Increased expression of sonic hedgehog in temporal lobe epileptic foci in humans and experimental rats

Sonic hedgehog (Shh) is a soluble signaling protein that is crucial in regulating cell proliferation, migration and differentiation, axonal guidance and neural progenitor cell survival during nervous system development. Recent evidence suggests that the Shh plays an important role in adulthood in regulating structural plasticity. Here we investigated the expression of Shh in temporal lobe epileptic foci in patients and experimental animals in order to explore the probable relationship between Shh expression and temporal lobe epilepsy (TLE). The Shh expression was assessed in 30 human brain tissues derived from patients undergoing operation for intractable TLE and was also detected in 12 histological normal temporal lobes from controls. Meanwhile, we investigated the Shh expression in the temporal neocortex and hippocampus from lithium-pilocarpine-treated rats on days 1, 3, 7, 14, 30, and 60 post-seizure, and from control rats. Expression of Shh was assessed by immunohistochemistry, immunofluorescence, and Western blot analysis. Shh was mainly expressed in neurons in temporal lobe epileptic foci in humans and experimental rats. Compared to the control group, Shh expression was enhanced in the temporal neocortex of patients with intractable TLE. In experimental rats, Shh expression gradually increased from 7 to 60 days post-seizure in temporal neocortex and elevated from 3 to 60 days in hippocampus with the peak levels at 30 days as compared with the control group. These results suggest that Shh may play an important role in the development of TLE.