Cells of origin of the branches of the facial nerve: A retrograde HRP study in the rabbit

The origin of different branches of the facial nerve in the rabbit was determined by using retrograde transport of HRP. Either the proximal stump of specific nerves was exposed to HRP after transection, or an injection of the tracer was made into particular muscles innervated by a branch of the facial nerve. A clear somatotopic pattern was observed. Those branches which innervate the rostral facial musculature arise from cells located in the lateral and intermediate portions of the nuclear complex. Orbital musculature is supplied by neurons in the dorsal portion of the complex, with the more rostral orbital muscles receiving input from more laterally located cells while the caudal orbital region receives innervation from more medial regions of the dorsal facial nucleus. The rostral portion of the ear also receives innervation from cells located in the dorsomedial part of the nucleus, but the caudal aspect of the ear is supplied exclusively by cells located in medial regions. The cervical platysma, the platysma of the lower jaw, and the deep muscles (i.e., digastric and stylohyoid) receive input from cells topographically arranged in the middle and ventral portions of the nuclear complex. It is proposed that the topographic relationship between the facial nucleus and branches of the facial nerve reflects the embryological derivation of the facial muscles. Those muscles that develop from the embryonic sphincter colli profundus layer are innervated by lateral and dorsomedial portions of the nuclear complex. The muscles derived from the embryonic platysma layer, including the deep musculature, receive their input from mid to ventral regions of the nuclear complex.     

Topographical arrangement of hypoglossal motoneurons: an HRP study in the cat

Myotopical localization of hypoglossal motoneurons and representation of the main branches of the hypoglossal nerve within the hypoglossal nucleus were examined in the cat by the HRP method. The hypoglossal nucleus is divided cytoarchitectonically into the ventromedial and dorsolateral divisions; the medial and lateral branches of the hypoglossal nerve are represented respectively in the ventromedial and dorsolateral divisions. The genioglossus motoneurons are located in the ventrolateral part of the ventromedial division, and the geniohyoid motoneurons are in the most ventral part of the ventromedial division. The hypoglossus and styloglossus motoneurons are located in the lateral and dorsolateral parts of the dorsolateral division.     

Somatotopic organization of facial nucleus of rabbit. With particular reference to intranuclear representation of perioral branches of the facial nerve

Somatotopic organization of the facial nucleus was examined in the rabbit by the retrograde HRP (horseradish peroxidase) method; HRP was applied to the peripheral branches of the facial nerve. The facial nucleus is cytoarchitectonically divided into 5 division: the ventromedial, medial, dorsal, lateral and intermediate divisions. The ventromedial division contains neurons supplying the cervical branch. The medial division supplies the anterior auricular branch as well as the posterior auricular branch. The dorsal division is small and contains motoneurons innervating the periorbital regions through the zygomatico-orbital branchlets as well as the anterior auricular branch. Motoneurons innervating the perioral regions are numerous and distributed in the lateral and intermediate division; each of the lateral and intermediate divisions supplies both superior labial and inferior labial branches.     

Correlation of the main peripheral branches of the facial nerve with the cytoarchitectonic subdivisions of the facial nucleus in the guinea pig

Summary Correlation of the main peripheral branches of the facial nerve with morphological subdivisions of the facial nucleus was examined in the guinea pig by the retrograde horseradish peroxidase method. The facial nucleus of the guinea pig was divided cytoarchitectonically into the dorsolateral, lateral, intermediate, medio-intermediate, medial, and ventromedial divisions; the ventromedial division was further divided into the major, dorsal and lateral parts. Six main branches of the facial nerve were identified; the zygomatico-orbital, cervical, posterior auricular, anterior auricular, superior labial, and inferior labial branches. After applying HRP to the main branches of the facial nerve, the pattern of distribution of HRP-labelled neuronal cell bodies within the facial nucleus was examined: the dorsolateral division, dorsal part of the ventromedial division, major part of the ventromedial division, lateral part of the ventromedial division, or medial division contained the cell bodies of respectively the zygomatico-orbital, cervical, posterior auricular, anterior auricular, or superior labial branches, while each of the lateral, intermediate, and medio-intermediate divisions contained the cell bodies of both the superior labial and inferior labial branches.     

Primary afferent fibers in the glossopharyngeal nerve terminate in the dorsal division of the principal sensory trigeminal nucleus: an HRP study in the cat

After applying horseradish peroxidase to the central cut end of the pharyngo-esophageal branch of the glossopharyngeal nerve in the cat, axon terminals labeled transganglionically with the enzyme were found ipsilaterally in the dorsomedial tip regions and ventromedial border regions of the dorsal division of the principal sensory trigeminal nucleus (dorsal Vp), as well as in the solitary, spinal trigeminal and medial cuneate nuclei. The area of termination in the dorsal Vp extended about 200 micron rostrocaudally in the caudal two-thirds of the dorsal Vp.     

Connections between postparotid terminal branches of the facial nerve: An immunohistochemistry study

It has been assumed that connections between the postparotid terminal branches of the facial nerve are purely motor. However, the nature of their fibers remains unexplored. The aim of this study is to determine whether these connections comprise motor fibers exclusively. In total 17 connections between terminal facial nerve branches were obtained from 13 different facial nerves. Choline acetyltransferase antibody (ChAT) was used to stain the fibers in the connections and determine whether or not all of them were motor. All connections contained ChAT positive and negative fibers. The average number of fibers overall was 287 (84–587) and the average proportion of positive fibers was 63% (37.7%–91.5%). In 29% of the nerves, >75% of the fibers were ChAT+ (strongly positive); in 52.94%, 50%–75% were ChAT+ (intermediately positive); and in 17.65%, <50% were ChAT+ (weakly positive). Fibers traveling inside the postparotid terminal cranial nerve VII branch connections are not exclusively motor.     

Ultrastructural studies of the nucleus ambiguus in cat and monkey following injection of HRP into the vagus nerve

Summary The fine structure of retrogradely labelled neurons in the nucleus ambiguus (NA) has been examined in cat and monkey (Macaca fascicularis) following injections of horseradish peroxidase (HRP) into the vagus nerve. Many retrogradely labelled neurons were observed in the NA although unlabelled neurons were also present within the boundaries of the NA as identified by the distribution of retrogradely labelled cells. In both species a wide range of sizes of labelled neurons (20–60 m in long axis) was observed from rostral to caudal levels of the NA. Large labelled neurons were generally oval or spindle-shaped while smaller neurons were oval in cross-section. Unlabelled neurons observed among labelled NA neurons tended to be smaller on average than the labelled neurons and ranged in size from 15 to 30 m in long axis. The unlabelled neurons typically had nuclei which were more invaginated than those of the labelled neurons.Quantitative analyses of the synaptic organization in the NA revealed high proportions of terminals containing round vesicles and making asymmetrical or symmetrical contact with the somata in both monkey and cat. Terminals containing pleomorphic vesicles and making symmetrical contact with somata were slightly less numerous. Retrogradely labelled neurons exhibited a positive correlation between the size of neuron and density of synapses on the surface. There tended to be a greater synaptic density on monkey NA neurons than on cat NA neurons of comparable size.     

Anatomical study of the zygomatic and buccal branches of the facial nerve: Application to facial reanimation procedures

The facial nerve is responsible for any facial expression channeling human emotions. Facial paralysis causes asymmetry, lagophthalmus, oral incontinence, and social limitations. Facial dynamics may be re‐established with cross‐face‐nerve‐grafts (CFNG). Our aim was to reappraise the zygomaticobuccal branch system relevant for facial reanimation surgery with respect to anastomoses and crossings. Dissection was performed on 106 facial halves of 53 fresh frozen cadavers. Study endpoints were quantity and relative thickness of branches, correlation to “Zuker's point”, interconnection patterns and crossings. Level I and level II branches were classified as relevant for CFNG. Anastomoses and fusion patterns were assessed in both levels. The zygomatic branch showed 2.98 ± 0.86 (range 2–5) twigs at level II and the buccal branch 3.45 ± 0.96 (range 2–5), respectively. In the zygomatic system a single dominant branch was present in 50%, two co‐dominant branches in 9% and three in 1%. In 66% of cases a single dominant buccal twig, two co‐dominant in 12.6%, and three in 1% of cases were detected. The most inferior zygomatic branch was the most dominant branch (P = 0.003). Using Zuker's point, a facial nerve branch was found within 5 mm in all facial halves. Fusions were detected in 80% of specimens. Two different types of fusion patterns could be identified. Undercrossing of branches was found in 24% at levels I and II. Our study describes facial nerve branch systems relevant for facial reanimation surgery in a three‐dimensional relationship of branches to each other. Clin. Anat. 32:480–488, 2019. © 2019 Wiley Periodicals, Inc.     

面神经局部缺血对面神经及面神经核的影响

目的　探讨面神经局部缺血对面神经及面神经核的影响,为临床腮腺切除术提供参考。方法选用家兔,采用同体对照的方法,模拟人腮腺切除手术。实验侧于手术显微镜下,游离面神经并破坏其外血管系,切除腮腺。术后家兔存活4周,观察以下指标：分别检测家兔实验侧和对照侧面神经颊支的传导速度、CMAP波幅和潜伏期;取双侧茎乳孔外面神经干,透射电镜下观察面神经超微结构的变化;取双侧面神经核,Western Blotting法检测面神经核乙酰胆碱转移酶（CHAT）表达的变化,PCR-ELISA法观察面神经核端粒酶活性的变化。 结果　实验侧面神经颊支的传导速度明显低于对照侧、潜伏期明显长于对照侧、波幅明显低于对照侧（P＜0.01,P＜0.05）。实验侧面神经超微结构发生明显变化,以轴索变性为主,包括轴索内微丝增生、断裂,线粒体肿胀、嵴断裂,变性轴索溶解等。实验侧面神经核CHAT的表达和端粒酶活性明显低于对照侧（P＜0.01,P＜0.05）。 结论　游离面神经破坏其外血管系切除腮腺,可导致面神经超微结构发生明显改变、面神经传导功能下降,进而导致面神经核神经元合成乙酰胆碱的含量下降、神经元凋亡增加;提示临床腮腺切除时,应尽可能保护面神经外血管系,以减少面瘫的发生。     

Identification of the inferior salivatory nucleus in the cat as studied by HRP bathings of the transected glossopharyngeal nerve root

The localization of the inferior salivatory nucleus that gives rise to parasympathetic fibers to the parotid gland was identified by means of horseradish peroxidase (HRP) method in the cat. The inferior salivatory nucleus does exist in the medulla oblongata and is situated in the dorsal part of the reticular formation. The nucleus is well-circumscribed caudally but rostrally the nucleus becomes scattered within the wide area of the dorso-lateral reticular formation. The inferior salivatory nucleus, demonstrated by the present study is composed of medium-sized multipolar neurons with well-developed slender dendrites and densely stained Nissl substance.     

Brain stem neurons projecting to neocortex: A HRP study in the cat

Summary The cortical projections of the brain stem were investigated in detail in the cat by means of the horseradish peroxidase (HRP) retrograde axonal transport. Most of the cells providing ascending fibers to the neocortex were located in the pons (locus coeruleus and related structures, central gray substance, dorsal tegmental nucleus, raphe nuclei, reticular nuclei); labeled neurons were also identified in the mesencephalon, mainly in the periaqueductal gray and in the nucleus linearis rostralis. These projections, and particularly the pontine fibers, were diffusely distributed throughout the cerebral cortex.The results are compared with the data previously obtained by the use of anterograde and retrograde tracing techniques.     

Direct projections from the Ediger-Westphal nucleus to the cerebellum and spinal cord in the cat: An HRP study

A vast majority of neurons in the Edinger-Westphal nucleus (EW), consisting of the anteromedian nucleus (AM) and the posterior part of the EW (EWp: so-called visceral nucleus), were labeled retrogradely with horseradish peroxidase (HRP) injected into the cerebellum in the cat. The pattern of distribution of these HRP-labeled EW neurons was similar to that of EW neurons labeled with HRP injected into the spinal cord. A tendency, however, was noted that EW neurons located in the nuclear areas close to the midline remained unlabeled in the cats injected with the enzyme into the spinal cord. It was assumed that some EW neurons might contribute fibers by way of axon collaterals both to the cerebellum and to the spinal cord. Possible function of the EW as a relay nucleus for retinal inputs to the cerebellum and the spinal cord was discussed.     

Fiber contribution from the mesencephalic nucleus of the trigeminal nerve to the trochlear nerve in the cat: A histological quantitative study

The fiber connections between the trigeminal mesencephalic nucleus and tract and the trochlear nerve root of 15 cats were examined after silver impregnation of the pontomescencephalic region of the brains. The results revealed that: (a) some of the mesencephalic root fascicles join the trochlear root, (b) some of the mesencephalic root cells contribute their processes to the trochlear root, and (c) some mesencephalic cells are found amidst the fibers of the trochlear nerve during its intrabulbar course. The fibers of the trochlear nerve were counted at certain preselected sites before and after crossing the mesencephalic nucleus. The statistical data obtained indicated that the trigeminal mesencephalic root contributes 4–10% of the fibers of the trochlear nerve, before it crosses the mesencephalic nucleus.     

Changes in expression of prosaposin in the rat facial nerve nucleus after facial nerve transection

Prosaposin is the precursor of saposins A, B, C and D, which are activators of sphingolipid hydrolases. In addition, unprocessed prosaposin functions as a neurotrophic factor in the central and peripheral nervous systems by acting to prevent neuronal apoptosis, to elongate neurites and to facilitate myelination. In this study, the expression pattern of prosaposin in the facial nerve nucleus after facial nerve transection was examined by immunohistochemistry and in situ hybridization. Prosaposin immunoreactivity in the neurons on the operated side facial nerve nucleus showed a biphasic pattern: it was significantly increased on day 3 after transection, decreased dramatically on day 7, started to increase gradually on day 14 and reached another peak on day 21 after transection. Significant increases in the levels of prosaposin mRNA were identified in the neurons on the operated side, suggesting that prosaposin was synthesized vigorously by the neurons themselves in the case of facial nerve transection. The diverse changes in prosaposin immunoreactivity during the process of facial nerve regeneration may reflect the diverse neurotrophic activities of prosaposin in facial motoneurons.     

Anatomic landmarks of the buccal branches of the facial nerve

The aim of this study was to classify the buccal branches of the facial nerve in relation to the parotid duct and its relevance to surgical procedures such as rhytidectomy and parotid gland surgery. In this study, 30 cadaver heads (60 specimens) were dissected. The vertical and horizontal relationships between the buccal branches of the facial nerve and tragus, and parotid duct were recorded and analyzed. The buccal branches of the facial nerve were classified into four types: Type I: a single buccal branch of the facial nerve at the point of emergence from the parotid gland and inferior to the parotid duct. Type II: a single buccal branch of the facial nerve at the point of emergence from the parotid gland and superior to the parotid duct. Type III: buccal and other branches of the facial nerve formed a plexus. Type IV: two branches of buccal branch; one superior and one inferior to the duct at the point of emergence from the parotid gland. The buccal branches of the facial nerve are very vulnerable to surgical injury because of its location in the midface. For this reason, the surgeons who are willing to operate on this area should have a true knowledge about the anatomy of these branches.