The effect of seizures on hippocampal neurogenesis

Some of the factors that are known to affect the extent of neurogenesis in the subgranular zone of the hippocampus are exercise (enhances), exposure to enriched environment (ie, more ways for rats to be active in their cages; enhances), and seizures. Seizures are perhaps the most interesting of the three, because the way that they impact the rate of neurogenesis depends on the type. Acute or persistent seizures induce new neurons to migrate to different regions of the CA3 network, while spontaneous motor seizures in temporal lobe epilepsy reduce neurogenesis altogether.

In their recent paper, Kuruba et al review the literature on the subject and suggest a number of mechanisms for these observations. For the acute seizure migration, one possibility is that the secreted migration cue reelin is expressed less after seizures and that without this cue new neurons do not know which path to follow and end up in unintended locations. There is in vitro evidence that blocking reelin expression causes anomalies in dentate gyrus cell migration, which provides evidence for this hypothesis.

It is possible that the altered migration in hippocampal migration is partly responsible for why single-shot seizures often develop into chronic epilepsy. As evidence for this, the authors discuss some animal models in which blocking abnormal neurogenesis was beneficial reducing cognitive deficiencies following seizure. It is interesting to contrast the effect of neurogenesis on recovery from seizures to the effect of neurogenesis on recovery from stroke, where neurogenesis is believed to be instrumental in a normal recovery.

Reference

Kuruba R, Hattiangady B, Shetty AK. 2009 Hippocampal neurogenesis and neural stem cells in temporal lobe epilepsy. Epilepsy & Behavior 14: 65-73. PubMed link.