Calcium/calmodulin dependent protein kinase II (CaMKII) is highly expressed in the hippocampus, which has a pivotal role in learning, memory, tolerance and dependence to morphine. In the present study after induction of tolerance to morphine in male Wistar rats, level of expression of CaMKII gene in the hippocampus of the rat brain was evaluated. Tolerance to morphine was examined by a hotplate test of analgesia on one day after the final repeated administrations. A semi-quantitative RT-PCR method was selected for evaluating gene expression. To induce dependence to morphine, the drug was administered for seven consecutive days. For evaluating changes in mRNA of CaMKII gene in the hippocampus in response to dependence to morphine, extractions of the hippocampus in separate groups were done at 1, 3, 7, 14, and 21 days after repeated administrations of morphine. The control group received saline for seven consecutive days. The brain was removed one day after the final injection, the hippocampus dissected and gene expression evaluated. Statistical analyses by one-way ANOVA revealed that ratio of CaMKII/β-actin gene expression at 1, 3, 7, 14 and 21 days after the final injection of repeated administrations of morphine compared with the ratio in the control group had a significant difference. Post hoc Tukey’s test revealed that the ratio of CaMKII/β-actin gene expression at 14 days after dependence to morphine was more significant. It can be concluded that the CaMKII gene in morphine withdrawal period would be increased until 14 days and then would be decreased, so the animal may have a strong memory for morphine reward in the hippocampus during14 days after morphine withdrawal.
