I.P.Pavlov Institute of Physiology RAS, St. Petersburg, Russia;2St.Petersburg state pediatric medical university, St. Petersburg, Russia; Irinabutkevich@yandex.ru
Interrelations between the serotonergic system and hypothalamo-pituitary-adrenocortical (HPA) axis play an important role in the formation of adaptive mechanisms. Prenatal stress impairs in the offspring the functional activity of the HPA axis and lowers threshold of pain. Activation of 5-HT1A receptors during prenatal period may prevent adverse influence of stress impacts on the raphe nucleus serotoninergic neurons, improving functional activity of stress system. Although glucocorticoids inhibit inflammation and are used for treatment of painful inflammatory reaction, there are a lot of controversial points in relationship between the HPA axis and the nociceptive system. Studies during early ontogeny favour understanding of adaptive mechanisms in adults in conditions of reintegration after noxious influences. The aim of the present work was to investigate effects of injections of buspirone, an agonist of 5-HT1A receptors, to rat dams prior to stress during pregnancy on the dynamics of behavioral nociceptive reaction and stress corticosterone response in the male infant and juvenile offspring in the formalin test. Dams from the 9th day of pregnancy were exposed to chronic injections of buspirone and from the 15th to the 21st days of pregnancy, to restraint stress. Experiments were performed on the offspring at 7, 10 and 14 days of age. Pain-like flexes/shakes patterns were recorded in the formalin test during 60 min. At 3, 9, 21, 30 и 60 min after formalin injection blood samples were collected by decapitation in the rats with different prenatal treatments and in controls for determination of the plasma corticosterone levels by microfluorometry. Additionally, samples of blood were collected for determination of basal corticosterone levels. Prenatal stress was found to cause an increase in pain reaction in the formalin test. The chronic injections of buspirone to rat dams prior to stress during pregnancy normalized the behavioral pain inflammatory reaction in the offspring. Formalin-induced pain increased plasma corticosterone level in animals. Age differences in the dynamics of the tonic nociceptive reaction and stress hormonal response were revealed in conditions of inflammatory pain. The new data obtained enhance the idea about relatività of the HPA axis hyporeactive period, testify that 5-HT1A activation prior to prenatal stress enhances adaptation of the nociceptive system in inflammatory conditions and indicate the age peculiarities in the relationship between the serotonergic system and the HPA axis in male rat pups of infant and juvenile periods of development.
This research was supported by the Russian Foundation for Basic Research No 11-04-01381-a.