Abstract
The nucleus locus coeruleus (LC) and the nucleus subcoeruleus (SC) have been confirmed to be involved in descending modulation of nociceptive transmission at the spinal cord dorsal horn. We examined the age-related difference in modulating nociceptive processing at the spinal dorsal horn. Four age groups (8, 20, 50 and 70 months old) of male SD rats were used. Each group of rats was divided into the following two subgroups: LC/SC-lesioned (DC, 1 mA, 20 s) and LC/SC-intact rats. In behavioral experiments, following hindpaw inflammation (carrageenan, 2 mg, 0.1 ml), there was a significant difference in the development of hyperalgesia between the LC/SC-lesioned and the LC/SC-intact rats in young age (8 and 20 months old) but not in old age groups (50 and 70 months old). In dorsal horn neuronal activity, following hindpaw inflammation, a significant difference in both spontaneous activity and heat-evoked response was observed between the LC/SC-lesioned and the LC/SC-intact rats in young age, but not in old age. Electrical stimulation of the LC/SC significantly inhibited heat-evoked responses of dorsal horn neurons in young age, while the inhibitory effect of LC/SC stimulation was not observed when applied in old age rats. The microinjection of S-glutamate (50 nmol, 0.5 μl) into the LC/SC produced an inhibition of heat-evoked responses of dorsal horn neurons in young age but not in old age rats. These results suggest that there is an age-related difference in the function of the coeruleospinal antinociception system. [J Physiol Sci. 2006;56 Suppl:S221]
