Simultaneous measurement of central amygdala neuronal activity and sympathetic nerve activity during daily activities in rats.

NEW FINDINGS: What is the central question of this study? The functional relationships between central amygdala neuronal activity (CeANA) and sympathetic nerve activity in daily activities remain unclear. We aimed to measure CeANA, renal and lumbar sympathetic nerve activity (RSNA and LSNA, respectively), heart rate (HR) and arterial pressure simultaneously in freely moving rats. What is the main finding and its importance? The CeANA was significantly related to RSNA and LSNA and HR in a behavioural state-dependent and regionally different manner; meanwhile, CeANA was tightly associated with RSNA and HR across all behavioural states. Thus, it is likely that the amygdala is a component of neural networks generating regional differences in RSNA and LSNA. ABSTRACT: The central amygdala (CeA) is involved in generating diverse changes in sympathetic nerve activity (SNA) in response to changes in daily behavioural states. However, the functional relationships between CeA neuronal activity (CeANA) and SNA in daily activities are still unclear. In the present study, we developed a method for simultaneous and continuous measurement of CeANA and SNA in freely moving rats. Wistar rats were chronically instrumented with multiple electrodes (100-µm-thick stainless-steel wire) for the measurement of CeANA, renal SNA (RSNA) and lumbar SNA (LSNA), and electroencephalogram, EMG and ECG electrodes, in addition to catheters for measurement of arterial pressure (AP). During the transition from non-rapid eye movement sleep to quiet wakefulness, moving and grooming states, a significant linear relationship was observed between CeANA and RSNA (P < 0.0001), between CeANA and LSNA (P = 0.0309), between CeANA and heart rate (HR) (P = 0.0123) and between CeANA and EMG (P = 0.0089), but no significant correlation was observed between CeANA and AP (P = 0.5139). During rapid eye movement sleep, the relationships between CeANA and RSNA, LSNA, HR, AP and EMG deviated from the previously observed linear relationships, but the time course of RSNA and HR changes was the mirror image of that of CeANA, whereas the time course of changes in LSNA and AP was not related to that of CeANA. In conclusion, CeANA was related to RSNA, LSNA and HR in a behavioural state-dependent and regionally different manner, and CeANA was tightly associated with RSNA and HR across all behavioural states.

Regional Differences in Sympathetic Nerve Activity Are Generated by Multiple Arterial Baroreflex Loops Arranged in Parallel.

In this review, by evaluating the responses during freezing, rapid eye movement (REM) sleep, and treadmill exercise, we discuss how multiple baroreflex loops arranged in parallel act on different organs to modulate sympathetic nerve activity (SNA) in a region-specific and coordinated manner throughout the body. During freezing behaviors, arterial pressure (AP) remains unchanged, heart rate (HR) persistently decreases, renal SNA (RSNA) increases, and lumbar SNA (LSNA) remains unchanged. The baroreflex curve for RSNA shifts upward; that for LSNA remains unchanged; and that for HR shifts to the left. These region-specific changes in baroreflex curves are responsible for the region-specific changes in RSNA, LSNA, and HR during freezing. The decreased HR could allow the heart to conserve energy, which is offset by the increased RSNA caused by decreased vascular conductance, resulting in an unchanged AP. In contrast, the unchanged LSNA leaves the muscles in readiness for fight or flight. During REM sleep, AP increases, RSNA and HR decrease, while LSNA is elevated. The baroreflex curve for RSNA during REM sleep is vertically compressed in comparison with that during non-REM sleep. Cerebral blood flow is elevated while cardiac output is decreased during REM sleep. To address this situation, the brain activates the LSNA selectively, causing muscle vasoconstriction, which overcomes vasodilation of the kidneys as a result of the decreased RSNA and cardiac output. Accordingly, AP can be maintained during REM sleep. During treadmill exercise, AP, HR, and RSNA increase simultaneously. The baroreflex curve for RSNA shifts right-upward with the increased feedback gain, allowing maintenance of a stable AP with significant fluctuations in the vascular conductance of working muscles. Thus, the central nervous system may employ behavior-specific scenarios for modulating baroreflex loops for differential control of SNA, changing the SNA in a region-specific and coordinated manner, and then optimizing circulatory regulation corresponding to different behaviors.

Differential shifts in baroreflex control of renal and lumbar sympathetic nerve activity induced by freezing behaviour in rats.

NEW FINDINGS: What is the central question of this study? Is the arterial baroreflex involved in causing patterned, region-specific changes in sympathetic nerve activity during freezing behaviour in conscious rats? What is the main finding and its importance? Freezing behaviour is accompanied by differential shifts in the baroreflex control of renal and lumbar sympathetic nerve activity and heart rate. It is noteworthy that baroreflex pathways may be discretely separated, allowing differential modification of baroreflex curves that may generate differential changes in sympathetic nerve activity during freezing behaviour. ABSTRACT: The present study was designed to test whether the baroreflex stimulus-response curves for renal sympathetic nerve activity (RSNA), lumbar sympathetic nerve activity (LSNA) and heart rate (HR) were shifted in a regionally specific manner during freezing behaviour in conscious rats. Male Wistar rats were chronically instrumented with electrodes and arterial and venous catheters for measurement of RSNA, LSNA and electrocardiogram. After a 60-min control period, freezing behaviour in conscious rats was induced by exposure to loud white noise (90 dB) for 10 min. The baroreflex curves for RSNA, LSNA and HR were generated by changing systemic arterial pressure using rapid intravenous infusions of vasoactive drugs and then fitted to an inverse sigmoid function curve. During the freezing behaviour, the baroreflex curve for RSNA was expanded upward with a significant (P < 0.001) increase (by 153% compared with the control level) in the upper plateau (maximum capacity of RSNA drive), whereas the baroreflex curve for LSNA remained unchanged. Conversely, the baroreflex curve for HR was shifted leftward with a significant (P = 0.004) decrease (by 11 mmHg relative to the control level) in the midpoint pressure. Our results indicate that baroreflex curve shifts for RSNA, LSNA and HR occur in a regionally specific manner during freezing behaviour. This indicates that baroreflex pathways may be discretely separated, allowing differential modification of baroreflex curves that may generate differential changes in sympathetic nerve activity during freezing behaviour.

Renal and Lumbar Sympathetic Nerve Activity During Development of Hypertension in Dahl Salt-Sensitive Rats.

To study the contribution of sympathetic nerve activity (SNA) to the development of hypertension, experiments were designed to continuously and simultaneously measure renal (RSNA) and lumbar SNA (LSNA) during the development of hypertension induced by 8% salt loading in Dahl salt-sensitive (DS) rats. Male DS and salt-resistant rats were instrumented with bipolar electrodes to record RSNA and LSNA and a telemeter to record arterial pressure (AP). AP increased during the first 3 days after the onset of salt loading by ≈10 mm Hg in both DS and Dahl salt-resistant rats. AP continued to increase progressively from day 4 to day 14 of salt loading by 33±1 mm Hg in DS rats, while it remained the same in Dahl salt-resistant rats. RSNA and LSNA increased in the initial few days by 6% to 8%, and decreased gradually thereafter, suggesting that increases in neither RSNA nor LSNA are directly linked with the progressive increase in AP induced by salt loading in DS rats. After the cessation of salt loading, AP pressure returned to the presalt loading level in both DS and Dahl salt-resistant rats. RSNA increased significantly by 32±3% after the cessation of salt loading, while LSNA remained the same in DS rats, suggesting that salt-sensitive mechanisms respond to a loss of sodium, not a gain, and selectively activate RSNA in DS rats. In summary, RSNA and LSNA are not likely to be a primary trigger to initiate the progressive increase in AP induced by 8% salt loading in DS rats.

Exercise-Induced Modulation of Baroreflex Control of Sympathetic Nerve Activity.

Exercise modulates arterial pressure (AP) regulation over various time spans. AP increases at the onset of exercise and this increase is then sustained during exercise. Once exercise is stopped, AP is suppressed for up to an hour afterwards. Prolonged endurance training is associated with dysfunction of the sympathetic regulation of AP in response to posture changes (orthostatic intolerance). Baroreflex control of sympathetic nerve activity (SNA) has been extensively studied to understand the mechanisms underlying exercise-induced changes in AP. We have previously presented entire baroreflex AP-SNA curves during and after exercise, and during central volume expansion, obtained using direct measurements of renal sympathetic nerve activity (RSNA) in conscious animals. In this review, we describe the modulatory effects of exercise on baroreflex control of AP based on these entire AP-RSNA baroreflex curves. We suggest that both acute and chronic exercise can have modulatory effects on the entire baroreflex curve for SNA, and that these effects differ among time periods.

Ghrelin Preserves Ischemia-Induced Vasodilation of Male Rat Coronary Vessels Following ß-Adrenergic Receptor Blockade.

Acute myocardial infarction (MI) triggers an adverse increase in cardiac sympathetic nerve activity (SNA). Whereas ß-adrenergic receptor (ß-AR) blockers are routinely used for the management of MI, they may also counter ß-AR-mediated vasodilation of coronary vessels. We have reported that ghrelin prevents sympathetic activation following MI. Whether ghrelin modulates coronary vascular tone following MI, either through the modulation of SNA or directly as a vasoactive mediator, has never been addressed. We used synchrotron microangiography to image coronary perfusion and vessel internal diameter (ID) in anesthetized Sprague-Dawley rats, before and then again 30 minutes after induction of an MI (left coronary artery ligation). Rats were injected with either saline or ghrelin (150 µg/kg, subcutaneously), immediately following the MI or sham surgery. Coronary angiograms were also recorded following ß-AR blockade (propranolol, 2 mg/kg, intravenously). Finally, wire myography was used to assess the effect of ghrelin on vascular tone in isolated human internal mammary arteries (IMAs). Acute MI enhanced coronary perfusion to nonischemicregions through dilation of small arterioles (ID 50 to 250 µm) and microvessel recruitment, irrespective of ghrelin treatment. In ghrelin-treated rats, ß-AR blockade did not alter the ischemia-induced vasodilation, yet in saline-treated rats, ß-AR blockade abolished the vasodilation of small arterioles. Finally, ghrelin caused a dose-dependent vasodilation of IMA rings (preconstricted with phenylephrine). In summary, this study highlights ghrelin as a promising adjunct therapy that can be used in combination with routine ß-AR blockade treatment for preserving coronary blood flow and cardiac performance in patients who suffer an acute MI.

Widespread Coronary Dysfunction in the Absence of HDL Receptor SR-B1 in an Ischemic Cardiomyopathy Mouse Model.

Reduced clearance of lipoproteins by HDL scavenger receptor class B1 (SR-B1) plays an important role in occlusive coronary artery disease. However, it is not clear how much microvascular dysfunction contributes to ischemic cardiomyopathy. Our aim was to determine the distribution of vascular dysfunction in vivo in the coronary circulation of male mice after brief exposure to Paigen high fat diet, and whether this vasomotor dysfunction involved nitric oxide (NO) and or endothelium derived hyperpolarization factors (EDHF). We utilised mice with hypomorphic ApoE lipoprotein that lacked SR-B1 (SR-B1-/-/ApoER61h/h, n = 8) or were heterozygous for SR-B1 (SR-B1+/-/ApoER61h/h, n = 8) to investigate coronary dilator function with synchrotron microangiography. Partially occlusive stenoses were observed in vivo in SR-B1 deficient mice only. Increases in artery-arteriole calibre to acetylcholine and sodium nitroprusside stimulation were absent in SR-B1 deficient mice. Residual dilation to acetylcholine following L-NAME (50 mg/kg) and sodium meclofenamate (3 mg/kg) blockade was present in both mouse groups, except at occlusions, indicating that EDHF was not impaired. We show that SR-B1 deficiency caused impairment of NO-mediated dilation of conductance and microvessels. Our findings also suggest EDHF and prostanoids are important for global perfusion, but ultimately the loss of NO-mediated vasodilation contributes to atherothrombotic progression in ischemic cardiomyopathy.

Chronic intermittent hypoxia accelerates coronary microcirculatory dysfunction in insulin-resistant Goto-Kakizaki rats.

Chronic intermittent hypoxia (IH) induces oxidative stress and inflammation, which impair vascular endothelial function. Long-term insulin resistance also leads to endothelial dysfunction. We determined, in vivo, whether the effects of chronic IH and insulin resistance on endothelial function augment each other. Male 12-wk-old Goto-Kakizaki (GK) and Wistar control rats were subjected to normoxia or chronic IH (90-s N2, 5% O2 at nadir, 90-s air, 20 cycles/h, 8 h/day) for 4 wk. Coronary endothelial function was assessed using microangiography with synchrotron radiation. Imaging was performed at baseline, during infusion of acetylcholine (ACh, 5 µg·kg(-1)·min(-1)) and then sodium nitroprusside (SNP, 5 µg·kg(-1)·min(-1)), after blockade of both nitric oxide (NO) synthase (NOS) with N(ω)-nitro-l-arginine methyl ester (l-NAME, 50 mg/kg) and cyclooxygenase (COX, meclofenamate, 3 mg/kg), and during subsequent ACh. In GK rats, coronary vasodilatation in response to ACh and SNP was blunted compared with Wistar rats, and responses to ACh were abolished after blockade. In Wistar rats, IH blunted the ability of ACh or SNP to increase the number of visible vessels. In GK rats exposed to IH, neither ACh nor SNP were able to increase visible vessel number or caliber, and blockade resulted in marked vasoconstriction. Our findings indicate that IH augments the deleterious effects of insulin resistance on coronary endothelial function. They appear to increase the dependence of the coronary microcirculation on NO and/or vasodilator prostanoids, and greatly blunt the residual vasodilation in response to ACh after blockade of NOS/COX, presumably mediated by endothelium-derived hyperpolarizing factors.

Monoamine oxidase-induced hydroxyl radical production and cardiomyocyte injury during myocardial ischemia-reperfusion in rats.

To elucidate the involvement of monoamine oxidase (MAO) in hydroxyl radical production and cardiomyocyte injury during ischemia as well as after reperfusion, we applied microdialysis technique to the heart of anesthetized rats. Dialysate samples were collected during 30 min of induced ischemia followed by 60 min of reperfusion. We monitored dialysate 3,4-dihydrobenzoic acid (3,4-DHBA) concentration as an index of hydroxyl radical production using a trapping agent (4-hydroxybenzoic acid), and dialysate myoglobin concentration as an index of cardiomyocyte injury in the ischemic region. The effect of local administration of a MAO inhibitor, pargyline, was investigated. Dialysate 3,4-DHBA concentration increased from 1.9 ± 0.5 nM at baseline to 3.5 ± 0.7 nM at 20-30 min of occlusion. After reperfusion, dialysate 3,4-DHBA concentration further increased reaching a maximum (4.5 ± 0.3 nM) at 20-30 min after reperfusion, and stabilized thereafter. Pargyline suppressed the averaged increase in dialysate 3,4-DHBA concentration by ∼72% during occlusion and by ∼67% during reperfusion. Dialysate myoglobin concentration increased from 235 ± 60 ng/ml at baseline to 1309 ± 298 ng/ml at 20-30 min after occlusion. After reperfusion, dialysate myoglobin concentration further increased reaching a peak (5833 ± 1017 ng/ml) at 10-20 min after reperfusion, and then declined. Pargyline reduced the averaged dialysate myoglobin concentration by ∼56% during occlusion and by ∼41% during reperfusion. MAO plays a significant role in hydroxyl radical production and cardiomyocyte injury during ischemia as well as after reperfusion.

Pulmonary vascular tone is dependent on the central modulation of sympathetic nerve activity following chronic intermittent hypoxia.

Chronic intermittent hypoxia (IH) provokes a centrally mediated increase in sympathetic nerve activity (SNA). Although this sympathetic hyperexcitation has been linked to systemic hypertension, its effect on the pulmonary vasculature is unclear. This study aimed to assess IH-mediated sympathetic excitation in modulating pulmonary vasculature tone, particularly acute hypoxia vasoconstrictor response (HPV), and the central ß-adrenergic signaling pathway for facilitating the increase in SNA. Sprague-Dawley rats were exposed to IH (cycle of 4% O2 for 90 s/air for 90 s) for 8 h/day for 6 weeks. Subsequently, rats were anesthetized and either pulmonary SNA was recorded (electrophysiology), or the pulmonary vasculature was visualized using microangiography. Pulmonary sympathetic and vascular responses to acute hypoxia were assessed before and after central ß1-adrenergic receptor blockade (Metoprolol, 200 nmol i.c.v.). Chronic IH increased baseline SNA (110% increase), and exacerbated the sympathetic response to acute hypoxia. Moreover, the magnitude of HPV in IH rats was blunted compared to control rats (e.g., 10 and 20% vasoconstriction, respectively). In only the IH rats, ß1-receptor blockade with metoprolol attenuated the hypoxia-induced increase in pSNA and exacerbated the magnitude of acute HPV, so that both sympathetic and HPV responses were similar to that of control rats. Interestingly, the expression of ß1-receptors within the brainstem was similar between both control and IH rats. These results suggest that the centrally mediated increase in SNA following IH acts to blunt the local vasoconstrictor effect of acute hypoxia, which reflects an inherent difference between vasodilator and vasoconstrictor actions of SNA in pulmonary and systemic circulations.

Role of cardiac sympathetic nerves in blood pressure regulation.

Stellate ganglionectomy (SGx) was used to assess the contribution of cardiac sympathetic nerves to neurogenic hypertension in deoxycorticosterone (DOCA)-salt treated rats. Experiments were conducted in two substrains of Sprague-Dawley (SD) rats since previous studies reported bradycardia in Charles River-SD (CR-SD) rats and tachycardia in SASCO-SD (SA-SD) rats with DOCA treatment suggesting different underlying neural mechanisms. Uninephrectomized male rats underwent SGx or SHAM surgery and were instrumented for telemetric monitoring of mean arterial pressure (MAP) and heart rate (HR). After recovery, 0.9% saline solution and DOCA (50mg) were administered. Baseline MAP (Days 0-5 average) after SGx in CR-SD rats (96±2mmHg; n=7) was not significantly different (p=0.08) than CR-SD SHAM rats (103±3mmHg; n=9); however, there was a significantly lower HR during the baseline period (377±7 vs. 432±7bpm, p<0.05) in SGx rats. In SA-SD rats baseline MAP was not different between SGx and SHAM rats and HR was lower in SGx rats (428±8 vs. 371±5bpm, p<0.05). After DOCA treatment in both substrains, MAP and HR were elevated similarly in SHAM and SGx groups showing minimal impact in both groups of SGx on hypertension development. However, overall MAP in SA-SD SHAM rats reached a significantly higher level (155±10mmHg vs 135±5mmHg, p<0.05) than that observed in CR-SD SHAM rats demonstrating that the magnitude of hypertensive response to DOCA-salt treatment varies between substrains. In conclusion, removal of cardiac sympathetic nerves did not alter the development or maintenance of DOCA-salt hypertension in SD rats.

Acute Rho-kinase inhibition improves coronary dysfunction in vivo, in the early diabetic microcirculation.

OBJECTIVES: Activation of RhoA/Rho-kinase (ROCK) is increasingly implicated in acute vasospasm and chronic vasoconstriction in major organ systems. Therefore we aimed to ascertain whether an increase in ROCK activity plays a role in the deterioration of coronary vascular function in early stage diabetes. METHODS: Synchrotron radiation microangiography was used to determine in vivo coronary responses in diabetic (3 weeks post streptozotocin 65 mg/kg ip) and vehicle treated male Sprague-Dawley rats (n = 8 and 6). Changes in vessel number and calibre during vasodilator stimulation before and after blockade of nitric oxide synthase and cyclooxygenase were compared between rats. Acute responses to ROCK inhibitor, fasudil (10 mg/kg iv) was evaluated. Further, perivascular and myocardial fibrosis, arterial intimal thickening were assessed by histology, and capillary density, nitrotyrosine and ROCK1/2 expressions were evaluated by immunohistochemical staining. RESULTS: Diabetic rats had significantly elevated plasma glucose (P < 0.001 vs control), but did not differ in fibrotic scores, media to lumen ratio, capillary density or baseline visible vessel number or calibre. Responses to acetylcholine and sodium nitroprusside stimulation were similar between groups. However, in comparison to control rats the diabetic rats showed more segmental constrictions during blockade, which were not completely alleviated by acetylcholine, but were alleviated by fasudil. Further, second order vessel branches in diabetic rats were significantly more dilated relative to baseline (37% vs 12% increase, P < 0.05) after fasudil treatment compared to control rats, while visible vessel number increased in both groups. ROCK2 expression was borderline greater in diabetic rat hearts (P < 0.053). CONCLUSIONS: We found that ahead of the reported decline in coronary endothelial vasodilator function in diabetic rats there was moderate elevation in ROCK expression, more widespread segmental constriction when nitric oxide and prostacyclin production were inhibited and notably, increased calibre in second and third order small arteries-arterioles following ROCK inhibition. Based on nitrotyrosine staining oxidative stress was not significantly elevated in early diabetic rats. We conclude that tonic ROCK mediated vasoconstriction contributes to coronary vasomotor tone in early diabetes.

Assessment of the serotonin pathway as a therapeutic target for pulmonary hypertension.

Blockade of the serotonin reuptake transporter (5-HTT), using fluoxetine, has been identified as a potential therapeutic target for preventing and, importantly, reversing pulmonary hypertension (PH). This study utilized synchrotron radiation microangiography to determine whether fluoxetine could prevent or reverse endothelial dysfunction and vessel rarefaction, which underpin PH. PH was induced by a single injection of monocrotaline (MCT; 60 mg kg(-1)). Following MCT administration, rats received daily injections of either saline or fluoxetine (MCT+Fluox; 10 mg kg(-1)) for three weeks. A third group of rats also received the fluoxetine regime, but only three weeks after MCT (MCT+FluoxDelay). Control rats received daily injections of saline. Pulmonary microangiography was performed to assess vessel branching density and visualize dynamic changes in vessel diameter following (i) acute fluoxetine or (ii) acetylcholine, sodium nitroprusside, BQ-123 (ET-1A receptor blocker) and L-NAME (NOS inhibitor). Monocrotaline induced PH that was inevitably terminal. `Delayed' treatment of fluoxetine (MCT+FluoxDelay) was unable to reverse the progression of PH. Early fluoxetine treatment pre-PH (i.e. MCT+Fluox) attenuated but did not completely prevent vascular remodeling, vessel rarefaction and an increase in pulmonary pressure, and it did not prevent pulmonary endothelial dysfunction. Interestingly, fluoxetine treatment did counter-intuitively prevent the onset of right ventricular hypertrophy. Using synchrotron radiation microangiography, selective blockade of the serotonin reuptake transporter alone is highlighted as not being sufficient to prevent pulmonary endothelial dysfunction, which is the primary instigator for the inevitable onset of vascular remodeling and vessel rarefaction. Accordingly, potential therapeutic strategies should aim to target multiple pathways to ensure an optimal outcome.

Reprint of "Sympathetic nerve activity during sleep, exercise, and mental stress".

This brief review describes recent findings on the differential regulation of sympathetic nerve activity and its role in regulating systemic arterial pressure during rapid eye-movement sleep, non-rapid-eye movement sleep, exercise and freezing behavior (mental stress). We describe the mechanisms underlying the differential regulation of sympathetic outflows and how they act in concert to orchestrate adjustments of cardiovascular function for the whole body, which are optimized to match changes in organ activity in daily activity.

Sympathetic nerve activity during sleep, exercise, and mental stress.

This brief review describes recent findings on the differential regulation of sympathetic nerve activity and its role in regulating systemic arterial pressure during rapid eye-movement sleep, non-rapid-eye movement sleep, exercise and freezing behavior (mental stress). We describe the mechanisms underlying the differential regulation of sympathetic outflows and how they act in concert to orchestrate adjustments of cardiovascular function for the whole body, which are optimized to match changes in organ activity in daily activity.

Functional role of diverse changes in sympathetic nerve activity in regulating arterial pressure during REM sleep.

STUDY OBJECTIVES: This study aimed to investigate whether REM sleep evoked diverse changes in sympathetic outflows and, if so, to elucidate why REM sleep evokes diverse changes in sympathetic outflows. MEASUREMENTS: Male Wistar rats were chronically implanted with electrodes to measure renal (RSNA) and lumbar sympathetic nerve activity (LSNA), electroencephalogram, electromyogram, and electrocardiogram, and catheters to measure systemic arterial and central venous pressure; these parameters were measured simultaneously and continuously during the sleep-awake cycle in the same rat. RESULTS: REM sleep resulted in a step reduction in RNSA by 36.1% ± 2.7% (P < 0.05), while LSNA increased in a step manner by 15.3% ± 2% (P < 0.05) relative to the NREM level. Systemic arterial pressure increased gradually (P < 0.05), while heart rate decreased in a step manner (P < 0.05) during REM sleep. In contrast to REM sleep, RSNA, LSNA, systemic arterial pressure, and heart rate increased in a unidirectional manner associated with increases in physical activity levels in the order from NREM sleep, quiet awake, moving, and grooming state. Thus, the relationship between RSNA vs. LSNA and systemic arterial pressure vs. heart rate observed during REM sleep was dissociated compared with that obtained during the other behavioral states. CONCLUSIONS: It is suggested that the diverse changes in sympathetic outflows during REM sleep may be needed to increase systemic arterial pressure by balancing vascular resistance between muscles and vegetative organs without depending on the heart.

Imaging of the closed-chest mouse pulmonary circulation using synchrotron radiation microangiography.

Structural and functional changes of pulmonary circulation related to pathophysiology of pulmonary arterial hypertension (PAH) remain to be fully elucidated. Angiographic visualization in in vivo animals provided a powerful tool for assessing the major indexes associated with the pathogenesis of PAH. In this study, we have exploited the full potential of synchrotron radiation (SR) microangiography to show the ability to visualize pulmonary hemodynamics in a closed-chest mouse. Male adult mice were anesthetized and cannulated with a customized 24-gauge catheter into the right ventricle via the jugular vein for administering iodine contrast agent. The microangiography was performed on the left lung. We measured dynamic changes in vessel diameter in response to acetylcholine (ACh) and acute exposure to hypoxic gas (10% O(2)). Moreover, the pulmonary transit time was estimated by the time of contrast agent circulating. We were able to visualize the pulmonary arteries from the left pulmonary artery (LPA) to the third generation of branching (inner diameter <100 µm). ACh and acute hypoxia induced vascular responses chiefly in the second and third branching vessels rather than the LPA and the first branching vessels. The transit time was only 0.83 s. These results demonstrate the effectiveness of SR for visualizing the pulmonary circulation in a closed-chest mouse. Future studies using SR microangiography on specific gene-targeted knockout and transgenic mice will provide new insights into the pathophysiology of pulmonary dysfunction and functional adaptation to survive in hypoxic condition.

Differential control of renal and lumbar sympathetic nerve activity during freezing behavior in conscious rats.

The present study was designed to document changes in sympathetic nerve activity and cardiovascular function when conscious rats were challenged with a noise stressor to induce freezing behavior. The potential contribution of the arterial baroreceptors in regulating sympathetic nerve activity and cardiovascular adjustments during the freezing behavior was then examined. Wistar male rats were assigned to sham-operated (SO) and sinoaortic-denervated (SAD) groups and instrumented chronically with electrodes for measurements of renal (RSNA) and lumbar (LSNA) sympathetic nerve activity, electroencephalogram, electromyogram, and electrocardiogram and catheters for measurements of systemic arterial and central venous pressure. Both SO and SAD rats were exposed to 90 dB of white noise for 10 min, causing freezing behavior in both groups. In SO rats, freezing behavior was associated with an immediate and significant (P < 0.05) increase in RSNA, no changes in LSNA or mean arterial pressure, and a significant (P < 0.05) decrease in heart rate. SAD attenuated the magnitude of the immediate increase in RSNA and had no influence on the response in LSNA during freezing behavior compared with SO rats. Moreover, in SAD rats, mean arterial pressure increased significantly (P < 0.05) while heart rate did not change during the freezing behavior. These data indicate that freezing behavior evokes regionally different changes in sympathetic outflows, which may be involved in generating the patterned responses of cardiovascular function to stressful or threatening sensory stimulation. Moreover, it is suggested that the arterial baroreceptors are involved in generating the differential changes in RSNA and LSNA and thus the patterned changes in cardiovascular functions observed during freezing behavior in conscious rats.

Chronic angiotensin II infusion causes differential responses in regional sympathetic nerve activity in rats.

Angiotensin II (AngII)-induced hypertension in experimental animals has been proposed to be attributed in part to activation of the sympathetic nervous system. This sympathetic activation appears to be accentuated in animals consuming a high-salt diet (AngII-salt hypertension). However, accurate quantification of sympathetic activity is difficult, and controversy remains. It is particularly important to ask which are the critical vascular beds targeted by increased sympathetic nerve activity (SNA) in AngII-salt hypertension. To address this issue, mean arterial pressure and renal SNA or lumbar SNA were continuously recorded during a 5-day control period, 11 days of AngII (150 ng/kg per minute, SC), and a 5-day recovery period in conscious rats on a high-salt (2% NaCl) diet. Although mean arterial pressure reached a new steady-state level of 30 to 35 mm Hg above control levels by the end of the AngII period, renal SNA decreased by 40% during the first 7 days of AngII and then returned toward control levels by day 10 of AngII. In contrast, lumbar SNA remained at control levels throughout the AngII period. In another experiment we measured hindlimb norepinephrine spillover in conscious rats on normal (0.4%) or high- (2.0%) salt diets before and during 14 days of AngII administration. AngII had no significant affect on hindlimb norepinephrine spillover in either group. We conclude that chronic AngII modulates renal and lumbar SNAs differentially in rats consuming a high-salt diet and that AngII-salt hypertension in the rat is not caused by increased SNA to the renal or hindlimb vascular beds.

Role of differential changes in sympathetic nerve activity in the preparatory adjustments of cardiovascular functions during freezing behaviour in rats.

Freezing behaviour is associated with a distinct pattern of changes in cardiovascular function, which has been considered as a preparatory reflex for 'fight or flight' behaviour. However, the detailed mechanisms underlying preparatory cardiovascular adjustments and their physiological implications have received less attention. We studied responses in renal and lumbar sympathetic nerve activity and cardiovascular function during freezing behaviour in conscious rats, which was induced by exposure to loud white noise. Freezing behaviour was associated with regionally specific alterations in sympathetic nerve activity, in that renal sympathetic nerve activity increased while lumbar sympathetic nerve activity did not change. Moreover, freezing behaviour was associated with differential shifts in baroreflex control of sympathetic outflows, which could help to explain the selective responses in renal and lumbar sympathetic nerve activity during freezing behaviour. These differential changes in sympathetic outflows would result in a visceral vasoconstriction without having any impact on the skeletal muscle vasculature. These cardiovascular adjustments during freezing behaviour may help to explain the immediate and massive increase in muscular blood flow that occurs at the onset of fight or flight behaviour. It is hypothesized that central command originating from the defence area could somehow modulate separate baroreflex pathways, causing differential changes in sympathetic nerve activity to generate the preparatory cardiovascular adjustments during the freezing behaviour.