Abstracts

Febrile seizures, defined as seizures induced by fever without underlying encephalitis, other symptomatic etiologies or a previous history of epilepsy, affect approximately 3-5% of children between the ages of 6 months to 6 years. The pathophysiology of febrile seizures is unknown. We have developed hyperthermic spreading depression (SD) in immature hippocampal slices, which may serve as an [italic]in vitro[/italic] febrile seizure model. Here, we further present different pharmacological profiles to elucidate cellular mechanisms of hyperthermic SD.
Standard sharp electrode intracellular and extracellular field recordings were employed in transverse immature hippocampal slices (Sprague Dawley rats, P21-P59). Artificial cerebrospinal fluid (CSF) was comprised of the following composition (mM): NaCl 117; KCl 5.4; NaHCO[sub]3[/sub] 26; MgSO[sub]4[/sub] 1.3; NaH[sub]2[/sub]PO[sub]4[/sub] 1.2; CaCl[sub]2[/sub] 2.5; glucose 10. An interface slice chamber was used for slice recordings. Experimental hyperthermia was induced by increasing bath temperature from 34 to 41[deg] C. Pharmacological agents were applied through the bath media.
(1) Both competitive and non-competitive NMDA receptor antagonists, APV and MK 801, failed to prevent hyperthermic SD, suggesting that NMDA receptor activation is not necessary for genesis of hyperthermic SD.
(2) Diazepam, an allosteric GABA[sub]A[/sub] receptor positive modulator, also failed to block hyperthermic SD.
(3) Pre-incubation of slices with 3 mM creatine for 3 hours to supply more intracellular ATP did not prevent hyperthermic SD. Direct measurement of intracellular ATP concentration from hyperthermic slices showed that intracellular ATP concentration doubled. These results indicate that depletion of intracellular energy during experimental hyperthermia may not serve as the primary mechanism for hyperthermic SD generation.
(4) Pre-incubation of slices with mannital to increase extracellular osmolarity significantly impaired hyperthermic SD, suggesting that reduction of extracellular space by swollen cells may play an important role in generation of hyperthermic SD.
Pharmacological alterations of excitatory or inhibitory synaptic transmission does not eliminate acute hyperthermic SDs in this model system, but mannitol-induced increase in extracellular space impairs hyperthermic SD. Hyperthermic SDs appear to result from temperature-related Na+/K+ pump failure from mechanisms not depending upon synaptic transmission or ATP stores.
[Supported by: The Marjorie Newsome and Sandra Solheim Aiken Funds for Epilepsy and the Women[rsquo]s Board of the Barrow Neurological Institute. JW was supported by the Seed Foundation of Bioengineering, Arizona State University. RSF was supported by the Maslah Saul, MD, Chair and the James and Carrie Anderson Laboratory fund for epilepsy research. ]