Spatio-temporal differences in perineuronal net expression in the mouse hippocampus, with reference to parvalbumin

Perineuronal net (PNN) is a specialized aggregate of the extracellular matrix, which is considered to be involved in regulation of structural plasticity of neuronal circuits. Here we examined the spatial and temporal differences in Wisteria floribunda agglutinin-labeled PNN intensity in single cells in the mouse hippocampus, where the neuronal circuits engaged in cognition and emotion are embedded in the dorsal and ventral parts, respectively. In young mice, the intensity of PNN was very low, and there were no significant dorsoventral differences in all hippocampal regions. Developmental increase in PNN intensity was larger in the dorsal part than in the ventral part. As a result, PNN intensity was higher in the dorsal part than in the ventral part in adult mice. Aging dissimilarly affects different regions of the dorsal hippocampus. Namely, PNN intensity in the dorsal part of old mice declined in the CA1 region, remained unchanged in the CA3 region, increased in the dentate gyrus. By contrast, there were no significant aging-related changes in PNN intensity in the ventral hippocampus. We also examined the intensity of parvalbumin (PV), an EF-hand calcium-binding protein, because it has been shown that PNNs are closely related to PV-containing GABAergic inhibitory neurons. Contrary to expectations, developmental and aging-related changes in PV intensity were not comparable to those seen in PNN intensity. The correlation coefficients between PNN and PV intensities in single cells showed gradual decline during development and aging in the CA1 and CA3 regions, while there were little correlations in the dentate gyrus regardless of age. In summary, PNNs are differentially expressed in the dorsal and ventral hippocampal circuits during development and aging, indicating their possible role for cognition and emotion control.