Effects of the Female Estrous Cycle on the Sexual Behaviors and Ultrasonic Vocalizations of Male C57BL/6 and Autistic BTBR T+ tf/J Mice

A primary characteristic of autism, which is a neurodevelopmental disorder, is impaired social interaction and communication. Furthermore, patients with autism frequently show abnormal social recognition. In mouse models of autism, social recognition is usually assessed by examining same-sex social behavior using various tests, such as the three-chamber test. However, no studies have examined the ability of male mice with autism to recognize the estrous cycle of female partners. In this study, we investigated the sexual behaviors, especially mounting and ultrasonic vocal communication (USV), of BTBR T+ tf/J (BTBR) mice, which are used as a well-known mouse model of autism, when they encountered estrus or diestrus female mice. As expected, C57BL/6 mice mounted more female mice in the estrus stage compared with the diestrus stage. We found that BTBR mice also mounted more female mice in the estrus stage than female mice in the diestrus stage. Although the USV emission of male mice was not different between estrus and diestrus female mice in both strains, the mounting result implies that BTBR mice distinguish sexual receptivity of females.

Effects of Auditory Environment on Freezing Behavior of Mice in a Novel Context

Freezing behavior is a widely used parameter that represents the level of fear. A number of studies on emotional learning have used this behavior for quantification of fear that results from a cue or a context. Even though the expression of freezing behavior is based on the dynamic interaction of mice with the environment, the effect of environmental stimuli on freezing behavior has not been studied extensively because of its minority compared to the effect of conditioning-stimuli. In this study, we found that the auditory environment of a context affects the freezing behavior of a mouse in it. This effect was not observed when the mouse was exposed to the context for the first time. However, during the second exposure, the level of freezing behavior increased significantly in an intensity-dependent manner, while the type, pitch, and rhythm of additional sounds involved in the context did not induce notable effects. This intensity-dependent effect was unrelated to the level of fear and anxiety, reflecting another aspect of the freezing behavior as a parameter for recognizing the pattern of normal behaviors.