Abstract
Ventilatory differences between rat strains and genders have been described but the morphology of the phrenic nerve has not been investigated in spontaneously hypertensive (SHR) and normotensive Wistar-Kyoto (WKY) rats. A descriptive and morphometric study of the phrenic nerves of male (N = 8) and female (N = 9) SHR, and male (N = 5) and female (N = 6) WKY is presented. After arterial pressure and heart rate recordings, the phrenic nerves of 20-week-old animals were prepared for epoxy resin embedding and light microscopy. Morphometric analysis performed with the aid of computer software that took into consideration the fascicle area and diameter, as well as myelinated fiber profile and Schwann cell nucleus number per area. Phrenic nerves were generally larger in males than in females on both strains but larger in WKY compared to SHR for both genders. Myelinated fiber numbers (male SHR = 228 ± 13; female SHR = 258 ± 4; male WKY = 382 ± 23; female WKY = 442 ± 11 for proximal right segments) and density (N/mm²; male SHR = 7048 ± 537; female SHR = 10355 ± 359; male WKY = 9457 ± 1437; female WKY = 14351 ± 1448) for proximal right segments) were significantly larger in females of both groups and remarkably larger in WKY than SHR for both genders. Strain and gender differences in phrenic nerve myelinated fiber number are described for the first time in this experimental model of hypertension, indicating the need for thorough functional studies of this nerve in male and female SHR.
Highlights
Animal studies have provided evidence for genetic transmission of ventilatory traits
No significant differences were observed in mean arterial pressure (MAP) or DAP between spontaneously hypertensive rats (SHR) genders
Animal model SHR, initially bred in the WKY strain, are widely used to study the natural history, genetic determinants and physiopathological alterations of spontaneous hypertension. They are used in studies involving abnormal control of breathing [9] and male SHR have been shown to exhibit increased post-sigh apneas during sleep compared to normotensive controls [21]
Summary
Animal studies have provided evidence for genetic transmission of ventilatory traits. Differences among inbred rat strains [1], as well as differences between inbred and outbred rat strains [2], have been documented during eupnea, hypoxia, hypercapnia, and exercise [2,3]. Some of these differences are associated with genotypic differences localized on specific chromosomes [3]. Despite recent literature reviews focusing on the relationship between breathing and hypertension [10,11], a possible relationship between hypertension and abnormal ventilatory control was never examined before in spontaneously hypertensive rats (SHR), an outstanding hypertensive model. The literature lacks a thorough description of phrenic nerve morphology and morphometry in this experimental model and in the normotensive controls, the Wistar-Kyoto (WKY) rats
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