Vestibular Discharge Research Articles

Evolution in the Findings of Head-Impulse Tests During the Attacks of Menière's Disease.

To determine the vestibulo-ocular reflex (VOR) performance during the attacks of Menière's disease (MD) using video head-impulse tests (video-HITs) according to each ictal phase. Retrospective case series review. We analyzed the results of video-HITs in 24 patients with unilateral definite MD during and between the attacks. The head impulse gain of the VOR was usually normal (81%, 39 of the 48 semicircular canals [SCCs] in 16 patients) in the affected ear during the irritative or recovery phase, and did not differ from that for each SCC between the attacks (horizontal [HCs], p = 0.412; anterior [ACs], p = 0.920; posterior canals [PCs], p = 0.477). During the paretic phase, however, the head impulse gains of the VOR were equally normal (22/42, 52%) or decreased (20/42, 48%) for the affected ear (42 SCCs in 14 patients). The gains for the HCs were lower during the paretic phase than those between the attacks in the affected ear, while those for the ACs and PCs did not differ (HCs, p = 0.001; ACs, p = 0.158, PCs, p = 0.401). Covert saccades were more frequently observed even in the presence of normal VOR gains during the paretic phase as well. During the attacks of MD, HITs are usually normal during the irritative/recovery phases, but become positive in more than a half of the patients during the paretic phase. This evolution in the ictal findings of HITs may reflect characteristic ictal vestibular discharges in MD and should be considered in evaluating patients with MD according to each ictal phase during the attacks.

IP3 receptor in the hair cells of frog semicircular canal and its possible functional role

The presence and functional role of inositol trisphosphate receptors (IP3R) was investigated by electrophysiology and immunohistochemistry in hair cells from the frog semicircular canal. Intracellular recordings were performed from single fibres of the posterior canal in the isolated, intact frog labyrinth, at rest and during rotation, in the presence of IP3 receptor inhibitors and drugs known to produce Ca2+ release from the internal stores or to increase IP3 production. Hair cell immunolabelling for IP3 receptor was performed by standard procedures. The drug 2-aminoethoxydiphenyl borate (2APB), an IP3 receptor inhibitor, produced a marked decrease of mEPSP and spike frequency at low concentration (0.1 mm), without affecting mEPSP size or time course. At high concentration (1 mm), 2APB is reported to block the sarcoplasmic-endoplasmic reticulum Ca2+-ATPase (SERCA pump) and increase [Ca2+]i; at the labyrinthine cytoneural junction, it greatly enhanced the resting and mechanically evoked sensory discharge frequency. The selective agonist of group I metabotropic glutamate receptors (RS)-3,5-dihydroxyphenylglycine (DHPG, 0.6 mm), produced a transient increase in resting mEPSP and spike frequency at the cytoneural junction, with no effects on mEPSP shape or amplitude. Pretreatment with cyclopiazonic acid (CPA, 0.1 mm), a SERCA pump inhibitor, prevented the facilitatory effect of both 2APB and DHPG, suggesting a link between Ca2+ release from intracellular stores and quantal emission. Consistently, diffuse immunoreactivity for IP3 receptors was observed in posterior canal hair cells. Our results indicate the presence and a possibly relevant functional role of IP3-sensitive stores in controlling [Ca2+]i and modulating the vestibular discharge.

Differential effect of current rise time on short and medium latency vestibulospinal reflexes.

To investigate the effect of varying current rise time on galvanic-evoked short (SL) and medium (ML) latency vestibulospinal reflexes. We recorded the soleus EMG of standing subjects in response to 3 mA direct current transmastoid stimulation with a series of current ramps with rise times of 0-300 ms. Longer current rise times significantly delayed the onset of both SL (P<<0.001) and ML (P<<0.001) vestibulospinal responses, by approximately 20 and 39 ms, respectively. The SL response amplitude was reduced with increasing rise time (P<<0.001), whereas the ML response amplitude was relatively unaffected by stimulus rise time. With very slow rise times a prolonged ML response alone was evoked. Both SL and ML reflexes can be evoked by changes in vestibular activity produced by transmastoid galvanic stimulation with a ramp onset. We found a differential effect of current rise time on SL and ML vestibulospinal reflexes, suggesting different potential functional roles for the two reflexes. SL reflexes can participate in the response to abrupt disturbances only. ML reflexes are evoked by both fast and slow changes in vestibular discharge and may be particularly effective for slowly-changing disturbances.

Influence of stimulation of auditory and somatosensory systems on the activity of vestibular nuclear neurons in the frog.

In the frog, we have recorded extracellularly the activity of vestibular nuclear neurons driven by the horizontal semicircular canals. About 28% of the neurons recorded (n = 300) responded to auditory stimulation (clicks 150/s and pure tones 300-2,000 Hz, about 80 dB above threshold) or to somatosensory stimulation (electrical stimulation of the ipsilateral or contralateral sciatic nerve and vibratory stimulation of the ipsilateral gastrocnemius). Whatever the stimulus, the response was always an increase of the discharge frequency. Such a frequency increase was much more important for somatosensory stimulation (62-145%) than for auditory (20%) and sciatic nerve input was about twice as efficient as gastrocnemius input. Except for type IV units which were only exceptionally recorded, all the other neuronal types (according to Duensing and Schaefer 's classification, 1959) responded to auditory or somatosensory volleys. In particular, activation of type III units, which are partly efferent vestibular neurons ending at the base of the sensory hair cells, may result in a modulation of the peripheral vestibular discharges. The latencies of the responses varied over a wide range (5-40 ms); long latency responses are probably mediated by polysynaptic pathways including the reticular formation and/or the cerebellum, and short latency ones by oligosynaptic pathways. These pathways and the functional meaning of convergence of auditory and somatosensory input onto vestibular nuclei are discussed.

Prophylaxis of motion sickness; evaluation of some drugs in seasickness.

MOTION sickness represents a response to a particular pattern of vestibular discharges which are generated chiefly in the utriculus of the labyrinth and stimulate pathways through the cerebellum to the brain stem. 1 The response requires a lengthy process of summation since minutes to hours are needed until the vestibular discharges induce a variety of symptoms which culminate in vomiting. Conversely, a relatively rapid process of adaptation may suppress the manifestations of motion sickness. In addition, there are other ways of weakening or preventing the response. Thus, the effect of motion is minimized by assuming a supine position, which greatly reduces the stimulation of the utriculus. Further, the reduction of psychological, visual, visceral or other facilitating influences may lower the incidence of motion sickness. Finally, there are certain drugs which are preventive. During World War II extensive investigations centered on parasympatholytic agents, central nervous system stimulants or depressants, vitamins or