Morphine Reduces Expression of TRPV1 Receptors in the Amygdala but not in the Hippocampus of Male Rats

Background: Chronic use of opioids usually results in physical dependence. The underlying mechanisms for this dependence are still being evaluated. Transient receptor potential vanilloid type 1 (TRPV1) are important receptors of pain perception. Their role during opioid dependence has not been studied well. The aim of this study was to evaluate the effect of morphine-dependence on the expression of TRPV1 receptors in the amygdala and CA1 region of the hippocampus. Methods: This study used four groups of rats. Two groups of rats (morphine and morphine+naloxone) received morphine based on the following protocol: 10 mg/kg (twice daily, 3 days) followed by 20, 30, 40 and 50 mg/kg (twice daily), respectively, for 4 consecutive days. Another group received vehicle (1 ml/kg) instead of morphine given using the same schedule. The morphine+naloxone group of rats additionally received naloxone (5 mg/kg) at the end of the protocol. The control group rats received no injections or intervention. The amygdala and CA1 regions of the morphine, saline-treated and intact animals were isolated and prepared for real-time PCR analysis. Results: Administration of naloxone induced withdrawal signs in morphine-treated animals. The results showed a significant decrease in TRPV1 gene expression in the amygdala (P<0.05) but not the CA1 region of morphine dependent rats. Conclusion: TRPV1 receptors may be involved in morphine-induced dependence.