Perineuronal Nets Regulate the Inhibitory Perisomatic Input onto Parvalbumin Interneurons and c Activity in the Prefrontal Cortex

Abstract

Parvalbumin-expressing (PV1) interneurons play a key role in the maturation and synchronization of cortical circuitry and alterations in these inhibitory neurons, especially in the medial prefrontal cortex (mPFC), have been found in different psychiatric disorders. The formation of perineuronal nets (PNNs) around many of these interneurons at the end of the critical periods reduces their plasticity and sets their connectivity. Consequently, the presence of PNNs must have an important impact on the synaptic input and the physiology of PV1 cells. In the present study, we have found that in adult male mice, prefrontocortical PV1 cells surrounded by PNNs show higher density of perisomatic excitatory and inhibitory puncta, longer axonal initial segments (AISs), and higher PV expression when compared with PV1 cells lacking PNNs. In order to better understand the impact of PNNs on the connectivity and physiology of PV1 interneurons in the mPFC, we have digested enzymatically these structures and have found a decrease in the density of inhibitory puncta on their perisomatic region but not on the PV1 perisomatic puncta on pyramidal neurons. Moreover, extracellular recordings show that the digestion of PNNs induces a decrease in c activity, an oscillation dependent on PV1 cells, in the mPFC of anesthetized mice. Our results suggest that the presence of PNNs enwrapping PV1 cells regulates their inhibitory input and has a potent influence on their activity. These results may be relevant for psychiatric research, given the alterations in PNNs, PV1 interneurons and their physiology described in different mental disorders.