title: Similar half-octave TTS protection of the cochlea by xylazine/ketamine or sympathectomy.
abstract: Cochlear efferents, sympathetic control and stress conditions have been shown to influence sound-induced hearing loss. These factors are also known to be modified by sedation/anesthesia. We tested here the effect of sedation/anesthesia on temporary threshold shift (TTS) compared to that in the same awake animals. The effect of sympathectomy was also tested. We employed awake guinea pigs with a chronically implanted electrode on the round window of each of the cochleae. Each ear was tested for its sensitivity to TTS induced by a 1 min or a 10 min exposure to an 8 kHz pure tone at 96 dB sound pressure level. After an intramuscular injection of xylazine or ketamine together with xylazine, TTS at half-octave frequencies was reduced compared to that in awake animals. The second half-octave frequencies were less affected. This specific pattern of protection was also observed here after surgical ablation of a superior cervical ganglion. The data lead to the speculation that protection from TTS under sedation/anesthesia might be due to diminished sympathetic influence. Xylazine is a pre-synaptic alpha2-adrenoreceptor agonist which blocks noradrenaline release from the sympathetic system. Ketamine is a N-methyl-D-aspartic acid receptor antagonist which could reduce glutamate excitotoxicity as well as reduce sympathetic activity.
authors.affiliation: Inserm EPI 9902, Laboratoire d'Otologie Neuro-Otologie, Université Aix-Marseille II, Faculté de Médecine Nord, Boulevard Pierre Dramard, 13916 Cedex 20, Marseille, France.
authors.forename: Fabrice
authors.initials: F
authors.lastname: Giraudet
authors.forename: Kathleen C
authors.initials: KC
authors.lastname: Horner
authors.forename: Yves
authors.initials: Y
authors.lastname: Cazals
mesh_terms: D000316:Adrenergic alpha-Agonists / Q000494:pharmacology*; D000758:Anesthesia; D000818:Animals; D001309:Auditory Threshold / Q000187:drug effects* / Q000502:physiology; D003051:Cochlea / Q000187:drug effects* / Q000502:physiology*; D018691:Excitatory Amino Acid Antagonists / Q000494:pharmacology*; D006168:Guinea Pigs; D006993:Hypnotics and Sedatives / Q000494:pharmacology; D007649:Ketamine / Q000494:pharmacology*; D013562:Sympathectomy; D013997:Time Factors; D014991:Xylazine / Q000494:pharmacology*
chemical_list: D000316:Adrenergic alpha-Agonists; D018691:Excitatory Amino Acid Antagonists; D006993:Hypnotics and Sedatives; D014991:Xylazine; D007649:Ketamine