Effect of prenatal stress upon parameters of the behavioral response induced by a tonic pain focus in male and female rats during postnatal ontogenesis

The long-term effects of prenatal stress (immobilization of females during the last week of pregnancy) were studied on pain sensitivity to a prolonged irritant in Wistar rats during prepubertal, pubertal periods of development and in adults. Pain sensitivity was evaluated from indices of the biphasic behavioral response in the classical formalin test--the intensity of patterns of flexes, shakes and time spent licking, and from duration of the first, acute and the second, tonic phases and from the duration of interphase. Consequences of the prenatal stress manifested themselves differently in the patterns of the response organized at the spinal and supraspinal levels, during tonic phase mainly, differently in females and males; there were peculiarities of effects of prenatal stress in each age period. The data obtained suggest that the consequences of the prenatal stress at the spinal level manifest themselves in activation of modulating descending facilitating and in suppression of inhibitory monoaminergic systems in prepubertal and pubertal rats, and on the contrary, in activation of descending inhibitory and suppression of facilitating systems in adults. Furthermore, considerable evidence is obtained corroborating the idea of inhibitory nature of the interphase and the mechanisms of modulation of acute and tonic phases in the formalin test during different age periods of the individual development.