Stress-induced activation of nitric oxide-producing neurons in the rat brain

Stress Adaptation and the Brainstem with Focus on Corticotropin-Releasing Hormone

Stress adaptation is of utmost importance for the maintenance of homeostasis and, therefore, of life itself. The prevalence of stress-related disorders is increasing, emphasizing the importance of exploratory research on stress adaptation. Two major regulatory pathways exist: the hypothalamic–pituitary–adrenocortical axis and the sympathetic adrenomedullary axis. They act in unison, ensured by the enormous bidirectional connection between their centers, the paraventricular nucleus of the hypothalamus (PVN), and the brainstem monoaminergic cell groups, respectively. PVN and especially their corticotropin-releasing hormone (CRH) producing neurons are considered to be the centrum of stress regulation. However, the brainstem seems to be equally important. Therefore, we aimed to summarize the present knowledge on the role of classical neurotransmitters of the brainstem (GABA, glutamate as well as serotonin, noradrenaline, adrenaline, and dopamine) in stress adaptation. Neuropeptides, including CRH, might be co-localized in the brainstem nuclei. Here we focused on CRH as its role in stress regulation is well-known and widely accepted and other CRH neurons scattered along the brain may also complement the function of the PVN. Although CRH-positive cells are present on some parts of the brainstem, sometimes even in comparable amounts as in the PVN, not much is known about their contribution to stress adaptation. Based on the role of the Barrington’s nucleus in micturition and the inferior olivary complex in the regulation of fine motoric—as the main CRH-containing brainstem areas—we might assume that these areas regulate stress-induced urination and locomotion, respectively. Further studies are necessary for the field.

The controlling role of nitric oxide within the shell of nucleus accumbens in the stress-induced metabolic disturbance

CONTEXT AND OBJECTIVES

The involvement of the nitricergic system within the shell part of the nucleus accumbens (NAc) was evaluated in the metabolic disturbances due to stress.

MATERIALS AND METHODS

Male Wistar rats were cannulated in the shell of the left NAc. They received either saline or different doses of L-arginine and/or L-NAME five minutes before each stress session, for four days. Plasma cortisol concentration, food and water intake, time elapsing for eating, animal weight changes and adrenal gland weight were recorded.

RESULTS

The L-arginine 1 μg/rat decreased the level of cortisol, water and food intake and time of feeding and increased the adrenal weight. But L-NAME at 1 μg/rat had opposite effects on these factors. However, the drugs showed similar effects at 10 μg/rat.

CONCLUSION

Injection of nitric oxide modifiers into the left side of NAc shell part may have an interactive role with sub-chronic stress in metabolic behaviour.

Role of angiotensin receptors in the medial amygdaloid nucleus in autonomic, baroreflex and cardiovascular changes evoked by chronic stress in rats

This study investigated the role of AT₁ , AT₂ and Mas angiotensinergic receptors within the MeA in autonomic, cardiovascular and baroreflex changes evoked by a 10-day (1  hr daily) repeated restraint stress (RRS) protocol. Analysis of cardiovascular function after the end of the RRS protocol indicated increased values of arterial pressure, without heart rate changes. Arterial pressure increase was not affected by acute MeA treatment after the RRS with either the selective AT₁ receptor antagonist losartan, the selective AT₂ receptor antagonist PD123319 or the selective Mas receptor antagonist A-779. Analysis of heart rate variability indicated that RRS increased the sympathetic tone to the heart, which was inhibited by MeA treatment with either losartan, PD123319 or A-779. Baroreflex function assessed using the pharmacological approach via intravenous infusion of vasoactive agents revealed a facilitation of tachycardia evoked by blood pressure decrease in chronically stressed animals, which was inhibited by MeA treatment with losartan. Conversely, baroreflex responses during spontaneous fluctuations of blood pressure were impaired by RRS, and this effect was not affected by injection of the angiotensinergic receptor antagonists into the MeA. Altogether, the data reported in the present study suggest an involvement of both angiotensinergic receptors present in the MeA in autonomic imbalance evoked by RRS, as well as an involvement of MeA AT₁ receptor in the enhanced baroreflex responses during full range of blood pressure changes. Results also indicate that RRS-evoked increase in arterial pressure and impairment of baroreflex responses during spontaneous variations of arterial pressure are independent of MeA angiotensinergic receptors.

Fear renewal requires nitric oxide signaling in the lateral amygdala

Fear renewal is defined as return of the conditioned fear responses after extinction when a conditioned stimulus (CS) is given outside of the extinction context. Previously, we have suggested that extinction induces S-nitrosylation of GluA1 in the lateral amygdala (LA), and that the extinction-induced S-nitrosylation of GluA1 lowers the threshold of GluA1 phosphorylation (at Ser 831) which is required for fear renewal. This fits nicely with the fact that fear renewal is induced by weak stimuli. However, it has not been tested whether S-nitrosylation of GluA1 in the LA is indeed required for fear renewal. In the present study, we used three different chemicals to impede protein S-nitrosylation via distinct mechanisms. Fear renewal was inhibited by microinjection of 7-Nitroindazole (nNOS inhibitor), and ZL006 (a blocker of PSD-95-nNOS interaction) before fear renewal. Furthermore, fear renewal was also attenuated by microinjection of a strong antioxidant (N-acetyl cysteine), which scavenges reactive oxygen including nitric oxide, into the LA before each extinction training. These findings suggest that protein S-nitrosylation is required for fear renewal.

The influence of early postnatal chronic mild stress stimulation on the activation of amygdala in adult rat

Amygdala is a limbic structure involved in the stress response. The immunohistochemical and morphometric methods were used to examine whether the chronic mild psychological stress during the early postnatal period would change activation of amygdaloid nuclei in response to the same stressor in adult. In the study we focused on the role of neurons containing calbindin (CB), calretinin (CR), parvalbumin (PV) and nitric oxide synthase (NOS). The rats were divided into three groups: control non-stressed animals and two experimental: EI consisted of animals that were exposed to acute stress in the high-light, open-field test (HL-OF) at P90 (P - postnatal day) and EII consisted of rats that were exposed to chronic stress in HL-OF, daily during the first 21 postnatal days and then once at P90. The scheme of activation of amygdaloid nuclei under stress in EI and EII group was similar. The highest density of c-Fos-ir cells (c-Fos - a marker of neuronal activation) was demonstrated by the medial nucleus (Me) and bed nucleus of the accessory olfactory tract (BAOT). The amygdaloid nuclei diversity after HL-OF was determined by the high activation of the NOS-ir cells in the Me and NOS- and CR-ir cells in the BAOT. These are probably projection neurons involved in modulation of defensive, reproductive and autonomic behavior in stress response and creation/storage of aversive memory. However, in comparison with EI group, significant decrease in density of c-Fos-ir cells, in almost all amygdaloid nuclei of EII group was revealed. Particularly in BAOT and Me the strong decrease of activity of NOS- and CR-ir neurons was observed. It probably results in attenuation of stress responses what, depending on the circumstances, can be adaptive or maladaptive.

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.

Regional Specific Modulation of Stress-Induced Neuronal Activation Associated with the PSD95/NOS Interaction Inhibitor ZL006 in the Wistar Kyoto Rat

BACKGROUND

To determine brain areas involved in the antidepressant-related behavioral effects of the selective neuronal nitric oxide synthase inhibitor 1-(2-Trifluoro-methyl-phenyl) imidazole (TRIM) and experimental test compound 4-((3,5-dichloro-2-hydroxybenzyl)amino)-2-hydroxybenzoic acid (ZL006), an inhibitor of the PSD of 95 kDa/neuronal nitric oxide synthase interaction in the N-methyl-D-aspartic acid receptor signalling pathway, regional specific expression of the neuronal activation marker c-FOS was assessed following exposure to the forced swimming test in the Wistar Kyoto rat.

METHODS

Wistar Kyoto rats were subjected to a 15-minute swim pretest (pre-forced swimming test) period on day 1. At 24, 5, and 1 hour prior to the 5-minute test, which took place 24 hours following the pre-forced swimming test, animals were treated with TRIM (50 mg/kg; i.p.), ZL006 (10 mg/kg; i.p.), or saline vehicle (1 mL/kg i.p). Behavior was recorded during both pretest and test periods.

RESULTS

Both TRIM and ZL006 decreased immobility time in Wistar Kyoto rats in the forced swimming test. Exposure to the forced swimming test increased c-FOS immunoreactivity in the lateral septum, paraventricular nucleus of the hypothalamus, periaqueductal grey, dentate gyrus, and ventral CA1 of the hippocampus compared with non-forced swimming test-exposed controls. Forced swimming test-induced c-FOS immunoreactivity was further increased in the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus following treatment with TRIM or ZL006. By contrast, forced swimming test-induced c-FOS immunoreactivity was reduced in dorsal dentate gyrus and ventral CA1 following treatment with TRIM or ZL006. Exposure to the forced swimming test resulted in an increase in NADPH diaphorase staining in the paraventricular nucleus of the hypothalamus. This forced swimming test-induced increase was attenuated following treatment with ZL006 and points to the paraventricular nucleus as a brain region where ZL006 acts to attenuate forced swimming test-induced neuronal nitric oxide synthase activity while concomitantly regulating region specific neuronal activation associated with an antidepressant-related response.

CONCLUSIONS

This study identified a pattern of enhanced and reduced forced swimming test-related c-FOS immunoreactivity indicative of a regulated network where inhibition of nitric oxide coupled to the N-methyl-D-aspartic acid receptor leads to activation of the lateral septum, periaqueductal gray, and paraventricular nucleus of the hypothalamus with concomitant inhibition of the hippocampus.

GluA2-Lacking AMPA Receptors and Nitric Oxide Signaling Gate Spike-Timing-Dependent Potentiation of Glutamate Synapses in the Dorsal Raphe Nucleus

The dorsal raphe nucleus (DRn) receives glutamatergic inputs from numerous brain areas that control the function of DRn serotonin (5-HT) neurons. By integrating these synaptic inputs, 5-HT neurons modulate a plethora of behaviors and physiological functions. However, it remains unknown whether the excitatory inputs onto DRn 5-HT neurons can undergo activity-dependent change of strength, as well as the mechanisms that control their plasticity. Here, we describe a novel form of spike-timing–dependent long-term potentiation (tLTP) of glutamate synapses onto rat DRn 5-HT neurons. This form of synaptic plasticity is initiated by an increase in postsynaptic intracellular calcium but is maintained by a persistent increase in the probability of glutamate release. The tLTP of glutamate synapses onto DRn 5-HT is independent of NMDA receptors but requires the activation of calcium-permeable AMPA receptors and voltage-dependent calcium channels. The presynaptic expression of the tLTP is mediated by the retrograde messenger nitric oxide (NO) and activation of cGMP/PKG pathways. Collectively, these results indicate that glutamate synapses in the DRn undergo activity-dependent synaptic plasticity gated by NO signaling and unravel a previously unsuspected role of NO in controlling synaptic function and plasticity in the DRn.

Ethanol withdrawal induces anxiety-like effects: Role of nitric oxide synthase in the dorsal raphe nucleus of rats

Nitric oxide (NO) mediated transmission in the dorsal raphe nucleus (DRN) has been shown to be involved in the modulation of anxiety-like behaviors. We investigated whether inhibition of nitric oxide synthase (NOS) in the DRN would prevent anxiety-like behavior induced by ethanol withdrawal. Male Wistar rats were treated with ethanol 2-6% (v/v) for a period of 21 days. Ethanol withdrawal was induced by abrupt discontinuation of the treatment. Experiments were performed 48 h after ethanol discontinuation. Rats with a guide cannula aimed at the DRN received intra-DRN injections of the non-selective NOS inhibitor NG-nitro-l-arginine methyl ester (l-NAME), selective neuronal NOS (nNOS) inhibitor N(ω)-propyl-l-arginine (NPLA), or selective inhibitor of inducible NOS (iNOS) N-([3-(aminomethyl)phenyl] methyl) ethanimidamidedihydrochloride (1400W). Five minutes later, the animals were tested in the elevated plus maze (EPM). Plasma ethanol levels were determined by gas chromatography. There was a reduction in plasma ethanol levels 48 h after ethanol withdrawal. Rats from the ethanol withdrawal group showed decreased exploration of the open arms of the EPM with no change in the exploration of enclosed arms. Intra-DRN treatment with l-NAME (100 nmoles/0.2 μL) and 1400W (1 nmol/0.2 μL), but not NPLA (10 nmoles/0.2 μL) in the DRN attenuated the decrease in the exploration of the open arms of the EPM induced by ethanol withdrawal. The major new finding of the present study is that iNOS in the DRN plays a role in the anxiety-like behavior induced by ethanol withdrawal.

Activation of the hypothalamic-pituitary-adrenal axis in lithium-induced conditioned taste aversion learning

Intraperitoneal injections (ip) of lithium chloride at large doses induce c-Fos expression in the brain regions implicated in conditioned taste aversion (CTA) learning, and also activate the hypothalamic-pituitary-adrenal (HPA) axis and increase the plasma corticosterone levels in rats. A pharmacologic treatment blunting the lithium-induced c-Fos expression in the brain regions, but not the HPA axis activation, induced CTA formation. Synthetic glucocorticoids at conditioning, but not glucocorticoid antagonist, attenuated the lithium-induced CTA acquisition. The CTA acquisition by ip lithium was not affected by adrenalectomy regardless of basal corticosterone supplement, but the extinction was delayed in the absence of basal corticosterone. Glucocorticoids overloading delayed the extinction memory formation of lithium-induced CTA. ip lithium consistently induced the brain c-Fos expression, the HPA activation and CTA formation regardless of the circadian activation of the HPA axis. Intracerebroventricular (icv) injections of lithium at day time also increased the brain c-Fos expression, activated the HPA axis and induced CTA acquisition. However, icv lithium at night, when the HPA axis shows its circadian activation, did not induce CTA acquisition nor activate the HPA axis, although it increased the brain c-Fos expression. These results suggest that the circadian activation of the HPA axis may affect central, but not peripheral, effect of lithium in CTA learning in rats, and the HPA axis activation may be necessary for the central effect of lithium in CTA formation. Also, glucocorticoids may be required for a better extinction; however, increased glucocorticoids hinder both the acquisition and the extinction of lithium-induced CTA.

Brain mechanisms of sympathetic activation in heart failure: Roles of the renin‑angiotensin system, nitric oxide and pro‑inflammatory cytokines (Review)

Patients with chronic heart failure (CHF) have an insufficient perfusion to the peripheral tissues due to decreased cardiac output. The compensatory mechanisms are triggered even prior to the occurrence of clinical symptoms, which include activation of the sympathetic nervous system (SNS) and other neurohumoral factors. However, the long‑term activation of the SNS contributes to progressive cardiac dysfunction and has toxic effects on the cardiomyocytes. The mechanisms leading to the activation of SNS include changes in peripheral baroreceptor and chemoreceptor reflexes and the abnormal regulation of sympathetic nerve activity (SNA) in the central nervous system (CNS). Recent studies have focused on the role of brain mechanisms in the regulation of SNA and the progression of CHF. The renin‑angiotensin system, nitric oxide and pro‑inflammatory cytokines were shown to be involved in the abnormal regulation of SNA in the CNS. The alteration of these neurohumoral factors during CHF influences the activity of neurons in the autonomic regions and finally increase the sympathetic outflow. The present review summarizes the brain mechanisms contributing to sympathoexcitation in CHF.

Hypertensive response to stress: the role of histaminergic H1 and H2 receptors in the medial amygdala

Different brain areas seem to be involved in the cardiovascular responses to stress. The medial amygdala (MeA) has been shown to participate in cardiovascular control, and acute stress activates the MeA to a greater extent than any of the other amygdaloid structures. It has been demonstrated that the brain histaminergic system may be involved in behavioral, autonomic and neuroendocrine responses to stressful situations. The aim of the present study was to investigate the role of the histaminergic receptors H1 and H2 in cardiovascular responses to acute restraint stress. Wistar rats (280-320g) received bilateral injections of cimetidine, mepyramine or saline into the MeA and were submitted to 45min of restraint stress. Mepyramine microinjections at doses of 200, 100 and 50nmol promoted a dose-dependent blockade of the hypertensive response induced by the restraint stress. Cimetidine (200 and 100nmol) promoted a partial blockade of the hypertensive response to stress only at the highest dose administered. Neither drugs altered the typical stress-evoked tachycardiac responses. Furthermore, mepyramine and cimetidine were unable to modify the mean arterial pressure or heart rate of freely moving rats under basal conditions (non-stressed rats). The data suggest that in the MeA the histaminergic H1 receptors appear to be more important than H2 receptors in the hypertensive response to stress. Furthermore, there appears to be no histaminergic tonus in the MeA controlling blood pressure during non-stress conditions.

Estrous cycle and sex affect cocaine-induced behavioural changes in CD1 mice

RATIONALE

Several findings on sex differences in cocaine response suggest a role for hormonal milieu in modulating the subjective effects of cocaine. Nitric oxide (NO) has been involved in the neurochemical, hormonal, and behavioral changes related to stress and anxiety. Within the brain, the anteroventral subdivision of the medial amygdala (MeAV) is an important area involved in processing emotional responses such as anxiety and a high density of NO-producing neurons is observed in this area.

OBJECTIVES

In this study, we hypothesize the possibility of sex/hormonal differences in response to cocaine and that these differences may reflect a change in the MeAV nitrergic system. We have examined cocaine's acute effects on nicotinamide adenine dinucleotide phosphate diaphorase (nadph-d) expression, as well as its effect on motor activity and anxiety in male and estrus and diestrus females.

RESULTS

Our results show that acute cocaine administration produces an increase in both anxiety behaviors and nadph-d expression in the MeAV. Male and diestrus female mice were more susceptible to these effects of cocaine than estrus female mice in which no differences were detected. In addition, we examined individual differences in male and female mice responding to intravenous cocaine reinforcement in a self-administration paradigm. Female mice acquired cocaine self-administration at a faster rate than males and showed a higher motivation to self-administer cocaine under a progressive ratio schedule of reinforcement.

CONCLUSIONS

Our data suggest a complex interaction between hormonal milieu and the behavioral and reinforcing effects of cocaine.

Increased nitric oxide-mediated neurotransmission in the medial prefrontal cortex is associated with the long lasting anxiogenic-like effect of predator exposure

Posttraumatic stress disorder (PTSD) is an anxiety disorder caused by the experience of a severe traumatic event. In rats this disorder has been modeled by exposure to a predator threat. PTSD has been associated to structural and functional changes in the medial prefrontal cortex (mPFC). Direct injections into this brain region of glutamate antagonists or inhibitors of the nitric oxide synthase (NOS) enzyme cause anxiolytic-like effects in rodents. In the present work we investigated if the behavioral changes induced by predator exposure are associated with changes in the mPFC nitrergic system. Since the hippocampus, amygdala and dorsal periaqueductal grey have also been associated to anxiety disorders, including PTSD, we also verified if this procedure would modify the nitrergic system in these regions. Male Wistar rats were exposed to a dummy or live cat for ten minutes and tested in the elevated plus maze test (EPM) seven days later. Immediately after the test their brains were removed for neuronal NOS (nNOS) immunohistochemistry detection and measurements of nitrite/nitrate (NOx) levels. Exposure to the live cat increased freezing responses. One week later the animals that froze when confronted with the cat presented a decreased percentage of entries in the open arms of the EPM and an increased number of nNOS positive neurons in the mPFC and basolateral nucleus of amygdala, but not in the hippocampus, central and medial nuclei of amygdaloid complex or dorsal-lateral periaqueductal grey. Moreover, cat exposed animals showed increased NOx levels in the mPFC but not in the hippocampus one week later. The number of nNOS neurons and NOx levels in the mPFC showed a significant correlation with freezing time during cat exposure. Our results suggest that plastic modifications of the nitrergic system in the mPFC could be related to long lasting behavioral changes induced by severe traumatic events such as predator exposure.

Chronic social isolation induces NF-κB activation and upregulation of iNOS protein expression in rat prefrontal cortex

Exposure of an organism to stress, results in oxidative stress and increased nitric oxide (NO) production in the brain. The role of the processes caused by chronic stress in the prefrontal cortex has not been fully investigated. Considering that chronic stress increases NO production by the enzyme nitric oxide synthase (NOS), we examined the cytosolic neuronal (nNOS) or inducible (iNOS) protein levels in the prefrontal cortex of rats exposed to 21d of chronic social isolation stress, an animal model of depression, alone or in combination with 2h of acute immobilization or cold (4°C) stress (combined stress). Antioxidative status via cytosolic CuZnSOD and mitochondrial MnSOD activity, cytosolic redox status via reduced glutathione (GSH) concentration were determined. Furthermore, cytosolic inducible heat shock protein 70 (Hsp70i), cytosolic/nuclear distributions of NF-κB and serum corticosterone (CORT) were also investigated to elucidate the possible mechanism involved in the cellular NOS pathway. Our results showed that both acute stressors led to increases of CORT and nNOS protein while iNOS protein expression was unaffected. In contrast to the acute stress, chronic social isolation compromised hypothalamic-pituitary-adrenal axis functioning such that the normal stress response was impaired following subsequent acute stressors. Downregulated redox GSH status as well as decreased activity of CuZnSOD and MnSOD suggests the existence of oxidative stress which remained as such following combined stressors. Changes in redox-status associated with decreased Hsp70i protein expression enabled NF-κB translocation into the nucleus, causing increased cytosolic nNOS and iNOS protein expression. Results suggest that NOS signaling pathway plays a differential role between acute and chronic stress whereby state of oxidative/nitrosative stress after chronic social isolation is caused, at least in part, by NF-κB activation and increased iNOS protein expression.

Myelophil ameliorates brain oxidative stress in mice subjected to restraint stress

We evaluated the pharmacological effects of Myelophil, a 30% ethanol extract of a mix of Astragali Radix and Salviae Radix, on oxidative stress-induced brain damage in mice caused by restraint stress. C57BL/6 male mice (eight weeks old) underwent daily oral administration of distilled water, Myelophil (25, 50, or 100mg/kg), or ascorbic acid (100mg/kg) 1h before induction of restraint stress, which involved 3h of immobilization per day for 21days. Nitric oxide levels, lipid peroxidation, activities of antioxidant enzymes (superoxide dismutase, catalase, and glutathione redox system enzymes), and concentrations of adrenaline, corticosterone, and interferon-γ, were measured in brain tissues and/or sera. Restraint stress-induced increases in nitric oxide levels (serum and brain tissues) and lipid peroxidation (brain tissues) were significantly attenuated by Myelophil treatment. Restraint stress moderately lowered total antioxidant capacity, catalase activity, glutathione content, and the activities of glutathione reductase, glutathione peroxidase, and glutathione S-transferase; all these responses were reversed by Myelophil. Myelophil significantly attenuated the elevated serum concentrations of adrenaline and corticosterone and restored serum and brain interferon-γ levels. Moreover, Myelophil normalized expression of the genes encoding monoamine oxidase A, catechol-O-methyltransferase, and phenylethanolamine N-methyltransferase, which was up-regulated by restraint stress in brain tissues. These results suggest that Myelophil has pharmacological properties protects brain tissues against stress-associated oxidative stress damage, perhaps in part through regulation of stress hormones.

Region-specific changes in activities of cell death-related proteases and nitric oxide metabolism in rat brain in a chronic unpredictable stress model

Effects of a chronic combined unpredictable stress on activities of two cell death-related proteases, calpain and cathepsin B, were studied along with indices of nitrergic system in rat brain structures. Male Wistar rats were subjected to a 2-week-long combined stress (combination of unpaired flash light and moderate footshock associated with a white noise session). Stress resulted in a significant loss in the body and thymus weight and increased defecation in the open field test, though neither motor and exploratory activity, nor plasma corticosterone differed from the respective control levels. Decreased calpain activity and increased cathepsin B activity were demonstrated in the hippocampus of stressed rats (previously we have shown that caspase-3 activity was significantly suppressed in the brain of rats subjected to same type of stress). A significant reduction in the number of NOS-containing neurons was accompanied by a chronic stressinduced decline in NOS activity in the neocortex. Similar changes were observed in the hippocampus. However, levels of NO metabolites were elevated in both structures. Thus, stress-induced structural modifications in the brain may be mediated by disturbances in the nitrergic system and increased lysosomal proteolysis.

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.

Active coping with stress suppresses glucose metabolism in the rat hypothalamus

We used 18F-fluorodeoxyglucose small-animal positron-emission tomography to determine whether different styles of coping with stress are associated with different patterns of neuronal activity in the hypothalamus. Adult rats were subjected to immobilization (IMO)-stress or to a non-immobilized condition for 30 min, in random order on separate days, each of which was followed by brain-scanning. Some rats in the immobilized condition were allowed to actively cope with the stress by chewing a wooden stick during IMO, while the other immobilized rats were given nothing to chew on. Voxel-based statistical analysis of the brain imaging data shows that chewing counteracted the stress-induced increased glucose uptake in the hypothalamus to the level of the non-immobilized condition. Region-of-interest analysis of the glucose uptake values further showed that chewing significantly suppressed stress-induced increased glucose uptake in the paraventricular hypothalamic nucleus and the anterior hypothalamic area but not in the lateral hypothalamus. Together with the finding that the mean plasma corticosterone concentration at the termination of the IMO was also significantly suppressed when rats had an opportunity to chew a wooden stick, our results showed that active coping by chewing inhibited the activation of the hypothalamic-pituitary-adrenal axis to reduce the endocrine stress response.

Nitric oxide modulates dopaminergic regulation of prepulse inhibition in the basolateral amygdala

Systemic injection of the nitric oxide (NO) synthase inhibitor N(G)-nitro-L-arginine (LNO) prevents the disruptive effect of amphetamine (Amph) on prepulse inhibition (PPI), a sensorimotor gating model in which the amplitude of the acoustic startle response (ASR) to a startling sound (pulse) is reduced when preceded immediately by a weaker stimulus (prepulse). Given that dopamine (DA) projections to the basolateral amygdala (BLA) are involved in the control of information processing, our aim was to investigate if intra-BLA administration of LNO would modify the disruption caused by the DA agonists, Amph, apomorphine (Apo) and quinpirole (QNP), on PPI. Male Wistar rats received bilateral intra-BLA microinjections (0.2 µL/min/side) of combined treatments (saline or LNO 11 µg followed by saline, QNP 3 µg, Apo 10 µg or Amph 30 µg). PPI was disrupted by intra-BLA Apo, QNP or Amph but not by LNO. Prior bilateral intra-BLA injection of LNO prevented the Apo- and QNP-induced disruption of PPI but did not affect that caused by Amph. APO- or QNP-induced increases in ASR to prepulse + pulse were also restored by LNO. Since local inhibition of NO formation affected the effects of direct, but not indirect, DA agonists, the results suggest that this modulation is not occurring at the level of DA release but may involve complex interactions with other neurotransmitter systems.

Ethanol withdrawal activates nitric oxide-producing neurons in anxiety-related brain areas

The present study investigated whether nitric oxide (NO)-producing neurons localized in brain areas related to anxiety are also activated after ethanol withdrawal. Male Wistar rats were subjected to an oral ethanol self-administration procedure, in which they were offered 6-8% (vol/vol) ethanol solution for a period of 21 days followed by abrupt discontinuation of the treatment. Control animals received control dietary fluid for similar periods of time. Twenty-four or 48 h after ethanol discontinuation, the animals were exposed to the open field for 10 min. Two hours later, their brains were removed and processed for Fos immunohistochemistry and nicotinamide adenine dinucleotide phosphate-diaphorase histochemistry (which is used to detect NO-producing neurons). Decreased exploratory activity was observed in animals subjected to 24-h withdrawal, characterized by a shorter distance traveled in the open field. Additionally, increased Fos expression was detected in brain areas, such as the cingulate and piriform cortices, several hypothalamic nuclei, amygdaloid nuclei, most subdivisions of the periaqueductal gray matter, and dorsal raphe nucleus (DRN). Ethanol withdrawal activated NO-producing neurons in the paraventricular nucleus (PVN) of the hypothalamus, dorsolateral periaqueductal gray matter (DLPAG), and DRN. The results show that ethanol withdrawal activates NO-producing neurons in the PVN, DLPAG, and DRN, which are brain areas implicated in the modulation of emotional, autonomic, and motor expression of anxiety-like behaviors.

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.

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.

Control of systemic and pulmonary blood pressure by nitric oxide formed through neuronal nitric oxide synthase

Nitric oxide formed by neuronal nitric oxide synthase (nNOS) in the brain, autonomic inhibitory (nitrergic) nerves, and heart plays important roles in the control of blood pressure. Activation of nitrergic nerves innervating the systemic vasculature elicits vasodilatation, decreases peripheral resistance, and lowers blood pressure. Impairment of nitrergic nerve function, as well as endothelial dysfunction, results in systemic and pulmonary hypertension and decreased regional blood flow. Blockade of nNOS activity in the brain, particularly the medulla and hypothalamus, causes systemic hypertension. Under hypertensive states, such as those in spontaneously hypertensive and Dahl salt-sensitive rats, the expression of the nNOS gene in the brain is increased; this appears to counteract the activated sympathetic function in the vasomotor center. The present article summarizes information concerning the modulation of systemic and pulmonary hypertension through nNOS-derived nitric oxide produced in the brain and periphery.

c-Fos protein expression is increased in cholinergic neurons of the rodent basal forebrain during spontaneous and induced wakefulness

It has been proposed that cholinergic neurons of the basal forebrain (BF) may play a role in vigilance state control. Since not all vigilance states have been studied, we evaluated cholinergic neuronal activation levels across spontaneously occurring states of vigilance, as well as during sleep deprivation and recovery sleep following sleep deprivation. Sleep deprivation was performed for 2h at the beginning of the light (inactive) period, by means of gentle sensory stimulation. In the rodent BF, we used immunohistochemical detection of the c-Fos protein as a marker for activation, combined with labeling for choline acetyl-transferase (ChAT) as a marker for cholinergic neurons. We found c-Fos activation in BF cholinergic neurons was highest in the group undergoing sleep deprivation (12.9% of cholinergic neurons), while the spontaneous wakefulness group showed a significant increase (9.2%), compared to labeling in the spontaneous sleep group (1.8%) and a sleep deprivation recovery group (0.8%). A subpopulation of cholinergic neurons expressed c-Fos during spontaneous wakefulness, when possible confounds of the sleep deprivation procedure were minimized (e.g., stress and sensory stimulation). Double-labeling in the sleep deprivation treatment group was significantly elevated in select subnuclei of the BF (medial septum/vertical limb of the diagonal band, horizontal limb of the diagonal band, and the magnocellular preoptic nucleus), when compared to spontaneous wakefulness. These findings support and provide additional confirming data of previous reports that cholinergic neurons of BF play a role in vigilance state regulation by promoting wakefulness.

Effects of estrogen on stress-induced activation of peptide neurons in PVN of ovariectomized rats

Estrogen has been implicated in brain function related to stress responses. We investigated whether estrogen affects psychological stress-induced activation of peptide-containing or nitric oxide-producing neurons in the paraventricular hypothalamic nucleus (PVN) in ovariectomized (OVX) rats, both placebo-treated (OVX + Pla) and estrogen-treated (OVX + E2) by comparison of c-Fos expression using immunohistochemistry. Cage-switch stress increased activation in oxytocinergic neurons in the parvocellular PVN (pPVN) in OVX + Pla, but not in that of OVX + E2, rats. Moreover, the stress-induced activation in NADPH-diaphorase-positive neurons in the pPVN was larger in the OVX + E2 than in the OVX + Pla group. These findings suggest that estrogen attenuates the activation of oxytocinergic neurons in the pPVN, at least in part via nitric oxide.

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.

Adrenomedullin acts in the lateral parabrachial nucleus to increase arterial blood pressure through mechanisms mediated by glutamate and nitric oxide

Adrenomedullin (ADM) acts in a site-specific manner within autonomic centers of the brain to modulate mean arterial pressure (MAP). To determine the role of ADM in the pontine autonomic center, the lateral parabrachial nucleus (LPBN), we used urethane-anesthetized adult Sprague-Dawley male rats to test the hypothesis that ADM increases MAP at this site through glutamate- and nitric oxide (NO)-dependent mechanisms. ADM microinjected into the LPBN increased MAP in a dose-dependent manner. The pressor effect of ADM (0.01 pmol) had a peak value of 11.9 +/- 1.9 mmHg at 2 min and lasted for 7 min. We demonstrated that ADM's effect is receptor mediated by blocking the effect with the ADM receptor antagonist, ADM22-52. We showed that glutamate mediates ADM's pressor response, as this response was blocked using coinjections of ADM with dizolcipine hydrogen maleate or 6-cyano-7-nitroquinoxaline-2,3-dione, N-methyl-D-aspartate (NMDA) and non-NMDA glutamate receptor antagonists, respectively. We tested the roles of NO with coinjections of ADM with either N5-(1-iminoethyl)-L-ornithine or 7-nitroindazole monosodium salt, nonspecific and neuronal NO synthase (NOS) inhibitors, respectively; both inhibitors blocked ADM's pressor effect. Finally, we studied the role of calcium influx in ADM's pressor effect, as intracellular calcium is important in both glutamate and NO neurotransmission. ADM's effect was blocked when nifedipine, an L-type calcium channel blocker, was coinjected with ADM into the LPBN. This study is the first to show that ADM acts in the LPBN to increase MAP through mechanisms dependent on activation of ionotropic glutamate receptors, neuronal and endothelial NOS-mediated NO synthesis, and L-type calcium channel activation.

Developmental expression of NMDA and AMPA receptor subunits in vestibular nuclear neurons that encode gravity-related horizontal orientations

We examined the expression profile of subunits of ionotropic glutamate receptors [N-methyl-D-aspartate (NMDA) and alpha-amino-3-hydroxy-5-methyl-4-isoxazole-proprionate (AMPA)] during postnatal development of connectivity in the rat vestibular nucleus. Vestibular nuclear neurons were functionally activated by constant velocity off-vertical axis rotation, a strategy to stimulate otolith organs in the inner ear. These neurons indicated Fos expression as a result. By immunodetection for Fos, otolith-related neurons that expressed NMDA/AMPA receptor subunits were identified as early as P7, and these neurons were found to increase progressively up to adulthood. Although there was developmental invariance in the percentage of Fos-immunoreactive neurons expressing the NR1, NR2A, GluR1, or GluR2/3 subunits, those expressing the NR2B subunit decreased from P14 onward, and those expressing the GluR4 subunit decreased in adults. These double-immunohistochemical data were corroborated by combined immuno-/hybridization histochemical data obtained from Fos-immunoreactive neurons expressing NR2B mRNA or GluR4 mRNA. The staining of both NR2B and GluR4 in the cytoplasm of these neurons decreased upon maturation. The percentage of Fos-immunoreactive neurons expressing the other ionotropic glutamate receptor subunits (viz. NR1, NR2A, GluR1, and GluR2/3) remained relatively constant throughout postnatal maturation. Triple immunofluorescence further demonstrated coexpression of NR1 and NR2 subunits in Fos-immunoreactive neurons. Coexpression of NR1 subunit with each of the GluR subunits was also observed among the Fos-immunoreactive neurons. Taken together, the different expression profiles of ionotropic glutamate receptor subunits constitute the histological basis for glutamatergic neurotransmission in the maturation of central vestibular connectivity for the coding of gravity-related horizontal head movements.

Lack of effects of clomipramine on Fos and NADPH-diaphorase double-staining in the periaqueductal gray after exposure to an innate fear stimulus

Lack of effects of clomipramine on Fos and NADPH-diaphorase double-staining in the periaqueductal gray after exposure to an innate fear stimulus--nitric oxide (NO) acts as a neurotransmitter in the rat dorsolateral periaqueductal gray (dlPAG), a midbrain structure that modulates fear and defensive behavior. Since defensive reactions can be alleviated by anxiolytic/anti-panic drugs, the present study tested the effect of clomipramine, a serotonin re-uptake inhibitor, on the activation of NO-producing neurons in the dlPAG of rats exposed to a live predator. Double staining was performed using Fos immunohistochemistry and NADPH-diaphorase as techniques to mark neural activation and to detect NO-producing neurons, respectively. Male Wistar rats received acute or chronic (21 days) injections of saline or clomipramine (10 or 20 mg/kg/day) and were exposed to a live cat. The animals exhibited a robust defensive reaction accompanied by an increase in the number of Fos- and double-stained neurons in the dlPAG, suggesting that cat exposure activates NO-producing neurons. Such effects were not significantly attenuated by clomipramine treatments. The intensity of fear reaction correlated with the intensity of neural staining in the dlPAG, regardless the drug treatment. Thus, the present results reinforce the hypothesis that NO may coordinate defensive responses in the dlPAG and indicate that this mechanism may not be modulated by a serotonin re-uptake inhibitor.

Induction of Fos-immunoreactivity in the rat brain following disinhibition of the dorsomedial hypothalamus

Activation of neurons in the dorsomedial hypothalamus (DMH) appears to play an important role in signaling the excitation of brain regions responsible for experimental fever and for many of the physiological and behavioral changes seen in experimental stress or anxiety in rats. Here, we examined the effect of disinhibition of the DMH by unilateral microinjection of bicuculline methiodide (BMI) on Fos expression in selected regions of the brain that have been implicated in anxiety and responses to stress and fever in rats. Disinhibition of the DMH resulted in dramatic increases in local Fos expression and also increased the numbers of Fos-positive neurons in the lateral septal nucleus and in both the parvocellular and magnocellular subdivisions of the paraventricular nucleus, with greater increases ipsilateral to the injection site in the DMH. However, microinjection of BMI had no significant effect on Fos expression in the bed nucleus of the stria terminalis, another forebrain area implicated in stress and anxiety. In the brainstem, disinhibition of the DMH increased Fos expression in the nucleus tractus solitarius and the ventrolateral medulla bilaterally with greater increases again ipsilateral to the site of the microinjection, and also in the midline rostral raphe pallidus. Thus, disinhibition of neurons in the DMH in conscious rats results in increases in Fos expression in selected forebrain and brainstem regions that have been implicated in stress-induced physiological changes, anxiety, and experimental fever.

Stress- and lipopolysaccharide-induced c-fos expression and nNOS in hypothalamic neurons projecting to medullary raphe in rats: a triple immunofluorescent labeling study

Neurons in the rostral raphe pallidus (rRP) have been proposed to mediate experimental stress-induced tachycardia and fever in rats, and projections from the dorsomedial hypothalamus (DMH) may signal their activation in these settings. Thus, we examined c-fos expression evoked by air jet/restraint stress and restraint stress or by systemic administration of lipopolysaccharide (10 microg/kg and 100 microg/kg) as well as the distribution of the neuronal nitric oxide synthase (nNOS) in neurons retrogradely labeled from the raphe with cholera toxin B in key hypothalamic regions. Many neurons in the medial preoptic area and the dorsal area of the DMH were retrogradely labeled, and approximately half of those in the medial preoptic area and moderate numbers in the dorsal DMH were also positive for nNOS. Either stress paradigm or dose of lipopolysaccharide increased the number of c-fos-positive neurons and nNOS/c-fos double-labeled neurons in all regions examined. However, retrogradely labeled neurons positive for c-fos were increased only in the dorsal DMH and adjoining region in both stressed and lipopolysaccharide-treated groups, and triple-labeled neurons were found only in this area in rats subjected to either stress paradigm. Thus, hypothalamic neurons that project to the rRP and express c-fos in response to either experimental stress or systemic inflammation are found only in the dorsal DMH, and many of those activated by stress contain nNOS, suggesting that nitric oxide may play a role in signaling in this pathway.

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.

Osmotic regulation of neuronal nitric oxide synthase expression in the rat amygdala: functional role for nitric oxide in adaptive responses?

Water-deprivation-induced osmotic stress leads to activation of a number of adaptive responses. Nitric oxide (NO) has been implicated in the modulation of these responses, as the amygdala has been implicated in ingestive behavior and modulation of autonomic homeostatic functions. Here we investigated the effects of water deprivation on neuronal nitric oxide synthase (nNOS) expression within the rat amygdala; a brain area involved in modulating ingestive behavior and autonomic function. Water deprivation resulted in significant increases in nNOS immunoreactivity (-ir) within different regions of the amygdala compared with euhydrated rats. Maximal increases were observed in the anteroventral (118 +/- 9 vs. 47 +/- 3 neurons), anteriodorsal (133 +/- 9 vs. 77 +/- 3), and posterioventral (175 +/- 5 vs. 71 +/- 5) parts of the medial amygdala. The basomedial nucleus (65 +/- 4 vs. 39 +/- 3) and posterior basolateral nucleus (19 +/- 2 vs. 5 +/- 1) of the amygdala and the capsular (21 +/- 2 vs. 6 +/- 1) and medial (44 +/- 6 vs. 22 +/- 3) parts of the central nucleus of the amygdala also showed increased nNOS-ir in dehydrated rats. Water deprivation had no effect on nNOS-ir in areas such as the cortical, anterior basolateral, and intercalated nuclei of the amygdala. Microinjection of an NO donor, DEA-NONOate, into the central amygdala resulted in a pressor and tachycardic response that was attenuated by a soluble guanylate cyclase inhibitor. These observations suggest that activation of the nitrergic system is prevalent throughout the amygdala following water deprivation and suggest that the up-reguation of nNOS could play a significant role in the integrative response to osmotic stress.

Nitric oxide synthase-containing neurons in the amygdaloid nuclear complex of the rat

The nitric oxide-producing neurons in the rat amygdala (Am) were studied, using reduced nicotinamide adenine dinucleotide phosphate diaphorase (NADPHd) histochemistry. Almost all nuclei of the Am contained NADPHd-positive neurons and fibers, but the somatodendritic morphology and the intensity of staining of different subpopulations varied. The strongly stained neurons displayed labeling of the perikaryon and the dendritic tree with Golgi impregnation-like quality, whilst the dendrites of the lightly stained neurons were less successfully followed. Many strongly positive neurons were located in the external capsule and within the intraamygdaloid fiber bundles. A large number of small, strongly stained cells was present in the amygdalostriatal transition area. In the Am proper, a condensation of deeply stained cells occurred in the lateral amygdaloid nucleus. In the basolateral nucleus, the strongly NADPHd-positive neurons were few, and were located mainly along the lateral border of the nucleus. These cells clearly differed from the large, pyramidal, and efferent cells. The basomedial nucleus contained numerous positive cells but most of them were only lightly labeled. A moderate number of strongly stained neurons appeared in the medial division of the central nucleus, and a larger accumulation of strongly positive cells was present in the lateral and the capsular divisions. The medial amygdaloid nucleus contained numerous moderately stained neurons and displayed the strongest diffuse neuropil staining in Am. In the nucleus of the lateral olfactory tract, the first layer contained only NADPHd-stained axons, in the second layer, there were numerous moderately stained cells, and in the third layer, a few but deeply stained neurons. From the cortical nuclei, the most appreciable number of stained neurons was seen in the anterior cortical nucleus. The anterior amygdaloid area contained numerous NADPHd-positive neurons; in its dorsal part the majority of cells were only moderately stained, whereas in the ventral part the neurons were very strongly stained. The intercalated amygdaloid nucleus lacked NADPHd-positive neurons but an appreciable plexus of fine, tortuous axons was present. In the intra-amygdaloid part of the bed nucleus of the stria terminalis (st) some lightly stained cells were seen but along the entire course of st strongly stained neurons were observed. Some Am nuclei, and especially the central lateral nucleus and the intercalated nucleus, display considerable species differences when compared with the primate Am. The age-related changes of the nitrergic Am neurons, as well as their involvement in neurodegenerative diseases is discussed.

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.