The hypothesis that synaptic functions can be regulated by neurotrophins secreted from the postsynaptic cell was examined in Xenopus nerve-muscle cultures. Neuromuscular synapses formed on myocytes over-expressing neurotrophin-4 (M+ synapses) exhibited a higher level of spontaneous synaptic activity and enhanced evoked synaptic transmission as compared to those formed on normal control myocytes (M- synapses). The NT-4 effects involve a potentiation of presynaptic transmitter secretion as well as a lengthening of the mean burst duration of postsynaptic low conductance acetylcholine channels. Repetitive stimulation of either the presynaptic neuron or the postsynaptic myocyte led to a potentiation of synaptic transmission at M+ synapses. All potentiation effects of NT-4 overexpression were abolished by the extracellular presence of TrkB-IgG but not by the presence of TrkA-IgG, indicating that postsynaptic secretion of NT-4 was responsible for the synaptic modification.
Wang, X. H., & Poo, M. M. (1997). Potentiation of developing synapses by postsynaptic release of neurotrophin-4. Neuron, 19(4), 825–835. https://doi.org/10.1016/S0896-6273(00)80964-2