Lowering barometric pressure aggravates mechanical allodynia and hyperalgesia in a rat model of neuropathic pain.

To examine the effects of meteorological change on the pain-related behaviors of neuropathic rats, animals with a chronic constriction injury (CCI) to the sciatic nerve were exposed to low barometric pressure (LP), 20 mmHg below the natural atmospheric pressure in a climate-controlled room. CCI caused a decreased hindpaw withdrawal threshold to von Frey hair (VFH) stimulation (mechanical allodynia) and prolonged duration of hindpaw withdrawal in response to pinprick stimulation (mechanical hyperalgesia). When the CCI rats were exposed to LP, both these pain-related behaviors were aggravated, whereas no change was seen in a group of controls. In the CCI rats sympathectomy inhibited this LP-induced augmentation of pain-related behaviors. These results show that LP intensifies the abnormalities in the pain-related behaviors of neuropathic rats, and that sympathetic activity contributes to the LP effect.