Increase in p-MAPK/ERK after the induction of LTP.a, Immunocytochemical images representing p-MAPK/ERK in the ipsilateral dentate gyrus show that it is increased at LTP 0 compared with the contralateral side. No change was observed in the controls or LTP 15. b, High magnification (630×) of images show p-MAPK/ERK labeling in both cell bodies and dendrites of the granule cells in the ipsilateral dentate gyrus. c, Densitometric quantification of immunolabeled sections shows that p-MAPK/ERK is significantly increased only at LTP 0 (p < 0.05). d, Western blots of p-ERK1 and p-ERK2 confirm immunohistochemical results showing that the increase in p-MAPK/ERK occurs at LTP 0 (top panel), and this increase was only observed with the activated forms (bottom panel).