Effect of xylazine and yohimbine on the phasic pain during the estrous cycle in the rat

The aim of the present study was to investigate the effect of α2-adrenergic agonist (xylazine) andantagonist (yohimbine) on phasic pain during estrous cycle in female rats. Adult female rats weighing 180-220 g were kept under controlled temperature (21-24°C) and light/dark conditions (light on at 6:00 a.m. and light off at 6:00 p.m.). Animals were divided into four groups: 1) control group which received 0.3 ml ofnormal saline by intraperitoneal (IP) route; 2) IP experimental group which received 0.3 ml xylazine 3, 4.5and 6 mg/kg and yohimbine 1, 2 and 4 mg/kg by IP route; 3) sham group which received 2 μl of artificialcerebrospinal fluid by intra cerebral ventricle (ICV) route and 4) ICV experimental which received 2 μlxylazine 10 and 20 μg/rat and yohimbine 5 and 10 μg/rat by ICV route. Cannulae were implanted into the left lateral ventricle using stereotaxic method. Pain sensitivity was measured by tail flick test, which wasperformed before injection, 15 and 30 min after injection in all groups. Xylazine decreased pain sensitivitysignificantly (P