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Childhood absence epilepsy (CAE) is the most common pediatric epilepsy syndrome and is characterized by typical absence seizures (AS). AS are non-convulsive epileptic seizures characterized by a sudden loss of awareness and bilaterally generalized synchronous 2.5–4 Hz spike and slow-wave discharges (SWD). Gamma butyrolactone (GBL) is an acute pharmacological model of AS and induces bilaterally synchronous SWDs and behavioral arrest. Despite the long use of this model, little is known about its strain and sex-dependent features. We compared the dose-response profile of GBL-evoked SWDs in three rat strains (Long Evans, Sprague-Dawley, and Wistar), and examined the modulatory effects of estrous cycle on SWDs in female Wistar rats. We evaluated the number of seizures, the cumulative time seizing, and the average seizure duration as a function of dose, strain, and sex/estrous phase. Long Evans rats displayed the greatest sensitivity to GBL, followed by Wistar rats, and then by Sprague-Dawley rats. GBL-evoked SWDs were modulated by estrous cycle in female rats, with the lowest sensitivity to GBL occurring during metestrus. Wistar rats showed the greatest variability as a function of dose, and the least variability within dose; these features make this strain desirable for interventional studies. Moreover, our finding that the SWD response to GBL differs as a function of estrous cycle underscores the importance of cycle monitoring in studies examining female animals using this model. Together, these strain and sex-dependent findings provide guidance for future studies.

Summary The NADase SARM1 is a central switch in injury-activated axon degeneration, an early hallmark of many neurological diseases. Here, we present cryo-electron microscopy (cryo-EM) structures of autoinhibited (3.3 A) and active SARM1 (6.8 A) and provide mechanistic insight into the tight regulation of SARM1’s function by the local metabolic environment. Although both states retain an octameric core, the defining feature of the autoinhibited state is a lock between the autoinhibitory Armadillo/HEAT motif (ARM) and catalytic Toll/interleukin-1 receptor (TIR) domains, which traps SARM1 in an inactive state. Mutations that break this lock activate SARM1, resulting in catastrophic neuronal death. Notably, the mutants cannot be further activated by the endogenous activator nicotinamide mononucleotide (NMN), and active SARM1 is product inhibited by Nicotinamide (NAM), highlighting SARM1’s functional dependence on key metabolites in the NAD salvage pathway. Our studies provide a molecular understanding of SARM1’s transition from an autoinhibited to an injury-activated state and lay the foundation for future SARM1-based therapies to treat axonopathies.