Modulatory effect of L-NAME, a specific nitric oxide synthase (NOS) inhibitor, on stress-induced changes in plasma adrenocorticotropic hormone (ACTH) and corticosterone levels in rats: physiological significance of stress-induced NOS activation in hypothalamic-pituitary-adrenal axis

The effect of magnesium sulfate on memory and anxiety-like behavior in a rat model: an investigation of its neuronal molecular mechanisms

BACKGROUND

Anxiety is an adaptive response to potentially threatening conditions. Excessive and uncontrolled anxiety responses become nonadaptive and cause anxiety disorders. To better understand the anxiety-modulating effects of Mg sulfate, behavioral test batteries in the assessment of anxiety and learning and memory functions were performed simultaneously over a time period. This study also examines the effects of Mg sulfate compared to diazepam, an anxiolytic drug with amnestic effects on anxiety-like behavior, as well as possible oxidative-nitrosative stress and hippocampal changes in male rats exposed to predator odor.

METHODS

Young adult Sprague-Dawley male rats were used. The rats were assessed using a comprehensive neurobehavioral test battery consisting of novel object recognition, open field, and successive alleys tasks. Anxiety was induced by cat odor, and diazepam and Mg were used as study drugs. Of the frontal cortex and hippocampus, the state of total oxidant and antioxidant and NO levels and histological examination of hippocampal CA1, CA2, CA3, and DG regions were performed.

RESULTS

Diazepam- and Mg-treated rats showed an improvement in anxiety-related behavior to predator odors. Furthermore, Mg treatment alleviated some of the increasing oxidative stress in the frontal cortex and hippocampus of rats, while diazepam treatment in particular enhanced hippocampal oxidant and antioxidant activity. In addition, brain NO increase induced by animal odor exposure or diazepam treatment was ameliorated by Mg administration.

CONCLUSIONS

Overall, our work suggests that Mg had a partial anxiolytic effect on anxiety-like behaviors, although not as much as diazepam, and this effect varied depending on the dose. Mg treatment might counteract increased oxidative stress and elevated NO levels in the brain.

Current Aspects of Selected Factors to Modulate Brain Health and Sports Performance in Athletes

This review offers a comprehensive evaluation of current aspects related to nutritional strategies, brain modulation, and muscle recovery, focusing on their applications and the underlying mechanisms of physiological adaptation for promoting a healthy brain, not only in athletes but also for recreationally active and inactive individuals. We propose that applying the rule, among others, of good sleep, regular exercise, and a properly balanced diet, defined as "SPARKS", will have a beneficial effect on the function and regeneration processes of the gut-brain-muscle axis. However, adopting the formula, among others, of poor sleep, stress, overtraining, and dysbiosis, defined as "SMOULDER", will have a detrimental impact on the function of this axis and consequently on human health as well as on athletes. Understanding these dynamics is crucial for optimizing brain health and cognitive function. This review highlights the significance of these factors for overall well-being, suggesting that adopting the "SPARKS" approach may benefit not only athletes but also older adults and individuals with health conditions.

In Vitro Assessment of Myorelaxant and Antispasmodic Effects of Stigmas, Tepals, and Leaves Hydroethanolic Extracts of Crocus sativus

The valorization of Crocus sativus focuses mainly on the plant’s stigma because it is one of the most expensive and valuable spices in the world and has great value in the food, cosmetics, and pharmacological industries. Due to this high stigma value, the other parts of the plant are considered as by-products; our study aimed to evaluate the myorelaxant and antispasmodic activities of the byproducts (tepals and leaves) to compare them with the stigma of the plant. To investigate the myorelaxant and antispasmodic activities of the Crocus sativus on isolated rabbit and rat jejunum, we used an in vitro technic with an organ bath and an isotonic transducer. Our results showed that the STG (hydroethanolic extract of stigmas) and LV (hydroethanolic extract of leaves) had a moderate myorelaxant effect with IC50 = 6.61 ± 1.5 and 5.08 ± 0.45 mg/ml, respectively. TPL (hydroethanolic extract of tepals) had a significant ( $p˂0.001$ ) inhibitory effect on the amplitude of the rabbit jejunum basic contractions with an IC50 = 1.36 ± 0.15 mg/ml. TPL also caused a significant ( $p˂0.001$ ) antispasmodic activity depending on the dose of the contraction induced by CCh (10−6 M) and KCl (25 mM). The antispasmodic effect of the TPL is slightly altered in the presence of nifedipine by a percentage of 26.8%. This difference is statistically significant ( $p˂0.01$ ). Therefore, the extract could induce the inhibitory effect on L-type voltage-dependent Ca2+ channels, but not on the guanylate cyclase and nitric oxide pathways. That confirmed that the TPL has a comparable effect to the verapamil. The HPLC-DAD analysis of various parts of C. sativus shows that the three extracts contain the kaempferol flavanol compound, the STG also was revealed to be rich in carotenoids crocin, and these isomers are trans and cis-crocin, safranal, and picrocrocin. In contrast, the TPL revealed the presence of isorhamnetin and quercetin, but the LV was rich in hesperidin and mangiferin. In conclusion, this study supports the traditional use of this plant to treat digestive problems and will allow us to explore future possibilities for treating bowel spasms using natural molecules derived from saffron.

Myorelaxant and antispasmodic effect of an aqueous extract of Artemisia campestris L. via calcium channel blocking and anticholinergic pathways

Intestinal spasms are violent contractions that occur in the intestine, which cause discomfort to people who have them. Medicinal plants are widely used in traditional Moroccan medicine to treat these problems, among these being Artemisia campestris L. This study aims to evaluate the relaxant and antispasmodic effects of an aqueous extract of this plant (ACAE). It was performed in vitro on isolated segments of both isolated rat and rabbit jejunum mounted in an organ bath and tension recordings made via an isotonic transducer. ACAE caused a myorelaxant effect on baseline rabbit jejunum contractions in a dose-dependent and reversible manner with an IC₅₀ of 1.52 ± 0.12 mg/ml. This extract would not act via adrenergic receptors pathway. On the other hand, the extract caused a dose-dependent relaxation of the jejunum tone in rat jejenum segments pre-contracted with either Carbachol (CCh; 10^-6 M) or high K⁺ (KCl 75 mM) with an IC₅₀ = 0.49 ± 0.02 mg/ml and 0.36 ± 0.02 mg/ml respectively. In the presence of different doses of the extract, the maximum response to CCh and CaCl₂ was significantly reduced. This demonstrates that ACAE acts on both muscarinic receptors and voltage-dependent calcium channels. Thus, the plant extract acted on both muscarinic and nicotinic receptors and acts on the guanylate cyclase pathway, but not the nitric oxide pathway. These results indicate the mechanism by which Artemisia campestris L. acts as an effective antispasmodic agent in traditional Moroccan medicine.

Possible Effects of Beetroot Supplementation on Physical Performance Through Metabolic, Neuroendocrine, and Antioxidant Mechanisms: A Narrative Review of the Literature

Athletes often seek to use dietary supplements to increase performance during exercise. Among various supplements, much attention has been paid to beetroot in recent years. Beetroot is a source of carbohydrates, fiber, protein, minerals, and vitamins; also, it is a natural source of nitrate and associated with improved sports performance. Nitrates can the modification of skeletal muscle contractile proteins or calcium handling after translation. The time to reach the peak plasma nitrate is between 1 and 3 h after consumption of a single dose of nitrate. Nitrate is metabolized by conversion to nitrite and subsequently nitric oxide. Beetroot can have various effects on athletic performance through nitric oxide. Nitric oxide is an intracellular and extracellular messenger for regulating certain cellular functions and causes vasodilation of blood vessels and increases blood flow. Nitric oxide seems to be effective in improving athletic performance by increasing oxygen, glucose, and other nutrients for better muscle fueling. Nitric oxide plays the main role in anabolic hormones, modulates the release of several neurotransmitters and the major mediators of stress involved in the acute hypothalamic-pituitary-adrenal response to exercise. Beetroot is an important source of compounds such as ascorbic acid, carotenoids, phenolic acids, flavonoids, betaline, and highly active phenolics and has high antioxidant properties. Beetroot supplement provides an important source of dietary polyphenols and due to the many health benefits. Phytochemicals of Beetroot through signaling pathways inhibit inflammatory diseases. In this study, the mechanisms responsible for these effects were examined and the research in this regard was reviewed.

Nitric oxide role in anxiety-like behavior, memory and cognitive impairments in animal model of chronic migraine

The occurrence of cognitive dysfunctions and anxiety and mood disorders has been shown to be higher in migraine patients. Nitric Oxide (NO) is a significant neurotransmitter in the pathophysiology of migraine, anxiety and neurodegenerative disorders. Therefore, the present study was conducted to evaluate the role of NO system in migraine-induced memory impairment and anxiety like behaviors. Nitroglycerin (NTG) was administered to the animals as an animal model of migraine and pretreatment with L-Arginine, L-NAME and saline were implemented to evaluate the role of NO system in possible cognitive impairments in animal model of migraine. Avoidance learning and memory performance, object recognition memory, anxiety-like behavior and motor activity were assessed using a shuttle box apparatus, novel object recognition, elevated plus-maze, and open field tests respectively. The data showed that the injection of nitroglycerin disturbs learning and memory and elicit anxiety like behavior in the animals. L-NAME administration suppressed the observed effect of nitroglycerin on memory and anxiety. Overall, the results indicated that nitric oxide system is implicated in memory impairments and anxiety like behavior in an animal model of migraine.

Understanding the effects of beetroot juice intake on CrossFit performance by assessing hormonal, metabolic and mechanical response: a randomized, double-blind, crossover design

BACKGROUND

Acute beetroot juice (BJ) intake has shown to enhance aerobic and anaerobic performance. However, no studies have evaluated the effects of BJ intake on CrossFit (CF) performance by linking hormonal, metabolic, and mechanical responses. The purpose of this study was to determine the causal physiological association between hormonal, metabolic and mechanical responses, and CF workouts performance after acute BJ intake.

METHODS

Twelve well-trained male practitioners undertook a CF workout after drinking 140 mL of BJ (~ 12.8 mmol NO3-) or placebo. The two experimental conditions (BJ or placebo) were administered using a randomized, double-blind, crossover design. The CF workout consisted of repeating the same exercise routine twice: Wall ball (WB) shots plus full back squat (FBS) with 3-min rest (1st routine) or without rest (2nd routine) between the two exercises. A 3-min rest was established between the two exercise routines.

RESULTS

An interaction effect was observed in the number of repetitions performed (p = 0.04). The Bonferroni test determined a higher number of repetitions after BJ than placebo intake when a 3-min rest between WB and FBS (1st routine) was established (p = 0.007). An interaction effect was detected in cortisol response (p = 0.04). Cortisol showed a higher increase after BJ compared to placebo intake (76% vs. 36%, respectively). No interaction effect was observed in the testosterone and testosterone/cortisol ratio (p > 0.05). A significant interaction effect was found in oxygen saturation (p = 0.01). A greater oxygen saturation drop was observed in BJ compared to placebo (p <  0.05). An interaction effect was verified in muscular fatigue (p = 0.03) with a higher muscular fatigue being observed with BJ than placebo (p = 0.02).

CONCLUSIONS

BJ intake improved anaerobic performance only after the recovery time between exercises. This increase in performance in the first routine probably generated greater hypoxia in the muscle mass involved, possibly conditioning post-exercise performance. This was observed with a fall in oxygen saturation and in muscle fatigue measured at the end of the CF workout. The greatest perceived changes in cortisol levels after BJ intake could be attributed to the nitrate-nitrite-nitric oxide pathway.

Nitric oxide signalling and antidepressant action revisited

Studies about the pathogenesis of mood disorders have consistently shown that multiple factors, including genetic and environmental, play a crucial role on their development and neurobiology. Multiple pathological theories have been proposed, of which several ultimately affects or is a consequence of dysfunction in brain neuroplasticity and homeostatic mechanisms. However, current clinical available pharmacological intervention, which is predominantly monoamine-based, suffers from a partial and lacking response even after weeks of continuous treatment. These issues raise the need for better understanding of aetiologies and brain abnormalities in depression, as well as developing novel treatment strategies. Nitric oxide (NO) is a gaseous unconventional neurotransmitter, which regulates and governs several important physiological functions in the central nervous system, including processes, which can be associated with the development of mood disorders. This review will present general aspects of the NO system in depression, highlighting potential targets that may be utilized and further explored as novel therapeutic targets in the future pharmacotherapy of depression. In particular, the review will link the importance of neuroplasticity mechanisms governed by NO to a possible molecular basis for the antidepressant effects.

Chronic cocaine induces HIF-VEGF pathway activation along with angiogenesis in the brain

Cocaine induces vasoconstriction in cerebral vessels, which with repeated use can result in transient ischemic attacks and cerebral strokes. However, the neuroadaptations that follow cocaine's vasoconstricting effects are not well understood. Here, we investigated the effects of chronic cocaine exposure (2 and 4 weeks) on markers of vascular function and morphology in the rat brain. For this purpose we measured nitric oxide (NO) concentration in plasma, brain neuronal nitric oxide synthase (nNOS or NOS1), HIF-1α, and VEGF expression in different brain regions, i.e., middle prefrontal cortex, somatosensory cortex, nucleus accumbens, and dorsal striatum, using ELISA or Western blot. Additionally, microvascular density in these brain regions was measured using immunofluorescence microscopy. We showed that chronic cocaine significantly affected NOS1, HIF-1α and VEGF expression, in a region- and cocaine treatment-time- dependent manner. Cerebral microvascular density increased significantly in parallel to these neurochemical changes. Furthermore, significant correlations were detected between VEGF expression and microvascular density in cortical regions (middle prefrontal cortex and somatosensory cortex), but not in striatal regions (nucleus accumbens and dorsal striatum). These results suggest that following chronic cocaine use, as cerebral ischemia developed, NOS1, the regulatory protein to counteract blood vessel constriction, was upregulated; meanwhile, the HIF-VEGF pathway was activated to increase microvascular density (i.e., angiogenesis) and thus restore local blood flow and oxygen supply. These physiological responses were triggered presumably as an adaptation to minimize ischemic injury caused by cocaine. Therefore, effectively promoting such physiological responses may provide novel and effective therapeutic solutions to treat cocaine-induced cerebral ischemia and stroke.

Blood pressure regulation in stress: focus on nitric oxide-dependent mechanisms

Stress is considered a risk factor associated with the development of various civilization diseases including cardiovascular diseases, malignant tumors and mental disorders. Research investigating mechanisms involved in stress-induced hypertension have attracted much attention of physicians and researchers, however, there are still ambiguous results concerning a causal relationship between stress and long-term elevation of blood pressure (BP). Several studies have observed that mechanisms involved in the development of stress-induced hypertension include increased activity of sympathetic nervous system (SNS), glucocorticoid (GC) overload and altered endothelial function including decreased nitric oxide (NO) bioavailability. Nitric oxide is well known neurotransmitter, neuromodulator and vasodilator involved in regulation of neuroendocrine mechanisms and cardiovascular responses to stressors. Thus NO plays a crucial role in the regulation of the stress systems and thereby in the BP regulation in stress. Elevated NO synthesis, especially in the initial phase of stress, may be considered a stress-limiting mechanism, facilitating the recovery from stress to the resting levels via attenuation of both GC release and SNS activity as well as by increased NO-dependent vasorelaxation. On the other hand, reduced levels of NO were observed in the later phases of stress and in subjects with genetic predisposition to hypertension, irrespectively, in which reduced NO bioavailability may account for disruption of NO-mediated BP regulatory mechanisms and accentuated SNS and GC effects. This review summarizes current knowledge on the role of stress in development of hypertension with a special focus on the interactions among NO and other biological systems affecting blood pressure and vascular function.

Agmatine attenuates chronic unpredictable mild stress-induced anxiety, depression-like behaviours and cognitive impairment by modulating nitrergic signalling pathway

Agmatine, a neurotransmitter/neuromodulator, has shown to exert numerous effects on the CNS. Chronic stress is a risk factor for development of depression, anxiety and deterioration of cognitive performance. Compelling evidences indicate an involvement of nitric oxide (NO) pathway in these disorders. Hence, investigation of the beneficial effects of agmatine on chronic unpredictable mild stress (CUMS)-induced depression, anxiety and cognitive performance with the involvement of nitrergic pathway was undertaken. Mice were subjected to a battery of stressors for 28days. Agmatine (20 and 40mg/kg, i.p.) alone and in combination with NO modulators like L-NAME (15mg/kg, i.p.) and l-arginine (400mg/kg i.p.) were administered daily. The results showed that 4-weeks CUMS produces significant depression and anxiety-like behaviour. Stressed mice have also shown a significant high serum corticosterone (CORT) and low BDNF level. Chronic treatment with agmatine produced significant antidepressant-like behaviour in forced swim test (FST) and sucrose preference test, whereas, anxiolytic-like behaviour in elevated plus maze (EPM) and open field test (OFT) with improved cognitive impairment in Morris water maze (MWM). Furthermore, agmatine administration reduced the levels of acetylcholinesterase and oxidative stress markers. In addition, agmatine treatment significantly increased the BDNF level and inhibited serum CORT level in stressed mice. Treatment with L-NAME (15mg/kg) potentiated the effect of agmatine whereas l-arginine abolished the anxiolytic, antidepressant and neuroprotective effects of agmatine. Agmatine showed marked effect on depression and anxiety-like behaviour in mice through nitrergic pathway, which may be related to modulation of oxidative-nitrergic stress, CORT and BDNF levels.

Serum methylarginines and incident depression in a cohort of older adults

BACKGROUND

Methylarginines are endogenous nitric oxide synthase inhibitors that have been implicated in depression. This study measured serum concentrations of l-arginine, asymmetric (ADMA) and symmetric (SDMA) dimethylarginine in a representative sample of older community-dwelling adults and determined their association with incident depression over 6-years of follow-up.

METHODS

Data on clinical, lifestyle, and demographic characteristics, methylated arginines, and l-arginine (measured using LC-MS/MS) were collected from a population-based sample of older Australian adults (Median age=64 years; IQR=60-70) from the Hunter Community Study. Clinical depression was defined as a Centre for Epidemiological Studies Depression Scale (CES-D) score ≥16 or use of antidepressant medications.

RESULTS

In adjusted analyses ADMA (Q3), SDMA (Q2), l-arginine (Q2), gender, and asthma remained statistically significant predictors of incident depression at follow-up. Quartile 3 of ADMA concentration was associated with 3.5 times the odds of developing depression compared with Q1 (OR=3.54; 95% CI: 1.25-9.99).

LIMITATIONS

Limitations of our study include the use of a subjective self-reported questionnaire tool using a dichotomous cut-off, together with use of antidepressant medications, as proxies for clinical depression. Moreover, similarly to most population studies on methylated arginines, the measurement of ADMA and SDMA from blood does not necessarily reflect intracellular concentrations of these compounds. Finally, there were no measures of nitric oxide metabolites to determine if these levels were altered in the presence of elevated methylarginines and depression.

CONCLUSIONS

After adjusting for clinical, demographic, biochemical, and pharmacological confounders, higher serum ADMA was independently associated with incident depression at 6-years follow-up.

The differential role of NOS inhibitors on stress-induced anxiety and neuroendocrine alterations in the rat

The inhibitors of nitric oxide synthase (NOS) have been shown to possess antidepressant- and anxiolytic-properties in animal model. In order to examine the involvement of nitric oxide (NO) on stress-induced neurobehavioral changes and the concomitant alterations of neuroendocrinological factors, we studied the effects of the nonselective NOS inhibitor, N(ω)-Nitro L-arginine methyl ester hydrochloride (L-NAME) and the specific neuronal NOS inhibitor, 7-nitroindazole (7-NI) on restraint stress-induced anxiety in the elevated plus maze (EPM) test and biochemical analysis. Restraint stress significantly reduced the latency time in open arm and the percentage of open arm entries of the plus maze. Pretreatment with L-NAME (10 mg/kg) or 7-NI (10 mg/kg) significantly attenuated stress-induced anxiety response. In addition, administration of L-NAME (10 mg/kg) reversed stress-induced increase in corticosterone and NO metabolites (NO(x)) in plasma. The administration of 7-NI, but not L-NAME, reversed stress-induced NO(x) in paraventricular nucleus of the hypothalamus (PVN) and locus coeruleus (LC), accompanying with decrease of NADPH-d reactivity in the PVN and lateral dorsal tegmental nucleus (LTDg). These results showed that L-NAME influences HPA axis activity such as corticosterone levels and NO(x) in plasma, whereas 7-NI produced anxiolytic-like effects through the direct reduction in NO(x) in the brain. The results of this study demonstrated that NOS inhibitors have differential effect on stress responses and inhibition of NO could be responsible for the beneficial effect on regulation of stress.

The phosphodiesterases type 5 inhibitor tadalafil reduces the activation of the hypothalamus-pituitary-adrenal axis in men during cycle ergometric exercise

Phosphodiesterase type 5 inhibitors may influence human physiology, health, and performance by also modulating endocrine pathways. We evaluated the effects of a 2-day tadalafil administration on adenohypophyseal and adrenal hormone adaptation to exercise in humans. Fourteen healthy males were included in a double-blind crossover trial. Each volunteer randomly received two tablets of placebo or tadalafil (20 mg/day with a 36-h interval) before a maximal exercise was performed. After a 2-wk washout, the volunteers were crossed over. Blood samples were collected at -30 and -15 min and immediately before exercise, immediately after, and during recovery (+15, +30, +60, and +90 min) for adrenocorticotropin (ACTH), β-endorphin, growth hormone (GH), prolactin, cortisol (C), corticosterone, dehydroepiandrosterone-sulfate (DHEAS), and cortisol binding globulin (CBG) assays. C-to-CBG (free cortisol index, FCI) and DHEAS-to-C ratios were calculated. Exercise intensity, perceived exertion rate, O₂ consumption, and CO₂ and blood lactate concentration were evaluated. ACTH, GH, C, corticosterone, and CBG absolute concentrations and/or areas under the curve (AUC) increased after exercise after both placebo and tadalafil. Exercise increased DHEAS only after placebo. Compared with placebo, tadalafil administration reduced the ACTH, C, corticosterone, and FCI responses to exercise and was associated with higher β-endorphin AUC and DHEAS-to-C ratio during recovery, without influencing cardiorespiratory and performance parameters. Tadalafil reduced the activation of the hypothalamus-pituitary-adrenal axis during exercise by probably influencing the brain's nitric oxide- and cGMP-mediated pathways. Further studies are necessary to confirm our results and to identify the involved mechanisms, possible health risks, and potential clinical uses.

Diphenyleneiodonium chloride, an inhibitor of reduced nicotinamide adenine dinucleotide phosphate oxidase, suppresses light-dependent induction of clock and DNA repair genes in zebrafish

In most species, solar light is both a DNA-damaging agent and the key entraining stimulus for the endogenous circadian clock. The zebrafish is an attractive vertebrate system in which to study the influence of light on gene expression because the DNA repair proteins and circadian oscillators in this species are light-responsive. At the molecular level, light treatment of zebrafish cells induces the production of reactive oxygen species (ROS). ROS both alters the reduction-oxidation (redox) state of these cells and stimulates intracellular extracellular signal-regulated kinase (ERK)/mitogen activated protein kinase (MAPK) cascades that transduce photic signals activating the transcription of particular light-responsive genes, including some clock genes and some DNA repair genes involved in photoreactivation. To date, however, the phototransducing molecules responsible for light-dependent ROS production have not been identified. Flavin-containing oxidases, such as reduced nicotinamide adenine dinucleotide phosphate (NADPH) oxidase, are versatile flavoenzymes that catalyze molecular oxidation in numerous metabolic pathways. Importantly, light induces the photoreduction of the flavin adenine dinucleotide (FAD) moiety in these oxidases, leading to ROS production. Here, we show in cultured zebrafish cells that diphenyleneiodonium chloride (DPI), an inhibitor of NADPH oxidase, both suppresses ERK/MAPK activation and efficiently reduces light-dependent expression of clock and photoreactivation genes. Our results suggest that flavin-containing oxidases may be responsible for light-dependent ROS production and thus light-dependent gene expression in zebrafish. Our findings also support the existence of a regulatory link between photoreactivation and the circadian clock in this species.

Possible underlying influence of p38MAPK and NF-κB in the diminished anti-anxiety effect of diazepam in stressed mice

The present study was designed to explore the possible nitriergic influence and role of p38MAPK and NF-κB in the diminished anti-anxiety effect of diazepam in stressed mice, using the elevated plus maze and light/dark box to assess anxiety. Immobilization stress for 6 h enhanced an anxiety-like behavior and increased plasma nitrite levels in mice. Diazepam (2 mg/kg, i.p.) produced an anti-anxiety effect in unstressed mice, but could not produce any change in anxiety levels of stressed mice. SB-203580 (2 mg/kg, i.p.), a specific inhibitor of p38MAPK, per se produced a significant antianxiety-like activity in stressed mice. Administration of a combination of SB-203580 (2 mg/kg, i.p.) and diazepam (2 mg/kg) in stressed mice produced a significantly higher antianxiety-like activity than that produced by SB-203580 alone. Pyrrolidine dithiocarbamate (PDTC), an inhibitor of the activation of NF-κB, per se produced a significant antianxiety-like activity in stressed mice. Combination of PDTC and diazepam also served to produce a higher significant antianxiety-like activity in stressed mice than that produced by PDTC alone. Diazepam could not produce any change in plasma nitrite levels in both unstressed and stressed mice. Both SB-203580 (2 mg/kg, i.p.) and PDTC (100 mg/kg, i.p.) significantly decreased plasma nitrite levels in stressed mice. The observations indicate that the diminished anti-anxiety effect of diazepam in stressed mice may involve strong nitriergic influence and may further be p38MAPK- and NF-κB-dependent.

Roles of nitric oxide, carbon monoxide, and hydrogen sulfide in the regulation of the hypothalamic-pituitary-adrenal axis

The importance of stress in modifying human behavior and lifestyle is no longer a matter of debate. Although mild stress enhances the immune response and prevents infections, prolonged stress seems to play pathogenic roles in depression and neurodegenerative disorders. The body has developed an adaptive stress response consisting of cardiovascular, metabolic, and psychological changes, which act in concert to eliminate stressors. One of the major components of this response is the hypothalamic-pituitary-adrenal axis, also known as the stress axis. Over the last 30 years, many studies have documented the integrated stress-axis regulation by neurotransmitters. They have also demonstrated that gaseous neuromodulators, such as NO, CO, and H(2)S, regulate the hypothalamic release of neuropeptides. The specific effects (stimulatory vs. inhibitory) of these gases on the stress axis varies, depending on the type of stress (neurogenic or immuno-inflammatory), its intensity (low or high), and the species studied (rodents or humans). This review examines the complex roles of NO, CO, and H(2)S in modulation of stress-axis activity, with particular emphasis on the regulatory effects they exert at the hypothalamic level.

Involvement of NO-cGMP pathway in anti-anxiety effect of aminoguanidine in stressed mice

In the present study, effect of aminoguanidine (12.5, 25 and 50mg/kg, i.p.), a selective inhibitor of inducible nitric oxide synthase, was evaluated for its anti-anxiety activity in stressed mice employing elevated plus maze, open field test, light/dark test and social interaction test. Restraint stress induced by immobilizing for 6h enhanced an anxiety-like behavior and increased plasma nitrite levels in mice. Only the highest dose (50mg/kg) employed of aminoguanidine attenuated the stress-induced anxiety-like behavior and decreased plasma nitrite levels. There was no significant anxiolytic effect of aminoguanidine in unstressed mice. Sildenafil (1mg/kg i.p.), was used to explore the probable mechanism of anti-anxiety activity of aminoguanidine through NO-cGMP signaling. Aminoguanidine (50mg/kg) attenuated the anxiogenic effect of sildenafil. Aminoguanidine and sildenafil per se and in combination did not affect the locomotor activity of stressed and unstressed mice as compared to their respective control groups. Thus, aminoguanidine produced anti-anxiety activity in stressed mice through iNOS-NO-cGMP pathway.

The type 5 phosphodiesterase inhibitor tadalafil influences salivary cortisol, testosterone, and dehydroepiandrosterone sulphate responses to maximal exercise in healthy men

CONTEXT

Physical exercise-related stress activates hypothalamus-pituitary-adrenal (HPA) axis; nitric oxide is one of the mediators of the HPA axis response to stress, and phosphodiesterase type 5 inhibitors influences nitric oxide-linked biological activities.

OBJECTIVE

The objective of the study was to investigate whether a single oral long half-life phosphodiesterase type 5 inhibitor (tadalafil) administration influences the HPA axis response to exercise-related stress.

DESIGN

This was a double-blind, cross-over trial.

PARTICIPANTS

Participants included nine healthy male athletes.

INTERVENTIONS

All subjects performed a maximal exercise test in normoxia, after which they received a single oral administration of tadalafil or placebo. Then after a 2-wk washout period, they were crossed over and repeated the exercise test. Each subject was his own control. Salivary collections, for steroid evaluations [cortisol, dehydroepiandrosterone sulphate (DHEAS), testosterone] and respective ratio calculation (DHEAS to cortisol, testosterone to cortisol, testosterone to DHEAS), were performed before each exercise (Pre-Ex), immediately after (Post-Ex), and at 30 min during recovery.

RESULTS

As expected, mean salivary cortisol concentration increased immediately after exercise after both tadalafil and placebo (P = 0.014 and P =0.036 vs. Pre-Ex, respectively); however, the cortisol increase was significantly higher after tadalafil administration (P = 0.034 vs. placebo). Furthermore, an increased salivary testosterone after exercise was observed only after tadalafil administration (P = 0.029 vs. Pre-Ex). No effects of either exercise and/or tadalafil administration on salivary DHEAS concentrations were observed. DHEAS to cortisol and testosterone to cortisol ratios significantly decreased after exercise after tadalafil administration (P = 0.037, and P = 0.02 vs. placebo, respectively).

CONCLUSION

Tadalafil administration amplified the salivary cortisol and testosterone responses to a maximal exercise-related stress in healthy trained humans.

NO netting, health and stress – Studying wellness from a net perspective

On the nature of wellness, stress, netting and the radical gas nitric oxide (NO). The multi-complex role of NO resulted in its discoverers receiving a Nobel award, its presence everywhere and volatility makes it a suitable candidate to be a main signal in an instantaneous communication network. Such network, with the capacity of tight physiological monitoring, enables assets distributions in the body. A model is presented suggesting that an inter-cellular communication network coordinates the various bodily functions. Radical gases like nitric oxide (NO) are signals in this net and its usability affects health and indicates wellness. From this netting point of view, stress is the sense of flow interruption or blockage of the information stream. Such flow interruption affects also physiological functions and can explain the association between stress and many ailments. It is suggested that netting is a prerequisite route of wellness, enabling bodily unconscious managerial decisions. This vital diffusive network is extremely labile and potentially could contain the interplay of consciousness and unconsciousness effected by activities such as yoga or guided imagery. Vast data from studies on NO signals, health and the relaxation/stress processes have already been accumulated. Integration of these data supports this novel look of an NO network as a coordinator. Interactions between stress and health are discussed in net perspective and include basic concepts of some integrative health approaches. Studying the nature of such communication network and of NO may suggest new ways to reduce stress and approach wellness.

Nitric oxide impairs baroreflex gain during acute psychological stress

Psychological stress can suppress baroreflex function, but the mechanism has not been fully elucidated. Nitric oxide in the brain and in the adrenal cortex, as well as plasma glucocorticoids, increases during stress and has been shown to suppress reflex gain in unstressed animals. Therefore, the purpose of this study was to test the hypothesis that stress, caused by exposure to a novel environment, decreases baroreflex gain in rabbits through the actions of nitric oxide to increase corticosterone release. Baroreflex control of heart rate and plasma corticosterone levels was quantified before and after blockade of nitric oxide synthase (NOS) with N(omega)-nitro-L-arginine (L-NNA; 20 mg/kg iv) in conscious rabbits exposed to a novel environment and in the same rabbits once they had been conditioned to the environment. Stress significantly reduced baroreflex gain from -23.4 +/- 2 to -12.2 +/- 1.6 beats x min(-1) x mmHg(-1) (P < 0.05) and increased plasma corticosterone levels from 5.4 +/- 0.7 to 15.5 +/- 5.0 ng/ml (P < 0.05). NOS blockade increased gain in stressed animals (to -27.2 +/- 5.4 beats x min(-1) x mmHg(-1), P < 0.05) but did not alter gain in unstressed rabbits (-26.8 +/- 4.9 beats x min(-1) x mmHg(-1)) such that gain was equalized between the two states. NOS blockade increased plasma corticosterone levels in unstressed animals (to 14.3 +/- 2.1 ng/ml, P < 0.05) but failed to significantly alter levels in stressed rabbits (14.0 +/- 3.9 ng/ml). In conclusion, psychological stress may act via nitric oxide, independently of increases in corticosterone, to decrease baroreflex gain.

Exposure to stress

Stress-induced vascular adaptive response in SHR was investigated, focusing on the endothelium. Noradrenaline responses were studied in intact and denuded aortas from 6-week-old (prehypertensive) and 14-week-old (hypertensive) SHR and age-matched Wistar rats submitted or not to acute stress (20-min swimming and 1-h immobilization 25 min apart), preceded or not by chronic stress (2 sessions 2 days apart of 1-h day immobilization for 5-consecutive days). Stress did not alter the reactivity of denuded aorta. Moreover, no alteration in the EC50 values was observed after stress exposure. In intact aortas, acute stress-induced hyporeactivity to noradrenaline similar between strains at both age. Chronic stress potentiated this adaptive response in 6- and 14-week-old Wistar but not in 6-week-old SHR, and did not alter the reactivity of 14-week-old SHR. Maximum response (g) in intact aortas [6-week-old: Wistar 3.25+/-0.12, Wistar/acute 1.95+/-0.12*, Wistar/chronic 1.36+/-0.21*(+), SHR 1.75+/-0.11, SHR/acute 0.88+/-0.08*, SHR/chronic 0.85+/-0.05*; 14-week-old: Wistar 3.83+/-0.13, Wistar/acute 2.72+/-0.13*, Wistar/chronic 1.91+/-0.19*(+), SHR 4.03+/-0.17, SHR/acute 2.26+/-0.12*, SHR/chronic 4.10+/-0.23; inside the same strain: *P < 0.05 relate to non-stressed rat, +P < 0.05 related to acute stressed rat; n = 6-18]. Independent of age and strain, L-NAME and endothelium removal abolished the stress-induced aorta hyporeactivity.

CONCLUSION

The vascular adaptive response to stress is impaired in SHR, independently of the hypertensive state. Moreover, this vascular adaptive response is characterized by endothelial nitric oxide-system hyperactivity in both strains.

The hypothalamo-pituitary axis responses to lipopolysaccharide-induced endotoxemia in mice lacking inducible nitric oxide synthase

Nitric oxide (NO) generated by inducible NO synthase (iNOS) may be implicated in the biological responses of the central nervous system to immune stimuli. To elucidate the role of iNOS in the hypothalamo-pituitary axis in responses to endotoxemia, using iNOS knockout (KO) mice, we examined the levels of c-fos, a neural activational marker, and corticotropin-releasing hormone (CRH) gene transcription in the paraventricular nucleus (PVN) and central amygdala (CeAMY) during lipopolysaccharide (LPS)-induced endotoxemia. In addition, the serum adrenocorticotropic hormone (ACTH) levels were also examined during endotoxemia. Following the intraperitoneal administration of LPS (1 mg/kg), the levels of the c-fos gene expression significantly increased in the PVN and the CeAMY regardless of the genotype. However, the disruption of the iNOS gene resulted in a significant decrease in the c-fos gene induction in the PVN in comparison to that observed in control mice. LPS administration caused a significant increase in CRH mRNA levels in the PVN and CeAMY regardless of genotype. However, the LPS-induced upregulation of CRH mRNA was significantly attenuated in the PVN of iNOS KO mice in comparison to that in the control mice. In contrast, no such genotype differences in the neural activity or CRH gene transcription were observed in the CeAMY. The serum ACTH responses to LPS were also significantly blunted in the iNOS KO mice in comparison to the control mice. These results suggest that iNOS-derived NO may therefore play a stimulatory role in the activity of the hypothalamo-pituitary axis during endotoxemia.

Effect of chronic social stress on nitric oxide synthesis and vascular function in rats with family history of hypertension

Genetic predisposition and psychosocial stress are known risk factors in the aetiology of hypertension. The aim of this study was to investigate the as yet unknown role of nitric oxide (NO) in mechanisms of social stress-induced hypertension in rats with a family history of hypertension. Male adult rats used in the study were offspring of normotensive (Wistar) dams and spontaneously hypertensive sires. The rats were exposed to 6-week crowding stress (5 rats/cage, 200 cm2/rat). Control rats were kept four per cage (480 cm2/rat). Blood pressure was determined non-invasively on the tail. Basal blood pressure of all rats was 131 +/- 2 mm Hg. Crowding stress increased significantly blood pressure (p < 0.02 vs. basal value). Crowding had no influence on NO synthase activity in the left ventricle, adrenal glands and kidney. However, crowding stress reduced significantly NO synthase activity in the aorta by 37% (p < 0.01 vs. control). Acetylcholine-induced relaxation and noradrenaline-induced vasoconstriction of the femoral artery were reduced in stressed rats by 58% (p < 0.001) and 41% (p < 0.003), respectively. On balance then, the results indicate that chronic social stress produced by crowding was associated with reduced vascular NO synthesis and altered vascular function in adult borderline hypertensive rats of normotensive mothers.

Hypothalamic monoamines in cold stress on the background of changes in the activity of the nitric oxide system

The effects of the NO donor sodium nitroprusside and the NO synthase blocker L-omega-N-nitroarginine (LNA) on body temperature, hypothalamic monoamines, and plasma corticosterone in conditions of cooling were studied in Male Wistar rats. Reductions in body temperature on cooling, both after administration of sodium nitroprusside and LNA, were no different from those seen without treatment. The basal corticosterone level after treatment with sodium nitroprusside increased from 5.3 +/- 2.2 to 29.1 +/- 1.8 microg%. Cooling led to a multiple increase in corticosterone levels in all animals, both in control conditions and after treatment with sodium nitroprusside and LNA. Sodium nitroprusside significantly decreased the basal hypothalamic noradrenaline level, by 37%. Cooling of the animals in these conditions led to an additional drop in the noradrenaline level. Noradrenaline levels 48 h after cold stress applied to animals cooled after treatment with LNA or sodium nitroprusside were significantly higher than in those cooled without treatment. No changes in serotonin and 5-hydroxyindoleacetic acid levels were seen in these experiments. The basal dihydroxyphenylacetic acid and dopamine levels increased after treatment with sodium nitroprusside, by 379% and 239% respectively. No dopamine response to cold was observed, though the dihydroxyphenylacetic acid level in the control group and animals treated with LNA increased. Thus, cold stress did not reveal differently directed directions for the actions of the NO donor and the NO synthase blocker, as seen with other types of stress.

Endothelin 1 and 3 enhance neuronal nitric oxide synthase activity through ETB receptors involving multiple signaling pathways in the rat anterior hypothalamus

We have previously reported that endothelin 1 and 3 (ET-1, ET-3) through the ETB receptor decrease norepinephrine release in the anterior hypothalamus and activate the nitric oxide (NO) pathway. In the present work we sought to establish the receptors and intracellular mechanisms underlying the increase in nitric oxide synthase (NOS) activity stimulated by ET-1 and ET-3 in the rat anterior hypothalamus. Results showed that ETs-stimulated NOS activity was inhibited by a selective ETB antagonist (BQ-788), but not by a selective ETA antagonist (BQ-610). In addition, NOS activity was not altered in the presence of an ETA agonist (sarafotoxin 6b), but it was enhanced in the presence of a ETB agonist (IRL-1620). Both Nomega-nitro-L-arginine methyl ester (NOS inhibitor), and 7-nitroindazole (neuronal NOS inhibitor) diminished ETs-stimulated NOS activity. The stimulatory effect of ETs on NOS activity was inhibited in the presence of PLC, PKC, PKA and CaMK-II inhibitors (U-73122, GF-109203X, H-89 and KN-62, respectively), and the IP3 receptor selective antagonist, 2-APB. Our results showed that both ET-1 and ET-3 modulate neuronal NOS activity through the ETB receptor in the rat anterior hypothalamus involving the participation of the PLC-PKC/IP3 pathway as well as PKA and CaMK-II.

Effects of N-nitro l-arginine methyl ester (l-NAME), a potent nitric oxide synthase inhibitor, on visual evoked potentials of rats exposed to different experimental stress models

AIM

The aim of our study was to investigate the effects of the nitric oxide synthase inhibitor, N-nitro l-arginine methyl ester (l-NAME, 10 mg kg-1 day-1 i.p.), on visual evoked potentials (VEPs) and lipid peroxidation expected to occur during chronic stress (15 days).

METHODS

Eight experimental groups, each consisting of 10 rats, were formed: control group (C), the group injected with l-NAME (L), groups exposed to cold stress (CS), immobilization stress (IS), and both cold and immobilization stress (CIS), groups exposed to stress and injected with l-NAME (CSL, ISL, CISL).

RESULTS

l-NAME decreased brain and retina nitrite levels in all experimental groups compared with their corresponding control groups. l-NAME decreased glutathione peroxidase (GSH-Px) activity in the brain and retina in the L group, but increased it in the CSL and CISL groups compared with the C group. Lipid peroxidation was increased in the brain and retina tissues of all stress groups with respect to the C group. l-NAME markedly increased brain thiobarbituric acid reactive substances (TBARS) levels in the L group, while significantly decreasing brain and retina TBARS levels in all stress groups in comparison with their respective control groups. l-NAME caused a significant delay in all components of VEPs in the L group compared with the C group. However, l-NAME significantly decreased latencies of P1, N1, P2 and P3 components in the CSL group and all components in the ISL and CISL groups with respect to their corresponding control groups.

CONCLUSION

This study clearly indicated that lipid peroxidation may be one possible factor affecting VEP components.

Effet d'une déshydratation sur le monoxyde d'azote, l'axe vasopressinergique et l'axe corticotrope chez le rat

Effect of dehydration on nitric oxide, corticotropic and vasopressinergic axis in rat. The purpose of our work is to study, in the male 'Wistar' rat, the effects of a chronic dehydration, by deprivation of water for three days out of four, during four repeated cycles, on the evolution of certain blood variables, on the activities of both corticotropic and vasopressinergic axis and on the synthesis of nitric oxide. The chronic dehydration causes a considerable reduction of the body weight, an activation of the vasopressinergic axis and an increase in the circulating rates of the nitrates/nitrites, which represent the final metabolites of the reaction of oxidation of nitric oxide. The pituitary-adrenal axis is not statistically affected by the chronic dehydration. This seems to be in favour of a possible adaptation of corticotropic axis to chronic water deprivation. The activation of synthesis of nitric oxide shows its implication in the regulation of the water balance and its buffer effect on vasoconstriction and hypertension induced by water stress.

The effect of vitamin E on stress-induced changes in visual evoked potentials (VEPs) in rats exposed to different experimental stress models

PURPOSE

The aim of the study was to investigate the effects of vitamin E on stress-induced changes in visual evoked potentials (VEPs) and lipid peroxidation.

METHODS

Eight experimental groups of 10 rats per group were formed. These consisted of the control group (C); the group treated with vitamin E (E); groups exposed to cold stress (CS), immobilization stress (IS) and both cold and immobilization stress (CIS), and groups exposed to equivalent stresses and treated with vitamin E (CSE, ISE, CISE). Vitamin E was injected intramuscularly in a dose of 30 mg/kg/day.

RESULTS

Following chronic stress (15 days), plasma corticosterone concentrations in all experimental groups were significantly increased over those in C group. Vitamin E significantly decreased corticosterone levels in all stress groups compared with their respective control groups. Brain nitrite levels were significantly more elevated in all stress groups than in the C group. Vitamin E reduced retina and brain nitrite levels in all stress and E groups compared with their respective control groups. Vitamin E decreased glutathione peroxidase (GSH-Px) activity in retina and brain tissues in the CSE group, but increased it in the ISE group compared with their respective control groups. Lipid peroxidation was increased in brain and retina tissues in all stress groups as indicated by the significant increase in thiobarbituric acid-reactive substance (TBARS) levels with respect to the C group. Vitamin E produced a significant decrease in brain and retina TBARS levels in all stress groups with respect to their corresponding control groups. The mean latencies of P1, N1, P2, N2 and P3 components were significantly prolonged in all stress groups compared with the C group.

CONCLUSION

Vitamin E returned the VEP latencies in the stress groups to control values. Our findings clearly indicated that vitamin E has the potential to prevent VEP changes caused by stress.

Cytokines and neuro-immune-endocrine interactions: a role for the hypothalamic-pituitary-adrenal revolving axis

Cytokines, peptide hormones and neurotransmitters, as well as their receptors/ligands, are endogenous to the brain, endocrine and immune systems. These shared ligands and receptors are used as a common chemical language for communication within and between the immune and neuroendocrine systems. Such communication suggests an immunoregulatory role for the brain and a sensory function for the immune system. Interplay between the immune, nervous and endocrine systems is most commonly associated with the pronounced effects of stress on immunity. The hypothalamic-pituitary-adrenal (HPA) axis is the key player in stress responses; it is well established that both external and internal stressors activate the HPA axis. Cytokines are chemical messengers that stimulate the HPA axis when the body is under stress or experiencing an infection. This review discusses current knowledge of cytokine signaling pathways in neuro-immune-endocrine interactions as viewed through the triplet HPA axis. In addition, we elaborate on HPA/cytokine interactions in oxidative stress within the context of nuclear factor-kappaB transcriptional regulation and the role of oxidative markers and related gaseous transmitters.

Daily exercise normalizes the number of diaphorase (NOS) positive neurons in the hypothalamus of hypertensive rats

It is well known that nitric oxide (NO), within the paraventricular nucleus (PVN) of the hypothalamus, mediates sympatho-inhibition via an inhibitory GABA-ergic mechanism. Furthermore, the inhibitory GABA-ergic mechanism is impaired in the spontaneously hypertensive rat (SHR). These data suggest that the NO system, within the PVN, may also be impaired in the SHR. In addition, previous studies have documented that daily exercise attenuates the development of tachycardia, hypertension and blood pressure related cardiovascular disease risk factors in SHR. These data suggest that daily exercise enhances the inhibitory GABA-ergic and/or NO systems. Therefore, this study was designed to test the hypothesis that hypertension, in the SHR, is associated with a lower number of NADPH-diaphorase (a commonly used marker for neuronal NOS activity) positive neurons within the PVN and that daily exercise increases the number of NOS positive neurons. Using a standard histochemical protocol, NOS positive neurons were measured in the PVN, supraoptic nucleus, median preoptic area, lateral hypothalamus, nucleus of the tractus solitarius and rostral ventrolateral medulla. Results document that SHR have significantly fewer NOS-positive neurons in the PVN than their genetic control, the Wistar-Kyoto (WKY) rats (110+/-11 versus 139+/-17). Furthermore, daily exercise increased the number of NOS positive neurons in the SHR to levels seen in the WKY rats. These data demonstrate that hypertension, in the SHR, is associated with a lower number of NOS positive neurons within the PVN and that daily exercise increases the number of NOS positive neurons within the PVN.

Influence of estradiol on NADPH diaphorase/neuronal nitric oxide synthase activity and colocalization with progesterone or type II glucocorticoid receptors in ovine hypothalamus

Nitric oxide (NO) has been shown to play an important role in both the neuroendocrine reproductive and stress axes, which are closely linked. Because progesterone (P4) receptors (PRs) and glucocorticoid receptors (GRs) are not found in GnRH neurons and the NOergic system has been implicated in the control of GnRH secretion, this study aimed to ascertain whether steroids altered the NOergic system. Our first objective was to map the distribution of NO synthase (NOS) cells in the ovine preoptic area (POA) and hypothalamus and to determine whether NOS activity is enhanced by estradiol (E2) treatment. Using NADPH diaphorase (NADPHd) histochemistry, we found that NADPHd-positive neurons were spread throughout the ovine POA and hypothalamus, and that all NADPHd cells were immunoreactive for NOS. In response to estradiol, a significant increase in the number of NADPHd cells was noted only in the ventrolateral region of the ventromedial nucleus (VMNvl), with no significant difference in the POA or arcuate nucleus. Progesterone and glucocorticoid receptors were colocalized with NADPHd reactive neurons in the POA, arcuate nucleus, and VMNvl of ewes in both treatment groups. In ewes receiving estradiol, the number of NADPHd-positive cells containing steroid receptors in the POA (PR, 81%; GR, 79%) and arcuate nucleus (PR, 89%; GR, 84%) was similar, but in the VMNvl, fewer NADPHd-positive cells contained GR (PR, 88%, GR, 31%). These data show that estradiol up-regulates NOS activity in a site-specific manner and that the influence and possible interaction of progesterone and corticosteroids on NO producing cells may differ according to the neural location.

Endothelin-1 and -3 diminish neuronal NE release through an NO mechanism in rat anterior hypothalamus

The existence of endothelin binding sites on the catecholaminergic neurons of the hypothalamus suggests that endothelins (ETs) participate in the regulation of noradrenergic transmission modulating various hypothalamic-controlled processes such as blood pressure, cardiovascular activity, etc. The effects of ET-1 and ET-3 on the neuronal release of norepinephrine (NE) as well as the receptors and intracellular pathway involved were studied in the rat anterior hypothalamus. ET-1 (10 nM) and ET-3 (10 nM) diminished neuronal NE release and the effect blocked by the selective ET type B receptor antagonist BQ-788 (100 nM). N(omega)-nitro-L-arginine methyl ester (10 microM), methylene blue (10 microM), and KT5823 (2 microM), inhibitors of nitric oxide synthase activity, guanylate cyclase, and protein kinase G, respectively, prevented the inhibitory effects of both ETs on neuronal NE release. In addition, both ETs increased nitric oxide synthase activity. Furthermore, 100 microM picrotoxin, a GABA(A)-receptor antagonist, inhibited ET-1 and ET-3 response. Our results show that ET-1 as well as ET-3 has an inhibitory neuromodulatory effect on NE release in the anterior hypothalamus mediated by the ET type B receptor and the involvement of a nitric oxide-dependent pathway and GABA(A) receptors. ET-1 and ET-3 may thus diminish available NE in the synaptic gap leading to decreased noradrenergic activity.

Microinfusion of a nitric oxide donor in discrete brain regions activates the hypothalamic-pituitary-adrenal axis

We previously showed that the intracerebroventricular injection of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) released adrenocorticotropic hormone (ACTH) and upregulated transcripts for corticotropin-releasing factor (CRF) and vasopressin in the paraventricular nucleus (PVN) of the rat hypothalamus. In the present work, we microinfused SIN-1 into the PVN itself, the amygdala, the hippocampus or the frontal cortex to identify the brain regions that modulate the influence of NO on the hypothalamic-pituitary-adrenal (HPA) axis. Microinfusion into the PVN, which contains most of the CRF and vasopressin neurones that control HPA axis activity, significantly released ACTH. Microinfusion into the amygdala or the hippocampus, areas which also regulate HPA axis activity, similarly increased plasma ACTH levels. However, these responses were smaller and showed a delayed onset, compared to that observed following PVN treatment. In contrast, microinfusion of SIN-1 into the frontal cortex, which is not believed to exert a major direct influence on the HPA axis, was without effect. The observation that compared to microinfusion into the PVN, peak ACTH levels were both smaller and delayed when SIN-1 was microinfused into the amygdala or the hippocampus, and that SIN-1 only increased NO levels when injected into the PVN, suggests that the NO donor injected outside the PVN activates this nucleus by targeting pathways that connect it to these other regions rather than by leakage. Collectively, our results provide important clues regarding the putative role of these regions in modulating the influence of NO on the HPA axis.

Lack of neuronal NOS has consequences for the expression of POMC and POMC-derived peptides in the mouse pituitary

The relevance of NO in neuroendocrine signalling has been investigated by analysis of cellular expression of pro-opiomelanocortin (POMC) and the POMC-derived peptides beta-endorphin, alpha-melanocyte stimulating hormone and adrenocorticotropin. Expression patterns were studied in the pituitary gland of 150-day old wild-type and neuronal-NOS (nNOS) knock-out mice by using immunohistochemistry, in situ hybridization and Northern blot analysis. Remaining NO-generating capacities in the knock-out mice were demonstrated by immunohistochemical localization of inducible, endothelial and neuronal NOS isoforms. Quantitative analysis revealed that cellular expression of POMC mRNA was drastically reduced in the pituitary of knock-out mice in comparison to controls. In situ hybridization studies demonstrated that this reduction was most pronounced in the intermediate lobe, while the anterior lobe was much less affected. Immunostaining for the proteolytic fragments of POMC was significantly reduced in the intermediate lobe cells of knock-out mice. A moderate reduction of immunostaining for these peptides was also observed in adenopituitary cells of nNOS knock-out mice. Our data demonstrate that the lack of nNOS substantially affects cellular levels of pituitary opioid peptides, which may have consequences for the response of these animals to stress and pain.

The sympathetic adrenomedullary system, but not the hypothalamic-pituitary-adrenal axis, participates in aorta adaptive response to stress: nitric oxide involvement

Stress induced a decrease in the reactivity of the aorta to noradrenaline (NA), as a consequence of an endothelial nitric oxide (NO) system hyperactivity. The main characteristic of the stress response is activation of the hypothalamic-pituitary-adrenal (HPA) axis and sympathetic adrenomedullary (SA) system. The participation of the HPA axis and SA system in the decreased reactivity to NA in the aorta of rats exposed to 4-h immobilization was investigated. Concentration-response relationships for NA were obtained in the aorta, with and without endothelium, isolated from normal and stressed rats, following these procedures: (1) in the absence and presence of L-NAME; (2) after adrenalectomy (ADX) or not, in the absence or presence of L-NAME; (3) ADX rats treated or not with corticosterone; (4) ADX associated with stress; and (5) treated or not with reserpine. The reactivity of aorta without endothelium was unaffected by the procedures. The reactivity of aorta with endothelium was decreased by either stress or ADX. This effect was reversed by both L-NAME and corticosterone. ADX did not potentiate the decrease in the aorta reactivity induced by stress. Reserpine did not change the reactivity of aorta with endothelium from normal rats, but prevented the decrease in reactivity induced by stress. It is concluded that the HPA axis participates in endothelium-dependent modulation of aorta reactivity in normal conditions and that the SA system participates in hyperactivity of the endothelial NO-system induced by stress, which is responsible for the decreased aorta reactivity to NA.

Nitric oxide and carbon monoxide have a stimulatory role in the hypothalamic-pituitary-adrenal response to physico-emotional stressors in rats

We tested the hypothesis that nitric oxide and carbon monoxide, which are produced in the brain by nitric oxide synthase (NOS) and heme oxygenase (HO), modulate the hypothalamic-pituitary-adrenal response to physico-emotional stressors by acting at the hypothalamus. Accordingly, we determined 1) whether the intracerebroventricular (icv) injection of NOS or HO inhibitors at doses that were confined to the brain attenuated electroshock-induced ACTH release; and 2) whether the decreases in this ACTH response were concurrent with decreases in NOS or HO activity levels at the hypothalamus. Icv injection of the NOS inhibitor Nomega-nitro-L-arginine-methylester (L-NAME; 50 microg) or the HO inhibitor tin protoporphyrin (SnPP; 20-25 microg) significantly blunted the plasma ACTH response to a 45-min session of intermittent electroshocks. Importantly, in these same animals there were concurrent decreases in hypothalamic NOS or HO activities, respectively. There were little or no effects of these inhibitors on anterior pituitary NOS or HO activities, indicating that there was only minimal leakage of the drug from the brain after icv administration. The specificity of action of these inhibitors was confirmed by the fact that SnPP did not affect NOS activity, and L-NAME did not affect HO activity. Finally, L-NAME produced no effect, whereas SnPP produced only transient increases in blood pressure, suggesting that these inhibitors do not affect activity indirectly through alterations in blood pressure. These data support the hypothesis that in the whole animal, both NO and CO exert a stimulatory influence on the acute ACTH response to physico-emotional stressors, and that the hypothalamus is the critical site of their actions.

Nitric oxide stimulates ACTH secretion and the transcription of the genes encoding for NGFI-B, corticotropin-releasing factor, corticotropin-releasing factor receptor type 1, and vasopressin in the hypothalamus of the intact rat

We investigated the effect of the intracerebroventricular injection of the nitric oxide (NO) donor 3-morpholino-sydnonimine (SIN-1) on the release of adrenocorticotropin hormone (ACTH) and the neuronal response of hypothalamic neurons responsible for this release. Rats that were administered SIN-1 showed significant elevations in plasma ACTH levels, a response that was virtually abolished by antibodies against corticotropin-releasing factor (CRF) and significantly blunted by vasopressin (VP) antiserum. SIN-1 also upregulated heteronuclear (hn) transcripts for CRF and VP and messenger RNA (mRNA) levels for the immediate early gene NGFI-B and for CRF receptor type 1 (CRF-R(1)) in the parvocellular portion of the paraventricular nucleus (PVN) of the hypothalamus. Blockade of prostaglandin synthesis with ibuprofen did not alter the ACTH or the PVN response to SIN-1. The central nucleus of the amygdala and the supraoptic nucleus, regions that are involved in autonomic adjustments to altered cardiovascular activity, also responded to SIN-1 with elevated NGFI-B mRNA levels. However, the only change in mean arterial blood pressure caused by this NO donor was a transient and modest increase. To our knowledge, this is the first demonstration that in the intact rat NO stimulates the activity of PVN neurons that control the hypothalamic-pituitary-adrenal axis. It must be noted, however, that our results do not allow us to determine whether this effect was direct or mediated through PVN afferents. This study should help resolve the controversy generated by the use of isolated brain tissues to investigate the net effect of NO on hypothalamic peptide production.