High magnification of phosphorylated MAPK/ERK and Elk-1, and expression of zif268 at LTP 0 in the presence of DMSO or SL327. a, In the presence of DMSO, there is heavy labeling of p-MAPK/ERK in both dendrites and the cell bodies of granule cells. In addition, there is hyperphosphorylation of Elk-1 (b) and an upregulation of zif268mRNA (c). d, In some cases, there was some labeling of p-MAPK/ERK in the SL327-treated rats, but this was restricted to the dendrites. In these rats, p-Elk-1 was greatly reduced (e), and there was no upregulation ofzif268 mRNA (f), suggesting the need for translocation of MAPK/ERK to the nucleus to phosphorylate Elk-1 and upregulate zif268.