Anita R Sterns

Syracuse University, Syracuse, New York, United States

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Publications (3)8.24 Total impact

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    ABSTRACT: Many studies of the auditory system are performed on animals under general anesthesia. A concern for researchers is that these agents may significantly alter the underlying neurophysiologic mechanisms being studied. The effects may very across species, and even among individuals within a species. An investigation was undertaken to study whether DPOAE measures differ using three different anesthetic regimens: acetylpromazine-ketamine, xylazine-ketamine, and sodium pentobarbital. The same rat was anesthetized in three consecutive weeks using a different anesthetic regimen each week. DPOAE magnitude and phase temporal responses were recorded from which several measures were taken: DPOAE levels at the onset of the primaries, changes in DPOAE level as a function of time during presentation of the primaries (DeltaLI) and changes in DPOAE level (DeltaLC) and phase (DeltaPC) during presentation of a broad-band noise presented contralateral to the probe. Each week the same measurements were repeated with the rat anesthetized using a different regimen and at the end of the third week, the middle ear muscles were sectioned and the measurements repeated once again. Results showed that the anesthetic regimens did not differentially alter the DPOAE onset levels. When sodium pentobarbital was used as the anesthetic regimen, DeltaLC and DeltaPC were significantly smaller relative to those measured when the rats were anesthetized with acetylpromazine-ketamine and xylazine-ketamine. Based on the assumption that large, positive (DeltaPC) values are related to middle ear muscle activation, the middle ear muscle reflex remained at least partially active in some rats under sodium pentobarbital anesthesia. The DeltaLI measures were significantly smaller when the animals were anesthetized with xylazine-ketamine and sodium pentobarbital than when they were anesthetized with acetylpromazine-ketamine. Recordings taken after sectioning the middle ear muscles suggested that the middle ear muscle reflex substantially contributes to DeltaLC and DeltaPC measures under the anesthetic regimens xylazine-ketamine and acetylpromazine-ketamine. Data indicated that anesthetic agents variably alter neurophysiologic mechanisms involved with the complex control of the auditory signal even among individuals in the same species. Extreme care should be taken when comparing DeltaLI, DeltaLC and DeltaPC across studies when different anesthetic regimens are used within and across species.
    Hearing Research 02/2008; 235(1-2):47-59. · 2.85 Impact Factor
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    ABSTRACT: An investigation was undertaken to measure medial olivocochlear (MOC) reflexes in anesthetized rats before and after sectioning of the middle-ear muscles. Distortion product otoacoustic emission (DPOAE) magnitude and phase temporal responses were measured ipsilaterally to study MOC-mediated "DPOAE onset adaptation" and in the presence of a contralateral noise to study MOC-mediated contralateral "suppression" (terms as used by previous researchers). Distortion product otoacoustic emission onset adaptation and contralateral suppression had predictable changes in direction of magnitude and phase that were dependent on the input-output function. After sectioning of the middle-ear muscles (MEMs), DPOAE onset adaptation and contralateral suppression were greatly reduced, and there were little, if any, changes in phase. These "residual" changes were interpreted as a result of the MOC reflex. The results suggest that what appears to be DPOAE onset adaptation and contralateral suppression can be mediated primarily by MEM reflexes. When studying MOC effects on otoacoustic emissions (OAEs) using acoustic stimulation, it is necessary to make recordings over a span of stimulus levels. In addition, looking at both magnitude and phase of the OAE may help separate what is due to the MOC reflex from MEM reflex.
    Journal of the Association for Research in Otolaryngology 07/2005; 6(2):119-35. · 2.55 Impact Factor
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    ABSTRACT: Although the chinchilla is widely used as a model for auditory research, little is known about the distribution and morphology of its olivocochlear neurons. Here, we report on the olivocochlear neurons projecting to one cochlea, as determined by single and double retrograde fluorescent tracer techniques. 10 adult chinchillas were anesthetized and given either unilateral or bilateral injections of a fluorescent tracer (either Fluoro-Gold or Fast Blue) into scala tympani or as a control, a unilateral injection into the middle ear cavity. The results indicate that there are similarities as well as significant differences between the chinchilla and other species of rodents in the distributions of their olivocochlear neurons. Based on three well-labelled cases, there was a mean total of 1168 olivocochlear neurons in the chinchilla. Of these, the majority (mean 787) were small, lateral olivocochlear neurons found almost exclusively within the ipsilateral lateral superior olivary nucleus. The next largest group consisted of a mean of 280 medial olivocochlear neurons virtually all of which were located in the dorsomedial peri-olivary nucleus. Chinchilla medial olivocochlear neurons were more predominantly crossed in their projections (4:1) than in any known species. The smallest group of olivocochlear neurons (mean 101) consisted of larger lateral olivocochlear neurons (shell neurons) which were located on the margins of the superior olivary nucleus and which projected mainly (2.2:1) ipsilaterally. Double retrograde labelling was observed only in medial olivocochlear neurons and occurred in only 1-2% of these cells. The results confirm previous findings which indicated a relative paucity of fibers belonging to the uncrossed as compared to the crossed olivocochlear bundle. This, together with the strong apical bias of the uncrossed projection reported previously, offers possible explanations for the apparent absence of efferent-mediated suppressive effects of contralateral acoustic stimulation in this species. Regarding the lateral olivocochlear system, the chinchilla is shown to possess both intrinsic and shell neurons, as in the rat.
    Hearing Research 09/1999; 134(1-2):57-70. · 2.85 Impact Factor