Clarifying the mechanism of augmentation of chronic pain by climate changes-Relationship with sympathetically maintained pain-

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1.To examine the effects of change in meteorological factors on autonomic parameters in conscious unrestrained animals, male rats were exposed to lowering barometric pressure (LP;27 hPa over 8 min) and lowering ambient temperature (LT;7℃ decrease from 22℃) in a climate-controlled room. Mean arterial pressure(MAP) clearly increased after reaching the pre-set low pressure. Heart rate(HR) and LF/HF ratio in the pulse interval variability were clearly increased in the early part of the LP-exposure period and then gradually decreased to the level before exposure. LT increased BP and HR gradually, LF/HF sharply. These results show that lowering barometric pressure within the range of natural environmental fluctuation induces autonomic responses in conscious rats. The increase in the LF/HF ratio during LP or LT exposure indicates that low-pressure and low-temperature environments induce sympathetic>parasympathetic activation.2.We investigated long-term and circadian changes in autonomic funct … More ion in rats rendered neuropathic by chronic constriction injury(CCI) on the sciatic nerve in SD, Wistar and Lewis rats. MAP and HR during the rest period in the daytime increased on postoperative day(POD) 4-11. The high-frequency power in pulse interval variability increased on POD 11-19, indicating parasympathetic activation synchronized with the reduction of sympathetic tone. The circadian patterns of MAP and HR were preserved up to POD 12 in Lewis rats. These results indicate that sympathetic activation occurred in early period after the CCI surgery.3.The inner ear of CCI rats to investigate the hypothesis that the barometric sensor is located in the inner ear. When the CCI rats were exposed to LP, the already increased number of foot lifts in response to the noxious filaments (hyperalgesia) was further increased, and foot lifts to the innocuous filament were induced (allodynia). In the CCI rats with inner ear destruction, on the other hand, LP failed to augment the mechanical allodynia or hyperalgesia. These results demonstrate that barometric sensor and/or sensing system in rats is located in the inner ear. Less