Figure 2.

Proposed functions of spinules in mediating localized structural synaptic plasticity. (A) A smaller, non-potentiated spine with a simple PSD occasionally forms small, dynamic short-lived spinules, which emerge from close to the PSD edge. Small spinules may be trans-endocytosed or explore their environment. (B) A large, potentiated spine displays a complex PSD, with multiple nanomodules, and an elongated long-lived spinule. The spinule forms a secondary synaptic connection with a bouton from the same axon as the one forming a synapse with the spine head. (C) A large, potentiated spine with multiple PSD nanomodules displays a long-lived spinule that contacts an adjacent bouton originating from a different axon than the one synapsing with the spine head. These interactions may facilitate secondary synapse formation, potentially leading to alterations in synaptic plasticity, connectivity, and down-stream brain function.