Narkoseeinfl�sse auf akustisch evozierte Potentiale aus dem Colliculus inferior und dem auditiven Cortex beim Meerschweinchen

The value of fentanyl/diazepam anesthesia for experimental operations and recordings of compound action potentials in the guinea pig cochlea

Fentanyl/diazepam anesthesia is an appropriate combination for surgical operations on the guinea pig, since it ensures definitive anesthesia and analgesia without respiratory depression. Comparative investigations with pentobarbital and urethane were carried out to check their applicability for electrocochleographic recordings. We found that fentanyl/diazepam combination anesthesia is more suitable for electrocochleographic investigations than pentobarbital. We were thereby able to prove that pentobarbital has an attenuating effect on electrocochleographic recordings in contrast to the findings reported in the available literature. For this reason, and because the lowest rates of animal morbidity occurred with fentanyl/diazepam, this combination anesthesia should be used preferentially for electrophysiological experiments in guinea pigs.

The influence of moderate-intensity noise on the click-evoked compound action potential of the guinea pig, Cavia porcellus

Noise-induced alterations of the click-evoked compound potential (CAP) were studied by means of electrodes chronically implanted near the round window in 15 pigmented guinea pigs aged 3-6 months. The potentials were recorded before, during and after exposure to continuous pink noise maintained at an intensity of 80, 90 or 100 dB SPL for 120 h. During the exposure phase the CAP thresholds of all the animals tested increased exponentially, nearly leveling out by approximately 48 h to form an asymptotic threshold shift. Recovery after the end of exposure also occurred exponentially, with a return to the original threshold for neural excitation after at most 72 h. There was no detectable change in amplitude, latency or inter-peak interval of the CAP when correlated with the change in threshold.

The influence of moderate-intensity noise on the compound action potential evoked by tone bursts in the guinea pig, Cavia porcellus

Noise-induced changes in the compound action potential (CAP) evoked by tone bursts in the frequency range 0.5-24 kHz were studied in 15 pigmented guinea pigs by means of chronically implanted electrodes positioned near the round window. The animals were exposed for 120 h to continuous pink noise at the intensities 80, 90 and 100 dB SPL. During the exposure period, all the animals exhibited an exponential rise in CAP threshold, leveling out after 24-72 h (asymptotic threshold shift, ATS). The largest threshold shifts were recorded during exposure to 100 dB SPL, for frequencies in the range 8-12 kHz. In the recovery phase, after the end of noise exposure, the threshold to tones at all frequencies tested fell exponentially, reaching the original level in about 72 h in all cases.

Effects of age upon auditory evoked potentials from the inferior colliculus and cortex in the guinea pig

Auditory evoked potentials from the inferior colliculus and cortex were examined for evidence of the effect of aging in central regions of the auditory system of the guinea pig. The threshold was 25 dB higher in the responses from the inferior colliculus and 44 dB higher in the cortical potentials in old animals than in young animals. The latency of the collicular responses in the old group was greater by 1.5 ms and, in the high-frequency range, the amplitudes were smaller at all intensities tested. The latency of responses recorded from the auditory cortex in the old guinea pigs was 3.6 ms greater at threshold and the amplitudes were smaller. With stimuli well above threshold, the latency differences were no longer significant, whereas the amplitudes in old animals became significantly greater than those in the young.