BDNF signaling in Hebbian and Stentian structural plasticity in the developing visual system

During development, patterned neural activity instructs topographic map refinement. Axons with similar patterns of neural activity, converge onto target neurons and stabilize their synapses with these postsynaptic partners, restricting exploratory branch elaboration (Hebbian plasticity). On the other hand, non-correlated firing in inputs leads to synapse weakening and increased exploratory growth of axons (Stentian plasticity). We used visual stimulation to control the correlation structure of neural activity in a few ipsilaterally projecting (ipsi) retinal ganglion cell axons with respect to the majority contralateral eye inputs in the optic tectum of albino Xenopus laevis tadpoles. Multiphoton live imaging of ipsi axons, combined with specific disruptions of brain-derived neurotrophic factor (BDNF) signaling, revealed that both presynaptic p75NTR and TrkB promoted Stentian axonal branch addition, whereas presumptive postsynaptic BDNF signaling mediated Hebbian axon stabilization. Additionally, we found that BDNF signaling contributes to suppression of branch elimination locally in response to correlated firing of inputs.