Laterality and sex differences in the expression of brain-derived neurotrophic factor in developing rat hippocampus

Brain-derived neurotrophic factor (BDNF), as a member of neurotrophin family, plays an important role in neurogenesis, neuronal survival and synaptic plasticity. BDNF is strongly expressed in the hippocampus, where has been associated with memory consolidation, learning, and cognition. In this study, Real-time PCR, immunohistochemistry, and stereology were used to evaluate the gender differences and left-right asymmetries in the expression of BDNF in the developing rat hippocampus during the neurogenesis-active period, at postnatal days P0, P7 and P14. We found the lowest expression of BDNF in the right side and the highest in the left side hippocampi of both male and female neonates at P14 (P ≤ 0.05 each). At the same time, there were significant differences in the hippocampal expression of BDNF between males and females (P ≤ 0.05 each). No important differences in the number of BDNF expressing neurons in different subregions of right/left hippocampus were observed between male and female animals at P0 and P7 (P > 0.05). Furthermore, the highest numerical density of BDNF positive cells was detected in the both sides hippocampal CA₁ in the male/female offspring at P7, and in the CA₂, CA₃ and dentate gyrus at P14 (P ≤ 0.05 each). Based on these findings, it can be concluded that there are prominent sex and interhemispheric differences in the expression of BDNF in the developing rat hippocampus, suggesting a probable mechanism for the control of gender and laterality differences in development, structure, and function of the hippocampus.