Inactivation of MEK with SL327 results in disruption of the downstream activation of p-MAPK/ERK, p-Elk-1, andzif268 mRNA expression induced by LTP. a, After the induction of LTP in the presence of SL327, the EPSP declined to basal levels within 60 min, and there was no effect on LTP after injections of DMSO. b, Immunocytochemical images of p-MAPK/ERK in the dentate gyrus at LTP 0 shows that DMSO had no effect on LTP-induced p-MAPK/ERK, whereas injections of SL327 resulted in inhibition of p-MAPK/ERK. c, Similarly, p-Elk-1 was also inhibited by SL327 at LTP 0, with no effect on LTP-induced activation of p-Elk-1 after DMSO. d, In situhybridization images of zif268 at LTP 0 and LTP 60 in rats injected with either SL327 or DMSO. Zif268 was upregulated in the potentiated dentate gyrus in the DMSO control group at both time points, whereas in the SL327 group, LTP-induced upregulation of zif268 was blocked at both time points.e, Quantification of densitometric measures of p-MAPK/ERK and p-Elk-1 at LTP 0 and optical density measures of the expression of zif268 mRNA at LTP 0 and LTP 60 confirm blockade of MAPK/ERK and Elk-1 phosphorylation, and ofzif268 induction in the presence of SL327 (asterisks indicate significant difference from DMSO controls).