Maternal stress differently alters nociceptive behaviors in the formalin test in adult female and male rats.

The long-term effects of restraint stress in Wistar rats during the last week of gestation were investigated on the acute and tonic phases of the specific biphasic nociceptive behavioral response in the formalin test in offspring, females and males, at 90 days. Prenatal stress produced significant changes in formalin-induced pain, which was more pronounced in females as compared to males. The distorted response in females was more at the supraspinal level with an increased intensity of the licking response in both phases as well as with an increased their duration. Results concerning changes of the interphase length indicate the impairments of inhibitory mechanisms in the central nervous system. Furthermore, profound difference in the effects of prenatal stress on the first phase but similarity in these effects on the second phase in females and males are indirect strong support of the view that the second phase in the formalin test can not be mediated by central sensitization alone but greatly depends on signals ongoing from nociceptive primary afferents. Finally, the results obtained in males are important argument in favor of assumption about different mechanisms of acute and tonic pain. Taken together, these studies show that prenatal stress alters nociceptive behaviors in the formalin test in rats at 90 days in a sex-specific manner.