Background and Aim: Introduction: Pain is a feeling that produces unpleasant experience along with tissue damage. Cannabinoids are compounds, found endogenous in the body, in plant and synthetic types and exert different effects on body via activation of endocannabinoid system. Flower of female cannabis sativa have the largest amount of cannabinoids. This research is to investigate the effects of intrathecal injection of female cannabis flowers hydroalcoholic extract on thermal and chemical pain. Methods: Material and methods: 50 grams of dried flowers were extracted after heating. 21 rats weighing 200-250 grams were categorized in 3 groups (n=7): control, sham (i.t. injection of solvent containing ethanol+Tween80+salin with respects of 1/1/8) and i.t. injection of the extract in 0.01mg/10µl. In order to investigate the chemical pain sensation, formalin test and to evaluate thermal pain threshold, Tail flick test were conducted. Results: Results: I.t. injection of hydroalchoholic extract of heated flowers could significantly decrease both the neurogenic and inflammatory phases of pain caused by formalin injection. (p<0.01, p<0.01 respectively). But has no reliable decreasing effect on threshold of thermal pain. Conclusion: Conclusion: Heating makes phytocannabinoid to become decarboxylated and this form is usually known as active form. These compounds have high affinity to CB1 and TRPV1 receptors which are present on the neurons in the dorsal root of spinal cord. May be the plant extract Carboxylated cannabinoids here, inhibit release of nervous mediators effective in pain such as Glutamate via connecting to CB1 receptors at the level of spinal cord. It is possible that activation of CB1 modulates TRPV1 activity here to diminish the chemical pain conduction.

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