Ocular vestibular evoked myogenic potential (VEMP) reveals mesencephalic HTLV-1-associated neurological disease.

PURPOSE: Vestibular Myogenic Evoked Potential (VEMP) evaluates vestibulo-ocular and vestibulo-collic reflexes involved in the function of the otolithic organs and their afferent pathways. We compared the results of cervical and ocular VEMP in HTLV-1 associated myelopathy (HAM) and HTLV-1-asymptomatic infection. PARTICIPANTS AND METHODS: This cross-sectional study included 52 HTLV-1-infected individuals (26 HAM and 26 asymptomatic carriers) and 26 seronegative controls. The groups were similar regarding age and gender. Participants underwent simultaneous ocular and cervical VEMP. The stimulus to generate VEMP was a low-frequency tone burst sound tone burst, with an intensity of 120 decibels normalized hearing level, bandpass filter from 10 to 1,500 Hertz (Hz), with 100 stimuli at 500 Hz and 50 milliseconds recording time. The latencies of the electrophysiological waves P13 and N23 for cervical VEMP and N10 and P15 waves for ocular VEMP were compared among the groups. The absence or delay of the electrophysiological waves were considered abnormal results. RESULTS: Ocular VEMP was similar among the groups for N10 (p = 0.375) and different for P15 (p≤0.001). Cervical VEMP was different for P13 (p = 0.001) and N23 (p = 0.003). About ocular VEMP, in the HTLV-1-asymptomatic group, normal waves were found in 23(88.5%) individuals; in HAM group, normal waves were found in 7(26.9%). About cervical VEMP, 18(69.2%) asymptomatic carriers presented normal waves and only 3(11.5%) patients with HAM presented normal waves. Abnormalities in both VEMPs were found in 1(3.8%) asymptomatic carrier and in 16(61.5%) patients with HAM. CONCLUSION: Neurological impairment in HAM was not restricted to the spinal cord. The mesencephalic connections, tested by ocular VEMP, have been also altered. Damage of the oculomotor system, responsible for eye stabilization during head and body movements, may explain why dizziness is such a frequent complaint in HAM.

Functional expression of P2 receptors in the inner ear of chicken embryo.

The purpose of the present study was to investigate the modulation of spontaneous afferent activity by ATP during embryonic development in a preparation isolated chicken inner ear. This work was performed using multiunit and single-unit extracellular recordings from the posterior semicircular canal nerve and the basilar papilla nerve. α,ß-meATP, a P2X receptor agonist, notably increased the discharge frequency of the vestibular afferents between E15 and E18, but not in the basilar papilla. In contrast, the P2Y receptor agonist UTP produced a slight increase in the discharge frequency of basilar papilla afferents, without apparent changes in the vestibular afferent activity. 2-MeSATP, a P2Y agonist, increased the basal discharge of the primary afferents in a dose-age dependent way, but when we applied the antagonist of P2Y receptor, Reactive Blue 2 (10(-4)M), the effect of 2-MeSATP decreased significantly. This was observed both in vestibule and basilar papilla. Using RT-PCR the presence of P2X3, P2Y1, P2Y2 and P2Y6 mRNA was documented in the vestibular system with more important presence during the early stage (E15) than the later stage (E21), however in the basilar papilla we found only the P2Y1, P2Y2 and P2Y6 mRNA with the same temporal course as in the vestibule. These results confirm our pharmacological findings. Together this data suggests a role for P2X receptors-mediated purinergic signaling in vestibular synaptic organization. Temporal changes in P2Y receptors during development might be involved in the establishment of the endolymphatic ion composition needed for normal vestibular and auditory transduction and/or specific cellular differentiation.

Avaliação do controle postural em adultos jovens através da posturografia dinâmica Foam-laser e plataforma de força / Evaluation of the postural control in young adults by use of foam-laser dynamic posturography and power plataform

Uma das tarefas mais importantes do sistema do controle postural humano é a manutenção do equilíbrio do corpo sobre a base de apoio fornecida pelos pés. Como um sensor de gravidade, o sistema vestibular é uma das ferramentas mais importantes do sistema nervoso no controle da postura. Quando há um desequilíbrio neste sistema o indivíduo passa a apresentar um conjunto de sintomas no qual a vertigem geralmente é preponderante. Objetivou-se no presente estudo avaliar e correlacionar o controle postural de adultos jovens através da posturografia dinâmica Foam-Laser (FLP) e plataforma de força. Para a realização do estudo participaram 31 voluntários (19 homens e 11 mulheres) sendo submetidos à avaliação do controle postural através da posturografia dinâmica Foam-Laser e plataforma de força simultaneamente. Para análise dos dados registrados na plataforma de força, utilizou-se o programa MATLAB® 7.4. Os resultados da FLP foram obtidos através da fórmula matemática para cálculos de ângulos de oscilações apresentados. Os resultados revelaram que houve forte correlação entre os valores obtidos nos testes de organização sensorial (SOT) e a área de deslocamento do centro de pressão (CP) registrada pela plataforma de força em todos os SOT. Nos SOT III, V e VI, respectivamente, observou-se forte correlação entre os resultados dos exames da FLP e plataforma de força, com r = -0,78, r = -0,70 e r = -0,80. Conclui-se que a FLP é um método eficaz para avaliação do equilíbrio, e seus resultados demonstraram forte correlação com a área de deslocamento do centro de pressão.

One of the most important tasks of the human postural control system is to keep the body balanced on the base of support provided by the feet. As a gravity sensor, the vestibular system is one of the most important tools of the nervous system in the control of the posture. When there is a malfunction in this system the individual starts to present a group of symptoms in which the vertigo generally is preponderant. The present study had as objective to correlate the results of the postural control evaluation in young peolple obtained through the Dynamic Posturography Foam-laser (FLP) and platform force. For the accomplishment of the study were invited 31 volunteers (19 men and 11 women) that were submitted to the evaluation of the postural control through the Dynamic Posturography Foam-laser and power platform simultaneously. The results reveled that there was strong correlation among the values obteined in the tests of sensorial organization (TOS) and area displacement pressure center (PC) at power platform in all TOS. In TOS III, V e VI respectively, correlation was observed strong enters the results of the examinations in FPL and power platform, with r = - 0,79, r = 0,70 and r = - 0,80. This study concludes that the FLP is a very useful method for evaluation of the balance, and this results show strong correlation with pressure center displacement area.

Acid-sensing ionic-channel functional expression in the vestibular endorgans.

In the vestibular system, the electrical discharge of the afferent neurons has been found to be highly sensitive to external pH changes, and acid-sensing ionic-channels (ASIC) have been found to be functionally expressed in afferent neurons. No previous attempt to assay the ASIC function in vestibular afferent neurons has been done. In our work we studied the electrical discharge of the afferent neuron of the isolated inner ear of the axolotl (Ambystoma tigrinum) to determine the participation of proton-gated currents in the postransductional information processing in the vestibular system. Microperfusion of FMRF-amide significantly increased the resting activity of the afferent neurons of the semicircular canal indicating that ASIC currents are tonically active in the resting condition. The use of ASIC antagonists, amiloride and acetylsalicylic acid (ASA), significantly reduced the vestibular-nerve discharge, corroborating the idea that the afferent neurons of the vestibular system express ASICs that are sensitive to amiloride, ASA, and to FMRF-amide. The sensitivity of the vestibular afferent-resting discharge to the microperfusion of ASIC acting agents indicates the participation of these currents in the establishment of the afferent-resting discharge.

A role for chloride in the suppressive effect of acetylcholine on afferent vestibular activity.

Afferents of the frog semicircular canal (SCC) respond to acetylcholine (ACh) application (0.3-1.0 mM) with a facilitation of their activity while frog saccular afferents respond with suppression (Guth et al., 1994). All recordings are of resting (i.e., non-stimulated) multiunit activity as previously reported (Guth et al., 1994). Substitution of 80% of external chloride (Cl-) by large, poorly permeant anions of different structures (isethionate, methanesulfonate, methylsulfate, and gluconate) reduced the suppressive effect of ACh in the frog saccular afferents. This substitution did not affect the facilitatory response of SCC afferents to ACh. Chloride channel blockers were also used to test further whether Cl- is involved in the ACh suppressive effect. These included: niflumic and flufenamic acids, picrotoxin, 5-nitro-2-(-3-phenylpropylamino)benzoic acid (NPPB), and 4,4'-dinitrostilbene-2,2'-disulfonic acid (DNDS). As with the Cl- substitutions, all of these agents reduced the suppressive response to ACh in the saccule, but not the facilitatory response seen in the SCC. The suppressive effect of ACh on saccular afferents is considered to be due to activation of a nicotinic-like receptor (Guth et al., 1994; Guth and Norris, 1996). Taking into account the effects of both Cl- substitutions and Cl- channel blockers, we conclude that changes in Cl- availability influence the suppressive effect of ACh and that therefore Cl- may be involved in this effect.