Caracterização da produção vocal ultrassônica neonatal induzida por separação materna e avaliação de sua validade como biomarcador da atividade exploratória ao desmame em um modelo animal de autismo

Abstract

Communication during social interaction is a key factor in choosing the most fitting behavioral response in each situation. Rats vocalize at the ultrasound range (USVs) that convey information on their emotional states and contribute to engagement in social interaction. The adult vocal repertoire is developmentally established by the maturation of innate neonatal 40-kHz calls elicited under stressful situations, which evoke maternal care responses towards the pup. Because of this evoked response, the 40-kHz USVs have great weight in the pups’ survival during the first three weeks of life. Although this is a period of fast growth and great physiological changes for the pup, the majority of studies about 40-kHz USVs lack of longitudinal analyses during this critical phase of development. Understanding how emission patterns and acoustic properties change with aging can help us to identify abnormality signs of developmental disorders such as autism. Here, we analyzed the postnatal development of acoustic parameters and emission patterns of 40-kHz USVs produced by infant rats during 5 min of maternal separation at postnatal days 07, 14 and 21. We also investigate the effects of VPA exposition over vocal production. Our result showed a reduction in emissions of VPA-exposed animals and alterations in the acoustic parameters and emission patterns compared to control animals. After applying two different classification methods, a convolution neural network (CNN) and a gaussina mixture model (GMM), to spectro-temporally distinguish individual USVs, we found a significant reduction in the number of vocal classes in the animals with autistic phenotype. Complexity of emissions, measured by the degrees of possible transitions between pairs of USVs, were also dramatically reduced in those animals, indicating a less diverse vocal repertoire compared to controls. By the end of the third postnatal week, when animals were weaned, we evaluated exploratory behavior during the open-field test. VPA-treated animals showed reduced exploratory behaviors. Behavioral analyses showed a positive correlation between the amount of frequency modulated calls and exploratory behavior in the open-field, in contrast to a negative correlation between non-modulated calls and this behavior. Therefore, we conclude that VPA-exposed rats show alterations in vocal development, characterized not only by quantitative reduction in vocal production but also by altered bioacoustic and dynamical vocalization patterns, which correlates to post-weaning behavior. In conclusion, we showed through semi-automatized classification methods that 40-kHz USVs can be separated in distinct types and that such classifications have biological correspondence, since we observe significant correlations between these USV types and exploratory behaviors at the end of the third week of life.