Neuronal plasticity is a crucial mechanism for an adapting nervous system to change. It is shown to be regulated by perineuronal nets (PNNs), the condensed forms of the extracellular matrix (ECM) around neuronal bodies. By assessing the changes in the number, intensity, and structure of PNNs, the ultrastructure of the PNN mesh, and the expression of inhibitory and excitatory synaptic inputs on these neurons, we aimed to clarify the role of an ECM glycoprotein, tenascin-C (TnC), in the dorsal hippocampus. To enhance neuronal plasticity, TnC-deficient (TnC-/-) and wild-type (TnC+/+) young adult male mice were reared in an enriched environment (EE) for 8 weeks. Deletion of TnC in TnC-/- mice showed an ultrastructural reduction of the PNN mesh and an increased inhibitory input in the dentate gyrus (DG), and an increase in the number of PNNs with a rise in the inhibitory input in the CA2 region. EE induced an increased inhibitory input in the CA2, CA3, and DG regions; in DG, the change was also followed by an increased intensity of PNNs. No changes in PNNs or synaptic expression were found in the CA1 region. We conclude that the DG and CA2 regions emerged as focal points of alterations in PNNs and synaptogenesis with EE as mediated by TnC.

To better understand adult neurogenesis, the biomolecular specificity of the subgranular zone should be investigated in comparison to other layers of the hippocampus. Adult neurogenesis occurs at a reduced rate in adulthood compared to the period of development, but it can be increased with exposure to an enriched environment (EE). This can be used to investigate the regulatory role of molecules present in the extracellular matrix, such as tenascin C (TnC). This study, using Synchrotron radiation Fourier Transform Infrared spectroscopy (SR-FTIR), shows that the differences between the hippocampal layers in adolescence are maintained as subtle and significant in adulthood. The main difference in FTIR spectra was observed for nucleic acid and carbohydrate and for the comparison of the subgranular zone (SGZ) with hippocampal CA3. Moreover, we have detected changes in the protein and nucleic acid content of the SGZ that accompany the process of neurogenesis under the influence of an enriched environment. The latter effects are, however, lacking in mice with a gene ablation for tenascin C. Overall, these results show that observed discrete biomolecular differences in hippocampal layers follow the rate of neurogenesis that is enhanced by EE and dependent on TnC.

To better understand adult neurogenesis, the biomolecular specificity of the subgranular zone should be investigated in comparison to other layers of the hippocampus. Adult neurogenesis occurs at a reduced rate in adulthood compared to the period of development, but it can be increased with exposure to enriched environment. This can be used to investigate the regulatory role of molecules present in the extracellular matrix, such as tenascin C. This study using Synchrotron radiation Fourier Transform Infrared spectroscopy (SR-FTIR) shows that the differences between the hippocampal layers in adolescence are maintained as subtle and significant in adulthood. Moreover, we have detected biomolecular changes that accompany the process of neurogenesis under the influence of enriched environment, while these effects are lacking in mice with a gene ablation for tenascin C.