Abstracts

Rationale: Earlier age of traumatic brain injury (TBI) exposure is associated with worsened outcomes; also, children 0-3 years of age are one of the highest risk groups for exposure. Moreover, TBI even mild (mTBI) in severity is known to increase development of post-traumatic epilepsy up to 8-fold (doi: 10.3171/2017.2.PEDS16585); however, there is currently a general lack of early-life TBI paradigms using rodent models to study post-traumatic epileptogenesis (doi: 10.1089/neu.2018.6127). Collectively, this has led to a major gap in the field’s knowledge surrounding how pediatric TBI leads to long-term consequences, such as epileptogenesis. Thus, it is my hypothesis that early life mTBI disrupts the timing of critical developmental processes such as circuit formation that will ultimately prime the cortical microenvironment towards seizure activity when challenged later in life.  

Methods: Male and female postnatal day (pnd) 7 wildtype C57BL6/J mice underwent a mild weight drop TBI or sham injury paradigm, adopted from the Fleiss lab (doi: 10/1016/j.bbi.2016.11.001). We implemented microelectrode array (MEA) field recording of acute brain slices placed on a 64-multielectrode probe to detect electrical transduction changes at 1 day post injury (dpi), 1-week or 3-week post injury (pnd 8, 14, or 28, respectively). Spike generation over a period of 10 minutes was recorded in injured cortex compared to non-injured cortex to determine overall cortical field potentials. Sections were then post-fixed and cut on a cryostat to allow for IHC analysis of immature (NKCC1) and mature (KCC2) GABA cotransporter markers throughout brain development.  An image of probe placement was acquired for each slice to allow for spatial correlation of spike formation and GABA cotransporter expression relative to injury site. Additionally, we challenged injured or non-injured sham mice with repeated low dose pentylenetetrazol via intraperitoneal injection at pnd 60 and classified seizure threshold (dose and latency) and seizure severity (modified Racine scale).  

Results: As analysis is currently in progress, we expect to see heightened random spike generation in mTBI versus sham injured mice throughout neural maturation. We also expect to see a delay of the GABA shift from expression of excitatory NKCC1 to inhibitory KCC2 chloride cotransporters after mTBI compared to un-injured shams, as has been reported in various other neurodevelopmental disorders (i.e., doi: 10.1016/j.neubiorev.2018.05.001). Importantly, we also expect to find that brain circuitry will remain impacted long-term through decreased threshold of seizure activity when chemically challenged.  

Conclusions: The results from this study will have a significant impact on the field as we will for the first time evaluate how mTBI during early postnatal life alters circuit formation and excitatory/inhibitory balance through different stages of neural development. Furthermore, these results could explain for the first-time mechanisms responsible for the natural progression of post- traumatic epilepsies. 

Funding: Funded by Internal Startup funds for Tracy Bedrosian (Nationwide Children's Hospital, Columbus, Ohio)