampal BDNF mRNA expression and memory performance in senescent rats

Nitric oxide is involved in the mechanism of hyperbaric oxygen (HBO₂) brain toxicity as nitric oxide synthase (NOS) inhibitors delay latent time before the onset of seizures. The purpose of this study was to investigate if seizures affect sensitivity to convulsions during subsequent exposure to HBO₂ and to determine if NOS activity and expression is changed after HBO₂ seizures. Rats were exposed to 5 atm (gauge pressure) 100% O₂ until seizures recorded by electroencephalograph (EEG) and reexposed 1, 2, or 6 days later. Latency to seizures was significantly shorter (P<0.05) in animals reexposed 1 or 2 days after the first exposure. Activity of calcium-dependent NOS activity in cortex was significantly higher 1 and 2 days after seizures compared with controls (P<0.05), while calcium-independent NOS activity was not changed during the 6-day post-seizure interval. The expression of neuronal NOS (nNOS) protein determined by Western blot was higher 1 and 2 days after seizures (P<0.05), while the expression of endothelial (eNOS) and inducible (iNOS) remained unchanged. nNOS upregulation 1 and 2 days after seizures and protection against HBO₂ seizures by nNOS-specific inhibitor 7-nitroindazole (7-NI) suggest possible involvement of NO in the mechanism of increased sensitivity to HBO₂ in reexposures.     

Aminoguanidine treatment ameliorates inflammatory responses and memory impairment induced by amyloid-beta 25–35 injection in rats

Alzheimer disease (AD) is a neurodegenerative disorder caused by accumulation of the amyloid-beta peptide (Aβ) in neuritic plaques. Its neurotoxic mechanisms are associated with inflammatory responses and nitrosative stress generation that promote expression of inducible nitric oxide synthase (iNOS) and increased nitric oxide causing neuronal death and memory impairment. Studies suggest that treatment with anti-inflammatory and anti-oxidant agents decreases the risk of developing AD. Aminoguanidine (AG) is an iNOS inhibitor with anti-inflammatory and anti-oxidant effects. In this study, we evaluated the effects of systemic administration of AG (100 mg/kg/day for 4 days) on spatial memory and inflammatory responses induced by an injection of Aβ_25–35 [100 μM] into the temporal cortex (TCx) of rats. A significant improvement of spatial memory was evident in the Aβ_25–35-treated group at day 30 post-injection subjected to AG treatment; this effect was correlated with decreases in reactive gliosis, IL-1β, TNF-α, and nitrite levels, as well as a reduction in neurodegeneration in the TCx and hippocampus (Hp). These results suggest that AG treatment inhibited glia activation and cytokine release, which may help to counteract neurodegenerative events induced by the toxicity of Aβ.     

Nitric oxide synthase inhibition and MPTP-induced toxicity in the common marmoset

Nitric oxide, produced following activation of N-methyl-D-aspartate (NMDA) receptors, may be involved in 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) toxicity since NMDA receptor antagonists have been shown to prevent MPTP induced nigral cell loss in primates. Common marmosets were treated with either saline or MPTP or L-N^Gnitro arginine methyl ester (L-NAME) or MPTP and L-NAME. MPTP-treated common marmosets showed motor deficits including bradykinesia, rigidity, and tremor accompanied by a marked loss of tyrosine hydroxylase-immunoreactive neurones in the substantia nigra pars compacta and of [³H]-mazindol binding in the caudate-putamen. MPTP treatment also caused an increase in glial fibrillary acidic protein (GFAP) staining in the substantia nigra compared to controls. However, MPTP treatment did not alter the number of constitutive nitric oxide synthase-immunoreactive neurones in the caudate-putamen. Furthermore, neurones or glial cells immunoreactive for inducible nitric oxide synthase were not observed in the substantia nigra pars compacta following MPTP treatment. L-NAME treatment alone did not produce any behavioural changes in marmosets and did not alter the number of tyrosine hydroxylase-immunoreactive cells in the substantia nigra pars compacta, the number of constitutive nitric oxide synthase-immunoreactive neurones or [³H]-mazindol binding in the caudate-putamen compared to saline-treated control animals. Furthermore, L-NAME did not affect the motor deficits, loss of tyrosine hydroxylase-immunoreactive neurones in the substantia nigra pars compacta, loss of [³H]-mazindol binding in the caudate-putamen, or the increase in GFAP staining in the substantia nigra induced by MPTP treatment of common marmosets. The failure of L-NAME to protect against MPTP-induced toxicity in the marmoset suggests that nitric oxide does not play a major role in such toxicity and casts doubt over the involvement of the NMDA:nitric oxide system in neurodegeneration in MPTP-treated primates. Synapse 26:301–316, 1997. © 1997 Wiley-Liss, Inc.     

Feed-forward excitation of striatal neuron activity by frontal cortical activation of nitric oxide signaling in vivo

The gaseous neurotransmitter nitric oxide plays an important role in the modulation of corticostriatal synaptic transmission. This study examined the impact of frontal cortex stimulation on striatal nitric oxide efflux and neuron activity in urethane-anesthetized rats using amperometric microsensor and single-unit extracellular recordings, respectively. Systemic administration of the neuronal nitric oxide synthase inhibitor 7-nitroindazole decreased spontaneous spike activity without affecting activity evoked by single-pulse stimulation of the ipsilateral cortex. Train (30 Hz) stimulation of the contralateral frontal cortex transiently increased nitric oxide efflux in a robust and reproducible manner. Evoked nitric oxide efflux was attenuated by systemic administration of 7-nitroindazole and the non-selective nitric oxide synthase inhibitor N(G)-nitro-L-arginine methyl ester. Train stimulation of the contralateral cortex, in a manner identical to that used to evoke nitric oxide efflux, had variable effects on spike activity assessed during the train stimulation trial, but induced a short-term depression of cortically evoked activity in the first post-train stimulation trial. Interestingly, 7-nitroindazole potently decreased cortically evoked activity recorded during the train stimulation trial. Moreover, the short-term depression of spike activity induced by train stimulation was enhanced following pretreatment with 7-nitroindazole and attenuated after systemic administration of the dopamine D2 receptor antagonist eticlopride. These results demonstrate that robust activation of frontal cortical afferents in the intact animal activates a powerful nitric oxide-mediated feed-forward excitation which partially offsets concurrent D2 receptor-mediated short-term inhibitory influences on striatal neuron activity. Thus, nitric oxide signaling is likely to play an important role in the integration of corticostriatal sensorimotor information in striatal networks.     

Intermittent ethanol exposure induces inflammatory brain damage and causes long-term behavioural alterations in adolescent rats

Adolescent brain development seems to be important for the maturation of brain structures and behaviour. Intermittent binge ethanol drinking is common among adolescents, and this type of drinking can induce brain damage. Because we have demonstrated that chronic ethanol treatment induces inflammatory processes in the brain, we investigate whether intermittent ethanol intoxication enhances cyclooxygenase-2 (COX-2) and inducible nitric oxide synthase (iNOS) in adolescent rats, and whether these mediators induce brain damage and cause permanent cognitive dysfunctions. Adolescent rats were exposed to ethanol (3.0 g/kg) for two consecutive days at 48-h intervals over 14 days. Levels of COX-2, iNOS and cell death were assessed in the neocortex, hippocampus and cerebellum 24 h after the final ethanol administration. The following day or 20 days after the final injection (adult stage), animals were tested for different behavioural tests (conditional discrimination learning, rotarod, object recognition, beam-walking performance) to assess cognitive and motor functions. Our results show that intermittent ethanol intoxication upregulates COX-2 and iNOS levels, and increases cell death in the neocortex, hippocampus and cerebellum. Furthermore, animals treated with ethanol during adolescence exhibited behavioural deficits that were evident at the end of ethanol treatments and at the adult stage. Administration of indomethacin, a COX-2 inhibitor, abolishes the induction of COX-2 and iNOS expression and cell death, preventing ethanol-induced behavioural deficits. These findings indicate that binge pattern exposure to ethanol during adolescence induces brain damage by inflammatory processes and causes long-lasting neurobehavioural consequences. Accordingly, administering indomethacin protects against ethanol-induced brain damage and prevents detrimental ethanol effects on cognitive and motor processes.     

Anesthesia alters NO-mediated functional hyperemia

Many properties of nitric oxide, NO, (localization, diffusiveness, half-life, vasodilatory affects) have supported its potential role in mediating the link between local cerebral activity and blood flow. However, evidence that both supports and refutes a role for NO in functional hyperemia have been presented. The present study employed multiple nitric oxide synthase inhibitors, two anesthetic regimes and laser-Doppler flowmetry to test the hypothesis that NO is critically involved in mediating the functional hyperemic response within rodent whisker-barrel cortex (WBC). In urethane anesthetized animals, functional hyperemic responses were obtained both before and after 1 mg/kg atropine infusion, 30 mg/kg i.v. -NAME (N-Nitro- -arginine methylester) infusion, 30 mg/kg -NA (N-Nitro- -arginine) infusion or 25 mg/kg 7-NI (7-nitroindazole). -NAME was also tested in a group of animals pretreated with halothane before urethane anesthesia. Neither the magnitude of the blood flow response nor its time course was altered by NO blockade or atropine administration when compared to pre-infusion controls in urethane anesthetized rats. In contrast, animals that were pretreated with halothane exhibited a 33% inhibition of functional hyperemia after -NAME administration. Taken together, these data do not support a primary role for NO in rat WBC functional hyperemia and suggest that previous reports of inhibition may have been secondary to the anesthesia employed.     

7-Nitroindazole blocks nicotine-induced conditioned place preference but not LiCl-induced conditioned place aversion

We have shown previously that the neuronal nitric oxide synthase (nNOS) is involved in the rewarding effect of cocaine as determined by the conditioned place preference (CPP) paradigm. In the present study we investigated the effect of the nNOS inhibitor 7-nitroindazole (7-NI) on nicotine-induced CPP and LiCl-induced conditioned place aversion (CPA) in Swiss Webster mice. Mice treated with nicotine (0.5 mg/kg) or saline every other day for 8 days (four drug and four saline sessions) developed CPP that was completely blocked by pretreatment with 7-NI (25 mg/kg). Mice treated with LiCl (150 mg/kg) developed marked aversion to the LiCl-paired compartment. LiCl-induced CPA was not affected by the pretreatment with 7-NI. These findings suggest that nitric oxide (NO) plays a role in the acquisition of reward but not of aversion and that the blockade of nicotine-induced CPP is probably not due to impairment of learning and memory.     

nNOS inhibitors attenuate methamphetamine-induced dopaminergic neurotoxicity but not hyperthermia in mice

Methamphetamine (METH)-induced dopaminergic neurotoxicity is associated with hyperthermia. We investigated the effect of several neuronal nitric oxide synthase (nNOS) inhibitors on METH-induced hyperthermia and striatal dopaminergic neurotoxicity. Administration of METH (5 mg/kg; q. 3 h x 3) to Swiss Webster mice produced marked hyperthermia and 50-60% depletion of striatal dopaminergic markers 72 h after METH administration. Pretreatment with the nNOS inhibitors S-methylthiocitrulline (SMTC; 10 mg/kg) or 3-bromo-7-nitroindazole (3-Br-7-NI; 20 mg/kg) before each METH injection did not affect the persistent hyperthermia produced by METH, but afforded protection against the depletion of dopaminergic markers. A low dose (25 mg/kg) of the nNOS inhibitor 7-nitroindazole (7-NI) did not affect METH-induced hyperthermia, but a high dose (50 mg/kg) produced significant hypothermia. These findings indicate that low dose of selective nNOS inhibitors protect against METH-induced neurotoxicity with no effect on body temperature and support the hypothesis that nitric oxide (NO) and peroxynitrite have a major role in METH-induced dopaminergic neurotoxicity.     

The behavioural effects of intrahypothalamic multistage versus single injections of 6-hydroxydopamine

16 μg of 6-hydroxydopamine were injected bilaterally into the lateral hypothalamus of male Sprague-Dawley rats in either a single injection or in a series of multistage injections over a period of 75 days. While the single injection produced behavioural deficits typical of those seen following catecholamine depletion of the forebrain, the behaviour of animals injected incrementally with the same dose was indistinguishable from that of controls. Fluorescent histochemical assessment revealed that the animals in the multistage injection group, the behaviourally unimpaired, suffered more severe depletion of forebrain catecholamines than those in the single-stage injection group. Accumulation of amines proximal to the site of drug injection was extensive only in those animals displaying behavioural deficits, that is, the group with the lesser amount of forebrain catecholamine depletion. It is suggested that the severity of deficits in consummatory and motor behaviour occurring after hypothalamic trauma is determined by a lesion's effectiveness in producing amine accumulation rather than catecholamine depletion.     

Anorexigenic action of nitric oxide synthase inhibition in the raphe nuclei

The present report examined the effects of midbrain raphe nuclei injections of nitric oxide synthase inhibitors NG-nitro-L-arginine methyl ester (L-NAME) and 7-nitroindazole (7-NI) on eating behavior. L-NAME (5-500 pmol) and 7-NI (2-200 pmol) were administered into either the dorsal or median raphe nucleus. Both nitric oxide synthase inhibitors decreased food intake in adult male Sprague-Dawley rats when injected into either raphe site. Further, eating elicited by dorsal and median raphe injections of the 5-HT1A agonist 8-OH-DPAT (0.8 nmol) was attenuated by L-NAME or 7-NI pretreatment. Our findings indicate that nitric oxide acts within the raphe to alter food intake. The inhibitory effects of L-NAME and 7-NI on eating elicited by 8-OH-DPAT further suggest that nitric oxide and 5-HT systems interact in the control of food intake.