Slit3 secreted from M2-like macrophages increases sympathetic activity and thermogenesis in adipose tissue.

Beiging of white adipose tissue (WAT) is associated with an increase of anti-inflammatory M2-like macrophages in WAT. However, mechanisms through which M2-like macrophages affect beiging are incompletely understood. Here, we show that the macrophage cytokine Slit3 is secreted by adipose tissue macrophages and promotes cold adaptation by stimulating sympathetic innervation and thermogenesis in mice. Analysing the transcriptome of M2-like macrophages in murine inguinal WAT (iWAT) after cold exposure, we identify Slit3 as a secreted cytokine. Slit3 binds to the ROBO1 receptor on sympathetic neurons to stimulate Ca2+/calmodulin-dependent protein kinase II signalling and norepinephrine release, which enhances adipocyte thermogenesis. Adoptive transfer of Slit3-overexpressing M2 macrophages to iWAT promotes beiging and thermogenesis, whereas mice that lack Slit3 in myeloid cells are cold-intolerant and gain more weight. Our findings shed new light on the integral role of M2-like macrophages for adipose tissue homeostasis and uncover the macrophage-Slit3-sympathetic neuron-adipocyte signalling axis as a regulator of long-term cold adaptation.

Muscle sympathetic single-unit responses during rhythmic handgrip exercise and isocapnic hypoxia in males: the role of sympathoexcitation magnitude.

A small proportion of postganglionic muscle sympathetic single units can be inhibited during sympathoexcitatory stressors in humans. However, whether these responses are dependent on the specific stressor or the level of sympathoexcitation remains unclear. We hypothesize that, when matched by sympathoexcitatory magnitude, different stressors can evoke similar proportions of inhibited single units. Multiunit and single-unit muscle sympathetic nerve activity (MSNA) were recorded in seven healthy young males at baseline and during 1) rhythmic handgrip exercise (40% of maximum voluntary contraction) and 2) acute isocapnic hypoxia (partial pressure of end-tidal O2 47 ± 3 mmHg). Single units were classified as activated, nonresponsive, or inhibited if the spike frequency was above, within, or below the baseline variability, respectively. By design, rhythmic handgrip and isocapnic hypoxia similarly increased multiunit total MSNA [Δ273 ± 208 vs. Δ254 ± 193 arbitrary units (AU), P = 0.84] and single-unit spike frequency (Δ8 ± 10 vs. Δ12 ± 13 spikes/min, P = 0.12). Among 19 identified single units, the proportions of activated (47% vs. 68%), nonresponsive (32% vs. 16%), and inhibited (21% vs. 16%) single units were not different between rhythmic handgrip and isocapnic hypoxia (P = 0.42). However, only 9 (47%) single units behaved with concordant response patterns across both stressors (7 activated, 1 nonresponsive, and 1 inhibited during both stressors). During the 1-min epoch with the highest increase in total MSNA during hypoxia (Δ595 ± 282 AU, P < 0.01) only one single unit was inhibited. These findings suggest that the proportions of muscle sympathetic single units inhibited during stress are associated with the level of sympathoexcitation and not the stressor per se in healthy young males.NEW & NOTEWORTHY Subpopulations of muscle sympathetic single units can be inhibited during mild sympathoexcitatory stress. We demonstrate that rhythmic handgrip exercise and isocapnic hypoxia, when matched by multiunit sympathoexcitation, induce similar proportions of single-unit inhibition, highlighting that heterogeneous single-unit response patterns are related to the level of sympathoexcitation independent of the stressor type. Interestingly, only 47% of single units behaved with concordant response patterns between stressors, suggesting the potential for functional specificity within the postganglionic neuronal pool.

Increased muscle sympathetic nerve activity and impaired baroreflex control in isolated REM-sleep behavior disorder.

OBJECTIVE: Changes in baroreflex sensitivity have been reported in patients with idiopathic Parkinson's disease (PD). We sought to investigate the hypothesis that patients with isolated rapid eye movement (REM)-sleep behavior disorder (iRBD), known to be a prodromal stage for PD, will show abnormalities in baroreflex control. METHODS: Ten iRBD patients were compared to 10 sex- and age-matched healthy controls. Their cardiovascular parameters and muscle sympathetic nerve activity (MSNA) were evaluated at rest and during baroreflex stimulation. RESULTS: MSNA at rest was higher in iRBD patients (burst frequency [BF]: 44 ± 3 bursts/min; burst incidence [BI]: 60 ± 8 bursts/100 heartbeats) as compared to the controls (BF: 29 ± 3 bursts/min, p < 0.001; BI: 43 ± 9 bursts/100 heartbeats, p < 0.001). During baroreflex stimulation, iRBD patients showed increased absolute values of MSNA (BF: F = 62.728; p < 0.001; BI: F = 16.277; p < 0.001) as compared to the controls. The iRBD patients had decreased diastolic blood pressure at baseline and during lower body negative pressure, but the level of significance was not met. CONCLUSION: Our study shows increased MSNA and impaired baroreflex control in iRBD patients. We propose that the inhibitory effect of locus coeruleus on baroreflex function might be impaired, leading to the disinhibition of sympathetic outflow. SIGNIFICANCE: These findings might reflect the destruction of brain areas due to the ascending P-α-synuclein deposits in iRBD patients.

Sympathetic nerve outflow to skin in a case with dentatorubral-pallidoluysian atrophy.

Dentatorubral-pallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder characterized by slowly progressive cerebellar ataxia. Previously, autonomic symptoms or dysfunction have not been reported. To evaluate subclinical autonomic dysfunction regarding thermoregulatory function in SCA, we recorded sympathetic outflow to skin in a DRPLA patient confirmed by genetic analysis. We recorded skin sympathetic nerve activity (SSNA), which was elicited and recorded by using the microneurographical technique. In results, the resting frequency of SSNA bursts was very low (8.2 ± 0.4 bursts/min [institutional normal range: 20.8 ± 2.4 bursts/min]). However, acceleration of SSNA bursts induced by mental arithmetic stress was confirmed. The amplitude of reflex bursts induced by electrical stimuli was slightly low (9.6 ± 1.6 µV [institutional normal range: 10.9 ± 2.2 µV]), and the reflex latency was mildly prolonged (872 ± 23.7 msec [institutional normal range: 761.9 ± 51.7 msec]). These results suggest potentially central autonomic dysfunction in this patient with DRPLA. To our knowledge, this is the first report to record SSNA and confirm subclinical autonomic dysfunction in a case with DRPLA.

Evaluation of sympathetic adrenergic branch of cutaneous neural control throughout thermography and its relationship to nitric oxide levels in patients with fibromyalgia.

BACKGROUND: Fibromyalgia syndrome is defined as a complex disease, characterized by chronic widespread musculoskeletal pain and other symptoms. The factors underlying physiopathology of fibromyalgia are not well understood, complicating its diagnosis and management. OBJECTIVES: To evaluate the peripheral vascular blood flow of the skin of the hands and the core body temperature as indirect measures of sympathetic adrenergic activity of the nervous system and its relationship to nitric oxide levels (NO) in women with fibromyalgia compared with healthy controls. METHODS: Forty-two women with fibromyalgia and 52 healthy women were enrolled in this observational pilot study. We used infrared thermography of the hands and an infrared dermal thermometer to evaluate the peripheral vascular blood flow and tympanic and axillary core body temperature, respectively. We measured NO levels using the ozone chemiluminescence-based method. RESULTS: Two-way analysis of covariance (ANCOVA) showed that the tympanic (P=0.002) and hand temperatures were significantly higher in the patients with fibromyalgia than in the controls (P≤0.001). Significant associations were also found between serum NO levels and minimum temperatures at the dorsal center of the dominant hand (ß=-3.501; 95% confidence interval [CI] -6.805, ­0.198; P= 0.038), maximum temperature (ß=-5.594; 95% CI ­10.106, ­1.081; P=0.016), minimum temperature (ß=-4.090; 95% CI ­7.905, ­0.275; P=0.036), and mean temperature (ß=-5.519; 95% CI ­9.933, ­1.106; P=0.015) of the center of the palm of the non-dominant hand, maximum temperature at the thenar eminence of the dominant hand (ß=-5.800; 95% CI ­10.508, ­1.092; P=0.017), and tympanic temperature (ß=-9.321; 95% CI ­17.974, ­0.669; P=0.035) in the controls. CONCLUSIONS: Our findings indicate that the women with fibromyalgia showed higher tympanic core body and hand temperature than the healthy controls. Moreover, there were negative associations between hand peripheral vasodilation and NO in the healthy women but not in those with fibromyalgia, suggesting a dysfunction of sympathetic cutaneous neural control.

Splenic sympathetic signaling contributes to acute neutrophil infiltration of the injured spinal cord.

BACKGROUND: Alterations in the immune system are a complication of spinal cord injury (SCI) and have been linked to an excessive sympathetic outflow to lymphoid organs. Still unknown is whether these peripheral immune changes also contribute for the deleterious inflammatory response mounted at the injured spinal cord. METHODS: We analyzed different molecular outputs of the splenic sympathetic signaling for the first 24 h after a thoracic compression SCI. We also analyzed the effect of ablating the splenic sympathetic signaling to the innate immune and inflammatory response at the spleen and spinal cord 24 h after injury. RESULTS: We found that norepinephrine (NE) levels were already raised at this time-point. Low doses of NE stimulation of splenocytes in vitro mainly affected the neutrophils' population promoting an increase in both frequency and numbers. Interestingly, the interruption of the sympathetic communication to the spleen, by ablating the splenic nerve, resulted in reduced frequencies and numbers of neutrophils both at the spleen and spinal cord 1 day post-injury. CONCLUSION: Collectively, our data demonstrates that the splenic sympathetic signaling is involved in the infiltration of neutrophils after spinal cord injury. Our findings give new mechanistic insights into the dysfunctional regulation of the inflammatory response mounted at the injured spinal cord.

Noradrenergic projections from the locus coeruleus to the amygdala constrain fear memory reconsolidation.

Memory reconsolidation is a fundamental plasticity process in the brain that allows established memories to be changed or erased. However, certain boundary conditions limit the parameters under which memories can be made plastic. Strong memories do not destabilize, for instance, although why they are resilient is mostly unknown. Here, we investigated the hypothesis that specific modulatory signals shape memory formation into a state that is reconsolidation-resistant. We find that the activation of the noradrenaline-locus coeruleus system (NOR-LC) during strong fear memory encoding increases molecular mechanisms of stability at the expense of lability in the amygdala of rats. Preventing the NOR-LC from modulating strong fear encoding results in the formation of memories that can undergo reconsolidation within the amygdala and thus are vulnerable to post-reactivation interference. Thus, the memory strength boundary condition on reconsolidation is set at the time of encoding by the action of the NOR-LC.

New memories must go through a period of consolidation to become stable and long-lasting in the brain. Recalling memories can make them unstable again, so that they need reconsolidating. Treatments in which the reconsolidation process is interrupted have been used to help weaken traumatic fear memories. However, memories of severe trauma, such as in post-traumatic stress disorder, are particularly resistant to reconsolidation treatments. Haubrich et al. used rats to study how trauma shapes memory formation and what biological mechanisms are involved in preventing the destabilization/reconsolidation cycle. The rats were exposed to a sound at the same time as receiving a mild electric shock. Half of the rats experienced the shock once, creating a 'weak' memory. The other half experienced it ten times, creating a 'strong' memory. The rats' memory of the electric shock was measured by seeing how they responded when they heard the sound again without the shock. Some of the rats were given the drug anisomycin, an antibiotic that stops cells from making new proteins and is known for producing amnesia, to block reconsolidation of the memory after hearing the sound again. Treatment with the drug reduced future responses in the rats that had experienced the shock once, but had no effect on the rats that had experienced it ten times, demonstrating that the stronger memories were resistant to reconsolidation therapy. The rats with the strong memories also had lower levels of proteins in the brain that are involved in plasticity ­ the ability of the brain to change and adapt. Haubrich et al. hypothesized that the stability of the strong memories could be caused by signaling from the locus coeruleus, a region of the brainstem involved in the response to stress. When the signaling from the locus coeruleus was blocked in the strong-memory rats, they became responsive to reconsolidation therapy with anisomycin. These results help to better understand how traumatic memories become engrained, potentially leading to new treatment options for people with post-traumatic stress disorder.

Adrenergic and Cholinergic Uterine Innervation and the Impact on Reproduction in Aged Women.

In recent years, the development of Assisted Reproductive Technique, the egg and embryo donation changed substantially the role of the uterus in recent years. It provided a higher chance for a pregnancy even in women over 45 years or post-menopause. In fact, the number of aged patients and in peri/post-menopause in pregnancy is nowadays increasing, but it increases obstetrical and neonatal related problems. The human uterus is richly innervated and modified especially during pregnancy and labor, and it is endowed with different sensory, parasympathetic, sympathetic and peptidergic neurofibers. They are differently distributed in uterine fundus, body and cervix, and they are mainly observed in the stroma and around arterial vessel walls in the myometrial and endometrial layers. Many neurotransmitters playing important roles in reproductive physiology are released after stimulation by adrenergic or cholinergic nerve fibers (the so called sympathetic/parasympathetic co-transmission). Immunohistochemical study demonstrated the localization and quantitative distribution of neurofibers in the fundus, the body and cervix of young women of childbearing age. Adrenergic and cholinergic effects of the autonomous nervous system are the most implicated in the uterine functionality. In such aged women, the Adrenergic and AChE neurofibers distribution in the fundus, body and cervix is progressively reduced by increasing age. Adrenergic and AChE neurotransmitters were closely associated with the uterine arteries and myometrial smooth muscles, and they reduced markedly by ageing. The Adrenergic and AChE neurofibers decreasing has a dramatical and negative impact on uterine physiology, as the reduction of pregnancy chance and uterine growth, and the increase of abortion risk and prematurity.

Myocardial blood flow and cardiac sympathetic innervation in young adults late after arterial switch operation for transposition of the great arteries.

BACKGROUND: The arterial switch operation (ASO) for repair of transposition of the great arteries (TGA) requires transection of the great arterial trunks and re-implantation of the coronary arteries into the neoaortic root resulting in cardiac sympathetic denervation which may affect myocardial blood flow (MBF) regulation. The aims of the present study were to evaluate sympathetic (re-)innervation in young adults after ASO and its impact on MBF. METHODS: Twelve patients (age 22.5 ±â€¯2.6 years) after ASO for TGA in the neonatal period and ten healthy controls (age 22.0 ±â€¯1.7 years) were included. Positron emission tomography (PET) was used for measuring cardiac sympathetic innervation with [11C]meta-hydroxyephedrine (mHED) and MBF with [15O]H2O PET at rest, during adenosine stimulation, and during sympathetic stimulation with cold pressor test. Cold pressor-induced MBF response capacity was calculated as maximal global MBF over peak rate-pressure product multiplied by 10'000. RESULTS: Global [11C]mHED uptake was significantly lower in patients compared to controls (7.0 ±â€¯2.3 versus 11.8 ±â€¯2.1%/min, p < 0.001). Global MBF was lower in patients compared to controls at rest and during adenosine-induced hyperemia (0.66 ±â€¯0.08 versus 0.82 ±â€¯0.15 ml/min/g, p = 0.005; 2.23 ±â€¯1.19 versus 3.36 ±â€¯1.04 ml/min/g, p = 0.030, respectively). Interestingly, MBF during cold pressor test did not differ between patients and controls (0.99 ±â€¯0.20 versus 1.07 ±â€¯0.16 ml/min/g, p = 0.330). However, cold pressor-induced MBF response capacity was significantly lower for patients as compared to controls (1.09 ±â€¯0.35 versus 1.44 ±â€¯0.39 ml/g/10,000 mmHg, p = 0.040). CONCLUSIONS: With only partial sympathetic re-innervation of the coronary arteries, maximal dilator capacity of the coronary microvasculature and cold pressor-induced MBF response capacity remain substantially impaired in young adults after ASO compared to healthy controls.

Blockade of 5-HT2 receptors with sarpogrelate uncovers 5-HT7 receptors inhibiting the tachycardic sympathetic drive in pithed rats.

Our group has previously shown in pithed rats that the cardiac sympathetic drive, which produces tachycardic responses, is inhibited by 5-HT via the activation of prejunctional 5-HT1B/1D/5 receptors. Interestingly, when 5-HT2 receptors are chronically blocked with sarpogrelate, the additional role of cardiac sympatho-inhibitory 5-HT1F receptors is unmasked. Although 5-HT2 receptors mediate tachycardia in rats, and the chronic blockade of 5-HT2 receptors unmasked 5-HT7 receptors mediating cardiac vagal inhibition, the role of 5-HT7 receptors in the modulation of the cardiac sympathetic tone remains virtually unexplored. On this basis, male Wistar rats were pretreated during 14 days with sarpogrelate (a 5-HT2 receptor antagonist) in drinking water (30 mg/kg/day; sarpogrelate-pretreated group) or equivalent volumes of drinking water (control group). Subsequently, the rats were pithed to produce increases in heart rate by either electrical preganglionic spinal (C7 -T1 ) stimulation of the cardiac sympathetic drive or iv administration of exogenous noradrenaline. The iv continuous infusion of AS-19 (a 5-HT7 receptor agonist; 10 µg/kg/min) (i) inhibited the tachycardic responses to sympathetic stimulation, but not those to exogenous noradrenaline only in sarpogrelate-pretreated rats. This inhibition was completely reversed by SB258719 (a selective 5-HT7 receptor antagonist; 1 mg/kg, iv) or glibenclamide (an ATP-sensitive K+ channel blocker; 20 mg/kg, iv). These results suggest that chronic 5-HT2 receptor blockade uncovers a cardiac sympatho-inhibitory mechanism mediated by 5-HT7 receptors, involving a hyperpolarization due to the opening of ATP-sensitive K+ channels. Thus, these findings support the role of 5-HT7 receptors in the modulation of the cardiac sympathetic neurotransmission.

Adrenergic Innervation of the thyroid Gland, Blood and Lymph Vessels, and Lymph Nodes in Hypothyroidism.

Adrenergic innervation in the tissue of the thyroid gland, blood vessels of the thyroid gland, cervical lymphatic vessel, and lymph nodes in rats with hypothyroidism was studied by using a specific histochemical fluorescent-microscopic method of visualization of catecholamines. The presence of adrenergic innervation in the blood and lymph vessels and nodes was demonstrated. In hypothyroidism, diffusion of norepinephrine from nerve fibers and varicose thickenings was observed in the wall of the upper and lower thyroid arteries and adjacent cervical lymphatic vessels and nodes.

Anatomic Conformation of Renal Sympathetic Nerve Fibers in Living Human Tissues.

Renal denervation using radiofrequency catheter ablation is known to eliminate the renal sympathetic nerve and to lower blood pressure in patients with resistant hypertension. We sought to investigate the detailed anatomic conformation of the peri-renal arterial sympathetic nerve fibers with living human specimens. Peri-renal arterial tissue was harvested from patients undergoing elective radical or simple nephrectomy. Digital images of each section from the distal arterial bifurcation to the proximal margin were obtained and analyzed after immunohistochemical staining with anti-tyrosine hydroxylase antibodies. A total of 3,075 nerve fibers were identified from 84 sections of peri-renal arterial tissue from 28 patients (mean age 62.5 ± 10.2 years, male 68%). Overall, 16% of nerve fibers were located at distances greater than 3 mm from the endoluminal surface of the renal artery. The median distance from the arterial lumen to the nerve fibers of the proximal, middle, and distal renal arterial segments was 1.51 mm, 1.48 mm, and 1.52 mm, respectively. The median diameter of the nerve fibers was 65 µm, and there was no significant difference between the segments. A substantial proportion of the sympathetic nerve fibers were located deeper in the peri-arterial soft tissue than in the lesion depth created by the conventional catheter-based renal sympathetic denervation system.

On the interrelation of 1/f neural noise and norepinephrine system activity during motor response inhibition.

Several lines of evidence suggest that there is a close interrelation between the degree of noise in neural circuits and the activity of the norepinephrine (NE) system, yet the precise nexus between these aspects is far from being understood during human information processing and cognitive control in particular. We examine this nexus during response inhibition in n = 47 healthy participants. Using high-density EEG recordings, we estimate neural noise by calculating "1/f noise" of those data and integrate these EEG parameters with pupil diameter data as an established indirect index of NE system activity. We show that neural noise is reduced when cognitive control processes to inhibit a prepotent/automated response are exerted. These neural noise variations were confined to the theta frequency band, which has also been shown to play a central role during response inhibition and cognitive control. There were strong positive correlations between the 1/f neural noise parameter and the pupil diameter data within the first 250 ms after the Nogo stimulus presentation at centro-parietal electrode sites. No such correlations were evident during automated responding on Go trials. Source localization analyses using standardized low-resolution brain electromagnetic tomography show that inferior parietal areas are activated in this time period in Nogo trials. The data suggest an interrelation of NE system activity and neural noise within early stages of information processing associated with inferior parietal areas when cognitive control processes are required. The data provide the first direct evidence for the nexus between NE system activity and the modulation of neural noise during inhibitory control in humans. NEW & NOTEWORTHY This is the first study showing that there is a nexus between norepinephrine system activity and the modulation of neural noise or scale-free neural activity during inhibitory control in humans. It does so by integrating pupil diameter data with analysis of EEG neural noise.

Pro-contractile role of chloride in arterial smooth muscle: Postnatal decline potentially governed by sympathetic nerves.

NEW FINDINGS: What is the topic of this review? This symposium report discusses the previously unrecognized pro-contractile role of chloride ions in rat arteries at early stages of postnatal development. What advances does it highlight? It highlights the postnatal decline in the contribution of chloride ions to regulation of arterial contractile responses and potential trophic role of sympathetic nerves in these developmental alterations. ABSTRACT: Chloride ions are important for smooth muscle contraction in adult vasculature. Arterial smooth muscle undergoes structural and functional remodelling during early postnatal development, including changes in K+ currents, Ca2+ handling and sensitivity. However, developmental change in the contribution of Cl- to regulation of arterial contraction has not yet been explored. Here, we provide the first evidence that the role of Cl- in α1 -adrenergic arterial contraction prominently decreases during early postnatal ontogenesis. The trophic influence of sympathetic nerves is a potential mechanism for postnatal decline of the contribution of Cl- to the vascular contraction.

Cutaneous adrenergic nerve blockade attenuates sweating during incremental exercise in habitually trained men.

It remains unknown whether cutaneous adrenergic nerves functionally contribute to sweat production during exercise. This study examined whether cutaneous adrenergic nerve blockade attenuates sweating during incremental exercise, specifically in habitually trained individuals. Accordingly, 10 habitually trained and 10 untrained males (V̇o2max: 56.7 ± 5.4 and 38.9 ± 6.7 ml·kg-1·min-1, respectively; P < 0.001) performed incremental semirecumbent cycling (20 W/min) until exhaustion. Sweat rates (ventilated capsule) were measured at two bilateral forearm skin sites on which either 10 mM bretylium tosylate (BT) (an inhibitor of neurotransmitter release from sympathetic adrenergic nerve terminals) or saline (Control) was transdermally administered via iontophoresis. BT treatment delayed sweating onset in both groups (∼0.66 min; P = 0.001) and suppressed the sweat rate relative to the Control treatment at ≥70% relative total exercise time in trained individuals (each 10% increment; all P ≤ 0.009) but not in untrained counterparts ( P = 0.122, interaction between relative time × treatment). Changes in total sweat production at the BT site relative to the Control site were greater in trained individuals than in untrained counterparts (area under the curve, -0.86 ± 0.67 and -0.22 ± 0.39 mg/cm2, respectively; P = 0.023). In conclusion, we demonstrated that cutaneous adrenergic nerves do modulate sweating during incremental exercise, which appeared to be more apparent in habitually trained men (e.g., ≥70% maximum workload). Although our results indicated that habitual exercise training may augment neural adrenergic sweat production during incremental exercise, additional studies are required to confirm this possibility. NEW & NOTEWORTHY We demonstrated for the first time that cutaneous adrenergic nerves do modulate sweating during high-intensity exercise in humans (≥70% maximum workload). In addition, neural adrenergic sweating appeared to be greater in habitually trained individuals than in untrained counterparts, although further studies are necessary to confirm such a possibility. Nonetheless, the observations presented herein advance our understanding on human thermoregulation while providing new evidence for the neutral mediation of adrenergic sweating during exercise.

The Changing Sensory and Sympathetic Innervation of the Young, Adult and Aging Mouse Femur.

Although bone is continually being remodeled and ultimately declines with aging, little is known whether similar changes occur in the sensory and sympathetic nerve fibers that innervate bone. Here, immunohistochemistry and confocal microscopy were used to examine changes in the sensory and sympathetic nerve fibers that innervate the young (10 days post-partum), adult (3 months) and aging (24 months) C57Bl/6 mouse femur. In all three ages examined, the periosteum was the most densely innervated bone compartment. With aging, the total number of sensory and sympathetic nerve fibers clearly declines as the cambium layer of the periosteum dramatically thins. Yet even in the aging femur, there remains a dense sensory and sympathetic innervation of the periosteum. In cortical bone, sensory and sympathetic nerve fibers are largely confined to vascularized Haversian canals and while there is no significant decline in the density of sensory fibers, there was a 75% reduction in sympathetic nerve fibers in the aging vs. adult cortical bone. In contrast, in the bone marrow the overall density/unit area of both sensory and sympathetic nerve fibers appeared to remain largely unchanged across the lifespan. The preferential preservation of sensory nerve fibers suggests that even as bone itself undergoes a marked decline with age, the nociceptors that detect injury and signal skeletal pain remain relatively intact.

Chronic lead exposure enhances the sympathoexcitatory response associated with P2X4 receptor in rat stellate ganglia.

Chronic lead exposure causes peripheral sympathetic nerve stimulation, including increased blood pressure and heart rate. Purinergic receptors are involved in the sympathoexcitatory response induced by myocardial ischemia injury. However, whether P2X4 receptor participates in sympathoexcitatory response induced by chronic lead exposure and the possible mechanisms are still unknown. The aim of this study was to explore the change of the sympathoexcitatory response induced by chronic lead exposure via the P2X4 receptor in the stellate ganglion (SG). Rats were given lead acetate through drinking water freely at doses of 0 g/L (control group), 0.5 g/L (low lead group), and 2 g/L (high lead group) for 1 year. Our results demonstrated that lead exposure caused autonomic nervous dysfunction, including blood pressure and heart rate increased and heart rate variability (HRV) decreased. Western blotting results indicated that after lead exposure, the protein expression levels in the SG of P2X4 receptor, IL-1ß and Cx43 were up-regulated, the phosphorylation of p38 mitogen-activated protein kinase (MAPK) was activated. Real-time PCR results showed that the mRNA expression of P2X4 receptor in the SG was higher in lead exposure group than that in the control group. Double-labeled immunofluorescence results showed that P2X4 receptor was co-expressed with glutamine synthetase (GS), the marker of satellite glial cells (SGCs). These changes were positively correlated with the dose of lead exposure. The up-regulated expression of P2X4 receptor in SGCs of the SG maybe enhance the sympathoexcitatory response induced by chronic lead exposure.

Carotid chemoreceptor control of muscle sympathetic nerve activity in hypobaric hypoxia.

NEW FINDINGS: What is the central question of this study? High-altitude hypoxia increases muscle sympathetic nerve activity (MSNA), but whether intravenous infusion of dopamine, to blunt the responsiveness of the carotid chemoreceptors, reduces MSNA at high altitude is not known. What is the main finding and its importance? Muscle sympathetic nerve activity was elevated after 15-17 days of high-altitude hypoxia (3454 m) compared with values at 'sea level' (432 m). However, intravenous dopamine infusion to blunt the responsiveness of the carotid chemoreceptors did not significantly decrease MSNA either at sea level or at high altitude, suggesting that high-altitude sympathoexcitation arises via a different mechanism. High-altitude hypoxia causes pronounced sympathoexcitation, but the underlying mechanisms remain unclear. We tested the hypothesis that i.v. infusion of dopamine to attenuate carotid chemoreceptor responsiveness would reduce muscle sympathetic nerve activity (MSNA) at high altitude. Nine healthy individuals [mean (SD); 26 (4) years of age] were studied at 'sea level' (SL; Zurich) and at high altitude (ALT; 3454 m; 15-17 days after arrival), both while breathing the ambient air and during an acute incremental hypoxia test (eight 3 min stages; partial pressure of end-tidal O2 90-45 mmHg). Intravenous infusions of dopamine (3 µg kg-1  min-1 ) and placebo (saline) were administered on both study days, according to a single-blind randomized cross-over design. Sojourn to high altitude decreased the partial pressure of end-tidal O2 (to ∼60 mmHg) and increased minute ventilation [V̇E; mean ± SEM, SL versus ALT: saline, 8.6 ± 0.5 versus 11.3 ± 0.6 l min-1 ; dopamine, 8.2 ± 0.5 versus 10.6 ± 0.8 l min-1 ; P < 0.05] and MSNA burst frequency by ∼80% [SL versus ALT: saline, 16 ± 3 versus 28 ± 4 bursts min-1 ; dopamine, 16 ± 4 versus 31 ± 4 bursts min-1 ; P < 0.05) when breathing the ambient air, but were not different with dopamine. Increases in MSNA burst frequency and V̇E during the acute incremental hypoxia test were greater at ALT than SL (P < 0.05). Dopamine did not affect the magnitude of the MSNA burst frequency response to acute incremental hypoxia at either SL or ALT. However, V̇E was lower with dopamine than saline administration throughout the acute incremental hypoxia test at ALT. These data indicate that i.v. infusion of low-dose dopamine to blunt the responsiveness of the carotid chemoreceptors does not significantly decrease MSNA at high altitude.

CaMKII Regulates Synaptic NMDA Receptor Activity of Hypothalamic Presympathetic Neurons and Sympathetic Outflow in Hypertension.

NMDAR activity in the hypothalamic paraventricular nucleus (PVN) is increased and critically involved in heightened sympathetic vasomotor tone in hypertension. Calcium/calmodulin-dependent protein kinase II (CaMKII) binds to and modulates NMDAR activity. In this study, we determined the role of CaMKII in regulating NMDAR activity of PVN presympathetic neurons in male spontaneously hypertensive rats (SHRs). NMDAR-mediated EPSCs and puff NMDA-elicited currents were recorded in spinally projecting PVN neurons in SHRs and male Wistar-Kyoto (WKY) rats. The basal amplitude of evoked NMDAR-EPSCs and puff NMDA currents in retrogradely labeled PVN neurons were significantly higher in SHRs than in WKY rats. The CaMKII inhibitor autocamtide-2-related inhibitory peptide (AIP) normalized the increased amplitude of NMDAR-EPSCs and puff NMDA currents in labeled PVN neurons in SHRs but had no effect in WKY rats. Treatment with AIP also normalized the higher frequency of NMDAR-mediated miniature EPSCs of PVN neurons in SHRs. CaMKII-mediated phosphorylation level of GluN2B serine 1303 (S1303) in the PVN, but not in the hippocampus and frontal cortex, was significantly higher in SHRs than in WKY rats. Lowering blood pressure with celiac ganglionectomy in SHRs did not alter the increased level of phosphorylated GluN2B S1303 in the PVN. In addition, microinjection of AIP into the PVN significantly reduced arterial blood pressure and lumbar sympathetic nerve discharges in SHRs. Our findings suggest that CaMKII activity is increased in the PVN and contributes to potentiated presynaptic and postsynaptic NMDAR activity to elevate sympathetic vasomotor tone in hypertension.SIGNIFICANCE STATEMENT Heightened sympathetic vasomotor tone is a major contributor to the development of hypertension. Although glutamate NMDA receptor (NMDAR)-mediated excitatory drive in the hypothalamus plays a critical role in increased sympathetic output in hypertension, the molecular mechanism involved in potentiated NMDAR activity of hypothalamic presympathetic neurons remains unclear. Here we show that the activity of calcium/calmodulin-dependent protein kinase II (CaMKII) is increased and plays a key role in the potentiated presynaptic and postsynaptic NMDAR activity of hypothalamic presympathetic neurons in hypertension. Also, the inhibition of CaMKII in the hypothalamus reduces elevated blood pressure and sympathetic nerve discharges in hypertension. This new knowledge extends our understanding of the mechanism of synaptic plasticity in the hypothalamus and suggests new strategies to treat neurogenic hypertension.

Carotid artery reactivity during sympathetic activation following acute resistance exercise.

OBJECTIVE: Acute resistance exercise has been shown to reduce brachial endothelial function. Whether there are concomitant reductions in carotid endothelial function remains unexplored. METHODS: Cold pressor test-mediated vasodilation of the carotid artery was used to assess carotid endothelial function in 15 young and healthy participants (age 26 ± 1 years, body mass index 24 ± 1 kg/m2) after acute resistance exercise or an inactive time control condition. RESULTS: Acute resistance exercise had no effect on the cold pressor test-mediated vasodilation compared to time control (5.8 ± 0.8 vs 6.2 ± 0.9% dilation, p > 0.05). INTERPRETATION: Carotid endothelial function may not be compromised following acute resistance exercise in young healthy adults.