Abstract
Traumatic brain injury (TBI) increases hippocampal neurogenesis, which may contribute to cognitive recovery after injury. However, it is unknown whether TBI-induced adult-born neurons mature normally and functionally integrate into the hippocampal network. We assessed the generation, morphology, and synaptic integration of new hippocampal neurons after a controlled cortical impact (CCI) injury model of TBI. To label TBI-induced newborn neurons, we used 2-month-old POMC-EGFP mice, which transiently and specifically express EGFP in immature hippocampal neurons, and doublecortin-CreERT2 transgenic mice crossed with Rosa26-CAG-tdTomato reporter mice, to permanently pulse-label a cohort of adult-born hippocampal neurons. TBI increased the generation, outward migration, and dendritic complexity of neurons born during post-traumatic neurogenesis. Cells born after TBI had profound alterations in their dendritic structure, with increased dendritic branching proximal to the soma and widely splayed dendritic branches. These changes were apparent during early dendritic outgrowth and persisted as these cells matured. Whole-cell recordings from neurons generated during post-traumatic neurogenesis demonstrate that they are excitable and functionally integrate into the hippocampal circuit. However, despite their dramatic morphologic abnormalities, we found no differences in the rate of their electrophysiological maturation, or their overall degree of synaptic integration when compared to age-matched adult-born cells from sham mice. Our results suggest that cells born after TBI participate in information processing, and receive an apparently normal balance of excitatory and inhibitory inputs. However, TBI-induced changes in their anatomic localization and dendritic projection patterns could result in maladaptive network properties.
- adult neurogenesis
- functional integration
- hippocampus
- maturation
- synaptic integration
- traumatic brain injury
Footnotes
The authors declare no competing financial interests.
This work was funded by a Department of Veterans Affairs Career Development Award (VA BLR&D CDA-2 005-10S; E.S.), a PVARF Summer Fellowship (K.N.K.), National Institutes of Health (NIH) Grant F32-NS083109 NRSA (L.E.V.), an Ellison Medical Foundation Award (G.L.W.), and NIH Grants R01-NS080979 (GLW) and P30-NS061800 (Oregon Health & Science University Imaging Center). We thank Drs. Zhi-Qi Xiong and Xuewen Cheng for providing Dcx-CreERT2 mice; and Dr. Stefanie Kaech-Petrie of the Oregon Health & Science University Advanced Light Microscopy Core for assistance with imaging.
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