Exploring the reasons why melatonin can improve tinnitus.

Melatonin has been proposed as a treatment for tinnitus, especially on the basis of its favourable effects on sleep and its vasoactive and antioxidant properties. However, to our knowledge no attempts of interpretation have been advanced through a detailed analysis of the various specific properties of melatonin possibly cooperating in a coincidental way to relieve tinnitus: among these, its modulatory effect on central nervous system resulting in a protective mechanism against an exaggerated sympathetic drive; its capacity to induce a more steady hemodynamic condition, through a multifactorial and multi-organ activity, resulting in a more regular labyrinthine perfusion; a possible action on the skeletal muscle tending to a reduction of the muscular tone, which could relieve tinnitus of muscular origin deriving from tensor tympani tonic contractions; its possible reported antidepressive effect, which could indirectly act on tinnitus; a direct regulation of inner ear immunity as proposed in literature when melatonin was reported to be present in the inner ear. All these observations seem to indicate melatonin as a tool deserving a greater attention than other antioxidants in the attempt of relieving tinnitus, justifying its application from a more precise rationale based on a series of physio-pathological aspects.

Neurons in the cochlear nuclei controlling the tensor tympani muscle in the rat: a study using pseudorabies virus.

The middle ear muscle reflex has been implicated in modulation of auditory input and protection of the inner ear from acoustic trauma. However, the identification of neurons in the cochlear nuclei participating in this reflex has not been fully elucidated. In the present study, we injected the retrograde transynaptic tracer pseudorabies virus into single tensor tympani (TT) muscles, and identified transynaptically labeled cochlear nucleus neurons at multiple survival times. Motoneurons controlling TT were located ventral to the ipsilateral motor trigeminal nucleus and extended rostrally towards the medial aspect of the lateral lemniscus. Transynaptically labeled neurons were observed bilaterally in the dorsal and dorso-medial parts of ventral cochlear nuclei as early as 48 h after virus injection, and had morphological features of radiate multipolar cells. After >or=69 h, labeled cells of different types were observed in all cochlear nuclei. At those times, labeling was also detected bilaterally in the medial nucleus of the trapezoid body and periolivary cell groups in the superior olivary complex. Based on the temporal course of viral replication, our data strongly suggest the presence of a direct projection of neurons from the ventral cochlear nuclei bilaterally to the TT motoneuron pool in rats. The influence of neurons in the cochlear nuclei upon TT activity through direct and indirect pathways may account for multifunctional roles of this muscle in auditory functions.

[Topical anesthesia of the tympanic membrane and tubal function--is there a correlation?]. / Topische Trommelfellanästhesie und Tubenfunktion--gibt es Zusammenhänge?

The influence of topical anaesthesia of the tympanic membrane on Eustachian tube function was investigated using the pressure chamber impedance method, thus obtaining quantitative data. Anaesthesia was performed by application to the tympanic membrane of small cotton balls containing lidocaine and dimethylsulfoxide. We did not observe significant alterations of tubal parameters after unilateral or bilateral anaesthesia. Our observations are in contrast to investigations published by Nagai. We suppose that differences in methods of topical anaesthesia are responsible for this discrepancy. Our technique of topical anaesthesia of the tympanic membrane excludes any effect on the Eustachian tube, thereby avoiding negative consequences of middle ear pressure on wound healing.

Effect of central depressants on the acoustic middle ear reflex in rabbit. A method for quantitative measurements of drug effect on the CNS.

The respective effects of pentobarbital-sodium, enibumal-sodium, urethane, urethane-chloralose and lidocaine on the function of the acoustic middle ear reflex in the rabbit were studied. The response of the middle ear muscles was measured by recording changes in both ears' acoustic impedance when the reflex was elicited by applying pure tone stimuli (2,000 Hz) to the two ears one at a time. In that way both the crossed and the uncrossed reflexes were studied. All the drugs were found to depress the reflex in such a way that a higher sound intensity was required after administration to achieve the same impedance change as before. The effect of the anesthetics was roughly proportional to their known anesthetic power. Lidocaine produced only a slight depression of the reflex. The crossed reflex showed a greater susceptibility to the general anesthetics than did the uncrossed reflex which suggests a greater complexity of the crossed reflex. Because the method of recording the reflex response does not require any surgery and is equally well applicable in unrestrained rabbits and in humans, it is suggested as a way of testing the effect of drugs on the central nervous system.