Analgesic effect of trans-anethole via downregulation of hypothalamic orexin and melanin-concentrating hormone gene expression in the rat

The role of the central nervous system in pain control is prominent via the regulation of neuropeptides. Plant derivatives such as trans-anethole could be effective due to analgesic properties. The present study investigated the analgesic effect of trans-anethole via modulation of hypothalamic orexin and melanin-concentrating hormone (MCH) gene expression in rats.

Twenty male Wistar rats (180-200 g) grouped into four groups of five rats (n=5). To induce pain, 50 μl of formalin was injected into the hind paws of the animals. The intact and formalin control groups received saline. Formalin induced pain groups received 150 or 250 mg/kg of trans-anethole. Pain score was evaluated by performing the formalin test. The hypothalamic samples were removed to analyze the gene expression levels via real-time PCR technique.

The pain score decreased in rats receiving 150 or 250 mg/kg trans-anethole compared to formalin control group. The relative gene expression of Orexin and MCH significantly increased in the formalin group compared to the intact rats. Injection of 150 or 250 mg/kg trans-anethole significantly reduced the relative gene expression of orexin and MCH in formalin induced pain groups compared to the formalin control rats.

Trans anethole caused downregulation of hypothalamic orexin and MCH gene expression due to its pain relieving properties. So, analgesic effects of trans anethole may be mediated via central mechanism.