title: Reduced cholinergic and glutamatergic synaptic input to regenerated motoneurons after facial nerve repair in rats: potential implications for recovery of motor function.
abstract: Deafferentation of motoneurons after facial nerve injury is a well-documented phenomenon but whether synaptic inputs to facial motoneurons are completely restored after reinnervation is unknown. Here, we tested the hypothesis that deficits in motor performance after transection/suture of the facial nerve (facial-facial anastomosis, FFA) in adult rats are associated with incomplete recovery of synaptic inputs. At 2 months after FFA, we found, in congruence with previous results, that the amplitude of whisking had recovered to only 31 % of control (sham operation). In the same FFA-treated rats, estimates of number of chemically defined synaptic terminals in the facial nucleus by immunohistochemistry and stereology showed a significant loss, compared with sham controls, of glutamatergic terminals (-26 %) and cholinergic perisomatic boutons (-31 %), but not inhibitory (GABA/glycinergic) terminals (-14 %). Synaptic deficits were accompanied by persistent microgliosis in the facial nucleus but soma area, dendritic arbor volume, and total number of motoneurons were normal. Correlation analyses revealed significant co-variations of whisking amplitude with number of glutamatergic and cholinergic synapses. Compared with 2 months, analyses of animals at 4 months after FFA showed no attenuation of the functional deficit and structural aberrations with one exception, increase of inhibitory terminal numbers beyond control level (+11 %) leading to further reduction of the excitatory/inhibitory terminal ratio. We suggest that deficits in motoneuron innervation in the regenerated facial nucleus-reduced glutamatergic and cholinergic input and reduced excitatory/inhibitory terminal ratio-could attenuate the motor output and, thus, negatively impact the functional performance after facial nerve regeneration.
authors.affiliation: Department of Otorhinolaryngology, University Hospital Jena, Lessingstrasse 2, 07740, Jena, Germany.
authors.forename: Abdulrahman
authors.initials: A
authors.lastname: Raslan
authors.forename: Philipp
authors.initials: P
authors.lastname: Ernst
authors.forename: Marlen
authors.initials: M
authors.lastname: Werle
authors.forename: Heike
authors.initials: H
authors.lastname: Thieme
authors.forename: Katja
authors.initials: K
authors.lastname: Szameit
authors.forename: Mira
authors.initials: M
authors.lastname: Finkensieper
authors.forename: Orlando
authors.initials: O
authors.lastname: Guntinas-Lichius
authors.forename: Andrey
authors.initials: A
authors.lastname: Irintchev
mesh_terms: D000818:Animals; D005145:Face / Q000294:innervation; D005154:Facial Nerve / Q000601:surgery*; D020220:Facial Nerve Injuries / Q000503:physiopathology*; D008297:Male; D009046:Motor Neurons / Q000502:physiology*; D009416:Nerve Regeneration / Q000502:physiology*; D017729:Presynaptic Terminals / Q000502:physiology; D017208:Rats, Wistar; D020127:Recovery of Function / Q000502:physiology; D013569:Synapses / Q000502:physiology*