Adolescence is a critical period for brain maturation, characterized by the reorganization of many interacting neural networks. The medial prefrontal cortex (mPFC), a region involved in executive function, is particularly known to undergo synaptic and neuronal pruning during this time. Disruptions of normal mPFC development have been associated with a variety of clinical disorders associated with mPFC dysfunction including schizohprenia, ADHD and depression. We have previously shown that rats lose neurons in the mPFC between early adolescence and adulthood. However, neuronal loss was substantially greater in females during this time. Previous data from our lab also show that an increase in ovarian hormones during puberty play a significant role in neuronal loss in females, as OVX prevented this cellular loss. In the present study, we track neuronal and glial changes in the male and female mPFC at multiple time points from preadolescence to adulthood (P25, P35, P45, P60 and P90). In addition, we correlate the cellular changes during this time with observed puberty markers. Our preliminary analysis confirmed a greater neuronal loss in the female mPFC between adolescence and adulthood, and that the timing of neuronal loss in females coincides with the onset of puberty (between P35 and P45). Further data will be collected to delineate the timing of loss in males. Elucidation of the precise timing of cellular pruning of the mPFC may have clinical implications in respect to mental illnesses characterized by mPFC dysfunction, and could potentially explain the observed sex differences in prevalence of these disorders.