In recent years, a growing body of research has shown sex differences in the prevalence and symptomatology of psychopathologies, such as depression, anxiety, and fearrelated disorders, all of which show high incidence rates in early life. This has highlighted the importance of including female subjects in animal studies, as well as delineating sex differences in neural processing across development. Of particular interest is the corticolimbic system, comprising the hippocampus, amygdala, and medial prefrontal cortex. In rodents, these corticolimbic regions undergo dynamic changes in early life, and disruption to their normative development is believed to underlie the age and sexdependent effects of stress on affective processing. In this review, we consolidate research on sex differences in the hippocampus, amygdala, and medial prefrontal cortex across early development. First, we briefly introduce current principles on sexual differentiation of the rodent brain. We then showcase corticolimbic regional sex differences in volume, morphology, synaptic organization, cell proliferation, microglia, and GABAergic signaling, and explain how these differences are influenced by perinatal and pubertal gonadal hormones. In compiling this research, we outline evidence of what and when sex differences emerge in the developing corticolimbic system, and illustrate how temporal dynamics of its maturational trajectory may differ in male and female rodents. This will help provide insight into potential neural mechanisms underlying sex-specific critical windows for stress susceptibility and behavioral emergence.

The medial prefrontal cortex (mPFC) is critically involved in cognitive and emotional function and underlies many neuropsychiatric disorders, including mood, fear and anxiety disorders. In rodents, disruption of mPFC activity affects anxiety- and depression-like behavior, with evidence supporting specialized contributions from its subdivisions. The rodent mPFC is often subdivided into the anterior cingular cortex (ACC), prelimbic cortex (PL), and the infralimbic cortex (IL), and broken down into the dorsomedial prefrontal cortex (dmPFC), spanning ACC and dorsal PL, and the ventromedial prefrontal cortex (vmPFC), which includes the ventral PL, IL, and in some studies the dorsal peduncular cortex (DP) and dorsal tenia tecta (DTT). The DP/DTT have recently been implicated in the regulation of stress-induced sympathetic responses via projections to the hypothalamus. While many studies implicate the PL and IL in anxiety-, depression-like and fear behavior, the contribution of the DP/DTT to affective and emotional behavior remains unknown. Here, we used chemogenetics to bidirectionally modulate DP/DTT activity and examine its effects on affective behaviors, cognition and stress responses in naive male and female C57BL/6J mice. We found that acute chemogenetic activation of DP/DTT neurons caused a significant increase in anxiety-like behavior in the open field and elevated plus maze tests, as well as in passive coping in the tail suspension test. In contrast, chemogenetic inhibition of the DP/DTT had no effect on affective behavior, but facilitated auditory fear memory acquisition without affecting memory retrieval. Additionally, DP/DTT activation led to an increase in plasma corticosterone levels. These findings point to the DP/DTT as a new regulator of affective behavior in mice.