Hippocampal memory-associated synaptic plasticity is driven by a cascade of transcription and new protein synthesis. In vitro electrophysiological studies on acute hippocampal slices have elucidated much of what we know about this molecular cascade. Curiously, these slices require a period of "equilibration" for the recovery of electrophysiological properties such as LTP, implying ongoing time-dependent molecular events necessary for full expression of plasticity. Using standard immunofluorescence combined with confocal imaging and a novel data analysis approach, we implicate the transcription factor NF-B in this plasticity-related molecular adaptation during equilibration. Marked differences in basal NF-B activity in distinct cell types of the hippocampus were observed, with the amount of active NF-B increasing throughout the 2-h equilibration period in all cell types. Moreover, distinct hippocampal neuronal subfields exhibit very different responses to the GABA A receptor blocker picrotoxin, the presence of which is required to achieve LTP in the dentate gyrus. These findings have implications for the use of acute hippocampal slices to study the effects of compounds that signal through NF-B on synaptic plasticity. Further investigation into the cellular processes that occur during this molecular adaptation may increase our understanding of plasticity-related events common to both LTP and memory formation.

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