Histochemical studies on cell death and histolysis during regeneration I. Distribution of acid phosphomonoesterase activity in the normal, the regenerating and the resorbing forelimb of the larval spotted salamander, Amblystoma maculatum

Histochemical methods, especially azo dye methods for detecting acid phosphomonoesterase activity were applied to normal, regenerating and denervated, amputated limbs from larval Amblystoma maculatum . Efforts were made to control inactivation of enzymic activity and diffusion of both enzyme and reaction product. “Base‐line” values for enzymic activity were determined for normal limbs. Activity appeared most intense in macrophages, less intense in epidermis and cartilage matrix. Some activity was detected in Schwann cells, peri‐ and endoneurium and muscle fibers form normal limbs. Enzymic activity in regenerating limbs was strongest within macrophages which appeared in increased numbers especially in early stages. Wound tissue showed little increased activity. As the blastema formed, increased enzymic activity was detected in epidermis and within increased numbers of macrophages. Chondrocytes showed increased activity especially during cartilage matrix deposition. Amputated, denervated limbs showed large numbers of active macrophages beneath and within epidermis and along muscle. As regression commenced, areas of cartilage matrix breakdown showed increased enzymic activity but, in general, greatest activity was in macrophages. The various possible roles of acid phosphomonoesterase activity in the specific biological situations dealt with are considered in light of such observations.