Hypothalamic POMC neural modulation of infant vocalization in mice: Infants vocalize when isolated from their primary caregivers, attracting their attention to receive comfort, care, and nutrition. Impaired infant vocal behavior can lead to maternal neglect and even death in some species. Despite the importance of infant vocalization for the proper development of individuals, we still know little about how the brain controls this behavior. Beta-endorphin is an opioid that is strongly implicated in infant-caregiver bonding and is only synthesized by POMC neurons which are mainly found in the arcuate nucleus of the hypothalamus. Therefore, our aim was to determine the role of POMC neurons and beta-endorphin in the suppression of infant vocal behaviors. Our approach was to quantify ultrasonic vocalizations (USV) of infant mice during isolation and maternal reunion under genetic, pharmacologic and chemogenetic conditions. While the hypothesis of this study was that beta-endorphin is released by POMC neurons upon social reunion, leading the suppression of infant vocalization; our results lead to a different conclusion. Our data suggests that beta-endorphin does not suppress USVs during maternal reunion and instead is released after prolonged isolation, lowering the vocal rate of infant mice. For our next experiments, we will further elucidate beta-endorphin role during isolation and its possible interaction with other hypothalamic neural groups. Understanding the mechanisms driving infant vocalization is key to reveal how the infant brain regulates behaviors and to study disorders impacting early social and speech development. Bosque Ortiz GM, Yale University, New Haven, CT, gabriela.bosque.ortiz@yale.edu Leao D, Federal University of Rio Grande do Sul Porto Alegre, Brazil Dietrich MO, Yale University, New Haven, CT