Activation of tyrosine hydroxylase in the lateral efferent terminals by sound conditioning.
Preconditioning to sound is a well-documented strategy to provide protections against a subsequent acoustic trauma. In the present study, preconditioning (1.0 kHz tone at 81 dB sound pressure level (SPL) for 24 h) protected ABR thresholds by 17-28 dB from an acoustic trauma (2.7 kHz, 103 dB SPL, 30 min) that resulted in a temporary threshold shift. The protection afforded by sound conditioning was shown to be blocked by the administration of 6-hydroxydopamine which disrupts tyrosine hydroxylase in the nerve terminals of the lateral efferent fibers. Furthermore, tyrosine hydroxylase immunoreactivity was up-regulated both by sound conditioning alone, and by the combined treatment of sound conditioning and acoustic trauma. In contrast, acoustic trauma alone resulted in a reduction in tyrosine hydroxylase immunoreactivity compared to unexposed controls. These findings are the first demonstration that tyrosine hydroxylase in the lateral efferents are up-regulated during sound conditioning and suggests a role for the lateral efferent system in protecting against acoustic trauma by sound conditioning.
Niu
Xianzhi
X
Department of Physiology and Pharmacology, Karolinska Institutet, 171 77, Stockholm, Sweden.
Canlon
Barbara
B
D018663:Adrenergic Agents / Q000494:pharmacology; D000818:Animals; D015153:Blotting, Western; D003056:Cochlear Nerve / Q000201:enzymology*; D003213:Conditioning, Psychological / Q000502:physiology*; D004789:Enzyme Activation; D016057:Evoked Potentials, Auditory, Brain Stem / Q000502:physiology; D006168:Guinea Pigs; D006317:Hearing Loss, Noise-Induced / Q000201:enzymology / Q000517:prevention & control; D009411:Nerve Endings / Q000201:enzymology*; D009476:Neurons, Efferent / Q000187:drug effects / Q000201:enzymology*; D016627:Oxidopamine / Q000494:pharmacology; D013016:Sound; D014446:Tyrosine 3-Monooxygenase / Q000037:antagonists & inhibitors / Q000378:metabolism*; D015854:Up-Regulation
D018663:Adrenergic Agents; D016627:Oxidopamine; D014446:Tyrosine 3-Monooxygenase