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CaMKII mediates activity-induced changes in hippocampal dendritic structure.
Xiang-ming Zha, Steven H. Green, and Michael E. Dailey.
Dept. of Biological Sciences, University of Iowa, Iowa
City, IA 52242
CaMKII has been shown to play
important roles in synaptogenesis and synaptic plasticity. We here
examine the role of CaMKII in the control of dendritic spine density by
neuronal activity in developing hippocampal neurons. Hippocampal
slices were prepared from neonatal (P5-P7) rats and maintained in culture
for 4 to 7d. Calcium imaging shows that blockade of GABA-A receptors
by treatment with SR-75531 (gabazine) induces epileptiform activity in
neurons. This increased activity reduces spine density on pyramidal
neuron dendrites by ~50%. In contrast, blocking activity with TTX
results in ~30% increase in spine density. Quantitation of postsynaptic
densities in neurons expressing GFP-tagged PSD95 shows that gabazine-induced
reduction of spines coincides with a net loss of synapses, there being
no significant change in the density of synapses on dendritic shafts.
Western blot analysis shows that gabazine treatment increases CaMKII activity
(assessed by Thr286 phosphorylation) and expression of CaMKIIalpha and
CaMKIIbeta. Immunofluorescence (IF) staining shows punctate CaMKIIalpha
and CaMKIIbeta immunoreactivity in dendrites. PhosphoCaMKII IF increases
following gabazine treatment, with greater increase in dendrites of CA1
than that of CA3 neurons. The effects of gabazine on CaMKII are
blocked by TTX. Biolistic transfection of slices with GFP-AIP, a specific
peptide blocker of CaMKII, reverses the effect of gabazine on spine loss,
showing that CaMKII activity is required. Conversely, transfection
of a constitutively active form of CaMKIIalpha in hippocampal neurons
results in retraction of the dendritic tree. Thus, we show that
increased CaMKII activity is necessary for spine loss induced by epileptiform
activity, and that activation of CaMKII is sufficient to induce the retraction
of dendritic spines and branches.
Supported by NIH grants NS37159 (MED) and DC02961 (SHG).
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