Plasticity of primary afferent acid phosphatase expression following rerouting of afferents from muscle to skin in the adult rat.

Abstract

We have examined the possibility that reinnervation of a new peripheral target by primary afferent neurones can alter the histochemical properties of those afferents in the adult rat. The hindlimb sural and gastrocnemius nerves largely supply skin and muscle, respectively. In adult animals these nerves were cut and rejoined to either their own distal stumps (self-anastomosis) or that of the other nerve (cross-anastomosis) and allowed to regenerate for 12-16 weeks to reinnervate an appropriate or inappropriate target. Fluoride-resistant acid phosphatase (FRAP) is a chemical marker found in many unmyelinated afferents. We have determined the FRAP expression in normal and regrown nerves and examined its distribution in the dorsal horn of animals with self- and cross-anastomosed nerves. While normal and self-anastomosed sural nerves stained heavily for FRAP, gastrocnemius nerves showed either no staining or only the occasional fibre. Cross-anastomosed gastrocnemius nerves, now innervating the skin, showed a significant increase in staining, in some cases approaching the levels normally seen in sural nerves. Conversely, cross-anastomosed sural nerves (innervating muscle) showed decreased FRAP staining. In the normal dorsal horn the terminals of FRAP containing afferents form a thin band extending throughout the mediolateral extent of lamina II (Devor and Claman: Brain Res. 190:17-28, '80). One week after axotomy of the sural nerve, FRAP is depleted from its terminals and a gap appears in the normal FRAP staining pattern in the lumbar enlargement of the spinal cord. The new expression of FRAP in cross-anastomosed nerves was also seen in their terminals in the dorsal horn.(ABSTRACT TRUNCATED AT 250 WORDS)