Kainate is known as a neurotoxin acting on the glutamate receptors in the central nervous system (CNS). Glutamate acts an excitatory neurotransmitter at physiological concentration but has a neurotoxic effect in excess amount. BDNF (brain-derived neurotrophic factor) has been reported to have a protective effect against the cellular toxicity and to plays an important role in neuronal survival and differentiation in peripheral nervous system. However, the functional mechanism of BDNF in CNS is unclear. This study was performed to examine the protective effect of BDNF in kainate-induced neurotoxicity and to observe the relation between BDNF mRNA expression and increasing pathways of intracellular Ca2+ concentration. Cultured hippocampal neurons were prepared from 17-18 day embryonic rats and used at the 7th day after neuronal culture. The amounts of BDNF mRNA were measured by reverse transcription polymerase chain reaction after the treatment of several glutamate receptor agonists: glutamate, kainate, -amino-3-hydroxyl-4-isoxazolepropionic acid, N-methyl-D-aspartate. Kainate showed the most prominent effect in an increase of BDNF mRNA expression among the glutamate receptor agonists. The maximal increase of BDNF mRNA expression was obtained in 50 M kainate at 3 hr after the treatment. Adding BDNF to kainate containing cultured hippocampal neurons diminished the increasing level of lactic dehydrogenase according to the single treatment of kainate. In the experiment to evaluate the Ca2+ influx pathways related in BDNF mRNA expression, nifedipine (10 M), a voltage-dependent Ca2+ channel blocker, decreased the both kainate (50 M) and KCl (50 mM) induced BDNF mRNA expressions by 18.4% and 35.0%, respectively. Ryanodine (10 M), a blocker of intracellular release from Ca2+ storage, however, did not show any effect in the both kainate- and KCl-treated neurons.These results suggest that BDNF has a protecting effect against the kainate-induced neurotoxicity in cultured rat hippocampal neurons, and its expression is more related with the Ca2+ influx through the voltage-dependent Ca2+ channels than the release from intracellular Ca2+ storage.