We have examined the relationship between brain-derived neurotrophic factor gene expression in the hippocampus and memory retention as well as long-term potentiation of rats. One-way inhibitory avoidance learning was adopted as the behavioural paradigm. Results revealed that brain-derived neurotrophic factor messenger RNA levels in the dentate gyrus of the hippocampus were markedly increased at 1 h, 3 h and 6 h post-training in rats showing good retention performance when compared with the poor retention controls. Direct injection of brain-derived neurotrophic factor antisense oligonucleotide into the dentate gyrus of the hippocampus before memory consolidation takes place markedly impaired retention performance in rats. It also significantly decreased brain-derived neurotrophic factor messenger RNA level in the dentate gyrus. The same antisense treatment also markedly reduced the amplitude and slope of excitatory postsynaptic potential as well as the brain-derived neurotrophic factor messenger RNA level in the dentate gyrus. These results suggest that hippocampal brain-derived neurotrophic factor gene expression plays an important role in the memory consolidation process and in the expression of long-term potentiation in rats. These results provide the first evidence to relate brain-derived neurotrophic factor gene expression and memory function in vertebrates. It further suggests that brain-derived neurotrophic factor gene expression is involved in behavioural plasticity.