Postnatal development of vibrissae motor output following neonatal infraorbital nerve manipulation.

Using the model of infraorbital nerve (IoN) injury, we have studied the role IoN signals have on the developing vibrissal motor system. To this end, in ten rats, the IoN was severed on the day of birth: in five rats, the IoN was repaired to promote axon regeneration (Reinnervated group) while axon regeneration was prevented in the remaining five rats (Deafferented group). In another five rats, the isolated IoN was left intact (Sham group) and still another group of five rats was left untouched (Control group). After these rats had reached adulthood, the compound muscle action potential (MAP) was recorded from the vibrissa muscle and intracortical microstimulation (ICMS)-evoked movements were mapped in the frontal cortex contralateral to the operated side. We found: (i) no difference between Control, Sham and Reinnervated groups in the integrated MAPs and in the size and excitability of the M1 vibrissal representation. (ii) the Deafferented group showed a 42.9% decrease in the integrated MAP plus a 47.2% and 36.9% reduction, respectively, in the size and excitability of the M1 vibrissae representation. We conclude that, during perinatal life, IoN signals regulate the development of both the peripheral and central vibrissal motor system and that IoN reinnervation restores sensory signals able to stabilize normal development of the vibrissal motor system.