Microanalysis of ultrasound vocalizations of young rats: Assessment of the behavioral teratogenicity of methylmercury

Abstract

An on-line real-time computer system for the analysis of ultrasound vocalizations of rats is presented. The calls of young rats are recorded by an ultrasound microphone, transformed by an amplitude envelope and a frequency to voltage converter, digitized and stored by a microcomputer. The data management and analysis of the recorded vocalizations are entirely automated, allowing a high throughput of experiments in a routine laboratory. The frequency values are analyzed with respect to number, duration, base-interval, and mean frequency of the calls. Also, the frequency distributions of the call to call intervals, the call durations and the ultrasound frequencies, as well as the power spectra of the frequency modulations, are calculated. This system was used for the assessment of the behavioral teratogenicity of methylmercury chloride. Wistar rat dams were treated with 0, 1.5 or 5 mg/l in their drinking water from two weeks prior to pairing until the end of the experiment. The ultrasound vocalizations of two female and two male offspring per litter were recorded on days 5, 7, 9, 11, 13, and 15 for one minute in a clean glass beaker cooled to 20°C. Methylmercury treatment resulted in a developmental delay and an overall reduction in the number of calls, a shortening of the base-interval and the call durations, a flattening and shift of the frequency distributions, and an alteration in the development with age of the frequency distributions. The frequency modulations of the calls also differed, their power being lower (smaller frequency variation) on several occasions.