Neurotrophin-evoked rapid excitation through TrkB receptors.

Neurotrophins are a family of structurally related proteins that regulate the survival, differentiation and maintenance of function of different populations of peripheral and central neurons. They are also essential for modulating activity-dependent neuronal plasticity. Here we show that neurotrophins elicit action potentials in central neurons. Even at low concentrations, brain-derived neurotrophic factor (BDNF) excited neurons in the hippocampus, cortex and cerebellum. We found that BDNF and neurotrophin-4/5 depolarized neurons just as rapidly as the neurotransmitter glutamate, even at a more than thousand-fold lower concentration. Neurotrophin-3 produced much smaller responses, and nerve growth factor was ineffective. The neurotrophin-induced depolarization resulted from the activation of a sodium ion conductance which was reversibly blocked by K-252a, a protein kinase blocker which prefers tyrosine kinase Trk receptors. Our results demonstrate a very rapid excitatory action of neurotrophins, placing them among the most potent endogenous neuro-excitants in the mammalian central nervous system described so far.