Auditory brainstem responses after ovariectomy and estrogen replacement in rat

Previous work has suggested possible influences of ovarian hormones on evoked potentials in the auditory system. The aim of this project was to study the effects of ovariectomy and subsequent administration of estrogen replacement on the auditory brainstem response and the middle latency response. Groups of 90 day-old Long-Evans hooded rats were anesthetized for bilateral ovariectomies (ovex) and recordings made 3 weeks later. During the week prior to recordings some ovariectomized groups received subcutaneous injections of 10, 100 or 500 micrograms/kg Premarin in peanut oil, and other unoperated animals received vehicle injections. Recordings from vertex/chin using needle electrodes and pure tone stimulus parameters were made under Rompun/Ketamine. The results using 40 kHz tone stimuli showed that mean latencies for ovex animals were longer than animals in the 100 micrograms/kg Premarin group for waves 1a, 1an, 1b, 11, 111, 111n, and 1V/V. Other posthoc comparisons at 40 kHz stimulation revealed differences between control and 100 micrograms/kg Premarin groups for latencies of waves 1b, 1bn, 11 and 111. Latency reduction appeared for waves 1b, 1bn, 11 and 111 for the 10 ovex group, but only at wave 11 for the 500 ovex group, compared to ovex-only animals. Data from 8 kHz stimulation also demonstrated significant differences between the ovex and ovex 100 groups at waves 1bn and Vn. Observations of interpeak latency differences, especially between waves 1a and 11, suggested central as well as cochlear involvement in hormone action.(ABSTRACT TRUNCATED AT 250 WORDS)