Sympathetic nerve activity is decreased during device-guided slow breathing

It is known that slow breathing (<10 breaths min(-1)) reduces blood pressure ( BP), but the mechanisms involved in this phenomenon are not completely clear. The aim of this study was to evaluate the acute responses of the muscle sympathetic nerve activity, BP and heart rate (HR), using device-guided slow breathing ( breathe with interactive music (BIM)) or calm music. In all, 27 treated mild hypertensives were enrolled. Muscle sympathetic nerve activity, BP and HR were measured for 5min before the use of the device (n=14) or while subjects listened to calm music (n=13), it was measured again for 15 min while in use and finally, 5min after the interventions. BIM device reduced respiratory rate from 16 +/- 3 beats per minute (b.p.m) to 5.5 +/- 1.8 b.p.m (P<0.05), calm music did not affect this variable. Both interventions reduced systolic (-6 and -4mmHg for both) and diastolic BPs (-4mmHg and -3mmHg, respectively) and did not affect the HR (-1 and -2 b.p.m respectively). Only the BIM device reduced the sympathetic nerve activity of the sample (-8bursts min(-1)). In conclusion, both device-guided slow breathing and listening to calm music have decreased BP but only the device-guided slow breathing was able to reduce the peripheral sympathetic nerve activity. Hypertension Research ( 2010) 33, 708-712; doi: 10.1038/hr.2010.74; published online 3 June 2010

Tyrosine hydroxylase immunoreactivity as indicator of sympathetic activity: simultaneous evaluation in different tissues of hypertensive rats

Burgi K, Cavalleri MT, Alves AS, Britto LRG, Antunes VR, Michelini LC. Tyrosine hydroxylase immunoreactivity as indicator of sympathetic activity: simultaneous evaluation in different tissues of hypertensive rats. Am J Physiol Regul Integr Comp Physiol 300: R264-R271, 2011. First published December 9, 2010; doi: 10.1152/ajpregu.00687.2009.-Vasomotor control by the sympathetic nervous system presents substantial heterogeneity within different tissues, providing appropriate homeostatic responses to maintain basal/stimulated cardiovascular function both at normal and pathological conditions. The availability of a reproducible technique for simultaneous measurement of sympathetic drive to different tissues is of great interest to uncover regional patterns of sympathetic nerve activity (SNA). We propose the association of tyrosine hydroxylase immunoreactivity (THir) with image analysis to quantify norepinephrine (NE) content within nerve terminals in arteries/arterioles as a good index for regional sympathetic outflow. THir was measured in fixed arterioles of kidney, heart, and skeletal muscle of WistarKyoto rats (WKY) and spontaneously hypertensive rats (SHR) (123 +/- 2 and 181 +/- 4 mmHg, 300 +/- 8 and 352 +/- 8 beats/min, respectively). There was a differential THir distribution in both groups: higher THir was observed in the kidney and skeletal muscle (similar to 3-4-fold vs. heart arterioles) of WKY; in SHR, THir was increased in the kidney and heart (2.4- and 5.3-fold vs. WKY, respectively) with no change in the skeletal muscle arterioles. Observed THir changes were confirmed by either: 1) determination of NE content (high-performance liquid chromatography) in fresh tissues (SHR vs. WKY): +34% and +17% in kidney and heart, respectively, with no change in the skeletal muscle; 2) direct recording of renal (RSNA) and lumbar SNA (LSNA) in anesthetized rats, showing increased RSNA but unchanged LSNA in SHR vs. WKY. THir in skeletal muscle arterioles, NE content in femoral artery, and LSNA were simultaneously reduced by exercise training in the WKY group. Results indicate that THir is a valuable technique to simultaneously evaluate regional patterns of sympathetic activity.

Switching control of sympathetic activity from forebrain to hindbrain in chronic dehydration

We investigated the mechanisms responsible for increased blood pressure and sympathetic nerve activity (SNA) caused by 2-3 days dehydration (DH) both in vivo and in situ preparations. In euhydrated (EH) rats, systemic application of the AT(1) receptor antagonist Losartan and subsequent pre-collicular transection (to remove the hypothalamus) significantly reduced thoracic (t) SNA. In contrast, in DH rats, Losartan, followed by pre-collicular and pontine transections, failed to reduce tSNA, whereas transection at the medulla-spinal cord junction massively reduced tSNA. In DH but not EH rats, selective inhibition of the commissural nucleus tractus solitarii (cNTS) significantly reduced tSNA. Comparable data were obtained in both in situ and in vivo (anaesthetized/conscious) rats and suggest that following chronic dehydration, the control of tSNA transfers from supra-brainstem structures (e. g. hypothalamus) to the medulla oblongata, particularly the cNTS. As microarray analysis revealed up-regulation of AP1 transcription factor JunD in the dehydrated cNTS, we tested the hypothesis that AP1 transcription factor activity is responsible for dehydration-induced functional plasticity. When AP1 activity was blocked in the cNTS using a viral vector expressing a dominant negative FosB, cNTS inactivation was ineffective. However, tSNA was decreased after pre-collicular transection, a response similar to that seen in EHrats. Thus, the dehydration-induced switch in control of tSNA from hypothalamus to cNTS seems to be mediated via activation of AP1 transcription factors in the cNTS. If AP1 activity is blocked in the cNTS during dehydration, sympathetic activity control reverts back to forebrain regions. This unique reciprocating neural structure-switching plasticity between brain centres emphasizes the multiple mechanisms available for the adaptive response to dehydration.

The variability of baroreflex sensitivity in juvenile, spontaneously hypertensive rats

In this study the baroreflex sensitivity of conscious, juvenile, spontaneously hypertensive rats (SHRs) was compared. The study population consisted of 19 eight-week-old male SHRs. The baroreflex sensitivity was quantified as the derivative of the variation in heart rate (HR) and the variation of mean arterial pressure (baroreflex sensitivity = Delta HR/Delta MAP). MAP was manipulated with sodium nitroprusside (SNP) and phenylephrine (PHE), administered via an inserted cannula in the right femoral vein. The SHRs were divided into four groups: (1) low bradycardic baroreflex (LB) where the baroreflex gain (BG) was between 0 and 1 bpm/mmHg with PHE; (2) high bradycardic baroreflex (HB), where the BG was < -1 bpm/mmHg with PHE; (3) low tachycardic baroreflex (LT) where the BC was between 0 and 3 bpm/mmHg with SNP; (4) high tachycardic baroreflex (HT) where the BG was > 3 bpm/mmHg with SNP. We noted that 36.8% of the rats presented with an increased bradycardic reflex, while 27.8% demonstrated an attenuated tachycardic reflex. No significant alterations were noted regarding the basal MAP and HR. There were significant differences in the baroreflex sensitivity between SHRs in the same laboratory. One should be careful when interpreting studies employing the SHR as a research model.

Exercise improves cardiovascular control in a model of dislipidemia and menopause

The present study investigated the effects of exercise training on arterial pressure, baroreflex sensitivity, cardiovascular autonomic control and metabolic parameters on female LDL-receptor knockout ovariectomized mice. Mice were divided into two groups: sedentary and trained. Trained group was submitted to an exercise training protocol. Blood cholesterol was measured. Arterial pressure (AP) signals were directly recorded in conscious mice. Baroreflex sensitivity was evaluated by tachycardic and bradycardic responses to AP changes. Cardiovascular autonomic modulation was measured in frequency (FFT) and time domains. Maximal exercise capacity was increased in trained as compared to sedentary group. Blood cholesterol was diminished in trained mice (191 +/- 8 mg/dL) when compared to sedentary mice (250 +/- 9 mg/dL, p<0.05). Mean AP and HR were reduced in trained group (101 +/- 3 mmHg and 535 +/- 14 bpm, p<0.05) when compared with sedentary group (125 +/- 3 mmHg and 600 +/- 12 bpm). Exercise training induced improvement in bradycardic reflex response in trained animals (-4.24 +/- 0.62 bpm/mmHg) in relation to sedentary animals (-1.49 +/- 0.15 bpm/mmHg, p<0.01); tachycardic reflex responses were similar between studied groups. Exercise training increased the variance (34 +/- 8 vs. 6.6 +/- 1.5 ms(2) in sedentary, p<0.005) and the high-frequency band (HF) of the pulse interval (IP) (53 +/- 7% vs. 26 +/- 6% in sedentary, p<0.01). It is tempting to speculate that results of this experimental study might represent a rationale for this non-pharmacological intervention in the management of cardiovascular risk factors in dyslipidemic post-menopause women. (C) 2009 Elsevier Ireland Ltd. All rights reserved.

Autonomic impairment after myocardial infarction: Role in cardiac remodelling and mortality

P>1. Impairmant of baroreflex sensitivity (BRS) has been implicated in the reduction of heart rate variability (HRV) and in the increased risk of death after myocardial infarction (MI). In the present study, we investigated whether the additional impairment in BRS induced by sinoaortic baroreceptor denervation (SAD) in MI rats is associated with changes in the low-frequency (LF) component of HRV and increased mortality rate. 2. Rats were randomly divided into four groups: control, MI, denervated (SAD) and SAD + MI rats. Left ventricular (LV) function was evaluated by echocardiography. Autonomic components were assessed by power spectral analysis and BRS. 3. Myocardial infarction (90 days) reduced ejection fraction (by similar to 42%) in both the MI and SAD + MI groups; however, an increase in LV mass and diastolic dysfunction were observed only in the SAD + MI group. Furthermore, BRS, HRV and the LF power of HRV were reduced after MI, with an exacerbated reduction seen in SAD + MI rats. The LF component of blood pressure variability (BPV) was increased in the MI, SAD and SAD + MI groups compared with the control group. Mortality was higher in the MI groups compared with the non-infarcted groups, with an additional increase in mortality in the SAD + MI group compared with the MI group. Correlations were obtained between BRS and the LF component of HRV and between LV mass and the LF component of BPV. 4. Together, the results indicate that the abolishment of BRS induced by SAD in MI rats further reduces the LF band of HRV, resulting in a worse cardiac remodelling and increased mortality in these rats. These data highlight the importance of this mechanism in the prognosis of patients after an ischaemic event.

Ace gene dosage influences the development of renovascular hypertension

P>1. Clinical and experimental evidence highlights the importance of the renin-angiotensin system in renovascular hypertension. Furthermore, genetic factors affecting angiotensin-converting enzyme (ACE) could influence the development of renovascular hypertension. 2. To test the effect of small gene perturbations on the development of renovascular hypertension, mice harbouring two or three copies of the Ace gene were submitted to 4 weeks of two-kidney, one-clip (2K1C) hypertension. Blood pressure (BP), cardiac hypertrophy, baroreflex sensitivity and blood pressure and heart rate variability were assessed and compared between the different groups. 3. The increase in BP induced by 2K1C was higher in mice with three copies of the Ace gene compared with mice with only two copies (46 vs 23 mmHg, respectively). Moreover, there was a 3.8-fold increase in the slope of the left ventricle mass/BP relationship in mice with three copies of the Ace gene. Micewith three copies of the Ace gene exhibited greater increases in cardiac and serum ACE activity than mice with only two copies of the gene. Both baroreflex bradycardia and tachycardia were significantly depressed in mice with three copies of the Ace gene after induction of 2K1C hypertension. The variance in basal systolic BP was greater in mice with three copies of the Ace gene after 2K1C hypertension compared with those with only two copies of the gene (106 vs 54%, respectively). In addition, the low-frequency component of the pulse interval was higher mice with three copies of the Ace gene after 2K1C hypertension compared with those with only two (168 vs 86%, respectively). Finally, in mice with three copies of the Ace gene, renovascular hypertension induced a 6.1-fold increase in the sympathovagal balance compared with a 3.2-fold increase in mice with only two copies of the gene. 4. Collectively, these data provide direct evidence that small genetic disturbances in ACE levels per se have an influence on haemodynamic, cardiac mass and autonomic nervous system responses in mice under pathological perturbation.

Circulating renin-angiotensin system and catecholamines in childhood: is there a role for birthweight?

There have been only a few reports on the sympathoadrenal and renin-angiotensin systems in children of small gestational age. The purpose of the present study was to investigate plasma levels of ACE (angiotensin-converting enzyme) activity, angiotensin and catecholamines in 8- to 13-year-old children and to determine whether there are correlations between the components of these systems with both birthweight and BP (blood pressure) levels. This clinical study included 66 children (35 boys and 31 girls) in two groups: those born at term with an appropriate birthweight [AGA (appropriate-for-gestational age) group, n = 31] and those born at term but with a small birthweight for gestational age [SGA (small-for-gestational age) group, n = 35]. Concentrations of angiotensin, catecholamines and ACE activity were determined in plasma. Circulating noradrenaline levels were significantly elevated in SGA girls compared with AGA girls (P = 0.036). In addition, angiotensin 11 and ACE activity were higher in SGA boys (P = 0.024 and P = 0.050 respectively). There was a significant association of the circulating levels of both angiotensin 11 and ACE activity with BP levels in our study population. Although the underlying mechanisms that link restricted fetal growth with later cardiovascular events are not fully understood, the findings in the present study support the link between low birthweight and overactivity of both sympathoadrenal and renin-angiotensin systems into later childhood.

SGLT1 protein expression in plasma membrane of acinar cells correlates with the sympathetic outflow to salivary glands in diabetic and hypertensive rats

Salivary gland dysfunction is a feature in diabetes and hypertension. We hypothesized that sodium-glucose cotransporter 1 (SGLT1) participates in salivary dysfunctions through a sympathetic- and protein kinase A (PKA)-mediated pathway. In Wistar-Kyoto (WKY), diabetic WKY (WKY-D), spontaneously hypertensive (SHR), and diabetic SHR (SHR-D) rats, PKA/SGLT1 proteins were analyzed in parotid and submandibular glands, and the sympathetic nerve activity (SNA) to the glands was monitored. Basal SNA was threefold higher in SHR (P < 0.001 vs. WKY), and diabetes decreased this activity (similar to 50%, P < 0.05) in both WKY and SHR. The catalytic subunit of PKA and the plasma membrane SGLT1 content in acinar cells were regulated in parallel to the SNA. Electrical stimulation of the sympathetic branch to salivary glands increased (similar to 30%, P < 0.05) PKA and SGLT1 expression. Immunohistochemical analysis confirmed the observed regulations of SGLT1, revealing its location in basolateral membrane of acinar cells. Taken together, our results show highly coordinated regulation of sympathetic activity upon PKA activity and plasma membrane SGLT1 content in salivary glands. Furthermore, the present findings show that diabetic- and/or hypertensive-induced changes in the sympathetic activity correlate with changes in SGLT1 expression in basolateral membrane of acinar cells, which can participate in the salivary glands dysfunctions reported by patients with these pathologies.

Exercise changes regional vascular control by commissural NTS in spontaneously hypertensive rats

Ogihara CA, Schoorlemmer GHM, Levada AC, Pithon-Curi TC, Curi R, Lopes OU, Colombari E, Sato MA. Exercise changes regional vascular control by commissural NTS in spontaneously hypertensive rats. Am J Physiol Regul Integr Comp Physiol 299: R291-R297, 2010. First published April 21, 2010; doi: 10.1152/ajpregu.00055.2009.-Inhibition of the commissural nucleus of the solitary tract (commNTS) induces a fall in sympathetic nerve activity and blood pressure in spontaneously hypertensive rats (SHR), which suggests that this subnucleus of the NTS is a source of sympathoexcitation. Exercise training reduces sympathetic activity and arterial pressure. The purpose of the present study was to investigate whether the swimming exercise can modify the regional vascular responses evoked by inhibition of the commNTS neurons in SHR and normotensive Wistar-Kyoto (WKY) rats. Exercise consisted of swimming, 1 h/day, 5 days/wk for 6 wks, with a load of 2% of the body weight. The day after the last exercise session, the rats were anesthetized with intravenous alpha-chloralose, tracheostomized, and artificially ventilated. The femoral artery was cannulated for mean arterial pressure (MAP) and heart rate recordings, and Doppler flow probes were placed around the lower abdominal aorta and superior mesenteric artery. Microinjection of 50 mM GABA into the commNTS caused similar reductions in MAP in swimming and sedentary SHR (-25 +/- 6 and -30 +/- 5 mmHg, respectively), but hindlimb vascular conductance increased twofold in exercised vs. sedentary SHR (54 +/- 8 vs. 24 +/- 5%). GABA into the commNTS caused smaller reductions in MAP in swimming and sedentary WKY rats (-20 +/- 4 and -16 +/- 2 mmHg). Hindlimb conductance increased fourfold in exercised vs. sedentary WKY rats (75 +/- 2% vs. 19 +/- 3%). Therefore, our data suggest that the swimming exercise induced changes in commNTS neurons, as shown by a greater enhancement of hindlimb vasodilatation in WKY vs. SHR rats in response to GABAergic inhibition of these neurons.

Intratemporal facial nerve ultrastructure in patients with idiopathic facial paralysis. Viral infection evidence study

The etiology of idiopathic peripheral facial palsy (IPFP) is still uncertain; however, some authors suggest the possibility of a viral infection. Aim: to analyze the ultrastructure of the facial nerve seeking viral evidences that might provide etiological data. Material and Methods: We studied 20 patients with peripheral facial palsy (PFP), with moderate to severe FP, of both genders, between 18-60 years of age, from the Clinic of Facial Nerve Disorders. The patients were broken down into two groups - Study: eleven patients with IPFP and Control: nine patients with trauma or tumor-related PFP. The fragments were obtained from the facial nerve sheath or from fragments of its stumps - which would be discarded or sent to pathology exam during the facial nerve repair surgery. The removed tissue was fixed in 2% glutaraldehyde, and studied under Electronic Transmission Microscopy. Results: In the study group we observed an intense repair cellular activity by increased collagen fibers, fibroblasts containing developed organelles, free of viral particles. In the control group this repair activity was not evident, but no viral particles were observed. Conclusion: There were no viral particles, and there were evidences of intense activity of repair or viral infection.

Reduction of acethylcolinesterase activity in the brain of mdx mice

Lack of dystrophin in brain structures have been involved with impaired cognitive functions. Acethylcolinesterase (AChE) is implicated in many cognitive functions and probably plays important roles in neurodegenerative disorders. In the present study, we investigated AChE activity in the prefrontal cortex, hippocampus, striatum and cortex of mdx mice. To this aim, brain tissues from male dystrophic mdx and normal control mice were used. We observed that mdx mice display a reduction in AChE activity of 40-60% in all brain structures evaluated. In conclusion, dystrophin deficiency may be affecting AChE activity and contributing negatively, in part, to memory storage and restoring. (C) 2011 Elsevier B.V. All rights reserved.

beta-ADRENERGIC ACTIVITY PRESERVES GLUT4 PROTEIN IN GLYCOLYTIC FIBERS IN FASTING

Glucose transporter 4 (GLUT4) expression in adipose tissue decreases during fasting. In skeletal muscle, we hypothesized that GLUT4 expression might be maintained in a beta-adrenergic-dependent way to ensure energy disposal for contractile function. Herein we investigate beta-blockade or beta-stimulation effects on GLUT4 expression in oxidative (soleus) and glycolytic [extensor digitorum longus (EDL)] muscles of fasted rats. Fasting increased GLUT4 mRNA in soleus (24%) and EDL (40%) but the protein content increased only in soleus (30%). beta 1-beta 2-, and beta 1-beta 2-beta 3-blockade decreased (20-30%) GLUT4 mRNA content in both muscles, although GLUT4 protein decreased only in EDL. When mRNA and GLUT4 protein regulations were discrepant, changes in the mRNA poly(A) tail length were detected, indicating a posttranscriptional modulation of gene expression. These results show that beta-adrenergic activity regulates GLUT4 gene expression in skeletal muscle during fasting, highlighting its participation in preservation of GLUT4 protein in glycolytic muscle. Muscle Nerve 40: 847-854, 2009

Alpha7 Nicotinic Acetylcholine Receptor Expression and Activity During Neuronal Differentiation of PC12 Pheochromocytoma Cells

Nicotinic acetylcholine receptors (nAChR) exert pivotal roles in synaptic transmission, neuroprotection and differentiation. Particularly, homomeric alpha 7 receptors participate in neurite outgrowth, presynaptic control of neurotransmitter release and Ca(2+) influx. However, the study of recombinant alpha 7 nAChRs in transfected cell lines is difficult due to low expression of functional receptor channels. We show that PC12 pheochromocytoma cells induced to differentiation into neurons are an adequate model for studying differential nAChR gene expression and receptor activity. Whole-cell current recording indicated that receptor responses increased during the course of differentiation. Transcription of mRNAs coding for alpha 3, alpha 5, alpha 7, beta 2 and beta 4 subunits was present during the course of differentiation, while mRNAs coding for alpha 2, alpha 4 and beta 3 subunits were not expressed in PC12 cells. alpha 7 subunit expression was highest following 1 day of induction to differentiation. Activity of alpha 7 nAChRs, however, was most elevated on day 2 as revealed by inhibition experiments in the presence of 10 nM methyllycaconitine, rapid current decay and receptor responsiveness to the alpha 7 agonist choline. Increased alpha 7 receptor activity was noted when PC12 were induced to differentiation in the presence of choline, confirming that chronic agonist treatment augments nAChR activity. In summary, PC12 cells are an adequate model to study the role and pharmacological properties of this receptor during neuronal differentiation.