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

Reports on the morphology of the baroreceptor terminal of spontaneously hypertensive rats (SHR) did not demonstrate any difference when compared to the axonal terminal of normotensive rats. Although several studies reporting baroreceptor terminal and blood vessel wall morphology have been carried out to better understand the baroreceptor function and resetting to hypertensive levels, there are no reports examining the morphology of the fibers of the aortic depressor nerve (ADN) in hypertensive models. Therefore, the objective of the present study was to investigate the morphological aspects of SHR ADN compared to Wistar-Kyoto (WKY) rats. Before the morphologic study, the nerves were isolated and the pressure-nerve activity curve was determined for each ADN. SHR exhibited an increase in the threshold pressure for baroreceptor activation, a rightward shift in the pressure-nerve activity curve with decreases in slope and maximum activity. Semithin (0.3 to 0.5 microm thick) sections of the proximal (close to the nodose ganglion) and distal (close to the aortic arch) segments of the ADN were analyzed by light microscopy. A morphometric study of the nerve fascicles and myelinated fibers was performed. Comparison between proximal and distal segments of the two strains revealed that the ADN of WKY rats were consistently larger. All morphometric parameters studied in myelinated fibers and their respective axons were smaller in SHR. The area of the myelin sheath was comparatively larger in WKY rats. These data show morphologic differences between the ADN of SHR and WKY rats, which may explain, at least in part, the decreased slope and maximum activity of the pressure-nerve activity curve observed with the baroreceptor resetting in SHR.

[1]  B. Andrew.  A laryngeal pathway for aortic baroceptor impulses , 1954, The Journal of physiology.

[2]  J M Krauhs,et al.  Structure of rat aortic baroreceptors and their relationship to connective tissue , 1979, Journal of neurocytology.

[3]  K. Okamoto,et al.  Modified characteristics of the aortic baroreceptor activities in the spontaneously hypertensive rat. , 1970, Japanese circulation journal.

[4]  R. Friede,et al.  Relation between the number of myelin lamellae and axon circumference in fibers of vagus and sciatic nerves of mice , 1967, The Journal of comparative neurology.

[5]  Thomas Pk,et al.  The connective tissue of peripheral nerve: an electron microscope study. , 1963 .

[6]  M. Andresen,et al.  Differential frequency-dependent reflex integration of myelinated and nonmyelinated rat aortic baroreceptors. , 1998, American journal of physiology. Heart and circulatory physiology.

[7]  J. Michael Schro¨der,et al.  Altered ratio between axon diameter and myelin sheath thickness in regenerated nerve fibers. , 1972 .

[8]  A. Brown,et al.  A Comparison of Aortic Baroreceptor Discharge in Normotensive and Spontaneously Hypertensive Rats , 1976, Circulation research.

[9]  J. H. Green,et al.  Baroceptor Function in Chronic Renal Hypertension , 1956, Circulation research.

[10]  W. Rushton.  A theory of the effects of fibre size in medullated nerve , 1951, The Journal of physiology.

[11]  F. Abboud,et al.  Mechanisms of resetting of arterial baroreceptors: an overview. , 1988, The American journal of the medical sciences.

[12]  I. A. Boyd,et al.  Scaling factor relating conduction velocity and diameter for myelinated afferent nerve fibres in the cat hind limb. , 1979, The Journal of physiology.

[13]  H. Aars.  Aortic baroreceptor activity in normal and hypertensive rabbits. , 1968, Acta physiologica Scandinavica.

[14]  M. S. Devanandan.  A study of the myelinated fibres of the aortic nerve of cats , 1964, The Journal of physiology.

[15]  S. C. Wang,et al.  Modification of aortic barorecptor resetting in the spontaneously hypertensive rat. , 1976, The American journal of physiology.

[16]  J. Angell-James,et al.  Characteristics of Single Aortic and Right Subclavian Baroreceptor Fiber Activity in Rabbits with Chronic Renal Hypertension , 1973, Circulation research.

[17]  E. M. Schmidt,et al.  The myelinated fibers in the aortic nerve of the swine , 1967, The Anatomical Record.

[18]  W. Talman,et al.  ALTERATION OF BARORECEPTOR AND CHEMORECEPTOR REFLEXES IN SPONTANEOUSLY HYPERTENSIVE RATS , 1995, Clinical and experimental pharmacology & physiology. Supplement.

[19]  E. Krieger,et al.  Neural control in experimental renal hypertension. The role of baroreceptor and splanchnic fibers. , 1966, Acta physiologica latino americana.

[20]  H. Salgado,et al.  A descriptive and quantitative light and electron microscopy study of the aortic depressor nerve in normotensive rats. , 1997, Hypertension.

[21]  H. Salgado,et al.  Resetting of the baroreceptors. , 1982, International review of physiology.

[22]  M. Andresen,et al.  Relationship of Aortic Wall and Baroreceptor Properties during Development in Normotensive and SpontaneouslyHypertensive Rats , 1978, Circulation research.