Degradation of Perineuronal Nets in the Ventral Hippocampus of Adult Rats Recreates an Adolescent-Like Phenotype of Stress Susceptibility.

Background: Psychiatric disorders often emerge during late adolescence/early adulthood, a period with increased susceptibility to socioenvironmental factors that coincides with incomplete parvalbumin interneuron (PVI) development. Stress during this period causes functional loss of PVIs in the ventral hippocampus (vHip), which has been associated with dopamine system overdrive. This vulnerability persists until the appearance of perineuronal nets (PNNs) around PVIs. We assessed the long-lasting effects of adolescent or adult stress on behavior, ventral tegmental area dopamine neuron activity, and the number of PVIs and their associated PNNs in the vHip. Additionally, we tested whether PNN removal in the vHip of adult rats, proposed to reset PVIs to a juvenile-like state, would recreate an adolescent-like phenotype of stress susceptibility.

Methods: Male rats underwent a 10-day stress protocol during adolescence or adulthood. Three to 4 weeks poststress, we evaluated behaviors related to anxiety, sociability, and cognition, ventral tegmental area dopamine neuron activity, and the number of PV and PNN cells in the vHip. Furthermore, adult animals received intra-vHip infusion of ChABC (chondroitinase ABC) to degrade PNNs before undergoing stress.

Results: Unlike adult stress, adolescent stress induced anxiety responses, reduced sociability, cognitive deficits, ventral tegmental area dopamine system overdrive, and decreased PV and PNN cells in the vHip. However, intra-vHip ChABC infusion caused the adult stress to produce changes similar to the ones observed after adolescent stress.

Conclusions: Our findings underscore adolescence as a period of heightened vulnerability to the long-lasting impact of stress and highlight the protective role of PNNs against stress-induced damage in PVIs.