Influences of age and pubertal status on number of perineuronal nets in the rat medial prefrontal cortex

The prefrontal cortex (PFC) is a late developing region of the cortex, and its protracted maturation during adolescence may confer a period of plasticity. Closure of critical, or sensitive, periods in sensory cortices coincides with perineuronal net (PNN) expression, leading to enhanced inhibitory function and synaptic stabilization. PNN density is known to increase across adolescence in the male rodent medial PFC (mPFC). However, the trajectory of female PNN development has not been explored nor has the potential role of pubertal onset in PNN expression. Here, we examined rats at four time points spanning adolescent development to quantify the number of PNNs in the mPFC, as well as the total volume of the prefrontal white matter. Additionally, because puberty coincides with broad behavioral and neuroanatomical changes, we collected tissue from age-matched pre- and post- pubertal siblings within a litter. Results indicate that both males and females show an increase the total number of mPFC PNNs and in white matter under the mPFC between postnatal day (P) 30 and P60. Male puberty did not affect PNNs, while female pubertal onset led to an abrupt decrease in the total number of PNNs that persisted through mid-adolescence before increasing at P60. This decrease in female rats may indicate a difference in timing of maximal plasticity between the sexes during adolescence.