Abstract
There are many patients who are suffering from chronic muscle pain, however, neural mechanisms for it were not well understood. Previously we reported that animals exposed to RCS (4ºC) showed muscle mechanical hyperalgesia. However, effect of RCS to thermal nociception has not been studied yet. Furthermore, different temperature (4ºC or -3ºC) was used in different reports, but the difference in effect of used temperature is not clear. Therefore we examined effects of RCS on thermal nociception and effects of different exposure temperature. Rats were exposed to RCS (from room temperature to 4ºC or -3ºC for 30 min every an hour from 10 am to 5 pm, and 4ºC or -3ºC from 5 pm to 10 am on the next day) for 5 days. Deep mechanical hyperalgesia of the lower leg in both sides was observed up to 42 days after RCS at -3 ºC, and cutaneous mechanical hyperalgesia was also observed. The thermal hyperalgesia was observed 1, 4 , 21, and 28 days after RCS. In contrast, RCS at 4 ºC induced deep mechanical hyperalgesia up to only 21 days, thermal hyperalgesia for a shorter period, and no cutaneous mechanical hyperalgesia. These results suggest more severe RCS (-3ºC) can induce longer lasting mechanical hyperalgesia in the muscle, and additionally it can induce cutaneous mechanical and thermal hyperalgesia. Hyperalgesia by RCS has been considered to be induced by impaired descending pain inhibitory system. Taking this into consideration, present observation suggests that descending pain inhibitory system more strongly inhibits deep nociception than skin nociception. [J Physiol Sci. 2008;58 Suppl:S107]
