Tagging proliferating cells with thymidine analogs is an indispensable research tool; however, the issue of the potential in vivo cytotoxicity of these compounds remains unresolved. Here, we address these concerns by examining the effects of BrdU and EdU on adult hippocampal neurogenesis and EdU on the perinatal somatic development of mice. We show that, in a wide range of doses, EdU and BrdU label similar numbers of cells in the dentate gyrus shortly after administration. Furthermore, whereas the administration of EdU does not affect the division and survival of neural progenitor within 48 h after injection, it does affect cell survival, as evaluated 6 weeks later. We also show that a single injection of various doses of EdU on the first postnatal day does not lead to noticeable changes in a panel of morphometric criteria within the first week; however, higher doses of EdU adversely affect the subsequent somatic maturation and brain growth of the mouse pups. Our results indicate the potential caveats in labeling the replicating DNA using thymidine analogs and suggest guidelines for applying this approach.

Traumatic brain injury (TBI) is one of the major causes of severe neurological disorders and long-term dysfunction in the nervous system. Besides inducing neurodegeneration, TBI alters stem cell activity and neurogenesis within primary neurogenic niches. However, the fate of dividing cells in other brain regions remains unclear despite offering potential targets for therapeutic intervention. Here, we investigated cell division and differentiation in non-neurogenic brain regions during the acute and delayed phases of TBI-induced neurodegeneration. We subjected mice to lateral fluid percussion injury (LFPI) to model TBI and analyzed them 1 or 7 weeks later. To assess cellular proliferation and differentiation, we administered 5-ethinyl-2′-deoxyuridine (EdU) and determined the number and identity of dividing cells 2 h later using markers of neuronal precursors and astro-, micro-, and oligodendroglia. Our results demonstrated a significant proliferative response in several brain regions at one week post-injury that notably diminished by seven weeks, except in the optic tract. In addition to active astro- and microgliosis, we detected oligodendrogenesis in the striatum and optic tract. Furthermore, we observed trauma-induced neurogenesis in the striatum. These findings suggest that subcortical structures, particularly the striatum and optic tract, may possess a potential for self-repair through neuronal regeneration and axon remyelination.

Background: Critical periods (CP) in brain development are characterized by heightened neural plasticity in the relevant brain regions. They are associated with changes in gene expression cascades, in particular with altered expression of genes involved in plasticity regulation, such as immediate early genes. Here we examine the expression of the immediate early genes c-Fos and Egr1 at different stages of mouse visual cortex (VC) development. Methods: Mice 11, 25, and 50 days of age were maintained under standard light-dark conditions, deprived of light for 5 days, or deprived of light for 5 days and then exposed to light for 90 min. Their brains were analyzed at PND16 (before the onset of the CP), PND30 (during the CP) and PND55 (after the CP) to determine the changes in the number of cells expressing c-Fos and Egr1 in the binocular primary visual and primary somatosensory cortices. Results: We found highly specific induction of c-Fos expression in the primary VC in response to light. We also observed transient cross-modal activation of c-Fos in the barrel field of the primary somatosensory cortex in response to light before and during the CP; such activation disappeared after the CP. Expression of Egr1 was not induced by light in the VC before the CP, but was evident during and after the CP, although the induction was much less pronounced than that of c-Fos. Conclusions: Dynamic changes in c-Fos and Egr1 expression may reflect their contribution to the VC plasticity during the CPs of postnatal brain development.