Effect of Topiramate on Morphine-induced Conditioned Place Preference (CPP) in Rats: Role of ERK and CREB Proteins in Hippocampus and Cerebral Cortex

Abstract

In this study, the effect of topiramate, as an antiepileptic drug, was evaluated on morphine craving in rats. The conditioned place preference (CPP) test was used for this purpose. Repeated administration of morphine (10 mg/kg, i.p. for 4 days) induced significant CPP. Administration of topiramate (50 and 100 mg/kg, i.p. for 4 days) with each morphine administration decreased the acquisition of morphine-induced CPP. At the next step, the levels of extracellular signal-regulated kinase (ERK), p-ERK, cAMP responsive element binding (CREB), and p-CREB proteins were evaluated in hippocampus and cerebral cortex using western blot analysis. Following the repeated administration of morphine, the level of p-ERK protein markedly enhanced in both tissues, while topiramate could significantly reduce the phosphorylation of ERK in these brain regions. Additionally, the level of CREB and p-CREB proteins did not change in different groups. Memantine as a positive control reduced the acquisition of morphine-induced CPP. Also, memantine significantly decreased the level of p-ERK protein in hippocampus and cerebral cortex. These results demonstrated that topiramate can attenuate the acquisition of morphine-induced CPP in rats. This effect in part can be mediated through down regulation of p-ERK protein in hippocampus and cerebral cortex.

Keywords: CREB; Conditioned place preference; ERK; Morphine; Topiramate.

Figure1

General design of CPP experiment

Figure 2

Effects of topiramate (10, 50 and 100 mg/kg) on the acquisition of morphine-induced CPP in rat. During the conditioning phase animals received the different treatments in the drug-paired compartment. Data are expressed as mean ± SEM of 6 animals per group. The bars represent the time spent in the drug-paired compartment before conditioning sessions in pre-conditioning test and after conditioning sessions in post-conditioning test. *p < 0.05 significant differences in the time spent in the drug-paired compartment in pre-conditioning vs. post-conditioning sessions tests. NS: Normal saline; Mor: Morphine; Top: Topiramate; Mem: Memantine

Figure 3

Effect of morphine and topiramate on locomotor activity during open field test in morphine-induced CPP in rat. Bars represent mean ± SEM (n = 6). ^*p < 0.05 and ^**p < 0.01 vs. NS. The statistical analysis was performed by One-way ANOVA followed by Tukey test. NS: Normal saline; Mor: Morphine; Top: Topiramate; Mem: Memantine

Figure 4.

Effect of morphine and topiramate on the protein expression of ERK and p-ERK in hippocampus following morphine-induced CPP in rat. (A and C) Specific bonds of ERK and p-ERK proteins according to western blot analysis. (B and D) Densitometric data of protein analysis. Data are expressed as the mean ± SEM of 4 separate experiments. ANOVA and Tukey-Kramer post-test were used for statistical analysis. ^###p < 0.001 vs. NS, ^**p < 0.01 and ^***p < 0.001 vs. Mor. NS: Normal saline; Mor: Morphine; Top: Topiramate; Mem: Memantine

Figure 5

Effect of morphine and topiramate on the protein expression of ERK and p-ERK in cerebral cortex following morphine-induced CPP in rat. (A and C) Specific bonds of ERK and p-ERK proteins according to western blot analysis. (B and D) Densitometric data of protein analysis. Data are expressed as the mean ± SEM of 4 separate experiments. ANOVA and Tukey-Kramer post-test were used for statistical analysis. ^##p < 0.01 vs. NS, ^*p < 0.05 and ^**p < 0.01 and Mor. NS: Normal saline; Mor: Morphine; Top: Topiramate; Mem: Memantine

Figure 6

Effect of morphine and topiramate on the protein expression of CREB and p-CREB in hippocampus following morphine-induced CPP in rat. (A and C) Specific bonds of CREB and p-CREB proteins according to western blot analysis. (B and D) Densitometric data of protein analysis. Data are expressed as the mean ± SEM of 4 separate experiments. ANOVA test was used for statistical analysis. NS: Normal saline; Mor: Morphine; Top: Topiramate; Mem: Memantine

Figure 7

Effect of morphine and topiramate on the protein expression of CREB and p-CREB in cerebral cortex following morphine-induced CPP in rat. (A and C) Specific bonds of CREB and p-CREB proteins according to western blot analysis. (B and D) Densitometric data of protein analysis. Data are expressed as the mean ± SEM of 4 separate experiments. ANOVA test was used for statistical analysis. NS: Normal saline; Mor: Morphine; Top: Topiramate; Mem: Memantine