XXXX /calmodulin-dependent protein kinase II clusters in adult @entity35 hippocampal slices.

@entity35 @entity1249 @entity63 @entity460 @entity972 @entity141
We have previously reported the formation of @entity460 /calmodulin-dependent protein kinase II (CaMKII) clusters approximately 110 nm in diameter in hippocampal neurons in culture and in the intact adult brain, under conditions that simulate ischemic stress and increase [ @entity141 ](i) [Dosemeci et al. (2000) J. Neurosci. 20, 3076-3084; Tao-Cheng et al. (2001) Neuroscience 106, 69-78]. These observations suggest that @entity63 -like conditions that prevail during the dissection of brain tissue for the preparation of hippocampal slices could lead to the formation of CaMKII clusters. We now show by pre-embedding immuno-electron microscopy that, indeed, CaMKII clusters are present in the @entity1249 pyramidal neurons in hippocampal slices from adult @entity35 fixed immediately after dissection, and that the number of CaMKII clusters increases with the delay time between decapitation and fixation. Moreover, CaMKII clusters are typically localized near the endoplasmic reticulum. When acute slices are allowed to recover in oxygenated medium for 2 h, CaMKII clusters mostly disappear, indicating that clustering is reversible. Also, the postsynaptic density, another site for CaMKII accumulation under excitatory conditions, becomes thinner upon recovery. Treatment of recovered slices with high @entity972 for 90 s causes the re-appearance of CaMKII clusters in nearly all @entity1249 pyramidal cells examined. On the other hand, when dissociated hippocampal neurons in primary culture are exposed to the same depolarizing conditions, only approximately 25% of neurons exhibit CaMKII clusters, indicating a difference in the susceptibility of the neurons in culture and in acute slices to excitatory stimuli. Altogether these observations indicate that the effect of CaMKII clustering should be considered when interpreting experimental results obtained with hippocampal slices.
