In the present study we have investigated the effects of galanin and/o
r oxytocin on carrageenan-induced hyperalgesia, the relationship betwe
en oxytocin and galanin-containing nerve fibers in the spinal cord and
the influence of galanin on oxytocin secretion. Galanin (1 mug) given
intrathecally (i.t.) decreased significantly the mechanical nocicepti
ve threshold of the carrageenan-treated hindpaw, with no significant e
ffect on thermal nociception. The decrease in the mechanonociceptive t
hreshold exerted by galanin was modulated by oxytocin (1 mug, i.t.) ad
ministered simultaneously. There was a close relationship between gala
nin- and oxytocin-immunoreactive fibers in the dorsal horn of the thor
acic spinal cord, although there was no evidence for colocalization. G
alanin 0.1 and 1 mug given intracerebroventricularly or intraperitonea
lly significantly decreased the oxytocin level in plasma 60 min after
injection. Taken together, these data indicate that galanin may contri
bute to mechanical hyperalgesia by inhibiting the release of oxytocin
from nerve terminals in the spinal cord and that oxytocin may be a pot
ential analgesic agent.