Suppression of 2f1-f2 distortion product otoacoustic emissions by electrical stimulation of the inferior colliculus in guinea pigs

Electrical stimulation of certain parts of the IC resulted in the depression of the DPOAE amplitude by 0.1-2 dB. The value of maximal DPOAE suppression was similar to the DPOAE suppression produced by acoustical stimulation of the contralateral ear. Our results indicate that electrical stimulation of the external cortex of the IC can activate the efferent system and produce DPOAE suppression by similar mechanisms as does acoustical stimulation of the contralateral ear

The effect of parvalbumin deficiency on the acoustic startle response and prepulse inhibition in mice

The strength of the acoustic startle response (ASR) to short bursts of broadband noise or tone pips (4, 8 and 16 kHz) and the prepulse inhibition (PPI) of the ASR elicited by prepulse tones (4, 8 and 16 kHz) were measured in parvalbumin-deficient (PV−/−) mice and in age-matched PV+/+ mice as controls. Hearing thresholds as determined from recordings of auditory brainstem responses were found to be similar in both genotypes. The ASRs to broadband noise and tones of low and middle frequencies were stronger than the ASRs in response to high-frequency tones in both groups. In PV−/− mice, we observed smaller ASR amplitudes in response to relatively weak startling stimuli (80–90 dB sound pressure level (SPL)) of either broadband noise or 8-kHz tones compared to those recorded in PV+/+ mice. For these startling stimuli, PV−/− mice had higher ASR thresholds and longer ASR latencies. PPI of the ASR in PV−/− mice was less effective than in PV+/+ mice, for all tested prepulse frequencies (4, 8 or 16 kHz) at 70 dB SPL. Our findings demonstrate no effect of PV deficiency on hearing thresholds in PV−/− mice. However, the frequency-specific differences in the ASR and the significant reduction of PPI of ASR likely reflect specific changes of neuronal circuits, mainly inhibitory, in the auditory centers in PV-deficient mice

Relationship between the response to whistle and the response to time-reversed whistle in individual neurons (n = 502).

<p>Each dot represents one unit. The slope of the regression line (solid line) is not significantly different from one (dashed line), P>0.05.</p

Cortical Representation of Species-Specific Vocalizations in Guinea Pig

<div><p>We investigated the representation of four typical guinea pig vocalizations in the auditory cortex (AI) in anesthetized guinea pigs with the aim to compare cortical data to the data already published for identical calls in subcortical structures - the inferior colliculus (IC) and medial geniculate body (MGB). Like the subcortical neurons also cortical neurons typically responded to many calls with a time-locked response to one or more temporal elements of the calls. The neuronal response patterns in the AI correlated well with the sound temporal envelope of chirp (an isolated short phrase), but correlated less well in the case of chutter and whistle (longer calls) or purr (a call with a fast repetition rate of phrases). Neuronal rate vs. characteristic frequency profiles provided only a coarse representation of the calls’ frequency spectra. A comparison between the activity in the AI and those of subcortical structures showed a different transformation of the neuronal response patterns from the IC to the AI for individual calls: i) while the temporal representation of chirp remained unchanged, the representations of whistle and chutter were transformed at the thalamic level and the response to purr at the cortical level; ii) for the wideband calls (whistle, chirp) the rate representation of the call spectra was preserved in the AI and MGB at the level present in the IC, while in the case of low-frequency calls (chutter, purr), the representation was less precise in the AI and MGB than in the IC; iii) the difference in the response strength to natural and time-reversed whistle was found to be smaller in the AI than in the IC or MGB.</p></div

Comparisons of the rate-CF profiles (n = 502, top) and call short-term spectra (bottom) for three consecutive parts of whistle (A–C – the appropriate time interval is indicated above every rate-CF profile), for purr (D – data calculated over the first phase containing four elementary phrases), for chirp (E) and for chutter (F – calculated over the first phrase of the call).

<p>Comparisons of the rate-CF profiles (n = 502, top) and call short-term spectra (bottom) for three consecutive parts of whistle (A–C – the appropriate time interval is indicated above every rate-CF profile), for purr (D – data calculated over the first phase containing four elementary phrases), for chirp (E) and for chutter (F – calculated over the first phrase of the call).</p

Comparison of subcortical nuclei (IC, MGB) and the auditory cortex.

<p>The correlation coefficients between the sound envelope and the averaged PSTH (A) and the correlation coefficients between the sound frequency spectrum and rate vs. CF profile (C) are compared in the inferior colliculus (IC, open), medial geniculate body (MGB, blue) and auditory cortex (AI, red) for individual call. Panel (B) shows a schematic drawing of a part of the ascending auditory pathway. IC data based on 153 neurons are taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065432#pone.0065432-uta1" target="_blank">[2]</a>; MGB data calculated from 209 neurons are taken from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0065432#pone.0065432-uta2" target="_blank">[18]</a>. The bootstrap method was used to determine whether the values of the correlation coefficients in individual nuclei were statistically different (P<0.01). The blue stars indicate cases of tecto-thalamic transformation of the neuronal response in which the IC data were significantly different from the MGB and AI data, while the difference between the MGB and AI was not significant. The red star indicates a case of thalamo-cortical transformation of the neuronal response in which the AI data were significantly different from MGB and IC data, while the difference between the MGB and IC was not significant.</p

Age-Related Differences in Hearing Function and Cochlear Morphology between Male and Female Fischer 344 Rats

Fischer 344 (F344) rats represent a strain that is frequently used as a model for fast aging. In this study, we systematically compare the hearing function during aging in male and female F344 rats, by recording auditory brainstem responses (ABRs) and distortion product otoacoustic emissions (DPOAEs). In addition to this, the functional parameters are correlated with the cochlear histology. The parameters of the hearing function were not different in the young (3-month-old) male and female F344 rats; the gender differences occurred only in adult and aged animals. In 8–24-month-old males, the ABR thresholds were higher and the ABR amplitudes were smaller than those measured in females of the same age. There were no gender differences in the neural adaptation tested by recording ABRs, elicited by a series of clicks with varying inter-click interval (ICI). Amplitudes of DPOAEs in both the males and females decreased with age, but in the males, the decrease of DPOAE amplitudes was faster. In males older than 20 months, the DPOAEs were practically absent, whereas in 20–24-month-old females, the DPOAEs were still measurable. There were no gender differences in the number of surviving outer hair cells (OHC) and the number of inner hair cell ribbon synapses in aged animals. The main difference was found in the stria vascularis (SV). Whereas the SV was well preserved in females up to the age of 24 months, in most of the age-matched males the SV was evidently deteriorated. The results demonstrate more pronounced age-related changes in the cochlear morphology, hearing thresholds, ABR amplitudes and DPOAE amplitudes in F344 males compared with females

Minimally invasive drug delivery to the cochlea through application of nanoparticles to the round window membrane

Direct drug delivery to the cochlea is associated with the risk of irreversible damage to the ear. In this study liposome and polymersome nanoparticles (NPs), both formed from amphiphilic molecules (lipids in liposomes, block copolymers in polymersomes), were tested as potential tools for drug delivery to the cochlea through application onto the round window membrane (RWM) in adult mice (strain C3H). One day after RWM application both types of NPs labelled with fluorescent markers were identified in the spiral ganglion in all cochlear turns without producing any distinct morphological or functional damage to the inner ear. NPs were detected, although to a lesser extent, in the organ of Corti and the lateral wall. The potential of liposome and polymersome NPs as therapeutic delivery systems into the cochlea via the RWM was evaluated using disulfiram, a neurotoxic agent as a model payload. Disulfiram-loaded NP delivery resulted in significant decrease in the number of spiral ganglion cells starting two days post-application, with associated pronounced hearing loss reaching 20-35 dB two weeks post-application as assessed through auditory brainstem responses. No changes in hair cell morphology and function (as assessed by recording of otoacoustic emissions) were detected after disulfiram-loaded NP application. No effects were observed in controls where solution of free disulfiram was similarly administered. The results demonstrate that polymersome and liposome NPs are capable of carrying a payload into the inner ear that elicits a biological effect, with consequences measurable by a functional readout