Postural asymmetry in rats induced by stress and pain stimuli.

A significant number of rats (31-68%) subjected to pain stimulation (intraperitoneal injection of 1% or 5% acetic acid, 5 ml/kg), immobilization stress (6 hrs in a supine position) or cold stress (3 hrs at 4-6 degrees C) exhibited postural asymmetry of hind limbs after spinal cord transection at T7 level. The number of rats with right and left limb flexions was approximately equal. Naloxone (2 mg/kg intraperitoneally) prevented the development of postural asymmetry induced by pain and stress stimuli. Postural asymmetry of hind limbs appears to be due to an asymmetric CNS response to stress and pain stimuli. Our data imply that endogenous opioid peptides and opiate receptors may be involved in the regulation of this response.