ABSTRACT
One of the factors which can affect the amount of temporary threshold shift (TTS) due to acoustic overstimulation is known to be the general metabolic state of the exposed subject. The present study was conducted to elucidate how preexisting intense emotional stress in awake guinea pigs could influence the TTS induced by exposure of 4 kHz at 120 dB SPL for 20 min. Considering the hypersympathetic activity in both 'stress' and 'noise' it was assumed that the two factors would act synergetically on the cochlear function. However, an unexpected result was obtained. The mean threshold for the stressed animals following noise exposure was significantly lower (better) than that of the controlled, sedated, guinea pigs.
Subject(s)
Auditory Threshold/physiology , Noise/adverse effects , Stress, Psychological/physiopathology , Acoustic Stimulation , Action Potentials , Animals , Blood Pressure , Cochlea/blood supply , Cochlea/physiopathology , Guinea Pigs , Heart Rate , Norepinephrine/blood , Regional Blood Flow , Sympathetic Nervous System/physiopathologyABSTRACT
The mechanism by which noise damages the inner ear has not as yet been fully elucidated. Experiments were done to study the influence of the sedation in temporary threshold shift (TS) induced by acoustic overstimulation, as barbiturates were found to improve the brain's tolerance to ischemia. Four groups of guinea pigs (GP) were used. The temporary TS was decreased with the reduction of the temperature in awake, as well as sedated, sound-exposed GP. However, the temporary TS in the sedated, but normothermic GP was as great as in the awake, normothermic group. The high temperature counteracts the protection effect of the sedation in nose-induced hearing loss.
Subject(s)
Auditory Threshold/physiology , Noise/adverse effects , Acoustic Stimulation , Animals , Auditory Threshold/drug effects , Body Temperature , Cricetinae , Hearing Loss, Noise-Induced/etiology , Hearing Loss, Noise-Induced/prevention & control , Pentobarbital/pharmacologyABSTRACT
The cochlea is innervated by sympathetic nerves originating or passing the superior cervical ganglion. The termination of one type (the vascular independent) is in the habenular region close to the auditory nerve fibers, and the other, the perivascular type, is associated with blood vessels, particularly in the spiral vessel of the tympanic lip. Suggested functions have so far received partial evidence in the literature. Borg (1982) suggested the protective value of sympathectomy of the ear in noise. Our experiments further elaborate this protective value, as it was seen that bilateral cervical sympathectomy diminished the temporary threshold shift in awake, sound exposed GP.