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Santos CR, Ruggeri A, Ceroni A, Michelini LC. Exercise training abrogates age-dependent loss of hypothalamic oxytocinergic circuitry and maintains high parasympathetic activity. J Neuroendocrinol 2018; 30:e12601. [PMID: 29656427 DOI: 10.1111/jne.12601] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2018] [Accepted: 04/05/2018] [Indexed: 11/27/2022]
Abstract
Neuroanatomical studies associating neuronal tract tracing and immunohistochemistry identified reciprocal (ascending noradrenergic/descending oxytocinergic, OTergic) connections between brainstem cardiovascular nuclei and the paraventricular hypothalamic nucleus (PVN). Previous functional studies indicated that exercise training (T) augmented the expression/activity of OTergic pathway and improve the autonomic control of the heart. Knowing that ageing is associated with autonomic dysfunction and sinoaortic denervation blocked T-induced beneficial effects, we hypothesized that T was able to reduce age-dependent impairment by improving the afferent signaling to PVN and augmenting OTergic modulation of cardiovascular control. We evaluated the combined effects of T and age on plastic remodeling of ascending dopamine β-hydroxylase (DBH+) and descending OT+ pathways and correlated them with cardiovascular parameters. Male Wistar rats were submitted to T or kept sedentary for 8 weeks. After evaluating arterial pressure, heart rate (HR), their variabilities and spectral components in conscious rats at rest, brains were harvested to analyze the plastic remodeling of brain autonomic nuclei (immunofluorescence + confocal microscopy). The density of DBH+ neurons within the nucleus of solitary tract (NTS) and caudal ventrolateral medulla, the number of DBH+ terminals overlapping OT+ neurons in PVN preautonomic nuclei, as well as the density of OT+ neurons and their projections to NTS and dorsal motor nucleus of the vagus were markedly reduced in S rats during 8-weeks of inactivity In contrast, these effects were completely blocked by T and reversed to a large augmentation of DBH+ and OT+ densities in both cell bodies and terminals within autonomic nuclei and target areas. All plastic changes observed correlated positively with parasympathetic activity to the heart (HF-PI, but not with LF-PI) and negatively with resting HR. Data indicate that T, by increasing beneficial neuroplastic adaptive changes within brainstem-PVN reciprocal network, abrogates age-dependent deleterious remodeling and augments parasympathetic modulation of the heart, therefore improving autonomic function. This article is protected by copyright. All rights reserved.
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Affiliation(s)
- Carla R Santos
- Department of Physiology, Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo/SP, Brazil
| | - Adriana Ruggeri
- Department of Physiology, Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo/SP, Brazil
| | - Alexandre Ceroni
- Department of Physiology, Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo/SP, Brazil
| | - Lisete C Michelini
- Department of Physiology, Biophysics, Institute of Biomedical Sciences, University of Sao Paulo, Sao Paulo/SP, Brazil
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Neto OB, de Sordi CC, da Mota GR, Marocolo M, Chriguer RS, da Silva VJD. Exercise training improves hypertension-induced autonomic dysfunction without influencing properties of peripheral cardiac vagus nerve. Auton Neurosci 2017; 208:66-72. [PMID: 28964689 DOI: 10.1016/j.autneu.2017.09.012] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2017] [Revised: 09/13/2017] [Accepted: 09/13/2017] [Indexed: 01/10/2023]
Abstract
We examined the vagal transfer function of autonomic heart rate (HR) control in anesthetized sedentary and exercise-trained Spontaneously Hypertensive Rats (SHR). To this end, male SHR and Wystar-Kyoto (WKY) rats with 48-50weeks of age-old were divided into 4 groups: sedentary (SHRS, n=12) and trained (SHRT, n=14) hypertensive rats, sedentary (WKYS, n=13) and trained (WKYT, n=13) normotensive rats. The trained groups were submitted to swimming protocol for 9weeks. Blood pressure (BP), HR, HR variability (HRV), BP variability (BPV), baroreflex sensitivity and cardiac tonus were recorded in baseline conditions. Following, electric stimulation of peripheral vagus nerve was performed in anesthetized conditions. Resting bradycardia was observed in SHRT and WKYT when compared to their respective sedentary groups (p<0.001). The BP was lower in SHRT than in SHRS (p<0.001). The SHRT and WKYT rats showed higher baroreflex-mediated tachycardia values when compared to their respective sedentary counterparts (p<0.001). Baroreflex bradycardic response in SHRT was higher than in SHRS (p<0.005). The SHRT and WKYT rats showed a decreased sympathetic activity in comparison to their respective sedentary groups (p<0.05). The cardiac vagal tonus was higher in SHRT than in SHRS (p<0.05). Regarding the dynamic transducer properties of peripheral vagus nerve to the heart no difference was observed among the groups. In conclusion, our results demonstrate that exercise training decreased BP in SHR and improved cardiovascular autonomic balance to the heart without changes in transduction properties of peripheral cardiac vagus nerve.
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Affiliation(s)
- Octávio Barbosa Neto
- Human Performance and Sport Research Group, Department of Sport Sciences, Federal University of Triângulo Mineiro, Uberaba, Brazil; Department of Physiology, Institute of Biological and Natural Sciences, Federal University of Triângulo Mineiro, Uberaba, Brazil.
| | - Carla Cristina de Sordi
- Department of Endocrinology and Metabolism, Postgraduate Course on Health Science, Federal University of Triângulo Mineiro, Uberaba, Brazil
| | - Gustavo Ribeiro da Mota
- Human Performance and Sport Research Group, Department of Sport Sciences, Federal University of Triângulo Mineiro, Uberaba, Brazil
| | - Moacir Marocolo
- Department of Physiology, Federal University of Juiz de Fora, Juiz de Fora, Brazil
| | | | - Valdo José Dias da Silva
- Department of Physiology, Institute of Biological and Natural Sciences, Federal University of Triângulo Mineiro, Uberaba, Brazil
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Abnormal central control underlies impaired baroreflex control of heart rate and sympathetic nerve activity in female Lewis polycystic kidney rats. J Hypertens 2016; 33:1418-28. [PMID: 26039532 DOI: 10.1097/hjh.0000000000000572] [Citation(s) in RCA: 16] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
OBJECTIVE Why baroreflex dysfunction occurs in females with chronic kidney disease is unknown. We therefore aimed to examine whether temporal changes in baroreflex control of heart rate (HR) and renal sympathetic nerve activity (RSNA) occur in female Lewis polycystic kidney (LPK) rats and whether this is associated with any changes in afferent, central or efferent processing of the reflex pathway. METHOD Using urethane-anaesthetized juvenile and adult LPK and Lewis control rats (n = 40), baroreflex-mediated changes in HR, RSNA and aortic depressor nerve activity (ADNA) were examined. Reflex changes to aortic depressor and vagal efferent nerve stimulation were also determined. RESULTS In the juvenile LPK rats, except for a slight reduction in the gain of the normalized HR and RSNA baroreflex function curves, no difference in baroreflex control of HR, RSNA or ADNA was observed. Responses to aortic depressor and vagal efferent nerve stimulation were also comparable. In the adult hypertensive LPK rats, the range of both HR (35 ± 8 vs. 78 ± 9 bpm, P ≤ 0.05 LPK vs. Lewis) and RSNA (60 ± 7 vs. 80 ± 3%, P ≤ 0.05 LPK vs. Lewis) was also reduced. This was not associated with any change in the ADNA baroreflex function curves or reflex HR responses to vagal efferent nerve stimulation, but was associated with a reduction in the reflex bradycardic (-21 ± 4 vs. -34 ± 8 bpm, P < 0.01 LPK vs. Lewis) and sympathoinhibitory (-30 ± 8 vs. -54 ± 12%, P < 0.001 LPK vs. Lewis) responses to aortic depressor nerve stimulation. CONCLUSION In female LPK rats, baroreflex dysfunction results from impaired central processing of the reflex.
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Shanks J, Manou-Stathopoulou S, Lu CJ, Li D, Paterson DJ, Herring N. Cardiac sympathetic dysfunction in the prehypertensive spontaneously hypertensive rat. Am J Physiol Heart Circ Physiol 2013; 305:H980-6. [PMID: 23913706 DOI: 10.1152/ajpheart.00255.2013] [Citation(s) in RCA: 46] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Recent studies in prehypertensive spontaneously hypertensive rats (SHR) have shown larger calcium transients and reduced norepinephrine transporter (NET) activity in cultured stellate neurons compared with Wistar-Kyoto (WKY) controls, although the functional significance of these results is unknown. We hypothesized that peripheral sympathetic responsiveness in the SHR at 4 wk of age would be exaggerated compared with the WKY. In vivo arterial pressure (under 2% isoflurane) was similar in SHRs (88 ± 2/50 ± 3 mmHg, n = 18) compared with WKYs (88 ± 3/49 ± 4 mmHg, n = 20). However, a small but significant (P < 0.05) tachycardia was observed in the young SHR despite the heart rate response to vagus stimulation (3 and 5 Hz) in vivo being similar (SHR: n = 12, WKY: n = 10). In isolated atrial preparations there was a significantly greater tachycardia during right stellate stimulation (5 and 7 Hz) in SHRs (n = 19) compared with WKYs (n = 16) but not in response to exogenous NE (0.025-5 μM, SHR: n = 10, WKY: n = 10). There was also a significantly greater release of [(3)H]NE to field stimulation (5 Hz) of atria in the SHR (SHR: n = 17, WKY: n = 16). Additionally, plasma levels of neuropeptide Y sampled from the right atria in vivo were also higher in the SHR (ELISA, n = 12 for both groups). The difference in [(3)H]NE release between SHR and WKY could be normalized by the NET inhibitor desipramine (1 μM, SHR: n = 10, WKY: n = 8) but not the α2-receptor antagonist yohimbine (1 μM, SHR: n = 7, WKY: n = 8). Increased cardiac sympathetic neurotransmission driven by larger neuronal calcium transients and reduced NE reuptake translates into enhanced cardiac sympathetic responsiveness at the end organ in prehypertensive SHRs.
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Affiliation(s)
- Julia Shanks
- Burdon Sanderson Cardiac Science Centre, Department of Physiology, Anatomy and Genetics, Sherrington Building, University of Oxford, Oxford, United Kingdom
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Kawada T, Akiyama T, Shimizu S, Kamiya A, Uemura K, Sata Y, Shirai M, Sugimachi M. Central vagal activation by alpha(2) -adrenergic stimulation is impaired in spontaneously hypertensive rats. Acta Physiol (Oxf) 2012; 206:72-9. [PMID: 22463699 DOI: 10.1111/j.1748-1716.2012.02439.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Revised: 12/21/2011] [Accepted: 03/22/2012] [Indexed: 11/28/2022]
Abstract
AIM To elucidate the abnormality of vagal control in spontaneously hypertensive rats (SHR) by measuring left ventricular myocardial interstitial acetylcholine (ACh) release in response to α(2) -adrenergic stimulation as an index of in vivo vagal nerve activity. METHODS A cardiac microdialysis technique was applied to the rat left ventricle in vivo, and the effect of α(2) -adrenergic stimulation by medetomidine or electrical vagal nerve stimulation on myocardial interstitial ACh levels was examined in normotensive Wistar-Kyoto rats (WKY) and SHR under anaesthetized conditions. RESULTS Intravenous medetomidine (0.1 mg kg(-1) ) significantly increased the ACh levels in WKY (from 2.4 ± 0.6 to 4.2 ± 1.3 nmol L(-1) , P < 0.05, n = 7) but not in SHR (from 2.5 ± 0.7 to 2.7 ± 0.7 nmol L(-1) , n = 7). In contrast, electrical vagal nerve stimulation increased the ACh levels in both WKY (from 1.0 ± 0.4 to 2.9 ± 0.9 nmol L(-1) , P < 0.001, n = 6) and SHR (from 0.9 ± 0.2 to 2.2 ± 0.4 nmol L(-1) , P < 0.001, n = 6). Intravenous administration of medetomidine (0.1 mg kg(-1) ) did not affect the vagal nerve stimulation-induced ACh release in either WKY or SHR. CONCLUSION Medetomidine-induced central vagal activation was impaired in SHR, whereas peripheral vagal control of ACh release was preserved. In addition to abnormal sympathetic control, vagal control by the central nervous system may be impaired in SHR.
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Affiliation(s)
- T. Kawada
- Department of Cardiovascular Dynamics; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - T. Akiyama
- Department of Cardiac Physiology; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - S. Shimizu
- Department of Cardiovascular Dynamics; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - A. Kamiya
- Department of Cardiovascular Dynamics; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - K. Uemura
- Department of Cardiovascular Dynamics; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - Y. Sata
- Department of Cardiovascular Dynamics; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - M. Shirai
- Department of Cardiac Physiology; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
| | - M. Sugimachi
- Department of Cardiovascular Dynamics; National Cerebral and Cardiovascular Center Research Institute; Osaka; Japan
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Durand MT, Mota AL, Barale AR, Castania JA, Fazan R, Salgado HC. Time course of the hemodynamic responses to aortic depressor nerve stimulation in conscious spontaneously hypertensive rats. Braz J Med Biol Res 2012; 45:444-9. [PMID: 22415118 PMCID: PMC3854280 DOI: 10.1590/s0100-879x2012007500032] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2011] [Accepted: 02/28/2012] [Indexed: 11/22/2022] Open
Abstract
The time to reach the maximum response of arterial pressure, heart rate and vascular resistance (hindquarter and mesenteric) was measured in conscious male spontaneously hypertensive (SHR) and normotensive control rats (NCR; Wistar; 18-22 weeks) subjected to electrical stimulation of the aortic depressor nerve (ADN). The parameters of stimulation were 1 mA intensity and 2 ms pulse length applied for 5 s, using frequencies of 10, 30, and 90 Hz. The time to reach the hemodynamic responses at different frequencies of ADN stimulation was similar for SHR (N = 15) and NCR (N = 14); hypotension = NCR (4194 ± 336 to 3695 ± 463 ms) vs SHR (3475 ± 354 to 4494 ± 300 ms); bradycardia = NCR (1618 ± 152 to 1358 ± 185 ms) vs SHR (1911 ± 323 to 1852 ± 431 ms), and the fall in hindquarter vascular resistance = NCR (6054 ± 486 to 6550 ± 847 ms) vs SHR (4849 ± 918 to 4926 ± 646 ms); mesenteric = NCR (5574 ± 790 to 5752 ± 539 ms) vs SHR (5638 ± 648 to 6777 ± 624 ms). In addition, ADN stimulation produced baroreflex responses characterized by a faster cardiac effect followed by a vascular effect, which together contributed to the decrease in arterial pressure. Therefore, the results indicate that there is no alteration in the conduction of the electrical impulse after the site of baroreceptor mechanical transduction in the baroreflex pathway (central and/or efferent) in conscious SHR compared to NCR.
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Affiliation(s)
- M T Durand
- Departamento de Fisiologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Brasil.
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Pinilla L, Castellano JM, Romero M, Tena-Sempere M, Gaytán F, Aguilar E. Delayed puberty in spontaneously hypertensive rats involves a primary ovarian failure independent of the hypothalamic KiSS-1/GPR54/GnRH system. Endocrinology 2009; 150:2889-97. [PMID: 19228890 DOI: 10.1210/en.2008-1381] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Spontaneously hypertensive (SH) rats, extensively used as experimental models of essential human hypertension, display important alterations in the neuroendocrine reproductive axis, which manifest as markedly delayed puberty onset in females but whose basis remains largely unknown. We analyze herein in female SH rats: 1) possible alterations in the expression and function of KiSS-1/GPR54 and GnRH/GnRH-receptor systems, 2) the integrity of feedback mechanisms governing the hypothalamic-pituitary-ovarian axis, and 3) the control of ovarian function by gonadotropins. Our data demonstrate that, despite overtly delayed puberty, no significant decrease in hypothalamic KiSS-1, GPR54, or GnRH mRNA levels was detected in this strain. Likewise, in vivo gonadotropin responses to ovariectomy and systemic kisspeptin-10 or GnRH administration, as well as in vitro gonadotropin responses to GnRH, were fully preserved in SH rats. Moreover, circulating LH levels were grossly conserved during prepubertal maturation, whereas FSH levels were even enhanced from d 20 postpartum onwards. In striking contrast, ovarian weight and hormone (progesterone and testosterone) responses to human chorionic gonadotropin (CG) in vitro were profoundly decreased in SH rats, with impaired follicular development and delayed ovulation at puberty. Such reduced hormonal responses to human CG could not be attributed to changes in LH/CG or FSH-receptor mRNA expression but might be linked to blunted P450scc, 3beta-hydroxy steroid dehydrogenase, and aromatase mRNA levels in ovaries from SH rats. In conclusion, our results indicate that the expression and function of KiSS-1/GPR54 and GnRH/GnRH-receptor systems is normal in SH rats, whereas ovarian development, steroidogenesis, and responsiveness to gonadotropins are strongly compromised.
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Affiliation(s)
- L Pinilla
- Medical Research Council Human Reproductive Sciences Unit, Queen's Medical Research Institute, Edinburgh, United Kingdom
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Spary EJ, Maqbool A, Saha S, Batten TFC. Increased GABA B receptor subtype expression in the nucleus of the solitary tract of the spontaneously hypertensive rat. J Mol Neurosci 2008; 35:211-24. [PMID: 18338268 DOI: 10.1007/s12031-008-9055-9] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2008] [Accepted: 02/14/2008] [Indexed: 02/07/2023]
Abstract
Expression of GABA(B) receptor messenger RNA (mRNA) in the central nervous system was compared between the spontaneously hypertensive (SHR) and normotensive Wistar Kyoto (WKY) rat. Polymerase chain reaction (PCR) revealed all the isoforms except B1e in cortex, hypothalamus, and medulla oblongata. In the nucleus of the solitary tract (NTS) and ventrolateral medulla (VLM), the B1a-c and 1 g isoforms were present as well as B2. Real-time PCR detected significantly higher levels of B1a (p < 0.01) and B2 (p < 0.05) mRNA in the NTS of SHR compared to WKY. A significant increase in B1a expression (p < 0.05) was detected in VLM. Immunolabeling suggested presynaptic and postsynaptic expression of B1a, B1b, and B2 subtypes throughout the NTS, with significant differences in distribution patterns and labeling between subtypes and between SHR and WKY. These findings suggest that GABA(B) receptors expressed by neurones in NTS may be involved in cardiovascular regulation and that changes in GABA(B) mRNA expression levels may contribute to the hypertensive state in SHR.
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Affiliation(s)
- Emma J Spary
- Division of Cardiovascular and Neuronal Remodelling, LIGHT Institute, Faculty of Medicine & Health, University of Leeds, Worsley Building, Leeds, LS2 9JT, UK.
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Corbett EKA, Mary DASG, McWilliam PN, Batten TFC. Age-related loss of cardiac vagal preganglionic neurones in spontaneously hypertensive rats. Exp Physiol 2007; 92:1005-13. [PMID: 17644704 DOI: 10.1113/expphysiol.2007.038216] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Despite the findings that impaired vagal control of the heart rate occurs in human hypertension, leading to greater cardiovascular risk, the mechanism of this impairment is as yet unknown. Observations in humans and experiments in the spontaneously hypertensive rat (SHR) suggested that such impairment may be related to an anomaly in central vagal neurones. We therefore set out to determine whether the numbers and distribution of cardiac-projecting vagal preganglionic neurones in the medulla of adult (12 week) hypertensive SHR are different from those in young (4 week) prehypertensive SHR and in age-matched Wistar-Kyoto (WKY) rats of two age groups. The number of vagal neurones, identified by labelling with the fluorescent tracer DiI applied to the heart, was essentially similar in the three areas of the medulla analysed (dorsal vagal nucleus, nucleus ambiguus and intermediate reticular zone) in young SHR and young or adult WKY rats. In contrast, fewer vagal neurones were labelled in adult SHR compared with young SHR or WKY rats. This difference was due to highly significant reductions in vagal neurones in the dorsal vagal nucleus and nucleus ambiguus on the right side of the medulla. These observations suggest that a loss of parasympathetic preganglionic neurones supplying the heart with axons in the right vagus nerve, or a remodelling of their cardiac projections, may explain the known impairment of the baroreceptor reflex gain controlling heart rate in hypertension.
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Affiliation(s)
- Eric K A Corbett
- Institute for Cardiovascular Research (CRISTAL), Worsley Building, Clarendon Way, University of Leeds, Leeds LS2 9JT, UK
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Schiavoni MCL, Fazan VPS. There is no relation between the fascicular and the endoneural blood vessel areas on the cervical vagus nerve of normotensive rats. J Neurosci Methods 2006; 158:171-8. [PMID: 16814392 DOI: 10.1016/j.jneumeth.2006.05.028] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/16/2006] [Revised: 05/09/2006] [Accepted: 05/24/2006] [Indexed: 11/18/2022]
Abstract
The aim of this study was to determine the existence of a relation between the fascicular area and total vessel area on the cervical vagus nerve of Wistar-Kyoto female rats. Animals aged 30, 180 or 360 days had their right vagus nerves prepared for epoxy resin embedding and light microscopy study. Semithin serial sections were studied every 100 microm of the longitudinal extension of the nerve. The fascicular area and the total endoneural vessel area were obtained for each nerve segment (proximal, middle and distal) and compared between segments and ages. The relation between fascicular area and endoneural vessel area was accessed by linear regression analysis and correlation coefficient calculations. No significant relationship between the two variables was detected in all nerves studied. This suggests that the entrance of blood vessels to the endoneural space is not accompanied by an increase in the fascicular area and this may have implications on the fiber density calculations since, in the presence of large vessels, this density can be underestimated if the vessel area is not discounted. The endoneural vessel area increased from proximal to distal in all groups but got smaller with ageing, suggesting that older animals may be more susceptible to nerve ischemia.
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Affiliation(s)
- Maria Cristina Lopes Schiavoni
- Department of Neurology, School of Medicine of Ribeirão Preto, University of São Paulo, Av. Bandeirantes 3900, Ribeirão Preto, São Paulo 14049-900, Brazil
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Gava AL, Peotta VA, Cabral AM, Meyrelles SS, Vasquez EC. Decreased baroreflex sensitivity in isoproterenol-treated mice with cardiac hypertrophy. Auton Neurosci 2004; 114:47-54. [PMID: 15331044 DOI: 10.1016/j.autneu.2004.07.003] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/17/2004] [Revised: 07/11/2004] [Accepted: 07/19/2004] [Indexed: 11/18/2022]
Abstract
The baroreflex has been shown to be impaired in rat models of cardiac hypertrophy. In the present study, we investigated the effects of beta-adrenoceptor-induced cardiac hypertrophy on the baroreflex in mice. Male Swiss Webster mice weighing 20-25 g were treated with the beta-adrenoceptor agonist isoproterenol (IPM; 15 microg/g/day, s.c.) for 7 days or with vehicle (control, CM). After treatment, IPM (n=9) and CM (n=9) were anesthetized with ketamine + xylazine (91.0: 9.1 mg/kg, i.p.) and had their carotid artery and jugular vein cannulated to test the arterial baroreflex. The baroreflex was evaluated by measuring changes in heart rate (HR) in response to acute increases and decreases in mean arterial pressure (MAP) induced by bolus injections of phenylephrine and sodium nitroprusside (1.5-24.0 microg/kg, i.v.) in conscious animals. IPM showed an increased cardiac weight/body weight (1.18 +/- 0.03 mg/g) ratio compared to CM (0.95 +/- 0.03 mg/g, p<0.05), but similar values of resting MAP (108 +/- 4 vs. 111 +/- 2 mm Hg) and HR (606 +/- 25 vs. 629 +/- 26 bpm). Sigmoidal barocurve analysis showed that isoproterenol treatment significantly reduced the following parameters: baroreflex sensitivity (IPM: -4.26 +/- 0.19 vs. CM: -5.92 +/- 0.54 bpm/mm Hg, p<0.05), reflex bradycardia plateau (IPM: 387 +/- 26 vs. CM: 318 +/- 19 bpm, p<0.05) and HR range (IPM: 369 +/- 30 vs. CM: 442 +/- 20 bpm, p<0.05). Linear regression analysis of baroreflex function also showed a diminished reflex bradycardia (CM: -8.92 +/- 0.87 bpm/mm Hg vs. IPM: -4.94 +/- 0.52 bpm/mm Hg, p<0.05), but similar reflex tachycardia (CM: -3.88 +/- 0.45 bpm/mm Hg vs. IPM: -3.52 +/- 0.43 bpm/mm Hg). In conclusion, beta-adrenoceptor-induced cardiac hypertrophy in mice led to impaired sensitivity of the cardiac baroreflex, which could be due to a diminished vagal activity to the heart.
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Affiliation(s)
- Agata L Gava
- Laboratory of Transgenes and Cardiovascular Control, Physiological Sciences Graduate Program, Biomedical Center, Federal University of Espirito Santo, Av Marechal Campos 1468, 29042-755 Vitoria, ES, Brazil
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Saha S, Spary EJ, Maqbool A, Asipu A, Corbett EKA, Batten TFC. Increased expression of AMPA receptor subunits in the nucleus of the solitary tract in the spontaneously hypertensive rat. ACTA ACUST UNITED AC 2004; 121:37-49. [PMID: 14969735 DOI: 10.1016/j.molbrainres.2003.11.003] [Citation(s) in RCA: 17] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 11/13/2003] [Indexed: 01/21/2023]
Abstract
The expression of alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid (AMPA) receptor subunits GluR1-4 in the nucleus of the solitary tract (NTS) of adult Wistar rats was examined by polymerase chain reaction (PCR), and the neuronal localisation of these receptor subunits in the NTS were confirmed by immunohistochemistry using subunit-specific antibodies. Semi-quantitative PCR was used to investigate differences in AMPA receptor subunit expression between spontaneously hypertensive rats (SH) and age-matched normotensive Wistar Kyoto rats (WKY). All four receptor subunits were expressed in both strains, but compared to WKY, total AMPA receptor and the GluR3 mRNA expressions were significantly higher in SH. No differences were detected in cDNA form the cerebral cortex or cerebellum. Immunolabelling for GluRs 1, 2 and 2/3 in the neuropil relative to neuronal somata in the cardioregulatory areas of the NTS appeared to be increased in SH, with an overall increase in the density of GluR2/3 labelling in the medial and commissural NTS of SH. These results indicate a possible role for changes in AMPA receptor subunit expression in NTS neurones, involving an increase in GluR3 associated with development of hypertension in SH.
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Affiliation(s)
- Sikha Saha
- School of Medicine, University of Leeds, Leeds LS2 9JT, UK
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Liu JL, Kulakofsky J, Zucker IH. Exercise training enhances baroreflex control of heart rate by a vagal mechanism in rabbits with heart failure. J Appl Physiol (1985) 2002; 92:2403-8. [PMID: 12015354 DOI: 10.1152/japplphysiol.00039.2002] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Moderate exercise training (Ex) enhances work capacity and quality of life in patients with chronic heart failure (CHF). We investigated the autonomic components of resting heart rate (HR) and the baroreflex control of HR in conscious, instrumented rabbits with pacing-induced CHF after Ex. Sham and CHF rabbits were exercise trained for 4 wk at 15-18 m/min, 6 days/wk. Arterial pressure and HR were recorded before and after metoprolol (1 mg/kg iv) or after atropine (0.2 mg/kg iv). Mean arterial pressure was altered by infusions of sodium nitroprusside and phenylephrine. The data were fit to a sigmoid (logistic) function. Baseline HRs were 266.5 +/- 8.4 and 232.1 +/- 1.6 beats/min in CHF and CHF Ex rabbits, respectively (P < 0.05). In the unblocked state, CHF rabbits had a significantly depressed peak baroreflex slope (1.7 +/- 0.3 vs. 5.6 +/- 0.7 beats. min(-1). mmHg(-1); P < 0.001) and HR range (128.6 +/- 34.5 vs. 253.2 +/- 20.3 beats/min; P < 0.05) compared with normal subjects. Ex increased baroreflex slope to 4.9 +/- 0.3 from 1.7 +/- 0.3 beats. min(-1). mmHg(-1) in unblocked rabbits (P < 0.001 compared with CHF non-Ex). Ex did not alter baroreflex function in sham animals. After metoprolol, baroreflex slope was significantly increased in CHF Ex rabbits (1.5 +/- 0.2 vs. 3.0 +/- 0.2 beats. min(-1). mmHg(-1); P < 0.05). After atropine, there was no significant change in baroreflex slope or HR range between CHF Ex and CHF rabbits. These data support the view that enhancement of baroreflex control of HR after Ex is due to an augmentation of vagal tone.
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Affiliation(s)
- Jun-Li Liu
- Department of Physiology and Biophysics, University of Nebraska Medical Center, Omaha, Nebraska 68198-4575, USA
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Abstract
1. The purpose of the present study was to assess the changes to renal sympathetic nerve activity (RSNA) baroreflexes during the development of hypertension after renal clipping in conscious rabbits. 2. Rabbits were fitted with a clip on the right renal artery or underwent a sham operation under halothane anaesthesia. A recording electrode was implanted on the left renal nerve 1 week before the experiment, 3 or 6 weeks after the initial operation. During the experiment, drug-induced ramp rises and falls in mean arterial pressure (MAP) were used to produce RSNA and heart rate (HR) baroreflex curves. The RSNA for each experiment was calibrated against maximum RSNA evoked by stimulation of baroreceptor-independent trigeminal afferents. 3. Mean arterial pressure was 20 and 36% higher 3 and 6 weeks after clip implantation, respectively. Renal sympathetic nerve activity baroreflex curves were reset rightwards accordingly, but the shape of the RSNA curves was differentially affected. 4. At both hypertensive periods, MAP-HR baroreflex gain was markedly reduced due to a reduction in curvature. The HR baroreflex range was increased. The RSNA baroreflex gain was reduced at 3 weeks, which was due to a 35% lower RSNA baroreflex range, but was similar to sham animals at 6 weeks. 5. The results show that, in established two kidney, one clip hypertension in rabbits, the sympathetic baroreflex is relatively well preserved but sensitivity of cardiac baroreflexes is attenuated. Therefore, the short-term inhibition of RSNA baroreflexes is not related to the level of blood pressure or the development of secondary changes, such as cardiac or vascular hypertrophy, but may be related to circulating angiotensin, which is known to increase at this time.
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Affiliation(s)
- G A Head
- Neuropharmacology Laboratory, Baker Medical Research Institute, Melbourne, Victoria, Australia.
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