Evidence for a Role of Dendritic Filopodia in Synaptogenesis and Spine Formation

TLDR

Live hippocampal cultures were imaged with DiO‑labeled dendrites and FM 4‑64–labeled presynaptic boutons to track axo‑dendritic synaptogenesis. Transient dendritic filopodia extended from shafts, contacted axons, and, as synaptic boutons formed, were stabilized into dendritic spines, indicating filopodia actively initiate synaptogenic contacts and later become spines.

Abstract

Axo-dendritic synaptogenesis was examined in live hippocampal cell cultures using the fluorescent dyes DiO to label dendrites and FM 4–64 to label functional presynaptic boutons. As the first functional synaptic boutons appeared in these cultures, numerous filopodia (up to 10 μm long) were observed to extend transiently (mean lifetime 9.5 min) from dendritic shafts. With progressively increasing numbers of boutons, there were coincident decreases in numbers of transient filopodia and increases in numbers of stable dendritic spines. Dendritic filopodia were observed to initiate physical contacts with nearby axons. This sometimes resulted in filopodial stabilization and formation of functional presynaptic boutons. These findings suggest that dendritic filopodia may actively initiate synaptogenic contacts with nearby (5–10 μm) axons and thereafter evolve into dendritic spines.