Abstracts

Rationale: The main causes of Sudden Unexplained Death in Epilepsy (SUDEP) still remain unknown; however, several possibilities have been hypothesized. Cardiac and respiratory arrest as a result of seizures is the number one candidates for SUDEP. The cardiovascular and respiratory system is subject to precise reflex regulation to ensure appropriate oxygen supply to different organs under a wide range of circumstances. The barosensory and chemosensory afferents send information via the cranial nerves to the Nucleus Tractus Solitarius (NTS), which relays this information to the higher centers of the Central Nervous System (CNS). The CNS integrates this information and produces changes in heart rate, peripheral resistance and respiration to maintain arterial pressure and blood gas levels within normal limits. The NTS is the initial step in information processing that culminates in homeostatic reflex responses. We hypothesize that the increased susceptibility to SUDEP observed in models of intractable partial epilepsy is due to NTS dysfunction as a result of seizure-induced neuronal loss.Methods: Sprague Dawley rats (250-300g) were injected with KA (5mg/kg, i.p.) or saline (0.9% NaCl) and observed for 6 hours post injection to verify SE. Only those animals that experienced SE were used in this study. Animals were perfused transcardially with Timm s perfusion after 1-3 weeks survival period. The brainstem from control (n=5) and KA-SE (n=6) was sliced frozen in a coronal axis in a cryostat at 30 m. Brainstem slices were stained with Cresyl Violet, and neuronal densities were obtained using modern stereological techniques. We counted neurons in three brainstem nuclei: (1) Hypoglossal, (2) Dorsal Motor Nucleus of the Vagus and (3) the NTS. Hypoglossal and Dorsal Motor Nucleus of the Vagus cell counts were estimated from images taken at 10X magnification while the NTS images were taken at 20X from both control and KA-SE slices to compensate for the smaller diameter cells. Neuronal densities in KA-SE and control brainstem nuclei were compared with Student t-test with unequal varianceResults: In our experiments, we examined whether KA-SE and repeated spontaneous seizures resulted in neuronal loss in NTS. At the initial stage of epileptogenesis, just few weeks after KA injection, we found neuronal population loss in the NTS: 97 7.64 in controls vs. 81 3.52 in KA rats (p = 0.03) with no significant reductions in Hypoglossal Nucleus and Dorsal Motor Nucleus of the Vagus. We also examined single pair of the horizontal brainstem sections from KA rats 23 and 365 days after injection, and observed 24% reduction of the neuronal population in the mNTS in the older one. Conclusions: Selective neuronal loss was observed in the NTS after KA-SE. An interesting and novel finding that appears in our studies supports our hypothesis. The consequence of neuronal loss in the NTS opens the door for our exploration of the novel physiological mechanisms responsible for SUDEP. Supported by AHA grant 0865151F (GT) and VA Merit award (JEC)