Acoustic Trauma of Guinea Pigs Caused by ^(60) Cobalt γ-Ray

Auditory cortical cvokod rcsponse(ACER) and auditory brainstom cvoked response (ABR) were recorded in guinea pigs before and after irradiation of ^(60)Co γ-ray. A single dose of irradiation on head was 90Gy and 70Gy in two groups, respectively. Two h after irradiation. the threshold shift was 12. 5 dB and 9 dB, and the ACER post-irradiation amplitude ex- ceeded the maximum pre-irradiation value by 20% and 37%. Six h after irradiation, the threshold shift increased to 37 dB and the maximum amplitnde decreased to the level of pre-irradiation in 70Gy-group. In another group, right auditory bulla arca was irradiated with a total dose of 45Gy in a course of six fractions/two weeks. Fourteen d after irradiation, the threshold shift of ABR was 118 dB and the latency of wave I was longer. The amplitude-intensity curve was after irradiation. Histological observation using scanning showed that only outer hair- cells in the basal coil of the cochlea were 6 h after irrdiation 50Gy-group. Bul 16 h later, outer, hair cells in all coils of the cochlea were found to be destroyed extensively and inner cells were destroyed slightly. In 45Gy-group, 14 d after irradiation, outer hair cells in all coils of the cochlea were damaged and no inmer hair cell was injured severely.

Effects of delayed brain-derived neurotrophic factor application on cochlear pathology and auditory physiology in rats

Background The development and maintenance of spiral ganglion cells （SGCs） appear to be supported by neurotrophins Removal of this support leads to their gradual degeneration. Intracochlear infusion with neurotrophins can provide trophic support to SGCs in animal deafness models if given shortly after deafening. However, it is not known whether delayed intervention will provide similar protection, which might be clinically relevant. The present research was conducted to determine the effects of brain-derived neurotrophic factor （BDNF） administration on the capacity of the peripheral processes to resprout. Methods The left cochlea of 20 profoundly deafened rats, which were divided into 2 groups equally, was implanted with an electrode and drug-delivery system 30 days after deafening. Either BDNF or artificial perilymph （AP） was delivered continuously for 28 days. Electrically evoked auditory brainstem responses （EABRs） were recorded during the period. SGC body and peripheral process density were measured. Results The EABR thresholds of AP increase continually. Those of BDNF increase slowly at the beginning then decrease, and were significantly less than those of the AP group from day 14 to 28 （P 〈0.01）. In terms of SGC and peripheral process density, the difference between the treated and control ears of BDNF group was clearly significant （P 〈0.01）, but not in AP group （P 〉0.05）. Analysis of the left cochlea between the two groups demonstrated that SGC/peripheral process density of the BDNF group was significantly greater than that of the AP group. Finally, a functional formula was developed relating the last EABR threshold and SGC density and process density, which was as follows： T= 466.184-2.71 （F.B.L）. Conclusions Under the conditions of delayed intervention following 30 days after deafening in rats, it can be concluded that BDNF enhances SGC bodies and peripheral processes survival after differentiation and so improves auditory sensitivity. SGC peripheral processes influence the auditory sensitivity.

Frequency Following Response of Speech-ABR by Instantaneous Energy Spectrum

A frequency following response(FFR) of speech auditory brainstem response(speech-ABR) elicited by the speech syllable/da/contains three distinct waves named as D, E and F, corresponding to the structure of the stimulus sound. The detection and characterization of FFRs are critical in the study and application of speech-ABRs. Conventional methods detect the latencies of the waves in time domain by measuring the maximal amplitudes of the waveform in the preset windows, which suffers the problem of low quality of FFR waves. In this paper, we defined an instantaneous energy(IE) spectrum based on empirical mode decomposition(EMD)method(EMD-IE method) to detect FFR and measured the latencies of the waves. The results reveal that the FFRs are mostly evident on the second layer of the IE spectra,which would benefit the detection and measurement of the FFRs in clinic.