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171.
172.
The behavior of neural crest cells from various origins and of neural crest derivatives were investigated when they were transplanted into a host embryo as supernumerary crest structures. They were inserted into the dorsal trunk between the neural primordium and the somites. In this situation the grafted cells (of quail origin) migrated in the chick host and could be recognized any time after the graft by the structure of their nucleus. After a migration phase, they became exclusively localized in the various sites of arrest of neural crest cells and were found mixed with host crest cells. Their localizations varied according to their origin and their developmental stages at grafting time. Cells of autonomic ganglia (ciliary and sympathetic) had a definitive localization restricted to the autonomic structures of the host. They differentiated into adrenergic or cholinergic cells irrespective of their sympathetic or parasympathetic origin, according exclusively to their localization in the host. They were practically never found in the host dorsal root ganglion (DRG). In contrast, the developmental potentialities of DRG cells are broader and, as far as peripheral nervous system potentialities are concerned, they behave like neural crest cells, i.e., they gave rise to both sensory and autonomic neurones plus adrenomedullary cells. A model for cell line segregation from the neural crest is proposed. Several aspects of this model need further analysis, others are based on well-established experimental data. 相似文献
173.
Annemijn Vis Jan CAM Lammers Roel de Vroege Martijn MJ van Nieuwburg Marlijn S Jansen Joyce MJ Visser Bart Meuris Paul F Gründeman Jolanda Kluin 《Comparative medicine》2021,71(3):235
Sheep are a commonly used and validated model for cardiovascular research and, more specifically, for heart valve research. Implanting a heart valve on the arrested heart in sheep is complex and is often complicated by difficulties in restarting the heart, causing significant on-table mortality. Therefore, optimal cardioprotective management during heart valve implantation in sheep is essential. However, little is known about successful cardioprotective management techniques in sheep. This article reports our experience in the cardioprotective management of 20 female sheep that underwent surgical aortic valve replacement with a stented tissue-engineered heart valve prosthesis. During this series of experiments, we modified our cardioprotection protocol to improve survival. We emphasize the importance of total body hypothermia and external cooling of the heart. Furthermore, we recommend repeated cardioplegia administration at 20 min intervals during surgery, with the final dosage of cardioplegia given immediately before the de-clamping of the aorta. To reduce the number of defibrillator shocks during a state of ventricular fibrillation (VF), we have learned to restart the heart by reclamping the aorta, administering cardioplegia until cardiac arrest, and de-clamping the aorta thereafter. Despite these encouraging results, more research is needed to finalize a protocol for this procedure.Sheep are a commonly used and well-validated model for cardiovascular research, particularly for heart valve research, as blood pressure, heart rate, cardiac output, and intracardiac pressures are similar between sheep and humans. Sheep are particularly useful for heart valve research because observable changes in implanted heart valve bioprostheses that would take several years to develop in humans are apparent after only a few months in sheep.3,11 This feature allows the ovine model to provide relevant and important information about heart valve prostheses in a relatively short time span. The first preclinical step in developing novel heart valves is to test the valve in the pulmonary position in sheep. This surgical technique is relatively easy, as the procedure can be performed on a beating heart in a low-pressure circulation. However, aortic valve surgery is the most frequently performed valvular surgical intervention in human patients.12 Thus, an important next step is to prove the clinical applicability of a new valve by testing the valve in-vivo in the aortic position in an animal model. In contrast to pulmonary valve replacement, aortic valve replacement must be performed on an arrested heart, which makes the surgical procedure significantly more complex. The sheep is a difficult model for aortic valve replacements due to its narrow annulus, short distance between the annulus and coronary ostia, a short ascending aorta, and difficulty in de-airing of the heart prior to suturing the aortotomy.19 Consequently, high on-table mortality rates, ranging from 9% to 33%, have been reported.1,18,21,24 Furthermore, the incidence of mortality during the first 30 d after surgery, directly related to the surgical procedure, is often high, ranging from 17% to 50%.1,2,16,18,21 Therefore, optimizing cardioprotective strategies during surgery would improve postoperative survival. However, little is known about protective strategies in sheep. In the current series of experiments, we implanted stented, tissue engineered, aortic heart valve prostheses in 20 adult domestic sheep and developed cardioprotective techniques to increase survival rates. In this observational study, we share our experience and insights regarding cardioprotective management to potentially improve the outcome of future surgeries that require an arrested heart in sheep. 相似文献