Cholinomimetics mimic efferent effects on semicircular canal afferent activity in the frog

Acetylcholine (Ach) has received strong support as the neurotransmitter at vestibular efferent nerve endings. Ach, cholinomimetics and cholinergic antagonists were therefore applied to frog isolated whole labyrinths and isolated semicircular canals. Both spontaneous and evoked single unit and multiple unit activities were recorded from the decentralized posterior semicircular canal afferent nerve. In a manner analogous to efferent nerve stimulation, Ach produced both facilitatory and inhibitory changes in afferent firing rates. The facilitatory effect is likely mediated by muscarinic receptors (i.e. atropine antagonizes it at low concentrations). The facilitatory effect can also be elicited by muscarine and carbachol and it is likely produced presynaptically on the vestibular sensory cell. That is, the effects of Ach are not changed by removal of the efferent neurons but they are absent when afferent transmitter release is blocked. The inhibitory effect is not as well characterized as is the facilitatory effect but it can be blocked by strychnine. The results are consistent with the hypothesis that Ach is the transmitter responsible for both the facilitatory and the inhibitory effects of efferent vestibular nerve stimulation.     

Cupulolithiasis of the horizontal semicircular canal

To clarify whether positional nystagmus of horizontal cupulolithiasis contains vertical and torsional components, and to quantify the asymmetry, we analyzed nystagmus in four positions (healthy-ear-down, affected-ear-down, supine, nose-down), using 3-dimensional video-oculography. Subjects were 20 patients with direction-changing apogeotropic positional nystagmus, 11 females and 9 males, with a mean age of 58.1 years. Nystagmus was recorded using an infrared camera and the findings were converted to digital data. Using ImageJ, we performed 3-dimensional video-oculography and measured maximum slow-phase velocity (MSV) of three components. Positional nystagmus was not purely horizontal. Eleven (55%) patients revealed a vertical component, and 14 (70%) patients had a torsional component in the healthy-ear-down position. The mean value of MSV of the horizontal component in the healthy-ear-down position was 18°/s and that in the affected-ear-down position was 7.8°/s. For the horizontal component, MSV in the healthy-ear-down position was significantly greater than that in the affected-ear-down position (p < 0.01). These results suggest that vertical and torsional components occur from the horizontal semicircular canal, and the response to ampullopetal bending is more than two times as strong as that to ampullofugal bending.     

Prostaglandins in the semicircular canal of the frog

The synthesis of prostaglandins by ampulla and duct tissue isolated from the frog posterior semicircular canal was investigated in vitro. Ampulla and duct produced PGE2 (9 and 6 pg/structure, respectively) and prostacyclin (26 and 12 pg/structure). In the ampulla, prostaglandins mostly originated from the part containing dark and sensory cells and was not altered by 10(-3) M streptomycin. Prostaglandin levels were time-dependent and temperature-dependent. Arachidonic acid (3 X 10(-5) M) stimulated PGI2 synthesis by ampulla and duct (by 11.4 and 17 times) and PGE2 synthesis by 50 times in both structures. Ionophore A23187 stimulated ampulla and duct PGI2 synthesis (by 4.8 and 5.6 times) and PGE2 synthesis (by 2.4 and 1.8 times). Subcutaneous 100 mg/kg aspirin reduced PGI2 and PGE2 synthesis (ampulla: -87%, -33%; duct: -100%, -33%). Indomethacin (10(-6) M), in vitro, decreased PGI2 and PGE2 synthesis (ampulla: -47%, -47%; duct; -22%, -77%). Within 3 h, aspirin (5 X 10(-6) M) or arachidonic acid (2 X 10(-5) M) did not change Na and K concentrations in endolymph. It is concluded that frog inner ear produces PGI2 and PGE2, mostly from the part containing the dark cells, and that prostaglandins could be involved in the physiology of inner ear.     

An experimental study on the inhibitory response of the frog semicircular canal nerve

The inhibitory response of the posterior semicircular canal (p.s.c.) ampullary nerve was studied in comparison with the excitatory response. The isolated p.s.c. of the bull frog was stimulated by the mechanical endolymphatic flow toward either the ampullofugal (AF, excitatory) or the ampullopetal (AP, inhibitory) direction. Three experiments were performed. 1) Experiment I: The influence of the endolymphatic K+ concentration. In both the high (50mM) and the low (2.5mM) K+ environment, the inhibitory response was smaller than the excitatory response. This was more pronounced in the low K+ environment. 2) Experiment II: The influence of the initial position of the cupula. The magnitudes of the responses when the cupula was moved from various positions were compared. When the same amount of stimulus was given in the same direction, the responses were equal regardless of the initial position of the cupula. The inhibitory response yielded a time constant approximately 2-3 times as long as the excitatory response. 3) Experiment III: The interaction of the AF and the AP stimulus. The influence of the inhibitory response upon the following excitatory response and vice versa, were studied by changing the timing of the stimulus onset. Both the action potential and the DC potential were recorded for comparison. The AP stimulus which immediately followed the AF stimulus suppressed the action potential and the negative DC potential was observed. On the other hand the AF stimulus which immediately followed the AP stimulus gave rise to the distinct positive DC potential but the action potential could hardly be evoked. That AF stimulus resulted in different responses between the action potential and the DC potential indicates that the DC potential recorded in this study is possibly a generator potential.     

An experimental study on the isolated lateral semicircular canal of the bull frog

Summary We used isolated lateral semicircular canals from the bull frog, Rana catesbeiana. The cupula was removed from the crista and a glass micropipette was used to depress the sensory cilia on the crista toward the utricular side. Five points on the crista were selected for stimulation. Decremental time constants of the lateral ampullary nerve action potentials were measured. The longest time constant was obtained from stimulation to the wide portion of the crista. The time constant progressively decreased as the narrow side of the crista was approached. These results indicate that the lateral semicircular canal crista is equivalent to the halved posterior semicircular canal crista in terms of both morphology and physiology.     

Secretion of endolymph by the isolated frog semicircular canal.

Secretion of endolymph is localized in some structures of the inner ear, namely the stria vascularis in the cochlea and the dark cells in the vestibule and in the lower vertebrate inner ear. In isolated semicircular canal it is possible to study separately the endolymphatic composition in the ampulla, which contains the dark cells, and in its non-ampullar part, which is devoid of these cells. Further, in vitro preparation of the semicircular canal provides access to both faces of the epithelium so that different agents can be applied separately to the apical or to the basolateral membranes of the epithelium. In this structure, the following results were obtained: i) in vitro, the semicircular canal secreted a K-rich, positively polarized fluid; ii) this fluid was secreted only in the ampulla of the semicircular canal; iii) the secretion of endolymph was dependent on basolateral Na+, K(+)-ATPase, inhibited by ouabain, and basolateral Na-K-Cl co-transporter, inhibited by bumetanide; iv) approximately 60% of luminal Na absorption occurred across a luminal Na channel inhibited by amiloride; v) the permeability of the paracellular pathway of the semicircular canal epithelium was 7.10(-7) cm/s. These results indicate that endolymph secretion involves basolateral Na+, K(+)-ATPase and Na-K-Cl co-transporter. An Na channel has been shown at the apical membrane.     

An experimental study on the isolated lateral semicircular canal of the bull frog

We used isolated lateral semicircular canals from the bull frog, Rana catesbeiana. The cupula was removed from the crista and a glass micropipette was used to depress the sensory cilia on the crista toward the utricular side. Five points on the crista were selected for stimulation. Decremental time constants of the lateral ampullary nerve action potentials were measured. The longest time constant was obtained from stimulation to the wide portion of the crista. The time constant progressively decreased as the narrow side of the crista was approached. These results indicate that the lateral semicircular canal crista is equivalent to the halved posterior semicircular canal crista in terms of both morphology and physiology.     

Effect of cochlear implantation on horizontal semicircular canal function

The objective of this study was to assess the influence of a cochlear implant (CI) on horizontal semicircular canal (hSCC) function, to test the correlation with symptomatic vertigo and to identify possible risk factors for a postoperative vestibular impairment. In a prospective observational study design, forty-seven adult patients who had undergone cochlear implantation at Cochlear Implant Center at a tertiary referral university hospital, Munich, between 2003 and 2007, were studied. Postoperative vertigo symptoms were assessed using a questionnaire followed by a structured interview. Patients were subjected to caloric and rotational chair vestibular function tests pre- and postoperatively. The CI operation was performed with a retroauricular transmastoidal approach by three different surgeons. Thirty-six implants were Cochlear Nucleus 24 devices and 11 implants were MedEl devices. Twenty-one (45%) patients reported vertigo symptoms after CI. Functional testing of the hSCC yielded valid results in 45 of the 47 patients. Thirty-two percent of patients had a substantially reduced hSCC function after CI. Responses of caloric irrigation showed a significant worsening postoperatively in the CI ears. No direct correlation between a decrease in caloric response and risk of postoperative vertigo symptoms could be established. For the criteria age, sex, implant type, surgeon, cause of deafness, petrous bone CT findings and preoperative vertigo, there were no significant differences between the patients with and the patients without postoperative vertigo. Besides morphological changes, a cochlear implantation also causes functional damage of vestibular parts of the labyrinth. Our study showed a significant worsening of the caloric response. However, this alteration did not lead to vertigo complaints in all patients. It is therefore presumed that additional damage to sensory or visual afferents and central vestibular compensatory mechanisms play a role.     

Granddaughter's somersault treats cupulolithiasis of the horizontal semicircular canal

We report on a 61-year-old woman with cupulolithiasis of the right horizontal semicircular canal, which is usually difficult to treat. The patient reported that several years ago, similar symptoms relieved completely after having performed several somersaults together with her granddaughter. This time, repetitive somersaults were again effective to treat her benign paroxysmal positional vertigo. Acceleration during a somersault may induce an intracanalicular force strong enough to detach otoconia debris from the cupula. Rolling may then promote their reentrance into the utricle. This case suggests that repetitive somersaults may be an alternative treatment of cupulolithiasis of the horizontal semicircular canal.     

Benign paroxysmal positional vertigo of the horizontal semicircular canal

ObjectiveAssesment of 8 new cases of benign paroxysmal positional vertigo of the horizontal semicircular canal (BPPV-HC), since this variant of benign positional vertigo occurs rarely. An oculographic study of features in the positional response was carried out. Electrooculograpy (EOG) allows an exhaustive study of positional nystagmus.Material and methodsWe have studied retrospectively 8 patients with BPPV-HC and positive head rotation manoeuvre registered by EOG techniques. Possible alterations in other EOG tests in the group of patients were analyzed.ResultsMost of the patients (7/8) expressed bilateral horizontal geotropic changing-direction nystagmus. One patient exhibited apogeotropic horizontal nystagmus. 5/8 cases showed caloric hypofunction.ConclusionsWe have proven that BPPVHC is an uncommon disorder. In most of the cases, provocative manoeuver generates bilateral horizontal geotropic changing-direction nystagmus that probably is due to canalitiasis of the horizontal semicircular canal. The rest, a few cases, exhibit apogeotropic horizontal response that can be secondary to cupulolitiasis or location particles in the anterior portion of the horizontal canal. A caloric test showed abnormal in many and can help to locatize the affected ear.     

Fenestration of the horizontal semicircular canal in congenital conductive deafness

Fenestration of the horizontal semicircular canal enables the otologic surgeon to restore hearing in those patients with congenital conductive deafness who are not candidates for stapedectomy, ossicular reconstruction, or tympanoplasty. Since the development of stapedectomy, much of the finesse technique of fenestration surgery has been lost, and many otologic surgeons today are unfamiliar with the fenestration operation. The surgical technique for creating a permanently patent fenestra in the horizontal semicircular canal is described. The causes of failure in fenestration surgery are reviewed. Thirty-three patients who have undergone fenestration for congenital conductive deafness over a 30-year period, and 100 patients who underwent fenestration for otosclerosis in 1950, are reviewed to demonstrate patient selection and the efficacy of this operation in establishing long-term hearing improvement.     

Antidiuretic-hormone-induced morphological changes in the ampullary epithelium of the frog semicircular canal

Summary Morphological changes induced by in vitro treatment with arginine-vasotocin, the frog antidiuretic hormone, were studied in the ampullary epithelium of the frog semicircular canal. Morphological changes appeared only in the apical side of the dark cells, while the basal part of these cells and the other cells lining the semicircular canal did not show any change. Changes consisted of the appearance of numerous small vesicles in the apical cytoplasm and the development of microvilli on the apical plasma membrane of the dark cells. These results suggest that arginine-vasotocin could play a role in the regulation of endolymph section.     

水平半规管良性阵发性位置性眩晕的诊断

目的探讨水平半规管良性阵发性位置性眩晕（BPPV）的诊断。方法自2003年1月至2006年9月，本眩晕中心共确诊为水平半规管BPPV（HSC BPPV）患者46例。诊断依据为典型的病史及用红外视频眼震电图仪记录患者在Dix—Hallpike试验和滚转试验中的眼震结果，并排除其他疾病。研究HSC BPPV的眼震特点。结果441例诊断为BPPV患者中，46例（10．43％）为水平半规管BPPV。其中38例（82．61％）为单侧病变，5例（10．87％）患者合并同侧后半规管病变，3例（6．52％）为双侧病变。35例患者通过两种试验诱发出水平眼震，11例患者仅通过滚转试验诱发出水平眼震。25例患者眼震方向向地，13例患者眼震方向背地，3例患者眼震方向不固定，5例患者各种手法诱发出同一方向的眼震。29例患者在双侧手法中出现眼震，17例患者在一侧手法中出现眼震。结论HSC BPPV眼震为完全水平性且多为快相向地。通常受累耳在双侧手法中均可出现眼震，以向患侧为重。一侧水平半规管和后半规管可同时受累。滚转试验在HSC BPPV检查中比Dix—Hallpike试验更加敏感。Dix—Hallpike试验结合滚转试验可使更多的HSCBPPV患者得到确诊．     

Regional distribution of calcium currents in frog semicircular canal hair cells

In the present work we studied the regional expression of voltage-dependent Ca channels in hair cells from the frog semicircular canals, employing whole-cell patch-clamp on isolated and in situ hair cells. Although Ca channels are thought to play a major role in afferent transmission, up to now no data were available regarding their distribution in vestibular organs. The problem appears of interest, especially in the light of recent results showing the presence of multiple Ca current components in semicircular canal hair cells. Our data suggest the presence, in all regions of the crista ampullaris, of two classes of cells, one displaying an inactivating Ca current (R1) and one lacking it. In the former cells, Ca current amplitude decreased from the central to the peripheral zone (the maximal currents being observed in the intermediate zone). Only L-type and R2 current components displayed regional differences in expression, whereas the size and properties of R1, although variable among cells, were not regionalized. However, in cells lacking R1, Ca current amplitudes were similar regardless of cell shape and location. The possible contributions of this Ca current distribution to afferent discharge properties are discussed.     

水平半规管良性阵发性位置性眩晕的临床特点

目的 探讨水平半规管良性阵发性位置性眩晕(benign paroxysmal positional vertigo,BPPV)的临床特点.方法 回顾性分析2003年8月至2010年12月诊治的239例水平半规管BPPV患者的临床表现.结果 水平半规管BPPV占同期全部BPPV患者的25.7％(239/931).平卧侧头试验见水平向地性眼震者197例,眼震的平均潜伏期为(0.88±0.72)s,持续时间(26.36±19.71)s;水平离地性眼震者42例,平均潜伏期(2.69±1.83)s,持续时间(53.48±43.12)s;其中39例眼震表现为水平略带扭转向上而非纯水平,占16.3％(39/239).离地组眼震潜伏期明显长于向地组(t=-6.33,P＜0.001),眼震持续时间亦明显长于向地组(t=-3.99,P＜0.001).水平向地性眼震者予以Barbecue翻滚法治疗,192例经(1.6±0.8)个循环复位成功;水平离地性眼震者经左右侧头训练后,40例眼震转化为向地性,经(1.9±0.8)个循环后复位成功.结论 水平半规管BPPV占同期BPPV的比例较预期高.水平向地性眼震患者可直接给予Barbecue翻滚法治疗,水平离地性眼震患者应先行左右侧头训练,再给予Barbecue翻滚法复位.