effects of intra-fourth ventricle injection of crocin on capsaicin-induced orofacial pain in rats

objectives: crocin, a constituent of saffron and yellow gardenia, possesses anti-nociceptive effects. in the present study, we investigated the effects of intra-fourth ventricle injection of crocin in a rat model of orofacial pain. the contribution of opioid system was assessed using intra-fourth ventricle injection of naloxone, an opioid receptor antagonist. materials and methods: a guide cannula was implanted into the fourth ventricle of brain in anesthetized rats. orofacial pain was induced by subcutaneous (s.c.) injection of capsaicin (1.5 µg/20 µl) into the right vibrissa pad. the time spent face rubbing/grooming was recorded for a period of 20 min. locomotor activity was measured using an open-field test. results: intra-fourth ventricle injection of crocin (10 and 40 µg/rat) and morphine (10 and 40 µg/rat) and their co-administration (2.5 and 10 µg/rat of each) suppressed capsaicin-induced orofacial pain. the analgesic effect induced by 10 µg/rat of morphine, but not crocin (10 µg/rat), was prevented by 20 µg/rat of naloxone pretreatment. the above-mentioned chemical compounds did not affect locomotor activity. conclusion: the results of this study showed that the injection of crocin into the cerebral fourth ventricle attenuates capsaicin-induced orofacial pain in rats. the anti-nociceptive effect of crocin was not attributed to the central opioid receptors.