Stress, the hippocampus, and epilepsy

Stress is among the most frequently self-reported precipitants of seizures in patients with epilepsy. This review considers how important stress mediators like corticotropin-releasing hormone, corticosteroids, and neurosteroids could contribute to this phenomenon. Cellular effects of stress mediators in the rodent hippocampus are highlighted. Overall, corticosterone-with other stress hormones-rapidly enhances CA1/CA3 hippocampal activity shortly after stress. At the same time, corticosterone starts gene-mediated events, which enhance calcium influx several hours later. This later effect serves to normalize activity but also imposes a risk for neuronal injury if and when neurons are concurrently strongly depolarized, for example, during epileptic activity. In the dentate gyrus, stress-induced elevations in corticosteroid level are less effective in changing membrane properties such as calcium influx; here, enhanced inhibitory tone mediated through neurosteroid effects on gamma-aminobutyric acid (GABA) receptors might dominate. Under conditions of repetitive stress (e.g., caused from experiencing repetitive and unpredictable seizures) and/or early life stress, hormonal influences on the inhibitory tone, however, are diminished; instead, enhanced calcium influx and increased excitation become more important. In agreement, perinatal stress and elevated steroid levels accelerate epileptogenesis and lower seizure threshold in various animal models for epilepsy. It will be interesting to examine how curtailing the effects of stress in adults, for example, by brief treatment with antiglucocorticoids, may be beneficial to the treatment of epilepsy.