Reduced serotonin synthesis during early embryogeny changes effect of subsequent prenatal stress on persistent pain in the formalin test in adult male and female rats.

The considerable evidence supporting a role for serotonin (5-HT) in the embryonic formation of CNS, mediation of prenatal stress, and pain processing is reviewed. Long-term influences of prenatal 5-HT depletion as well as its combination with prenatal stress effects on tonic nociceptive system in 90-day-old Wistar rats were studied in the formalin test. Pregnant dams were injected with para-chlorophenylalanine (pCPA, 400 mg/kg/2 ml, ip), producing 5-HT depletion during the early period of fetal serotonergic system development.

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.