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PubMed2006

The effect of beta-bungarotoxin, or geniculate ganglion lesion on taste bud development in the chick embryo.

Chick taste bud (gemmal) primordia normally appear on embryonic day (E) 16 and incipient immature, spherical-shaped buds at E17. In ovo injection of beta-bungarotoxin at E12 resulted in a complete absence of taste buds in lower beak and palatal epithelium at developmental ages E17 and E21. However, putative gemmal primordia (solitary clear cells; small, cell groupings) remained, lying adjacent to salivary gland duct openings as seen in normal chick gemmal development. Oral epithelium was immunonegative to neural cell adhesion molecule (NCAM) suggesting gemmal primordia are nerve-independent. Some NCAM immunoreactivity was evident in autonomic ganglion-like cells and nerve fibers in connective tissue. After unilateral geniculate ganglion/otocyst excision on E2.5, at developmental ages E18 and posthatching day 1, approximately 12% of surviving ipsilateral geniculate ganglion cells sustained approximately 54% of the unoperated gemmal counts. After E18, proportional stages of differentiation in surviving developing buds probably reflect their degree of innervation, as well as rate of differentiation. Irrespective of the degree of geniculate ganglion damage, the proportion of surviving buds can be sustained at the same differentiated bud stage as on the unoperated side, or may differentiate to a later bud stage, consistent with the thesis that bud maturation, maintenance, and survival are nerve-dependent.

Animals↗
PubMed1999

Neurotrophin receptors in the geniculate ganglion.

We examined the distribution of the high affinity neurotrophin receptors (trkA, trkB, and trkC) in the rat geniculate ganglion. Previous work had shown that during early (prenatal) development, trkB and its two ligands, BDNF and NT-4/5, were most important for survival of almost all neurons. Using nested polymerase chain reaction (PCR), we showed that trkA, trkB, and trkC transcripts were expressed, and the mRNAs for trkB and trkC were more abundant than that for trkA. We modified and improved the method for direct reverse transcription in situ PCR and localized trkB mRNA in approximately one third of the neurons in the ganglion. Immunohistochemical data confirmed that approximately the same fraction of neurons was immunoreactive with antibody vs. trkB, and an approximately equal fraction was immunoreactive with trkC antibody. These results are consistent with the notion that both BDNF/trkB and NT-3/trkC play important roles in maintenance of the geniculate ganglion neurons and possibly the peripheral taste system in the young postnatal rat.

Animals↗
PubMed1997

Identification of the HSV-1 genome by "Dot Blot hybridization" in the geniculate ganglion of rabbits.

Herpes simplex Virus type 1 (HSV-1) was inoculated into 48 rabbits by 3 different routes: 10 rabbits were dosed by mouth, 18 rabbits injected in the tongue and 14 injected in the perineurium of the facial nerve at its entrance into the stylomastoid foramen. Some of the animals were killed after a week and others after three weeks. Facial palsy was produced in none of the cases. Seroconversion was demonstrated in the peripheral blood of 100% of the inoculated animals. Cultures of macerate of the facial nerve and geniculate ganglion, as well as of the ipsilateral medulla, were negative. DNA from HSV-1 was found by "Dot Blot hybridization" technique in 30% of the macerates of the geniculate ganglion and facial nerve and in 60% of the medulla macerate in those animals killed after one week and in 0% of both samples in those killed in the third week. The fact that the HSV-1 could be isolated in the geniculate ganglion of the facial nerve continues to support the possibility of this virus as the causal agent for facial palsy, either as a single disease or associated with other symptoms.

Animals↗
PubMed1980

Quantitative and histomorphological studies on the geniculate ganglion of the facial nerve in man.

The human geniculate ganglion was studied histologically and quantitatively. It appeared pyramidal in shape. The mean diameter of the side of the triangle constituting its base was 1,050 micrometer and its mean height 1,800 micrometer; the volume of the ganglion was 26 X 10(7) micrometer 3. The ganglionic cells were arranged in clusters with longitudinally extending bundles of nerve fibres in between. At the apex of the ganglion compact neurons were delineated from those in the rest of the ganglion by a bundle of nerve fibres. Moreover, scattered solitary nerve cells were met with between fibres of the greater petrosal and the chorda tympani nerves. The mean neuronal population was 1,070, the mean cell volume 11,913 micrometer 3, the cell territory 242,990 micrometer 3 and the volume of the intercellular space 231,077 micrometer 3. Extraganglionic vessels approximated the ganglion perpendicular to its long axis, while further intraganglionic vessels extended in a direction parallel to the long axis of the ganglion and vertical terminal ramifications formed dense vascular channels around the capsule of the nerve cells. The significance of that pattern of blood supply was discussed.

Chorda Tympani Nerve↗
PubMed2002

A rapid and safe middle fossa approach to the geniculate ganglion and labyrinthine segment of the facial nerve.

The middle fossa approach provides neurotologic surgical access to lesions of the geniculate ganglion and the labyrinthine portion of the facial nerve as well as to the internal acoustic canal, and therefore helps preserve cochlear function. Although this approach is widely used, surgeons are still not certain which anatomic landmarks are best to locate the facial nerve and internal acoustic canal without causing labyrinthine damage. The purpose of this article is to describe a fast and safe technique to expose the geniculate ganglion and the labyrinthine portion of the facial nerve in two structures of the middle ear: the cochleariform process and the tympanic portion of the facial nerve. We prospectively evaluated 32 patients who underwent surgical facial nerve exploration via the middle fossa approach. Our goal was to determine the incidence of intraoperative difficulties and complications; we found none, and hearing levels could not be maintained in only one of the 32 patients. Our technique allowed us to decompress the first genu and the labyrinthine segment of the nerve. It also allowed us to reach and manipulate its tympanic segment in a very short amount of surgical time.

Adult↗
PubMed2004

[Geniculate ganglion tumors. Therapeutic and reconstructive management].

We present five cases of patients diagnosed of a facial nerve tumoral lesion localised at the Geniculate Ganglion and all of which underwent surgical resection. The initial symptoms were in four cases of peripheral facial nerve paralysis and in the fifth case facial paresis. Two trans-mastoid extralabyrinthine approaches were performed and one through a combined path (middle fossa and trans-mastoid) with reconstruction of the facial nerve through a termino-terminal graft. In the fourth case, an approach through fossa media was done, and did not include nerve reconstruction but palliative treatment with a palpebral gold plaque. In the fifth case, a modified trans-labyrinthine approach with facial-hypoglossus termino-terminal anastomosis. Histological diagnosis was 3 neurinomas and 2 hemangiomas. Of the termino-terminal grafts two managed a functional Grade III of the House-Brackmann classification. The third one sustained a Grade VI and therefore a suspension with temporal muscle was carried out. The patient with facial-hypoglossus anastomosis is in a functional Grade IV. Geniculate ganglion tumors are in their majority benign and their treatment is the total resection of the tumor. Nerve reconstruction can be primary or deferred with the aid of a nerve graft or anastomosis, being necessary palliative techniques when resection is not possible.

Adult↗
PubMed1976

Quantitative studies on the mouse facial nerve trunk distal to the geniculate ganglion. An electron-microscopic study.

A fiber count analysis was performed with the electron microscope on the facial nerve trunk distal to the geniculate ganglion in seven mice. On an average, 4,836 (93%) of the total nerve fibers (5,201) were myelinated and 328 (6.3%) unmyelinated. The large part of the nerve consisted mostly of large myelinated fibers (large-fiber group). The small part of the nerve consisted of small myelinated and unmyelinated fibers (small-fiber group). The fiber constitution of the small-fiber group in the nerve was more like that in the intermediate nerve than that of the small-fiber group in the motor root of the facial nerve. Thus, it is postulated that the nerve fibers of the small-fiber group in the facial nerve trunk distal to the geniculate ganglion may be derived from the intermediate nerve, and that the nerve fibers of the small-fiber group in the motor root of facial nerve may course to the greater petrosal nerve.

Animals↗
PubMed1991

[A case of angiomatous meningioma near the geniculate ganglion].

A 57-year-old male was admitted with pulsatile tinnitus and hearing disturbance of the right ear and right peripheral facial palsy. Otological examination revealed a pulsatile red mass in his right ear and right conductive hearing disturbance. CT and MRI showed the mass lesion at his right middle fossa near the geniculate ganglion. Right external carotid angiogram disclosed a tumor stain fed by the middle meningeal artery. The tumor was removed via a combination of subtemporal and transmastoidal approaches. Histologically, this tumor was diagnosed as angiomatous meningioma partly with meningotheliomatous meningioma. Meningioma in this region is very rare. We discussed its clinical and radiological characteristics in comparison with chemodectoma and facial neurinoma at the geniculate ganglion.

Angiography↗
PubMed2005

Neuronal cell death and population dynamics in the developing rat geniculate ganglion.

In contrast to many neuronal systems, the pattern of developmental neuronal degeneration in the rat geniculate ganglion has remained undefined. To address this issue sectioned geniculate ganglia from embryonic day 13 to postnatal day 3 have been examined using standard histological techniques, TdT-mediated dUTP-digoxigenin nick end labeling to verify apoptotic activity, bromo-deoxyuridine incorporation to monitor neuronal precursor proliferation, and anti-beta-neurotubulin III to verify the neuronal identity of pycnotic cells. Results summed from alternate (embryonic day 13) or every third (embryonic day 14-postnatal day 3) section show that neuronal degeneration occurs as early as embryonic day 13 (6.8% of neurons counted), well before geniculate innervation of lingual taste buds at embryonic day 16. A degenerative peak occurs at embryonic day 17 (9.5%) followed by a decline (1.7% at embryonic day 18) and leveling off (0.1%-0.2% at embryonic day 22-postnatal day 3). Thus, geniculate neuronal degenerative pattern includes both innervation-associated histogenetic and morphogenetic cell death. Corresponding counts of mean neuronal numbers in the sections showed a continual rise from embryonic day 13 through embryonic day 18 (approx. 330-760) followed by a slight decline at embryonic day 19 (to approx. 630) and then a final leveling off at 800-825 by embryonic day 20. This pattern differs from many other developing neural systems which show a major population crash during initial target contact. It likely reflects different but slightly overlapping neuronal precursor proliferation and degeneration patterns in multiple geniculate neuronal subpopulations.

Animals↗
PubMed2006

Mice lacking the p75 receptor fail to acquire a normal complement of taste buds and geniculate ganglion neurons by adulthood.

Brain-derived neurotrophic factor and neurotrophin-4 are required for normal taste bud development. Although these neurotrophins normally function via the tyrosine kinase receptor, trkB, they also bind to the pan-neurotrophin receptor, p75. The goal of the present study was to determine whether the p75 receptor is required for the development or maintenance of a full complement of adult taste buds. Mice with p75 null mutations lose 34% of their circumvallate taste buds, 36% of their fungiform papillae, and 26% of their fungiform taste buds by adulthood. The reduction of taste buds in the adult circumvallate papilla was similar to that observed previously at postnatal day 7 (Fan et al. Brain Res Dev Brain Res 2004;150:23-39). Taken together, these findings indicate that the p75 receptor is critical for the development of a full complement of taste buds, but is not required for maintenance of circumvallate taste buds in adulthood. Immunolabeling for p75 was not observed in taste buds, indicating that p75 signaling influences taste bud number indirectly. Geniculate ganglion neurons, which provides innervation to fungiform taste buds, express the p75 receptor. Mice with p75 null mutations also have fewer neurons in the geniculate ganglion. Together, these results suggest that the p75 receptor is important for the survival of geniculate neurons and geniculate neuron survival is required for the development of a full complement of taste buds by adulthood.

Aging↗
PubMed2003

[Facial nerve schwannoma in the inner auditory canal and geniculate ganglion].

BACKGROUND: Schwannoma of the vestibular nerve is the most common tumor found in the inner auditory canal. If a schwannoma of the facial nerve is found unexpectedly during surgery, the original surgical plan may have to be changed. In our series, we describe the symptoms, diagnostic procedures and therapy of this infrequent, benign tumor. In particular, we want to analyse the influence of diagnostic techniques, such as magnetic resonance tomography and electrophysiology, on the diagnosis of these tumors. PATIENTS: Between 1975 and 2001, we diagnosed 17 cases of facial nerve schwannoma in the inner auditory canal or the geniculate ganglion. All patients were treated surgically. In 16 cases, we used the enlarged middle fossa approach and in the remaining patient the translabyrinthine approach was used. RESULTS: In 11 cases, the facial nerve could be saved but in six the nerve had to be rebuilt with a transplant. During the first years of our study, palsy of the facial nerve was a frequent finding. In the later years, a hearing impairment and tinnitus became the most frequent symptoms. CONCLUSIONS: Advances in magnetic resonance imaging have, in many cases, facilitated the differentiation between schwannomas of the facial nerve and the vestibular nerve over the last years. Signal enhancement at the geniculate ganglion is important for the diagnosis of facial nerve schwannoma. In individual cases, we found significant findings using electrophysiological procedures. In three cases, the temporal delay was elongated. Based on these findings, the therapeutic procedures can be discussed together with the patients.

Adolescent↗
PubMed2006

Differential expression of capsaicin-, menthol-, and mustard oil-sensitive receptors in naive rat geniculate ganglion neurons.

The roles of capsaicin, menthol, and mustard oils and their receptors in geniculate ganglion (GG) neurons still remain to be elucidated. These receptors belong to the transient receptor potential (TRP) family. Capsaicin-, menthol-, and mustard oil-sensitive receptors are TRPV1, TRPM8, and TRPA1, respectively. The present study aimed to investigate the expression of TRPV1, TRPM8, and TRPA1 in naive rat GG neurons. Furthermore, we examined whether these TRP-expressing GG neurons are myelinated A-fiber or unmyelinated C-fiber neurons. Firstly, using reverse transcription-polymerase chain reaction, TRPV1 mRNA and TRPA1 mRNA were distinctly detected in the naive GG. TRPM8 mRNA was faintly detected. Secondly, using in situ hybridization, TRPV1 mRNA- or TRPA1 mRNA-labeled neurons (signal/noise ratio >or= 10) were observed in 15-20% of GG neurons. Few neurons were labeled by TRPM8 mRNA. Thirdly, neurofilament 200 (NF200) protein, a marker of mylinated A-fiber neurons, was detected in 57% of naive GG neurons. Coexpression of TRPV1 mRNA or TRPA1 mRNA with NF200 was detected in 10% of GG neurons. The present study confirmed the expression of the TRP receptors in the naive GG. The possible roles of TRP receptors in naive GG neurons in somatosensory or gustatory function were suggested.

Animals↗
PubMed1999

Gustatory neuron types in rat geniculate ganglion.

We used extracellular single-cell recording procedures to characterize the chemical and thermal sensitivity of the rat geniculate ganglion to lingual stimulation, and to examine the effects of specific ion transport antagonists on salt transduction mechanisms. Hierarchical cluster analysis of the responses from 73 single neurons to 3 salts (0.075 and 0.3 M NaCl, KCl, and NH(4) Cl), 0.5 M sucrose, 0.01 M HCl, and 0.02 M quinine HCl (QHCl) indicated 3 main groups that responded best to either sucrose, HCl, or NaCl. Eight narrowly tuned neurons were deemed sucrose-specialists and 33 broadly tuned neurons as HCl-generalists. The NaCl group contained three identifiable subclusters: 18 NaCl-specialists, 11 NaCl-generalists, and 3 QHCl-generalists. Sucrose- and NaCl-specialists responded specifically to sucrose and NaCl, respectively. All generalist neurons responded to salt, acid, and alkaloid stimuli to varying degree and order depending on neuron type. Response order was NaCl > HCl = QHCl > sucrose in NaCl-generalists, HCl > NaCl > QHCl > sucrose in HCl-generalists, and QHCl = NaCl = HCl > sucrose in QHCl-generalists. NaCl-specialists responded robustly to low and high NaCl concentrations, but weakly, if at all, to high KCl and NH(4) Cl concentrations after prolonged stimulation. HCl-generalist neurons responded to all three salts, but at twice the rate to NH(4) Cl than to NaCl and KCl. NaCl- and QHCl-generalists responded equally to the three salts. Amiloride and 5-(N,N-dimethyl)-amiloride (DMA), antagonists of Na(+) channels and Na(+)/H(+) exchangers, respectively, inhibited the responses to 0.075 M NaCl only in NaCl-specialist neurons. The K(+) channel antagonist, 4-aminopyridine (4-AP), was without a suppressive effect on salt responses, but, when applied alone in solution, it evoked a response in many HCl-generalists and one QHCl-generalist neuron so tested. Of the 39 neurons tested for their sensitivity to temperature, 23 responded to cooling and chemical stimulation, and 20 of these neurons were HCl-generalists. Moreover, the responses to the four standard stimuli were reduced progressively at lower temperatures in HCl- and QHCl-generalist neurons, but not in NaCl-specialists. Thus sodium channels and Na(+)/H(+) exchangers appear to be expressed exclusively on the membranes of receptor cells that synapse with NaCl-specialist neurons. In addition, cooling sensitivity and taste-temperature interactions appear to be prominent features of broadly tuned neuron groups, particularly HCl-generalists. Taken all together, it appears that lingual taste cells make specific connections with afferent fibers that allow gustatory stimuli to be parceled into different input pathways. In general, these neurons are organized physiologically into specialist and generalist types. The sucrose- and NaCl-specialists alone can provide sufficient information to distinguish sucrose and NaCl from other stimuli, respectively.

Animals↗
PubMed1997

Hemifacial spasm caused by a hemangioma at the geniculate ganglion: case report.

OBJECTIVE AND IMPORTANCE: Hemifacial spasm is rarely caused by facial nerve lesions in the temporal bone. Intratemporal facial nerve hemangiomas may initially present as facial spasm. CLINICAL PRESENTATION: A 30-year-old woman developed right hemifacial spasm. Physicians observed slight weakness on the right side of her face, in addition to the hemifacial spasm, but routine radiological examinations did not detect any abnormal findings along the course of the facial nerve. Although the patient underwent neurovascular decompression, the spasm persisted postoperatively. Two years after surgery, the right facial palsy progressed. Concurrently, the hemifacial spasm diminished. High-resolution computed tomography demonstrated a small mass lesion expanding the cortex of the right petrosal bone involving the geniculate ganglion of the facial nerve. INTERVENTION: The patient underwent a second craniotomy through a subtemporal extradural route, and the tumor was completely removed. A pathological examination demonstrated a cavernous hemangioma. CONCLUSION: Routine radiological examinations may fail to detect small intratemporal facial nerve hemangiomas, particularly at the geniculate ganglion. Therefore, when physicians encounter atypical facial spasm, the intratemporal portion of the facial nerve should be carefully examined using high-resolution computed tomography.

Adult↗
PubMed1984

Examination of geniculate ganglion cells contributing sensory fibers to the rat facial 'motor' nerve.

Using a method to visualize HRP-containing cells in the geniculate ganglion (GG) in situ after decalcifying surrounding bone, we found that about 30% of the total (about 1000) GG cells contributed sensory fibers to the posterior auricular branch of the facial motor nerve. These cells are relatively large for GG cells in general. The remaining facial motor nerve branches, including those involved in vibrissal movement, contained few sensory afferent fibers originating from GG cells.

Animals↗
PubMed2005

Neurotrophic factor receptor expression and in vitro nerve growth of geniculate ganglion neurons that supply divergent nerves.

We investigated which neurotrophic factors may contribute to the divergence of two peripheral nerves emanating from the geniculate ganglion. We compared receptor mRNA profiles of the neurons that supply the nerves, and also the growth of their neurites in response to neurotrophic factors in culture. Three mRNAs, Gfra2, TrkA, and TrkC, were differentially expressed. Only one ligand, Neurturin, promoted substantially different nerve regrowth from the nerves, and therefore may contribute to nerve divergence. Three receptor mRNAs were expressed in 100% of the neurons: TrkB, TrkB.T2 (kinase-lacking isoform), and NCAM-140. Ligands for these Trks and FRalpha-1 promoted more outgrowth than ligands for the other receptors. NT-3 and BDNF synergistically promoted outgrowth. Finally, receptors are coexpressed at random rates, arguing against the existence of neuronal subtypes defined by a combinatorial code of these receptors.

Animals↗