Limb regeneration in the narrow-mouthed toad, Gastrophryne carolinensis, (Amphibia; Anura; Microhylidae)

Abstract

This paper reports the response of the narrow-mouthed toad, Gastrophryne carolinensis, to forelimb amputation. The amputation wound was closed by epidermal migration within 24 h. Within the 1st week, the epidermis thickened, and a layer of fibrous connective tissue developed between the end of the bone stump and the overlying epidermis. Distal portions of muscle disappeared and their place was taken by fibrous connective tissue. By about 3 weeks postamputation, a blastemalike mass of cells had formed on the end of the stump, consisting of fibroblastlike cells in a matrix of fibrous extracellular material. By 5 weeks, a cartilaginous collar and cap could be seen around the distal end of the bone shaft. Subsequently, the cartilage cap elongated into a distal outgrowth of about 2.5 mm in length by 14 weeks after amputation. At later stages the histological appearance of these heteromorphic regenerates was quite uniform, consisting of a cartilaginous extension of the bone shaft, a layer of fibrous connective tissue surrounding the cartilage, with this in turn covered by the skin. All toads observed at 55 days or later after amputation through the radius-ulna, exhibited heteromorphic regenerative outgrowths.