Neurotrophins are secreted factors that influence growth, survival, and other functions of neurons. Kafitz et al. now report that two of these proteins, brain-derived neurotrophic factor (BDNF) and neurotrophin-4/5 (NT-4/5) can also function as a potent neurotransmitters. Application of BDNF or NT-4/5 to slices of hippocampus, cortex, or cerebellum from rat brain caused depolarization of neurons very similar to that caused by glutamate. The effects appear to result from stimulation of TrkB neurotrophin receptors and consequent activation of sodium channels. The very rapid effect on the channels is observer in recordings during which the concentration of cytoplasmic components is substantially reduced. Thus, it seems that direct interaction of neurotrophin receptors with sodium channels (rather than signaling through tyrosine kinase activity of the receptors) may mediate the depolarization.
Kafitz, K.W., Rose, C.R., Thoenen, H.., and Konnerth, A. (1999) Neurotrophin-evoked rapid excitation through TrkB receptors. Nature 401: 918-921. [Online Journal]