The protean actions of neurotrophins and their receptors on the life and death of neurons

At vanishingly low concentrations, factors of the neurotrophin family (NGF, BDNF, NT3 and NT4/5) can promote neuronal survival or death. Many investigations indicate that the survival-promoting signals of neurotrophins are generated by activation of Trk tyrosine kinase receptors and that their death-promoting signals are generated by activation of p75 neurotrophin receptors (p75^NTR). Despite this, a body of work indicates that p75^NTR can promote cell survival and Trk receptors can adversely affect neuron health. The potential mechanisms by which these receptors could have such diverse and antipodal effects are considered here.