Preliminary Assessment of Exploratory Behavior in Rats with Lifelong Absence of Brain Serotonin Using an RFID-Controlled Social Home-Cage Access Platform

Abstract Lifelong central serotonin deficiency affects behavioral development, yet its impact on spontaneous exploratory and engagement-related behavior in a social-housing context remains incompletely characterized. To address this gap, we studied adolescent male Tryptophan Hydroxylase 2 knockout (Tph2-KO) rats using two complementary automated approaches: a radio-frequency identification (RFID)-controlled Social RatPad access platform connected to a social home-cage compartment and the LABORAS behavioral profiling system. In the Social RatPad platform, the central cage served as the shared living environment, whereas the automated components controlled individual access to the touchscreen-equipped testing chambers and logged RFID-identified events. Following RFID implantation, adolescent male Dark Agouti Tph2-KO and wild-type (WT) littermate rats were monitored in the Social RatPad/RFID platform and tested individually in LABORAS during two standardized 2 h sessions. The present analysis focuses on spontaneous corridor use, chamber access, touchscreen trial initiation, and free-moving exploratory behavior; touchscreen accuracy and cognitive learning outcomes were not used as inferential endpoints. KO rats showed reduced early exploratory activation in LABORAS, delayed onset of voluntary touchscreen interaction, descriptively lower visual-discrimination trial engagement, and more heterogeneous access patterns across animals. LABORAS differences were most evident during initial exposure and attenuated during the second session. These findings suggest that lifelong absence of central serotonin alters the initiation and organization of spontaneous exploratory and engagement-related behavior during adolescence. The results also show that Social RatPad/RFID and LABORAS measurements provide complementary, but not directly interchangeable, information because they differ in duration, social context, and novelty/familiarity of the testing environment.