Effect of High Electrical Stimulus Intensities on the Auditory Nerve Using Brain Stem Response Audiometry

1987 ◽  
Vol 96 (1_suppl) ◽  
pp. 50-53 ◽  
Author(s):  
R. K. Shepherd ◽  
G. M. Clark
Keyword(s):  
Brain Stem ◽  
Speech Processing ◽  
Auditory Nerve ◽  
Electrical Stimulus ◽  
Metabolic Effects ◽  
Charge Densities ◽  
Processing Strategies ◽  
Auditory Brain Stem ◽  
High Charge Density ◽  
High Stimulus

The response of the auditory nerve to acute intracochlear electrical stimulation using charge-balanced biphasic current pulses was monitored using electrically evoked auditory brain stem responses (EABRs). Stimulation at moderate charge densities (64 μC cm−2 geom/phase; 0.8 mA, 200 μs/phase) for periods of up to 12 hours produced only minimal short-term changes in the EABR. Stimulation at a high charge density (144 μC cm−2 geom/phase; 1.8 mA, 200 μs/phase) resulted in permanent reductions in the EABR for high stimulus rates (> 200 pulses per second [pps]) or long stimulus durations (12 hours). At lower stimulus rates and durations, recovery to prestimulus levels was slow but complete. The mechanisms underlying these temporary and permanent reductions in the EABR are probably caused by neural adaptation and more long-term metabolic effects. These findings have implications for the design of speech-processing strategies using high stimulus rates.

scholarly journals Target-specific regulation of presynaptic release properties at auditory nerve terminals in the avian cochlear nucleus

2016 ◽  
Vol 115 (3) ◽  
pp. 1679-1690 ◽  
Author(s):  
J. Ahn ◽  
K. M. MacLeod
Keyword(s):  
Brain Stem ◽  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Auditory Information ◽  
Nerve Terminals ◽  
Release Probability ◽  
Auditory Brain Stem ◽  
Presynaptic Release ◽  
Specific Regulation ◽  
Synaptic Dynamics

Short-term synaptic plasticity (STP) acts as a time- and firing rate-dependent filter that mediates the transmission of information across synapses. In the auditory brain stem, the divergent pathways that encode acoustic timing and intensity information express differential STP. To investigate what factors determine the plasticity expressed at different terminals, we tested whether presynaptic release probability differed in the auditory nerve projections to the two divisions of the avian cochlear nucleus, nucleus angularis (NA) and nucleus magnocellularis (NM). Estimates of release probability were made with an open-channel blocker of N-methyl-d-aspartate (NMDA) receptors. Activity-dependent blockade of NMDA receptor-mediated excitatory postsynaptic currents (EPSCs) with application of 20 μM (+)-MK801 maleate was more rapid in NM than in NA, indicating that release probability was significantly higher at terminals in NM. Paired-pulse ratio (PPR) was tightly correlated with the blockade rate at terminals in NA, suggesting that PPR was a reasonable proxy for relative release probability at these synapses. To test whether release probability was similar across convergent inputs onto NA neurons, PPRs of different nerve inputs onto the same postsynaptic NA target neuron were measured. The PPRs, as well as the plasticity during short trains, were tightly correlated across multiple inputs, further suggesting that release probability is coordinated at auditory nerve terminals in a target-specific manner. This highly specific regulation of STP in the auditory brain stem provides evidence that the synaptic dynamics are tuned to differentially transmit the auditory information in nerve activity into parallel ascending pathways.

scholarly journals Expression and Neurotransmitter Association of the Synaptic Calcium Sensor Synaptotagmin in the Avian Auditory Brain Stem

2021 ◽  
Author(s):  
Katrina M. MacLeod ◽  
Sangeeta Pandya
Keyword(s):  
Brain Stem ◽  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Calcium Binding ◽  
Glutamate Transporter ◽  
Calcium Sensor ◽  
Double Labeling ◽  
Excitatory Transmission ◽  
Auditory Brain Stem ◽  
Synaptotagmin 1

AbstractIn the avian auditory brain stem, acoustic timing and intensity cues are processed in separate, parallel pathways via the two division of the cochlear nucleus, nucleus angularis (NA) and nucleus magnocellularis (NM). Differences in excitatory and inhibitory synaptic properties, such as release probability and short-term plasticity, contribute to differential processing of the auditory nerve inputs. We investigated the distribution of synaptotagmin, a putative calcium sensor for exocytosis, via immunohistochemistry and double immunofluorescence in the embryonic and hatchling chick brain stem (Gallus gallus). We found that the two major isoforms, synaptotagmin 1 (Syt1) and synaptotagmin 2 (Syt2), showed differential expression. In the NM, anti-Syt2 label was strong and resembled the endbulb terminals of the auditory nerve inputs, while anti-Syt1 label was weaker and more punctate. In NA, both isoforms were intensely expressed throughout the neuropil. A third isoform, synaptotagmin 7 (Syt7), was largely absent from the cochlear nuclei. In nucleus laminaris (NL, the target nucleus of NM), anti-Syt2 and anti-Syt7 strongly labeled the dendritic lamina. These patterns were established by embryonic day 18 and persisted to postnatal day 7. Double labeling immunofluorescence showed Syt1 and Syt2 were associated with Vesicular Glutamate Transporter 2 (VGluT2), but not Vesicular GABA Transporter (VGAT), suggesting these Syt isoforms were localized to excitatory, but not inhibitory, terminals. These results suggest that Syt2 is the major calcium binding protein underlying excitatory neurotransmission in the timing pathway comprising NM and NL, while Syt2 and Syt1 regulate excitatory transmission in the parallel intensity pathway via cochlear nucleus NA.

Effects of Inhibitory Feedback in a Network Model of Avian Brain Stem

2005 ◽  
Vol 94 (1) ◽  
pp. 400-414 ◽  
Author(s):  
Vasant K. Dasika ◽  
John A. White ◽  
Laurel H. Carney ◽  
H. Steven Colburn
Keyword(s):  
Brain Stem ◽  
Network Model ◽  
Auditory Nerve ◽  
Feedback Inhibition ◽  
Interaural Time Difference ◽  
Nerve Fibers ◽  
Sound Level ◽  
Inhibitory Input ◽  
Auditory Brain Stem ◽  
Inhibitory Feedback

The avian auditory brain stem consists of a network of specialized nuclei, including nucleus laminaris (NL) and superior olivary nucleus (SON). NL cells show sensitivity to interaural time difference (ITD), a critical cue that underlies spatial hearing. SON cells provide inhibitory feedback to the rest of the network. Empirical data suggest that feedback inhibition from SON could increase the ITD sensitivity of NL across sound level. Using a bilateral network model, we assess the effects of SON feedback inhibition. Individual cells are specified as modified leaky-integrate-and-fire neurons with time constants and thresholds that vary with inhibitory input. Acoustic sound level is reflected in the discharge rates of the model auditory-nerve fibers, which innervate the network. Simulations show that with SON inhibitory feedback, ITD sensitivity is maintained in model NL cells over a threefold range in auditory-nerve discharge rate. In contrast, without SON feedback inhibition, ITD sensitivity is significantly reduced as input rates are increased. Feedback inhibition is most beneficial in maintaining ITD sensitivity at high-input rates (simulating high sound levels). With SON inhibition, ITD sensitivity is maintained for both interaurally balanced inputs (simulating an on-center sound source) and interaurally imbalanced inputs (simulating a lateralized source). Further, the empirically observed temporal build-up of SON inhibition and the presence of reciprocal inhibitory connections between the ipsi- and contralateral SON both improve ITD sensitivity. In sum, our network model shows that inhibitory feedback can substantially increase the sensitivity and dynamic range of ITD coding in the avian auditory brain stem.

Synaptic Physiology in the Cochlear Nucleus Angularis of the Chick

2005 ◽  
Vol 93 (5) ◽  
pp. 2520-2529 ◽  
Author(s):  
Katrina M. MacLeod ◽  
Catherine E. Carr
Keyword(s):  
Brain Stem ◽  
Time Constant ◽  
Auditory Nerve ◽  
Sound Intensity ◽  
Sound Recognition ◽  
Auditory Information ◽  
Decay Kinetics ◽  
Cochlear Nuclei ◽  
Auditory Brain Stem ◽  
Nucleus Angularis

Nucleus angularis (NA), one of the two cochlear nuclei in birds, is important for processing sound intensity for localization and most likely has role in sound recognition and other auditory tasks. Because the synaptic properties of auditory nerve inputs to the cochlear nuclei are fundamental to the transformation of auditory information, we studied the properties of these synapses onto NA neurons using whole cell patch-clamp recordings from auditory brain stem slices from embryonic chickens (E16–E20). We measured spontaneous excitatory postsynaptic currents (EPSCs), and evoked EPSCs and excitatory postsynaptic potentials (EPSPs) by using extracellular stimulation of the auditory nerve. These excitatory EPSCs were mediated by AMPA and N-methyl-d-aspartate (NMDA) receptors. The spontaneous EPSCs mediated by AMPA receptors had submillisecond decay kinetics (556 μs at E19), comparable with those of other auditory brain stem areas. The spontaneous EPSCs increased in amplitude and became faster with developmental age. Evoked EPSC and EPSP amplitudes were graded with stimulus intensity. The average amplitude of the EPSC evoked by minimal stimulation was twice as large as the average spontaneous EPSC amplitude (∼110 vs. ∼55 pA), suggesting that single fibers make multiple contacts onto each postsynaptic NA neuron. Because of their small size, minimal EPSPs were subthreshold, and we estimate at least three to five inputs were required to reach threshold. In contrast to the fast EPSCs, EPSPs in NA had a decay time constant of ∼12.5 ms, which was heavily influenced by the membrane time constant. Thus NA neurons spatially and temporally integrate auditory information arriving from multiple auditory nerve afferents.

Auditory evoked potentials recorded from the cochlear nucleus and its vicinity in man

1983 ◽  
Vol 59 (6) ◽  
pp. 1013-1018 ◽  
Author(s):  
Aage R. Møller ◽  
Peter J. Jannetta
Keyword(s):  
Evoked Potentials ◽  
Brain Stem ◽  
Cochlear Nucleus ◽  
Auditory Nerve ◽  
Auditory Evoked Potentials ◽  
Auditory Pathway ◽  
Content Type ◽  
Negative Peak ◽  
Auditory Brain Stem ◽  
Stimulation Of

✓ Intracranial responses from the auditory nerve and the cochlear nucleus were recorded from patients undergoing neurosurgical operations during which these structures were exposed. Responses to stimulation of the ipsilateral ear with short tonebursts from the vicinity of the cochlear nucleus show a large surface-negative peak, the latency of which is close to that of peak III in the auditory brain-stem evoked potentials recorded from scalp electrodes. There was also a response to contralateral stimulation, smaller in amplitude and with a longer latency. It is concluded that the cochlear nucleus is the main generator of peak III responses, and that structures of the ascending auditory pathway that are more central than the cochlear nucleus are unlikely to contribute to wave III of the auditory brain-stem evoked potentials.

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