The role of acidic fibroblast growth factor in recovery of acoustic trauma.

We administered acidic fibroblast growth factor (aFGF) to the perilymph of the guinea pig cochlea after exposure to intense sound to investigate its effect on the process of recovery after acoustic trauma. We assessed auditory brain stem response (ABR) thresholds to evaluate cochlear function and observed the sensory epithelium using confocal laser-scanning microscopy. After noise exposure (120 dB SPL, 5 h), the ABR threshold showed an increase of approximately 50 dB SPL that recovered after 14 days. Cochlear function in aFGF treated ears recovered more quickly than that in control ears. These results suggest that aFGF may play an important role in cochlear recovery after acoustic injury.

Rapid correction of vestibular imbalance by intracochlear administration of ATP in a guinea pig model of unilateral peripheral vestibular disorder.

The effect of inner ear administration of adenosine triphosphate (ATP) on vestibular function was investigated in guinea pigs with vestibular disorder. The right lateral semicircular canal was cut surgically. Animals were then treated with saline, 5 mM ATP, 50 mM ATP, or 50 mM ATP+10 mM pyridoxal-phosphate-6-azophenyl-2', 4'-disulfonic acid (PPADS), a P2X receptor antagonist, administered directly into the scala tympani by osmotic pump. Before treatment, and at 3, 5 and 7 days after treatment, trapezoid rotation tests were performed on all animals, and the post-rotatory nystagmus (PRN) ratio (number of nystagmus beats after counterclockwise rotation/number of nystagmus beats after clockwise rotation) was calculated and compared between groups. The PRN ratio was statistically greater at 5 days after treatment in the 50 mM ATP group than in the saline group. A statistical difference was also observed in animals treated with 50 mM ATP+10 mM PPADS. Our results indicate that ATP plays an important role in the vestibular periphery to correct vestibular imbalance and that this action may not occur via P2X receptors.

Efficacy of intracochlear administration of betamethasone on peripheral vestibular disorder in the guinea pig.

We evaluated the effect of steroid hormone on vestibular function in a guinea pig of peripheral vestibular disorder. The right lateral semicircular canal was surgically damaged, and after surgery, animals were treated with 0.1 mg/ml of betamethasone in saline, 1 mg/ml of betamethasone in saline, or saline only, which was administrated directly into the scala tympani by osmotic pump. Rotation tests were performed, and the post-rotatory nystagmus (PRN) ratio (PRN number after counterclockwise rotation/PRN number after clockwise rotation) was calculated. The PRN ratio was recovered to normal at 5 days after treatment in the betamethasone administrated groups, but it did not recover to normal until 14 days after treatment in the saline administrated group. Results indicate that in the vestibular periphery steroid hormones may play an important role in recover of vestibular function.

[Second reconstructions after failure of free-tissue transfer in the head and neck region].

A retrospective study was performed on 74 patients seen in our hospital between 1990 and 1999 who underwent head and neck reconstructive surgery involving a free flap. Reconstructive surgery was unsuccessful in 5 cases (6.8%). A pedicled myocutaneus flap was used in two cases for the second reconstruction attempt, while a second free flap (jejunum) was used in two other patients. In these cases, a bilateral neck dissection was performed prior to the second free flap reconstruction and neck infection was found. The head and neck artery and vein were unsuitable as recipient vessels in the second operation. Instead, the cephalic vein was used as a source of vein grafts and as a recipient vein.

Effectiveness and utility of chemical labyrinthectomy with streptomycin using osmotic pump.

To investigate the utility of osmotic pumps, labyrinthectomy was performed surgically (surgical group) or chemically with 30% streptomycin sulfate (SM) using osmotic pumps (SM group) in guinea pigs. After treatment, no statistical difference was observed in the frequency of spontaneous nystagmus and the degree of yaw head tilt between the groups. These data indicate the reliability and efficacy of osmotic pumps, and it might be possible to make guinea pig models using osmotic pumps to predict various grades of damage in the vestibular periphery of humans.

Cell proliferation in spiral ligament of mouse cochlea damaged by dihydrostreptomycin sulfate.

Cell proliferation of the spiral ligament in the normal and drug-induced damaged mice cochleae was investigated using the mitotic tracer bromodcoxyuridine (BrdU). Only a few nuclei labelled by BrdU were seen in the spiral ligament of the control mouse. However, many BrdU labelled nuclei in the spiral ligament in the cochlea damaged by dihydrostreptomycin sulfate were found. The expression of fibroblast growth factor receptor and connexin 43 was detected in the spiral ligament where BrdU labelled cells were found. These results suggest that cell proliferation in the spiral ligament may occur after the drug-induced damage, and this process is probably related to the recovery of cochlear function.

A role of glucocorticoid receptors in the guinea pig vestibular system.

To investigate glucocorticoid receptor (GR) function in the vestibular periphery, GR antagonist RU38486 was administered to the guinea pig inner ear by osmotic pump, and we observed post-rotatory nystagmus (PRN) changes as a marker of vestibular function. Ten days after treatment, RU38486 (1 mM) resulted in ipsilateral vestibule hyperexcitability in response to rotation stimulation. This effect was dose-dependent. These data indicate that steroid hormones may play an important role in maintaining vestibular function.

The role of N-methyl-D-aspartate receptor in the guinea pig inner ear after unilateral labyrinthectomy.

To investigate the role of the N-methyl-D-aspartate (NMDA) receptor in the vestibular periphery, vestibular compensation in the guinea pig was studied following chemical unilateral labyrinthectomy by osmotic pump administration of streptomycin sulfate (SM) with or without D-2-amino-5-phosphonovalerate (D-APV), one of the NMDA receptor antagonists. All animals administrated SM (SM group) or SM and D-APV (SM + D-APV group) showed spontaneous nystagmus and head tilt. The maximum degree of yaw head tilt in the SM + D-APV group was statistically smaller than that in the SM group. Moreover the time constant for head tilt in the SM + D-APV group was statistically shorter than that in the SM group. These results indicate that the NMDA receptor in the vestibular periphery influences vestibular compensation after unilateral labyrinthectomy.

Expression of laminin in vestibular ganglia and nerves in herpes simplex virus infectious chick embryo.

The expression of laminin in the vestibular ganglia and nerves in herpes simplex virus I (HSV-I) infectious chick embryos was examined by immuno-histochemistry. In 9-day-old normal chick embryos, the surface of the vestibular ganglion cells and the vestibular nerves were labelled with laminin, while, in HSV-I infectious chick embryos, the staining of laminin in the vestibular ganglia and nerves was very weak. These results suggest that HSV-I injures vestibular ganglia and nerves, and that laminin is a good marker of the degeneration and innervation of developing vestibular nerves.

Detection of HSV-I nucleic acids in rat vestibular ganglia.

Rats were infected with HSV-I through the middle ear. DNA and RNA were extracted from the vestibular ganglia, trigeminal ganglia, cerebrum, cerebellum and brainstem in the productive or latent state after inoculation. DNA and RNA were applied for polymerase chain reaction (PCR) to detect HSV-I genomes. In particular, in the RNA PCR, the latent-associated transcript (LAT) mRNA, which is said to be present in the cervical or trigeminal ganglia at much lower levels during the productive state, was detected. In the productive state, DNA was clearly detected in all samples whereas LAT was detected only in the trigeminal ganglion on the inoculated side, cerebrum and cerebellum. In the latent state, DNA was detected in the vestibular ganglion only on the inoculated side, bilateral trigeminal ganglia, cerebrum, cerebellum and brainstem; LAT was detected in the vestibular ganglion on the inoculated side, the bilateral trigeminal ganglia and brainstem. These data indicate that HSV-I can establish latent infection in the vestibular ganglia in a similar way as in the cervical or trigeminai ganglia.

Bilateral vestibular neuronitis.

Bilateral vestibular neuronitis with a different onset time for each affected side was reported in two cases among 74 cases observed. The first case appeared 3 weeks and the other 5 years before involvement of the second ear. In the case with a short period before the second attack, the direction of nystagmus was unchanged throughout the clinical course. It is suggested that the direction of nystagmus depends upon the severity of each vestibular dysfunction. In the case with a long period when the vestibular compensation has been completed, paralytic nystagmus was observed and its direction corresponded with the side affected by canal.

Effects of carbonic anhydrase inhibitor on the otolithic organs of developing chick embryos.

Carbonic anhydrase appears to be involved in the process of otoconial formation. The purpose of this investigation was to observe the morphologic change in the surface structure of the otolithic organ in developing chick embryos after injection of the carbonic anhydrase inhibitor, acetazolamide. Acetazolamide (1.5, 3, or 6 mg/0.06 mL/egg) was injected into the yolk sac of the embryo of the fifth day of incubation. Embryo specimens were collected on the 11th, 13th, and 18th days of incubation. The chicks were killed on the third day posthatching, and the surfaces of the otolithic organs were observed under a scanning electron microscope. A marked disturbance in otoconial formation was noted in both utricle and saccule, marked by a decrease or absence of otoconia. A widely exposed meshwork structure of otolithic membrane was observed, with sensory cilia penetrating the meshwork small holes in many instances. There were also several otoconial abnormalities, such as the appearance of only a single giant otoconium, or from several to dozens of giant otoconia, and rough, spongy-surfaced global substances entirely covering the maculae. Clearly, carbonic anhydrase inhibitor (acetazolamide) injected into the yolk sac of developing chick embryos alters and inhibits normal otoconial morphogenesis.

Latent HSV-I infection in rat vestibular ganglia.

The vestibular ganglia of rats having no clinical symptoms after inoculation of HSV-I were examined by Polymerase Chain Reaction (PCR) in order to prove latent HSV-I infection. The rats were divided into two groups: one inoculated with HSV-I into the middle ear cavity (m.i. group), and the other into the peritoneal space (i.p. group). In the m.i. group, 67% of the vestibular ganglia on the inoculated side and 0% on the opposite side were positive. In the i.p. group, 60% of the vestibular ganglia on both sides were positive. These data indicate that HSV-I can establish latent infection in the vestibular ganglia. Furthermore, we assumed that reactivation of HSV-I genomes in the vestibular ganglia might lead to disorders of the vestibular system.

Cell culture study of the vestibular ganglion cells. Morphology and immunohistochemical activity.

Incubation of vestibular ganglion cells from the rat fetus and chick embryos was successfully done demonstrating bipolar cells and two types of multipolar cells, small round cells and large cells, in the cell cultures produced. Vestibular ganglion cells were found to be highly irregular in size. Furthermore, the presence of neurotransmitters (choline acetyltransferase and substance P) was confirmed immunohistochemically. Substance P positive cells had many bipolar cells and some multipolar cells. However, choline acetyl transferase positive cells had some small multipolar cells but few bipolar cells. These findings suggest that all vestibular ganglion cells do not have the same function.