An electrophysiological study into the effect of neurotrophin-3 on functional recovery after lingual nerve repair.
OBJECTIVE
Neurotrophin-3 (NT-3) is known to ameliorate central changes that result from peripheral nerve injury and may promote regeneration of myelinated axons. We have assessed its role in the functional recovery of sensory afferents and autonomic efferents after repair of the chorda tympani and lingual nerves in the cat.


METHODS
Six months after entubulation repair, with or without the incorporation of NT-3 at the repair site, the recovery of secretomotor and vasomotor efferents was determined by recording salivary flow from the submandibular gland and temperature changes on the tongue surface, each evoked by stimulation of the repaired nerve. Electrophysiological recordings from the lingual and chorda tympani nerves proximal to the repair allowed characterisation of mechanosensitive, thermosensitive and gustatory afferents.


RESULTS
When compared with data from uninjured control animals, both repair groups showed persistent reductions in conduction velocity, receptor sensitivity, spontaneous discharge, proportion of gustatory and thermosensitive units, and rate of salivary secretion. Comparisons between the two repair groups revealed that in the NT-3 group, salivary secretion rate was lower and the activity evoked in the chorda tympani by gustatory or thermal stimuli was lower, but the spontaneous discharge rate was higher. Mechanosensitive units in the lingual nerve had slower conduction velocities but the mechanoreceptive field size, adaptation time and discharge frequency had increased.


CONCLUSIONS
Despite its known trophic role in the lingual somatosensory system, NT-3 did not enhance functional recovery from injury and had a negative effect on the long-term outcome for sensory and autonomic fibres.
Department of Oral and Maxillofacial Surgery, School of Clinical Dentistry, Claremont Crescent, Sheffield S10 2TA, UK. p.robinson@sheffield.ac.uk
Peter P
PP
Robinson
Julian M
JM
Yates
Keith G
KG
Smith
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D001831:Body Temperature / Q000502:physiology; D002415:Cats; D002814:Chorda Tympani Nerve / Q000293:injuries / Q000503:physiopathology / Q000601:surgery*; D005071:Evoked Potentials / Q000187:drug effects / Q000502:physiology; D008036:Lingual Nerve / Q000503:physiopathology / Q000601:surgery*; D061222:Lingual Nerve Injuries; D009412:Nerve Fibers / Q000502:physiology; D009416:Nerve Regeneration / Q000187:drug effects*; D009431:Neural Conduction / Q000187:drug effects; D009475:Neurons, Afferent / Q000187:drug effects / Q000502:physiology; D009476:Neurons, Efferent / Q000187:drug effects / Q000502:physiology; D019635:Neurosurgical Procedures / Q000379:methods; D020933:Neurotrophin 3 / Q000494:pharmacology*; D020127:Recovery of Function / Q000502:physiology; D012472:Salivation / Q000187:drug effects; D013650:Taste Buds / Q000187:drug effects / Q000503:physiopathology; D014059:Tongue / Q000503:physiopathology; D014276:Trigeminal Nerve / Q000187:drug effects / Q000503:physiopathology
D020933:Neurotrophin 3