Mossy Fibers from Adult-generated Neurons in the Dentate Gyrus More Frequently Contact Hilar Interneurons Surrounded by Intense Perineuronal Nets

Abstract

In the present study, we aimed to research whether there was any significant relationship between hippocampal adult-born neurons’ maturation and perineuronal nets in the dorsal hippocampus. The dentate gyrus of the hippocampus is one of the only places in the mammalian brain in which adult neurogenesis takes place. Additionally, perineuronal nets (PNNs) have been implicated in the regulation of synaptic plasticity across different brain regions. The experiments that follow are investigations of the possible relationship that PNNs may have with adult-born neurons. Initially, we injected the dentate gyrus of adult mice with a CAG-GFP retrovirus in order to label new neurons with GFP and perfused the mice at three weeks and six weeks after the injection. To verify the results of this initial experiment, we then used the protein isoform 3RTau to label new neurons. Confocal imaging of parvalbumin (PV)-positive interneurons in the hilus revealed a significant positive correlation between Wisteria floribunda agglutinin (WFA) labeling of perineuronal net intensity and both GFP and 3RTau intensities. The significant positive correlation between GFP and WFA was only present in the mice that were perfused six weeks after injection with the retrovirus. Additionally, we found that PV-positive interneurons without PNNs had significantly lower GFP and 3RTau mean intensities surrounding the cell surface than interneurons positive for PNNs. These results suggest that there is a relationship between the PNNs and adult-born neurons that has influence over their growth and is time-sensitive. Keywords: dorsal hippocampus, perineuronal nets (PNNs), adult neurogenesis, parvalbumin, extracellular matrix