The inner ear is involved in the aggravation of nociceptive behavior induced by lowering barometric pressure of nerve injured rats

Patients suffering from neuropathic pain often complain of pain aggravation when the weather is changing. The exact mechanism for weather change-induced pain has not been clarified. We have previously demonstrated that experimentally lowering barometric pressure (LP) intensifies pain-related behaviors in rats with chronic constriction injury (CCI). In the present experiment we examined whether this pain aggravating effect of LP exposure in nerve injured rats is still present after lesioning of the inner ear. We used both CCI and spinal nerve ligation (SNL) models for this study. We injected into the middle ear sodium arsanilate solution (100 mg/ml, 50 μl/ear), which is known to degenerate vestibular hair cells, under anesthesia the day before surgery. Rats were exposed to LP (27 hPa decrease over 8 min) 7-9 days after CCI or 5-8 days after SNL surgery, and pain-related behavior (number of paw lifts induced by von Frey hair stimuli) was measured. When the inner ear lesioned SNL or CCI rats were exposed to LP, they showed no augmentation of pain-related behavior. On the other hand, the pain aggravating effect of a temperature decrease (from 24 to 17 °C) was maintained in both SNL and CCI rats. These results suggest that the barometric sensor/sensing system influencing nociceptive behavior during LP in rats is located in the inner ear.