Gekkonoid lizards increase in body size throughout life, and the present study investigates wheth... more Gekkonoid lizards increase in body size throughout life, and the present study investigates whether changes in auditory function accompany these increases. Middle-ear structures in four groups of animals, adults and juveniles of two gekkonoid species (Eublepharis macularius and Oedura marmorata), were examined. Tympanic membrane velocity and phase were also measured in all four groups. An indication of peripheral auditory function was obtained for each group by measuring compound action potentials (CAPs) from the round window membrane. The middle-ear contribution to CAP thresholds was obtained by comparing threshold levels of the CAP response with and without an intact middle-ear system. The results from these studies indicated that significant changes occurred in middle-ear structure, tympanic membrane velocity and CAP threshold between the younger and older animals. In addition, the adults of both species exhibited better auditory function when the acoustic stimulus was delivered ...
Pflügers Archiv - European Journal of Physiology, 2008
Do related, differently sized species differ in size-related structural or functional traits mere... more Do related, differently sized species differ in size-related structural or functional traits merely because they mature at different points of a uniform allometric ontogenetic growth curve, or do they evolutionarily diverge? We tested ears of gekkotan lizards through experiments distinguishing the two. Auditory sensitivity was assessed by compound action potential (CAP) thresholds in eight species. The best thresholds characterizing species ranged 22-72 dB sound pressure level at 0.5-1.0 kHz. Direct acoustic stimulation of the columella footplate elevated thresholds by 25-50 dB. Intraspecific CAP sensitivity was primarily affected by body length in Eublepharis macularius, but by tympanic-membrane velocity in Oedura marmorata. The chief factor determining middle-ear function (difference in CAP sensitivity before and after middle-ear ablation) was body length in both species. A secondary factor was the middle-ear hydraulic lever ratio in E. macularius, but the mechanical lever in O. marmorata. When intra-and interspecific data were compared, the relation of CAP thresholds to body size in E. macularius resembled the interspecific regression. The intraspecific regression of auditory sensitivity over tympanic membrane velocity in O. marmorata differed from that calculated interspecifically. Hence, the evolutionary contribution to size effects on CAP sensitivity exceeds the ontogenetic contribution. Putatively, body length affects CAP sensitivity through absolute sizes of tympanic membrane and columella footplate. These newly discovered effects join those of the hydraulic lever and (interspecifically) hair-cell number to improve the hearing of larger species that vocally communicate across wider spaces, apparently throughout the Tetrapoda.
The Journal of the Acoustical Society of America, 1991
This presentation considers important developments and new trends related to acoustic injury in t... more This presentation considers important developments and new trends related to acoustic injury in the peripheral auditory system reported during the past 5 years. The discussion begins with the effect overstimulation has on the "active" cochlear process, and the associated loss in receptive field (tuning curve) selectivity. Exposure to intense sound also changes the structure and function of the tectorial membrane, sensory hair bundles, tip links, and intracellular organelles. All of these injuries may change the way in which energy is delivered to the transduction channels of the hair cell. Important new evidence describing the quantitative relation between hair cell loss and permanent hearing loss is reviewed, and the possibility that specific exposure conditions cause unique lesions to the inner or outer hair cells is explored. Finally, the importance of hair cell regeneration in the chick cochlea, changes in the CNS following acoustic injury, and the cochlear vascular system are considered. Ashmore, J. F. (1987). "A fast motile response in guinea-pig outer hair cells: The cellular basis of the cochlear amplifier," J. Physiol. 388, 323-347. Axelsson, A., and Dengernik, H. (1987). "The effects of noise on histological measures of the cochlear vasculature and red blood cells: A review," Hear. Res. 31, 183-192. Billet, T. E., Thorne, P. R., and Gavin, J. B. (1989). "The nature and progression of injury to the organ of Corti during ischemia," Hear. Res. 41, 189-198. Bohne, B. A., Zahn, S. Z., and Bozzay, D. G. (1985). "Damage to the cochlear following interrupted exposure to low frequency noise," Ann. Otol. Rhinol. Laryngol. 94, 122-128. Borg, E., and EngstrSm, B. (1989). "Noise level, inner ear hair cell damage, audiometric features, and equal-energy hypothesis," J. Acoust. Soc. Am. 86, 1776-1782.
Middle-ear development: II. Morphometric changes in the conducting apparatus of the chick
Journal of Morphology, 1992
The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days... more The ontogeny of various middle-ear structures was examined in 11 groups of chicks between 10 days embryonic and adult. Measurements of the tympanic membrane surface area and height, columella length, and that of the columella footplate, annular ligament, and oval window area were obtained using video micrographs and computer digitization techniques. The oval window matures first at 53 days post-hatching, whereas the columella achieves adult size at 74 days. The tympanic membrane surface area is the last middle-ear variable studied to reach adult size (79 days post-hatch). The columella increases its length from 0.63 mm (10 days embryonic) to 2.73 mm in the adult. The tympanic membrane area expands by 280% whereas the columellar footplate area increases by 11x. As a result, the pressure amplification of the middle ear due to the tympanic membrane/columellar footplate area ratio improves by over 400%. These data further contribute to our understanding of the functional development of the middle ear.
Auditory structure and function in the mouse middle ear: An evaluation by SEM and capacitive probe
Journal of Comparative Physiology ? A, 1982
Page 1. J Comp Physiol (1982) 146:517-525 Journal of Comparative Physiology, A 9 Springer-Verlag ... more Page 1. J Comp Physiol (1982) 146:517-525 Journal of Comparative Physiology, A 9 Springer-Verlag 1982 Auditory Structure and Function in the Mouse Middle Ear: An Evaluation by SEM and Capacitive Probe James C. Saunders ...
Sound transmission through the avian interaural pathways
... John J. Rosowski** and James C. Saunders Departments of Physiology and Otorhinolaryngology an... more ... John J. Rosowski** and James C. Saunders Departments of Physiology and Otorhinolaryngology and Human Communication, University of Pennsylvania, Philadelphia, Pennsylvania ... I. Evidence of binaural interactions in dorsal medullary nucleus in bullfrogs (Rana catesbeiana ...
Morphometric changes in the chick nucleus magnocellularis following acoustic overstimulation
The Journal of Comparative Neurology, 1998
The present investigation considered the effects of cochlear damage caused by exposure to intense... more The present investigation considered the effects of cochlear damage caused by exposure to intense sound on the nucleus magnocellularis of the chick. Neonatal chicks exposed to intense sound were separated into four groups with post-exposure recovery durations of 0, 15, 27, and 43 days. Four age-matched, non-exposed control groups were also formed. At each recovery interval, the control and exposed birds were sacrificed and their brains prepared for paraffin embedding. The brain stem region containing the nucleus magnocellularis (NM) was serially sectioned in the coronal plane. All sections containing NM cells were identified and then coded in terms of their percentile distance from the most caudolateral section. Sections along the nucleus at the 15th, 30th, 50th, 65th, 80th, and 95th percentile positions were selected for evaluation, and the cross-sectional areas of individual NM cells in these sections were then measured. Cell areas were corrected for the bias introduced by eccentricity of the nucleus. The number of NM cells per 1,000 microm2 was also calculated at the 50th and 65th percentile positions. These procedures were repeated for the age-matched, non-exposed control animals. The cross-sectional cell area in exposed animals, immediately after the exposure, was reduced significantly at all positions, but returned to near normal by 43 days of recovery. However, the coronal area of NM in the sections at the 50th and 65th percentile position, as well as NM cell density, were unaffected by the exposure at all recovery intervals. The observation of structural recovery in NM cells at 43 days post-exposure was remarkable because it occurred at least 4 weeks after complete functional restoration of single-cell activity in the NM. The shrinkage in NM cell size throughout the nucleus may be due to a general reduction in spontaneous activity in the cochlear nerve fibers caused by the acoustic injury to the chick basilar papilla.
... The measures of CM threshold for the 1.0-tv level were within 5 db of previously reported thr... more ... The measures of CM threshold for the 1.0-tv level were within 5 db of previously reported thresholds (3, 4) while the intensity functions and click wave shapes were similar to those described by Mikaelian, Alford and Ruben (22). ... 22. MIKAELIAN, D., BR ALFORD, and RJ RUBEN. ...
The effects of sound overexposure on the spectral response patterns of nucleus magnocellularis in the neonatal chick
Experimental Brain Research, 1993
Spectral response plots from single cells in the chick nucleus magnocellularis were obtained foll... more Spectral response plots from single cells in the chick nucleus magnocellularis were obtained following a 48 h exposure to a 0.9 kHz pure tone at 120 dB sound pressure level and after a recovery period of 12 days. Immediately after removal from the exposure, a variety of changes in the spectral response patterns of nucleus magnocellularis cells were noted. In particular, at recovery day 0, there was a significant decrease in spontaneous rate; a substantial loss of threshold sensitivity and frequency selectivity; and alterations in both the slope and dynamic range of the rate-intensity function. Interestingly, the maximum discharge rate appeared unaffected by the intense sound. Twelve days after removal from overstimulation, auditory function appeared to be operating at normal levels of efficacy as spontaneous rate, threshold sensitivity, frequency selectivity, and the dynamic range of the rate-intensity function were statistically identical to similar measures in nonexposed control birds. The loss and restoration of auditory function is correlated to structural damage and repair of the avian basilar papilla.
Young and adult chickens exhibit substantial inner-ear damage and post-exposure deterioration in ... more Young and adult chickens exhibit substantial inner-ear damage and post-exposure deterioration in cochlear nerve activity following exposure to intense sound. Both the structural and functional losses largely recover in both age groups within 2-4 weeks after exposure. However, some aspects of acoustic trauma differ between the young and adult chicken ear. Overstimulation in the young chick causes considerable post-exposure loss and then recovery of the steady-state endocochlear potential, while in the adult animal there is little post-exposure effect on this potential. Moreover, in adults there is postexposure loss but little recovery in the distortion product otoacoustic emission (DPOAE). The present study explores the possibility of an age difference in the effects of overstimulation on the DPOAE by examining these emissions in young chicks following exposure to an intense pure tone. Chicks exposed to intense sound were formed into groups at 0 and 12 days of recovery, and these were complemented by two additional groups of age-matched controls. The cubic difference tone emission (the 2f 1 -f 2 DPOAE component) was measured at 9 levels for 13 frequencies in all groups. Shortly after the exposure, the DPOAE reliably declined with the maximum loss at or above the exposure tone frequency. The exposed chicks examined 12 days after exposure showed complete recovery of the DPOAE. It would appear that 12 days of recovery sufficiently repaired inner ear damage to completely restore DPOAE production. This result is different from that in adult chicken and may be related to the greater severity of acoustic damage in the adult ear, a reduced susceptibility of the young ear to acoustic trauma, or the ability of the young animal to more successfully repair the inner ear.
The Anatomical Record Part A: Discoveries in Molecular, Cellular, and Evolutionary Biology, 2005
The function of the ear depends in part on its absolute size and internal proportions. Thus, in b... more The function of the ear depends in part on its absolute size and internal proportions. Thus, in both young individuals and small species, the middle ear is expected to be allometrically enlarged despite its smaller absolute size. Here we aim to compare the ontogenetic allometry of relevant middle-ear structures as observed within gecko (gekkonomorph lizards) species, with the evolutionary allometry observed interspecifically. These observations also provide middle-ear data for future evaluation of variation in auditory sensitivity. The material comprised 84 museum specimens of geckos, representing nine species of three gekkonomorph subfamilies. The results of dissections and measurements show that different reports notwithstanding, the middle-ear ossicular chain is indeed structured as described for geckos by Werner and Wever (J Exp Zool 1972;179:1-16) and Wever (The reptile ear, 1978). Some sexual dimorphism is indicated, but this requires further study. During postnatal ontogeny, the allometric growth in the ratio of the columellar footplate area to body length differed between the intraspecific and interspecific levels, hence species differences in the middle ear do not merely result from animal size. The ratio of the tympanic membrane area to the columellar footplate area increased during ontogeny. In this, geckos resemble birds and probably also mammals. Similarly, when the comparison was among adults representing different species, the ratio of the tympanic membrane area to the columellar footplate area increased with body size. In this, however, the geckos differed from birds and mammals, in which this ratio varied taxonomically, irrespective of body size. It would thus seem that middle-ear proportions have evolved among geckos to produce small interspecific differences, but among amniote tetrapods they have evolved according to different principles in the classes reptiles, birds, and mammals.
6 other HighWire hosted articles, the first 5 are: This article has been cited by [PDF] [Full Tex... more 6 other HighWire hosted articles, the first 5 are: This article has been cited by [PDF] [Full Text] [Abstract] , April 1, 2007; 97 (4): 3082-3092. J Neurophysiol S. Wohlgemuth and B. Ronacher Trains Auditory Discrimination of Amplitude Modulations Based on Metric Distances of Spike [PDF] [Full Text] [Abstract] , May 1, 2007; 97 (5): 3376-3385. J Neurophysiol A. Vogel and B. Ronacher System of Locusts Neural Correlations Increase Between Consecutive Processing Levels in the Auditory [PDF] [Full Text] [Abstract] , June 13, 2007; 27 (24): 6461-6472. Adaptation Reduces Spike-Count Reliability, But Not Spike-Timing Precision, of [PDF] [Full Text] [Abstract] , September 1, 2007; 98 (3): 1706-1717. J Neurophysiol Information Rate and Spike-Timing Precision of Proprioceptive Afferents [PDF] [Full Text] [Abstract]
The Journal of neuroscience : the official journal of the Society for Neuroscience, Jan 15, 1999
Targeted mutagenesis in mice demonstrates that the POU-domain gene Brn4/Pou3f4 plays a crucial ro... more Targeted mutagenesis in mice demonstrates that the POU-domain gene Brn4/Pou3f4 plays a crucial role in the patterning of the mesenchymal compartment of the inner ear. Brn4 is expressed extensively throughout the condensing mesenchyme of the developing inner ear. Mutant animals displayed behavioral anomalies that resulted from functional deficits in both the auditory and vestibular systems, including vertical head bobbing, changes in gait, and hearing loss. Anatomical analyses of the temporal bone, which is derived in part from the otic mesenchyme, demonstrated several dysplastic features in the mutant animals, including enlargement of the internal auditory meatus. Many phenotypic features of the mutant animals resulted from the reduction or thinning of the bony compartment of the inner ear. Histological analyses demonstrated a hypoplasia of those regions of the cochlea derived from otic mesenchyme, including the spiral limbus, the scala tympani, and strial fibrocytes. Interestingly,...
The purpose of this study is to compare collateral tissue damage and wound healing in incisions c... more The purpose of this study is to compare collateral tissue damage and wound healing in incisions created by electro-dissociation and conventional electrosurgery. Conventional electrosurgery has been used as an alternative to the scalpel to improve hemostasis. However, the heat generated by this instrument can cause tissue damage surrounding the incision, limiting its use around nerves and large blood vessels. A new technology, Coblation (Arthrocare Corp., Sunnyvale, CA), uses "electro-dissociation" to achieve similar results by creating charged particles from a conductive medium to make an incision while simultaneously achieving hemostasis. This new approach to electrosurgery may reduce soft tissue damage. Two prospective, matched design experiments were performed. In experiment I, both devices were set at the same electrical power in watts and then used to create an incision on the tongue of rats. In experiment II, the electrical power settings of both devices were adjusted until they created incisions of the same size. Epithelial destruction and collateral tissue damage were measured in histologically prepared tissue in both experiments, and the wound healing process was observed in experiment II at 0, 3, 7, and 14 days after surgery. The results showed that the electro-dissociation method created significantly less epithelial destruction and collateral tissue damage in both experiments. Granulation tissue formation was also significantly less extensive in the electrodissociation-induced incision after 7 and 14 days of recovery. Wound healing may be faster than with conventional electrosurgery if the Coblation device is used.
A semi-intact preparation of the chick basilar papilla was developed to study calcium-dependent n... more A semi-intact preparation of the chick basilar papilla was developed to study calcium-dependent neurotransmitter release by tall hair cells (avian equivalent of cochlear inner hair cells).
Many non-mammalian ears lack physiological features considered integral to the generation of otoa... more Many non-mammalian ears lack physiological features considered integral to the generation of otoacoustic emissions in mammals, including basilar-membrane traveling waves and hair-cell somatic motility. To help elucidate the mechanisms of emission generation, this study systematically measured and compared evoked emissions in all four classes of tetrapod vertebrates using identical stimulus paradigms. Overall emission levels are largest in the lizard and frog species studied and smallest in the chicken. Emission levels in humans, the only examined species with somatic hair cell motility, were intermediate. Both geckos and frogs exhibit substantially higher levels of high-order intermodulation distortion. Stimulus frequency emission phase-gradient delays are longest in humans but are at least 1 ms in all species. Comparisons between stimulus-frequency emission and distortion-product emission phase gradients for low stimulus levels indicate that representatives from all classes except frog show evidence for two distinct generation mechanisms analogous to the reflection-and distortion-source (i.e., place-and wavefixed) mechanisms evident in mammals. Despite morphological differences, the results suggest the role of a scalingsymmetric traveling wave in chicken emission generation, similar to that in mammals, and perhaps some analog in the gecko.
Journal of the Association for Research in Otolaryngology, 2004
We have employed both in vitro patch clamp recordings of hair cell synaptic vesicle fusion and in... more We have employed both in vitro patch clamp recordings of hair cell synaptic vesicle fusion and in vivo single unit recording of cochlear nerve activity to study, at the same synapse, the time course, control, and physiological significance of readily releasable pool dynamics. Exocytosis of the readily releasable pool was fast, saturating in less than 50 ms, and recovery was also rapid, regaining 95% of its initial amplitude following a 200-ms period of repolarization. Longer depolarizations (greater than 250 ms) yielded a second, slower kinetic component of exocytosis. Both the second component of exocytosis and recovery of the readily releasable pool were blocked by the slow calcium buffer, EGTA. Sound-evoked afferent synaptic activity adapted and recovered with similar time courses as readily releasable pool exhaustion and recovery. Comparison of readily releasable pool amplitude, capture distances of calcium buffers, and number of vesicles tethered to the synaptic ribbon suggested that readily releasable pool dynamics reflect the depletion of release-ready vesicles tethered to the synaptic ribbon and the reloading of the ribbon with vesicles from the cytoplasm. Thus, we submit that rapid recovery of the cochlear hair cell afferent fiber synapse from short-term adaptation depends on the timely replenishment of the synaptic ribbon with vesicles from a cytoplasmic pool. This apparent rapid reloading of the synaptic ribbon with vesicles underscores important functional differences between synaptic ribbons in the auditory and visual systems.
We have demonstrated that the phenotype of the mouse mutant sex-linked fidget (slf) is caused by ... more We have demonstrated that the phenotype of the mouse mutant sex-linked fidget (slf) is caused by developmental malformations of the inner ear that result in hearing loss and vestibular dysfunction. Recently, pilot mapping experiments suggested that the mouse Brn4/Pou3f4 gene co-segregated with the slf locus on the mouse X chromosome. These mapping data, in conjunction with the observation that the vertical head-shaking phenotype of slf mutants is identical to that observed in mice with a targeted deletion of the Brn4 gene, suggested that slf is a mutant allele of the Brn4 gene. In this paper, we have identified the nature of the slf mutation, and demonstrated that it is an X chromosomal inversion with one breakpoint close to Brn4. This inversion selectively eliminates the expression of the Brn4 gene in the developing inner ear, but not the neural tube. Finally, these results demonstrate that the slf mutation is a good mouse model for the most prevalent form of X-linked congenital deafness in man, which is associated with mutations in the human Brn4 ortholog, POU3F4.
Intense sound exposure to the chick ear produces cochlear damage and losses in auditory function.... more Intense sound exposure to the chick ear produces cochlear damage and losses in auditory function. At twelve days post exposure there is considerable structural repair, although a defect on the sensory epithelium remains in the form of an incompletely healed 'patch' lesion. Auditory function significantly recovers 12 days after the exposure, but it, too, is incomplete. In this paper we describe the relationship between stimulus intensity and cochlear nerve discharge rate (the rate-intensity function) in two groups of chicks. One is exposed to damaging sound levels but allowed 12 days to recover, while the other is a group of non-exposed and age-matched control animals. Three different types of rate-intensity functions were identified; saturating, sloping, and straight. The percentage of saturating and sloping functions was compared across all characteristic frequencies in both groups of animals. A significant change was observed in the distribution of these types for recovered units with characteristic frequencies within the region of the patch lesion. In addition, the rate-intensity functions of these units exhibited a steeper slope and a higher maximum response. The distribution of rate-intensity function types and their slope and maximum responses, for units with characteristic frequencies outside of the patch lesion, was similar to those found in control ears. The changes in the cochlear nerve response in exposed chicks may be due to alterations in cochlear mechanics, hair cell or synaptic membrane properties, hair cell innervation, or the loss of a tonic suppression of afferent activity exerted by the damaged short hair cells.
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Papers by James Saunders