Abstracts

Rationale: Sudden Unexplained Death in Epilepsy (SUDEP) accounts for 10% of epilepsy-related deaths with 85% of these fatalities between the ages of 20-50. Its incidence is about 1/1000 people with epilepsy per year, but is higher in intractable epilepsy. The underlying mechanisms are not well understood, but seizure-induced cardiac and respiratory arrest is the final step. The cardiovascular and respiratory system is subject to precise reflex regulation to ensure adequate oxygen delivery to different organs under a wide range of circumstances. The barosensory and chemosensory afferents send information via cranial nerves to the nucleus tractus solitarius (NTS), which relays it to higher centers in the central nervous system (CNS). The CNS and NTS integrate this information producing changes in heart rate, peripheral resistance and respiration that maintain arterial pressure and blood gas levels within normal limits. NTS is, thus, positioned at the initial step for of the homeostatic reflex response suggesting a potential critical role in cardiovascular and respiratory regulation during seizures. In the CNS, voltage-dependent Kv7 (KCNQ) K channels regulate neuronal excitability by delaying action potentials through the M-current. However, they have not been studied in the NTS. Furthermore, we hypothesize that alterations in M-current at the NTS might contribute to the increased susceptibility to SUDEP in experimental models of intractable epilepsy. Methods: Glass micropipette electrodes were prepared with a Sutter P-97 puller to resistances of 3-6 M?. Recordings were obtained using a HEKA EPC-10 patch clump and PULSE data acquisition system. Currents were low-pass filtered at 0.5-2 kHz, sampled at 0.5-5 kHz, depending upon the experiment. At the amplifier, 40-80% series resistance compensation was applied. M-currents were recorded for a suitable baseline period before application of agonists. We examined the M-current properties from KCNQ channels in NTS neuronal cultures and brain slices of NTS in control and kainic acid treated rats. Results: We found that KCNQ channels were expressed in the NTS. The M-current in the NTS displays many of the classical characteristics of M-currents recorded from different CNS and peripheral neurons, including the lack of inactivation and slow kinetics. The M-current density in NTS neurons was 4.0 0.2 pA/pF. The M-current in the NTS was also completely blocked by the selective M-channel inhibitor XE991. Since many neurons also display EAG-like currents, which can mimic M-currents, we calculated the time constant of deactivation in these experiments by fitting the current relaxation at -60 mV to an exponential, with a t of 77 14 ms. This value is typical of M currents, but more than six-fold faster than ERG currents (Selyanko AA et al, 1999). Conclusions: Discovery of M-channels in the NTS opens the door to our exploration of the novel physiological mechanisms responsible for SUDEP. Supported by AHA grant 0865151F (GT) and VA Merit award (JEC).