Spinal serotonergic system is partially involved in antinociception induced by Trigonella foenum-graecum (TFG) leaf extract

It has been reported that Trigonella foenum-graecum (TFG) extract exerts analgesic, anti-inflammatory and anti-pyretic effects in different experimental models. The major objective of this paper was to investigate the site and mechanism of the analgesia induced by Trigonella foenum-graecum extract. We studied the analgesic effects of different doses of Trigonella foenum-graecum extract after i.p., i.t. and i.c.v. administration in formalin test, using male NMRI rats (200-250 g). Trigonella foenum-graecum extract showed analgesic effects in i.p. (1 g/kg) and i.t. (0.5, 1, and 2 mg/rat) (P < 0.05 in all groups) but not in i.c.v. (1 and 3 mg/rat) administrations. Based on the similarities between the effects of Trigonella foenum-graecum extract with those of nonsteroidal anti-inflammatory drugs (NSAIDs) and the role of 5-HT system in analgesic effects of NSAIDs, we tried to investigate the role of spinal 5-HT system in analgesic effects of Trigonella foenum-graecum extract. After lesioning of spinal 5-HT system by 5,7-dihydroxytryptamine (5,7-DHT), it was shown that the analgesic effect of Trigonella foenum-graecum extract (0.5 and 3 mg/rat) in the second phase of formalin test, was abolished completely and reduced relatively after using a low-dose (0.5 mg/rat) and a high-dose (3 mg/rat), respectively (P < 0.05). So, the antinociception partially remained (P < 0.05) after using the latter dose. Meanwhile, administration of naloxone (2mg/kg, i.p.) had no effect on the Trigonella foenum-graecum extract (1 g/kg, i.p.) analgesia. In conclusion, this study confirms the central action of Trigonella foenum-graecum extract and that spinal 5-HT system is partially involved in the analgesia induced by it in the second phase of formalin test and also indicates for co-existence of other analgesic mechanism(s).