Abstracts

The functions of vitamin D (1[alpha],25-dihydroxyvitamin D3) in the brain has not been studied extensively, even though the receptor for vitamin D [VDR] is widely distributed in neurons of the CNS including the hippocampus. Vitamin D has recently been shown to be neuroprotective. We reported previously that seizures induce increase in vitamin D receptor expression in the mouse hippocampus. Lithium-pilocarpine induced status epilepticus (LPSE) causes neuronal cell death that has features of both necrosis and apoptosis. Since LPSE-induced neuronal death is both selective and age-dependent, we investigated the expression of vitamin D receptor in the immature and adult rat hippocampus to begin to understand its role in LPSE-induced neuronal death.
Lithium chloride (3 mEq/kg) followed 24 h later by pilocarpine (35 mg/kg) was administered intraperitoneally in the 10-day (P10), 21-day-old (P21) and adult Sprague-Dawley rats. Saline injected animals served as control. The expression of vitamin D receptor was assessed by immunohistochemistry (N=3, each group) and Western blot (N=3, each group) in the hippocampus isolated at various times (4, 24, 72 hours) after LPSE. Neuronal injury was assessed by silver stain and cresyl violet stain (N= 6, each group).
VDR expression was relatively weak in control rat in the neurons of dentate gyrus, CA3 and CA1 region of hippocampus. Immunoreactivity appeared to be predominantly cytoplasmic. Following seizures, VDR-immunoreactivity increased dramatically in all regions of hippocampus in all age groups. The VDR expression peaked at 4 hours and returned to basal level at 24 hours. Western blot revealed that VDR immunoreactivity was increased at 4 hours after seizure and returned to basal level by 24 hours in all three aged groups. Also VDR expression was the highest in P10 rats and weakest in adults. The severity of neuronal injury by silver stain and cresyl violet stain at 72 h after the LPSE was in the following order: CA1[gt]CA3[gt]dentate gyrus; and adults[gt]P21[gt][gt]P10 (no damage).
Lithium-pilocarpine induced seizures result in a transient increase in VDR expression in neurons of dentate, CA1 and CA3 of rat hippocampus. The rapid time course suggests a role similar to immediate early genes. VDR immunoreactivity decreases as the brain matures. P10 rats that had the highest VDR expression showed no neuronal damage, whereas the adult rats with the lowest VDR expression suffered the most neuronal damage. These findings suggest that vitamin D and VDR may play a critical role in neuroprotection in this maturation-related evolution of neuronal cell death from status epilepticus.
[Supported by: NS37125 and Mayo Foundation.]