Immobilization-induced stress activates neuronal nitric oxide synthase (nNOS) mRNA and protein in hypothalamic-pituitary-adrenal axis in rats

Nitric Oxide in the Spinal Cord Is Involved in the Hyperalgesia Induced by Tetrahydrobiopterin in Chronic Restraint Stress Rats

It has been well recognized that exposure to chronic stress could increase pain responding and exacerbate pain symptoms, resulting in stress-induced hyperalgesia. However, the mechanisms underlying stress-induced hyperalgesia are not yet fully elucidated. To this end, we observed that restraint as a stressful event exacerbated mechanical and thermal hyperalgesia, accompanied with up-regulation of nitric oxide (NO) (P < 0.001), GTP cyclohydrolase 1 (GCH1) (GCH1 mRNA: P = 0.001; GCH1 protein: P = 0.001), and tetrahydrobiopterin (BH4) concentration (plasma BH4: P < 0.001; spinal BH4: P < 0.001) on Day 7 in restraint stress (RS) rats. Intrathecal injection of N ^ω-nitro-L-arginine methyl ester (L-NAME), a non-specific NO synthase inhibitor, or N-([3-(aminomethyl)phenyl]methyl) ethanimidamide, a special inhibitor of inducible NO synthase (iNOS), for seven consecutive days attenuated stress-induced hyperalgesia and decreased the production of NO (P < 0.001). Interestingly, 7-nitro indazole, a special inhibitor of neuronal NO synthase, alleviated stress-induced hyperalgesia but did not affect spinal NO synthesis. Furthermore, intrathecal injection of BH4 not only aggravated stress-induced hyperalgesia but also up-regulated the expression of spinal iNOS (iNOS mRNA: P = 0.015; iNOS protein: P < 0.001) and NO production (P < 0.001). These findings suggest that hyperalgesia induced by RS is associated with the modulation of the GCH1-BH4 system and constitutively expressed spinal iNOS. Thus, the GCH1-BH4-iNOS signaling pathway may be a new novel therapeutic target for pain relief in the spinal cord.

Nitrergic neurotransmission in the paraventricular nucleus of the hypothalamus modulates autonomic, neuroendocrine and behavioral responses to acute restraint stress in rats

We investigated the involvement of nitrergic neurotransmission within the paraventricular nucleus of the hypothalamus (PVN) in modulation of local neuronal activation, autonomic and neuroendocrine responses and behavioral consequences of acute restraint stress in rats. Bilateral microinjections of the selective neuronal nitric oxide (NO) synthase (nNOS) inhibitor Nw-Propyl-L-arginine (NPLA) or the NO scavenger carboxy-PTIO into the PVN reduced arterial pressure and heart rate increases, as well as the fall in cutaneous tail temperature induced by restraint stress. PVN injection of either NPLA or carboxy-PTIO also inhibited restraint-induced increases in anxiety-related behaviors in the elevated plus-maze 24 h later. Local microinjection of NPLA or carboxy-PTIO into the PVN reduced the number of c-fos-immunoreactive neurons in the dorsal parvocellular, ventromedial, medial parvocellular and lateral magnocelllular portions of the PVN in animals subjected to restraint stress. However, neither NPLA nor carboxy-PTIO into the PVN affected restraint-induced increases in plasma corticosterone concentration. The present results indicate that PVN nitrergic neurotransmission acting via nNOS activation has a facilitatory influence on autonomic responses to acute restraint and the delayed emotional consequences of restraint stress. Our results also provide evidence of a prominent role of local nitrergic neurotransmission in PVN neuronal activation during stress.

Neuronal nitric oxide synthase and affective disorders

Affective disorders including major depressive disorder (MDD), bipolar disorder (BPD), and general anxiety affect more than 10% of population in the world. Notably, neuronal nitric oxide synthase (nNOS), a downstream signal molecule of N-methyl-D-aspartate receptors (NMDARs) activation, is abundant in many regions of the brain such as the prefrontal cortex (PFC), hippocampus, amygdala, dorsal raphe nucleus (DRN), locus coeruleus (LC), and hypothalamus, which are closely associated with the pathophysiology of affective disorders. Decreased levels of the neurotransmitters including 5-hydroxytryptamine or serotonin (5-HT), noradrenalin (NA), and dopamine (DA) as well as hyperactivity of the hypothalamic-pituitary-adrenal (HPA) axis are common pathological changes of MDD, BPD, and anxiety. Increasing data suggests that nNOS in the hippocampus play a crucial role in the etiology of MDD whereas nNOS-related dysregulation of the nitrergic system in the LC is closely associated with the pathogenesis of BPD. Moreover, hippocampal nNOS is implicated in the role of serotonin receptor 1 A (5-HTR1 A) in modulating anxiety behaviors. Augment of nNOS and its carboxy-terminal PDZ ligand (CAPON) complex mediate stress-induced anxiety and disrupting the nNOS-CAPON interaction by small molecular drug generates anxiolytic effect. To date, however, the function of nNOS in affective disorders is not well reviewed. Here, we summarize works about nNOS and its signal mechanisms implicated in the pathophysiology of affective disorders. On the basis of this review, it is suggested that future research should more fully focus on the role of nNOS in the pathomechanism and treatment of affective disorders.

Neuronal activity regulates neurotransmitter switching in the adult brain following light-induced stress

The discovery that neurotransmitter identity is regulated by activity in the adult mammalian brain during a stress response raises questions about the extent and function of this plasticity. Specific synapses are associated with the release of a particular neurotransmitter or transmitters on the basis of evidence obtained under a single set of conditions. Transmitter switching endows the connectome with greater plasticity: Activity-dependent revision of signaling provides another dimension of flexibility to regulate normal behavior. Changes in transmitter identity are also positioned to contribute to diseases of the nervous system. Neurotransmitter imbalance has long been implicated in common neurological and psychiatric disorders, provoking interest in transmitter switching as a therapeutic tool for patients.

Neurotransmitter switching in the adult mammalian brain occurs following photoperiod-induced stress, but the mechanism of regulation is unknown. Here, we demonstrate that elevated activity of dopaminergic neurons in the paraventricular nucleus of the hypothalamus (PaVN) in the adult rat is required for the loss of dopamine expression after long-day photoperiod exposure. The transmitter switch occurs exclusively in PaVN dopaminergic neurons that coexpress vesicular glutamate transporter 2 (VGLUT2), is accompanied by a loss of dopamine type 2 receptors (D2Rs) on corticotrophin-releasing factor (CRF) neurons, and can lead to increased release of CRF. Suppressing activity of all PaVN glutamatergic neurons decreases the number of inhibitory PaVN dopaminergic neurons, indicating homeostatic regulation of transmitter expression in the PaVN.

Acute hypoxia activates neuroendocrine, but not presympathetic, neurons in the paraventricular nucleus of the hypothalamus: differential role of nitric oxide

Hypoxia results in decreased arterial Po₂, arterial chemoreflex activation, and compensatory increases in breathing, sympathetic outflow, and neuroendocrine secretions, including increased secretion of AVP, corticotropin-releasing hormone (CRH), adrenocorticotropin hormone (ACTH), and corticosterone. In addition to a brain stem pathway, including the nucleus tractus solitarius (nTS) and the rostral ventrolateral medulla (RVLM), medullary pathways to the paraventricular nucleus of the hypothalamus (PVN) contribute to chemoreflex responses. Experiments evaluated activation of specific cell phenotypes within the PVN following an acute hypoxic stimulus (AH; 2 h, 10% O₂) in conscious rats. Retrograde tracers (from spinal cord and RVLM) labeled presympathetic (PreS) neurons, and immunohistochemistry identified AVP- and CRH-immunoreactive (IR) cells. c-Fos-IR was an index of neuronal activation. Hypoxia activated AVP-IR (~6%) and CRH-IR (~15%) cells, but not PreS cells in the PVN, suggesting that sympathoexcitation during moderate AH is mediated mainly by a pathway that does not include PreS neurons in the PVN. Approximately 14 to 17% of all PVN cell phenotypes examined expressed neuronal nitric oxide synthase (nNOS-IR). AH activated only nNOS-negative AVP-IR neurons. In contrast ~23% of activated CRH-IR neurons in the PVN contained nNOS. In the median eminence, CRH-IR terminals were closely opposed to tanycyte processes and end-feet (vimentin-IR) in the external zone, where vascular NO participates in tanycyte retraction to facilitate neuropeptide secretion into the pituitary portal circulation. Results are consistent with an inhibitory role of NO on AVP and PreS neurons in the PVN and an excitatory role of NO on CRH secretion in the PVN and median eminence.

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.

Suppression of Stress-induced nNOS Expression in the Rat Hypothalamus by Biting

Nitric oxide (•NO) modulates the activity of the endocrine system in the behavioral response to stress. The purpose of this study was to investigate the effect of restraining the body of an animal on expression of neuronal nitric oxide synthase (nNOS) in the paraventricular nucleus (PVN) of the hypothalamus, and the inhibitory effect of para-masticatory activity on restraint-induced nNOS expression. We observed an increase in nNOS mRNA expression and nNOS-positive neurons in the rat hypothalamus after 30 or 60 min of restraint. Biting on a wooden stick during bodily restraint decreased nNOS mRNA expression in the hypothalamus. In addition, the number of nNOS-positive neurons was significantly reduced in the PVN of the hypothalamus. These observations clearly suggest a possible anti-stress effect of the masticatory activity of biting, and this mechanism might be unconsciously in operation during exposure to psychological stressors.

Upregulation of Neuronal Nitric Oxide Synthase mRNA and Protein in Adrenal Medulla of Water-deprived Rats

Experiments were performed to investigate whether adrenal neuronal nitric oxide synthase (nNOS) mRNA and protein expression are responsive to alterations in body volume. Using an RT-PCR technique, the relative quantities of nNOS mRNA as well as the tyrosine hydroxylase and phenylethanolamine N-methyltransferase mRNA in the adrenals of water-deprived rats significantly increased from 12 hr to 4 days. In situ hybridization and immunohistochemical study showed that water deprivation activated nNOS mRNA and protein expression in the adrenal medulla. Four days after water deprivation, nNOS protein expression determined by Western blot significantly increased in the adrenal gland. Our results are the first to demonstrate that nNOS syntheses in the adrenal medulla are markedly increased in water-deprived rats. This study also indicates that the upregulation of nNOS synthesis of the adrenal medulla is associated with the activation of adrenal medullary function in the face of volume depletion.

Increased Expression of Endothelial and Neuronal Nitric Oxide Synthase In Dura and Pia Mater After Air Stress

Stress is the leading precipitating factor for migraine attacks but the underlying mechanism is currently unknown. Nitric oxide (NO) has been implicated in migraine pathogenesis based on the ability of NO donors to induce migraine attacks. In the present study, we investigated in Wistar rats the effect of air stress on nitric oxide synthase (NOS) mRNA and protein expression in dura and pia mater using real-time polymerase chain reaction and Western blotting, respectively. Endothelial (e)NOS protein expression was significantly increased in dura and pia mater after air stress. Significantly augmented neuronal (n)NOS protein expression was detected in pia mater after air stress but not in dura mater. Inducible NOS mRNA and protein expression levels in dura and pia mater were unaffected by stress. The increased expression of eNOS in dura mater and eNOS and nNOS in pia mater seen after stress could not be antagonized by treatment with the migraine drug sumatriptan. These findings point towards the involvement of increased NO concentrations in dura and pia mater in response to air stress. However, the role of these findings in relation to migraine pathophysiology remains unclear.

Chronic Stress Decreases Cerebrovascular Responses During Rat Hindlimb Electrical Stimulation

Repeated stress is one of the major risk factors for cerebrovascular disease, including stroke, and vascular dementia. However, the functional alterations in the cerebral hemodynamic response induced by chronic stress have not been clarified. Here, we investigated the in vivo cerebral hemodynamic changes and accompanying cellular and molecular changes in chronically stressed rats. After 3 weeks of restraint stress, the elicitation of stress was verified by behavioral despair in the forced swimming test and by physical indicators of stress. The evoked changes in the cerebral blood volume and pial artery responses following hindpaw electrical stimulation were measured using optical intrinsic signal imaging. We observed that, compared to the control group, animals under chronic restraint stress exhibited a decreased hemodynamic response, with a smaller pial arterial dilation in the somatosensory cortex during hindpaw electrical stimulation. The effect of chronic restraint stress on vasomodulator enzymes, including neuronal nitric oxide synthase (nNOS) and heme oxygenase-2 (HO-2), was assessed in the somatosensory cortex. Chronic restraint stress downregulated nNOS and HO-2 compared to the control group. In addition, we examined the subtypes of cells that can explain the environmental changes due to the decreased vasomodulators. The expression of parvalbumin in GABAergic interneurons and glutamate receptor-1 in neurons were decreased, whereas the microglial activation was increased. Our results suggest that the chronic stress-induced alterations in cerebral vascular function and the modulations of the cellular expression in the neuro-vasomodulatory system may be crucial contributing factors in the development of various vascular-induced conditions in the brain.

Adrenal steroidogenesis following prenatal dexamethasone exposure in the spiny mouse

Antenatal stress disturbs the development of the fetal hypothalamic-pituitary-adrenal axis and adrenal steroidogenesis. We investigated the effect of brief maternal exposure to high glucocorticoids (dexamethasone (DEX)) at mid- and late-pregnancy on adrenal structure and production of steroids in spiny mouse. Pregnant spiny mice were treated for 60 h with 125 μg/kg DEX or saline s.c. by osmotic minipump at day 20 (0.5) or 30 (0.75) of gestation. Immunohistochemical expression of steroidogenic acute regulatory-protein (StAR), 3β-hydroxysteroid dehydrogenase (3βHSD), 17-hydroxylase,17-20lyase (P450C17), and cytochromeb5 (CYTB5) was determined in adrenals on postnatal (P) day 170±20. DHEA, testosterone, and cortisol were measured by RIA. Maternal DEX at 20 days significantly reduced the expression of STAR, P450C17 (CYP17A1), and CYTB5 in the adrenal zona reticularis (ZR) of adult offspring, with greater change in male vs female offspring (P<0.05). Plasma DHEA was decreased in male offspring from DEX-treated (6.84±1.24 ng/ml) vs saline-treated (13±0.06 ng/ml; P=0.01) dams, and the DHEA:cortisol ratio was lower in males (P<0.05). Testosterone levels increased in male offspring from DEX (266.03±50.75 pg/ml) vs saline (83.47±32.3 pg/ml, P<0.05)-treated dams. DEX treatment at 0.75 gestation had no significant effect on any parameters measured. This study shows that brief exposure to excess glucocorticoid has long-term impacts on the ZR and adrenal steroidogenesis, affecting the secretion of DHEA and testosterone in male offspring, an effect produced at 0.5 but not at 0.75 gestation. DHEA is important for brain development, and its suppression in adult life might contribute to the neurobehavioral pathologies that can arise after illness and stress during pregnancy.

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.

Effects of nitric oxide synthase inhibition in the dorsolateral periaqueductal gray matter on ethanol withdrawal-induced anxiety-like behavior in rats

RATIONALE

Nitric oxide (NO)-mediated transmission in the dorsolateral periaqueductal gray matter (dlPAG) has been involved in the expression of anxiety-like behaviors. Ethanol withdrawal sensitizes the dlPAG and results in increased anxiety-like responses.

OBJECTIVES

The objective of the study was to test the hypothesis that NO in the dlPAG is involved in the expression of ethanol withdrawal-induced anxiety.

METHODS

Male Wistar rats were implanted with guide cannulae aimed at the dlPAG. The animals were forced to consume a liquid diet containing ethanol 6-8 % (v/v) for 15 days as their only source of diet. Six days after surgery and 24 h after ethanol discontinuation, the animals received microinjections of the NO scavenger 2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide (carboxy-PTIO), nonselective nitric oxide synthase inhibitor N (G)-nitro-L-arginine methyl ester (L-NAME), selective neuronal nitric oxide synthase inhibitor 1-(2-[trifluoromethyl]phenyl) imidazole (TRIM), or selective inducible nitric oxide synthase (iNOS) inhibitor N-([3-(aminomethyl)phenyl]methyl) ethanimidamide dihydrochloride (1400W) into the dlPAG. Ten minutes later, the animals were tested in the light/dark box.

RESULTS

Carboxy-PTIO (1 nmol), L-NAME (200 nmol), TRIM (20 nmol), and 1400W (0.3 and 1 nmol) decreased the anxiogenic-like effects of ethanol withdrawal in rats in the light/dark box test. The NO precursor L-arginine reversed the effects of L-NAME.

CONCLUSIONS

NO production in the dlPAG may play a role in the modulation of ethanol withdrawal-induced anxiety-like behavior in rats. Furthermore, iNOS-mediated NO synthesis in the dlPAG is predominantly involved in the behavioral expression of anxiety-like behavior during ethanol withdrawal.

Long-term social stress induces nitric oxide-independent endothelial dysfunction in normotensive rats

As chronic stress is a significant risk factor for several cardiovascular disorders, this study investigated the hypothesis that long-term stress produced by crowding may lead to alterations in nitric oxide (NO) production and NO-dependent relaxation in the course of stress, resulting in endothelial dysfunction and hypertension in Wistar-Kyoto (WKY) rats. For this purpose, male WKY rats were divided into control (480 cm2/rat, four rats/cage, n = 8) and crowded (200 cm2/rat, five rats/cage, n = 10) groups for 8 or 12 weeks. Vasorelaxation was evaluated in vitro as a response to acetylcholine (ACh) of femoral arteries pre-contracted by serotonin, before and after NO synthase inhibition (N (G)-nitro-l-arginine methyl ester, 300 μmol/l). Crowding increased plasma corticosterone concentration but failed to affect blood pressure (determined by tail-cuff plethysmography) of rats. NO production was unchanged in the hypothalamus and left ventricle of both stressed groups; however it was significantly elevated in the aorta. Maximal ACh-induced relaxation was elevated significantly after 8-week stress, but reduced after 12 weeks. Stress elevated the NO-dependent component and reduced the NO-independent component of ACh-induced relaxation in both crowded groups. However, a reduction in the NO-independent component was more pronounced after 12-week versus 8-week stress. In conclusion, elevated endothelium-dependent relaxation was observed after 8-week stress, while the extension of stress exposure resulted in a reduction in arterial relaxation associated with a more pronounced decrease of its NO-independent component. Thus, elevation of the NO-dependent component of relaxation can be considered as an adaptation mechanism, and impairment of NO-independent relaxation might be the initial step in chronic stress-induced cardiovascular disorders.

eNOS activation and NO function: differential control of steroidogenesis by nitric oxide and its adaptation with hypoxia

Nitric oxide (NO) plays a role in a wide range of physiological processes. Aside from its widely studied function in the regulation of vascular function, NO has been shown to impact steroidogenesis in a number of different tissues. The goal of this review is to explore the effects of NO on steroid production and further, to discern its source(s) and mechanism of action. Attention will be given to the regulation of NO synthases in specific endocrine tissues including ovaries, testes, and adrenal glands. The effects of hypoxia on generation of NO and subsequent effects on steroid biosynthesis will also be examined. Finally, a potential model for the interaction of hypoxia on NO synthesis and steroid production is proposed.

Functional organization of the dorsal raphe efferent system with special consideration of nitrergic cell groups

The serotonin (5HT) system of the brain is involved in many CNS functions including sensory perception, stress responses and psychological disorders such as anxiety and depression. Of the nine 5HT nuclei located in the mammalian brain, the dorsal raphe nucleus (DRN) has the most extensive forebrain connectivity and is implicated in the manifestation of stress-related psychological disturbances. Initial investigations of DRN efferent connections failed to acknowledge the rostrocaudal and mediolateral organization of the nucleus or its neurochemical heterogeneity. More recent studies have focused on the non-5HT contingent of DRN cells and have revealed an intrinsic intranuclear organization of the DRN which has specific implications for sensory signal processing and stress responses. Of particular interest are spatially segregated subsets of nitric oxide producing neurons that are activated by stressors and that have unique efferent projection fields. In this regard, both the midline and lateral wing subregions of the DRN have emerged as prominent loci for future investigation of nitric oxide function and modulation of sensory- and stressor-related signals in the DRN and coinciding terminal fields.

Adrenal gland responses to lipopolysaccharide after stress and ethanol administration in male rats

All forms of stress, including restraint stress (RS) and lipopolysaccharide (LPS) administration, activate the hypothalamic-pituitary-adrenal (HPA) axis. LPS binds to a recognition protein (CD14) and toll-like receptor 2/4 in different cells and tissues, including the adrenal gland, to induce the production of cytokines and cause upregulation of cyclooxygenase and nitric oxide synthase (NOS) enzymes. Acute ethanol exposure activates the HPA axis, but in some conditions prolonged administration can dampen this activation as well as decrease the inflammatory responses to LPS. Therefore, this study was designed to evaluate the adrenal response to a challenge dose of LPS (50 μg/kg) injected i.p., after submitting male rats to RS, twice a day (2 h each time) for 5 days and/or ethanol administration (3 g/kg) by gavage also for 5 days, twice daily. At the end of the experiment, plasma corticosterone concentrations and adrenal gland content of prostaglandin E (PGE) and NOS activity were measured as stress mediators. The results showed that repetitive ethanol administration attenuated the adrenal stress response to LPS challenge alone and after RS, by preventing the increase in plasma corticosterone concentrations and by decreasing the PGE content and NOS activity in the adrenal gland. Therefore, we conclude that moderate alcohol consumption could attenuate the effects of psychophysical stress and impair an inflammatory response.

Cyclooxygenase and nitric oxide synthase in the presympathetic neurons in the paraventricular hypothalamic nucleus are involved in restraint stress-induced sympathetic activation in rats

Stress is one of the important factors to activate the sympathetic nervous system. We recently reported that central administration of corticotropin-releasing factor (CRF), known as a stress-related neuropeptide, increases the expression of both cyclooxygenase (COX) and nitric oxide synthase (NOS) in presympathetic neurons in the paraventricular hypothalamic nucleus (PVN). In the present study, therefore, we investigated whether brain COX and NOS can also mediate restraint stress (RS)-induced sympathetic activation by assessing the plasma catecholamine levels and neuronal activation of presympathetic neurons in the PVN. In addition, we examined effects of RS on the expression of both COX and NOS isozymes in the presympathetic PVN neurons. Intraperitoneal administration of an inhibitor for COX-1, COX-2 or inducible NOS (iNOS), but not for neuronal NOS (nNOS), reduced RS-induced elevation of plasma catecholamine levels and Fos expression in the presympathetic PVN neurons. Moreover, RS increased the expression of COX-1, COX-2 and iNOS in the presympathetic PVN neurons, whereas nNOS expression did not change. These results suggest that COX-1, COX-2 and iNOS in the presympathetic PVN neurons mediate acute RS-induced sympathetic activation.

Paraventricular nucleus modulates autonomic and neuroendocrine responses to acute restraint stress in rats

The paraventricular nucleus of the hypothalamus (PVN) has been implicated in several aspects of neuroendocrine and cardiovascular control. The PVN contains parvocellular neurons that release the corticotrophin release hormone (CRH) under stress situations. In addition, this brain area is connected to several limbic structures implicated in defensive behavioral control, as well to forebrain and brainstem structures involved in cardiovascular control. Acute restraint is an unavoidable stress situation that evokes corticosterone release as well as marked autonomic changes, the latter characterized by elevated mean arterial pressure (MAP), intense heart rate (HR) increases and decrease in the tail temperature. We report the effect of PVN inhibition on MAP and HR responses, corticosterone plasma levels and tail temperature response during acute restraint in rats. Bilateral microinjection of the nonspecific synaptic blocker CoCl(2) (1 mM/100 nL) into the PVN reduced the pressor response; it inhibited the increase in plasma corticosterone concentration as well as the fall in tail temperature associated with acute restraint stress. Moreover, bilateral microinjection of CoCl(2) into areas surrounding the PVN did not affect the blood pressure, hormonal and tail vasoconstriction responses to restraint stress. The present results show that a local PVN neurotransmission is involved in the neural pathway that controls autonomic and neuroendocrine responses, which are associated with the exposure to acute restraint stress.

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.

Role of neuronal nitric oxide synthase in ovine sepsis model

Smoke inhalation injury is often complicated with pneumonia, which frequently leads to subsequent development of sepsis. Excessive NO has been shown to mediate many sepsis-related pathological responses. In the present study, we used our well-established ovine smoke inhalation and pneumonia/sepsis model to examine the hypothesis that neuronal NO synthase (NOS) may be primarily responsible for these pathological alterations. We report the beneficial effects of the specific neuronal NOS (nNOS) inhibitor ZK234238. Adult female sheep were surgically prepared for the study. After 5 to 7 days' recovery, sheep were anesthetized and given double injury: insufflation of 48 breaths of cotton smoke (<40 degrees C) into the airway of each animal and subsequent instillation of live Pseudomonas aeruginosa (5 x 10(11) colony-forming units) into each sheep's lung via tracheostomy tube. All sheep were mechanically ventilated and fluid resuscitated by lactated Ringer's solution. Sheep were randomly allocated into groups: control (injured not treated, n = 6) and treated (injured, but treated with ZK234238, n = 4). Continuous infusion of ZK234238 (100 microg x kg(-1) x h(-1)) was started 1 h after insult. ZK234238 attenuated the hypotension (at 18 and 24 h) and fall in systemic vascular resistance (at 24 h) seen in control animals. ZK234238 significantly inhibited increased fluid accumulation as well as increased plasma nitrate/nitrite 24 h after injury. Neuronal NOS inhibition significantly reduced lung water content and attenuated inflammatory indices such as lung tissue myeloperoxidase activity, IL-6 mRNA, and reactive nitrogen species. The above results suggest that the nNOS-derived NO may be involved in the pathophysiology of sepsis-related multiorgan dysfunction.

THE EFFECT OF CHRONIC RESTRAINT STRESS ON SPATIAL LEARNING AND MEMORY: RELATION TO OXIDANT STRESS

The aim of this study was to investigate the effect of chronic restraint stress (RS) on spatial learning and memory. Fifty healthy male Wistar rats, aged three months were used. They were equally divided into five groups--C: Control, W: Water Maze, CS-1: Restrained for 21 days (1 h/day) + water maze protocol following stress period, CS-2: Restrained for 28 days (1 h/day) + water maze protocol during last 7 days of stress period, CS-3: Restrained for 21 days and allowed to recovery for 7 days (1 h/day). Corticosterone levels were higher in all stress groups than in C and W groups. Nitrite levels of frontal cortex and hippocampus were found to be elevated in chronic stress groups with respect to C and W groups. Thiobarbituric acid reactive substances (TBARS) of both tissues were increased significantly in CS1 and CS2 groups compared with C, W, and CS3 groups. Escape latencies of CS1 and CS2 groups were longer than those of the W group on each day of acquisition. In transfer test, CS1 and CS2 groups stayed significantly shorter in target quadrant according to the W group. Significant correlations between corticosterone and either nitrite or TBARS of hippocampus and frontal cortex were found. Both acquisition and memory performances were negatively correlated with plasma corticosterone level, nitrite, and TBARS levels of hippocampus and frontal cortex. The results of this study suggest that stress-induced lipid peroxidation may affect the acquisition and memory performances.

Long-term hypoxia increases endothelial nitric oxide synthase expression in the ovine fetal adrenal

This study was designed to test the hypothesis that fetal adrenal nitric oxide synthase (NOS) is elevated in response to long-term hypoxia (LTH). Pregnant ewes were maintained at high altitude (3820 m) for approximately the last 100 days of gestation. Between days 138 and 141 of gestation, adrenal glands were collected from LTH fetuses and age-matched normoxic controls. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western analysis were used to quantify NOS expression, and NOS distribution was examined by immunohistochemistry and double-staining immunofluorescence for endothelial NOS (eNOS) and 17alpha-hydroxylase (CYP17). Neuronal NOS (nNOS) was expressed at very low levels and with no differences between groups. Expression of eNOS was significantly greater in the LTH group compared with control. Neuronal NOS was distributed throughout the cortex while the greatest density of eNOS was observed in the zona fasciculata/reticularis area and eNOS co-localized with CYP17. We conclude that LTH enhances eNOS expression in the inner adrenal cortex which may play a role in regulation of cortisol biosynthesis in the LTH fetus.

Neuroprotective effects of Withania somnifera dunal.: A possible mechanism

Present study was carried out to understand the possible mechanism of neuroprotective action of the root extract of Withania somnifera Dunal (WS). The study is focused on WS mediated inhibition of nitric oxide production, which is known to mediate neurodegeneration during stress. Adult mice (28 +/- 5 g) were exposed to restraint stress for 30 days. Activity of NADPH diaphorase (NADPH-d) and factors (Acetylcholine, serotonin and corticosterone), which regulates NADPH-d activity were studied. Treatment with WS extract for 30 days during stress, significantly reversed the stress induced NADPH-d activation. Observations suggest that inhibition of NADPH-d by WS is not a direct effect of extract on NADPH-d, instead it inhibits via suppressing corticosterone release and activating cholineacetyltransferase, which in turn increase serotonin level in hippocampus to inhibit NADPH-d. Together, the main mechanism underlying the neuroprotective effects of WS can be attributed to its role in the down regulation of nNOS and neurochemical alterations of specific neurotransmitter systems. These observations thus suggest that WS root extract could be developed as a potential preventive or therapeutic drug for stress induced neurological disorders.

Low [NaCl]-induced neuronal nitric oxide synthase (nNOS) expression and NO generation are regulated by intracellular pH in a mouse macula densa cell line (NE-MD)

Changes in the luminal NaCl concentration ([NaCl]) at the macula densa (MD) modulate the tubuloglomerular feedback (TGF) responses via an affect on the release of nitric oxide (NO). This study was performed in a newly established mouse macula densa cell line (NE-MD) to investigate the effects of lowering [NaCl] on the neuronal NO synthase (nNOS) protein expression and L-arginine (Arg)-induced NO release. Expression of nNOS protein and release of NO were evaluated by Western blot analysis and an NO-sensitive electrode, respectively. Intracellular pH (pH(i)) was monitored by the BCECF assay. Although there was weak staining of the nNOS protein expression, L-Arg-induced NO generation was negligible in normal (140 mM NaCl) solution. Both were significantly (P < 0.05) increased either in the presence of furosemide (12 microM), an inhibitor of the Na(+)-K(+)-2Cl(-) cotransporter, or in a low (23 mM) Cl(-) solution. Furosemide- and low Cl(-)-induced NO generation was completely inhibited by 50 microM 7-nitroindasole (7-NI), a nNOS inhibitor. Moreover, these increases were significantly (P < 0.05) inhibited by the addition of 100 microM amiloride, an inhibitor of the Na(+)/H(+) exchanger, or by its analogue 5-(N)-ethyl-N-isopropyl amiloride (EIPA), and also at a lower pH of 7.1. Furthermore, nNOS expression and NO release were not stimulated in as low as 19 mM Na(+) solution. In conclusion, low [Cl(-)], but not low [Na(+)] in the lumen at the MD, increased nNOS protein expression and NO generation. Changes in the luminal [NaCl] may modulate the TGF system via an effect on the NO generation from the MD.

Normal responses to restraint stress in mice lacking the gene for neuronal nitric oxide synthase

The hormonal changes associated with immobilization stress (IMO) include a swift increase in corticosterone (CORT) concentration and a decrease in circulating testosterone (T) levels. There is evidence that the production of the short-lived neuromodulator nitric oxide (NO) is increased during stress in various tissues, including the brain. NO also suppresses the biosynthesis of T. Both the inducible and the neuronal isoforms of NO synthase (iNOS and nNOS, respectively) have been implicated in this suppression, but the evidence has not been conclusive. We used adult wild-type (WT) and nNOS knockout male mice (nNOS-/-) to assess the respective roles of CORT and nNOS-derived NO in stress mediated inhibition of T production. Animals were assigned to either basal control or 3-hour IMO groups. No difference in basal plasma and testicular T levels were observed between WT and nNOS-/-, although testicular weights of mutant mice were slightly lower compared to WT animals. The plasma contents of luteinizing hormone (LH) and CORT in unstressed mice of both genotypes were similar. Exposure to 3 hours of IMO increased plasma CORT and decreased T concentrations in mice of both genotypes. However, comparable levels of plasma LH and testicular nitrite and nitrate (NOx), NO stable metabolites, were detected in control and stressed WT and nNOS-/- mice. Adrenal concentrations of NOx declined after IMO, but the reduction was not statistically significant. These findings implicate CORT rather than NO generated by nNOS in the rapid stress-induced suppression of circulating T.

Neuronal nitric oxide synthase: structure, subcellular localization, regulation, and clinical implications

Nitric oxide (NO), a free gaseous signaling molecule, is involved in the regulation of the cardiovascular, nervous and immune system. The neurotransmitter function of nitric oxide is dependent on dynamic regulation of its biosynthetic enzyme, nitric oxide synthase (NOS). There are three types of NOS, neuronal nitric oxide synthase (nNOS), endothelial nitric oxide synthase (eNOS) and inducible nitric oxide synthase (iNOS). Of the three NOS, we focus on nNOS in the present review. Brain nNOS exists in particulate and soluble forms and the differential subcellular localization of nNOS may contribute to its diverse functions. Proteins bearing PDZ domains can interact directly with the PDZ domain of nNOS, influencing the subcellular distribution and/or activity of the enzyme. During the past several years, an increasing number of reports have demonstrated the importance of nNOS in a variety of synaptic signaling events. nNOS has been implicated in modulating physiological functions such as learning, memory, and neurogenesis, as well as being involved in a number of human diseases. In this review we concentrate on recent findings regarding the structural features, subcellular localization and factors regulating nNOS function. In particular, we conclude with a section discussing the role of nNOS in a wide range of physiological and pathological conditions.

The paraventricular nucleus of the hypothalamus is involved in cardiovascular responses to acute restraint stress in rats

The paraventricular nucleus of the hypothalamus (PVN) has been implicated in several aspects of cardiovascular control. Stimulation of the PVN evokes changes in blood pressure and heart rate. Additionally, this brain area is connected to several limbic structures implicated in behavioral control, as well as to forebrain and brainstem structures involved in cardiovascular control. This evidence indicates that the PVN may modulate cardiovascular correlates of behavioral responses to stressful stimuli. Acute restraint is an unavoidable stressor that evokes marked and sustained cardiovascular changes, which are characterized by elevated mean arterial pressure (MAP) and an intense heart rate (HR) increase. We report on the effect of inhibition of PVN synapses on MAP and HR responses evoked by acute restraint in rats. Bilateral microinjection of the nonspecific synaptic blocker cobalt (CoCl(2), 1 mM/100 nl) into the PVN did not change the HR response or the initial peak of the MAP response to restraint stress, but reduced the area under the curve of the MAP response. Moreover, bilateral microinjection of cobalt in areas surrounding the PVN did not change the cardiovascular response to restraint. These results indicate that synapses in the PVN are involved in the neural pathway that controls blood pressure changes evoked by restraint.

Changes in iNOS, GFAP and NR1 expression in various brain regions and elevation of sphingosine-1-phosphate in serum after immobilized stress

Several studies have been suggested that long-term exposure to stress has detrimental effects on various brain functions and leads to neurodegenerative changes. However, the precise mechanism by which stress induces brain damage or neurodegenerative change is still a matter of debate. This study investigated the damage of neuronal cells involving in the expression of iNOS, NR1, and GFAP in various brain regions and characterized the change of sphingolipid metabolites as a biomarker of physiological change in serum after 3 weeks of repeated immobilization. In this report, the expression of iNOS, GFAP and NR1 in the brain of rats exposed to chronic immobilization stress was investigated. The expression of iNOS, GFAP and NR1 was elevated in the cortex and hippocampal area after 3 weeks of repeated immobilization. Immunoreactivity for GFAP and vimentin, as a marker of reactive gliosis, was also elevated in the cortex and hippocampus. The level of sphingolipids was measured in order to assess the changes in sphingolipid metabolites in the serum of rats exposed to stress. Interestingly, the level of So-1-P was increased in the plasma of rats subjected to 6-h immobilization stress than repeated immobilization. To further investigate the modulating effect of increased So-1-P in various brain regions, So-1-P was infused into the lateral cerebroventricle at a rate of 100 pmol/10 mul/h for 7 days. The expression of iNOS and NR1 was elevated in the cortex, hippocampus, striatum, and cerebellum after So-1-P infusion into the cerebroventricle, while the level of GFAP was elevated in the hippocampus and striatum. Interestingly, the expression levels of iNOS, GFAP, and NR1 were increased by the direct application of So-1-P to cultured cortical cells. These results suggest that NO production via iNOS expression, the NR1 expression, the activation of astrocytes, and the elevation of So-1-P may cause neurodegenerative changes in rats subjected to chronic immobilization and that the elevation of So-1-P by stress exposure would be one of the stress signal molecules.

Nitric oxide synthase inhibition in rostral ventrolateral medulla attenuates pressor response to psychological stress in rabbits

Nitric oxide (NO) has been critically implicated in the central regulation of autonomic function. We recently found, however, that acute (up to 30min) blockade of NO synthase (NOS) in the rostral ventrolateral medulla (RVLM) inhibited sympathetic baroreflex transmission, without altering the cardiovascular response to psychological (air-jet) stress in rabbits. In the present study, we examined the effect of the later phase (1-3h) of NOS inhibition in the RVLM on the pressor and sympathetic responses to air-jet stress in conscious rabbits. Air-jet evoked a sustained increase in blood pressure (+14+/-2mmHg), heart rate (+37+/-9beats/min) and renal sympathetic nerve activity (+52+/-8%). Bilateral microinjection of a NOS inhibitor l-NAME (10nmol) into RVLM did not affect resting parameters or stress responses during the first 30min after injection. Conversely, in the later phase of NOS inhibition, the pressor, tachycardic and renal sympathetic responses to air-jet stress were reversibly attenuated by 48-72%. Microinjection of l-NAME outside the RVLM did not change stress responses. Microinjection of glutamate (3nmol) into the RVLM induced similar pressor effects before and after l-NAME (+30+/-6mmHg and +26+/-6mmHg, respectively). Microinjection of d-NAME altered neither stress responses nor pressor response to glutamate. These results suggest that NOS inhibition in the RVLM has a dual effect on the autonomic response to psychological stress. In the early phase, NOS inhibition has little impact on this response. However, in the later phase, NOS inhibition attenuates the stress response, perhaps via indirect mechanisms such as altering the local redox state.

Does nitric oxide act in the ventromedial preoptic area to mediate oestrogen negative feedback in the seasonally anoestrous ewe?

Seasonal anoestrus in the ewe results from enhanced oestrogen negative feedback. Recent data have implicated the ventromedial preoptic area (vmPOA) as an important site of oestrogen action. This study addressed whether NO acts within the vmPOA to inhibit LH during seasonal anoestrus. In Experiment 1, microimplants containingNω-nitro-l-arginine methyl ester (l-NAME, NOS inhibitor),S-methyl thiocitrulline (SMTC, neural NOS (nNOS) inhibitor) or empty implants (control) were administered during mid-anoestrus to the vmPOA.l-NAME, but not SMTC, significantly increased LH pulse frequency. For Experiment 2, ewes in late anoestrus were administered 7-nitroindazole (7NI; nNOS inhibitor),l-NAME, SMTC, or empty implants. 7NI, but notl-NAME or SMTC, increased LH pulse frequency. In Experiment 3, the effects of microimplants and microinjections ofl-NAME were compared in mid-anoestrus. Microinjections ofl-NAME (300 nl at 10 μg/μl) increased LH pulse frequency, but microimplants did not. In late anoestrus, similar microinjections were ineffective. Taken together, the results of Experiments 1–3 suggested that NO inhibition may be stronger during the middle than at the end of seasonal anoestrus. To test this hypothesis, ewes in Experiment 4 received microinjection ofl-NAME or vehicle thrice during the non-breeding season; none of the treatments increased LH pulse frequency. These results indicate that NO plays a role in the vmPOA in suppressing LH secretion during seasonal anoestrus because NOS inhibitors were consistently stimulatory when LH pulse frequency was low. However, the inconsistent and modest effects of these inhibitors suggest that NO actions in this area cannot completely account for the effects of inhibitory photoperiod.

Testosterone production in mice lacking inducible nitric oxide synthase expression is sensitive to restraint stress

Immobilization stress (IMO) induces a rapid increase in glucocorticoid secretion [in rodents, corticosterone CORT)] and this is associated with decreased circulating testosterone (T) levels. Nitric oxide (NO), a reactive free radical and neurotransmitter, has been reported to be produced at higher rates in tissues such as brain during stress. The biosynthesis of T is also known to be dramatically suppressed by NO. Specifically, the inducible isoform of nitric oxide synthase (iNOS) was directly implicated in this suppression. To assess the respective roles of CORT and NO in stress-mediated inhibition of T production, adult wild-type (WT) and inducible nitric oxide synthase knockout (iNOS(-/-)) male mice were evaluated. Animals of each genotype were assigned to either basal control or 3-h IMO groups. Basal plasma and testicular T levels were equivalent in both genotypes, whereas testicular weights of mutant mice were significantly higher compared with WT animals. Exposure to 3-h IMO increased plasma CORT and decreased T concentrations in mice of both genotypes. Testicular T levels were also affected by stress in WT and mutant males, being sharply reduced in both genotypes. However, the concentrations of nitrite and nitrate, the stable metabolites of NO measured in testicular extracts, did not differ between control and stressed WT and iNOS(-/-) mice. These results support the hypothesis that CORT, but not NO, is a plausible candidate to mediate rapid stress-induced suppression of Leydig cell steroidogenesis.

Down-regulation of adrenal neuronal nitric oxide synthase mRNAs and proteins after deoxycorticosterone acetate-salt treatment in rats

The aim of this study was to evaluate the possible changes of adrenal neuronal nitrite oxide synthase (nNOS) messenger RNA (mRNA) and protein of rats after deoxycorticosterone acetate (DOCA)-salt treatment. We determined adrenal nNOS expression in 12 vehicle-treated and 13 DOCA-salt-treated rats by in situ hybridization, immunohistochemistry, and multiplex RT-PCR methods. Adrenal nNOS was also detected by Western blot in five vehicle-treated and five DOCA-salt-treated rats. The results showed that adrenal nNOS mRNA and nNOS immunoreactivities were mainly localized in the medulla and some in the regions of zona glomerulosa. DOCA-salt treatment inactivated nNOS mRNA and peptide expression prominent in the adrenal medulla and slight in the zona glomerulosa. The relative quantities of nNOS mRNA in the adrenals of the DOCA-salt-treated group was 8.8-fold decreased. At the same time, the relative quantities of steroid acute regulatory protein mRNA and phenylethanolamine N-methyltransferase mRNA in the adrenals of the DOCA-salt-treated group were significantly decreased. Western blots showed that total adrenal nNOS were 3.7-fold down-regulated after DOCA-salt treatment. Our results indicated that the down-regulation of adrenal nNOS synthesis might be associated with the inactivation of adrenal function in face of volume expansion.

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.

Acute restraint increases NADPH-diaphorase staining in distinct subregions of the rat dorsal raphe nucleus: implications for raphe serotonergic and nitrergic transmission

The brainstem dorsal raphe nucleus (DRN) maintains a rough topographic cell ordering with respect to biological function. This study examined the influence of acute restraint on nitric oxide (NO) synthase (NOS) neurons in distinct DRN subregions. NADPH diaphorase staining (NOS index) intensity was higher in the DRN dorsomedial, ventromedial and lateral wings subregions of restrained vs. control rats. The mean number of cells was not significantly different between both groups of animals. The restrained-induced NADPH-diaphorase activity was significantly higher in the rostral ventromedial and caudal lateral wings than the corresponding caudal and rostral subregions but no significant difference was observed between rostral and caudal dorsomedial subregions. These observations suggest that restraint stress differentially activates NO-producing neurons in distinct DRN subregions.

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.

Lithium-induced gene expression of inducible cyclic adenosine monophosphate early repressor in the rat adrenal gland

Lithium has acute and chronic effects on the hypothalamic-pituitary-adrenal gland (HPA) axis that are important for both therapeutic (e.g., treatment of mood disorders) and experimental (e.g., as the toxin in conditioned taste aversion studies) applications. We visualized lithium-induced activation of the HPA axis in rats by the adrenal expression of inducible cAMP early repressor (ICER), which is activated by elevated intracellular cAMP. We have shown that 1) intraperitoneal lithium chloride (LiCl) induces transient expression of ICER and c-fos mRNAs in the rat adrenal cortex and increases plasma level of corticosterone; 2) the cortical expression of ICER mRNA by LiCl occurs in a dose-dependent manner; 3) adrenal induction of ICER expression is delayed compared with c-fos expression; 4) dexamethasone pretreatment (4 mg/kg) blocks corticosterone release and adrenocortical ICER induction either by systemic LiCl (76 mg/kg) or by restraint stress; and 5) intracerebroventricular LiCl (127 microg/5 microl) is sufficient for adrenocortical, but not medullary, ICER induction. These results suggest that adrenocortical ICER expression could serve as a reliable marker for lithium-induced activation of the HPA axis. Understanding the activation of immediate-early genes such as c-fos or ICER in response to a single LiCl injection is an important first step in understanding the long-term changes in gene expression elicited by lithium that are involved in its therapeutic and toxic effect. The pattern and mechanism by which lithium stimulates ICER transcription in the adrenal gland would serve as a useful model system in future studies of lithium.

Anxiolytic-like effects induced by nitric oxide synthase inhibitors microinjected into the medial amygdala of rats

RATIONALE

The amygdaloid complex plays a central role in the neuroanatomical circuits that coordinate defensive responses. Nitric oxide (NO) has been involved in the neurochemical, hormonal, and behavioral changes related to stress and anxiety. A high density of NO-producing neurons is observed in the medial amygdala (MeA). These neurons are activated after exposure to threatening stimuli such as a live predator.

OBJECTIVE

To test the hypothesis that microinjection into the MeA of two NO synthase inhibitors, NG-nitro-L-arginine methyl ester (L-NAME) or 7-nitroindazole (7-NI), would produce anxiolytic effects.

METHODS

Male Wistar rats (n=8-10/group) were submitted to stereotaxic surgery to implant bilateral stainless steel guide cannulae aimed at the MeA. Six days after the surgery, the animals received intra-MeA microinjections of the drugs or vehicle and, 10 min later, were submitted to the elevated plus-maze (EPM) or the light-dark transition procedures.

RESULTS

Both L-NAME (50-200 nmol) and 7-NI (5 and 10 nmol) increased open-arm exploration in the EPM without changing the number of enclosed arm entries, indicating an anxiolytic-like effect. The anxiolytic-like effect of L-NAME (200 nmol) was prevented by pretreatment with L-arginine (100 nmol). Injections of 7-NI or L-NAME outside the MeA did not produce any significant change in EPM exploration. When tested in the light-dark test, L-NAME (200 nmol) or 7-NI (10 nmol) increased the time when the animal remained in the light compartment of the light-dark box.

CONCLUSIONS

The present results suggest that inhibition of NO formation in the MeA produces anxiolytic-like effect in rats.

Expression of nitric oxide synthase isoforms in hypothalamo–pituitary–adrenal axis during the development of spontaneous hypertension in rats

This study was performed to investigate the expression of the major isoforms of nitric oxide synthase mRNA and protein in the hypothalamo-pituitary-adrenal axis (HPA axis) of spontaneously hypertensive rats (SHR) at two different postnatal ages corresponding to the development of genetic hypertension. Using RT-PCR and Western blot techniques, the mRNA and protein levels of neuronal (nNOS), endothelial (eNOS) and inducible (iNOS) isoforms were measured in 3- to 4-week-old (prehypertensive phase) and 12- to 13-week-old (established hypertension phase) SHR and age-matched normotensive Wistar-Kyoto (WKY) rats. nNOS but not eNOS mRNA levels were increased at prehypertensive and hypertensive phases in SHR HPA axis. Compared to age-matched WKY rats, significantly higher levels of nNOS protein were found in the hypothalamus, lower levels in the adrenal glands and no changes were observed in the pituitary gland. At both ages tested, there was no significant change in eNOS protein expression in SHR HPA axis. The expression of iNOS mRNA and protein was under detection limit. In the HPA axis, the expression of nNOS isoform appears to be differentially controlled at the transcriptional and translational levels in SHR. Increased mRNA levels and differential nNOS protein expression from birth in SHR HPA axis may contribute in the pathogenesis of genetic hypertension.

Altered diurnal variation of nitric oxide production in patients with panic disorder

The aim of this prospective study was to investigate the diurnal change in serum nitric oxide (NO) levels in active and remission phases of patients with panic disorder. This study included 15 patients fulfilling the criteria for panic disorder of Diagnostic and Statistical Manual of Mental Disorders--Fourth Edition and 15 healthy controls matched for age and sex. All patients were receiving a selective serotonin reuptake inhibitor at therapeutic doses. The serum nitrite and nitrate levels of subjects were determined at 10:00 a.m. after overnight fasting and at 3:00 p.m. 2 hours after lunch. NO levels of all patients measured in the morning were significantly higher than those of controls. The patients were also divided into active and remission groups according to clinical status and Panic Agoraphobia Scale's cut-off point. There were no statistically significant differences in serum nitrite and nitrate levels of the active group between the 10:00 a.m. and 3:00 p.m. measurements. In contrast, statistically significant differences were found in the serum levels of nitrite (p<0.05) and nitrate (p<0.05) in the remission group. Notably, the afternoon nitrite and nitrate levels of the remission group were higher than those of the morning levels as seen in control subjects. Thus, diurnal variation of NO production is altered in patients with panic disorder but is resumed in the remission phase. The present study suggests that serum NO levels are a good marker for evaluation of panic disorder.

Pharmacological and biochemical studies on the possible role of nitric oxide in stress adaptation in rats

The involvement of nitric oxide (NO) in stress adaptation was evaluated in rats using the elevated plus maze test. Repeated restraint stress RS(x 5) for 5 days resulted in an increase in the percentage number of entries and percentage time spent when compared to a single restraint stress RS(x 1) exposure. In the repeated RS treatment groups, the nitric oxide donor, L-arginine (500 and 1000 mg/kg, i.p.) slightly increased the elevated plus maze test parameters when compared to the corresponding vehicle-treated group. The nitric oxide synthase (NOS) inhibitors, N-nitro-L-arginine methyl ester (L-NAME, 10 and 50 mg/kg, i.p.) and 7-nitroindazole (10 and 50 mg/kg, i.p.) produced differential responses in both the parameters with L-NAME exhibiting greater reduction in open arm entries and open arm time, whereas 7-nitroindazole produced only small differences in both the elevated plus maze parameters. Biochemical data showed that repeated restraint stress resulted in higher levels of brain nitrates and nitrites (NOx) as compared to that of single restraint stress exposure. Further, in L-arginine (1000 mg/kg, i.p.)-treated rats, brain NOx was lowest in the single restraint stress group, followed by repeated restraint stress and (no restraint stress) controls. The results are suggestive of the role of nitric oxide in stress adaptation and this may be due to the effects of restraint stress on brain NOS activity.

Fluvoxamine, a selective serotonin reuptake inhibitor, suppresses tetrahydrobiopterin levels and dopamine as well as serotonin turnover in the mesoprefrontal system of mice

RATIONALE

Tetrahydrobiopterin (BH4) is a coenzyme of tyrosine hydroxylase (TH) and tryptophan hydroxylase (TPH), rate-limiting enzymes of monoamine biosynthesis. According to the monoamine hypothesis of depression, antidepressants will restore the function of the brain monoaminergic system, and BH4 concentration.

OBJECTIVE

To investigate the effects of fluvoxamine on BH4 levels and dopamine (DA) and serotonin (5-HT) turnover in the mesoprefrontal system, incorporating two risk factors of depression, social isolation and acute environmental change.

METHODS

Male ddY mice (6W) were divided into two housing groups, i.e. group-housing (eight animals per cage; 35 days), and isolation-housing (one per cage; 35 days), SC injected with fluvoxamine (20 or 40 mg/kg; days 29-35), and exposed to 20-min novelty stress (day 35). The levels of BH4, DA, homovanilic acid (HVA), 5-HT, and 5-hydroxyindoleacetic acid (5-HIAA) were measured in the prefrontal cortex and midbrain.

RESULTS

Under the group-housing condition, novelty stress significantly increased BH4 levels in both regions, and the HVA/DA ratio in the midbrain, whereas it did not change any parameters in either region under the isolation-housing condition. In the prefrontal cortex, fluvoxamine significantly decreased the 5-HIAA/5-HT ratio under the group-housing condition, and BH4 levels and the HVA/DA ratio under the isolation-housing condition. In the midbrain, fluvoxamine significantly decreased all parameters, except for an increasing in the 5-HIAA/5-HT ratio under the isolation-housing condition.

CONCLUSION

Isolation-housing suppressed the increase of BH4 levels and DA turnover elicited by novelty stress. Fluvoxamine suppressed BH4 levels, and DA and 5-HT turnover. Fluvoxamine may have altered DA turnover by suppressing BH4 levels.