Relative contribution of endogenous neurotrophins in hippocampal long-termpotentiation

Recent evidence has shown that brain-derived neurotrophic factor (BDNF) is involved in hippocampal long-term potentiation (LTP). Because the reagents used in acute experiments react not only with BDNF but also with neurotroph in-4/5 (NT4/5) and neurotrophin-3 (NT3), we examined the involvement of the se neurotrophins in LTP using two highly specific, function-blocking monocl onal antibodies against BDNF and NT3, as well as a TrkB-IgG fusion protein. Our results show that NT3 antibodies did not have any effects on LTP. Howe ver, both TrkB-IgG fusion proteins and BDNF antibody similarly reduced LTP, suggesting that only BDNF but no other ligands of the TrkB-receptor are li kely to be involved in LTP induction. The reduction in LTP depended on the inducing stimuli and was only observed with theta-burst stimulation (TBS) b ut not with tetanic stimulation. We further observed that LTP was only redu ced if BDNF was blocked before and during TBS stimulation, and BDNF antibod ies did not affect early or late stages of LTP if they were applied 10, 30, or 60 min after TBS stimulation. These results point toward a specific and unique role of endogenous BDNF but not of other neurotrophins in the proce ss of TBS-induced hippocampal LTP. Additionally, they suggest that endogeno us BDNF is required for a limited time period only shortly before or around LTP induction but not during the whole process of LTP.