Evaluation of antinociceptive effects of Tragia plukenetii: A possible mechanism

Tragia plukenetii R.Smith. (Euphorbiaceae) is an erect, prostate herb with sparsely hispid stinging hairs. In the present study, ethanolic extract and its fractions of T. plukenetii aerial parts were evaluated for antinociceptive and central nervous system (CNS) depressant effects. Among all the extracts, chloroform extract has produced significant analgesic activity at a test dose of 250 mg/kg in acetic acid induced writhing test and Eddy's hotplate test. The analgesic effect of chloroform extract (68.83% inhibition) is comparable with aspirin (72.09% inhibition) in acetic acid induced writhing test. Chloroform extract significantly increased the latency time in hotplate test. In the study of CNS depressant effect, the chloroform extract was found to produce a significant (P < 0.01) reduction of the exploratory capacity and depressant effect in locomotor activity. From the point of CNS depressant and good protective effect on chemical and thermal pain stimuli, indicates that T. plukenetii chloroform extract may have morphinomimetic properties. The naloxone is not able to alter the T. plukenetii induced antinociceptive effect in writhing and hotplate test. Thus, the observed antinociceptive activity of T. plukenetii might have resulted from the activation of peripheral receptors.