ONGOING ACTIVITY IN NEUROMA AFFERENTS BEARING RETROGRADE SPROUTS

Electrophysiological recordings were made from axons teased from the s ciatic nerve 17-34 mm (mean 26.8 mm) central to a chronic nerve-end ne uroma in adult Tats. 23 fibers (2% of those sampled) appeared to have had a sprout(s) that grew in the retrograde sprouting (central) direct ion for at least this distance. Nine of the 23 (39%) carried spontaneo us ongoing discharge. The parent fiber was myelinated (an A-fiber) in most instances, but unmyelinated (a C-fiber) in some. Thus, following nerve injury, a subset of afferent axons undergo retrograde sprouting, and many of them fire spontaneously. These contribute, along with the afferents whose trapped ends terminate at the injury site, to the ect opic afferent barrage generated in neuromas.