Activation of constitutive nitric oxide synthase(s) and absence of inducible isoform in aged rat brain

Decreased Hippocampal Neurogenesis in Aged Male Wistar Rats Is Not Associated with Memory Acquisition in a Water Maze

Brain aging is associated with a progressive decrease in learning abilities, memory, attention, decision making, and sensory perception. Age-related cognitive disturbances may be related to a decrease in the functional capacities of the hippocampus. This brain region is essential for learning and memory, and the lifelong neurogenesis occurring in the subgranular zone of the dentate gyrus may be a key event mediating the mnemonic functions of the hippocampus. In the present study, we investigated whether age-related changes in hippocampal neurogenesis are associated with learning and memory disturbances. Four- and 24-month-old rats were trained to find a hidden platform in a water maze. Though the older group showed higher latency to search the platform as compared to the younger group, both groups learned the task. However, the density of proliferating (PCNA-positive), differentiating (Dcx-positive), and new neurons (pre-labeled BrdU-positive) was significantly lower in the hippocampus of aged rats as compared to young ones. This inhibition of neurogenesis could be related to increased local production of nitric oxide since the density of neurons expressing neuronal NO-synthase was higher in the aged hippocampus. Thus, we can suggest that an age-related decrease in neurogenesis is not directly associated with place learning in aged rats.

Alterations in cyclic nucleotide signaling are implicated in healthy aging and age-related pathologies of the brain

It is not only important to consider how hormones may change with age, but also how downstream signaling pathways that couple to hormone receptors may change. Among these hormone-coupled signaling pathways are the 3',5'-cyclic guanosine monophosphate (cGMP) and 3',5'-cyclic adenosine monophosphate (cAMP) intracellular second messenger cascades. Here, we test the hypothesis that dysfunction of cAMP and/or cGMP synthesis, execution, and/or degradation occurs in the brain during healthy and pathological diseases such as Alzheimer's disease, Parkinson's disease, and Huntington's disease. Although most studies report lower cyclic nucleotide signaling in the aged brain, with further reductions noted in the context of age-related diseases, there are select examples where cAMP signaling may be elevated in select tissues. Thus, therapeutics would need to target cAMP/cGMP in a tissue-specific manner if efficacy for select symptoms is to be achieved without worsening others.

The bioactivity of neuronal-derived nitric oxide in aging and neurodegeneration: Switching signaling to degeneration

The small and diffusible free radical nitric oxide (^•NO) has fascinated biological and medical scientists since it was promoted from atmospheric air pollutant to biological ubiquitous signaling molecule. Its unique physical chemical properties expand beyond its radical nature to include fast diffusion in aqueous and lipid environments and selective reactivity in a biological setting determined by bioavailability and reaction rate constants with biomolecules. In the brain, ^•NO is recognized as a key player in numerous physiological processes ranging from neurotransmission/neuromodulation to neurovascular coupling and immune response. Furthermore, changes in its bioactivity are central to the molecular pathways associated with brain aging and neurodegeneration. The understanding of ^•NO bioactivity in the brain, however, requires the knowledge of its concentration dynamics with high spatial and temporal resolution upon stimulation of its synthesis. Here we revise our current understanding of the role of neuronal-derived ^•NO in brain physiology, aging and degeneration, focused on changes in the extracellular concentration dynamics of this free radical and the regulation of bioenergetic metabolism and neurovascular coupling.

Cyclic nucleotide signaling changes associated with normal aging and age-related diseases of the brain

Deficits in brain function that are associated with aging and age-related diseases benefit very little from currently available therapies, suggesting a better understanding of the underlying molecular mechanisms is needed to develop improved drugs. Here, we review the literature to test the hypothesis that a break down in cyclic nucleotide signaling at the level of synthesis, execution, and/or degradation may contribute to these deficits. A number of findings have been reported in both the human and animal model literature that point to brain region-specific changes in Galphas (a.k.a. Gαs or Gsα), adenylyl cyclase, 3',5'-adenosine monophosphate (cAMP) levels, protein kinase A (PKA), cAMP response element binding protein (CREB), exchange protein activated by cAMP (Epac), hyperpolarization-activated cyclic nucleotide-gated ion channels (HCNs), atrial natriuretic peptide (ANP), brain natriuretic peptide (BNP), soluble and particulate guanylyl cyclase, 3',5'-guanosine monophosphate (cGMP), protein kinase G (PKG) and phosphodiesterases (PDEs). Among the most reproducible findings are 1) elevated circulating ANP and BNP levels being associated with cognitive dysfunction or dementia independent of cardiovascular effects, 2) reduced basal and/or NMDA-stimulated cGMP levels in brain with aging or Alzheimer's disease (AD), 3) reduced adenylyl cyclase activity in hippocampus and specific cortical regions with aging or AD, 4) reduced expression/activity of PKA in temporal cortex and hippocampus with AD, 5) reduced phosphorylation of CREB in hippocampus with aging or AD, 6) reduced expression/activity of the PDE4 family in brain with aging, 7) reduced expression of PDE10A in the striatum with Huntington's disease (HD) or Parkinson's disease, and 8) beneficial effects of select PDE inhibitors, particularly PDE10 inhibitors in HD models and PDE4 and PDE5 inhibitors in aging and AD models. Although these findings generally point to a reduction in cyclic nucleotide signaling being associated with aging and age-related diseases, there are exceptions. In particular, there is evidence for increased cAMP signaling specifically in aged prefrontal cortex, AD cerebral vessels, and PD hippocampus. Thus, if cyclic nucleotide signaling is going to be targeted effectively for therapeutic gain, it will have to be manipulated in a brain region-specific manner.

Aqueous root extract of Asparagus cochinchinensis (Lour.) Merr. Has antioxidant activity in D-galactose-induced aging mice

Background

Extracts of plants have been considered as sources of natural antioxidant agents. In this study, we aimed to explore the antioxidant capacity of the aqueous root extract of Asparagus cochinchinensis (Lour.) Merr.

Methods

Using vitamin C (Vc) as a positive control, we analyzed the aqueous root extract of A. cochinchinensis free radical scavenging ability in vitro. We also established a mouse aging model using D-galactose and then treated it with aqueous root extract or Vc. The blood cell count and superoxide dismutase (SOD), catalase (CAT), and nitric oxide synthase (NOS) activities as well as malondialdehyde (MDA) and nitric oxide (NO) contents were measured; pathological examination of tissues was performed; and SOD, glutathione peroxidase (GPX), and NOS expression levels in the serum, liver, and brain tissues were investigated.

Results

In vitro, compared with the antioxidant Vc, the aqueous root extract showed similar 1,1-Diphenyl-2-picrylhydrazyl radical and 3-ethylbenzothiazoline-6-sulfonic·scavenging activities and even significantly increased superoxide anion (p < 0.05) and hydroxyl radical (OH) (p < 0.01) scavenging activities. The aqueous extract significantly increased the white blood cell count as well as enhanced SOD, CAT, and NOS activities (p < 0.01) in aging mice. In addition, the aqueous extract increased the NO content (p < 0.05) and reduced the MDA content (p < 0.05).

Conclusions

The aqueous root extract of A. cochinchinensis showed as strong antioxidant ability as Vc and might prevent aging by reducing radicals.

Protective effect of curcuminoids on age-related mitochondrial impairment in female Wistar rat brain

The present study demonstrated the neuroprotective effect of curcuminoids, the active polyphenols of Curcuma longa (L.) rhizomes on mitochondrial dysfunctioning in middle aged and aged female Wistar rat brain. Rats were orally treated with curcuminoids (100 mg/kg) for 3 months and their brain was collected for evaluation of mitochondrial enzymes and complexes activity, ultra structural changes in mitochondria, neuronal nitric oxide synthase (nNOS) protein expression, adenosine triphosphate (ATP) and lipofuscin content. Significant alterations were observed in all the tested parameters in highly aged rat brain when compared with young control. Long term curcuminoids administration prevented this age associated loss of mitochondrial enzymes and complexes activity in middle aged rat brain except for malate dehydrogenase, Complex II and IV activity when compared with young control. Among aged rats, curcuminoids treatment specifically elevated isocitrate and NADH dehydrogenase, cytochrome c oxidase, Complex I and total ATP content. A significant down-regulation of nNOS protein expression along with reduced lipofuscin content was also observed in curucminoids treated middle aged and aged rats. Thus, it was suggested that curcuminoids may act as a putative drug candidate for the prevention of deleterious effects of ageing and age associated neurodegenerative disorders through amelioration of aberrant mitochondrial functioning.

The potential role of ozone in ameliorating the age-related biochemical changes in male rat cerebral cortex

Controlled ozone (O(3)) administration is known to promote oxidative preconditioning and, thus, may reverse chronic oxidative stress that accompanies aging. Therefore, the present work was undertaken to study the potential role of O(3) in ameliorating certain age-related biochemical changes represented by impaired activities of inner mitochondrial membrane enzymes, compromised energy production and increased oxidative burden in male rat cerebral cortex. Prophylactic administration of O(3)-O(2) mixture to 3 month-old rats, at an intrarectal dose of 0.6 mg O(3) kg(-1) body weight twice/week for 3 months then once/week until the age of 15 months, normalized reduced glutathione content, adenosine triphosphate/adenosine diphosphate ratio, mitochondrial superoxide dismutase (SOD) and complex IV (cytochrome-c oxidase) activities, improved glutathione redox index (GSHRI), complex I (NADH-ubiquinone oxidoreductase) and mitochondrial nitric oxide synthase (mtNOS) activities, and attenuated the rise in malondialdehyde (MDA) and mitochondrial protein carbonyl levels. On the other hand, therapeutic administration of the same dose of O(3)-O(2) mixture to 14 month-old rats three times/week for 1 month, reduced mitochondrial protein carbonyl level only. Other favorable effects, including normalization of Na,K-adenosine triphosphatase (Na,K-ATPase) activity and reduction in lipofuscin level in the prophylactic group, as well as improvement in mitochondrial SOD and complex I activities with a decrease in total MDA level in the therapeutic group, were comparable to the effects observed in the corresponding O(2)-treated control groups. In conclusion, the present study revealed that prophylactic administration of O(3)-O(2) mixture provided better amelioration of age-related cerebrocortical alterations by combining the advantages of both O(3) and O(2) therapies.

Insights into mitochondrial dysfunction: aging, amyloid-β, and tau-A deleterious trio

SIGNIFICANCE

Alzheimer's disease (AD) is an age-related progressive neurodegenerative disorder mainly affecting elderly individuals. The pathology of AD is characterized by amyloid plaques (aggregates of amyloid-β [Aβ]) and neurofibrillary tangles (aggregates of tau), but the mechanisms underlying this dysfunction are still partially unclear.

RECENT ADVANCES

A growing body of evidence supports mitochondrial dysfunction as a prominent and early, chronic oxidative stress-associated event that contributes to synaptic abnormalities and, ultimately, selective neuronal degeneration in AD.

CRITICAL ISSUES

In this review, we discuss on the one hand whether mitochondrial decline observed in brain aging is a determinant event in the onset of AD and on the other hand the close interrelationship of this organelle with Aβ and tau in the pathogenic process underlying AD. Moreover, we summarize evidence from aging and Alzheimer models showing that the harmful trio "aging, Aβ, and tau protein" triggers mitochondrial dysfunction through a number of pathways, such as impairment of oxidative phosphorylation (OXPHOS), elevation of reactive oxygen species production, and interaction with mitochondrial proteins, contributing to the development and progression of the disease.

FUTURE DIRECTIONS

The aging process may weaken the mitochondrial OXPHOS system in a more general way over many years providing a basis for the specific and destructive effects of Aβ and tau. Establishing strategies involving efforts to protect cells at the mitochondrial level by stabilizing or restoring mitochondrial function and energy homeostasis appears to be challenging, but very promising route on the horizon.

Nos2 inactivation promotes the development of medulloblastoma in Ptch1(+/-) mice by deregulation of Gap43-dependent granule cell precursor migration

Medulloblastoma is the most common malignant brain tumor in children. A subset of medulloblastoma originates from granule cell precursors (GCPs) of the developing cerebellum and demonstrates aberrant hedgehog signaling, typically due to inactivating mutations in the receptor PTCH1, a pathomechanism recapitulated in Ptch1^+/− mice. As nitric oxide may regulate GCP proliferation and differentiation, we crossed Ptch1^+/− mice with mice lacking inducible nitric oxide synthase (Nos2) to investigate a possible influence on tumorigenesis. We observed a two-fold higher medulloblastoma rate in Ptch1^+/− Nos2^−/− mice compared to Ptch1^+/− Nos2^+/+ mice. To identify the molecular mechanisms underlying this finding, we performed gene expression profiling of medulloblastomas from both genotypes, as well as normal cerebellar tissue samples of different developmental stages and genotypes. Downregulation of hedgehog target genes was observed in postnatal cerebellum from Ptch1^+/+ Nos2^−/− mice but not from Ptch1^+/− Nos2^−/− mice. The most consistent effect of Nos2 deficiency was downregulation of growth-associated protein 43 (Gap43). Functional studies in neuronal progenitor cells demonstrated nitric oxide dependence of Gap43 expression and impaired migration upon Gap43 knock-down. Both effects were confirmed in situ by immunofluorescence analyses on tissue sections of the developing cerebellum. Finally, the number of proliferating GCPs at the cerebellar periphery was decreased in Ptch1^+/+ Nos2^−/− mice but increased in Ptch1^+/− Nos2^−/− mice relative to Ptch1^+/− Nos2^+/+ mice. Taken together, these results indicate that Nos2 deficiency promotes medulloblastoma development in Ptch1^+/− mice through retention of proliferating GCPs in the external granular layer due to reduced Gap43 expression. This study illustrates a new role of nitric oxide signaling in cerebellar development and demonstrates that the localization of pre-neoplastic cells during morphogenesis is crucial for their malignant progression.

Medulloblastoma is a common pediatric brain tumor, a subtype of which is driven by aberrant hedgehog pathway activation in cerebellar granule cell precursors. Although this tumor etiology has been intensively investigated in the well-established Ptch1^+/− mouse model, knowledge is still lacking about the molecular interactions between neoplastic transformation and other developmental processes. Nitric oxide (NO) has been reported to be involved in controlling proliferation and differentiation of these cells. Therefore, inactivation of the NO–producing enzyme Nos2 in combination with the mutated Ptch1 gene should provide insight into how developmental regulation influences pathogenesis. Here, we describe a new role for NO in developing neuronal precursors of the cerebellum facilitating physiologically accurate migration via regulation of Gap43. We further demonstrate that disturbance of these processes leads to retention of granule precursor cells to the cerebellar periphery. Together with the sustained proliferation of these cells in combined Ptch1^+/− Nos2^−/− mice, this effect results in an increased medulloblastoma incidence relative to Ptch1^+/− mice and demonstrates a new disease-promoting mechanism in this tumor entity.

Study of the nitric oxide system in the rat cerebellum during aging

Background

The cerebellum is the neural structure with the highest levels of nitric oxide, a neurotransmitter that has been proposed to play a key role in the brain aging, although knowledge concerning its contribution to cerebellar senescence is still unclear, due mainly to absence of integrative studies that jointly evaluate the main factors involved in its cell production and function. Consequently, in the present study, we investigate the expression, location, and activity of nitric oxide synthase isoenzymes; the protein nitration; and the production of nitric oxide in the cerebellum of adult and old rats.

Results

Our results show no variation in the expression of nitric oxide synthase isoforms with aging, although, we have detected some changes in the cellular distribution pattern of the inducible isoform particularly in the cerebellar nuclei. There is also an increase in nitric oxide synthase activity, as well as greater protein-nitration levels, and maintenance of nitrogen oxides (NOx) levels in the senescent cerebellum.

Conclusions

The nitric oxide/nitric oxide syntahses system suffers from a number of changes, mainly in the inducible nitric oxide synthase distribution and in overall nitric oxide synthases activity in the senescent cerebellum, which result in an increase of the protein nitration. These changes might be related to the oxidative damage detected with aging in the cerebellum.

Cyclic GMP and nitric oxide synthase in aging and Alzheimer's disease

Cyclic guanosine monophosphate (cGMP) is an important secondary messenger synthesized by the guanylyl cyclases which are found in the soluble (sGC) and particular isoforms. In the central nervous system, the nitric oxide (NO)-sensitive sGC isoform is the major enzyme responsible for cGMP synthesis. Phosphodiesterases (PDEs) are enzymes for hydrolysis of cGMP in the brain, and they are mainly isoforms 2, 5, and 9. The NO/cGMP signaling pathway has been shown to play an important role in the process underlying learning and memory. Aging is associated with an increase in PDE expression and activity and a decrease in cGMP concentration. In addition, aging is also associated with an enhancement of neuronal NO synthase, a lowering of endothelial, and no alteration in inducible activity. The observed changes in NMDA receptor density along with the Ca(2+)/NO/cGMP pathway underscore the lower synaptic plasticity and cognitive performance during aging. This notion is in agreement with last data indicating that inhibitors of PDE2 and PDE9 improve learning and memory in older rats. In this review, we focus on recent studies supporting the role of Ca(2+)/NO/cGMP pathway in aging and Alzheimer's disease.

Aging-dependent changes of microglial cells and their relevance for neurodegenerative disorders

Among multiple structural and functional brain changes, aging is accompanied by an increase of inflammatory signaling in the nervous system as well as a dysfunction of the immune system elsewhere. Although the long-held view that aging involves neurocognitive impairment is now dismissed, aging is a major risk factor for neurodegenerative diseases such as Alzheimer;s disease, Parkinson;s disease and Huntington's disease, among others. There are many age-related changes affecting the brain, contributing both to certain declining in function and increased frailty, which could singly and collectively affect neuronal viability and vulnerability. Among those changes, both inflammatory responses in aged brains and the altered regulation of toll like receptors, which appears to be relevant for understanding susceptibility to neurodegenerative processes, are linked to pathogenic mechanisms of several diseases. Here, we review how aging and pro-inflammatory environment could modulate microglial phenotype and its reactivity and contribute to the genesis of neurodegenerative processes. Data support our idea that age-related microglial cell changes, by inducing cytotoxicity in contrast to neuroprotection, could contribute to the onset of neurodegenerative changes. This view can have important implications for the development of new therapeutic approaches.

Compromised proteasome degradation elevates neuronal nitric oxide synthase levels and induces apoptotic cell death

The significance of impairment of proteasome activity in PC12 cells was examined in connection with nitrative/nitrosative stress and apoptotic cell death. Treatment of differentiated PC12 cells with MG132, a proteasome inhibitor, elicited a dose- and time-dependent increase in neuronal nitric oxide synthase (nNOS) protein levels, decreased cell viability, and increased cytotoxicity. Viability and cytotoxicity were ameliorated by L-NAME (a broad NOS inhibitor). Nitric oxide/peroxynitrite formation was increased upon treatment of PC12 cells with MG132 and decreased upon treatment with the combination of MG132 and 7-NI (a specific inhibitor of nNOS). The decreases in cell viability appeared to be effected by an activation of JNK and its effect on mitochondrial Bcl-x(L) phosphorylation. These effects are strengthened by the activation of caspase-9 along with increased caspase-3 activity upon treatment of PC12 cells with MG132. These results suggest that impairment of proteasome activity and consequent increases in nNOS levels lead to a nitrative stress that involves the coordinated response of JNK cytosolic signaling and mitochondrion-driven apoptotic pathways.

The effect of selective inhibition of cyclic GMP hydrolyzing phosphodiesterases 2 and 5 on learning and memory processes and nitric oxide synthase activity in brain during aging

Our previous studies have shown that there is a lower cGMP concentration in the aged brain as well as an alteration in the activity of cGMP-hydrolyzing phosphodiesterases (PDEs) and nitric oxide synthase (NOS). The aim of this study was to investigate the effect of specific inhibitors of selected PDEs on object recognition memory and locomotor activity during aging, and to correlate their action with NOS activity in the following brain regions: hippocampus, striatum, and cerebral cortex. The study was carried out using 3, 12, and 24 month-old rats. Inhibitors of PDE2 and PDE5 (Bayer 60-7550 and zaprinast, respectively) were used. Evaluation of memory and locomotor activity was carried out using an object recognition task and the open field test. NOS activity was determined using a radiochemical method after behavioral analysis in the cytosolic fraction from all brain areas investigated. We have found that the inhibitor of PDE2, Bay60-7550, improves object recognition memory in all age groups investigated and increases basal constitutive NOS activity in the hippocampus and striatum. Moreover, in 3 month-old rats, additional inhibition of PDE5 by zaprinast improves object memory and elevates NOS activity in all brain regions studied. Specific inhibition of nNOS eliminates the effect of Bay60-7550 on memory function and on NOS activity in 24 month-old rats. In summary, our results indicate that inhibition of PDE2 is able to improve cognition and memory function in 3, 12, and 24 month-old rats through the enhancement of nNOS activity in the brain, whereas inhibition of PDE5 is effective only in 3 month-old animals.

Role of nitric oxide in the brain during lipopolysaccharide-evoked systemic inflammation

Although the inducible isoform of nitric oxide synthase (iNOS) is a well-established source of nitric oxide (NO*) during inflammation of the central nervous system (CNS), little is known about the involvement of constitutive isoforms of NOS (cNOS) in the inflammatory process. The aim of this study was to compare the responses of the expression and activity of iNOS and the two cNOS isoforms, neuronal and endothelial (nNOS and eNOS, respectively), in the brain to systemic inflammation and their roles in the cascade of events leading to degeneration and apoptosis. A systemic inflammatory response in C57BL/6 mice was induced by intraperitoneal injection of lipopolysaccharide [LPS; 1 mg/kg body weight (b.w.)]. The relative roles of the NOS isoforms were evaluated after injection of NG-nitro-L-arginine (NNLA; 30 mg/kg b.w.), which preferentially inhibits cNOS, or 1400W (5 mg/kg b.w.), an inhibitor of iNOS. Biochemical and morphological alterations were analyzed up to 48 hr after administration of LPS. Systemic LPS administration evoked significant ultrastructural alterations in brain capillary vessels, neuropils, and intracellular organelles of neurons, astrocytes, and microglia. Apoptotic/autophagic processes occurred in many neurons of the substantia nigra (SN), which coincided with exclusive enhancement of iNOS expression and activity in this brain region. Moreover, inhibitors of both iNOS and cNOS prevented LPS-evoked release of apoptosis-inducing factor (AIF) from SN mitochondria. Collectively, the results indicate that synthesis of NO* by both the inducible and constitutive NOS isoforms contribute to the activation of apoptotic pathways in the brain during systemic inflammation.

Oxidative state in platelets and erythrocytes in aging and Alzheimer's disease

Several studies have shown involvement of peroxynitrite anion, a potent oxidative agent, in Alzheimer's disease (AD) neuropathology. Herein, we assessed in platelets and erythrocytes of AD patients, age-matched and young adults controls: thiobarbituric acid-reactive substances (TBARS) production; superoxide dismutase (SOD), nitric oxide synthase (NOS) and Na,K-ATPase activities; cyclic GMP (cGMP) content, both basal and after sodium nitroprusside (SNP) stimulation. Aging was associated with an increase in TBARS production and NOS activity, a decrease in basal cGMP content and no change in SOD and Na,K-ATPase activities. AD patients, compared to aged controls, have: increase in TBARS production and in NOS, SOD and Na,K-ATPase activities but no alteration in basal cGMP content. SNP increased cGMP platelets production in all groups. In conclusion, we demonstrated in platelets and erythrocytes a disruption in systemic modulation of oxidative stress in aging and with more intensity in AD.

Age-related alteration of activity and gene expression of endothelial nitric oxide synthase in different parts of the brain in rats

Nitric oxide (NO) plays important roles in aging and neurodegeneration. Our previous results indicated that aging differently affects NOS isoforms. Expression of nNOS mRNA was lower while iNOS was absent at any age. However, total NO synthesis increased in aged cerebral cortex and cerebellum as a consequence of changes of nNOS phosphorylation state. The question arise how aging influences activity and expression of eNOS in different parts of adult and aged brain. The levels of eNOS mRNA, protein and activity were measured using RT-PCR, immuno- and radiochemical methods, respectively. Our studies indicated that after inhibition of nNOS with 7-nitroindazole (7-NI) NO synthesis is lower in all parts of aged brain comparing to adults. However, eNOS activity significantly decreases only in cerebellum. The expression of eNOS determined on mRNA level was enhanced in all investigated aged brain parts to 140-190% of adult value and the data were statistically significant for cerebral cortex and cerebellum. The higher level of mRNA is probably the adaptive response to lower NOS activity. However, the Western-blot signal of eNOS protein was unchanged in aged brain parts comparing to adults suggesting age-related disturbances of protein synthesis and its function. It is also possible that a post-translational modification of the enzyme occurs in the aged rat brain. The lower eNOS activity in aged brain may significantly affects the signal transduction processes on the pathway NO/cGMP/PKG.

Hippocampal nitric oxide synthase and arginase and age-associated behavioral deficits

The present study investigated age-related changes in nitric oxide synthase (NOS) and arginase in the subregions of the hippocampus and their correlations with animals' performance in the open field, T-maze, and water maze tasks. Aged rats (24 months old) showed reduced exploratory activity and poorer spatial learning relative to the young adults (4 months old). Significant increases in total NOS activity were found in the aged dentate gyrus and a dramatic decrease in endothelial NOS expression was observed in the aged CA2/3. Activity or protein expression of inducible NOS was not detected in any subregion of the hippocampus. There were no age-related changes in total arginase activity or arginase I and arginase II protein expression. Correlation analysis revealed that animals' motor ability was associated with CA1 NOS and arginase, as well as hippocampal function. The present findings provide further support for the involvement of NOS/NO and arginase in the normal aging process. A strong positive correlation between CA1 eNOS protein expression and swimming speed in the water maze task may reflect a relationship between the local cerebral blood flow and neuronal activity.

Neuronal nitric oxide synthase expression in cerebellar mutant mice

Nitric oxide (NO) is a diffusible, multifunctional signaling molecule found in many areas of the brain. NO signaling is involved in a wide array of neurophysiological functions including synaptogenesis, modulation of neurotransmitter release, synaptic plasticity, central nervous system blood flow and cell death. NO synthase (NOS) activity regulates the production of NO and the cerebellum expresses high levels of nitric oxide synthase (NOS) in granule, stellate and basket cells. Cerebellar mutant mice provide excellent opportunities to study changes of NO/NOS concentrations and activities to gain a greater understanding of the roles of NO and NOS in cerebellar function. Here, we have reviewed the current understanding of the functional roles of NO and NOS in the cerebellum and present NO/NOS activities that have been described in various cerebellar mutant mice and NOS knockout mice. NO appears to exert neuroprotective effects at low to moderate concentrations, whereas NO becomes neurotoxic as the concentration increases. Excessive NO production can cause oxidative stress to neurons, ultimately impairing neuronal function and result in neuronal cell death. Based on their genetics and cerebellar histopathology, some of cerebellar mutant mice display similarities with human neurological conditions and may prove to be valuable models to study several human neurological disorders, such as autism and schizophrenia.

The role of nitric oxide synthases in the sleep responses to tumor necrosis factor-alpha

It is well established that cytokines such as tumor necrosis factor-alpha (TNFalpha) and interleukin-1beta (IL-1beta) are involved in physiological sleep regulation, yet their downstream somnogenic mechanisms remain largely uninvestigated. Nitric oxide (NO) is an effector molecule for some TNFalpha actions. Neuronal nitric oxide synthase (nNOS) and inducible nitric oxide synthase (iNOS) gene knockout (KO) mice sleep differently than their respective controls. In this study, we tested the hypothesis that NO mediates TNFalpha-induced sleep using iNOS and nNOS KO mice and their corresponding wild-type controls. Systemic administration of TNFalpha increased non-rapid eye movement sleep (NREMS) in the two control strains and in the iNOS KO mice during the first 4 h post-injection but failed to increase NREMS in nNOS KO mice. Rapid eye movement sleep (REMS) was suppressed by TNFalpha in nNOS controls but not in the other strains examined. The results suggest that TNFalpha affects sleep, in part, through nNOS.

Stromal cell-derived factor-1 production by spleen cells is affected by nitric oxide in protective immunity against blood-stage Plasmodium chabaudi CR in C57BL/6j mice

Malaria, a major endemic tropical disease, is caused by the infection of blood cells by Plasmodium protozoa. Most patients control their parasitemia by a not fully understood spleen-dependent mechanism. SDF-1alpha is a chemokine produced by stromal cells such as reticular spleen cells. Nitric oxide (NO) has several immune functions, including killing of intracellular pathogens and its function in malaria is debated. We have previously shown that SDF-1alpha production peaks during the ascending parasitemia in Plasmodium chabaudi infection and its supplementation in lethal models could reduce the parasitemia. In the present study, we analyzed SDF-1 production by spleen cells as related to NO metabolism in the P. chabaudi rodent malaria model using IFN-gamma; TNFR and iNOS-knockout mice or iNOS-blocked, L-NAME- or aminoguanidine-treated mice. Parasitemia and production of SDF-1alpha and SDF-1beta were determined by RT-PCR. In vitro NO production by spleen adherent cells was also tested. The data showed that parasitemia was less intense in both iNOS(-/-) or NO-inhibited mice than in controls, with increased and long-lasting production of SDF-1alpha mRNA. In the absence of cytokines involved in the final regulation of NO production by effector cells, as is the case for TNFR(-/-) and GKO mice, the infection progressed in an uncontrolled manner regardless of SDF-1alpha production, suggesting that these cytokines must be involved in the control of parasitemia after the SDF-1alpha dependent process. The SDF-1beta isoform was constitutive in all experiments, with elevated levels only clearly seen in TNFR(-/-) mice. We conclude that SDF-1 is involved in the promotion of parasitemia control in malaria, and excessive NO could affect its production.

Altered nitric oxide production in mouse brain after administration of 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridin or methamphetamine

Several studies have demonstrated the involvement of reactive nitrogen and oxygen species (RNOS) in the neurotoxic effects of 1-methyl-4-phenyl-1,2,3,6-tetrahydro-pyridin (MPTP) and methamphetamine (METH), so the contribution of altered nitric oxide synthase (NOS) enzyme function can be suspected. In this study, about 50% increase in nitric oxide (NO) production in the mouse striatum was found between 4 and 12 h after a single MPTP injection, allowing an increased peroxynitrite (ONOO-) formation in the target brain region. However, METH injection induced a rapid decrease of NO formation both in mouse striatum and hippocampus, reaching its minimum level at 2 h, and restored to the control value after 6 h in the striatum and 12 h in the hippocampus. The uncoupled function of NOS with increased superoxide (O2*-) production after METH injection is suggested.

Effects of cyclooxygenase inhibitor pretreatment on nitric oxide production, nNOS and iNOS expression in rat cerebellum

1. The therapeutic effect of nonsteroidal anti-inflammatory drugs (NSAIDs) is thought to be due mainly to its inhibition of cyclooxygenase (COX) enzymes, but there is a growing body of research that now demonstrates a variety of NSAIDs effects on cellular signal transduction pathways other than those involving prostaglandins. 2. Nitric oxide (NO) as a free radical and an agent that gives rise to highly toxic oxidants (peroxynitrile, nitric dioxide, nitron ion), becomes a cause of neuronal damage and death in some brain lesions such as Parkinson and Alzheimer disease, and Huntington's chorea. 3. In the present study, the in vivo effect of three NSAIDs (lysine clonixinate (LC), indomethacine (INDO) and meloxicam (MELO)) on NO production and nitric oxide synthase expression in rat cerebellar slices was analysed. Rats were treated with (a) saline, (b) lipopolysaccharide (LPS) (5 mg kg(-1), i.p.), (c) saline in combination with different doses of NSAIDs and (d) LPS in combination with different doses of NSAIDs and then killed 6 h after treatment. 4. NO synthesis, evaluated by Bred and Snyder technique, was increased by LPS. This augmentation was inhibited by coadministration of the three NSAIDs assayed. None of the NSAIDs tested was able to modify control NO synthesis. 5. Expression of iNOS and neural NOS (nNOS) was detected by Western blotting in control and LPS-treated rats. LC and INDO, but not MELO, were able to inhibit the expression of these enzymes. 6. Therefore, reduction of iNOS and nNOS levels in cerebellum may explain, in part, the anti-inflammatory effect of these NSAIDs and may also have importance in the prevention of NO-mediated neuronal injury.