Evaluation of anesthesia effects in a rat animal model using high and medium stimulus intensity otoacoustic emission protocols
Level: Advanced
Numbers of Slides: 32
Abstract:
INTRODUCTION: Recent studies (Harel et al,1997) have suggested that ketamine compounds increase the amplitude level of the TEOAE and DPOAE responses in a gerbil animal model. Since the major application of the OAEs is the detection of sensorineural hearing losses, expressed by alterations of the OAE responses, it is important to define the time window in which the anesthesia effect on the OAEs is not present.
MATERIALS AND METHODS: The anesthesia effect on the OAE recordings was evaluated in 3 groups of 64 Sprague -Dawley rats (mean weight 225 ± 20 gr). Thirty due animals were tested with TEOAEs, 27 animals with DPOAEs and 5 animals with both OAE types.The anaesthetic (equal volumes of ketamine mixed with xylazine or atropine and saline solution) was administered in two consecutive phases. In phase one, the animal received an intra-peritoneal dose (1 ml / kg of body weight) and upon the first signs of muscular relaxation (phase two) a second half-volume dose was administered subcutaneously. The TEOAEs were recorded according to a nonlinear protocol and were evoked by a 63.5 dB SPL click stimulus. The DPOAEs (cubic distortion products) were evoked by two different asymmetrical protocols with primaries set at 60-50 and 50-40 dB SPL. The OAE responses were recorded in 10 min intervals, starting 5 min after the first dose and ending at 60 min post treatment.
RESULTS: An analysis of the data of both OAE types with a repeated measures model indicated the following: (1) There is a decrease of the TEOAE response level, the TEOAE correlation value and the S/N ratios in the tested frequencies 12-14 min after the administration of the anesthesia, but these differences were not distinguishable from random variation (not statistically significant). (2) The DPOAE responses evoked by a 50-40 protocol showed the highest S/N decrease , but the time differences were also not significant.
CONCLUSIONS: These findings from the rat model contrast the data available in the literature from a gerbil animal model and suggest that the previous data were treated, erroneously, by statistical methods which did not consider time as a variable.