The organization of the facial nucleus of the brush-tailed possum (Trichosurus vulpecula).

The facial nucleus of the brush-tailed possum has been studied using Nissl staining and the horseradish peroxidase (HRP) retrograde tracing technique. In Nissl stained sections the nucleus is seen to comprise five distinct subnuclei. Injections of HRP into individual facial muscle groups have shown that these subnuclei reflect the peripheral innervation pattern of efferents from this nucleus. Although in most cases, injection of HRP into a single facial muscle group resulted in the labelling of neurons in more than one facial subnucleus, the following subnuclei were most completely labelled subsequent to intramuscular injection of HRP: the dorsal intermediate subnucleus was labelled with HRP reaction product following injection of m. auricularis anterior; the middle intermediate subnucleus was labelled following injection of the muscle underlying the malar vibrissae; the ventral intermediate subnucleus was labelled following injection of the m. mentalis; the medial subnucleus was labelled following injection of the m. auricularis posterior; the lateral subnucleus was labelled following injection of the m. nasolabialis with HRP. In general there is a mediolateral representation in the facial nucleus of neurons innervating facial muscle groups which are found in anteroposterior succession along the head of the animal. Muscle groups found in dorsoventral succession on the animal are represented dorsoventrally in the facial nucleus.