Hair Cell Activity Research Articles

Changes in endocochlear potential during anoxia after intense noise exposure

Endocochlear potentials (EPs) were investigated in healthy guinea pigs and in those exposed to white noise of 125 dB SPL for 20–80 min. EPs were measured during and after temporary anoxia (3.5 min, denoted as reversible anoxia) and then during continuous anoxia to evaluate noise-induced changes in EP properties. Succino-dehydrogenase (SDH) activity and morphologic changes in hair cells were also evaluated in surface preparations of the hair cells. It was found that changes in EPs correlated with the duration of noise exposure. The longer the noise exposure, the greater the decrease in EPs. EPs could recover in one week post-exposure, in roughly the same time needed for recovery of SDH activity in hair cells. Noise exposure also resulted in some changes in EP dynamic behaviour during and after reversible anoxia, but did not cause any significant change in maximal negative EP. The mechanisms underlying these results are discussed.

Frequency variation in spontaneous sound emissions from guinea pig and human ears

Spontaneous acoustic emissions were recorded from 7 of 15 human ears at frequencies between 900 and 4000 Hz and just above 1000 Hz in a guinea pig. The constancy or changes in the frequency composition of these emissions is of particular interest in the light of current models which implicate outer hair cell activity in their generation. In our present study, most emissions underwent continuous fluctuations in frequency over a bandwidth of 0.5-10 Hz in humans and more than 20 Hz in a young guinea pig. Jumps in frequency of emission by as much as 20 Hz occurred during test sessions in some of the human ears. Changes in emission frequency were also observed during suppression by an externally delivered tone. The frequency of the emissions at successive test sessions also varied in some human ears and in the guinea pig between the ages of 6 and 9 weeks. The guinea pig emission also underwent an increase of 50 Hz in frequency and a reduction of 25 dB in level during recovery from anaesthesia. Neely's model for the role of hair cells in the generation of spontaneous emissions suggests that changes in hair cell conductance could influence the frequency of spontaneous oscillation. The small, but continuous changes in spontaneous emission frequency seen in all ears may reflect changes in conductance at the hair cell level due to synaptic and transducer channel activity.

Functional role of the olivo-cochlear bundle: A motor unit control system in the mammalian cochlea

A fiber optic lever is applied to the measurement of the motion of the basilar membrane motion in guinea pigs. In response to intense tones from either ear, the motion includes a substantial summating shift in the mean position in addition to a travelling wave originally described by von Békésy. His stroboscopic technique and most techniques used since have been concentrated upon measuring vibrations of the basilar membrane synchronous with the stimulus and have been insensitive to variations in the baseline position such as a summating component of motion analogous to the extracellular summating potential. In addition to the role of the outer hair cells in providing normal hearing sensitivity, they evidently play a role in regulating the mean position of the basilar membrane. For a fixed frequency, the polarity of the mean position varies systematically with sound level and place and summates with time since onset. Since these cells are the target cells for the olivocochlear bundle, homeostasis in the cochlea would appear to be linked efferent function and involve cochlear mechanics. The negative damping hypothesis asserts that hair cell activity is necessary for low thresholds. The results presented here demonstrate that OHC activity exists independent of neural thresholds. The discussion develops the concept that threshold losses are due to a mismatch of opposing tonic forces which normally maintain the mean position of the basilar membrane. Structure is examined in relation to function and the group of outer hair cells innervated by a single medial efferent neuron is identified as a motor unit. Implications of central control of individual motor units include peripheral involvement in selective attention tasks.

Are delayed evoked oto-acoustic emissions (DEOE) solely the outcome of an active intracochlear mechanism?

Post-mumps and post-measles hearing losses are a result of the destruction of Corti's organ. Both the basilar and the Reissner membranes are unimpaired. In 11 subjects with post-mumps (8 cases) and post-measles (3 cases) unilateral anacusis, DEOE with a mean amplitude lower than that of the contralateral normal ear with the same sensation level were observed with 0.5, 1 and 2 kHz tone-bursts and air conduction stimulation. These findings lend credit to the view that DEOE could in part be produced by a passive intracochlear mechanism, probably a consequence of the basilar membrane travelling wave induced by the displacement of the perilymph. In a normal ear, this passive mechanism could be superimposed by an active mechanism linked to the contractile activity of the outer hair cells (OHC) which modulates and increases the travelling wave depth.

The influence of middle ear pressure on the otolith system in cats.

The influence of varying middle ear pressure on the otolith system was investigated in anesthetized cats. Extra-axonal recordings of action potentials were performed in the vestibular nerve fibers and in the neurons in the lateral vestibular nucleus that responded to lateral or anteroposterior steady-state tilt. Positive or negative pressure was applied to the ipsilateral middle ear during the recordings. Seventy-three percent of the fibers and 63% of the neurons responded to changes in the middle ear pressure. These response rates were higher than those previously reported on the units innervating semicircular canals. Findings suggest that the otolith organs are more sensitive to changes in the middle ear pressure than are the semicircular canals. The units responding to lateral tilt were more sensitive to middle ear pressure than those that responded to anteroposterior tilt. Displacement of endolymph caused by pressure changes in the middle ear was considered to have affected the activities of hair cells in otolith organs.

Selective attention modifies the active micromechanical properties of the cochlea

The micromechanical properties of the cochlea accounting for the exquisite properties of sensitivity and frequency selectivity depend on the integrity of an active biochanism probably based upon a motile activity of outer hair cells (OHCs). Evoked oto-acoustic emissions (EOAEs), i.e. sounds emitted by the cochlea in response to a click, reflect this active biomechanism. We demonstrate here that selective attention task in human subject alters EOAEs. This means that the central nervous system can modify active cochlear micromechanics prior to the transduction process, probably by using the medial efferent system which, coming from the brainstem, innervates the OHCS.

Computer-aided three-dimensional reconstruction and morphometry of the outer hair cells of the guinea pig cochlea.

The outer hair cells and their nerve endings in the basal and third turns of the guinea pig cochlea were reconstructed three-dimensionally from serial thin sections by means of computer graphics, and morphometric data were obtained. The number of nerve endings in the third turn was two to three times greater than that in the basal turn. Many afferent and efferent terminals in the third turn did not demonstrate synaptic specialization. Presynaptic dense bodies were missing in the majority of outer hair cells in both basal and third turns. The morphologic arrangement of the subsurface cisternae and efferent fiber synapses on the side and base of the outer hair cells suggests a close functional relationship. The nerve fibers and cisternae may be involved in the contractile process of the cells. The volume of the outer hair cells in the first row of the basal turn was about 656 micron 3, and third turn, 1358 micron 3. The total count of mitochondria in the outer hair cells of the first row in the basal turn was 1425, and 1963 in the third turn. The density of mitochondria in the sensory cell in the basal turn was higher. The highest density was seen in the infranuclear region. The mitochondrial distribution patterns suggest that metabolic activity of the outer hair cells is higher in the basal turn than in the third turn and the energy requirement is greatest in the region close to nerve endings.

The influence of Middle Ear Pressure on the Otolith System in Cats

The influence of varying middle ear pressure on the otolith system was investigated in anesthetized cats. Extra-axonal recordings of action potentials were performed in the vestibular nerve fibers and in the neurons in the lateral vestibular nucleus that responded to lateral or anteroposterior steadystate tilt. Positive or negative pressure was applied to the ipsilateral middle ear during the recordings. Seventy-three percent of the fibers and 63% of the neurons responded to changes in the middle ear pressure. These response rates were higher than those previously reported on the units innervating semicircular canals. Findings suggest that the otolith organs are more sensitive to changes in the middle ear pressure than are the semicircular canals. The units responding to lateral tilt were more sensitive to middle ear pressure than those that responded to anteroposterior tilt. Displacement of endolymph caused by pressure changes in the middle ear was considered to have affected the activities of hair cells in otolith organs.

High susceptibility to hypoxia of afferent synaptic transmission in the goldfish sacculus.

1. The effect of hypoxia on synaptic transmission between hair cells and afferent fibers was examined in the sacculus of goldfish. For this, we recorded potentials, intracellularly, from large afferent fibers. Anoxia was introduced by perfusing the gill with water deprived of oxygen or by halting the water flow to the gill. 2. The ear of the goldfish is most sensitive to hypoxia. Sound-evoked afferent activities were profoundly depressed within several minutes after the introduction of hypoxia. 3. The depressed afferent activity was attributed to a reduction in the amplitude of sound-evoked excitatory postsynaptic potentials (EPSPs) generated at afferent fiber terminals, since no significant change was detected in the resting and action potentials of afferent fibers or in intensity of the threshold current required to set up an action potential. Also, there was no marked change in the electrical activity of hair cells, determined by the finding that the amplitude of intramacularly recorded microphonic potentials and that of the coupling potentials was not altered. 4. A statistical analysis of the amplitude of sound-evoked EPSPs revealed that the binomial parameter n decreased during hypoxia, in parallel with a reduction in the amplitude of EPSPs, while the binomial parameter p either remained unaltered or was augmented. No change was found in the quantal size, thereby indicating that the sensitivity of the postsynaptic membrane remained unchanged. These results indicate that presynaptic mechanisms within hair cells, especially those playing a role in transmitter release or in replenishment of the latter, are suppressed during hypoxia.

Acoustic distortion from rodent ears: A comparison of responses from rats, guinea pigs and gerbils

The oto-acoustic emissions generated in response to two-tone stimulation have been studied in the ear canal sound pressure of three species of rodent: rat ( Rattus norvegicus), guinea pig ( Cavia porcellus) and Mongolian gerbil ( Meriones unguiculatus). The level of acoustic intermodulation distortion evoked by equal-level stimuli at different frequencies can be related to the threshold frequency response curves obtained by other workers for these species using evoked electrical responses or behavioural techniques. Gerbils produce higher levels of distortion below 9 kHz than the rat or guinea pig. This may be due to the greater efficiency of the middle ear at low frequencies. Growth of 2 f 1− f 2 with equal-level, widely-spaced stimuli ( f 2 f 1 = 1.3 ) can be divided into two regions. The low intensity part of the curve grows with a slope of 1 and saturates above 60 dB SPL. With higher level stimuli, there is rapid growth with a slope of, or approaching 3. Differences in growth rate may distinguish a low-level, saturating response which owes its response characteristics to the activity of hair cells from a high-level response attributable to passive mechanical properties of the cochlea. A broad, low-frequency spread of distortion components is seen as the stimulus frequencies converge. Sharp interruptions in the growth curves of these components may be due to interaction between out-of-phase components of ‘low’ and ‘high’ level distortion. The distortion in the gerbil can be distinguished from that of the other two species in a number of details. Structural specialisation of the gerbil cochlea may contribute to these distinctive features.

Responses of Cat Auditory Nerve Fibers to Biphasic Electrical Current Pulses

Discharge patterns of single auditory nerve fibers were recorded from normal-hearing cats implanted with a 12-band intracochlear electrode array. Stimuli were biphasic current pulses of specifiable width, amplitude, and rate. Acoustic tuning curves were obtained to determine the cochlear positions of the fibers. Response latencies to electrical stimuli formed two groups. Short latency (0.3 to 0.7 ms) responses were attributed to direct activation of spiral ganglion neurons. At high stimulus intensities, these often exhibited abrupt shifts toward even shorter latencies. Long latency (> 1.5 ms) responses were probably caused by electrophonic activation of functional hair cells. Response thresholds to electrical stimuli depended on a fiber's proximity to the stimulating electrodes, and they did not depend on a fiber's acoustic response threshold or spontaneous discharge rate. High intensity (> 1.5 mA) stimuli could excite fibers over a wide range of characteristic frequencies, even for the narrowest (0.45 mm) electrode separations. Response threshold was an exponentially decreasing function of pulse width for widths up to 300 μs/phase. Fiber discharges were highly phase-locked at all suprathreshold intensities, and saturation discharge rates usually equaled stimulus pulse rates for rates up to at least 800 pulses/s. Dynamic ranges were small (1 to 6 dB), increased with pulse rate, and were uncorrelated with electrical response threshold. Within the dynamic range, shapes of poststimulus time and interspike interval histograms resembled those obtained in response to acoustic stimuli. Depolarization block caused fiber activity to cease in 2 to 5 seconds for sustained stimuli presented at high (> 600 pulses/s) pulse rates and intensities.

Recent developments in cochlear physiology.

Recent findings in cochlear physiology have caused many of our long held ideas about how sound is analyzed by the ear to be reevaluated. This article describes changes which have occurred in three classical ideas of cochlear transduction: (1) There is a gradient of frequency representation along the cochlea with high frequencies being represented at the base and lower frequencies represented progressively toward the apex. It is now known that the specific frequency which is represented at a given location along the cochlea is not invariant but changes systematically during the normal development of hearing. (2) The place code and frequency tuning along the cochlea are due to the conventional traveling wave of von Békésy and basilar membrane mechanics. Experiments in nonmammalian vertebrates which lack a traveling wave have shown that other mechanisms, including the mechanical resonance of hair cell stereocilia, may contribute to tonotopic organization and frequency tuning. It is possible that hair cell stereocilia also contribute to frequency representation and tuning in the mammalian cochlea. (3) The vibration of the basilar membrane to sound is determined by its passive mechanical properties. It is now known that the response of the basilar membrane, and that of the cochlear partition as a whole, is influenced by physiological processes which utilize metabolic energy. The active processes are likely expressed through the motile activity of outer hair cells.

Ionic channels for mechanoelectrical transduction and frequency tuning by vertebrate hair cells

The electrical activity of vertebrate hair cells, including mechanoelectrical transduction, resonant frequency tuning, and synaptic transmission, results from the action of an ensemble of ionic channels. In an effort to understand how hair cells function as the sensory receptors of the internal ear, our research group is conducting in vitro investigations of the ionic channels of saccular hair cells from the bullfrog, Rana catesbeiana.Mechanoelectrical transduction commences when stimuli, derived from sounds or accelerations, deflect the hair bundle, a cluster of enlarged microvilli termed stereocilia.

Sensory interaction in the snailHelix lucorum

The activity of hair cells of statocysts inHelix lucorum was investigated by means of intra- and extracellular recording, applying appropriate stimulation of the organs of balance, optic photoreceptors, and the chemoreceptors of the optic tentacle bulb. Mechanical stimulation of the statocysts evoked a firing reaction in the hair cells as a result of generator potentials occurring at the receptors. The amplitude of generator potentials was proportional to the intensity of the reaction. Stimulating the optic photoreceptors by switching on a light produced a spike response in the hair cells with a short latency of 0.3–2 sec. The latent period of this response was inversely proportional to the intensity of the light. Appropriate stimulation of the chemoreceptors of the optic tentacle bulb caused a faint spike response with a long latent period of 20–40 sec in the hair cells. Illumination and stimulation of the chemoreceptors produced an inhibitory response in the form of bursts of IPSP in 2 out of more than 50 hair cells.

Spontaneous activity of hair cells of the snail statocyst and its changes during intracellular stimulation

The following conclusions were drawn from an electrophysiological study of statocyst hair cell activity inHelix lucorum using intracellular recording. The maximal input resistance of the receptors is observed with hyperpolarizing currents of not more than 0.1 nA, close in magnitude to that arising during inhibitory synaptic transmission. Background noise, a special type of activity of statocyst hair cells, is neither synaptic nor pacemaker in nature, but depends entirely on the degree of contact between the cilia and statoconia. The hair cells possess pacemaker properties which are manifested on depolarization. The zone of action potential generation of the receptors lies in the axon. Inhibitory interactions take place between hair cells, leading to the generation of IPSPs in their spontaneous activity, which do not disappear after division of the vestibular nerve.

Link between functional and morphological changes in the inner ear--functional changes produced by ototoxic agents and their interactions.

Common potentials used to evaluate cochlear function are the ac cochlear potential (ACCP), N1 and the positive dc endocochlear potential (EP). The ACCP is an electrical analogue of the sound stimulus; its source is the electrical activity of the cochlear hair cells. N1 is a volume conductor recorded action potential of the auditory nerve. The EP is the positive polarization of the middle compartment of the cochlea (scala media) with respect to the other compartments (the scalae tympani and vestibuli); the stria vascularis is apparently responsible for the EP. Generally, ototoxic drugs and very intense broad-band noise affect the basal portion of the cochlea first and, because of tonotopic organization, the ACCP responses to high frequency pure tones are affected before those to the low frequencies. However, the correlation between the effect of an ototraumatic agent on the ACCP and its effect on cochlear morphology is not always reliable. The correlations between changes in N1 and EP and in cochlear morphology are even less precise. Also discussed will be the cochlear effects of noise and the ototoxic interactions between drug/drug, noise/drug, and noise/drug/otitis media.

Efferent control of cochlear inner hair cell responses in the guinea-pig.

The efferent crossed olivocochlear bundle (c.o.c.b.) was electrically stimulated during intracellular recordings from cochlear inner hair cells in anaesthetized guinea-pigs. The effect of c.o.c.b. stimulation was to decrease the magnitude of the inner hair cell depolarizing component (d.c.) and alternating component (a.c.) receptor potentials evoked by tone bursts at the characteristic frequency. At low sound pressure levels, the decrease in receptor potentials caused by c.o.c.b. stimulation was equivalent to decreasing the sound intensity by 9-24 dB. C.o.c.b. stimulation usually had a similar effect on the compound action potential of the auditory nerve. The change in inner hair cell membrane resistance during moderate-level sound was measured for sound alone and when sound was accompanied by c.o.c.b. stimulation. Sound alone produced a greater membrane resistance change than sound with c.o.c.b. stimulation, in proportion to the d.c. receptor potential during the same conditions. The time course of the c.o.c.b. effect was slow, with 50-250 ms required for a full effect and for recovery. The effects of varying the frequency and voltage of electrical stimulation were similar for the d.c. receptor potential and for the compound action potential. For sounds of high level and for frequencies well below the characteristic frequency, c.o.c.b. stimulation was less effective in reducing receptor potentials. Frequency tuning curves for the d.c. receptor potential taken during intervals of continuous c.o.c.b. stimulation showed decreases in sensitivity primarily in the tip segment of the tuning curve. When no sound stimulus was present, the resting membrane potential was relatively unaltered during c.o.c.b. stimulation. The resting membrane resistance did not change during c.o.c.b. stimulation. Since the c.o.c.b. innervates mainly the outer hair cells, these results strongly suggest that changes in outer hair cell activity can influence the receptor potentials of inner hair cells and thus alter the transmission of acoustic responses to the central nervous system.

Suppression of auditory nerve responses. II. Suppression threshold and growth, iso-suppression contours.

Two-tone "synchrony suppression" was studied in responses of single auditory nerve fibers recorded from anesthetized cats. Suppression thresholds for suppressor tones set to a fiber's characteristic frequency (CF) were approximately equal to discharge rate thresholds for CF tones. Suppression thresholds above and below CF were usually lower than the corresponding discharge rate thresholds. However, at all frequencies studied (including CF), suppression thresholds were higher than the corresponding thresholds for discharge synchronization. Across fibers, rates of suppression growth for suppressors at CF were greatest in low-CF fibers and least in high-CF fibers, and there was a systematic decrease in suppression growth rate at CF as CF increased. Within fibers, rates of suppression growth above CF were typically less than at CF, and slopes were monotonically decreasing functions of frequency. Within-fiber rates of suppression growth below CF were variable, but they usually were greater than rates of growth at CF. Iso-suppression contours (frequencies and intensities producing criterion amounts of suppression) indicated that tones near CF are the most potent suppressors at near-threshold intensities, and that the frequency producing the most suppression usually shifts downward as the amount of suppression increases. These data support the notion that synchrony suppression arises primarily as a passive consequence of hair cell activation.

Sensory convergence on central visual neurons in Hermissenda.

Sensory convergence on central visual neurons in Hermissenda.T Akaike, and D L AlkonT Akaike, and D L AlkonPublished Online:01 Sep 1980https://doi.org/10.1152/jn.1980.44.3.501MoreSectionsPDF (2 MB)Download PDF ToolsExport citationAdd to favoritesGet permissionsTrack citations ShareShare onFacebookTwitterLinkedInWeChat Previous Back to Top Next Download PDF FiguresReferencesRelatedInformation Cited ByNetwork interneurons underlying ciliary locomotion in HermissendaTerry Crow, Nan Ge Jin, and Lian-Ming Tian1 February 2013 | Journal of Neurophysiology, Vol. 109, No. 3Serotonin regulates voltage-dependent currents in type Ie(A) and Ii interneurons of HermissendaNan Ge Jin, and Terry Crow1 November 2011 | Journal of Neurophysiology, Vol. 106, No. 55-HT and GABA Modulate Intrinsic Excitability of Type I Interneurons in HermissendaNan Ge Jin, Lian-Ming Tian, and Terry Crow1 November 2009 | Journal of Neurophysiology, Vol. 102, No. 5Polysensory Interneuronal Projections to Foot Contractile Pedal Neurons in HermissendaTerry Crow and Lian-Ming Tian1 February 2009 | Journal of Neurophysiology, Vol. 101, No. 2Sensory Regulation of Network Components Underlying Ciliary Locomotion in HermissendaTerry Crow, and Lian-Ming Tian1 November 2008 | Journal of Neurophysiology, Vol. 100, No. 5Random Noise Paradoxically Improves Light-Intensity Encoding in Hermissenda Photoreceptor NetworkChristopher R. Butson, and Gregory A. Clark1 January 2008 | Journal of Neurophysiology, Vol. 99, No. 1Pavlovian Conditioning in Hermissenda: A Circuit AnalysisThe Biological Bulletin, Vol. 210, No. 3Comparative Study of Visuo-Vestibular Conditioning in Lymnaea stagnalisThe Biological Bulletin, Vol. 210, No. 3Electrophysiological Responses to Light of Neurons in the Eye and Statocyst of Lymnaea stagnalisManabu Sakakibara, Tomoyo Aritaka, Akira Iizuka, Hiroyuki Suzuki, Tetsuro Horikoshi, and Ken Lukowiak1 January 2005 | Journal of Neurophysiology, Vol. 93, No. 1Statocyst Hair Cell Activation of Identified Interneurons and Foot Contraction Motor Neurons in HermissendaTerry Crow, and Lian-Ming Tian1 June 2004 | Journal of Neurophysiology, Vol. 91, No. 6Interneuronal Projections to Identified Cilia-Activating Pedal Neurons in HermissendaTerry Crow, and Lian-Ming Tian1 May 2003 | Journal of Neurophysiology, Vol. 89, No. 5Morphological Characteristics and Central Projections of Two Types of Interneurons in the Visual Pathway of HermissendaTerry Crow, and Lian-Ming Tian1 January 2002 | Journal of Neurophysiology, Vol. 87, No. 1Monosynaptic Connections Between Identified A and B Photoreceptors and Interneurons inHermissenda: Evidence for Labeled-LinesTerry Crow, and Lian-Ming Tian1 July 2000 | Journal of Neurophysiology, Vol. 84, No. 1Cellular correlates of classical conditioning in identified light responsive pedal neurons ofHermissenda crassicornisBrain Research, Vol. 570, No. 1-2Characterization of 4 light-responsive putative motor neurons in the pedal ganglia ofHermissenda crassicornisBrain Research, Vol. 557, No. 1-2Motor correlates of phototaxis and associative learning in Hermissenda crassicornisBrain Research Bulletin, Vol. 19, No. 2Correlated receptor and motorneuron changes during retention of associative learning of Hermissenda crassicornisComparative Biochemistry and Physiology Part A: Physiology, Vol. 73, No. 2 More from this issue > Volume 44Issue 3September 1980Pages 501-13 https://doi.org/10.1152/jn.1980.44.3.501PubMed6969298History Published online 1 September 1980 Published in print 1 September 1980 Metrics

A detection method for lactic dehydrogenase activity in the inner ear.

A method for the detection of lactic dehydrogenase enzymatic activity in outer hair cells of the rabbit is described. The membranous labyrinth with temporal bone was prefixed in glutaraldehyde. After being placed into the incubation medium, it was postfixed in osmium tetroxide. Specimens of the organ of Corti were removed. Then the specimens were embedded in water-soluble glycol and cut with a cryostat for light microscopy, and also they were embedded in Epon and cut for light and electron microscopy. Sectioning of the membranous labyrinth was very easily made when the specimens were embedded in both the water-soluble glycol and the Epon. The structures of the frozen sections as well as the Epon-embedded ones were well preserved. In the frozen sections the preservation and localization of reaction products were thoroughly kept, but monoformazan of the Epon-embedded sections was soluble.