The effect of the sympathetic and sensory nervous system on active eustachian tube function in the rat

Sympathetic Nervous System Regulation of Auditory Function

BACKGROUND

The auditory system processes how we hear and understand sounds within the environment. It comprises both peripheral and central structures. Sympathetic nervous system projections are present throughout the auditory system. The function of sympathetic fibers in the cochlea has not been studied extensively due to the limited number of direct projections in the auditory system. Nevertheless, research on adrenergic and noradrenergic regulation of the cochlea and central auditory system is growing. With the rapid development of neuroscience, auditory central regulation is an extant topic of focus in research on hearing.

SUMMARY

As such, understanding sympathetic nervous system regulation of auditory function is a growing topic of interest. Herein, we review the distribution and putative physiological and pathological roles of sympathetic nervous system projections in hearing. Key Messages: In the peripheral auditory system, the sympathetic nervous system regulates cochlear blood flow, modulates cochlear efferent fibers, affects hair cells, and influences the habenula region. In central auditory pathways, norepinephrine is essential for plasticity in the auditory cortex and affects auditory cortex activity. In pathological states, the sympathetic nervous system is associated with many hearing disorders. The mechanisms and pathways of sympathetic nervous system modulation of auditory function is still valuable for us to research and discuss.

Clinical Evaluation and Treatment of Patients with Postconcussion Syndrome

Postconcussion syndrome (PCS) is a complex set of symptoms occurring in a small percentage of patients following concussion. The condition is characterized by headaches, dizziness, cognitive difficulties, somatosensory issues, and a variety of other symptoms with varying durations. There is a lack of objective markers and standard treatment protocols. With the complexity created by premorbid conditions, psychosomatic issues, secondary gains, and litigations, providers often find themselves in a tough situation in the care of these patients. This article combines literature review and clinical insights with a focus on the underlying pathophysiology of PCS to provide a roadmap for evaluating and treating this condition.

Denervation of the Eustachian Tube and Hearing Loss Following Trigeminal Schwannoma Resection

Objectives To discuss eustachian tube dysfunction (ETD) as a cause of hearing loss and to discuss its pathogenesis following resection of trigeminal schwannomas.

Methods Presented herein are two cases of trigeminal schwannoma that were resected surgically with sacrifice of the motor branch of the trigeminal nerve. Neither of the cases had evidence of extracranial extension nor preoperative ETD. Both patients developed ETD and have been followed without evidence of schwannoma recurrence.

Conclusions Trigeminal schwannomas are rare tumors that typically require surgical resection. Hearing loss is a potential postsurgical deficit and warrants evaluation by an otolaryngologist with consideration given to a preoperative audiogram. ETD as a result of trigeminal motor branch sacrifice should be included in the differential diagnosis of postoperative hearing loss in this patient subset as it may be reversed with placement of a tympanostomy tube.

Topical application of betahistine improves eustachian tube function in an animal model

CONCLUSION

Betahistine dihydrochloride, a drug used widely in the systemic treatment of balance disorders such as Ménière's disease, was found to improve eustachian tube function when applied topically in the nasopharynx of rats.

OBJECTIVES

The study tested the effect of betahistine, a histamine receptor agonist, on eustachian tube function and tested the involvement of H1 and H3 histamine receptors.

METHODS

Eustachian tube function was measured in anaesthetized rats while middle ear pressure was increased and then monitored during induced swallowing. Betahistine and other drugs were applied topically in the nasopharynx, bulla and epipharynx, and administered intraperitoneally.

RESULTS

Systemic application of betahistine hardly changed eustachian tube function, but topical application significantly improved it. The action of topical betahistine was unaffected by the HI receptor antagonist mepyramine and was mimicked by the H3 agonist, ciproxifan.

Eustachian tube function in patients with Meniere's disease

OBJECTIVE

The aim of the present study was to clarify the relationship between Eustachian tube function and inner ear function, especially with respect to the hearing ability of patients with Meniere's disease.

METHODS

Patients with Meniere's disease underwent nystagmic examinations and audiometric measurements, including hearing tests, tympanometry, and Eustachian tube function tests (sonotubometry). We compared the audiometric examination results of normal subjects to those of patients with Meniere's disease.

RESULTS

Twenty-five percent of patients with Meniere's disease exhibited Eustachian tube dysfunction, but 92% displayed normal tympanometry findings. Their sonotubometry durations and amplitudes were not significantly different from those of normal subjects. However, the patients' hearing level was significantly correlated to sonotubometry duration and amplitude. Our patients were classified according to the four stages of Meniere's disease: stage 1 (n=9); stage 2 (n=5); stage 3 (n=8); and stage 4 (n=2). The incidence of Eustachian tube dysfunction in these four groups of patients were 0% (0/9); 40% (2/5); 38% (3/8); and 50% (1/2), respectively.

CONCLUSION

Our study provides evidence demonstrating that treatment of Eustachian tube dysfunction may be useful in preventing the hearing of Meniere's patients from becoming worse.