Nitric oxide synthase inhibitors cause motor deficits in mice

Paradoxical kinesia may no longer be a paradox waiting for 100 years to be unraveled

Parkinson's disease (PD) is a progressive neurodegenerative disorder mainly characterized by bradykinesia and akinesia. Interestingly, these motor disabilities can depend on the patient emotional state. Disabled PD patients remain able to produce normal motor responses in the context of urgent or externally driven situations or even when exposed to appetitive cues such as music. To describe this phenomenon Souques coined the term "paradoxical kinesia" a century ago. Since then, the mechanisms underlying paradoxical kinesia are still unknown due to a paucity of valid animal models that replicate this phenomenon. To overcome this limitation, we established two animal models of paradoxical kinesia. Using these models, we investigated the neural mechanisms of paradoxical kinesia, with the results pointing to the inferior colliculus (IC) as a key structure. Intracollicular electrical deep brain stimulation, glutamatergic and GABAergic mechanisms may be involved in the elaboration of paradoxical kinesia. Since paradoxical kinesia might work by activation of some alternative pathway bypassing basal ganglia, we suggest the IC as a candidate to be part of this pathway.

Whole-Brain Afferent Inputs to the Caudate Nucleus, Putamen, and Accumbens Nucleus in the Tree Shrew Striatum

Day-active tree shrews have a well-developed internal capsule (ic) that clearly separates the caudate nucleus (Cd) and putamen (Pu). The striatum consists of the Cd, ic, Pu, and accumbens nucleus (Acb). Here, we characterized the cytoarchitecture of the striatum and the whole-brain inputs to the Cd, Pu, and Acb in tree shrews by using immunohistochemistry and the retrograde tracer Fluoro-Gold (FG). Our data show the distribution patterns of parvalbumin (PV), nitric oxide synthase (NOS), calretinin (CR), and tyrosine hydroxylase (TH) immunoreactivity in the striatum of tree shrews, which were different from those observed in rats. The Cd and Pu mainly received inputs from the thalamus, motor cortex, somatosensory cortex, subthalamic nucleus, substantia nigra, and other cortical and subcortical regions, whereas the Acb primarily received inputs from the anterior olfactory nucleus, claustrum, infralimbic cortex, thalamus, raphe nucleus, parabrachial nucleus, ventral tegmental area, and so on. The Cd, Pu, and Acb received inputs from different neuronal populations in the ipsilateral (60, 67, and 63 brain regions, respectively) and contralateral (23, 20, and 36 brain regions, respectively) brain hemispheres. Overall, we demonstrate that there are species differences between tree shrews and rats in the density of PV, NOS, CR, and TH immunoreactivity in the striatum. Additionally, we mapped for the first time the distribution of whole-brain input neurons projecting to the striatum of tree shrews with FG injected into the Cd, Pu, and Acb. The similarities and differences in their brain-wide input patterns may provide new insights into the diverse functions of the striatal subregions.

Haloperidol-induced catalepsy as an animal model for parkinsonism: A systematic review of experimental studies

Several useful animal models for parkinsonism have been developed so far. Haloperidol-induced catalepsy is often used as a rodent model for the study of motor impairments observed in Parkinson's disease and related disorders and for the screening of potential antiparkinsonian compounds. The objective of this systematic review is to identify publications that used the haloperidol-induced catalepsy model for parkinsonism and to explore the methodological characteristics and the main questions addressed in these studies. A careful systematic search of the literature was carried out by accessing articles in three different databases: Web of Science, PubMed and SCOPUS. The selection and inclusion of studies were performed based on the abstract and, subsequently, on full-text analysis. Data extraction included the objective of the study, study design and outcome of interest. Two hundred and fifty-five articles were included in the review. Publication years ranged from 1981 to 2020. Most studies used the model to explore the effects of potential treatments for parkinsonism. Although the methodological characteristics used are quite varied, most studies used Wistar rats as experimental subjects. The most frequent dose of haloperidol used was 1.0 mg/kg, and the horizontal bar test was the most used to assess catalepsy. The data presented here provide a framework for an evidence-based approach to the design of preclinical research on parkinsonism using the haloperidol-induced catalepsy model. This model has been used routinely and successfully and is likely to continue to play a critical role in the ongoing search for the next generation of therapeutic interventions for parkinsonism.

Association of Rare Genetic Variants in Opioid Receptors with Tourette Syndrome

Background

Genes involved in Tourette syndrome (TS) remain largely unknown. We aimed to identify genetic factors contributing to TS in a French cohort of 120 individuals using a combination of hypothesis-driven and exome-sequencing approaches.

Methods

We first sequenced exons of SLITRK1-6 and HDC in the TS cohort and subsequently sequenced the exome of 12 individuals harboring rare variants in these genes to find additional rare variants contributing to the disorder under the hypothesis of oligogenic inheritance. We further screened three candidate genes (OPRK1, PCDH10, and NTSR2) preferentially expressed in the basal ganglia, and three additional genes involved in neurotensin and opioid signaling (OPRM1, NTS, and NTSR1), and compared variant frequencies in TS patients and 788 matched control individuals. We also investigated the impact of altering the expression of Oprk1 in zebrafish.

Results

Thirteen ultrarare missense variants of SLITRK1-6 and HDC were identified in 12 patients. Exome sequencing in these patients revealed rare possibly deleterious variants in 3,041 genes, 54 of which were preferentially expressed in the basal ganglia. Comparison of variant frequencies altering selected candidate genes in TS and control individuals revealed an excess of potentially disrupting variants in OPRK1, encoding the opioid kappa receptor, in TS patients. Accordingly, we show that downregulation of the Oprk1 orthologue in zebrafish induces a hyperkinetic phenotype in early development.

Discussion

These results support a heterogeneous and complex genetic etiology of TS, possibly involving rare variants altering the opioid pathway in some individuals, which could represent a novel therapeutic target in this disorder.

The preferential nNOS inhibitor 7-nitroindazole and the non-selective one N(G)-nitro-L-arginine methyl ester administered alone or jointly with L-DOPA differentially affect motor behavior and monoamine metabolism in sham-operated and 6-OHDA-lesioned rats

Reciprocal interactions between nitrergic and dopaminergic systems play a key role in the control of motor behavior. In the present study, we performed a comparative analysis of motor behavior (locomotor activity, catalepsy, rotational behavior) and monoamine metabolism in the striatum and substantia nigra of unilaterally sham-operated and 6-OHDA-lesioned rats treated with the preferential neuronal nitric oxide synthase (nNOS) inhibitor 7-nitroindazole (7-NI) or the non-selective one N(G)-nitro-L-arginine methyl ester (L-NAME), alone or in combination with L-DOPA. Each NOS inhibitor given alone (50mg/kg) induced a distinct catalepsy 30 min after injection but only 7-NI impaired spontaneous locomotion after 10 min. In 6-OHDA-lesioned rats, chronic L-DOPA (25mg/kg) induced 2.5-h long contralateral rotations. 7-NI (30 and 50mg/kg) markedly reduced the intensity of L-DOPA-induced contralateral rotations while extending their duration until 4.5h whereas L-NAME (50 and 100mg/kg) only tended to attenuate their intensity without affecting the duration. 7-NI but not L-NAME significantly increased endogenous tissue DA levels in the nigrostriatal system of both sham-operated and 6-OHDA-lesioned rats. In L-DOPA-treated group, 7-NI significantly enhanced the L-DOPA-derived tissue DA content in this system and decreased the level of the intracellular DA metabolite DOPAC produced by monoamine oxidase (MAO). In contrast to 7-NI, L-NAME decreased markedly DA content and did not affect DOPAC level in the ipsilateral striatum. It means that the differences in 7-NI and L-NAME-mediated modulation of L-DOPA-induced behavioral and biochemical effects resulted not only from the inhibition of NOS activity but also from differences in their ability to inhibit MAO.

Role of the endogenous nitric oxide inhibitor asymmetric dimethylarginine (ADMA) and brain-derived neurotrophic factor (BDNF) in depression and behavioural changes: clinical and preclinical data in chronic kidney disease

BACKGROUND

Patients with chronic kidney disease (CKD) exhibit a high prevalence of neuropsychiatric alterations, including depression and behavioural changes. CKD is also associated with decreased physical activity not fully explained by co-morbidities. In patients without CKD, the brain-derived neurotropic factor (BDNF) as well as the endogenous NOS inhibitor asymmetric dimethylarginine (ADMA) had been suspected to be involved in major depression. The aim of our study was to examine the role of ADMA and BDNF in the behaviour of haemodialysis patients (CKD5D) as well as in a rat model of 5/6 nephrectomy and chronic ADMA infusion alone.

METHODS

Eleven (5F/6M) CKD5D patients underwent Beck Depression Inventory (BDI) testing along with analysis of ADMA and BDNF. Male Sprague-Dawley rats were randomly assigned to four groups: (i) saline infusion; (ii) ADMA (250 µg/kg/day) infusion via osmotic mini pumps; (iii) 5/6 nephrectomy; (iv) untreated controls. After 28 days, the animals underwent behavioural tests measuring anxiety, locomotion and investigative behaviour. Animals were sacrificed, blood samples were drawn and analysed and hippocampal immunohistology for BDNF was performed.

RESULTS

In CKD5D patients, decreased BDNF levels correlated with higher scores of depression (Pearson r = -0.8156, P = 0.002). ADMA infusion led to a significant decrease of BDNF while the decrease of BDNF in 5/6 nephrectomy was not significant. However, an attenuated hippocampal BDNF expression could be detected in 5/6 nephrecomized animals. Decreased spontaneous locomotor activity was shown in ADMA-infused rats [15.9 (13.5-26.1) lines crossed/min] and 5/6 nephrectomy [14.6 (6.1-20.2) lines crossed/min] when compared with controls [32.5 (15.3-42.4) lines crossed/min]. Anxiety-like behaviour tested by hole investigation time was significantly more pronounced in 5/6 nephrectomy [24 (6-44) s] when compared with ADMA infusion [64 (28-93) s] and controls [33 (26-65) s].

CONCLUSIONS

Progressive renal failure in rats is accompanied by a marked increase of ADMA and a decrease in BDNF. 5/6 nephrectomy leads to significantly decreased exploratory behaviour and locomotion. Both behaviours could be reproduced by ADMA infusion alone. Indicators of anxiety were more pronounced in ADMA-infused animals when compared with 5/6 nephrectomized rats. Furthermore, an inverse relationship of BDNF and BDI in 11 CKD5D patients was shown.

Effect of 7-Nitroindazole, a Neuronal Nitric Oxide Synthase Inhibitor, on Behavioral and Physiological Parameters

The role of brain derived nitric oxide in the physiology and behavior remains disputable. One of the reasons of the controversies might be systemic side effects of nitric oxide synthase inhibitors. Therefore, under nNOS inhibition by 7-nitroindazole (7-NI) we carried out recordings of blood gasses, blood pressure and spontaneous EEG in conscious adult rats. Locomotion and spontaneous behavior were assessed in an open field. In addition skilled walking and limb coordination were evaluated using a ladder rung walking test. The blood gas analysis revealed a significant increase in pCO2 180 min and 240 min after the application of 7-NI. The power and entropy decreased simultaneously with a shift of the mean frequency of the spontaneous EEG toward slow oscillations after 7-NI treatment. The thresholds of evoked potentials underwent a significant drop and a trend towards a slight increase in the I-O curve slope was observed. 7-NI significantly suppressed open field behavior expressed as distance moved, exploratory rearing and grooming. As for the ladder rung walking test the 7-NI treated animals had more errors in foot placement indicating impairment in limb coordination. Therefore our findings suggest that 7-NI increased cortical excitability and altered some physiological and behavioral parameters.

N-nitro-L-arginine, a nitric oxide synthase inhibitor, aggravates iminodipropionitrile-induced neurobehavioral and vestibular toxicities in rats

Exposure of iminodipropionitrile (IDPN) to rodents produces permanent behavioral syndrome characterized by repetitive head movements, circling and back walking. Other synthetic nitriles of industrial importance such as crotonitrile and allylnitrile are also able to produce similar motor deficits in experimental animals. However, due to the well-defined behavioral deficits and their easy quantification, IDPN-induced behavioral syndrome is a preferential animal model to test the interaction of various agents with synthetic nitriles. This study reports the effect of non-specific nitric oxide synthase inhibitor, N-nitro-L-arginine (NARG) on IDPN-induced neurobehavioral toxicity in adult male Wistar rats. Four groups of animals were given i.p. injections of IDPN (100 mg/kg) for 6 days. These rats were treated with oral administration of NARG in the doses of 0 (IDPN alone group), 50, 150 and 300 mg/kg, 60 min before IDPN, respectively. Control rats received vehicle only, whereas another group was treated with 300 mg/kg of NARG alone (without IDPN). The results showed that NARG significantly exacerbated the incidence and intensity of IDPN-induced dyskinetic head movements, circling and back walking. The histology of inner ear showed massive degeneration of the sensory hair cells in the crista ampullaris of rats receiving the combined treatment with IDPN and NARG, suggesting a possible role of nitric oxide in IDPN-induced neurobehavioral syndrome in rats.

Chronic inhibition of nitric oxide synthase activity by NG-nitro-L-arginine induces nitric oxide synthase expression in the developing rat cerebellum

Studies on chronic inhibition of nitric oxide synthase (NOS) in the CNS suggest a plastic change in nitric oxide (NO) synthesis in areas related to motor control, which might protect the animal from the functional and behavioral consequences of NO deficiency. In the present study, the acute and chronic effect of the substrate analogue inhibitor N(G)-nitro-l-arginine (l-NNA) was examined on NO production, NO-sensitive cyclic guanosine monophosphate (cGMP) levels and the expression of NOS isoforms in the developing rat cerebellum. Acute intraperitoneal administration of the inhibitor (5-200mg/kg) to 21-day-old rats reduced NOS activity and NO concentration dose dependently by 70-90% and the tissue cGMP level by 60-80%. By contrast, chronic application of l-NNA between postnatal days 4-21 diminished the total NOS activity and NO concentration only by 30%, and the tissue cGMP level by 10-50%. Chronic treatment of 10mg/kg l-NNA induced neuronal (n)NOS expression in granule cells, as revealed by in situ hybridization, NADPH-diaphorase histochemistry and Western-blot, but it had no significant influence on tissue cGMP level or on layer formation of the cerebellum. However, a higher concentration (50mg/kg) of l-NNA decreased the intensity of the NADPH-diaphorase reaction in granule cells, significantly reduced cGMP production, and retarded layer formation and induced inducible (i)NOS expression & activity in glial cells. Treatments did not affect endothelial (e)NOS expression. The administration of the biologically inactive isomer D-NNA (50mg/kg) or saline was ineffective. The present findings suggest the existence of a concentration-dependent compensatory mechanism against experimentally-induced cronich inhibition of NOS, including nNOS or iNOS up-regulation, which might maintain a steady-state NO level in the developing cerebellum.

Reduction of L-type amino acid transporter 1 mRNA expression in brain capillaries in a mouse model of Parkinson's disease

The blood-brain barrier (BBB) expresses transporters that influence both dopaminergic neuronal function and drug therapy for Parkinson's disease (PD). The purpose of the present study was to clarify changes of transporter mRNA expression at the BBB in mice treated with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) as a model of PD, in order to understand the pathophysiological role of BBB transport function in PD. At 7 d after MPTP treatment, mice showed a motor deficit and a loss of dopaminergic neurons. At the same time, L-type amino acid transporter 1 (LAT1) mRNA expression in the brain capillary fraction of the MPTP-treated mice was significantly reduced by 62.6% compared with saline-treated mice, while no significant change was observed in the expression of glucose transporter 1, creatine transporter 1, taurine transporter, organic cation transporter 2, serotonin transporter, norepinephrine transporter and dopamine transporter. LAT1 mRNA expression in whole brain was not affected at 1, 3 and 5 d after the treatment, but was reduced by 46.3% at 7 d. LAT1 mediates the transport of large neutral amino acids, including tyrosine, as well as the PD-therapeutic drug levodopa, across the BBB. Our findings indicate that decreased LAT1 expression at the BBB in PD patients may adversely affect amino acid supply from the circulating blood and levodopa distribution into the brain.

Local isoform-specific NOS inhibition: a promising approach to promote motor function recovery after nerve injury

Physical injury to a nerve is the most frequent cause of acquired peripheral neuropathy, which is responsible for loss of motor, sensory and/or autonomic functions. Injured axons in the peripheral nervous system maintain the capacity to regenerate in adult mammals. However, after nerve transection, stumps of damaged nerves must be surgically joined to guide regenerating axons into the distal nerve stump. Even so, severe functional limitations persist after restorative surgery. Therefore, the identification of molecules that regulate degenerative and regenerative processes is indispensable in developing therapeutic tools to accelerate and improve functional recovery. Here, I consider the role of nitric oxide (NO) synthesized by the three major isoforms of NO synthases (NOS) in motor neuropathy. Neuronal NOS (nNOS) seems to be the primary source of NO that is detrimental to the survival of injured motoneurons. Endothelial NOS (eNOS) appears to be the major source of NO that interferes with axonal regrowth, at least soon after injury. Finally, NO derived from inducible NOS (iNOS) or nNOS is critical to the process of lipid breakdown for Wallerian degeneration and thereby benefits axonal regrowth. Specific inhibitors of these isoforms can be used to protect injured neurons from degeneration and promote axonal regeneration. A cautious proposal for the treatment of acquired motor neuropathy using therapeutic tools that locally interfere with eNOS/nNOS activities seems to merit consideration.

Regulation of striatal nitric oxide synthesis by local dopamine and glutamate interactions

Nitric oxide (NO) is a key neuromodulator of corticostriatal synaptic transmission. We have shown previously that dopamine (DA) D1/5 receptor stimulation facilitates neuronal NO synthase (nNOS) activity in the intact striatum. To study the impact of local manipulations of D1/5 and glutamatergic NMDA receptors on striatal nNOS activity, we combined the techniques of in vivo amperometry and reverse microdialysis. Striatal NO efflux was monitored proximal to the microdialysis probe in urethane-anesthetized rats during local infusion of vehicle or drug. NO efflux elicited by systemic administration of SKF-81297 was blocked following intrastriatal infusion of: (i) the D1/5 receptor antagonist SCH-23390, (ii) the nNOS inhibitor 7-nitroindazole, (iii) the non-specific ionotropic glutamate receptor antagonist kynurenic acid, and (iv) the selective NMDA receptor antagonist 3-phosphonopropyl-piperazine-2-carboxylic acid. Glycine co-perfusion did not affect SKF-81297-induced NO efflux. Furthermore, intrastriatal infusion of SKF-81297 potentiated NO efflux evoked during electrical stimulation of the motor cortex. The facilitatory effects of cortical stimulation and SKF-81297 were both blocked by intrastriatal infusion of SCH-23390, indicating that striatal D1/5 receptor activation is necessary for the activation of nNOS by corticostriatal afferents. These studies demonstrate for the first time that reciprocal DA-glutamate interactions play a critical role in stimulating striatal nNOS activity.

Protective action of neuronal nitric oxide synthase inhibitor in the MPTP mouse model of Parkinson's disease

We examined the effects of 7-nitroindazole on the dopaminergic system in mice after 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) treatment. The mice received four intraperitoneal injections of MPTP (20 mg/kg) at 2 h-intervals. Administration of 7-nitroindazole showed dose-dependent neuroprotective effects against striatal dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) depletion 7 days after MPTP treatment. Behavioral testing showed that MPTP-treated mice exhibited motor deficits in the catalepsy test after 7 days, but 7-nitroindazole prevented the appearance of motor abnormalities in this test. The MPTP-treated mice exhibited the loss of tyrosine hydroxylase-containing dopaminergic neurons in mice after 1, 3 and 7 days, but 7-nitroindazole-treated mice showed a protective effect. GFAP (glial fibrillary acidic protein)-positive astrocytes were accumulated in the striatum 3 and 7 days and in the substantia nigra 1, 3 and 7 days after MPTP treatment. In contrast, 7-nitroindazole prevented a significant increase in the number of GFAP-positive astrocytes in the striatum and substantia nigra after MPTP treatment. The reactive astrocytes in the striatum and substantia nigra after MPTP treatment increased the production of S100beta protein, which is thought to promote neuronal damage, but 7-nitoindazole suppressed the expression of S100 beta protein. Activation of microglia, with an increase in staining intensity and morphological changes, was observed in the striatum and substantia nigra 1 and 3 days after MPTP treatment, but 7-nitroindazole prevented a significant increase in the number of isolectin B(4) positive microglia in the striatum and substantia nigra. On the other hand, nestin-immunoreactive cells were increased significantly in the striatum 3 and 7 days after MPTP treatment. 7-Nitroindazole treatment facilitated nestin expression in the striatum 7 days after MPTP treatment. Thus, nNOS inhibitor 7-nitroindazole protected dopaminergic neurons against MPTP neurotoxicity in mice and ameliorated neurological deficits. The results suggest that the neuroprotection is mediated though the modulation of glial activation, including the inhibition of S100beta synthesis and the prevention of microglial activation. These results suggest the therapeutic strategy targeted to glial modulation with 7-nitoindazole offers a great potential for the development of new neuroprotective therapies for Parkinson's disease.

Exercise and food ad libitum reduce the impact of early in life nutritional inbalances on nitrergic activity of hippocampus and striatum

Nutritional imbalances were produced by varying litter size pups per dam: 3 (small), 6 (medium), and 12 (large). On the 21st day, 4 subjects of each litter, were sacrificed and the remaining were grouped, 2 per cage, with or without running wheels, with food and water ad libitum. Adult subjects were tested in water maze, their brains processed for NADPH-diaphorase histochemistry and quantified by densitometry. No differences were detected in water maze. At 21st day, S and L compared with M presented reduced NADPH-d in the stratum molecular of dentate gyrus (DG), stratum lacunosum of CA1 and in all CA3 layers but not in the striatum. On the 58th day, actvity remained low in S and L in CA3 and striatum and L in CA1 and DG. Voluntary exercise increased NADPH-d in DG, CA1, CA3, and striatum in S, and in the stratum lacunosum of CA1 and CA3 in L.

Anxiolytic effects induced by inhibition of the nitric oxide-cGMP pathway in the rat dorsal hippocampus

RATIONALE

Conflicting results have been reported regarding the role of the nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) pathway in the hippocampus on anxiety modulation.

OBJECTIVES

To investigate the effects of intrahippocampal injections of drugs that modify the NO-cGMP pathway in rats submitted to two animal models that are sensitive to anxiolytic drugs, the elevated plus-maze and the Vogel punished licking test.

MATERIALS AND METHODS

Male Wistar rats with cannulae aimed at the dentate gyrus of the dorsal hippocampus received microinjections of the NO synthase (NOS) inhibitors N (G)-nitro-L: -arginine methyl ester (LNAME, 15-300 nmol/0.2 microl), N (G)-nitro-L: -arginine (LNOARG, 50-300 nmol/0.2 microl), 7-nitroindazole (7NI, 10-100 nmol/0.2 microl), or the soluble guanylate cyclase inhibitor 1H-oxadiazolo-quinoxalin-1 one (ODQ, 10-100 nmol/0.2 microl), and were submitted to the elevated plus-maze. In a second group, the animals received 7NI, LNAME, or ODQ and were submitted to the Vogel punished licking test. To control for drug-induced changes in locomotor behavior, the animals were submitted to an open arena or to the Rota-rod test.

RESULTS

All drugs increased the exploration of the open arms of the elevated plus-maze. They also increased the number of punished licks in the Vogel test, indicating an anxiolytic effect. The anxiolytic effect of LNAME was prevented by previous treatment with L: -arginine (300 nmol/0.2 microl). Except for the lower dose of LNAME (15 nmol), administration of the NOS inhibitors or ODQ did not change exploratory activity in the open field nor cause any gross locomotor impairment in the Rota-rod test.

CONCLUSION

The results suggest that NO plays an anxiogenic role in the dentate gyrus of the dorsal hippocampus.

Sildenafil citrate attenuates a complex maze impairment induced by intracerebroventricular infusion of the NOS inhibitor Nomega-nitro-L-arginine methyl ester

In a previous study, our laboratory reported that sildenafil citrate, a cyclic nucleotide phosphodiesterase type 5 inhibitor, reversed a learning impairment in rats induced by systemic inhibition of nitric oxide synthase (60 mg/kg, i.p., Nomega-nitro-L-arginine methyl ester; L-NAME). To limit the peripheral effects of L-NAME and further localize the site of action of sildenafil, L-NAME (48 microg, i.c.v.) was infused bilaterally into the lateral cerebral ventricles 30 min prior to maze training. Saline or sildenafil citrate (1.5 or 3.0 mg/kg, i.p.) was administered systemically 15 min before training. Drug injections occurred 24 h after pretraining rats to avoid foot shock on a one-way active avoidance straight runway. Following drug treatment, the rats received 15 training trials on a 14-unit T-maze task that requires learning a complex sequence of turns to avoid mild foot shock. This complex maze paradigm is sensitive to aging and blockade of cholinergic, N-methyl-D-aspartate and nitric oxide signaling systems. Behavioral measures of performance included deviations from the correct pathway (errors), runtime from start to goal (latency), shock frequency and shock duration. Statistical analysis revealed that central infusion of L-NAME impaired maze performance and that sildenafil (3.0 mg/kg) significantly attenuated the impairment. These results suggest that sildenafil citrate may serve as a cognitive enhancer by modulating central nitric oxide/cGMP signal transduction following N-methyl-D-aspartate receptor activation. This pathway has been implicated in age-related cognitive decline and may be a useful target for pharmacological intervention of neurodegenerative disease.

Paeoniflorin attenuates neuroinflammation and dopaminergic neurodegeneration in the MPTP model of Parkinson's disease by activation of adenosine A1 receptor

1. This study examined whether Paeoniflorin (PF), the major active components of Chinese herb Paeoniae alba Radix, has neuroprotective effect in the 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease (PD). 2. Subcutaneous administration of PF (2.5 and 5 mg kg(-1)) for 11 days could protect tyrosine hydroxylase (TH)-positive substantia nigra neurons and striatal nerve fibers from death and bradykinesia induced by four-dose injection of MPTP (20 mg kg(-1)) on day 8. 3. When given at 1 h after the last dose of MPTP, and then administered once a day for the following 3 days, PF (2.5 and 5 mg kg(-1)) also significantly attenuated the dopaminergic neurodegeneration in a dose-dependent manner. Post-treatment with PF (5 mg kg(-1)) significantly attenuated MPTP-induced proinflammatory gene upregulation and microglial and astrocytic activation. 4. Pretreatment with 0.3 mg kg(-1) 8-cyclopentyl-1,3-dipropylxanthine, an adenosine A1 receptor (A1AR) antagonist, 15 min before each dose of PF, reversed the neuroprotective and antineuroinflammatory effects of PF. 5. In conclusion, this study demonstrated that PF could reduce the MPTP-induced toxicity by inhibition of neuroinflammation by activation of the A1AR, and suggested that PF might be a valuable neuroprotective agent for the treatment of PD.

Haplotype analysis of endothelial nitric oxide synthase (NOS3) genetic variants and tardive dyskinesia in patients with schizophrenia

OBJECTIVES

Several studies have indicated the involvement of nitric oxide (NO) in the pathogenesis of tardive dyskinesia (TD), an incapacitating adverse movement disorder associated with long-term antipsychotic treatment. In human brain, the NO could be generated by endothelial nitric oxide synthase (NOS3). In this study, we studied whether the genetic variants in human NOS3 gene is associated with TD in patients with schizophrenia.

METHODS

Two hundred and eighty-two chronic inpatients with schizophrenia treated with typical antipsychotics were recruited in this study. The patients were further grouped by the presence of TD or not according to the Research and Diagnostic Criteria for TD. The genetic variants in the NOS3 gene investigated in this study were -786T > C in the promotor region, 27-bp variable number of tandem repeats (27-bp VNTR) in intron 4, and Glu298Asp in exon 7. The frequencies of genotypes, alleles and haplotypes of the three markers were compared between the TD (n = 153) and non-TD (n = 129) groups.

RESULTS

There were no significant associations between the genotypes and alleles of the three markers and TD. However, in the haplotype-based case-control analysis, the frequency of haplotype T-4b-Glu was significantly higher in non-TD than in TD group (TD vs. non-TD = 72.7% vs. 81.0%, permutation P value = 0.021, OR = 0.648, 95% CI = 0.432-0.973).

CONCLUSIONS

We found that the haplotype T-4b-Glu represents a protective haplotype against TD after long-term antipsychotic treatment. This finding suggests that human NOS3 gene may be involved in the pathogenesis of TD.

The effect of nitric oxide on fentanyl and haloperidol-induced catalepsy in mice *

BACKGROUND AND OBJECTIVES

This study was designed to investigate the role of nitric oxide on catalepsy induced by fentanyl and haloperidol.

METHODS

Male albino mice were treated either with fentanyl (0.1-0.2 mg kg-1, s.c.) or haloperidol (0.5-2 mg kg-1, i.p.). The non-selective nitric oxide synthase inhibitor, NG-nitro-L-arginine (10 mg kg-1, i.p.), selective neuronal nitric oxide synthase inhibitor, 7-nitroindazole (3 mg kg-1, i.p.), and nitric oxide donors, L-arginine (30-300 mg kg-1, i.p.) and D-arginine (30 mg kg-1, i.p.), were applied 20 min prior to fentanyl or haloperidol injection. A mu-opioid receptor antagonist naloxone (1 mg kg-1, i.p.) was also given in some groups. The cataleptic status of mice was assessed by placing animals in a rearing position in the cage. If the mouse maintained cataleptic posture for more than 20 s, it was scored as cataleptic and duration of catalepsy was expressed in terms of minutes.

RESULTS

Both NG-nitro-L-arginine and 7-nitroindazole prolonged fentanyl-induced catalepsy (fentanyl: 3.6+/-0.8 min; fentanyl+NG-nitro-L-arginine: 77.4+/-14.6 min, fentanyl+7-nitroindazole: 56.0+/-10.4 min; n=6; P<0.01). This effect was reversed by L-arginine and naloxone, but not by D-arginine. Nitric oxide synthase inhibitors also prolonged the cataleptic action of haloperidol but to a lesser extent (haloperidol: 72.0+/-6.3 min; haloperidol+NG-nitro-L-arginine: 98.5+/-6.3 min, haloperidol+7-nitroindazole: 89.6+/-2.2 min; n=6; P<0.05). The prolongation of haloperidol-induced catalepsy with nitric oxide synthase inhibitors was not reversed by L-arginine.

CONCLUSION

These results suggest a common mechanism between mu-opioid receptors and the nitric oxide system in the development of fentanyl-induced catalepsy in mice different from haloperidol-induced catalepsy.

Combined application of behavior genetics and microarray analysis to identify regional expression themes and gene-behavior associations

In this report we link candidate genes to complex behavioral phenotypes by using a behavior genetics approach. Gene expression signatures were generated for the prefrontal cortex, ventral striatum, temporal lobe, periaqueductal gray, and cerebellum in eight inbred strains from priority group A of the Mouse Phenome Project. Bioinformatic analysis of regionally enriched genes that were conserved across all strains revealed both functional and structural specialization of particular brain regions. For example, genes encoding proteins with demonstrated anti-apoptotic function were over-represented in the cerebellum, whereas genes coding for proteins associated with learning and memory were enriched in the ventral striatum, as defined by the Expression Analysis Systematic Explorer (EASE) application. Association of regional gene expression with behavioral phenotypes was exploited to identify candidate behavioral genes. Phenotypes that were investigated included anxiety, drug-naive and ethanol-induced distance traveled across a grid floor, and seizure susceptibility. Several genes within the glutamatergic signaling pathway (i.e., NMDA/glutamate receptor subunit 2C, calmodulin, solute carrier family 1 member 2, and glutamine synthetase) were identified in a phenotype-dependent and region-specific manner. In addition to supporting evidence in the literature, many of the genes that were identified could be mapped in silico to surrogate behavior-related quantitative trait loci. The approaches and data set described herein serve as a valuable resource to investigate the genetic underpinning of complex behaviors.

Different effects of 7-nitroindazole in reserpine-induced hypolocomotion in two strains of mice

There are a number of reasons for believing that nitric oxide participates in motor control in the striatum. Therefore, effects of neuronal nitric oxide synthase inhibitor 7-nitroindazole (7-NI) were studied on the reserpine model of Parkinson's disease in Swiss and C57BL/6 mice using the open-field test. Mice received reserpine (1 mg/kg administered intraperitoneally). A significant hypolocomotion was observed 24 h and 48 h after reserpine injection. The treatment with 7-nitroindazole (25 mg/kg, administered intraperitoneally, 30 min after reserpine) attenuated reserpine-induced hypolocomotion 24 h and 48 h after the treatment in Swiss mice, but not completely in C57BL/6 mice. These results suggest that nitric oxide functions as an intercellular messenger in motor circuits in the brain. Moreover, our data suggests that the comparison of such mouse strains may provide information on genetic basis for strain differences in different sensitivity to these drugs.

Inhibition of neuronal nitric oxide synthase reduces isoflurane MAC and motor activity even in nNOS knockout mice

BACKGROUND

The glutamate-nitric oxide-cyclic GMP pathway has been identified as a potential target for volatile anaesthetic agents as acute inhibition of nitric oxide synthase (NOS) reduces the minimum alveolar concentration (MAC) in most animal studies. However, mice deficient in the type I NOS isoform (nNOS) are reported to have a similar MAC for isoflurane and are not affected by non-isoform specific inhibitors.

METHODS

We determined whether the nNOS specific inhibitor, 7-nitroindazole (7-NI), had an effect on isoflurane MAC and righting reflex (RRF) and investigated spontaneous motor activity in an open-field study in wild-type (WT) and knockout (KO) mice.

RESULTS

7-NI reduced isoflurane MAC and RRF in both WT and KO animals (all P<0.04). 7-NI profoundly reduced spontaneous motor activity in both the WT and KO animals in the open-field study as indicated by a reduction in the number of line crossings and rearings in both WT and KO mice (both P<0.001).

CONCLUSION

We conclude that isoform specific inhibition of nNOS reduces MAC and spontaneous motor activity even in nNOS KO animals. Our results indicate that the NMDA receptor-nitric oxide-cyclic GMP pathway remains a credible target in modulating the effects of isoflurane.

Phosphodiesterase inhibition by sildenafil citrate attenuates a maze learning impairment in rats induced by nitric oxide synthase inhibition

RATIONALE

The nitric oxide (NO)-cyclic guanosine monophosphate (cGMP) signal transduction pathway has been implicated in some forms of learning and memory. Recent findings suggest that inhibition of phosphodiesterase (PDE) enzymes that degrade cGMP may have memory-enhancing effects.

OBJECTIVES

We examined whether treatment with sildenafil citrate, a PDE type 5 inhibitor, would attenuate a learning impairment induced by inhibition of NO synthase [60 mg/kg N(omega)-nitro-L-arginine methyl ester (L-NAME), i.p.].

METHODS

Rats were pretrained in a one-way active avoidance of foot shock in a straight runway and, on the next day, received 15 training trials in a 14-unit T-maze, a task that has been shown to be sensitive to aging and impairment of central NO signaling systems. Combined treatments of L-NAME or saline and sildenafil (1.0, 1.5, 3.0, or 4.5 mg/kg, i.p.) or vehicle were given 30 and 15 min before training, respectively. Behavioral measures of performance included entries into incorrect maze sections (errors), run time from start to goal (latency), shock frequency, and shock duration.

RESULTS

Statistical analysis revealed that L-NAME impaired maze performance and that sildenafil (1.5 mg/kg) significantly attenuated this impairment. Control experiments revealed that administration of L-NAME alone did not significantly increase latencies in a one-way active avoidance test and that different doses of sildenafil alone did not significantly alter complex maze performance.

CONCLUSIONS

The results indicate that sildenafil may improve learning by modulating NO-cGMP signal transduction, a pathway implicated in age-related cognitive decline and neurodegenerative disease.

Role of nitric oxide on motor behavior

The present review paper describes results indicating the influence of nitric oxide (NO) on motor control. Our last studies showed that systemic injections of low doses of inhibitors of NO synthase (NOS), the enzyme responsible for NO formation, induce anxiolytic effects in the elevated plus maze whereas higher doses decrease maze exploration. Also, NOS inhibitors decrease locomotion and rearing in an open field arena. These results may involve motor effects of this compounds, since inhibitors of NOS, NG-nitro-L-arginine (L-NOARG), N(G)-nitro-L-arginine methylester (L-NAME), N(G)-monomethyl-L-arginine (L-NMMA), and 7-Nitroindazole (7-NIO), induced catalepsy in mice. This effect was also found in rats after systemic, intracebroventricular or intrastriatal administration. Acute administration of L-NOARG has an additive cataleptic effect with haloperidol, a dopamine D2 antagonist. The catalepsy is also potentiated by WAY 100135 (5-HT1a receptor antagonist), ketanserin (5HT2a and alfal adrenergic receptor antagonist), and ritanserin (5-HT2a and 5HT2c receptor antagonist). Atropine sulfate and biperiden, antimuscarinic drugs, block L-NOARG-induced catalepsy in mice. L-NOARG subchronic administration in mice induces rapid tolerance (3 days) to its cataleptic effects. It also produces cross-tolerance to haloperidol-induced catalepsy. After subchronic L-NOARG treatment there is an increase in the density NADPH-d positive neurons in the dorsal part of nucleus caudate-putamen, nucleus accumbens, and tegmental pedunculupontinus nucleus. In contrast, this treatment decreases NADPH-d neuronal number in the substantia nigra compacta. Considering these results we suggest that (i) NO may modulate motor behavior, probably by interfering with dopaminergic, serotonergic, and cholinergic neurotransmission in the striatum; (ii) Subchronic NO synthesis inhibition induces plastic changes in NO-producing neurons in brain areas related to motor control and causes cross-tolerance to the cataleptic effect of haloperidol, raising the possibility that such treatments could decrease motor side effects associated with antipsychotic medications. Finally, recent studies using experimental Parkinson's disease models suggest an interaction between NO system and neurodegenerative processes in the nigrostriatal pathway. It provides evidence of a protective role of NO. Together, our results indicate that NO may be a key participant on physiological and pathophysiological processes in the nigrostriatal system.

Neuronal nitric oxide synthase knock-out mice show impaired cognitive performance

Nitric oxide (NO) plays a role in a series of neurobiological functions, underlying behavior and memory. The functional role of nNOS derived NO in cognitive functions, however, is elusive. We decided to study cognitive functions in the Morris water maze (MWM) and the multiple T-maze (MTM) in 3-month-old male nNOS-knock-out mice (nNOS KO). To study the influence of neurology and behavior, we performed tests in an observational battery, the rota-rod, the elevated plus maze (EPM), the open field (OF), and a social interaction test. In the memory and relearning task of the MWM, most nNOS KO failed whereas performing better in the MTM. nNOS KO displayed significantly increased frequency of grooming, center crossings, and entries into the center in the OF. The observational battery revealed significantly increased scores for touch-escape reaction, body position, locomotion, and pelvic- and tail-elevation together with reduced vocalization. In the EPM, the time spent in the closed arm and the grooming frequency were significantly increased whereas urination was absent. We conclude that nNOS KO show impaired spatial performance in the MWM and herewith confirm the role of nNOS in cognitive functions such as processing, maintenance, and recall of memory. It must be taken into account that the major behavioral findings of increased grooming and anxiety-related behaviors may have led to impaired function in the MWM. The fact that nNOS KO performed well in the MTM, reflecting a low stress situation points to the interpretation that nNOS inhibition affects cognitive functions under stressful conditions (MWM) only.

Arundic acid, an astrocyte-modulating agent, protects dopaminergic neurons against MPTP neurotoxicity in mice

We examined the neuroprotective effects of a novel astrocyte-modulating agent, arundic acid (ONO-2506), in a 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) mouse model of Parkinson's disease. Male C57BL/6 mice received four intraperitoneal injections of MPTP (20 mg/kg) at 2 h intervals. Dopamine content in the striatum was reduced to 21% of the normal control after 7 days. Treatment with arundic acid (30 mg/kg, i.p.) administered 1 min, 6 h, 24 h, 48 h, and 72 h after the last MPTP injection prevented the dopamine depletion (52% of the control, p<0.01). In addition, this treatment resulted in behavioral benefits. Behavioral testing showed that MPTP-injected mice exhibited motor deficits in the pole test and catalepsy test after 7 days, but arundic acid prevented the appearance of motor abnormalities in these tests. The MPTP-injected animals exhibited an 87% loss of tyrosine hydroxylase-containing dopaminergic neurons in the substantia nigra after 7 days, but the arundic acid-treated mice showed only a 56% reduction (p<0.01). GFAP-positive reactive astrocytes were accumulated in the striatum and substantia nigra 7 days after the MPTP injection, whereas arundic acid treatment induced an earlier appearance of reactive astrocytes by 3 days. The reactive astrocytes increased the production of S-100 protein, which is thought to promote neuronal damage, but arundic acid suppressed the expression of S-100. Thus, arundic acid protected dopaminergic neurons against MPTP neurotoxicity in mice and ameliorated neurological deficits. The results suggest that the neuroprotection is mediated through the modulation of astrocytic activation, including the inhibition of S-100 protein synthesis.

Nitric Oxide Synthesis Inhibition Attenuates Conditioned Reinstatement of Ethanol-Seeking, but Not the Primary Reinforcing Effects of Ethanol

BACKGROUND

Nitric oxide (NO) signaling has been implicated in regulating aspects of the reinforcing and addictive actions of cocaine. These experiments were designed to examine whether NO-dependent neurotransmission also participates in mediating the addictive actions of another drug of abuse, ethanol, with emphasis on both the primary reinforcing effects of ethanol and the incentive motivational effects of ethanol-related contextual stimuli.

METHODS

Male Wistar rats were operantly trained to orally self-administer 10% (w/v) ethanol in daily 30-min sessions and to associate distinct discriminative stimuli with the availability of ethanol (S+) versus nonreward (S-). Rats were treated with the NO synthase inhibitor NG-nitro-L-arginine methyl ester (L-NAME; 0, 10, or 40 mg/kg intraperitoneally) 30 min before self-administration tests that were conducted after establishment of stable levels of daily ethanol intake and conditioned reinstatement tests that were performed after extinction of ethanol-maintained operant responding.

RESULTS

L-NAME did not alter the primary reinforcing effects of ethanol in self-administration tests. In contrast, L-NAME dose-dependently attenuated the recovery of extinguished responding induced by the ethanol S in the absence of ethanol availability during reinstatement tests.

CONCLUSIONS

These results suggest that the NO system does not play a role in behavior reinforced directly by ethanol. However, the results implicate NO-dependent neurotransmission in alcohol-seeking responses elicited by drug-related contextual stimuli.

Biochemical, behavioral and immunohistochemical alterations in MPTP-treated mouse model of Parkinson's disease

The biochemical, behavioral and immunohistochemical manifestations were investigated in mice subjected to four experimental schedules with 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP) hydrochloride treatment. The mice were treated intraperitoneally with MPTP (20 mg/kg in saline) four times a day at 2-h intervals showed severe and persistent depletions of dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) in the striatum and behavioral deficits, as compared with those (1) treated with MPTP (15 mg/kg in saline ip) once a day for 14 consecutive days; (2) MPTP (30 mg/kg in saline ip) twice a day for five consecutive days; and (3) MPTP (10 mg/kg in saline ip) four times a day at 1-h intervals for two consecutive days. The immunohistochemical study has shown that the acute treatment with MPTP caused severe loss of tyrosine hydroxylase (TH)- and dopamine transporter (DAT)-immunoreactive dopaminergic neurons and marked increase in glial fibrillary acidic protein (GFAP)-immunoreactive astrocytes in the striatum and the substantia nigra. Thus acute treatment of mice with MPTP was accompanied by sustained nigral degeneration and motor abnormalities. Furthermore, our results with Cu/Zn-superoxide dismutase (Cu/Zn-SOD) and manganese superoxide dismutase (Mn-SOD) immunostainings suggest that altered capacity of free radicals quenching may play a key role in the development of the neurons and interneuron damage after MPTP neurotoxicity. Thus, our findings provide valuable information on age-related disease progression and mechanisms of neurodegeneration.

Catalepsy induced by intra-striatal administration of nitric oxide synthase inhibitors in rats

Systemic administration of nitric oxide synthase (NOS) inhibitors induces catalepsy in a dose-dependent manner in male Albino-Swiss mice. The objective of the present work was to investigate if similar effects occur in rats and if these effects are centrally mediated. The results showed that systemic administration of N(G)-nitro-L-arginine (L-NOARG, 40-160 mg/kg, i.p.), a non-selective NOS inhibitor, induced catalepsy in rats. Similar effects were found after intracerebroventricular (i.c.v.) injection of L-NOARG (50-200 nmol) or N(G)-nitro-L-arginine methylester (L-NAME, 100-200 nmol). The dose-response curve of the former compound, however, had an inverted U shape. The effect of L-NOARG (100 nmol, i.c.v.) was completely prevented by pre-treatment with L-arginine (300 nmol, i.c.v.) but not by D-arginine (300 nmol, i.c.v.). Intra-striatal injection of N(G)-monomethyl-L-arginine (L-NMMA, 100 nmol), 7-nitroindazole (7-NIO, 100 nmol), L-NOARG (25-100 nmol) or L-NAME (50-200 nmol) also induced catalepsy. Similar to i.c.v. administration, the latter two compounds produced bell-shaped dose-response curves. The cataleptic effect of intra-striatal administration of L-NAME (100 nmol) was reversed by local treatment with L-arginine (100 nmol). These results suggest that interference with the striatal formation of nitric oxide may induce significant motor effects in rats.

Serotonergic mediation of the antidepressant-like effects of nitric oxide synthase inhibitors

Recent studies indicate that nitric oxide (NO) synthase inhibitors have antidepressant-like potential in various animal models. In the present study the behavioural activity of the NO synthase inhibitors, N(G)-nitro-L-arginine (L-NA) and 7-nitroindazole (7-NI), were assessed in a modified rat forced swimming test (FST). Both L-NA and 7-NI, dose dependently reduced immobility and increased swimming behaviour in the rat FST. This behavioural profile parallels the one previously shown with selective serotonin re-uptake inhibitors and serotonergic agonists. Thus, we examined the role of serotonin mediating the behavioural effects of L-NA and 7-NI in the rat FST. Depletion of endogenous serotonin using para-chlorophenylalanine (pCPA; 3 x 150 mg/kg, i.p.) completely blocked L-NA (20 mg/kg, i.p.) and 7-NI (20 mg/kg, i.p.)-induced reductions in immobility and increases in swimming behaviour during the FST. In conclusion these observations suggest that NO synthase inhibitors elicit their antidepressant-like activity in the modified swimming test through a serotonin dependent mechanism.

Antidepressant- and anxiolytic-like effects of selective neuronal NOS inhibitor 1-(2-trifluoromethylphenyl)-imidazole in mice

Various inhibitors of nitric oxide synthase (NOS) have been shown to possess antidepressant- and anxiolytic-like properties in animal models. The aim of this study was to compare the behavioural effects of NOS inhibitor 7-nitroindazole (7-NI) with the more selective neuronal NOS inhibitor 1-(2-trifluoromethylphenyl)imidazole (TRIM) in animal models predictive of antidepressant- and anxiolytic-like activity in order to clarify the role of distinct isoforms of NOS in the regulation of depression and anxiety. Both TRIM (50 mg/kg) and 7-NI (50 mg/kg) decreased the immobility time in the forced swimming test. The magnitude of the effect was comparable to that of the tricyclic antidepressant imipramine (15 mg/kg). The antidepressant-like effect of TRIM was counteracted by pretreatment with L-arginine (250 mg/kg). The systemic administration of TRIM (50 mg/kg), but not 7-NI (up to 50 mg/kg) increased the time spent in the light side of the apparatus in the light-dark compartment test. The anxiolytic-like effect of TRIM was antagonised by pretreatment with L-arginine. Both TRIM and 7-NI decreased the locomotion of animals in the open field and caused motor incoordination on rotarod. These motor side effects were more pronounced in the case of 7-NI and were not diminished by pretreatment with L-arginine. We conclude that neuronal NOS seems to play the key role in the antidepressant- and anxiolytic-like effects of NOS inhibitors.

Effects of Ca2+ antagonists on motor activity and the dopaminergic system in aged mice

We investigated the effects of the Ca(2+) antagonist nilvadipine on the dopaminergic system and motor activity in aged mice, in comparison with an other Ca(2+) antagonist, amlodipine. Furthermore, we examined the close correlation between the dopaminergic system and motor activity during the aging process. Striatal dopamine, 3,4-dihydroxyphenylacetic acid (DOPAC) and homovanillic acid (HVA) contents were measured in 2-, 4-, 8-, 18- and 36-week-old mice. Behavioral tests (pole and catalepsy test) were performed with 4- and 36-week-old mice. Nilvadipine or amlodipine was administered intraperitoneally twice a day for 3 consecutive days to 30-36-week-old mice. The striatal dopamine, DOPAC and HVA contents were examined and behavioral tests were performed 1h after the last injection of each Ca(2+) antagonist. The dopamine, DOPAC and HVA contents in 2-week-old mice were significantly decreased in the striatum, as compared with 4-week-old animals. Thereafter, age-related increases in the dopamine, DOPAC and HVA contents were observed from 4 to 18 weeks old. However, in 36-week-old mice, the dopamine and DOPAC contents were reduced in the striatum, as compared with 18-week-old animals. Age-related decreases in motor function between 5- and 36-week-old mice were observed in both pole test and catalepsy tests. On the other hand, nilvalipine treatment produced a significant and dose-dependent increase in the striatal dopamine and DOPAC contents in 30-36-week-old mice. In contrast, no significant changes were observed in the striatal dopamine content in amlodipine-treated mice, although this drug showed a significant and dose-dependent increase in the striatal DOPAC and HVA content. In our behavioral study, nilvadipine also showed a significant and dose-dependent inhibition against motor deficits in 30-36-week-old mice. In contrast, amlodipine showed no significant effect on motor deficits in 30-36-week-old mice. The present study demonstrated that nilvadipine has a protective effect against the deficits in both the striatal dopaminergic system and motor activity in aged mice. Our study also suggested that the beneficial effect of nilvadipine against motor abnormalities may be mediated by a protective effect against the reduced activity of the dopaminergic system in aged mice. These results suggested that nilvadipine may offer a new approach for the treatment of hypobulia in aged humans.

Age-related changes of the nitric oxide system in the rat brain

This work examines the age-related changes of the NO pathway in the central nervous system (CNS), analyzing nitric oxide synthase (NOS) isoform expression, the level of nitrotyrosine-modified proteins, and the NOS activity in the cerebral cortex, decorticated brain (basal ganglia, thalamus, hypothalamus, tegtum and tegmentum) and cerebellum of young, adult and aged rats. Our data demonstrate that the different NOS isoforms are not uniformly expressed across the CNS. In this sense, the nNOS and eNOS isoenzymes are expressed mainly in the cerebellum and decorticated brain, respectively, while the iNOS isoenzyme shows the highest level in cerebellum. Concerning age, in the cerebral cortex nNOS significantly increased its expression only in adult animals; meanwhile, in the cerebellum the eNOS expression decreased whereas iNOS increased in adult and aged rats. No age-related changes in any isoform were found in decorticated brain. NOS activity, determined by nitrate plus nitrite quantification, registered the highest levels in the cerebellum, where the significant increase detected with aging was probably related to iNOS activity. The number of nitrotyrosine-modified immunoreactive bands differed among regions; thus, the highest number was detected in the decorticated brain while the cerebellum showed the least number of bands. Finally, bulk protein nitration increased in cerebral cortex only in adult animal. No changes were found in the decorticated brain, and the decrease detected in the cerebellum of aged animals was not significant. According to these results, the NO pathway is differently modified with age in the three CNS regions analyzed.

Therapeutic effect of neuronal nitric oxide synthase inhibitor (7-nitroindazole) against MPTP neurotoxicity in mice

Effects of neuronal nitric oxide synthase (nNOS) inhibitor (7-nitroindazole), nonselective NOS inhibitor (N(G)-nitro-L-arginine methyl ester; L-NAME), and monoamine oxidase inhibitor (pargyline) were studied on 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-treated mice. The mice received four intraperitoneal injections of MPTP at 1-h intervals. A significant depletion in dopamine and DOPAC concentration was observed in the striatum from 1 day after MPTP treatment. The pretreatment of 7-nitroindazole and pargyline, but not L-NAME, dose-dependently protected against MPTP-induced depletion in dopamine content 3 days after MPTP treatment. Our histochemical study also showed that 7-nitroindazole and pargyline can prevent a marked decrease in the nigral cells and a marked increase in astrocytes in striatum 7 days after MPTP treatment. The protective effect of 7-nitroindazole against MPTP-induced dopamine and DOPAC depletion in the striatum was not attenuated by intraperitoneal pretreatment with L-arginine. Furthermore, the posttreatment of 7-nitroindazole or pargyline protected against MPTP-induced depletion of dopamine content. These results demonstrate that the protective mechanism by which 7-nitroindazole counteracts MPTP neurotoxicity in mice may be due not only to inhibition of nNOS, but also to MAO-B inhibition. Furthermore, our study suggests that the posttreatment of 7-nitroindazole and pargyline can prevent a significant decrease in dopamine levels in the striatum of MPTP-treated mice. These findings have important implications for the therapeutic time window and choice of nNOS or MAO inhibitors in patients with Parkinson's disease.