Neurofilament Subunits are Integral Components of Synapses and Modulate Neurotransmission and Behavior In Vivo

Synaptic roles for neurofilament proteins have rarely been considered. Here, we establish all four neurofilament subunits as integral resident proteins of synapses. Compared to the population in axons, neurofilament subunits isolated from synapses have distinctive stoichiometry and phosphorylation state, and respond differently to perturbations in vivo. Completely eliminating neurofilament proteins from brain by genetically deleting three subunits (α-internexin, NFH and NFL) markedly depresses hippocampal LTP induction without detectably altering synapse morphology. Deletion of NFM in mice, but not the deletion of any other neurofilament subunit, amplifies dopamine D1-receptor-mediated motor responses to cocaine while redistributing postsynaptic D1-receptors from endosomes to plasma membrane, consistent with a specific modulatory role of NFM in D1-receptor recycling. These results identify a distinct pool of synaptic neurofilament subunits and establish their key role in neurotransmission in vivo, suggesting potential novel influences of neurofilament proteins in psychiatric as well as neurological states.