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Comparative exploration of the carotid body in domestic animals: morphology, physiology, histology, and pathology

Semzenisi Ecaterina, Dragos Hodor, Ibrahima Mamadou Sall, et al.

Background
The study provides a comprehensive review of the carotid body (CB) in domestic animals, focusing on its morphology, physiology, histology, and pathology. It examines interspecies differences, embryological origins, and physiological roles, with specific attention to the implications of CB pathology, such as its involvement in chemoreception and paragangliomas. The review highlights how dogs serve as valuable models for studying CB neoplasia and its links to multiple endocrine neoplasia (MEN)-like syndromes.

Methods
The study followed PRISMA guidelines, systematically reviewing literature from databases like PubMed, Web of Science, and SpringerLink. The inclusion criteria targeted articles and book chapters on CB structure, function, pathology, and associated conditions, resulting in a dataset of 425 relevant sources after removing duplicates and unrelated results. The anatomical and physiological aspects of the CB across species were analyzed.

Results
-Embryology: CB arises from neural crest cells during embryogenesis, differentiating into Type I (chemoreceptive) and Type II (supportive) cells. Developmental timelines vary across species, with differentiation evident as early as embryonic days 9.5–17.5 in mice and weeks 7–16 in humans.

-Structure: CB consists of lobules of neuroendocrine Type I cells surrounded by capillaries, connective tissue, and nerves. Age-related changes, such as decreased sensitivity and fibrosis, reduce its functionality.

-Function: CB regulates respiratory, cardiovascular, and metabolic homeostasis by sensing blood oxygen, pH, and CO2 levels. Emerging research links it to neurogenic hypertension, obstructive sleep apnea, and neurogenesis, with potential therapeutic applications for Parkinson’s disease.

-Pathology:
-Non-Neoplastic: Hypoxia or hyperoxia-induced hypertrophy and atrophy alter CB size and function.
-Neoplastic: Paragangliomas of the CB and aortic body are frequent in brachycephalic dogs, with potential links to chronic hypoxia and genetic mutations (e.g., SDHD gene).

-Dogs with paragangliomas often exhibit systemic issues like neurogenic hypertension or multiple neoplasias.

Limitations
The review highlights gaps in comparative data for certain species, such as the effects of aging on CB in birds. Genetic studies linking specific mutations to CB tumors in animals remain limited. The authors also note the need for longitudinal studies to better understand the pathophysiology of CB-related diseases.

Conclusions
The carotid body is a pivotal organ in physiological regulation and pathology across species. Its role as a chemoreceptor organ and its involvement in systemic diseases make it a critical subject of study. Dogs, particularly brachycephalic breeds, are valuable models for understanding CB neoplasia. Advances in CB research may lead to novel therapeutic approaches for conditions like hypertension and Parkinson’s disease.