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Facial nerve injury produces a latent somatosensory input through recruitment of the motor cortex in the rat

Toldi, József1,2,3; Farkas, Tamás1,2; Perge, János1; Wolff, Joachim-R2

Motor Systems

SHORT-LATENCY effects of unilateral facial nerve transection were studied on neuronal activation evoked in the primary motor cortex (MI) on both sides by vibrissa stimulation in adult rats. In the controls, unilateral trigeminal stimulation evoked activity in the whisker representation of both the contralateral somatosensory cortex (SI) and MI, but never in the ipsilateral MI. Unilateral transection of the facial motoric nerve facilitated evoked responses in the contralateral MI, and induced further neuronal activation (gross potentials and unit activity) in the MI ipsilateral to the stimulation. Since these changes appeared rapidly and could be mimicked by picrotoxin application onto the SI contralateral to the stimulation, they are considered to be based on the disinhibition of preexisting associative and commissural connections, which are unmasked by facial nerve transection.

1Department of Comparative Physiology, József Attila University, H-6701 Szeged, POB 533, Hungary

2Department of Anatomy, University of Goöttingen, Kreuzbergring 36, D-37075 Göttingen, Germany

3Corresponding Author and Address: József Toldi, Department of Comparative Physiology, József Attila University, H-6701 Szeged, POB 533, Hungary

ACKNOWLEDGEMENTS: The present research was supported in part by Hungarian grants from OTKA (T016752, T022280) and FKFP 1195/1997, and by the Deutsche Forschungsgemeinschaft (SFB 406:TPA9).

Received 3 March 1999; accepted 17 May 1999

© 1999 Lippincott Williams & Wilkins, Inc.