BDNF signaling in correlation-dependent 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 structural plasticity). On the other hand, non-correlated firing in inputs leads to synapse weakening and increased exploratory growth of axons (Stentian structural plasticity). We used visual stimulation to control the correlation structure of neural activity in a few ipsilaterally projecting (ipsi) retinal ganglion cell (RGC) 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 targeted disruptions of brain-derived neurotrophic factor (BDNF) signaling, revealed that both presynaptic p75(NTR) and TrkB are required for Stentian axonal branch addition, whereas presumptive postsynaptic BDNF signaling is necessary for Hebbian axon stabilization. Additionally, we found that BDNF signaling mediates local suppression of branch elimination in response to correlated firing of inputs. Daily in vivo imaging of contralateral RGC axons demonstrated that p75(NTR) knockdown reduces axon branch elongation and arbor spanning field volume.

Automated summary

During development, patterned neural activity plays a crucial role in refining the topographic map. Stabilization of synapses and restricted branch elaboration are observed when axons share similar patterns of neural activity (Hebbian structural plasticity). Conversely, non-correlated firing leads to synapse weakening and increased axon growth (Stentian structural plasticity). Through visual stimulation and live imaging in Xenopus laevis tadpoles, the study shows that both presynaptic p75(NTR) and TrkB, along with postsynaptic BDNF signaling, contribute to axon branch addition and stabilization.