Introduction: ERK pathway plays a critical role in cellular adaptive responses to environments changes. Exposure to opioids or stressful conditions can induce the activation of ERK, and its downstream targets, CREB and c-fos, in neural cells. Therefore, in the current study we aimed to investigate effects of acute and subchronic stress on change in p-ERK, p-CREB and c-fos levels in rat hippocampus during morphine-induced conditioned place preference procedure.
Material and Methods: Male Wistar rats were divided into two saline- and morphine-treated super groups. Each super group contained of control, acute stress (AS, applied forced swim stress just one day) and subchronic stress (SS, applied forced swim stress for three consecutive days) groups. In all groups, the CPP procedure was performed, the hippocampus was dissected out and thereafter p-ERK/ERK ratio, p-CREB/CREB ratio and c-fos level were measured by Western blot analysis.
Results: The results revealed that in saline- or morphine- treated animals all cited factors were enhanced significantly during AS and SS except of p-ERK/ERK ratio which was not significant in morphine-control group.
Conclusion: Our findings suggest that in saline- or morphine-treated animals, AS and SS trigger the enhancement of p-ERK, p-CREB and c-fos levels in the hippocampus and stress intensifies the effect of morphine induced-CPP on the increase of these factors.