The Dynamics of Dendritic Structure in Developing Hippocampal Slices

TLDR

Time‑lapse confocal microscopy directly visualized dendritic branch and spine formation on pyramidal neurons in developing hippocampal slices. Over two weeks, pyramidal neurons in early postnatal rat slices developed complex dendritic arbors with numerous spines, with early filopodia rapidly extending and retracting, some maturing into branches, and a transitional phase of persistent protospines that dynamically altered length and shape, indicating a highly dynamic postsynaptic environment that likely supports synaptic formation and plasticity.

Abstract

Time-lapse fluorescence confocal microscopy was used to directly visualize the formation and dynamics of postsynaptic target structures (i.e., dendritic branches and spines) on pyramidal neurons within developing hippocampal tissue slices. Within a 2 week period of time, pyramidal neurons in cultured slices derived from early postnatal rat (postnatal days 2–7) developed complex dendritic arbors bearing numerous postsynaptic spines. At early stages (1–2 d in vitro ), many fine filopodial protrusions on dendrite shafts rapidly extended (maximum rate ∼2.5 μm/min) and retracted (median filopodial lifetime, 10 min), but some filopodia transformed into growth cones and nascent dendrite branches. As dendritic arbors matured, the population of fleeting lateral filopodia was replaced by spine-like structures having a low rate of turnover. This developmental progression involved a transitional stage in which dendrites were dominated by persistent (up to 22 hr) but dynamic spiny protrusions (i.e., protospines) that showed substantial changes in length and shape on a timescale of minutes. These observations reveal a highly dynamic state of postsynaptic target structures that may actively contribute to the formation and plasticity of synaptic connections during CNS development.