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Neural precursors (NPs) present in the hippocampus can be modulated by several neurogenic stimuli, including environmental enrichment (EE) acting through BDNF-TrkB signaling. We have recently identified NPs in meninges; however, the meningeal niche response to pro-neurogenic stimuli has never been investigated. To this aim, we analyzed the effects of EE exposure on NP distribution in mouse brain meninges. Following neurogenic stimuli, although we did not detect modification of the meningeal cell number and proliferation, we observed an increased number of neural precursors in the meninges. A lineage tracing experiment suggested that EE-induced β3-Tubulin+ immature neuronal cells present in the meninges originated, at least in part, from GLAST+ radial glia cells. To investigate the molecular mechanism responsible for meningeal reaction to EE exposure, we studied the BDNF-TrkB interaction. Treatment with ANA-12, a TrkB non-competitive inhibitor, abolished the EE-induced meningeal niche changes. Overall, these data showed, for the first time, that EE exposure induced meningeal niche remodeling through TrkB-mediated signaling. Fluoxetine treatment further confirmed the meningeal niche response, suggesting it may also respond to other pharmacological neurogenic stimuli. A better understanding of the neurogenic stimuli modulation for meninges may be useful to improve the effectiveness of neurodegenerative and neuropsychiatric treatments.

Recently, a population of “immature” neurons generated prenatally, retaining immaturity for long periods and finally integrating in adult circuits has been described in the cerebral cortex. Moreover, comparative studies revealed differences in occurrence/rate of different forms of neurogenic plasticity across mammals, the “immature” neurons prevailing in gyrencephalic species. To extend experimentation from laboratory mice to large-brained mammals, including humans, it is important to detect cell markers of neurogenic plasticity in brain tissues obtained from different procedures (e.g., post-mortem/intraoperative specimens vs. intracardiac perfusion). This variability overlaps with species-specific differences in antigen distribution or antibody species specificity, making it difficult for proper comparison. In this work, we detect the presence of doublecortin and Ki67 antigen, markers for neuronal immaturity and cell division, in six mammals characterized by widely different brain size. We tested seven commercial antibodies in four selected brain regions known to host immature neurons (paleocortex, neocortex) and newly born neurons (hippocampus, subventricular zone). In selected human brains, we confirmed the specificity of DCX antibody by performing co-staining with fluorescent probe for DCX mRNA. Our results indicate that, in spite of various types of fixations, most differences were due to the use of different antibodies and the existence of real interspecies variation.

Neural precursors (NPs) present in the hippocampus can be modulated by several neurogenic stimuli including environmental enrichment (EE) and antidepressant treatment acting through BDNF-TrkB signaling. We have recently identified NPs in meninges, however menigneal niche response to pro-neurogenic stimuli has never been investigated. To this aim, we analyzed the effects of 4 weeks fluoxetine administration or 1 week EE treatment on NP distribution in mouse brain meninges. Following neurogenic stimuli, although we did not detect modification of meningeal cell number and proliferation, we observed, in meninges, an increased number of β3-Tubulin+ immature neuronal cells. Lineage-tracing experiment confirmed that EE-induced β3-Tubulin+ immature neuronal cells present in meninges originated from GLAST+ radial glia cells. To investigate the molecular mechanism responsible for this response, we studied the BDNF-TrkB interaction. Treatment with ANA-12, a TrkB non-competitive inhibitor, abolished the EE-induced increase of β3-Tubulin+ immature neuronal cells in meninges.Overall these data showed, for the first time, that the meningeal niche responded to neurogenic stimuli by increasing the immature neuronal population through TrkB-mediated signaling. A better understanding of the neurogenic stimuli effects on NPs in meninges may be useful to improve the effectiveness of depression and mood disorders treatments.