Abstracts

Rationale:
Sudden unexpected death in epilepsy (SUDEP) is the leading cause of death in refractory epilepsy patients. A recent study conducted on human epilepsy patients shows that activation of amygdalar networks is associated with central apnea onset during seizures, suggesting that the amygdala brain region plays an important role in respiration and potentially in seizure-induced apneas. In particular, we hypothesize that the brain region, the Bed Nucleus Stria Terminalis (BNST), of the extended amygdala, which has projections to respiratory brainstem nuclei including the parabrachial nucleus (PBN), is involved in the neurocircuitry of respiration that may cause seizure-induced apneas. Prior work done in our lab suggests that BNST to PBN projection neurons in Dravet Syndrome (DS) mice have decreased excitability in the setting of overall loss of synaptic inhibition. However, we have not been able to identify the mechanisms causing these changes in excitability in the BNST. I hypothesize that altered excitability in BNST neurons of Dravet Syndrome mice is due to frequent activation of the BNST from seizures.
Method:
Experimental heterozygous F1 mice generated by breeding 129.Scn1a+/− mice with wild-type C57BL/6J mice were used along with their wildtype F1 littermates. Hyperthermia was used to prime mice for spontaneous seizures. Immunohistochemistry was used to quantify neuronal c-fos activation in the BNST one hour following an observed spontaneous seizure in DS mice. C-fos staining was also performed in wildtype (WT) and non-seizing DS mice to quantify baseline levels of c-fos activation. CRF neurons were co-stained with c-fos to identify the percentage of stress-related neurons activated in the BNST from seizures. Scn1a was stained using immunohistochemistry. RNAscope was performed to identify the presence of RNA for PV and SST interneurons.
Results:
I found a significant increase in neuronal c-fos activation in the BNST following spontaneous seizures in DS mice (170.5 +/- 35.6 DS n = 6, 17.6 +/- 12.8 WT n = 7, p < 0.0001). Wildtype littermates and non-seizing DS mice had no significant difference in their c-fos activation (26.5 +/- 12.7 DS n = 6, 34.5 +/- 11.2 WT n = 4), suggesting that altered excitability of the BNST was not driving baseline neuronal activation. CRF neurons in the BNST, which have been linked to stress-related behaviors, were co-activated with c-fos during seizures. Seizure-induced activation of these neurons may have further implications for neuropsychiatric comorbidities in DS. Scn1a protein expression in the BNST was very sparse at baseline in wildtype animals, and further decreased in DS mice compared to wildtype littermates. The overall lack of PV and SST interneurons co-expressed with Scn1a in the BNST suggests that BNST excitability may be more attributed to increased upstream hyperexcitability or frequent activation by seizures and not only due to changes attributed to the sparse neurons expressing Scn1a.