Early postnatal inhibitory circuit development in the mouse medial prefrontal and primary somatosensory cortex

The prefrontal cortex (PFC) is characterized by delayed maturation that extends until adulthood. Although the adolescent PFC has been well investigated, the cellular mechanisms controlling the early development of prefrontal circuits are still largely unknown. Our study delineates the developmental cellular processes that are on-going in the mouse medial PFC (mPFC) during the second and third postnatal weeks and compares them to those in the barrel cortex (BC). We show that basal synaptic transmission decreases from the second to the third postnatal week in both brain areas due to increased spontaneous inhibitory currents and reduced excitatory ones. Furthermore, increasing GABA receptor (GABAR) activity leads to increased basal synaptic response of neonatal mPFC, but not BC. Additionally, the K-Cl co-transporter 2 (KCC2) expression is decreased in the neonatal mPFC compared to the pre-juvenile one as well as to the neonatal and pre-juvenile BC, suggesting that GABAR function in the neonatal mPFC is non-inhibitory. Moreover, the intrinsic properties of both interneurons and pyramidal cells change with age and relate to augmented network activity across development.