Abstracts

Rationale: Post-traumatic epilepsy (PTE) accounts for 20% of symptomatic epilepsy cases and 5% of all epilepsy cases. The mechanisms underlying how traumatic brain injury (TBI) leads to PTE remain unknown, which has limited the development of interventions for preventing or curing PTE. The cortex is typically the most affected brain area at the onset of a TBI, but the thalamus may experience secondary damage and inflammation because of its reciprocal connections with the cortex. Thalamic dysfunction is associated with various epileptic disorders and with cognitive dysfunction after TBI. Additionally, the role of inflammation in both TBI and epilepsy is complex and involves many cellular responses and molecular factors, including the complement pathway. The classical complement pathway, initiated by C1q (the first subcomponent of the C1 complex), is implicated in neurotoxicity in central nervous system injury and is upregulated in human epileptic brains. However, one important question is whether C1q upregulation is protective or pathological at chronic time points after injury. It also remains unknown how cortical TBI alters thalamic function, and whether these alterations, including upregulated C1q, are involved in the development or expression of PTE. Methods: Controlled cortical impact model of PTE; patch-clamp electrophysiology in acute brain slices; chronic wireless electrocorticography (ECoG) for multiple months; multi-unit thalamic electrophysiology in freely behaving mice; immunofluorescent staining in free-floating brain sections. Results: To determine if TBI in the somatosensory cortex alters the intrinsic or synaptic properties of cortical and thalamic neurons, and to test whether the thalamus could be a therapeutic target for preventing or curing PTE, we used histology, in vitro, and in vivo electrophysiological approaches. We investigated these questions using the controlled cortical impact model of PTE in adult male CD1 mice. We first observed neuronal loss in the functionally connected reticular thalamus (p=0.002) along with a significant increase in C1q (p=0.002), GFAP (p=0.001), and Iba1 expression (p=0.001) in the thalamus in TBI vs. control littermates with craniotomy, using immunofluorescent staining three weeks after TBI. Using whole-cell patch-clamp recordings in thalamic slices, we showed that three to four weeks after TBI, there is a long-term reduction in inhibitory postsynaptic currents in the reticular thalamus (p=0.004, TBI vs. control littermates with craniotomy), which has been associated with hypersynchronous thalamic activity in various epileptic disorders. We then treated TBI mice with a novel anti-C1q antibody that functionally inhibits the classical complement pathway, starting 24 hours after TBI and administering twice weekly for three weeks. Notably, the treatment significantly reduced chronic inflammation and prevented secondary neuron loss in the reticular thalamus. Analyses are ongoing to determine if this intervention is also sufficient to prevent epileptogenesis in TBI mice. Conclusions: Our findings demonstrate that TBI causes secondary damage to the thalamus, in part via activation of the inflammatory complement pathway, implicating interactions between the immune system and the brain in determining post-traumatic outcomes. We propose that the long-term loss of GABAergic inhibition in the reticular thalamus after TBI could be responsible, at least in part, for the development of PTE seizures and cognitive dysfunction. Our results highlight a potential therapeutic strategy of targeting the complement pathway for enhancing functional recovery after injury. Funding: DOD EP150038Achievement Rewards for College Scientists FellowshipFord Foundation Dissertation FellowshipAnnexon Biosciences