Histomorphological characterization of major tissues and organ systems in neotenic Ambystoma mexicanum.

Ambystoma mexicanum has emerged as an important experimental model in regenerative biology due to its remarkable regenerative capacity and neotenic condition. Although histological descriptions of several organs have been previously reported, an integrative characterization of the tissues and organ systems of neotenic axolotls remains limited. To investigate the structural features and cellular organization of axolotl organs, we applied a systematic histological approach with comparative perspectives. Organ samples from neotenic axolotls were processed using conventional histological techniques and analyzed by light microscopy. Fundamental tissues and multiple organ systems, including digestive, cardiorespiratory, urinary, reproductive, tegumentary, nervous, endocrine, and lymphohematopoietic systems, were characterized. The analysis revealed several distinctive features, including cartilage characterized by predominantly isolated chondrocytes, trabeculated myocardial organization, epithelial transitions in the lung, the organization of exocrine pancreatic acini and endocrine islets, distinctive retinal organizational features, and extensive hematopoietic tissue associated with the liver capsule and pericardial serosa. In addition, this study provides detailed histomorphological descriptions of the pancreas and urinary bladder in neotenic axolotls. Overall, the findings demonstrate that while many tissues share organizational similarities with other amphibians and vertebrates, A. mexicanum exhibits particular structural adaptations potentially associated with neoteny and regenerative biology. This work expands the existing histological knowledge of the species and supports future studies in regeneration, developmental biology, comparative anatomy, pathology, and conservation.