The effects of imidazoline compounds on nociception in animal pain model

The discovery of imidazoline ligands has opened up a new field of study. The investigation of imidazoline actions independent of adrenoceptors started in the mid 1980s. Imidazoline receptors are classified in several subtypes, I1, I2 and I3 binding sites. Although imidazoline sites have been the subjects of research for several years, but there is still controversy about their actions especially their role in nociception. Therefore, during recent years, we have based our investigations on the study of antinociceptive effects of imidazoline and guanidinium compounds in different animal pain models. Visceral pain is one of the most common form of pain which is poorly understood. In this regard, we studied the influence of imidazoline/guanidinium compounds such as clonidine and guanfacine on visceral pain in the presence or absence of yohimbine and benazoline. We conclude that both imidazoline (I2) and ?2-adrenergic receptors may play a role in producing analgesia in visceral pain, although data remain fragmentary whether imidazoline (I2) receptors enhance or suppress nociception. Chronic pain is one of the most frequent reasons for patients to seek medical care. Since the involvement of imidazoline binding sites in the modulation of pain is still in debate, therefore, in our research, we investigated the anti-nociceptive effects of imidazoline compounds such as clonidine and rilmenidine in formalin test in rats. Formalin test is an animal model of chronic pain, which reflects both phasic and tonic responses to a subcutaneous injection of dilute formalin into the rodents paw. Finally, it may be concluded that clonidine and rilmenidine produce their anti-nociceptive activity via ?2–adreneoceptors rather than imidazoline (I1) receptors. However, the role of imidazoline (I1) binding sites in producing analgesia has not been well established yet.