Pathology of peripheral vestibular disorders in the elderly

Severe hearing loss and outer hair cell death in homozygous Foxo3 knockout mice after moderate noise exposure

Noise induced hearing loss (NIHL) is a disease that affects millions of Americans. Identifying genetic pathways that influence recovery from noise exposure is an important step forward in understanding NIHL. The transcription factor Foxo3 integrates the cellular response to oxidative stress and plays a role in extending lifespan in many organisms, including humans. Here we show that Foxo3 is required for auditory function after noise exposure in a mouse model system, measured by ABR. Absent Foxo3, outer hair cells are lost throughout the middle and higher frequencies. SEM reveals persistent damage to some surviving outer hair cell stereocilia. However, DPOAE analysis reveals that some function is preserved in low frequency outer hair cells, despite concomitant profound hearing loss. Inner hair cells, auditory synapses and spiral ganglion neurons are all present after noise exposure in the Foxo3KO/KO fourteen days post noise (DPN). We also report anti-Foxo3 immunofluorescence in adult human outer hair cells. Taken together, these data implicate Foxo3 and its transcriptional targets in outer hair cell survival after noise damage. An additional role for Foxo3 in preserving hearing is likely, as low frequency auditory function is absent in noise exposed Foxo3KO/KOs even though all cells and structures are present.

Vestibular disorders in elderly patients: characteristics, causes and consequences

Introduction

This study assessed vestibular disorders in elderly patients, describing the causes, clinical characteristics, therapies and treatment outcomes.

Methods

Five-year hospital-based prospective study, conducted at the ENT clinic of a tertiary referral center. Subjects were consecutive elderly patients with dizziness, treated and followed-up for a minimum of six months. Data was generated using structured questionnaire and case record files. Analyzed results were presented in simple descriptive forms as graphs and tables.

Results

Among the elderly patients, prevalence of vestibular disorders was 18.6%, 49.1% were retired, 71.9% were married, M:F was 1:1.1. Mean age ±SD were 69.4±1.1 and 69.0±0.8 years for males and females respectively. 56.9% of the patients presented early on experiencing the vestibular symptoms. The symptoms were associated with nausea or vomiting in 26.3%, with an aura in 12.3%. While 50.9% of the patients experienced intermittent symptoms, laterality of the symptoms was not clear in 45.6%. Positional vertigo was diagnosed in 33.3% while in 17.5%, the symptoms could be attributable to previous trauma or assaults. 31.6% of the elderly were referred to ENT surgeons by other specialties, 45.6% were managed with multidisciplinary approach, while 82.5% had the vestibular symptoms initially controlled with labyrinthine sedatives. At follow-up, 43.9% had intermittent periods of recurrence of symptoms.

Conclusion

Prevalence of vestibular disorders in elderly patients is high, most patients present early with intermittent, relatively innocuous symptoms which may be difficult to lateralize. Positional vertigo was the most common cause, it is frequently relieved with labyrinthine sedatives but tends to recur intermittently.

Is there a relationship between brain-derived neurotrophic factor for driving neuronal auditory circuits with onset of auditory function and the changes following cochlear injury or during aging?

Brain-derived neurotrophic factor, BDNF, is one of the most important neurotrophic factors acting in the peripheral and central nervous system. In the auditory system its function was initially defined by using constitutive knockout mouse mutants and shown to be essential for survival of neurons and afferent innervation of hair cells in the peripheral auditory system. Further examination of BDNF null mutants also revealed a more complex requirement during re-innervation processes involving the efferent system of the cochlea. Using adult mouse mutants defective in BDNF signaling, it could be shown that a tonotopical gradient of BDNF expression within cochlear neurons is required for maintenance of a specific spatial innervation pattern of outer hair cells and inner hair cells. Additionally, BDNF is required for maintenance of voltage-gated potassium channels (KV) in cochlear neurons, which may form part of a maturation step within the ascending auditory pathway with onset of hearing and might be essential for cortical acuity of sound-processing and experience-dependent plasticity. A presumptive harmful role of BDNF during acoustic trauma and consequences of a loss of cochlear BDNF during aging are discussed in the context of a partial reversion of this maturation step. We compare the potentially beneficial and harmful roles of BDNF for the mature auditory system with those BDNF functions known in other sensory circuits, such as the vestibular, visual, olfactory, or somatosensory system.

Aging effect on galvanic vestibular-evoked myogenic potentials

OBJECTIVE

This study compared the characteristic parameters of vestibular-evoked myogenic potentials (VEMPs) via galvanic vestibular stimulation (GVS) in healthy subjects of various ages to measure the effect of aging on GVS-VEMPs.

STUDY DESIGN

Prospective study.

SETTING

University hospital.

SUBJECTS AND METHODS

Fifty-two healthy subjects were divided into five groups by age. Each group consisted of 10 subjects in one decade (except 12 subjects in the group of 60 to 69 years). All subjects underwent VEMP testing via GVS with an intensity of 5 mA for 1 ms.

RESULTS

All 10 subjects (20 ears) in each group aged 20 to 29, 30 to 39, 40 to 49, and 50 to 59 years exhibited clear GVS-VEMPs, whereas 20 (83%) of 24 ears in the group aged 60 to 69 years had clear GVS-VEMPs, exhibiting nonsignificant differences in terms of prevalence between the groups of subjects younger and older than 60 years. The mean p13 and n23 latencies and p13-n23 amplitude of the subjects in the groups aged 20 to 29, 30 to 39, 40 to 49, 50 to 59, and 60 to 69 years differed significantly among the five groups: the p13 and n23 latencies of the group aged older than 60 years was significantly longer than those of subjects younger than 60 years and their p13-n23 amplitude was lower.

CONCLUSION

The decline of the amplitude and prolongation of the latencies in GVS-VEMPs after the age of 60 may, at least in part, be caused by the decrease in the number of vestibular afferents and their caliber.

The vestibulosympathetic reflex in humans: neural interactions between cardiovascular reflexes

1. Over the past 5 years, there has been emerging evidence that the vestibular system regulates sympathetic nerve activity in humans. We have studied this issue in humans by using head-down rotation (HDR) in the prone position. 2. These studies have clearly demonstrated increases in muscle sympathetic nerve activity (MSNA) and calf vascular resistance during HDR. These responses are mediated by engagement of the otolith organs and not the semicircular canals. 3. However, differential activation of sympathetic nerve activity has been observed during HDR. Unlike MSNA, skin sympathetic nerve activity does not increase with HDR. 4. Examination of the vestibulosympathetic reflex with other cardiovascular reflexes (i.e. barorereflexes and skeletal muscle reflexes) has shown an additive interaction for MSNA. 5. The additive interaction between the baroreflexes and vestibulosympathetic reflex suggests that the vestibular system may assist in defending against orthostatic challenges in humans by elevating MSNA beyond that of the baroreflexes. 6. In addition, the further increase in MSNA via otolith stimulation during isometric handgrip, when arterial pressure is elevated markedly, indicates that the vestibulosympathetic reflex is a powerful activator of MSNA and may contribute to blood pressure and flow regulation during dynamic exercise. 7. Future studies will help evaluate the importance of the vestibulosympathetic reflex in clinical conditions associated with orthostatic hypotension.

Interaction between vestibulosympathetic and skeletal muscle reflexes on sympathetic activity in humans

Evidence from animals indicates that skeletal muscle afferents activate the vestibular nuclei and that both vestibular and skeletal muscle afferents have inputs to the ventrolateral medulla. The purpose of the present study was to investigate the interaction between the vestibulosympathetic and skeletal muscle reflexes on muscle sympathetic nerve activity (MSNA) and arterial pressure in humans. MSNA, arterial pressure, and heart rate were measured in 17 healthy subjects in the prone position during three experimental trials. The three trials were 2 min of 1) head-down rotation (HDR) to engage the vestibulosympathetic reflex, 2) isometric handgrip (IHG) at 30% maximal voluntary contraction to activate skeletal muscle afferents, and 3) HDR and IHG performed simultaneously. The order of the three trials was randomized. HDR and IHG performed alone increased total MSNA by 46 +/- 16 and 77 +/- 24 units, respectively (P < 0.01). During the HDR plus IHG trial, MSNA increased 142 +/- 38 units (P < 0.01). This increase was not significantly different from the sum of the individual trials (130 +/- 41 units). This finding was also observed with mean arterial pressure (sum = 21 +/- 2 mmHg and HDR + IHG = 22 +/- 2 mmHg). These findings suggest that there is an additive interaction for MSNA and arterial pressure when the vestibulosympathetic and skeletal muscle reflexes are engaged simultaneously in humans. Therefore, no central modulation exists between these two reflexes with regard to MSNA output in humans.

Interaction of the vestibular system and baroreflexes on sympathetic nerve activity in humans

Muscle sympathetic nerve activity (MSNA) is altered by vestibular otolith stimulation. This study examined interactive effects of the vestibular system and baroreflexes on MSNA in humans. In study 1, MSNA was measured during 4 min of lower body negative pressure (LBNP) at either -10 or -30 mmHg with subjects in prone posture. During the 3rd min of LBNP, subjects lowered their head over the end of a table (head-down rotation, HDR) to engage the otolith organs. The head was returned to baseline upright position during the 4th min. LBNP increased MSNA above baseline during both trials with greater increases during the -30-mmHg trial. HDR increased MSNA further during the 3rd min of LBNP at -10 and -30 mmHg (Delta32% and Delta34%, respectively; P < 0.01). MSNA returned to pre-HDR levels during the 4th min of LBNP when the head was returned upright. In study 2, MSNA was measured during HDR, LBNP, and simultaneously performed HDR and LBNP. The sum of MSNA responses during individual HDR and LBNP trials was not significantly different from that observed during HDR and LBNP performed together (Delta131 +/- 28 vs. Delta118 +/- 47 units and Delta340 +/- 77 vs. Delta380 +/- 90 units for the -10 and -30 trials, respectively). These results demonstrate that vestibular otolith stimulation can increase MSNA during unloading of the cardiopulmonary and arterial baroreflexes. Also, the interaction between the vestibulosympathetic reflex and baroreflexes is additive in humans. These studies indicate that the vestibulosympathetic reflex may help defend against orthostatic challenges in humans by increasing sympathetic outflow.

Presumed vestibular hemorrhage secondary to warfarin

Hemorrhage secondary to anticoagulant therapy is well documented. We report a patient who presented with acute vertigo and unilateral deafness while on warfarin and was found to have a probable hemorrhage in the labyrinth, identified on MRI.