The morphogenesis of the renal plexus: Renal artery and sympathetic fibers

Unraveling Renal Arteries Morphogenesis from Tridimensional Human Embryos Reconstruction

BACKGROUND

During human morphogenesis, the definitive kidneys derive from the metanephros during Carnegie Stage 14 to 23. The pronephros and the mesonephros develop previously and successively to finally lead to the formation of the urinary tract. Renal vascularization, first described in 1912 by Félix using a "ladder theory" model, is highly variable and current available morphogenesis descriptions do not explain all reported anatomical variations. The aim of this work was to study the morphogenesis of the human metanephros and its vascularization by three-dimensional reconstructions of human embryos.

METHODS

Histological sections of 23 human embryos from the Carnegie Collection and 5 human embryos from the French collection (Carnegie stages 14 to 23) were completely digitalized and reconstructed in three dimensions using specific softwares and then analyzed by descriptive method using manual annotation.

RESULTS

In all studied embryos, the mesonephric arteries did not reach the metanephros irrespective to the position of the metanephros during its cranial ascent. Before the end of the cranial metanephros migration (15 embryos), at the level of the aorto-iliac bifurcation, a "primitive" vascularization was shown in 9 of them. The renal artery originated from the primitive iliac arteries for 8 embryos and from the inferior mesenteric artery in one embryo. Further, a capillary cluster emerging from the lateral wall of the aorta and extending toward the metanephros was found in 2 embryos (Carnegie stages 21 and 22). This may correspond to a phenomenon of neoangiogenesis responsible of the definitive renal artery.

CONCLUSIONS

The present study reported the morphogenesis of human renal arteries between Carnegie stages 14 and 23 using an original method of tridimensional computerized reconstructions of historical human embryos. Some original findings, in contradiction with the original Felix's description, may explain the most frequently reported anatomical variations.

Innervation of the developing kidney in vivo and in vitro

Within the adult kidney, renal neurites can be observed alongside the arteries where they play a role in regulating blood flow. However, their role and localization during development has so far not been described in detail. In other tissues, such as the skin of developing limb buds, neurons play an important role during arterial differentiation. Here, we aim to investigate whether renal nerves could potentially carry out a similar role during arterial development in the mouse kidney. In order to do so, we used whole-mount immunofluorescence staining to identify whether the timing of neuronal innervation correlates with the recruitment of arterial smooth muscle cells. Our results show that neurites innervate the kidney between day 13.5 and 14.5 of development, arriving after the recruitment of smooth muscle actin-positive cells to the renal arteries.

Regions of the human renal artery: histomorphometric analysis

The renal artery is frequently involved in the pathogenesis of vasculorenal diseases, and it is a target in kidney surgery and therapeutic techniques for refractory hypertension. However, few detailed structural studies on the human renal artery have been conducted. Using histocytochemistry, immunohistochemistry, and quantitative image analysis, the wall thickness, structure, smooth muscle cells, extracellular matrix, and proportion of elastic tissue in the tunica media of main human renal arteries were used estimated. Ninety-six tissue samples were collected from sections of the right and left main renal arteries. The results showed that the renal artery changed from an elastic vessel in its proximal segment to a muscular artery in its distal part. A critical characteristic of the renal artery was the presence of longitudinal smooth muscle cell formations in the tunica adventitia of middle and distal segments but not in the proximal part of the artery. In addition, the tunica adventitia of the renal artery showed a rich vascularization and the presence of numerous nerves profiles. The artery's regional structural and morphometric features explain that a particular arterial pathology is more frequent in a specific vessel sector than in others. In addition, those characteristics could determine a different therapeutic response attending to the arterial sector.

Brain-heart communication in health and diseases

Tight connections between the brain and heart have attracted a considerable amount of attention. This review focuses on the anatomical (extrinsic cardiac autonomic nervous system and intrinsic cardiac autonomic nervous system) and functional (neuroendocrine-heart axis and neuroimmune-heart axis) connections between the brain and heart, the linkage between central nervous system diseases and cardiovascular diseases, the harm of sympathetic hyperactivity to the heart, and current neuromodulation therapies. Depression is a comorbidity of cardiovascular diseases, and the two are causally related. This review summarizes the mechanisms and treatment of depression and cardiovascular diseases, providing theoretical evidence for basic research and clinical studies to improve treatment options.

Ectopic sympathetic ganglia cells of the ventral root of the spinal cord: an anatomical study

The sympathetic trunk ganglia contain the cell bodies of neurons. However, some patients who undergo sympathectomy can develop compensatory hyperhidrosis. To evaluate for ectopic pathways, the present anatomical study was performed. Ten adult cadavers underwent dissection of the spinal canal and removal of randomly selected ventral roots, which were submitted for histological analysis. Random ventral root samples were taken from cervical, thoracic, and lumbosacral regions in each specimen. Each histological section was then analyzed and the presence or absence of sympathetic cells documented for level and position within the ventral root. Of all samples, a sympathetic nerve cell was found in 80% of ventral roots. At least one sympathetic cell was found in these 80%. Most sympathetic cells were found in the proximal one-third of the ventral root. Such cells were found at all spinal levels and no specific level within a vertebral region was found to house a greater concentration of these cells. No statistical significance was found when comparing sides or sex. Our study confirmed that sympathetic cells exist in the majority of human ventral roots. Such data might better explain various clinical presentations and postoperative complications/findings.