Crocin suppressed cold allodynia and anxiety through α2- adrenoceptors in the anterior cingulate cortex followingchronic constriction injury of sciatic nerve in rats

Abstract

It is believed that α-adrenoceptors have critical contribution in the process of pain information. Anterior cingulate of cortex (ACC) is a key area of brain associated with pain perception. Pharmacological studies demonstrated that crocin, as a potent antioxidant, has analgesic effects. The underlying analgesic mechanism of the crocin is far from clear. Therefore, the present study was design to examine the interaction of anti-nociceptive effects of crocin with α1-and α2-adrenoceptors of ACC in chronic constriction injury (CCI) model of neuropathic pain. Intra-ACC injection of crocin significantly decreased cold allodynia (using acetone test) and anxiety (using elevated plus maze test) in neuropathic rats from 2 days to 6 days’ post-surgery. Co-injection of crocin and prazosin (α1-adrenoceptors antagonist, 30 μg/5μl) had no effect on the allodynia. However, co-injection of crocin and yohimbine (α2-adrenoceptors antagonist, 30 μg/5μl) significantly increased the allodynia on days 4 and 6 post-surgery as compared with CCI+crocin rats. Moreover, our data identified that neuropathy decreased open arm entries and locomotor activity. Additionally, crocin increased entries to open arms; but this increase was not significant as compared to CCI group. There was no significant difference between CCI+Crocin and CCI+crocin+prazosin groups. However, co-injection of crocin and yohimbine significantly decreased entries to open arms as compared with CCI+crocin group. Furthermore, co-injection of crocin with prazosin or yohimbine did not cause significant changes in locomotor activity. The present study suggested thatthe anti-nociceptive and anxiolytic effects of crocin appear to be mediated through α2-, and not α1-adrenoceptors in the ACC.