[Consequences of the prenatal depletion of serotonin and stress on nociceptive sensitivity in rats].

The long-term effects of serotonin (5-HT) synthesis alteration and of restraint stress experienced by pregnant Wistar rats on pain sensitivity (evaluated by the indices of the biphasic behavioral response in the formalin test) were studied in their 90-day-old offspring. Prenatal 5-HT depletion decreased pain sensitivity in one third of the rats and failed to change it in the rest of the rast. In these later, however, an obvious tendency for an increase of interphase duration in females and its decrease in males were revealed that indicates changing of the activity of the descending serotoninergic system modulating nociceptive signals at the level of the spinal dorsal horns. Prenatal stress decreased pain sensitivity in 50% of the rats with prenatal deficiency of 5-HT but increased it in the rest of the animals. Increase of pain sensitivity also occurred in the control rats but to a lesser extent (significantly in flexing + shaking behavior during the second phase) compared to the animals with prenatal 5-HT depletion. In the latter, sex differences were found in effects of prenatal stress on pain sensitivity. The present data point an important role of 5-HT in: 1) embryonic development of tonic nociceptive system which is modulated in the CNS by mechanisms differing from those of acute pain; 2) mediation of the prenatal stress influence on pain sensitivity in the formalin test in adult rats.