Histology and ultrastructure of the carotid sinus in experimental hypertension

High-resolution real-time ultrasound of the carotid bifurcation in patients with hyperactive carotid sinus syndrome

The carotid bifurcations and the common carotid arteries of 36 patients with the diagnosis hyperactive carotid sinus syndrome (HCSS) were investigated by continuous wave (CW) Doppler ultrasonography and high-resolution real-time B-scan. Using these non-invasive tests, the functional impact of luminal stenosis and the morphological changes resulting from arteriosclerotic deformities could be established. Significant differences were found in comparison with a reference group of 199 patients with a high risk of arteriosclerosis. In the HCSS group, 5 patients had a stenosis of more than 50% at the origin of the internal carotid artery on both sides, or on one side in combination with large plaques or a complete occlusion on the contralateral side. Seventy-five per cent of patients in the HCSS group, as compared to only 23.5% of the control group, had effective arteriosclerotic changes in the carotid bifurcation on both sides; 4 patients had such changes only unilaterally. Marked additional bilateral arteriosclerotic depositions were detected in the common carotid arteries of 17 patients (47.2%). In 5 patients no arteriosclerotic lesions were detectable in the carotid bifurcations, but marked changes were found in both common carotid arteries. These data indicate that bilateral arteriosclerotic changes in the carotid bifurcations and/or the common carotid arteries represent an important pathophysiological factor for the development of an HCSS.

Structure of rat aortic baroreceptors and their relationship to connective tissue

The ultrastructure of fibres and sensory terminals of the aortic nerve innervating the aorta between the left common carotid and left subclavian arteries was investigated in the rat. This is the region from which most baroreceptor responses are recorded electrophysiologically. The fibres of the aortic nerve enter the adventitia and separate into bundles generally containing one myelinated fibre and four or five unmyelinated fibres of various sizes. The bundles pursue a roughly helical course through the adventitia; when they are close to the aortic media, the myelinated fibre loses its myelin sheath. A complex sensory terminal region is formed, as both the unmyelinated and 'premyelinated' axons become irregularly varicose. The concentration of mitochondria becomes very dense and cytoplasmic deposits of glycogen are observed. Both unmyelinated and premyelinated axons branch, and the unmyelinated axons wind irregularly around the premyelinated axon. The latter may have several loops and small holes. The terminal regions of both types of axon contain clusters of clear 40 nm vesicles. Part of the surface of each terminal region is ensheathed by Schwann cells, but the rest of the axolemma is directly exposed to extracellular connective tissue. There are often several layers of basal lamina around the sensory terminals and parts of the axolemma and Schwann cell membranes are attached to it by fine fibrillar material. The basal laminae are also attached to fibroblasts, fibroblast-like perineurial cells and elastic laminae, and the whole cellular and extracellular system appears to be tightly bound together. No differences between baroreceptors of spontaneously hypertensive and normal rats were found.