Abstract
BackgroundHyperbaric oxygen therapy (HBOT) is a known adjuvant for treating ischemia-related inner ear diseases. Controversies still exist in the role of HBOT in cochlear diseases. Few studies to date have investigated the cellular changes that occur in inner ears after HBOT. Nitric oxide, which is synthesized by nitric oxide synthase (NOS), is an important signaling molecule in cochlear physiology and pathology. Here we investigated the effects of hyperbaric oxygen on eardrum morphology, cochlear function and expression of NOS isoforms in cochlear substructures after repetitive HBOT in guinea pigs.ResultsMinor changes in the eardrum were observed after repetitive HBOT, which did not result in a significant hearing threshold shift by tone burst auditory brainstem responses. A differential effect of HBOT on the expression of NOS isoforms was identified. Upregulation of constitutive NOS (nNOS and eNOS) was found in the substructures of the cochlea after HBOT, but inducible NOS was not found in normal or HBOT animals, as shown by immunohistochemistry. There was no obvious DNA fragmentation present in this HBOT animal model.ConclusionsThe present evidence indicates that the customary HBOT protocol may increase constitutive NOS expression but such upregulation did not cause cell death in the treated cochlea. The cochlear morphology and auditory function are consequently not changed through the protocol.
Highlights
Hyperbaric oxygen therapy (HBOT) is a known adjuvant for treating ischemia-related inner ear diseases
No significant auditory changes after repetitive customary HBOT All the animals in the experimental group tolerated the entire course of HBOT without signs of irritability or discomfort
Slight elevated hearing level at 1 kHz was recorded in the normobaric air (NBA) group, the intergroup hearing level between the control NBA and experimental HBOT groups did not significantly differ (Figure 2)
Summary
Hyperbaric oxygen therapy (HBOT) is a known adjuvant for treating ischemia-related inner ear diseases. Hyperbaric oxygen therapy (HBOT) is an effective treatment for decompression Sickness (DCS) and arterial gas embolism (AGE) [1], and is proposed as an adjunct in treating ischemia-related inner ear diseases [2,3,4], sudden deafness [4,5], and acute noise trauma [6,7]. Constitutive isoforms of NOS, both nNOS and eNOS, are expressed in the normal cochlea [16], but iNOS is expressed in the cochlea only after exposure to some pathologic conditions such as endotoxins [12], ischemia [13] or acoustic trauma [17]. The aim of this study was to investigate the effects of repetitive HBOT on cochlear function and the expression of NOS isoforms by means of immunohistochemical staining
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