Abstracts

Rationale: During the past decade, there has been growing interest in the gut microbiome, and in the role which it plays in health and disease. The concept of the gut-brain axis dysfunction has found its application in mental health. Most recently, the evidence has started to emerge that dysbiosis develops after, and may exacerbate chronic sequela of neurological disorders, including stroke, traumatic brain injury (TBI) and epilepsy. In the kindling model of epilepsy, using multidirectional microbiome transfer paradigm, we have shown that proepileptic effects of chronic stress are mediated by intestinal microbiome (Medel-Matus J-S et al., Epilepsia Open, 2018, doi:10.1002/epi4.12114). Here, we examined whether microbiome obtained from animals after TBI, can modify epileptogenesis. Methods: The experiments were performed in male and female Sprague-Dawley rats, 2 months- old at the beginning of the study. Microbiome donors underwent lateral fluid percussion injury (LFPI 3.2-3.5 atm, 20 ms, n=4), or no LFPI (n=2). The effectiveness of trauma was confirmed by the presence of behavioral seizures during the first week after LFPI. One week after the procedure, fecal samples were collected from free-moving rats, and stored at -80^oC. In microbiome recipients (n=18), commensal microbiota was first depleted by a standard antibiotic cocktail administered via oral gavage over 2 weeks. Afterwards, the animals were randomized and administered with microbiome samples from individual LFPI and no-LFPI donors, so that 3 recipients received microbiome from one donor (i.e. 4 triads of recipients from LFPI and 2 triads – from no-LFPI donors). For the transplantation, microbiome samples were reconstituted 1:10 in sterile PBS and administered via oral gavage 3 times, every other day. Additional 6 animals received tap water via oral gavage in lieu of microbiome. During the week of microbiome transplants, the animals were implanted with stimulating electrodes in basolateral amygdala and recording electrodes in the motor cortex. One week after surgery/last microbiome transplant, the animals were subjected to kindling (3 daily stimulations of amygdala, 4 hours apart at afterdischarge threshold). Statistical comparisons were performed by Kruskal-Wallis + Mann Whitney test. Results: Baseline afterdischarge properties (i.e. threshold and duration), kindling progression, and the duration of kindled seizures were similar in the animals of groups receiving microbiome from no-LFPI donors and water (p>0.05). Transplantation of microbiome from the LFPI rats had no effects on baseline afterdischarge properties in recipients. In one triad of microbiome recipients from LFPI donors, the progression to full kindling state (i.e. 3 consecutive stage 4-5 Racine seizures) was significantly slower, and in one triad - faster than in the animals of each of the control groups (p<0.05). In the latter triad, and in another triad of recipients (i.e. total n=6), the duration of kindled seizures was significantly longer than in the animals of control groups (p<0.05). Conclusions: The experiments suggest that gut microbiome modified by TBI may itself modulate the susceptibility to epilepsy. TBI-induced changes in microbiome can be either maladaptive/proepileptic, or compensatory/antiepileptic, despite similar parameters of, and responses to LFPI. Future analysis of microbiome before and after LFPI may help explaining causes of such variability. Funding: Sudha Neelakantan and Venky Harinarayan Charitable Fund endowment to Epilepsy Research Laboratories. Research grants NS065783 (NIH/NINDS) to Mazarati and NS100064 to Staba.