Loss of hippocampal neuronal nitric oxide synthase contributes to the stress-related deficit in learning and memory

Nitric oxide (NO) has been involved in many pathophysiological brain processes. However, the exact role of NO in the cognitive deficit associated to chronic stress exposure has not been elucidated. In this study, we investigated the participation of hippocampal NO production and their regulation by protein kinase C (PKC) in the memory impairment induced in mice subjected to chronic mild stress model (CMS). CMS mice showed a poor learning performance in both open field and passive avoidance inhibitory task respect to control mice. Histological studies showed a morphological alteration in the hippocampus of CMS mice. On the other hand, chronic stress induced a diminished NO production by neuronal nitric oxide synthase (nNOS) correlated with an increment in gamma and zeta PKC isoenzymes. Partial restoration of nNOS activity was obtained after PKC activity blockade. NO production by inducible nitric oxide synthase isoform was not detected. The magnitude of oxidative stress, evaluated by reactive oxygen species production, after excitotoxic levels of NMDA was increased in hippocampus of CMS mice. Moreover, ROS formation was higher in the presence of nNOS inhibitor in both control and CMS mice. Finally, treatment of mice with nNOS inhibitors results in behavioural alterations similar to those observed in CMS animals. These findings suggest a novel role for nNOS showing protective activity against insults that trigger tissue toxicity leading to memory impairments.     

Differential requirement for nitric oxide in IGF-1-induced anti-apoptotic, anti-oxidant and anti-atherosclerotic effects

We have shown previously that insulin like-growth factor I (IGF-1) suppressed atherosclerosis in Apoe(-/-) mice and activated endothelial nitric oxide (NO) synthase. To determine whether IGF-1-induced atheroprotection depends on NO, IGF-1- or saline-infused mice were treated with l-NAME, the pan-NO synthase inhibitor or with d-NAME (control). IGF-1 reduced atherosclerosis in both the d-NAME and l-NAME groups suggesting that IGF-1's anti-atherogenic effect was NO-independent. IGF-1 increased plaque smooth muscle cells, suppressed cell apoptosis and downregulated lipoprotein lipase and these effects were also NO-independent. On the contrary, IGF-1 decreased oxidative stress and suppressed TNF-α levels and these effects were blocked by l-NAME. Thus IGF-1's anti-oxidant effect is dependent on its ability to increase NO but is distinct from its anti-atherosclerotic effect which is NO-independent.     

Hepatic glutathione and nitric oxide are critical for hepatic insulin-sensitizing substance action

We tested the hypothesis that hepatic nitric oxide (NO) and glutathione (GSH) are involved in the synthesis of a putative hormone referred to as hepatic insulin-sensitizing substance HISS. Insulin action was assessed in Wistar rats using the rapid insulin sensitivity test (RIST). Blockade of hepatic NO synthesis with N(G)-nitro-l-arginine methyl ester (l-NAME, 1.0 mg/kg intraportal) decreased insulin sensitivity by 45.1 +/- 2.1% compared with control (from 287.3 +/- 18.1 to 155.3 +/- 10.1 mg glucose/kg, P < 0.05). Insulin sensitivity was restored to 321.7 +/- 44.7 mg glucose/kg after administration of an NO donor, intraportal SIN-1 (5 mg/kg), which promotes GSH nitrosation, but not after intraportal sodium nitroprusside (20 nmol x kg(-1) x min(-1)), which does not nitrosate GSH. We depleted hepatic GSH using the GSH synthesis inhibitor l-buthionine-[S,R]-sulfoximine (BSO, 2 mmol/kg body wt ip for 20 days), which reduced insulin sensitivity by 39.1%. Insulin sensitivity after l-NAME was not significantly different between BSO- and sham-treated animals. SIN-1 did not reverse the insulin resistance induced by l-NAME in the BSO-treated group. These results support our hypothesis that NO and GSH are essential for insulin action.     

无瓣海桑果实提取物对衰老小鼠学习 记忆能力的影响及其机制研究

无瓣海桑果实为真红树无瓣海桑的果实。研究无瓣海桑果实不同提取物对D-半乳糖所致衰老小鼠学习记忆能力影响及其作用机制。采用Morris水迷宫实验测量无瓣海桑果实不同提取物对小鼠的学习记忆能力影响,HE染色观察各组小鼠脑部神经细胞的变化情况,并测定脑组织超氧化物歧化酶(SOD)活力、谷胱甘肽过氧化物酶(GSH-Px)活力、一氧化氮(NO)含量和单胺氧化酶(MAO)活力。结果表明:与模型组相比,无瓣海桑果实不同提取物处理组小鼠在水迷宫实验中逃避潜伏期明显缩短(P0.05),目标象限停留时间明显增加(P0.05)。无瓣海桑果实不同提取物处理组小鼠脑部神经细胞损伤与模型组相比明显减少,小鼠脑部SOD酶活力和GSH-Px酶活力提高(P0.05),NO含量和MAO活力在脑部显著降低(P0.05)。无瓣海桑果实不同提取物对D-半乳糖致衰老小鼠学习记忆能力有改善作用,无瓣海桑果实不同提取物通过提高小鼠脑内源抗氧化酶(SOD、GSH-Px)活力,降低脑部NO含量和MAO活力来提高D-半乳糖致衰老小鼠的学习记忆能力。     

Inhibitory effects of NO on carotid body: contribution of neural and endothelial nitric oxide synthase isoforms

We tested the hypothesis that nitric oxide (NO) produced within the carotid body is a tonic inhibitor of chemoreception and determined the contribution of neuronal and endothelial nitric oxide synthase (eNOS) isoforms to the inhibitory NO effect. Accordingly, we studied the effect of NO generated from S-nitroso-N-acetylpenicillamide (SNAP) and compared the effects of the nonselective inhibitor N(omega)-nitro-l-arginine methyl ester (l-NAME) and the selective nNOS inhibitor 1-(2-trifluoromethylphenyl)-imidazole (TRIM) on chemosensory dose-response curves induced by nicotine and NaCN and responses to hypoxia (Po(2) approximately 30 Torr). CBs excised from pentobarbitone-anesthetized cats were perfused in vitro with Tyrode at 38 degrees C and pH 7.40, and chemosensory discharges were recorded from the carotid sinus nerve. SNAP (100 microM) reduced the responses to nicotine and NaCN. l-NAME (1 mM) enhanced the responses to nicotine and NaCN by increasing their duration, but TRIM (100 microM) only enhanced the responses to high doses of NaCN. The amplitude of the response to hypoxia was enhanced by l-NAME but not by TRIM. Our results suggest that both isoforms contribute to the NO action, but eNOS being the main source for NO in the cat CB and exerting a tonic effect upon chemoreceptor activity.     

Roles of NO Signaling in Long-Term Memory Formation in Visual Learning in an Insect

Many insects exhibit excellent capability of visual learning, but the molecular and neural mechanisms are poorly understood. This is in contrast to accumulation of information on molecular and neural mechanisms of olfactory learning in insects. In olfactory learning in insects, it has been shown that cyclic AMP (cAMP) signaling critically participates in the formation of protein synthesis-dependent long-term memory (LTM) and, in some insects, nitric oxide (NO)-cyclic GMP (cGMP) signaling also plays roles in LTM formation. In this study, we examined the possible contribution of NO-cGMP signaling and cAMP signaling to LTM formation in visual pattern learning in crickets. Crickets that had been subjected to 8-trial conditioning to associate a visual pattern with water reward exhibited memory retention 1 day after conditioning, whereas those subjected to 4-trial conditioning exhibited 30-min memory retention but not 1-day retention. Injection of cycloheximide, a protein synthesis inhibitor, into the hemolymph prior to 8-trial conditioning blocked formation of 1-day memory, whereas it had no effect on 30-min memory formation, indicating that 1-day memory can be characterized as protein synthesis-dependent long-term memory (LTM). Injection of an inhibitor of the enzyme producing an NO or cAMP prior to 8-trial visual conditioning blocked LTM formation, whereas it had no effect on 30-min memory formation. Moreover, injection of an NO donor, cGMP analogue or cAMP analogue prior to 4-trial conditioning induced LTM. Induction of LTM by an NO donor was blocked by DDA, an inhibitor of adenylyl cyclase, an enzyme producing cAMP, but LTM induction by a cAMP analogue was not impaired by L-NAME, an inhibitor of NO synthase. The results indicate that cAMP signaling is downstream of NO signaling for visual LTM formation. We conclude that visual learning and olfactory learning share common biochemical cascades for LTM formation.     

一氧化氮供体增强大鼠记忆及其与脑内ADP-核糖基转移酶的关系

为探讨与学习记忆有关的一氧化氮（ｎｉｔｒｉｃ ｏｘｉｄｅ,ＮＯ）信号转导通路,本文用ＮＯ供体硝普钠（ｓｏｄｉｕｍ ｎｉｔｒｏｐｒｕｓｓｉｄｅ,ＳＮＰ）或同时给予ＡＤＰ－核糖基转移酶（ＡＤＰ－ｒｉｂｏｓｙｌｔｒａｎｓｆｅｒａｓｅ,ＡＤＰＲＴ）抑制剂尼克酰胺（ｎｉｃｏｔｉｎａｍｉｄｅ,ＮＩＣ）侧脑室内流射,观察其对大鼠学习记忆行为的影响,并用高效液相色谱法测定脑内ＡＤＰＲＴ活性。结果表明,ＳＮＰ（０．     

Cryptotanshinone inhibits endothelin-1 expression and stimulates nitric oxide production in human vascular endothelial cells

The Chinese herb Salvia miltiorrhiza (SM) has been found to have beneficial effects on the circulatory system. In the present study, we investigated the effects of cryptotanshinone (derived from SM) on endothelin-1 (ET-1) expression in human umbilical vein endothelial cells (HUVECs). The effect of cryptotanshinone on nitric oxide (NO) in HUVECs was also examined. We found that cryptotanshinone inhibited basal and tumor necrosis factor-alpha (TNF-alpha) stimulated ET-1 secretion in a concentration-dependent manner. Cryptotanshinone also induced a concentration-dependent decrease in ET-1 mRNA expression. Cryptotanshinone increased basal and TNF-alpha-attenuated NO production in a dose-dependent fashion. Cryptotanshinone induced a concentration-dependent increase in endothelial nitric oxide synthase (eNOS) expression without significantly changing neuronal nitric oxide synthase (nNOS) expression in HUVECs in the presence or absence of TNF-alpha. NOS activities in the HUVECs were also induced by cryptotanshinone. Furthermore, decreased ET-1 expression in response to cryptotanshinone was not antagonized by the NOS inhibitor l-NAME. A gel shift assay further showed that TNF-alpha-induced Nuclear Factor-kappaB (NF-kappaB) activity was significantly reduced by cryptotanshinone. These data suggest that cryptotanshinone inhibits ET-1 production, at least in part, through a mechanism that involves NF-kappaB but not NO production.     

Adaptation to intermittent hypoxia restricts nitric oxide overproduction and prevents beta-amyloid toxicity in rat brain

This study tested the hypothesis that adaptation to intermittent hypoxia (AIH) can prevent overproduction of nitric oxide (NO) in brain and neurodegeneration induced by beta-amyloid (Aβ) toxicity. Rats were injected with a Aβ protein fragment (25–35) into the nucleus basalis magnocellularis. AIH (simulated altitude of 4000 m, 14 days, 4 h daily) was produced prior to the Aβ injection. A passive, shock-avoidance, conditioned response test was used to evaluate memory function. Degenerating neurons were visualized in stained cortical sections. NO production was evaluated in brain tissue by the content of nitrite and nitrate. Expression of nNOS, iNOS, and eNOS was measured in the cortex and the hippocampus using Western blot analysis. 3-Nitrotyrosine formation, a marker of protein nitration, was quantified by slot blot analysis. Aβ injection impaired memory of rats; AIH significantly alleviated this disorder. Histological examination confirmed the protective effect of AIH. Degenerating neurons, which were numerous in the cortex of Aβ-injected, unadapted rats, were essentially absent in the brain of hypoxia-adapted rats. Injections of Aβ resulted in significant increases in NOx and in expression of all NOS isoforms in brain; AIH blunted these increases. NO overproduction was associated with increased amounts of 3-nitrotyrosine in the cortex and hippocampus. AIH alone did not significantly influence tissue 3-nitrotyrosine, but significantly restricted its increase after the Aβ injection. Therefore, AIH affords significant protection against experimental Alzheimer’s disease, and this protection correlates with restricted NO overproduction.     

Role of nitric oxide mechanisms in gastric emptying of, and the blood pressure and glycemic responses to, oral glucose in healthy older subjects

The primary aims of this study were to evaluate the effects of the nitric oxide (NO) synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME) on gastric emptying (GE) of, and the blood pressure (BP), glycemic, insulin, and incretin responses to, oral glucose in older subjects. Eight healthy subjects (4 males and 4 females, aged 70.9 +/- 1.3 yr) were studied on two separate days, in double-blind, randomized order. Subjects received an intravenous infusion of either l-NAME (180 mug.kg(-1).h(-1)) or saline (0.9%) at a rate of 3 ml/min for 150 min. Thirty minutes after the commencement of the infusion (0 min), subjects consumed a 300-ml drink containing 50 g glucose labeled with 20 MBq (99m)Tc-sulfur colloid, while sitting in front of a gamma camera. GE, BP (systolic and diastolic), heart rate (HR), blood glucose, plasma insulin, and incretin hormones, glucose-dependant insulinotropic-polypeptide (GIP), and glucagon-like peptide-1 (GLP-1), were measured. l-NAME had no effect on GE, GIP, and GLP-1. Between -30 and 0 min l-NAME had no effect on BP or HR. After the drink (0-60 min), systolic and diastolic BP fell (P < 0.05) and HR increased (P < 0.01) during saline; these effects were attenuated (P < 0.001) by l-NAME. Blood glucose levels between 90 and 150 min were higher (P < 0.001) and plasma insulin were between 15 and 150 min less (P < 0.001) after l-NAME. The fall in BP, increase in HR, and stimulation of insulin secretion by oral glucose in older subjects were mediated by NO mechanisms by an effect unrelated to GE or changes in incretin hormones.     

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.     

Hyperbaric Oxygen Reduces Cerebral Blood Flow by Inactivating Nitric Oxide

Based on recent evidence that nitric oxide (NO(.)) is involved in hyperoxic vasoconstriction, we tested the hypothesis that decreases in NO(.) availability in brain tissue during hyperbaric oxygen (HBO(2)) exposure contribute to decreases in regional cerebral blood flow (rCBF). rCBF was measured in rats exposed to HBO(2) at 5 atmospheres (ATA) and correlated with interstitial brain levels of NO(.) metabolites (NO(X)) and production of hydroxyl radical ((.)OH). Changes in rCBF were also correlated with the effects of NO(.) synthase inhibitor (l-NAME), NO(.) donor PAPANONOate, and intravascular superoxide dismutase (MnSOD) during HBO(2). After 30 min of O(2) exposure at 5 ATA, rCBF had decreased in the substantia nigra, caudate putamen, hippocampus, and parietal cortex by 23 to 37%. These reductions in rCBF were not augmented by exposure to HBO(2) in animals pre-treated with l-NAME. After 30 min at 5 ATA, brain NO(X) levels had decreased by 31 +/- 9% and correlated with the decrease in rCBF, while estimated (.)OH production increased by 56 +/- 8%. The decrease in rCBF at 5 ATA was completely abolished by MnSOD administration into the circulation before HBO(2) exposure. Doses of NO(.) donor that significantly increased rCBF in animals breathing air had no effect at 5 ATA of HBO(2). These results indicate that decreases in rCBF with HBO(2) are associated with a decrease in effective NO(.) concentration and an increase in ROS production in the brain. The data support the hypothesis that inactivation of NO(.) antagonizes basal relaxation of cerebral vessels during HBO(2) exposure, although an effect of HBO(2) on NO(.) synthesis has not been excluded.     

Nitric oxide synthase inhibitor attenuates the anorexigenic effect of corticotropin-releasing hormone in neonatal chicks

Nitric oxide (NO) is known as an orexigenic factor in the brain of mammals and mediates the feeding-stimulatory effect of other factors such as neuropeptide Y (NPY). In neonatal chicks, however, we recently reported that NO might have an anorexigenic effect and suggested that the feeding-regulatory mechanism in chicks might be different from that in mammals regarding NO. In the present study, we investigated the involvement of NO in the effect of other orexigenic and anorexigenic factors in neonatal chicks. Intracerebroventricular co-injection of N(G)-nitro-l-arginine methyl ester (l-NAME), a NO synthase inhibitor, did not affect NPY- and prolactin-releasing peptide-induced feeding behavior. On the other hand, the co-injection of l-NAME significantly attenuated the anorexigenic effect of corticotropin-releasing hormone (CRH). The anorexigenic effects of glucagon-like peptide-1, alpha-melanocyte-stimulating hormone and ghrelin were not affected by the l-NAME treatment. These results suggest that NO might mediate the anorexigenic effect of CRH in the brain of neonatal chicks.     

Interactive modulation of renal myogenic autoregulation by nitric oxide and endothelin acting through ET-B receptors

In rats, nitric oxide modulates renal autoregulation in steady-state experiments and the myogenic mechanism in dynamic studies. Interactive modulation of autoregulation by nitric oxide and endothelin-1, predominantly involving endothelin B receptors, has been reported although it remains unclear whether the interaction is synergistic or obligatory or whether it affects the myogenic component of autoregulation. Nonselective inhibition of nitric oxide synthase (L(omega)-nitro-l-arginine methyl-ester; l-NAME) with endothelin A and B selective receptor antagonists BQ-123 and BQ-788, all infused into the renal artery, plus time series analysis were used to test the interactive actions of nitric oxide and endothelin on renal vascular conductance and on autoregulation. Nonselective endothelin receptor antagonism blunted the constrictor response to subsequent l-NAME but had no effect on previously established l-NAME-induced vasoconstriction. BQ-123 did not affect conductance and caused only minor reduction in myogenic autoregulatory efficiency. Responses to BQ-123 and l-NAME were additive and not interactive. BQ-788 and l-NAME each caused strong vasoconstriction alone and in the presence of the other, indicating that coupling between nitric oxide- and endothelin B-mediated events is not obligatory. l-NAME augmented myogenic autoregulation, and subsequent BQ-788 did not alter this response. However, BQ-788 infused alone also enhanced myogenic autoregulation but resulted in significant impairment of myogenic autoregulation by subsequent l-NAME. Thus the interaction between nitric oxide and endothelin is clearly nonadditive and, because it is asymmetrical, cannot be explained simply by convergence on a common signal pathway. Instead one must postulate some degree of hierarchical organization and that nitric oxide acts downstream to endothelin B activation.     

NO and cGMP mediate angiotensin AT2 receptor-induced renal renin inhibition in young rats

We hypothesized that angiotensin subtype-2 receptor (AT(2)R) inhibits renal renin biosynthesis in young rats via nitric oxide (NO). We monitored changes in renal NO, cGMP, renal renin content (RRC), and ANG II in 4-wk-old rats in response to low sodium (LNa(+)) intake alone and combined with 8-h direct renal cortical administration of AT(1) receptor blocker valsartan (VAL), AT(2)R blocker PD123319 (PD), NO synthase inhibitor N(G)-nitro-l-arginine methyl ester (l-NAME), NO donor S-nitroso-N-acetyl penicillamine (SNAP), or guanylyl cyclase inhibitor 1H-[1,2,4] oxadiazolo[4,2-alpha] quinoxaline-1-one (ODQ). In addition, we monitored renal endothelial nitric oxide synthase (eNOS) and neuronal nitric oxide synthase (nNOS) in response to VAL or PD. LNa(+), VAL, PD, l-NAME, and ODQ increased RRC, ANG II, and renin mRNA. PD and l-NAME decreased NO and cGMP, while SNAP reduced RRC, ANG II, renin mRNA, and reversed the effects of PD. PD also reduced eNOS and nNOS protein and mRNA. Combined treatment with PD, l-NAME, or ODQ and VAL reversed the effects of VAL and caused further increase in RRC, ANG II, renin mRNA, and protein. ODQ reversed the effects of SNAP. These data demonstrate that the renal AT(2) receptor decreases renal renin biosynthesis and ANG II production in young rats. Reversal of the PD effects by SNAP and SNAP effects by ODQ confirms that NO and cGMP mediate the AT(2) receptor inhibition of renal renin production.     

Quebrachitol-induced gastroprotection against acute gastric lesions: Role of prostaglandins, nitric oxide and KATP channels

The effect of Quebrachitol (2-O-methyl-l-inositol), a bioactive component from Magonia glabrata fruit extract was investigated against gastric damage induced by absolute ethanol (96%, 0.2 ml/animal) and indomethacin (30 mg/kg, p.o.), in mice. Quebrachitol at oral doses of 12.5, 25, and 50 mg/kg markedly attenuated the gastric lesions induced by ethanol to the extent of 69%, 64%, and 53% and against indomethacin by 55%, 59%, and 26%, respectively. While pretreatment with TRPV1 antagonist capsazepine (5 mg/kg, i.p.) failed to block effectively the gastroprotective effect of quebrachitol (25 mg/kg) against ethanol damage, the non-selective cyclooxygenase inhibitor indomethacin (10 mg/kg, p.o.), almost abolished it. Furthermore, quebrachitol effect was significantly reduced in mice pretreated with l-NAME, or glibenclamide, the respective inhibitors of nitric oxide synthase and K⁺_ATP channel activation. Thus we provide the first evidence that quebrachitol reduces the gastric damage induced by ethanol and indomethacin, at least in part, by mechanisms that involve endogenous prostaglandins, nitric oxide release, and or the activation of K⁺_ATP channels.     

Effects of oral administration of (L)-arginine, (L)-NAME and allopurinol on intestinal ischemia/reperfusion injury in rats

AimsIntestinal ischemia/reperfusion (I/R) injury is implicated in many clinical conditions, and it performs a fundamental role in their pathophysiologies. Oral administration of antioxidants and nitric oxide (NO) donors ameliorate intestinal injury. Here, the effects of l-arginine, allopurinol and N^G-nitro-l-arginine methyl ester (l-NAME) were investigated.Main methodsOne hundred twenty-eight male Wistar rats were separated into 4 groups and subjected to occlusion of the superior mesenteric artery for 60 min. The Control group did not receive any substance before the surgical operation. However, the 3 other groups received the following: l-arginine (800 mg/kg body weight; l-Arg group), l-NAME (50 mg/kg; l-NAME group) or allopurinol (100 mg/kg; Allo group). Each substance was given by mouth in 3 equal doses 24, 12 and 1 h before the surgical operation. Each group was then divided into 4 subgroups, which underwent different durations of reperfusion (0, 1, 8 or 24 h). At the end of each time point, blood and tissue samples were collected, and histological examinations were performed. Serum nitrite and catalase, intestinal tissue myeloperoxidase (MPO), inducible nitric oxide synthase (iNOS) and nitrotyrosine (NT) levels were determined.Key findingsAt each reperfusion time point, the Allo group exhibited the mildest histological lesions in contrast to the l-NAME group, which showed the most severe lesions. MPO was decreased significantly in the Allo and l-Arg groups during reperfusion, and allopurinol administration caused earlier and stronger effect. iNOS and NT levels were higher in the l-Arg group and lower in the Allo group. Serum nitrite and catalase were increased in the l-NAME group after 24 h.SignificanceOral administration of allopurinol exerted a strong and protective effect on the intestinal tissue that was subjected to I/R earlier than l-arginine. This finding was also supported with the MPO, iNOS and NT data.     

Nitric oxide inhibits metamorphosis in larvae of Crepidula fornicata, the slippershell snail

This paper concerns the role of nitric oxide (NO) in controlling metamorphosis in the marine gastropod Crepidula fornicata. Metamorphosis was stimulated by the nitric oxide synthase (NOS) inhibitors AGH (aminoguanidine hemisulfate) and SMIS (S-methylisothiourea sulfate) at concentrations of about 100-1000 micromol l(-1) and 50-200 micromol l(-1), respectively. Metamorphosis was not, however, induced by the NOS inhibitor l-NAME (l-N(G)-nitroarginine methyl ester) at even the highest concentration tested, 500 micromol l(-1). Moreover, pre-incubation with l-NAME at 20 and 80 micromol l(-1) did not increase the sensitivity of competent larvae to excess K(+), a potent inducer of metamorphosis in this species; we suggest that either l-NAME is ineffective in suppressing NO production in larvae of C. fornicata, or that it works only on the constitutive isoform of the enzyme. In contrast, metamorphosis was potentiated by the guanylate cyclase inhibitor ODQ (1H-[1,2,4]oxadiazolo[4,3, -a]quinoxalin-1-one) in response to a natural metamorphic inducer derived from conspecific adults. Because NO typically stimulates cGMP production through the activation of soluble guanylate cyclase, this result supports the hypothesis that NO acts as an endogenous inhibitor of metamorphosis in C. fornicata. The expression of NOS, shown by immunohistochemical techniques, was detected in the apical ganglion of young larvae but not in older larvae, further supporting the hypothesis that metamorphosis in C. fornicata is made possible by declines in the endogenous concentration of NO during development.     

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 Ca²⁺/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 Ca²⁺/NO/cGMP pathway in aging and Alzheimer's disease.     

花粉制剂对脑衰老动物各脑区的SOD和NO水平的影响

采用 D-半乳糖建立脑衰老动物模型 ,观察服用花粉制剂前后对脑衰老模型动物不同脑区组织中超氧化物歧化酶 ( SOD)活性、一氧化氮 ( NO)水平的影响。结果表明花粉制剂能明显升高脑衰老动物某些脑区 SOD活性和降低脑衰老动物某些脑区 NO水平。研究结果提示花粉制剂具有延缓衰老和增强记忆力等作用 ,其机制可能与其促进自由基的清除及减少 NO释放有关。