Morphology and Distribution of Motor Neurons in Cat Innervating the Orbicularis Oculi Muscle by Retrograde Horseradish Peroxidase

ABSTRACT

The facial nerve is mainly composed of motor fibers and is distributed to the muscles of facial expressions. In ophthalmology clinics, orbicularis oculi muscle innervated by the facial nerve is involved in spontaneous and voluntary blinking, winking, and more forceful eyelid closure. To understand pathophysiogy of facial nerve palsy due to brain stem lesion involving nucleus, 50% Horseradish Peroxidase (HRP) was injected into nerve stump innervating orbicularis oculi muscle of cat and serial sections of midbrain were studied with light and dark field of light microscope to examine morphology and distribution of the facial nuclei. The HRP-labelled motor neurons were located exclusively within the intermediate division of the ipsilateral facial nuclei and no labelled neurons were found in the contralateral facial nuclei, in the nuclei of the trigeminal nerve, or any other brain stem nuclei. The mean diameter of HRP-labelled motor neurons was 45 micrometer. Most of them were multipolar in shape containing many dendrites. These result suggest that the intermediate division of ipsilateral facial nuclei play an important role in innervating orbicularis oculi muscle.