间隔标记信号带宽和强度对豚鼠下丘间隔反应的影响

目的探讨间隔检测中间隔标记信号的带宽和强度对豚鼠下丘间隔反应阈值的影响。方法经豚鼠下丘埋植金属电极，记录4种带宽间隔标记信号和3个强度下的间隔反应，得出间隔阈值。结果与以往行为实验结果类似，相同声音强度下，豚鼠下丘的间隔反应阈值随着间隔标记信号带宽的增加而下降。例如在85dBSPL时，0．5～8kHz，0．5～16kHz及0．5～32kHz带宽下的间隔反应阈值分别为1．35±0．32ms，1．33±0．33ms及1．17±0．44ms。但是在最高频段（16～32kHz）和线性等带宽低频段（0．5～16kHz），间隔反应阈值未见显著差异，提示高频段的时间分辨可能与低频段相当。相同间隔标记带宽下，声音强度愈低，间隔反应阈值愈大；但仅在最低频段（0．5～8kHz）声音强度效应具有显著性意义。结论豚鼠下丘的间隔反应阈值主要决定于间隔标记信号的总带宽而非频带位置；信号强度也对该阈值有一定影响。     

The effect of gap-marker spectrum on gap-evoked auditory response from the inferior colliculus and auditory cortex of guinea pigs

The objective of this study is to verify the effects of gap marker spectrum on gap-evoked auditory responses. The gap-evoked potentials were recorded using electrodes implanted in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs. The gap markers were noise bursts in four frequency bands (500–8?000?Hz, 500–16?000?Hz, 500–32?000?Hz, and 16?000–32?000?Hz), and were tested at three sound levels. The onset response to the post-gap marker was measured to obtain the gap response threshold, and to establish input-output functions for latency and amplitude. Similar to previous behavioural studies, it was found that the gap-response threshold decreased with increasing marker bandwidth. This change was more significant at the cortical level in which the averaged gap-threshold decreased by approximately 2?ms with the bandwidth change. However, the gap threshold in the high frequency region (16?000–32?000?Hz) was comparable to that of the low frequency region (500–16?000?Hz). These results suggest that the total bandwidth of all auditory channels that are recruited determine the temporal resolution measured in gap-evoked potentials.

Sumario

El objetivo de este estudio es verificar los efectos del espectro de marcadores de brecha sobre las respuestas auditivas evocadas por una brecha. Se registraron los potenciales evocados por brecha utilizando electrodos implantados en el colículo inferior (IC) y la corteza auditiva (AC) de cobayos. Los marcadores de brecha fueron bursts de ruido en cuatro bandas de frecuencia (500–8000?Hz, 500–16?000?Hz, 500–32?000?Hz and 16?000–32?000?Hz), y se evaluaron a tres niveles sonoros. Se midió la respuesta de inicio del marcador post-brecha para obtener el umbral de respuesta de brecha, y establecer las funciones de ingreso-salida para latencia y amplitud. Al igual que en estudios conductuales previos, se encontró que el umbral de respuesta de brecha disminuyó con el incremento de los anchos de banda del marcador. Este cambio fue más significativo a nivel cortical en donde el umbral promediado de brecha disminuyó en aproximadamente 2 mseg con el cambio de ancho de banda. Sin embargo, el umbral de brecha en la región de alta frecuencia (16?000–32?000?Hz) fue comparable al umbral de la región de baja frecuencia (500–16?000?Hz). Estos resultados sugieren que el ancho de banda total de todos los canales auditivos reclutados determina la resolución temporal medida en los potenciales evocados por brecha.     

The effect of gap-marker spectrum on gap-evoked auditory response from the inferior colliculus and auditory cortex of guinea pigs

The objective of this study is to verify the effects of gap marker spectrum on gap-evoked auditory responses. The gap-evoked potentials were recorded using electrodes implanted in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs. The gap markers were noise bursts in four frequency bands (500-8,000 Hz, 500-16,000 Hz, 500-32,000 Hz, and 16,000-32,000 Hz), and were tested at three sound levels. The onset response to the post-gap marker was measured to obtain the gap response threshold, and to establish input-output functions for latency and amplitude. Similar to previous behavioural studies, it was found that the gap-response threshold decreased with increasing marker bandwidth. This change was more significant at the cortical level in which the averaged gap-threshold decreased by approximately 2 ms with the bandwidth change. However, the gap threshold in the high frequency region (16,000-32,000 Hz) was comparable to that of the low frequency region (500-16,000 Hz). These results suggest that the total bandwidth of all auditory channels that are recruited determine the temporal resolution measured in gap-evoked potentials.     

交叉听力对豚鼠听性脑干反应测试的影响

报告对８只听觉正常的及鼠，观察交叉听力对其耳蜗动作电位和听怀脑干反应测试结果的影响。先手术造成其左耳全聋，然后用四种方法分别记录ＡＢＲ反应阈和Ⅰ波潜伏期。结果发现，术耳虽已全聋，但该侧给声强度达１０ｄＢＨＬ以上时仍可记录到ＡＢＲ，而ＡＰ未能引出，代之出现的却是清晰的ＡＢＲ波形。     

Effect of noise on auditory evoked responses in awake guinea pigs

Changes in the auditory nerve action potential (AP), evoked responses from the inferior colliculus (IC-ER) and auditory cortex (AC-ER) were assessed after exposure to white noise of 120 dB SPL for 1 h in awake guinea pigs. Auditory thresholds were estimated with the aid of averaged AP, IC-ER and AC-ER, besides the threshold shifts also the changes in amplitude-intensity functions were evaluated. Auditory thresholds for tone pips and clicks increased by 20-30 dB 1 h after exposure and were similar in all the three investigated structures. The maximum threshold shifts for tone pips were observed at 8 kHz and were 33.2 +/- 12.9 dB for AP, 30.4 +/- 12.7 dB for IC-ER and 30.8 +/- 13.0 dB for AC-ER (n = 20). The thresholds recovered to preexposure levels within one week. Reduction in AP and IC-ER amplitudes 1 h after exposure was similar, the amplitude-intensity functions were shifted by 20-40 dB. In contrast, the amplitude-intensity functions in the auditory cortex 1 h after exposure were steeper than before exposure and this amplitude enhancement was present for 24 h after exposure. The enhancement of the AC-ER which resembles recruitment and which may be a sign of hypersensitivity of the animal to auditory stimuli was present only when the animals exposed to noise were awake. The noise exposure in animals anaesthetized with urethane reduced the amplitude-intensity functions of all three recorded potentials.     

General anesthesia changes gap-evoked auditory responses in guinea pigs

CONCLUSION. General anesthesia induced by sodium pentobarbital reduces temporal resolution as represented by an increase in the threshold of gap-evoked auditory responses in guinea pigs. OBJECTIVES. To explore the potential impact of general anesthesia by sodium pentobarbital (PB), a common anesthetic used in animal research, on gap-evoked responses. MATERIALS AND METHODS. The evoked potentials in response to gaps formed by bursts of broadband noise were recorded from electrodes implanted in the inferior colliculus (IC) and the auditory cortex (AC) of guinea pigs. The gap responses were compared in three conditions: unanesthetized and anesthetized with two doses of sodium pentobarbital (40 mg/kg and 20 mg/kg). RESULTS. PB increased the gap response thresholds, especially when applied at the higher dose. The threshold shift induced by PB was greater in the AC than in the IC. In addition, the higher dose of PB significantly increased the gap response latency in both IC and AC, and decreased response amplitude in IC only.     

The effect of noise-induced sloping high-frequency hearing loss on the gap-response in the inferior colliculus and auditory cortex of guinea pigs

Gap detection has been used as an evaluation tool for temporal processing in subjects with sensorineural hearing loss (SNHL). However, the results from other reports are varied making it difficult to clearly define the impact of SNHL on the temporal processing ability of the auditory system. Specifically, we do not know if and how a high-frequency hearing loss impacts, presumably through off-channel interaction, the temporal processing in low-frequency channels where hearing sensitivity is virtually normal. In this experiment, gap-evoked responses in a low-frequency band (0.5–8 kHz) were recorded in the inferior colliculus (IC) and auditory cortex (AC) of guinea pigs through implanted electrodes, before and after a slopping high-frequency hearing loss, which was induced by over-stimulation using a 12-kHz-tone. The results showed that the gap thresholds in the low-frequency region increased gradually and became significantly higher 8 weeks after the induced high-frequency hearing loss. In addition, the response latency was slightly increased in the IC but this was not true for the AC. These results strongly indicate that a high-frequency hearing loss exerted an off-channel impact on temporal processing in the low-frequency region of the auditory system.     

Effects of cisplatin and thiosulfate upon auditory brainstem responses of guinea pigs

Two side effects which limit the use of cisplatin in cancer chemotherapy are severe nephrotoxicity and ototoxicity. The concurrent administration of sodium thiosulfate with cisplatin reportedly protects from cisplatin nephrotoxicity, however, protection from ototoxicity has not been documented. The purpose of this study was to examine the efficacy of using thiosulfate to ameliorate the ototoxic effects of cisplatin. Toward this end, the effects of cisplatin alone, cisplatin administered concurrently with sodium thiosulfate (CIS/THIO), and sodium thiosulfate alone on the auditory brainstem response (ABR) of guinea pigs were compared. ABR waveforms, comparing latencies, amplitudes and response thresholds, were monitored before, immediately after, and 30 days post treatment. Sodium thiosulfate administered with cisplatin (CIS/THIO) consistently protected animals from hearing loss and surprisingly yielded significant increases in amplitude when compared to baseline and saline controls. However, ABRs of CIS/THIO animals returned toward baseline values after 30 days.     

effects of glutamate on distortion-product otoacoustic emissions and auditory brainstem responses in guinea pigs

Objective To investigate changes in evoked potentials and structure of the guinea pig cochleae during whole cochlear perfusion with glutamate. Methods CM, CAP, DPOAE, and ABR were recorded as indicators of cochlear functions during whole cochlear perfusion. The morphology of the cochlea was studied via transmission electron microscopy. Results There were no significant changes in DPOAE amplitude before and after glutamate perfusion. CM I/O function remained nonlinear during perfusion. ABR latencies were delayed following glutamate perfusion. The average CAP threshold was elevated 35 dB SPL following glutamate perfusion.. The OHCs appeared normal, but the IHCs and afferent dendrites showed cytoplasmic blebs after glutamate perfusion. Conclusions While being a primary amino acid neurotransmitter at the synapses between hair cells and spiral ganglion neurons, excessive glutamate is neurotoxic and can destroy IHCs and spiral ganglion neurons. The technique used in this study can also be used to build an animal model of auditory neuropathy.     

Effects of inner ear immune responses on auditory function in guinea pigs]

Following direct challenge with KLH antigen primary or secondary (after systemic immunization) to the ES (endolymphatic sac) in guinea pigs, ECoG (electrocochleograms) were recorded from the round window induced by click and tone pips. The recordings were carried out on the 2nd, 7th and 21st days after local antigen challenge. There were no abnormal findings in the ECoG of the primary antigen challenged animals. On the other hand, prolongation of latencies, decrease in amplitudes of APs (compound action potentials) and increases in SP/AP ratios were observed in the 2nd day recordings of the secondary antigen challenged animals. However, all parameters of ECoG in the 7th day recordings were normal. Decreases in AP amplitudes were again found in the 21st day recordings. The ECoG findings with click and tone pip stimulation showed similar results. From these findings, in conjunction with morphological observations, it is speculated that these ECoG findings are caused by immuno-injury to the ES and cochlea, as well as the resultant endolymphatic hydrops which develops acutely and gradually subsides after secondary challenge.