Morphology of aortic depressor nerve myelinated fibers in normotensive Wistar–Kyoto and spontaneously hypertensive rats

Fazan, Valéria Paula Sassoli; Júnior, Rubens Fazan; Salgado, Hélio César; Barreira, Amilton Antunes

doi:10.1016/s0165-1838(99)00042-9

Cited by 42 publications

(57 citation statements)

References 19 publications

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“…Baroreceptor afferent sensitivity (1,2,19,30,43) and baroreflex-mediated changes in HR (25,38) have been shown to be consistently impaired in SHR. The decreased baroreflex sensitivity for control of HR has been attributed primarily to a defect in parasympathetic control (25,38).…”

Section: Discussionmentioning

confidence: 99%

“…This approach allowed us to assess not only the fall in HR but also the decrease in BP and regional vascular resistances. Furthermore, we hypothesized that electrical activation of baroreceptor afferents would more effectively inhibit HR and BP in SHR due to bypassing mechanosensory transduction, which is known to be impaired in SHR (1,2,19,43), and the importance of elevated sympathetic activity in mediating the hypertension in this model (8,26,27,39). Impaired baroreflex control of HR in SHR has been attributed primarily to a defect in parasympathetic control (25,38).…”

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confidence: 99%

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Baroreflex responses to electrical stimulation of aortic depressor nerve in conscious SHR

Salgado¹,

Barale²,

Castania³

et al. 2007

American Journal of Physiology-Heart and Circulatory Physiology

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-Baroreflex responses to changes in arterial pressure are impaired in spontaneously hypertensive rats (SHR). Mean arterial pressure (MAP), heart rate (HR), and regional vascular resistances were measured before and during electrical stimulation (5-90 Hz) of the left aortic depressor nerve (ADN) in conscious SHR and normotensive control rats (NCR). The protocol was repeated after ␤-adrenergic-receptor blockade with atenolol. SHR exhibited higher basal MAP (150 Ϯ 5 vs. 103 Ϯ 2 mmHg) and HR (393 Ϯ 9 vs. 360 Ϯ 5 beats/min). The frequency-dependent hypotensive response to ADN stimulation was preserved or enhanced in SHR. The greater absolute fall in MAP at higher frequencies (Ϫ68 Ϯ 5 vs. Ϫ38 Ϯ 3 mmHg at 90-Hz stimulation) in SHR was associated with a preferential decrease in hindquarter (Ϫ43 Ϯ 5%) vs. mesenteric (Ϫ27 Ϯ 3%) resistance. In contrast, ADN stimulation decreased hindquarter and mesenteric resistances equivalently in NCR (Ϫ33 Ϯ 7% and Ϫ30 Ϯ 7%). Reflex bradycardia was also preserved in SHR, although its mechanism differed. Atenolol attenuated the bradycardia in SHR (Ϫ88 Ϯ 14 vs. Ϫ129 Ϯ 18 beats/min at 90-Hz stimulation) but did not alter the bradycardia in NCR (Ϫ116 Ϯ 16 vs. Ϫ133 Ϯ 13 beats/min). The residual bradycardia under atenolol (parasympathetic component) was reduced in SHR. MAP and HR responses to ADN stimulation were also preserved or enhanced in SHR vs. NCR after deafferentation of carotid sinuses and contralateral right ADN. The results demonstrate distinct differences in central baroreflex control in conscious SHR vs. NCR. Inhibition of cardiac sympathetic tone maintains reflex bradycardia during ADN stimulation in SHR despite impaired parasympathetic activation, and depressor responses to ADN stimulation are equivalent or even greater in SHR due to augmented hindquarter vasodilation. spontaneously hypertensive rats; arterial pressure; heart rate; atenolol BARORECEPTOR AFFERENT SENSITIVITY (1, 2, 19, 43) and baroreflex-mediated changes in heart rate (HR) (25, 38) are consistently impaired in spontaneously hypertensive rats (SHR). More controversial is baroreflex control of sympathetic nerve activity, which has been reported to be impaired (8, 10), preserved (22,33,46), or augmented (46) in SHR. The inconsistent findings may reflect, in part, differential baroreflex control of sympathetic activity to different regions and use of anesthesia in many of the studies. In the majority of studies, baroreflex responses were measured in response to drug-induced changes in arterial blood pressure (BP), which does not allow assessment of reflex changes in vascular resistance.The goal of the present study was to compare the magnitude of reflex responses to electrical stimulation of baroreceptor afferents in the aortic depressor nerve (ADN) in conscious normotensive control rats (NCR) and SHR. This approach allowed us to assess not only the fall in HR but also the decrease in BP and regional vascular resistances. Furthermore, we hypothesized that electrical activation of baroreceptor afferents would more eff...

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Section: Discussionmentioning

confidence: 99%

mentioning

confidence: 99%

Baroreflex responses to electrical stimulation of aortic depressor nerve in conscious SHR

Salgado¹,

Barale²,

Castania³

et al. 2007

American Journal of Physiology-Heart and Circulatory Physiology

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“…All microscopic fields of the distal segment of the radial nerve and of the lateral proper digital nerve of the third finger were analyzed. Morphometric parameters for the myelinated fibers of the nerve segments were obtained as described previously (Fazan et al, 1999;Jeronimo et al, 2005). Briefly, the total number of myelinated fibers present in each microscopic field was identified by visual inspection and counted.…”

Section: Methodsmentioning

confidence: 99%

Microscopic anatomy of brachial plexus branches in Wistar rats

Santos

Suaid

Fazan

et al. 2007

The Anatomical Record

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In the present study, we analyze the morphology and morphometry of the lateral proper digital nerve of the third finger, and of the proximal and distal segments of the ulnar, median, and radial nerves, in Wistar rats 4 or 7 weeks old. The fascicular area and diameter were generally significantly greater in the proximal compared to distal segments and tended to be larger in 7-week-old compared to 4-week-old rats (e.g., median nerve area of 0.13 mm 2 for the proximal and 0.07 mm 2 for distal segments in 4-weekold rats, and 0.17 and 0.10 mm 2 , respectively, for the proximal and distal segments of 7-week-old rats). The number of fascicles was significantly greater while the number of myelinated fibers was significantly less in the distal segments (e.g., 1,359 and 509 myelinated fibers, respectively, in the proximal and distal segments of the radial nerve 4-week-old rats). There was no significant difference in these parameters between the two age groups. The diameter of the myelinated fibers and their respective axons increased from 4 to 7 weeks of age (e.g., myelinated fiber diameter of 4.10 mm in 4-week-old animals and 4.7 mm in the ulnar nerve proximal segment of 7-week-old rats). The g-ratio regression line (axon diameter vs. fiber diameter quotient) was outlined for all the nerves studied here. Differences in myelinated fiber density were detected between the segments of the radial nerve, accompanying the number of myelinated fibers. Detailed knowledge of the microscopic anatomy of rat forelimb nerves provides control data for comparison with studies of experimentally induced neuropathies, which can shed more light on human neuropathies. Anat Rec, 290:477-485, 2007. 2007 Wiley-Liss, Inc.

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“…Esse achado explica a redução das dimensões fasciculares sem redução no número de fibras mielínicas, descrita anteriormente 42 . Discutimos que as diferenças observadas entre as duas linhagens podem contribuir, pelo menos em parte, para as alterações da função barorreceptora nos SHR.…”

Section: -Nervos E Hipertensãounclassified

“…Nossos dados de- pequenas no nervo isquiático dos SHR. Esse achado corrobora nossas observações prévias 42 , que mostra uma tendência das fibras mielínicas do NDA de SHR apresentarem diâmetros médios menores e histograma deslocado para a esquerda, em comparação com os WKY. Os autores sugerem que, provavelmente, as modificações observadas no nervo isquiático dos SHR dependem do aumento da pressão arterial e não apenas de uma característica intrínseca dos ratos espontaneamente hipertensos.…”

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Ratos Espontaneamente Hipertensos E Neuropatias Periféricas

Fazan¹,

Kalil²,

Alcântara³

et al. 2006

Medicina (Ribeirão Preto)

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Fazan VPS, Kalil ALR, Alcântara ACL, Genari AB, Tavares MR, Rodrigues AR, Salgado HC. Ratos espontaneamente hipertensos e neuropatias periféricas. Medicina (Ribeirão Preto) 2006; 39 (1): 39-50.Resumo: Modelo do Estudo: O presente estudo é uma revisão de literatura sobre o modelo de hipertensão espontânea e as conseqüências da hipertensão para o sistema nervoso periférico, somático e autonômico.Importância do problema: Hipertensão é o principal fator de risco para acidente vascular cerebral e demência vascular, por causar importantes mudanças cerebrovasculares, tornando o cérebro propenso a infartos, microaneurismas e isquemias. As principais mudanças causadas no sistema nervoso central (SNC) pela hipertensão, incluem: diminuição do volume cerebral, aumento no volume dos ventrículos e perda neuronal. Além das alterações no cérebro, a hipertensão causa outros danos que culminam em uma série de alterações patológicas renais e outras doenças, as quais sustentam a elevação da pressão arterial, aumento da freqüência cardíaca, e aumento da resistência vascular periférica. O rato espontaneamente hipertenso (SHR) é reconhecido como um excelente modelo de hipertensão experimental e pode servir como modelo de estudos clínicos da hipertensão essencial humana. Embora esse modelo tenha sido bastante explorado em termos fisiológicos, estudos morfológicos, quando presentes, se limitam aos vasos. Mesmo quando nervos periféricos foram estudados morfologicamente nesses animais, os vasos epineurais, perineurais e endoneurais foram o alvo do estudo. Raros são os estudos que envolvem as fibras nervosas nesse modelo de hipertensão.Comentários: Recentemente, estudamos as alterações do nervo depressor aórtico (NDA) em SHR. Nossos resultados mostraram redução do tamanho das fibras mielínicas e redução do tamanho e número das fibras amielínicas, comparados aos controles normotensos da linhagem Wistar-Kyoto. Outro estudo recente do nosso laboratório mostrou que, embora os níveis pressóricos dos SHR machos, bem como a freqüência cardíaca, sejam muito superiores aos das fêmeas, não há diferença morfológica nos nervos vagos cervicais entre SHR machos e fêmeas. Ainda, fazemos uma descrição morfológica e morfométrica do nervo sural de SHR, fornecendo parâmetros morfológicos para posteriores estudos funcionais.

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Morphology of aortic depressor nerve myelinated fibers in normotensive Wistar–Kyoto and spontaneously hypertensive rats

Cited by 42 publications

References 19 publications

Baroreflex responses to electrical stimulation of aortic depressor nerve in conscious SHR

Baroreflex responses to electrical stimulation of aortic depressor nerve in conscious SHR

Microscopic anatomy of brachial plexus branches in Wistar rats

Ratos Espontaneamente Hipertensos E Neuropatias Periféricas

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