Voltage-gated potassium current and resonance in the toadfish saccular hair cell

SUMMARYVertebrates displaying seasonal shifts in reproductive behavior provide the opportunity to investigate bidirectional plasticity in sensory function. The midshipman teleost fish exhibits steroid-dependent plasticity in frequency encoding by eighth nerve auditory afferents. In this study, evoked potentials were recorded in vivo from the saccule, the main auditory division of the inner ear of most teleosts, to test the hypothesis that males and females exhibit seasonal changes in hair cell physiology in relation to seasonal changes in plasma levels of steroids. Thresholds across the predominant frequency range of natural vocalizations were significantly less in both sexes in reproductive compared with non-reproductive conditions, with differences greatest at frequencies corresponding to call upper harmonics. A subset of non-reproductive males exhibiting an intermediate saccular phenotype had elevated testosterone levels, supporting the hypothesis that rising steroid levels induce non-reproductive to reproductive transitions in saccular physiology. We propose that elevated levels of steroids act via long-term (days to weeks) signaling pathways to upregulate ion channel expression generating higher resonant frequencies characteristic of nonmammalian auditory hair cells, thereby lowering acoustic thresholds.

Section: Mechanisms For Saccular Hair Cell Plasticitymentioning

confidence: 99%

Seasonal plasticity of auditory hair cell frequency sensitivity correlates with plasma steroid levels in vocal fish

Rohmann

Bass

2011

“…The mechanisms underlying such frequency tuning as well as the differences in filter-shape and bandwidth seen in primary otolithic afferents in fish are not well understood. However, they may arise from hair cell resonance (Sugihara and Furukawa, 1989;Steinacker and Romero, 1992) and micromechanical mechanisms between hair cells and their attachment to the otolithic membrane (Fay, 1997). Evidence for a place-frequency code in fish is unclear since only very few studies have suggested that response characteristics of different saccular or lagenar regions might vary (Furukawa and Ishii, 1967;Sand and Michelsen, 1978;Enger, 1981;Fay, 1997).…”

Section: Temporal Versus Spike Rate Codingmentioning

confidence: 99%

Frequency tuning and intensity coding of sound in the auditory periphery of the lake sturgeon, Acipenser fulvescens

Meyer

Fay

Popper

2010

SUMMARYAcipenser fulvescens, the lake sturgeon, belongs to one of the few extant non-teleost ray-finned (bony) fishes. The sturgeons (family Acipenseridae) have a phylogenetic history that dates back about 250 million years. The study reported here is the first investigation of peripheral coding strategies for spectral analysis in the auditory system in a non-teleost bony fish. We used a shaker system to simulate the particle motion component of sound during electrophysiological recordings of isolated single units from the eighth nerve innervating the saccule and lagena. Background activity and response characteristics of saccular and lagenar afferents (such as thresholds, response-level functions and temporal firing) resembled the ones found in teleosts. The distribution of best frequencies also resembled data in teleosts (except for Carassius auratus, goldfish) tested with the same stimulation method. The saccule and lagena in A. fulvescens contain otoconia, in contrast to the solid otoliths found in teleosts, however, this difference in otolith structure did not appear to affect threshold, frequency tuning, intensity-or temporal responses of auditory afferents. In general, the physiological characteristics common to A. fulvescens, teleosts and land vertebrates reflect important functions of the auditory system that may have been conserved throughout the evolution of vertebrates.

“…The auditory hair cells of fish, amphibians, reptiles and birds typically respond to a current step with a damped oscillation of the membrane potential (Crawford and Fettiplace, 1981;Ashmore, 1983;Lewis and Hudspeth, 1983;Sugihara and Furukawa, 1989;Steinacker and Romero, 1992) at a frequency that varies with the cell's position along a tonotopic axis (reviewed by Fettiplace and Fuchs, 1999). This phenomenon has been studied most extensively in the turtle cochlea, where small positive and negative current steps evoke symmetrical voltage oscillations around the resting potential that scale with the step amplitude.…”

Section: Evoked and Spontaneous Membrane Potential Oscillationsmentioning

confidence: 99%

Linear and nonlinear processing in hair cells

Roberts

Rutherford

2008

SummaryMechanosensory hair cells in the ear are exquisitely responsive to minute sensory inputs, nearly to the point of instability. Active mechanisms bias the transduction apparatus and subsequent electrical amplification away from saturation in either the negative or positive direction, to an operating point where the response to small signals is approximately linear. An active force generator coupled directly to the transducer enhances sensitivity and frequency selectivity, and counteracts energy loss to viscous drag. Active electrical amplification further enhances gain and frequency selectivity. In both cases, nonlinear properties may maintain the system close to instability, as evidenced by small spontaneous oscillations, while providing a compressive nonlinearity that increases the cell's operating range. Transmitter release also appears to be frequency selective and biased to operate most effectively near the resting potential. This brief overview will consider the resting stability of hair cells, and their responses to small perturbations that correspond to soft sounds or small accelerations.