Comparative Histological Study of the Mammalian Facial Nucleus

Abstract

ABSTRACT. We performed comparative Nissl, Klüver-Barrera and Golgi staining studies of the mammalian facial nucleus to classify the morphologically distinct subdivisions and the neuronal types in the rat, rabbit, ferret, Japanese monkey (Macaca fuscata), pig, horse, Risso's dolphin (Grampus griseus), and bottlenose dolphin (Tursiops truncatus). The medial subnucleus was observed in all examined species; however, that of the Risso's and bottlenose dolphins was a poorly-developed structure comprised of scattered neurons. The medial subnuclei of terrestrial mammals were well-developed cytoarchitectonic structures, usually a rounded column comprised of densely clustered neurons. Intermediate and lateral subnuclei were found in all studied mammals, with differences in columnar shape and neuronal types from species to species. The dorsolateral subnucleus was detected in all mammals but the Japanese monkey, whose facial neurons converged into the intermediate subnucleus. The dorsolateral subnuclei of the two dolphin species studied were expanded subdivisions comprised of densely clustered cells. The ventromedial subnuclei of the ferret, pig, and horse were richly-developed columns comprised of large multipolar neurons. Pig and horse facial nuclei contained another ventral cluster, the ventrolateral subnucleus. The facial nuclei of the Japanese monkey and the bottlenose dolphin were similar in their ventral subnuclear organization. Our findings show species-specific subnuclear organization and distribution patterns of distinct types of neurons within morphological discrete subdivisions, reflecting functional differences. KEY WORDS: facial nucleus, histology, mammal.J. Vet. Med. Sci. 70(4): 367-372, 2008 The facial musculature is responsible for a wide variety of motor movements, including eye blink, nasolabial, buccolabial, perioral, and auricular movements. Those movements are primarily initiated by motor neurons of the facial nucleus. The necessary neuronal pathways for respiration, mastication, and swallowing involve the facial neurons [2,12]. Projection from the facial nucleus to a facial muscular group has been identified in the mouse [9] [17]. Although the mammalian facial musculature shows differences across species, similarities are seen in the projection system from the facial nucleus to the target muscle. The origin of the posterior auricular branch is in the medial subnucleus, while the superior and inferior buccolabialis originate from the lateral and ventrolateral subnuclei of the facial nucleus in the rat [5,19], opossum [1], cat [10], and dog [13]. Those generalized origins, accompanied by the morphologically distinct subdivisions, also exist in other mammals [3,4,15,17]. However, many important species-specific differences are seen in the motor neurons innervating the nasolabial and buccolabial branches [3,5,11,17]. In particular, the facial muscles innervated by the buccolabial branch are important muscular hydrostats for animal food acquisition [11].The facial nucleus is a final outlet for innervati...

Elephant facial motor control

“…( F ) Facial nucleus neuron number in mammals. Species averages are given in black [dots data ( 5 ); triangles data ( 6 )]. In red, data are given for individual African and Asian elephant facial nuclei; filled symbols (cell counts), empty symbols (facial nerve fiber counts), squares (stillborn elephants), dots (adult elephants) (see fig.…”

“…4D, bottom). Such cell size heterogeneity is unusual in mammalian facial subnuclei, which typically encompass neurons of similar size (5,6) trunk innervation may drive this cell-size gradient. In Fig.…”

Functional Morphology of the Nasal Complex in the Harbor Porpoise (Phocoena phocoena L.)

“…This cone is subdivided on both sides into different muscle layers, the texture of which is more or less the same throughout the consecutive layers. Looking closer, it seems likely that single layers of the nasal muscles or parts of these layers are innervated by individual branches or fiber bundles of the facial nerve and that these axons belong to specific neuron populations of the facial motor nucleus in the brain stem as is true for various components of the facial muscles in other mammals (Papez, 1927; Breathnach, 1960; Voogd et al, 1998; Sherwood, 2005; Furutani and Sugita, 2008). This hypothesis has to be tested in the future by careful comparative investigations including ungulates and cetaceans.…”

Etv1 Controls the Establishment of Non-overlapping Motor Innervation of Neighboring Facial Muscles during Development

“…This musculature is thought to have evolved from the jaw-and gill slit-opening muscles of primitive aquatic tetrapods, with sometimes extensive remodeling (Baisden et al, 1987;Guest et al, 2018;Hinrichsen and Watson, 1984) to support adaptations, such as eyelid-closing muscles in terrestrial animals, somatosensory whisking in mammals, and facial expression in humans (Diogo et al, 2008;Grant et al, 2012). The adaptation of the relative sizes of facial subnuclei to specific evolutionary needs in different mammalian species (Furutani and Sugita, 2008) suggests they may serve as organizing centers for facial nerve branches, and multiple studies indicate that individual facial branches map to specific subnuclei to varying extents (Baisden et al, 1987;Courville, 1966;Han et al, 2018;Martin and Lodge, 1977;Papez, 1927;Semba and Egger, 1986;Uemura-Sumi et al, 1986;Wang-Bennett and Coker, 1990). However, a comprehensive map of facial nucleus musculotopic organization in mouse is lacking.…”