Stability of efferent-mediated protection against acoustic overexposure with long maintenance under barbiturate anaesthesia.
When anaesthetized animals are maintained over a long period, crossed-cochlear suppressive and enhancement-in-noise effects mediated by the olivocochlear bundle (OCB), as well as some OCB neuronal responses, show time-dependent variations. The present study determined if there were any such changes in OCB-mediated crossed-cochlear protection against compound action potential (CAP) threshold losses caused by a standard loud sound exposure at 11 kHz, presented under conditions either not evoking OCB-mediated protection (i.e. monaural exposure) or evoking protection (binaural exposure). Maintaining animals for periods up to approximately 30 h from initial anaesthetization resulted in non-significant changes in pre-exposure CAP thresholds. There were also only small changes over select frequency ranges in threshold losses caused by the monaural or binaural loud sound, after a single exposure as well as when the testing of OCB function was extended to examine effects after dual successive exposures, the latter result being determined by application of a previously described additivity model. The features of OCB-mediated protection also showed good stability over the long maintenance. These results are discussed as providing further circumstantial evidence that protection is mediated by a different OCB subcomponent to that/those responsible for other OCB-mediated crossed-cochlear effects. In general, the results show that the barbiturate anaesthetic used here does not significantly modulate the crossed-cochlear OCB effect of protection, even though it has been shown elsewhere to significantly depress other crossed-cochlear OCB effects.
Rajan
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Department of Physiology, Monash University, Clayton, Vic., Australia.
D000768:Anesthesia, General; D000818:Animals; D001305:Auditory Fatigue / Q000187:drug effects / Q000502:physiology*; D002415:Cats; D003056:Cochlear Nerve / Q000187:drug effects / Q000503:physiopathology*; D017626:Cochlear Nucleus / Q000187:drug effects / Q000503:physiopathology*; D004525:Efferent Pathways / Q000187:drug effects / Q000503:physiopathology; D016057:Evoked Potentials, Auditory, Brain Stem / Q000187:drug effects / Q000502:physiology; D006317:Hearing Loss, Noise-Induced / Q000503:physiopathology*; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D009847:Olivary Nucleus / Q000187:drug effects / Q000503:physiopathology*; D010424:Pentobarbital / Q000494:pharmacology
D006993:Hypnotics and Sedatives; D010424:Pentobarbital