Central expression of c-fos protein after peripheral noxious thermal stimulation in awake rats

This study applied immunohistochemistry method to examine the pattern of c-fos expression in the neuraxis following peripheral noxious thermal stimulation accomplished by immersion of tail of awake rat into hot water (50 degrees C). In unstimulated control rats, no obvious baseline expression of c-fos protein was found except in nucleus paraventricularis hypothalami and colliculus inferior, probably associated with restraint-induced stress and auditory stimulus, respectively. Noxious thermal stimulation resulted in the activation of c-fos expression, and bilateral increased nuclear immunostaining was counted in dorsal horn of lumbar and sacral segments of spinal cord (laminae I, II), nucleus raphe dorsalis, substantia grisea centralis (ventralis), nucleus paraventricularis thalami, nucleus anterior thalami, nucleus ventralis thalami, nucleus medialis thalami, nucleus reuniens, nucleus rhomboideus, nucleus habenulae lateralis, nucleus paraventricularis hypothalami, nucleus arcuatus, nucleus lateralis hypothalami, nucleus preopticus lateralis, nucleus septi lateralis, nucleus amygdala, nucleus striae terminalis, nucleus tractus diagonalis, and cortex cerebri. The results demonstrated that peripheral noxious stimulation induced central c-fos protein expression in a pattern of labeling nociresponsive cells.