OBJECTIVE Neurosteroids exert their antiepileptic effects via GABAA and NMDA receptors. Another cell death mechanism is excessive Ca(2+) influx into cells. Calbindin-D28k (CB) is a protein that modulates intracellular Ca(2+) in the nervous system. We evaluated whether androsterone up-regulates the expression of CB and has a neuroprotective effect by controlling Ca(2+) after pilocarpine-induced status epilepticus (SE) in mice. METHODS SE was induced in ICR mice by injection of pilocarpine. Two hours after SE, mice were treated intraperitoneally (i.p.) with androsterone (100-200 mg/kg) or vehicle, and compared with other control groups. Two days after injection, immunohistochemical staining for CB was performed using a hippocampal slice from each mice group. We also used cresyl violet staining to compare changes in hippocampal structures. RESULTS Two days after pilocarpine-induced SE, androsterone increased the expression of CB in the hippocampus compared with control SE mice. The number of CB-positive cells was 1±0.4 cells/mm(3) in pilocarpine-only group, 14±1.1 cells/mm(3) in pilocarpine plus androsterone 100 mg group and 29±2.5 cells/mm(3) in pilocarpine plus androsterone 200 mg group (p<0.001). CONCLUSIONS These results suggest that the neuroprotective effect of androsterone after pilocarpine- induced SE may be mediated by an increased expression of CB.