LOSS OF PRIMARY AFFERENT NERVE-TERMINALS IN THE BRAIN-STEM AFTER PERIPHERAL-NERVE TRANSECTION - AN ANATOMICAL STUDY IN MONKEYS

In order to investigate the changes in the somatosensory organization that occur after a peripheral nerve injury, a purely sensory nerve (ra dial nerve - superficial branch) was divided in adult monkeys (Macaca fascicularis). The nerve ends were immediately rejoined by an epineura l suturing technique. After 6-21 months the nerve investigated was exp osed to an intra-axonal nerve tracer (horseradish peroxidase conjugate ) in order to label the primary afferent terminals within the cuneate nucleus of the brainstem. The non-transected nerve on the contralatera l side was similarly exposed and served as a control. Terminal labelli ng was seen throughout the cuneate nucleus, mainly in the middle of it s rostro-caudal extension, and in this part it showed a patchy appeara nce superimposed on cell clusters within the pars rotunda. This patter n of distribution was seen both on the experimental and control sides, On the experimental side there was an obvious loss of terminal labell ing within the terminal field as estimated using an image-analysing sy stem: Compared with the contralateral side the median loss (peroxidase activity) was 83% and between 6 and 21 months only minor restoration of the terminal intensity was observed. These results in the primate c onfirm earlier results in the cat that transection and microsurgical r epair of a sensory nerve causes a considerable loss of neurons capable of intraaxonal transport.