Experience-dependent gene expression in the rat hippocampus after spatial learning: A comparison of the immediate-early genes Arc, c-fos, and zif268

Neuronal immediate-early gene (IEG) expression is regulated by synaptic act ivity and plays an important role in the neuroplastic mechanisms critical t o memory consolidation. IEGs can be divided into two functional classes: (1 ) regulatory transcription factors (RTFs), which can broadly influence cell function depending on the "downstream" genes they regulate, and (2) "effec tor" proteins, which may directly modulate specific cellular functions. The objective of the current study was to determine whether the expression of an effector IEG (Arc) was similar to, or different from, that of two well c haracterized RTF IEGs (c-fos and zif268) after learning. IEG RNA levels fro m rats trained in spatial and nonspatial water tasks were determined using RNase protection assays and in situ hybridization. Overall, the regulation of the three IEGs was similar in the hippocampus and the entorhinal and pri mary visual cortices. Consequently, IEG RNA levels were positively correlat ed within a structure. By contrast, Arc and zif268 RNA levels were not corr elated or only weakly correlated across structures, although c-fos RNA leve ls were moderately correlated across structures. Arc RNA expression differe d from that of zif268 and c-fos in two regards: (1) hippocampal Arc RNA lev els were correlated with learning of the hippocampal-dependent spatial, but not hippocampal-independent cued response, water task, and (2) Arc RNA lev els in the hippocampus and entorhinal cortex increased after spatial revers al learning relative to an asymptotic performance group. Thus, although the expression of Arc, zif268, and c-fos exhibited many similarities, Arc was most responsive to differences in behavioral task demands.