Objective   To investigate the morphological characteristics

quantity and distribution of rabbit limbal stem cells (LSCs).   Methods   Bilateral eyes of 30 healthy adult New Zealand rabbits weighing 2.0-2.5 kg were enucleated and handled by paraffin sections. The morphological characteristic of the limbus of the cornea was observed after Hematoxylin-Eosin staining. LSCs were detected and observed by immunohistochemistry technique (p63-staining) and electron microscopy. The p63-positive LSCs were counted by the BioMias software of image analysis.   Results   ① The limbal epithelial cells were closely aggregated and the layers of the cells were more than the central zone of the cornea. The cells of the basal layer were low columnar or cubic shape and their nuclei were centrally positioned and stained darker blue. The p63-positive LSCs appeared low columnar or cubic shape. Many p63-positive LSCs were located in the bottom of the limbal epithelium. There were a few of p63-positive LSCs in the superficial limbal and the edge of the corneal epithelium

but not in the central corneal epithelium. ② LSCs displayed the ultrastructural features of the primitive cells by transmission electron microscopy. The large nuclei were irregular in shape. Much euchromatin but less heterochromatin could be seen in the nuclei. The heterochromatin was scattered instead of condensation into pieces. Abundant ribosomes could be seen in the little cytoplasm. Other organelles were rarely found. Many gap junctions were seen between the adjacent cells. ③ There were 35.25±8.93 LSCs in the limbal epithelium of each view under high power microscope by analysis with Biomiaspro photo-analysis software.   Conclusion   LSCs show the ultrastructural characteristics of the primitive cells

similar to other stem cells. LSCs are mainly seen in the bottom of the limbal epithelium. A few of LSCs could be seen in the superficial limbal epithelium

but not in the central corneal epithelium.