The effect of gonadectomy on antinociception induced in mice by swim stress

A 30 s swim in water at 30 degrees C reduced the number of abdominal constrictions produced in mice by i.p. acetic acid. Naloxone antagonised this stress-induced antinociception in the female but not in the male. Orchidectomy altered neither the antinociception nor its insensitivity to naloxone antagonism. However, oophorectomy completely abolished the antinociception induced by the swim. These results suggest a sex difference in the involvement of the endogenous opioid system in swim stress-induced antinociception in mice.