scholarly journals Efferent Control of Hair Cell and Afferent Responses in the Semicircular Canals

2009 ◽  
Vol 102 (3) ◽  
pp. 1513-1525 ◽  
Author(s):  
Richard Boyle ◽  
Richard D. Rabbitt ◽  
Stephen M. Highstein
Keyword(s):  
Hair Cell ◽  
Brain Stem ◽  
Hair Cells ◽  
Intracellular Signaling ◽  
Dynamic Range ◽  
Reversal Potential ◽  
Semicircular Canals ◽  
Resting Potential ◽  
Efferent Neurons ◽  
The Brain

The sensations of sound and motion generated by the inner ear are controlled by the brain through extensive centripetal innervation originating within the brain stem. In the semicircular canals, brain stem efferent neurons make synaptic contacts with mechanosensory hair cells and with the dendrites of afferent neurons. Here, we examine the relative contributions of efferent action on hair cells and afferents. Experiments were performed in vivo in the oyster toadfish, Opsanus tau. The efferent system was activated via electrical pulses to the brain stem and sensory responses to motion stimuli were quantified by simultaneous voltage recording from afferents and intracellular current- and/or voltage-clamp recordings from hair cells. Results showed synaptic inputs to both afferents and hair cells leading to relatively long-latency intracellular signaling responses: excitatory in afferents and inhibitory in hair cells. Generally, the net effect of efferent action was an increase in afferent background discharge and a simultaneous decrease in gain to angular motion stimuli. Inhibition of hair cells was likely the result of a ligand-gated opening of a major basolateral conductance. The reversal potential of the efferent-evoked current was just below the hair cell resting potential, thus resulting in a small hyperpolarization. The onset latency averaged about 90 ms and latency to peak response was 150–400 ms. Hair cell inhibition often outlasted afferent excitation and, in some cases, latched hair cells in the “off” condition for >1 s following cessation of stimulus. These features endow the animal with a powerful means to adjust the sensitivity and dynamic range of motion sensation.

scholarly journals Inhibitory Postsynaptic Potentials in Lumbar Motoneurons Remain Depolarizing After Neonatal Spinal Cord Transection in the Rat

2006 ◽  
Vol 96 (5) ◽  
pp. 2274-2281 ◽  
Author(s):  
Céline Jean-Xavier ◽  
Jean-François Pflieger ◽  
Sylvie Liabeuf ◽  
Laurent Vinay
Keyword(s):  
Spinal Cord ◽  
Brain Stem ◽  
Time Window ◽  
Reversal Potential ◽  
Perinatal Period ◽  
Spinal Cord Transection ◽  
Resting Potential ◽  
Postsynaptic Potentials ◽  
Inhibitory Postsynaptic Potentials ◽  
The Brain

GABA and glycine are excitatory in the immature spinal cord and become inhibitory during development. The shift from depolarizing to hyperpolarizing inhibitory postsynaptic potentials (IPSPs) occurs during the perinatal period in the rat, a time window during which the projections from the brain stem reach the lumbar enlargement. In this study, we investigated the effects of suppressing influences of the brain on lumbar motoneurons during this critical period for the negative shift of the reversal potential of IPSPs ( EIPSP). The spinal cord was transected at the thoracic level on the day of birth [postnatal day 0 (P0)]. EIPSP, at P4–P7, was significantly more depolarized in cord-transected than in cord-intact animals ( EIPSP above and below resting potential, respectively). EIPSP at P4–P7 in cord-transected animals was close to EIPSP at P0–P2. K-Cl cotransporter KCC2 immunohistochemistry revealed a developmental increase of staining in the area of lumbar motoneurons between P0 and P7 in cord-intact animals; this increase was not observed after spinal cord transection. The motoneurons recorded from cord-transected animals were less sensitive to the experimental manipulations aimed at testing the functionality of the KCC2 system, which is sensitive to [K+]o and blocked by bumetanide. Although bumetanide significantly depolarized EIPSP, the shift was less pronounced than in cord-intact animals. In addition, a reduction of [K+]o affected EIPSP significantly only in cord-intact animals. Therefore influences from the brain stem may play an essential role in the maturation of inhibitory synaptic transmission, possibly by upregulating KCC2 and its functionality.

The inactivating potassium currents of hair cells isolated from the crista ampullaris of the frog

1992 ◽  
Vol 68 (5) ◽  
pp. 1642-1653 ◽  
Author(s):  
C. H. Norris ◽  
A. J. Ricci ◽  
G. D. Housley ◽  
P. S. Guth
Keyword(s):  
Steady State ◽  
Hair Cells ◽  
Reversal Potential ◽  
Semicircular Canals ◽  
Cell Voltage ◽  
Leopard Frog ◽  
Resting Potential ◽  
Voltage Response ◽  
Calcium Dependent ◽  
Steady State Inactivation

1. A-type outward currents were studied in sensory hair cells isolated from the semicircular canals (SCC) of the leopard frog (Rana pipiens) with whole-cell voltage- and current-clamping techniques. 2. There appear to be two classes of A-type outward-conducting potassium channels based on steady-state, kinetic, pharmacological parameters, and reversal potential. 3. The two classes of A-type currents differ in their steady-state inactivation properties as well as in the kinetics of inactivation. The steady-state inactivation properties are such that a significant portion of the fast channels are available from near the resting potential. 4. The inactivating channels studied do not appear to be calcium dependent. 5. The A-channels in hair cells appear to subserve functions that are analogous to IA functions in neurons, that is, modulating spike latency and Q (the oscillatory damping function). The A-currents appear to temporally limit the hair cell voltage response to a current injection.

Carboplatin ototoxicity: an animal model

1993 ◽  
Vol 107 (7) ◽  
pp. 585-589 ◽  
Author(s):  
Mark Wake ◽  
Sachio Takeno ◽  
Danyl Ibrahim ◽  
Robert Harrison ◽  
Richard Mount
Keyword(s):  
Animal Model ◽  
Light Microscopy ◽  
Hair Cell ◽  
Brain Stem ◽  
Auditory System ◽  
Hair Cells ◽  
Afferent Input ◽  
Evoked Responses ◽  
Auditory Thresholds ◽  
Scanning Electronmicroscopy

A new animal model of ototoxicity is presented using intravenous carboplatin in adult chinchillas. A range of physiological and morphological effects was produced using doses calculated from the recommended therapeutic range (200–400 mg/m2). Auditory thresholds to tone pips stimuli were monitored using brain stem evoked responses (ABR). Cochlear histopathology was studied by light microscopy (LM) and ultrstructural hair cell abnormalities investigated with scanning electronmicroscopy (SEM). Carboplatin in this animal model predominantly affected the inner hair cells. This may provide an important model for the study of selective loss of the main afferent input in the auditory system.

Imbalance of central nitric oxide and reactive oxygen species in the regulation of sympathetic activity and neural mechanisms of hypertension

2011 ◽  
Vol 300 (4) ◽  
pp. R818-R826 ◽  
Author(s):  
Yoshitaka Hirooka ◽  
Takuya Kishi ◽  
Koji Sakai ◽  
Akira Takeshita ◽  
Kenji Sunagawa
Keyword(s):  
Nitric Oxide ◽  
Reactive Oxygen Species ◽  
Nervous System ◽  
Sympathetic Nervous System ◽  
Brain Stem ◽  
Intracellular Signaling ◽  
Reactive Oxygen ◽  
Oxygen Species ◽  
Sympathetic Nervous ◽  
The Brain

Nitric oxide (NO) and reactive oxygen species (ROS) play important roles in blood pressure regulation via the modulation of the autonomic nervous system, particularly in the central nervous system (CNS). In general, accumulating evidence suggests that NO inhibits, but ROS activates, the sympathetic nervous system. NO and ROS, however, interact with each other. Our consecutive studies and those of others strongly indicate that an imbalance between NO bioavailability and ROS generation in the CNS, including the brain stem, activates the sympathetic nervous system, and this mechanism is involved in the pathogenesis of neurogenic aspects of hypertension. In this review, we focus on the role of NO and ROS in the regulation of the sympathetic nervous system within the brain stem and subsequent cardiovascular control. Multiple mechanisms are proposed, including modulation of neurotransmitter release, inhibition of receptors, and alterations of intracellular signaling pathways. Together, the evidence indicates that an imbalance of NO and ROS in the CNS plays a pivotal role in the pathogenesis of hypertension.

A study of active artificial hair cell models inspired by outer hair cell somatic motility

2016 ◽  
Vol 28 (6) ◽  
pp. 811-823 ◽  
Author(s):  
Bryan S Joyce ◽  
Pablo A Tarazaga
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Outer Hair Cell ◽  
Dynamic Range ◽  
Outer Hair Cells ◽  
Quality Factors ◽  
Control Laws ◽  
Sensor Performance ◽  
Nonlinear Amplification ◽  
Key Aspects

The cochlea displays an important, nonlinear amplification of sound-induced oscillations. In mammals, this amplification is largely powered by the somatic motility of the outer hair cells. The resulting cochlear amplifier has three important characteristics useful for hearing: an amplification of responses from low sound pressures, an improvement in frequency selectivity, and an ability to transduce a broad range of sound pressure levels. These useful features can be incorporated into designs for active artificial hair cells, bio-inspired sensors for use as microphones, accelerometers, or other dynamic sensors. The sensor consists of a cantilever beam with piezoelectric actuators. A feedback controller applies a voltage to the actuators to mimic the outer hair cells’ somatic motility. This article describes three control laws for an active artificial hair cell inspired by models of the outer hair cells’ somatic motility. The first control law is based on a phenomenological model of the cochlea while the second and third models incorporate physiological aspects of the biological cochlea to further improve sensor performance. Simulations show that these models qualitatively reproduce the key aspects of the mammalian cochlea, namely, amplification of oscillations from weak stimuli, higher quality factors, and a wider input dynamic range.

scholarly journals Single-unit labeling of medial olivocochlear neurons: the cochlear frequency map for efferent axons

2014 ◽  
Vol 111 (11) ◽  
pp. 2177-2186 ◽  
Author(s):  
M. Christian Brown
Keyword(s):  
Hair Cells ◽  
Single Unit ◽  
Dynamic Range ◽  
Organ Of Corti ◽  
Nerve Fibers ◽  
Outer Hair Cells ◽  
Cochlear Amplifier ◽  
Noise Masking ◽  
Efferent Neurons ◽  
Medial Olivocochlear

Medial olivocochlear (MOC) neurons are efferent neurons that project axons from the brain to the cochlea. Their action on outer hair cells reduces the gain of the “cochlear amplifier,” which shifts the dynamic range of hearing and reduces the effects of noise masking. The MOC effects in one ear can be elicited by sound in that ipsilateral ear or by sound in the contralateral ear. To study how MOC neurons project onto the cochlea to mediate these effects, single-unit labeling in guinea pigs was used to study the mapping of MOC neurons for neurons responsive to ipsilateral sound vs. those responsive to contralateral sound. MOC neurons were sharply tuned to sound frequency with a well-defined characteristic frequency (CF). However, their labeled termination spans in the organ of Corti ranged from narrow to broad, innervating between 14 and 69 outer hair cells per axon in a “patchy” pattern. For units responsive to ipsilateral sound, the midpoint of innervation was mapped according to CF in a relationship generally similar to, but with more variability than, that of auditory-nerve fibers. Thus, based on CF mappings, most of the MOC terminations miss outer hair cells involved in the cochlear amplifier for their CF, which are located more basally. Compared with ipsilaterally responsive neurons, contralaterally responsive neurons had an apical offset in termination and a larger span of innervation (an average of 10.41% cochlear distance), suggesting that when contralateral sound activates the MOC reflex, the actions are different than those for ipsilateral sound.

scholarly journals Hair-Cell Versus Afferent Adaptation in the Semicircular Canals

2005 ◽  
Vol 93 (1) ◽  
pp. 424-436 ◽  
Author(s):  
R. D. Rabbitt ◽  
R. Boyle ◽  
G. R. Holstein ◽  
S. M. Highstein
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Semicircular Canal ◽  
Time Course ◽  
Dynamic Range ◽  
Cell Voltage ◽  
Frequency Dependent ◽  
Adaptation Time ◽  
Phase Lead ◽  
Flat Gain

The time course and extent of adaptation in semicircular canal hair cells was compared to adaptation in primary afferent neurons for physiological stimuli in vivo to study the origins of the neural code transmitted to the brain. The oyster toadfish, Opsanus tau, was used as the experimental model. Afferent firing-rate adaptation followed a double-exponential time course in response to step cupula displacements. The dominant adaptation time constant varied considerably among afferent fibers and spanned six orders of magnitude for the population (∼1 ms to >1,000 s). For sinusoidal stimuli (0.1–20 Hz), the rapidly adapting afferents exhibited a 90° phase lead and frequency-dependent gain, whereas slowly adapting afferents exhibited a flat gain and no phase lead. Hair-cell voltage and current modulations were similar to the slowly adapting afferents and exhibited a relatively flat gain with very little phase lead over the physiological bandwidth and dynamic range tested. Semicircular canal microphonics also showed responses consistent with the slowly adapting subset of afferents and with hair cells. The relatively broad diversity of afferent adaptation time constants and frequency-dependent discharge modulations relative to hair-cell voltage implicate a subsequent site of adaptation that plays a major role in further shaping the temporal characteristics of semicircular canal afferent neural signals.

scholarly journals Good vibrations: Music and the single hair cell

2002 ◽  
Vol 24 (6) ◽  
pp. 12-14
Author(s):  
Corné Kros
Keyword(s):  
Hair Cell ◽  
Inner Ear ◽  
Hair Cells ◽  
Auditory Nerve ◽  
Sound Stimulus ◽  
Mechanical Stimuli ◽  
Sensory Receptors ◽  
Nerve Fibres ◽  
Sound Processing ◽  
The Brain

Hair cells are the sensory receptors in the inner ear, and the hair bundles that protrude from their upper surfaces transduce mechanical stimuli into electrical responses. This article examines the key molecules involved in the different stages of sound processing within these extraordinarily sensitive and intricate cells, from the reception of the sound stimulus to the release of neurotransmitters on to the auditory nerve fibres that signal to the brain that a sound has been received.

scholarly journals Stiffness and tension gradients of the hair cell’s tip-link complex in the mammalian cochlea

eLife ◽  
2019 ◽  
Vol 8 ◽  
Author(s):  
Mélanie Tobin ◽  
Atitheb Chaiyasitdhi ◽  
Vincent Michel ◽  
Nicolas Michalski ◽  
Pascal Martin
Keyword(s):  
Hair Cell ◽  
Hair Cells ◽  
Frequency Tuning ◽  
Cell Types ◽  
Outer Hair Cells ◽  
Tip Link ◽  
Biophysical Mechanism ◽  
Apical Half ◽  
Mechanosensory Hair Cells ◽  
The Brain

Sound analysis by the cochlea relies on frequency tuning of mechanosensory hair cells along a tonotopic axis. To clarify the underlying biophysical mechanism, we have investigated the micromechanical properties of the hair cell’s mechanoreceptive hair bundle within the apical half of the rat cochlea. We studied both inner and outer hair cells, which send nervous signals to the brain and amplify cochlear vibrations, respectively. We find that tonotopy is associated with gradients of stiffness and resting mechanical tension, with steeper gradients for outer hair cells, emphasizing the division of labor between the two hair-cell types. We demonstrate that tension in the tip links that convey force to the mechano-electrical transduction channels increases at reduced Ca2+. Finally, we reveal gradients in stiffness and tension at the level of a single tip link. We conclude that mechanical gradients of the tip-link complex may help specify the characteristic frequency of the hair cell.

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