KIM, Hyoung Tae; OLSON, Wendy M.; HALL, Brian K.; Dalhousie University, Halifax, N.S.: Effects of hind limb denervation on development of sesamoids in Hymenochirus boettgeri

Heterotopic skeletal elements, including sesamoids, are common in vertebrates but rare in amphibians. The pipid frog Hymenochirus is unusual among anurans in that it has nine (or more) different heterotopic elements, seven of which occur in the hind limb. Sesamoids are most often associated with muscles and tendons, and their development is thought to be mediated by or correlated with function. This study investigated the effects of paralysis (loss of function) on development of sesamoids in the hind limb of Hymenochirus. Complete denervation of the right sciatic nerves was performed at stages 63 and 66; animals were sacrificed after 6-7 (group A) and 12-13 (group B) weeks. Denervation was assessed by degree of paralysis and whole mount nerve staining. Specimens were cleared and double stained with alcian blue and alizarin red for cartilage and bone. Three heterotopic elements — the proximal os sesamoides tarsale (o.s.t.), tibialis anticus and cartilago sesamoides — are absent in all individuals. There were no gross morphological differences between the control and sham groups. In the experimental groups, the posterior lunula, distal o.s.t. and cartilago plantares were present in all individuals. The right fabella was present in 86% of group A, but 100% of group B. Ossification was more advanced in the left (non-paralyzed) limb for both the distal o.s.t. (62% of group A, 7% of group B) and the cartilago plantares (79% of group B). These results suggest that denervation of the hind limb affected both the timing of appearance and the rate of maturation of some heterotopic elements in Hymenochirus. This work was supported by NSERC and Chonbuk National University (Jeonju, South Korea).