Neurotrophin secretion from hippocampal neurons evoked by long- term-potentiation-inducing electrical stimulation patterns

The neurotrophin (NIT) brain-derived neurotrophic factor (BDNF) plays an essential role in the formation of long-term potentiation (LTP). Here, we address whether this modulation by BDNF requires its continuous presence, or whether a local increase in BDNF is necessary during a specific time period of LTP initiation. Using electrical field stimulation of primary cultures of hippocampal neurons, we demonstrate that short high-frequency bursts of stimuli that induce LTP evoke also an instantaneous secretion of BDNF. In contrast, stimuli at low frequencies, inducing long-term depression, do not enhance BDNF secretion, suggesting that BDNF is specifically present, and thus required, at the time of LTP induction. The field- stimulation-mediated BDNF secretion depends on the formation of action potentials and is induced by IP3-mediated Ca2+ release from intracellular stores. Experiments, aimed at determining the sites of NIT secretion that use NT6, showed similar patterns of surface labeling by field stimulation to those shown previously by high potassium