Smooth muscle in the annulus fibrosus of the tympanic membrane: physiological effects on sound transmission in the gerbil.
In a wide variety of mammals, the rim of the tympanic membrane (annulus fibrosus) has an array of contractile elements, either smooth muscle [Henson and Henson, J. Assoc. Res. Otolaryngol. 1 (2000) 25-32] or myofibroblasts [Kuijpers et al., Hear. Res. 128 (1999) 80-88]. These elements are anchored peripherally to the bony tympanic ring and centrally to incoming fibers of the pars tensa. Their arrangement suggests that they are involved in the control of tympanic membrane tension. In this study, cochlear microphonic (CM) threshold changes were recorded in gerbils to study the physiological effects of these contractile elements. It was demonstrated that the application of substances known to make smooth muscle contract (vanadate and norepinephrine) caused concentration-dependent elevations in CM thresholds. Maximum changes of 8-9 dB occurred with the lowest frequency tested (2.16 kHz). The application of muscle-relaxing drugs reversed these effects. Controls showed that the threshold changes were not induced by effects on middle or inner ear structures. These results add to emerging evidence that the tympanic membrane has intrinsic control of tension and is potentially able to have some control over energy levels reaching the cochlea.
Yang
Xinming
X
Department of Otolaryngology, The Second Affiliated Hospital, Xiang Ya School of Medicine, Central South University, Changsha, Hunan 01186, P R China.
Henson
O W
OW
D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester / Q000494:pharmacology; D000818:Animals; D001309:Auditory Threshold / Q000187:drug effects / Q000502:physiology; D003055:Cochlear Microphonic Potentials / Q000187:drug effects / Q000502:physiology; D005260:Female; D005849:Gerbillinae / Q000502:physiology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects; D009126:Muscle Relaxation / Q000187:drug effects; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D009599:Nitroprusside / Q000494:pharmacology; D009638:Norepinephrine / Q000494:pharmacology; D014432:Tympanic Membrane / Q000187:drug effects / Q000502:physiology*; D014638:Vanadates / Q000494:pharmacology
D009599:Nitroprusside; D014638:Vanadates; D001498:3-Pyridinecarboxylic acid, 1,4-dihydro-2,6-dimethyl-5-nitro-4-(2-(trifluoromethyl)phenyl)-, Methyl ester; D009638:Norepinephrine