Vol.99 No.5 contentsPRACTICA OTO-RHINO-LARYNGOLOGICA
Vol. 99 No. 5 May 2006
Histological Quantitative Examination of Viral Neuritis
in Mice with Facial Nerve Paralysis Induced by Herpes
Simplex Virus Type 1 Infection
Hisashi Kohno
(Ehime University School of Medicine)
In this study, mice with facial paralysis induced by herpes simplex type 1 (HSV-1) inoculation were investigated histopathologically to quantitatively analyze the histological changes in the facial nerve in order to elucidate the disease process in the facial nerve of Bell's palsy. The mice were divided into three groups: group 1; no facial palsy seven days after saline injection into the auricle, group 2; facial palsy seven days after HSV-1 injection into the auricle, group 3; facial palsy 14 days after HSV-1 injection into the auricle. All mice were sacrificed, and the facial nerve on the right (inoculated) side was removed for histological examination. Light microscopy of both the labyrinthine and horizontal portion demonstrated that the facial nerve filled the fallopian canal in all three groups. The ratio of interstitial (other than axonal filament) area/whole nerve area was larger in groups 2 and 3 than in group 1. The numbers of axonal filaments were lower in groups 2 and 3 than in group 1. Histogram of the area of axonal filament showed disorder of the larger axonal filaments. However, there were no significant differences between group 2 and group 3 on toluidine blue stained cross sections using new analysis software. These findings suggested: 1) Viral neuritis in the paralyzed nerve caused increased pressure within the fallopian canal, and the nerves became entrapped then edematous. This study provided evidence of increased pressure in the fallopian canal caused by neural edema. 2) The histological findings in groups 2 and 3 suggested that histological changes in the nerves were unrelated to the development of paralysis, and thus it is thought that the main cause of paralysis is demyelination.
Key words : histological examination, facial nerve paralysis, herpes simplex virus type 1, quantitative analysis, Bell's palsy,