Activation of lactate receptor HCAR1 down-modulates neuronal activity in rodent and human brain tissue.

Lactate can be used by neurons as an energy substrate to support their activity. Evidence suggests that lactate also acts on a metabotropic receptor called HCAR1, first described in the adipose tissue. Whether HCAR1 also modulates neuronal circuits remains unclear. In this study, using qRT-PCR, we show that HCAR1 is present in the human brain of epileptic patients who underwent resective surgery. In brain slices from these patients, pharmacological HCAR1 activation using a non-metabolized agonist decreased the frequency of both spontaneous neuronal Ca <sup>2+</sup> spiking and excitatory post-synaptic currents (sEPSCs). In mouse brains, we found HCAR1 expression in different regions using a fluorescent reporter mouse line and in situ hybridization. In the dentate gyrus, HCAR1 is mainly present in mossy cells, key players in the hippocampal excitatory circuitry and known to be involved in temporal lobe epilepsy. By using whole-cell patch clamp recordings in mouse and rat slices, we found that HCAR1 activation causes a decrease in excitability, sEPSCs, and miniature EPSCs frequency of granule cells, the main output of mossy cells. Overall, we propose that lactate can be considered a neuromodulator decreasing synaptic activity in human and rodent brains, which makes HCAR1 an attractive target for the treatment of epilepsy

Superior canal dehiscence in a patient with three failed stapedectomy operations for otosclerosis: a case report

<p>Abstract</p> <p>Introduction</p> <p>This case illustrates that superior semicircular canal dehiscence syndrome can be associated with a "pseudo"-conductive hearing loss, a symptom that overlaps with the clinical appearance of otosclerosis.</p> <p>Case presentation</p> <p>We present the case of a 48-year-old German Caucasian woman presenting with hearing loss on the left side and vertigo. She had undergone three previous stapedectomies for hearing improvement. Reformatted high-resolution computed tomographic scanning and the patient's history confirmed the diagnosis of concurrent canal dehiscence syndrome.</p> <p>Conclusion</p> <p>Failure of hearing improvement after otosclerosis surgery may indicate an alternative underlying diagnosis which should be explored by further appropriate evaluation.</p

Acoustic measures of low-frequency noise in extended high-frequency audiometry

A very high signal-to-noise ratio is required for equipment designed for extended high-frequency audiometry because listeners with almost no hearing ability in the extended high-frequency range may have normal hearing sensitivity in the lower frequencies. Two commercially available systems designed for pure-tone audiometry were evaluated both in the conventional and extended high-frequency range. Unwanted lower frequency signals greater than the noise floor occurred predominantly at presentation levels of approximately 110 dB SPL or higher. Test tones in the extended high-frequency range should be restricted to levels that are not associated with lower frequency noise

Automated pure-tone threshold estimations from extrapolated distortion product otoacoustic emission (DPOAE) input/output functions

A promising approach to the prediction of pure-tone thresholds through the estimation of DPOAE thresholds by input/output functions was recently published by Boege and Janssen [J. Acoust. Soc. Am. 111, 1810-1818 (2002)]. On the basis of their results, a device that enables automated measurements of these thresholds was recently developed. The purpose of the current study was to evaluate the reliability of this instrument for the objective assessment of hearing loss in 101 ears with either normal hearing or with cochlear hearing loss of up to 50 dB HL. The median difference between pure-tone hearing and DPOAE thresholds was approximately 2 dB. For individual subjects, however, DPOAE thresholds differed from pure-tone thresholds by up to 40 dB. We find, therefore, that the clinical benefits of this method are probably limited

Universal newborn hearing screening - a silent revolution

Significant hearing loss is one of the most frequent congenital diseases and present at birth in approximately one in 1000 newborns. During the first years of life, this number of children with permanent hearing loss rises by approximately the same amount. Hearing impairment is not an obvious condition in newborns in most cases and produces very few signs in infancy. Such hearing loss threatens normal speech and personality development. The longer the child is without auditory stimulation by speech, the more difficult it is to acquire the missed linguistic skills. Therefore, early detection and rehabilitation of such hearing loss is crucial. Universal newborn hearing screening is the most effective method to detect such impairment and is based on objective audiometric test methods that were recently developed and adapted for screening requirements. Useful tests are otoacoustic emissions and the auditory brainstem response. This article reviews this new screening tests in general and with special regard to the situation in Switzerland

Hearing in nonprofessional pop/rock musicians

OBJECTIVE: The purpose of this study was to evaluate the hearing and subjective auditory symptoms in a group of nonprofessional pop/rock musicians who had experienced repeated exposures to intense sound levels during at least 5 yr of musical activity. DESIGN: An evaluation of both ears in 42 nonprofessional pop/rock musicians included pure-tone audiometry in the conventional and extended high-frequency range, the measurement of uncomfortable loudness levels, and an assessment of tinnitus and hypersensitivity to sound. Exclusion criteria were (a) the occurrence of acoustic trauma, (b) excessive noise exposure during occupational activities, (c) a history of recurrent otitis media, (d) previous ear surgery, (e) a fracture of the cranium, (f) ingestion of potentially ototoxic drugs, and (g) reported hearing difficulties within the immediate family. These audiometric results were then compared with a control group of 20 otologically normal young adults with no history of long-term noise exposure. RESULTS: After adjusting for age and gender, relative to ISO 7029, the mean hearing threshold in the frequency range of 3 to 8 kHz was 6 dB in the musicians and 1.5 dB in the control group. This difference was statistically significant (Mann-Whitney rank sum test, p < 0.001). A significant difference was also observed between musicians using regular hearing protection during their activities (average 3 to 8 kHz thresholds = 2.4 dB) and musicians who never used such hearing protection (average 3 to 8 kHz thresholds = 8.2 dB), after adjusting for age and gender (Mann-Whitney rank sum test, p = 0.006). Eleven of the musicians (26%) were found to be hypersensitive to sound, and seven (17%) presented with tinnitus. Tinnitus assessment, however, did not reveal any clinically significant psychological distress in these individuals. CONCLUSIONS: Tinnitus and hypersensitivity to sound were observed in a significant minority within a group of nonprofessional pop/rock musicians who had experienced repeated exposure to intense sound levels over at least 5 yr but with minimal impact on their lives. Moreover, hearing loss was minimal in the subjects who always used ear protection, being only 0.9 dB higher than the control group. In contrast, hearing loss was significantly more pronounced, at 6.7 dB higher than the control group, in those musicians who never used ear protection. Continued education about the risk to hearing and the benefits of the persistent use of ear protection is warranted for musicians who are exposed frequently to intense sound levels

An assessment of threshold shifts in nonprofessional pop/rock musicians using conventional and extended high-frequency audiometry

The clinical value of extended high-frequency audiometry for the detection of noise-induced hearing loss has not been established conclusively. The purpose of this study was to assess the relative temporary threshold shift (TTS) in two frequency regions (conventional versus extended high frequency). In this exploratory study, pure-tone thresholds from 0.5 to 14 kHz were measured in both ears of 16 nonprofessional pop/rock musicians (mean age, 35 yr; range, 27 to 49 yr), before and after a 90-minute rehearsal session. All had experienced repeated exposures to intense sound levels during at least 5 yr of their musical careers. After the rehearsal, median threshold levels were found to be significantly poorer for frequencies from 0.5 to 8 kHz (Wilcoxon signed rank test, p <or= 0.004) but were unchanged in the extended high-frequency range from 9 to 14 kHz. Decreases in the median threshold values measured before the rehearsal were present across the conventional frequency range, most notably at 6 kHz, but were not observed in the extended high-frequency range. On the basis of these results, extended high-frequency audiometry does not seem advantageous as a means of the early detection of noise-induced hearing loss

Long-term assessment of auditory changes resulting from a single noise exposure associated with non-occupational activities

We examined the long-term sequelae in both ears of 42 patients who reported the occurrence of auditory changes resulting from a single exposure to intense sound levels during non-occupational activities. We divided these patients into two groups, based upon noise exposures of either continuous duration or single high-energy impulse. Audiometric data were available for each of these subjects shortly after their noise-exposure events and follow-up examinations took place more than one year after the noise occurrence (range: 1-16 years). The initial median hearing loss for the continuous-type noise exposure group at 3-8 kHz was found to be 9 dB, relative to the age-appropriate norms, in the more affected ears, and hearing function was found to have returned to normal levels at follow-up. The same initial hearing loss was measured for the impulse-type noise group, but a residual hearing loss of 4 dB was measured at follow-up. Furthermore, the majority of the subjects from both groups reported tinnitus and hypersensitivity to sound at follow-up, but with minimal impact on their lives