The Predictive Value of Infant Ultrasonic Vocalizations in a Longitudinal Study of Maternal Separation in Rats

Maternal separation (MS) is a well-established rodent model of early-life stress, implicated in the development of various neuropsychiatric conditions. Infant ultrasonic vocalizations (USVs) serve as key communicative signals and have been used to assess early emotional and social development. Here, we examined the long-term behavioral and neurobiological effects of MS across adolescence and adulthood, focusing on the predictive potential of separation-induced infant USVs (40-60 kHz). MS was conducted between postnatal days (PND) 2-14, followed by a maternal potentiation test on PND 15, during which USVs were recorded. Behavioral assessments included anxiety and social play in adolescence (PND 35-36); and anxiety, sociability, anhedonia, and fear memory in adulthood (PND 80-88). MS reduced USVs in the potentiation paradigm, suppressed social play, and ameliorated anxiety-like behavior in adolescence. In adulthood, MS induced anhedonia, impaired fear memory, and decreased c-Fos-immunopositive cells in the lateral amygdala. Path and regression analyses revealed that infant USVs predicted open arm duration in the elevated plus maze in adolescence. USVs were negatively correlated with stress-induced neuronal activation in the habenula in control, but not MS animals. These findings indicate that infant USVs constitute a biobehavioral marker for early-life adverse experiences and predict the development of later affective conditions.