Journal of Neuroscience, Vol 15, 1-11, Copyright © 1995 by Society for Neuroscience
Morphological analysis of dendritic spine development in primary cultures of hippocampal neurons
M Papa, MC Bundman, V Greenberger and M Segal
Department of Neurobiology, Weizmann Institute of Science, Rehovot, Israel.
We monitored developmental alterations in the morphology of dendritic
spines in primary cultures of hippocampal neurons using confocal laser
scanning microscopy (CLSM) and the fluorescent marker Dil. Dissociated rat
hippocampal neurons were plated on polylysine-coated glass cover slips and
grown in culture for 1-4 weeks. Fixed cultures were stained with Dil and
visualized with the CLSM. Spine density, spine length, and diameters of
spine heads and necks were measured. Some cultures were immunostained for
synaptophysin and others prepared for EM analysis. In the 1-3 week
cultures, 92-95% of the neurons contained spiny dendrites. Two
subpopulations of spine morphologies were distinguished. At 1 week in
culture, "headless" spines constituted 50% of the spine population and were
equal in length to the spines with heads. At 2, 3, and 4 weeks in culture
headless spines constituted a progressively smaller fraction of the
population and were, on average, shorter than spines with heads. Spines
with heads had narrower necks than headless spines. At 3 weeks in culture,
spines were associated with synaptophysin-immunoreactive labeling,
resembling synaptic terminals. At 4 weeks in culture, only 70% of the
Dil-filled cells had spiny dendrites, and the density of spines decreased.
Ultrastructurally, the majority of dendritic spine- like structures at 1
week resembled long filopodia without synaptic contacts. The majority of
axospinous synapses were on short "stubby" spines. At 3 weeks in culture,
the spines were characteristic of those seen in vivo. They contained no
microtubules or polyribosomes, were filled with a characteristic,
filamentous material, and formed asymmetric synapses. These studies provide
the basis for further analysis of the rules governing the formation,
development, and plasticity of dendritic spines under controlled, in vitro
conditions.