The frequency of teeth chattering in rats. Group 1; frequency of jumping in morphine-dependent rats (positive control). Group 2; frequency of teeth chattering in morphine-dependent rats with co-administration of clonidine hydrochloride (0.2 mg/kg i.p.). Group 3, 4, and 5; frequency of teeth chattering in morphine-dependent rats with co-administration of 100 mg/kg, 200 mg/kg, and 300 mg/ kg PFE, respectively. Group 6, 7, and 8; frequency of teeth chattering in morphine-dependent rats with co-administration of 30 mg/kg, 60 mg/ kg, and 90 mg/kg luteolin, respectively. Group 9; frequency of teeth chattering in morphine nondependent rats (saline). PFE – Prosopis farcta extract.