Abstract
Auditory brain-stem potentials (ABRs) were studied in cats for up to 45 days after kainic acid had been injected unilaterally or bilaterally into the superior olivary complex (SOC) to produce neuronal destruction while sparing fibers of passage and the terminals of axons of extrinsic origin connecting to SOC neurons. The components of the ABR in cat were labeled by their polarity at the vertex (P, for positive) and their order of appearance (the arabic numerals 1, 2, etc.). Component P1 can be further subdivided into 2 subcomponents labeled P1a and P1b. The correspondences we have assumed between the ABR components in cat and man are indicated by providing a Roman numeral designation for the human component in parentheses following the feline notation, e.g., P4 (V). With bilateral SOC destruction, there was a significant and marked attenuation of waves P2 (III), P3 (IV), P4 (V), P5 (VI), and the sustained potential shift (SPS) amounting to as much as 80% of preoperative values. Following unilateral SOC destruction the attenuation of many of these same ABR components, in response to stimulation of either ear, was up to 50%. No component of the ABR was totally abolished even when the SOC was lesioned 100% bilaterally. In unilaterally lesioned cats with extensive neuronal loss (> 75%) the latencies of the components beginnign at P3 (IV) were delayed to stimulation of the ear ipsilateral to the injection site but not to stimulation of the ear contralateral to the injection. Binaural interaction components of the ABR were affected in proportion to the attenuation of the ABR. These results are compatible with multiple brain regions contributing to the generation of the components of the ABR beginning with P2 (III) and that components P3 (IV), P4 (V), and P5 (VI) and the sustained potential shift depend particularly on the integrity of the neurons of the SOC bilaterally. The neurons of the lateral subdivision (LSO) and the medial nucleus of the trapezoid body (MNTB) of the SOC have a major role in generating waves P3 (IV) and P4 (V).
Highlights
Waves V and VI in human are most likely comparable to waves P4 and P5 respectively in cat, whereas the relationship of P3 to ipsilateral stimulation of P2 (III) or in generating waves P3 (IV) is uncertain (Fullerton et al 1987). In this and our subsequent paper (Zaaroor and Starr 1991) we suggest that P2, P3, P4 and P5 in cat are comparable to waves III, IV, V and VI in human and will refer to the Auditory brain-stem potentials (ABRs) components recorded from cat in this study by both types of designation, i.e., by their polarity and sequence as well as by their assumed human ABR counterparts using Roman numerals
Three animals had only a needle inserted into the superior olivary complex (SOC) to serve as 'controls.' Six animals were subsequently injected with kainic acid into the cochlear nucleus (CN) and are reported in the companion paper (Zaaroor and Starr, 1991)
Since the same earphones were always used for right and left ear stimulation, we cannot distinguish whether the observed effect reflects systematic differences in the brain-stem's responsiveness or in the earphones' characteristics
Summary
Recordings of nerve VIII and brain-stem activity in humans (Hashimoto et al 1981; M~ller et al 1981) and in animals (Achor and Starr 1980a; Caird et al 1985; Legatt et al 1986a,b; Kano and Starr 1987; Starr and Zaaroor 1990) correlating the latency of intracranial events with the components of scalp derived ABR; (4) experimental brain lesions in animals comparing the site of destruction with changes in the ABR (Buchwald and Huang 1975; Achor and Starr 1980b; Wada and Starr 1983a,b,c)
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