Early-weaned rodents showed changes in behavioral and emotional traits (Shimozuru et al., 2007) and myelin formation in the anterior basolateral amygdala (aBLA; Ono et al., 2008), which is innervated by the prefrontal efferents. At the meeting, we previously presented that early-weaned SD male rats (postnatal day [PND] 16) exhibited lower paired-pulse facilitation (PPF) than did late-weaned rats (PND 30), in the prefrontal-aBLA pathway under urethane anesthesia at PND 49 or later. Rosenkranz and Grace (e.g., 2001) reported that the efferents caused excitation of the inhibitory interneurons in the BLA to suppress the affective response of the BLA driven by the sensory cortex: Dopamine (DA) attenuated this effect and synergistically enhanced the sensory cortex-driving response. In this study, we measured amygdalar DA levels of the early- and late-weaned rats by in vivo microdialysis and trended to find differences as: The early-weaned group showed higher basal DA release but the evoked response following open-field exploration maintained lower and recovered faster to the base than the late-weaned group. These findings imply that there are associations between the structural and electrophysiological properties of the efferents and amygdalar DA. We will further study these associations by histological analysis of the positions of microdialysis probes in the amygdala and behavioral analysis of open-field locomotion.