The effects of tanshinone I on memory and extracellular signal-regulated kinase (ERK)–cAMP response element binding protein (CREB) signalling pathway involvement. Tanshinone I (0.5, 1, 2 or 4 mg·kg−1, p.o.) increased passive avoidance task latency (A). Data represent means ± SEM (n= 10 per group). *P < 0.05 versus vehicle controls. Increased latency by tanshinone I (4 mg·kg−1, p.o.) was reversed by U0126 (1 nmol, i.c.v.), an ERK1 and ERK2 inhibitor (B). Data represent means ± SEM (n= 15 per group). *P < 0.05 versus vehicle controls, #P < 0.05 versus tanshinone I only-treated animals. Immunoreactivities of phospho-CREB (pCREB) and phosphorylated ERK (pERK) by Western blotting after treatment with tanshinone I and/or U0126 (C) and densitometry results (D). Data represent means ± SEM (n= 6 per group). *P < 0.05 versus vehicle controls, #P < 0.05 versus tanshinone I-treated mice. Con, control; U, U0126; Tan, tanshinone I. (E) Representative immunoreactivities of pCREB and pERK in the hippocampal tissues of non-trained normal mice (Nor) and of passive avoidance test-trained control mice (Con). Values under the immunoblots represent immunoreactivity ratios versus corresponding individual total protein levels.