Short- and long-term influences of hypoxia during early postnatal period of development on behavioral and hormonal responses in rats.

Hypoxia is a common neonatal stress that leads to essential long-lasting complications in the brain development. The aim of this study was to determine short- and long-term effects of early postnatal hypoxia (on day 7) on depression- and pain-related behaviors and the plasma corticosterone levels. The plasma corticosterone levels increased after 3-h severe hypoxia in 7-day-old rat pups (hypoxic rats) as compared to basal corticosterone in naïve pups and corticosterone levels in pups removed from the experimental chamber without hypoxia (normoxic rats). Adult rats (110-day-old) that were exposed to hypoxia at the postnatal day 7 showed increased corticosterone levels as compared to the basal corticosterone in naïve adult rats. The "direction" of hormonal reaction in response to the forced swimming depended on age and differed in hypoxic and normoxic rats. The forced swimming increased plasma corticosterone in naïve and normoxic adults and decreased in pups but failed to alter it in hypoxic adults and in naïve and normoxic 7-day-old. Thus, short- and long-term effects of early postnatal hypoxia revealed themselves in the decrease of responsiveness of the HPA axis to the forced swimming. The hypoxia reduced the time of immobility in the forced swim test and enhanced pain-related response in pups in the formalin test as compared to these indices in normoxic pups. Hypoxic adult rats demonstrated the increased time of immobility during the forced swim test as compared to immobility in normoxic rats. Early postnatal hypoxia disturbed interrelations between depression- and pain-related indices.