Light microscopic studies of pedicle and early first antler development in red deer (Cervus elaphus)

BACKGROUND: Although it is known that deer antlerogenic potential resides in the periosteum of an antlerogenic region and antler forms through modified endochondral ossification, how a deciduous antler forms histologically through a permanent pedicle from the periosteum has not been reported. METHODS: Histogenesis of the pedicle and the early first antler in red deer was systematically examined using light microscopy techniques. RESULTS AND CONCLUSIONS: At the pre-pedicle stage, the frontal lateral crest (under 5 mm in height) consisted horizontally of antlerogenic periosteum and underlying cancellous bone. Both the cellular layer (3.74 times, P < 0.01) and the fibrous layer of the antlerogenic periosteum were much thicker than those of the margin of the antlerogenic region or the facial periosteum. The crest was formed through intramembranous ossification. When the pedicle began to develop (5-15 mm in height), some discrete clusters of mature chondrocytes appeared in the bony trabeculae, which signified the beginning of the transition of the ossification pattern from the intramembranous to the endochondral. The pedicle consisted of three portions from distal to proximal, periosteum/perichondrium, osseocartilaginous tissue, and osseous tissue. When the pedicle became visible (about 20 mm in height), it consisted of the same three portions as the pedicle initiation stage, but the osseocartilaginous portion was expanded compared to the initiation stage and the cartilaginous proportion increased distally. When the pedicle grew to 25-40 mm in height, continuous cartilaginous trabeculae appeared under the apical perichondrium. The pedicle consisted of four portions from distal to proximal: perichondrium, cartilaginous tissue, osseocartilaginous tissue, osseous tissue. It was formed through endochondral ossification. All these ossification pattern changes could not be seen externally as the overlying integument was characterised by typical scalp skin. When the pedicle grew to about 60 mm in height, antler tissue was visually apparent at the apex as the hair type changed from scalp hair to the velvet-like hair of growing antler. However, this transformation could not be distinguished internally as the inside tissues were all continuous between pedicle and antler. Therefore, the histogenesis of the deer pedicle and the first antler originated from the antlerogenic cells and covered two phases: an internal phase through which pedicle was formed and an external phase which signalled the beginning of antlerogenesis.