Mapping and plasticity of acid phosphatase afferents in the rat dorsal horn.

After peripheral nerve injury in rats, naturally occurring fluoride resistant acid phosphatase (FRAP) disappears from the substantia gelatinosa in that part of the dorsal horn in which the injured nerve afferents terminate. We have taken advantage of this fact to establish the spinal distribution of nerves innervating the skin of the hindlimb. The spinal map of the foot, the distal part of the lower lumbar dermatomes, is in the medial part of the substantia gelatinosa. More proximal skin of the thigh and lower back maps laterally. The zone of disappearance of FRAP after sciatic nerve section did not shrink detectably within the first few months after injury, provided that regeneration of the nerve was prevented. After one year, however, central FRAP activity was at least partially restored. Secondary transection of the sciatic nerve eliminated the new enzyme and transection of neighboring nerves failed to do so. The restored FRAP activity therefore reflects renewed synthesis and transport of enzyme in still injured neurons, and not central sprouting of intact neighboring afferents.