Abstracts

Calbindin is a 28 kDa calcium-binding protein expressed in restricted neuronal populations in the mammalian brain where it may play a role in protecting neurons against excitotoxic insults. Recent findings indicate that vitamin D can induce the expression of calbindin D28k in kidney, but chronic treatment results in a clinically mild hypervitaminosis can not affect the content of calbindin-D28k in the cerebral cortex and hippocampus. Calbindin D28k immunoreactivity decreased in the CA1/CA2 fields 1 and 3 days after kainic acid-induced seizure, and was lost extensively in the pyramidal layer 10 days after seizure, but the exact role of calbindin D28k in the hippocampus has been unknown. To evaluate the function of calbindin D28k in the hippocampus, we investigated whether Mega-dose vitamin D can induce the expression of calbindin D28k in the neurons of the hippocampus and examined the changes of calbindin D28k during lithium-pilocarpine-induced status epilepticus (LPSE) and the neuronal damage in the hippocampus 72 hours after seizure. Vitamin D (1 [mu]g/kg/ml) was administered daily intraperitoneally in Sprague-Dawley rats for 7 days and ethanol (1 [mu]l/kg/ml) was injected as control. Lithium chloride (3 mEq/kg) followed 24 h later by pilocarpine (35 mg/kg) was administered intraperitoneally 7days after vitamin D treatment. The expression of calbindin D28k was assessed by immunohistochemistry (N=3, each group) and Western blot (N=3, each group) in the hippocampus isolated at various times (0, 4, 8, 24 hours) after LPSE. Neuronal injuries were assessed by cresyl violet stain (N= 6, each group). Calbindin D28k immunoreactivity was increased in dentate granule cells, the pyramidal cells of the CA1/CA2 area of the hippocampus in the vitamin D group than that of the control group. The control group showed decreased calbindin D28k immunoreactivity in the CA1/CA2 areas 4 and 8 hours after LPSE, and extensively in the pyramidal layer 24 hours after seizure, whereas the vitamin D group revealed that Calbindin D28k immunoreactivity maintained in CA1/CA2 areas until 24 hours after seizure. The neuronal injury by cresyl violet stain at 72 h after the LPSE was more severe in CA1 area of the control group than that of the vitamin D group. Vitamin D induced calbindin D28k in the pyramidal cells of CA1/CA2 areas of the hippocampus and delayed the seizure-induced loss of calbindin D 28k. Also vitamin D had neuroprotective effect in the pyramidal cells of CA1/CA2 areas of the hippocampus. These findings suggest that neuroprotective effect of vitamin D may be mediated partially by induction of calbindin D28k.