Current concepts of vestibular nucleus function: transformation of vestibular signals in the vestibular nuclei

Readaptation Treatment of Mal de Debarquement Syndrome With a Virtual Reality App: A Pilot Study

Mal de Debarquement syndrome (MdDS) is composed of constant phantom sensations of motion, which are frequently accompanied by increased sensitivity to light, inability to walk on a patterned floor, the sensation of ear fullness, head pressure, anxiety, and depression. This disabling condition generally occurs in premenopausal women within 2 days after prolonged passive motion (e.g., travel on a cruise ship, plane, or in a car). It has been previously hypothesized that MdDS is the result of maladaptive changes in the polysynaptic vestibulo-ocular reflex (VOR) pathway called velocity storage. Past research indicates that full-field optokinetic stimulation is an optimal way to activate velocity storage. Unfortunately, such devices are typically bulky and not commonly available. We questioned whether virtual reality (VR) goggles with a restricted visual field could effectively simulate a laboratory environment for MdDS treatment. A stripes program for optokinetic stimulation was implemented using Google Daydream Viewer. Five female patients (42 ± 10 years; range 26-50), whose average MdDS symptom duration was 2 months, participated in this study. Four patients had symptoms triggered by prolonged passive motion, and in one, symptoms spontaneously occurred. Symptom severity was self-scored by patients on a scale of 0-10, where 0 is no symptoms at all and 10 is the strongest symptoms that the patient could imagine. Static posturography was obtained to determine objective changes in body motion. The treatment was considered effective if the patient's subjective score improved by at least 50%. All five patients reported immediate improvement. On 2-month follow-ups, symptoms returned only in one patient. These data provide proof of concept for the limited-visual-field goggles potentially having clinical utility as a substitute for full-field optokinetic stimulation in treating patients with MdDS in clinics or via telemedicine.

Central adaptation to repeated galvanic vestibular stimulation: implications for pre-flight astronaut training

Healthy subjects (N = 10) were exposed to 10-min cumulative pseudorandom bilateral bipolar Galvanic vestibular stimulation (GVS) on a weekly basis for 12 weeks (120 min total exposure). During each trial subjects performed computerized dynamic posturography and eye movements were measured using digital video-oculography. Follow up tests were conducted 6 weeks and 6 months after the 12-week adaptation period. Postural performance was significantly impaired during GVS at first exposure, but recovered to baseline over a period of 7–8 weeks (70–80 min GVS exposure). This postural recovery was maintained 6 months after adaptation. In contrast, the roll vestibulo-ocular reflex response to GVS was not attenuated by repeated exposure. This suggests that GVS adaptation did not occur at the vestibular end-organs or involve changes in low-level (brainstem-mediated) vestibulo-ocular or vestibulo-spinal reflexes. Faced with unreliable vestibular input, the cerebellum reweighted sensory input to emphasize veridical extra-vestibular information, such as somatosensation, vision and visceral stretch receptors, to regain postural function. After a period of recovery subjects exhibited dual adaption and the ability to rapidly switch between the perturbed (GVS) and natural vestibular state for up to 6 months.

Plane-specific Purkinje cell responses to vertical head rotations in the cat cerebellar nodulus and uvula

We recorded simple spike (SS) and complex spike (CS) firing of Purkinje cell in the cerebellar nodulus and uvula of awake, head-restrained cats during sinusoidal vertical rotation of the head in four stimulus planes (pitch, roll, and two vertical canal planes). Two SS response types (position- and velocity-types) with response phases close to those of head position and velocity, respectively, were recognized. Optimal response planes and directions for SS and CS of each cell were estimated from the response amplitudes in the four stimulus planes by fitting with a sinusoidal function. The principal findings are as follows: 1) two rostrocaudally oriented functional zones of Purkinje cells can be distinguished; 2) the medially located parasagittal band is active during rotation in the pitch plane; 3) the laterally located band is active during rotation in the roll plane. These two zones are the same as previously reported zones in the cerebellar flocculus active during head rotation in the canal planes in the point that both cerebellar sagittal zones are plane-specific functional zones, suggesting that the anatomical sagittal zones serve as functional plane-specific zones at least in the vestibulocerebellum.

Noradrenaline modulates neuronal responses to GABA in vestibular nuclei

The effects of noradrenaline (NA) on the inhibitory responses to GABA were studied in vivo in neurons of the vestibular nuclei of the rat using extracellular recordings of single unit electrical activity and a microiontophoretic technique of drug application in loco. NA application influenced GABA-evoked inhibitions in 82% of tested neurons, depressing them in 42% and enhancing them in 40% of cases. The more frequent action of NA on GABA responses was depressive in lateral and superior vestibular nuclei (50% of neurons) and enhancing in the remaining nuclei (56% of neurons). The most intense effect of NA application was the enhancement of GABA responses induced in a population of lateral vestibular nucleus neurons, characterized by a background firing rate significantly higher than that of other units. The alpha(2) noradrenergic receptor agonist clonidine mimicked the enhancing action of NA on GABA responses; this action was blocked by application of the specific alpha(2) antagonist yohimbine. The beta adrenergic agonist isoproterenol induced either depressive or enhancing effects on GABA responses; the former more than the latter were totally or partially blocked by application of the beta antagonist timolol. It is concluded that NA enhances GABA responses by acting on noradrenergic alpha(2) and to a lesser extent beta receptors, whereas depressive action involves beta receptors only. These results confirm the hypothesis that the noradrenergic system participates in the regulation of the vestibulospinal and the vestibulo-ocular reflexes and suggest that conspicuous changes of NA content in brain due to aging or stress could lead to a deterioration in the mechanisms of normal vestibular function.

Mapping oxytocin receptor gene expression in the mouse brain and mammary gland using an oxytocin receptor–LacZ reporter mouse

The hypothalamic nonapeptide oxytocin (OT) has an established role as a circulating hormone but can also act as a neurotransmitter and as a neuromodulator by interacting with its central OT receptor (OTR). To understand the role of the OTR in the mouse brain we investigated the expression of the OTR gene at the cellular level. We targeted the lacZ reporter gene to the OTR gene locus downstream of the endogenous OTR regulatory elements. Using lactating mouse mammary gland as a control for OTR promoter directed specificity of lacZ gene expression, X-gal histochemistry on tissue sections confirmed that gene expression was restricted to the myoepithelial cells. We also identified for the first time in mice the expression of the OTR gene in neighbouring adipocytes. Further, investigation in the mouse brain identified numerous nuclei containing neurons expressing the OTR gene. Whilst some of these regions had been described for rat or sheep, the OTR-LacZ reporter mouse enabled the identification of novel sites of central OTR gene expression. These regions include the accessory olfactory bulb, the medial septal nucleus, the posterolateral cortical amygdala nucleus, the posterior aspect of the basomedial amygdala nucleus, the medial part of the supramammillary nucleus, the dorsotuberomammillary nucleus, the medial and lateral entorhinal cortices, as well as specific dorsal tegmental, vestibular, spinal trigeminal, and solitary tract subnuclei. By mapping the distribution of OTR gene expression, depicted through histochemical detection of beta-galactosidase, we were able to identify single OTR gene expressing neurons and small neuron clusters that would have remained undetected by conventional approaches. These novel sites of OTR gene expression suggest additional functions of the oxytocinergic system in the mouse. These results lay the foundation for future investigation into the neural role of the OTR and provide a useful model for further study of oxytocin functions in the mouse.

Central projections of the vestibular nerve: a review and single fiber study in the Mongolian gerbil

The primary purpose of this article is to review the anatomy of central projections of the vestibular nerve in amniotes. We also report primary data regarding the central projections of individual horseradish peroxidase (HRP)-filled afferents innervating the saccular macula, horizontal semicircular canal ampulla, and anterior semicircular canal ampulla of the gerbil. In total, 52 characterized primary vestibular afferent axons were intraaxonally injected with HRP and traced centrally to terminations. Lateral and anterior canal afferents projected most heavily to the medial and superior vestibular nuclei. Saccular afferents projected strongly to the spinal vestibular nucleus, weakly to other vestibular nuclei, to the interstitial nucleus of the eighth nerve, the cochlear nuclei, the external cuneate nucleus, and nucleus y. The current findings reinforce the preponderance of literature. The central distribution of vestibular afferents is not homogeneous. We review the distribution of primary afferent terminations described for a variety of mammalian and avian species. The tremendous overlap of the distributions of terminals from the specific vestibular nerve branches with one another and with other sensory inputs provides a rich environment for sensory integration.