The Development of Perineuronal Nets Around Parvalbumin GABAergic Neurons in the Medial Prefrontal Cortex and Basolateral Amygdala of Rats

Perineuronal nets (PNNs) are extracellular matrix structures that preferentially surround mature GABAergic neurons that express the calcium-binding protein parvalbumin (PV). It has been suggested that aberrant PNN formation in humans may contribute to psychological disorders, many of which emerge during childhood and adolescence. The present experiment investigated the normative developmental trajectory of PNN formation in the medial prefrontal cortex (mPFC) and basolateral amygdala (BLA) in juvenile (P24), adolescent (P35-36), and adult (similar to P70) rats. Dual-immunofluorescence staining revealed that there was a marked increase in the number of PNNs in both the prelimbic and infralimbic regions of the mPFC across the transition from the juvenile to adolescent period. Although there were no differences in the number of PV neurons across age groups, adolescent and adult rats had more PNNs surrounding PV neurons than juveniles. In contrast to the mPFC, juvenile and adolescent rats had similar total numbers of PNNs in the BLA, and total numbers of PNNs were even higher in adults in this region. In the BLA, adults had more PNNs around non-PV cells whereas the number of PV cells with PNNs did not differ across ages. However, expression patterns differed within subregions of the BLA such that adults had the most PNNs around both PV and non-PV cells in the lateral nucleus, with no age differences observed in the basal nucleus. These findings demonstrate that the juvenile to adolescent developmental period is an important time for the formation of prefrontal PNNs and the maturation of PV inhibitory neurons.