Gestational hypoxia alone or combined with restraint sensitizes the hypothalamic-pituitary-adrenal axis and induces anxiety-like behavior in adult male rat offspring

We have reported that hypoxia affects the hypothalamic-pituitary-adrenal (HPA) axis and behavior by driving the expression of central corticotropin-releasing hormone (CRH) and its receptors in adult mammals, and this effect is modulated by other factors. Here, we address whether or not intermittent hypoxia (IH) or restraint (R) or a combination of both (IH+R) during gestation would result in differential alteration of the HPA axis and behavior of the adult male offspring. Gravid rats were exposed to IH in a hypobaric chamber (10.8% O2, altitude of 5 km), R, or both, daily for 4 h for 21 days. Control parameters were set at sea level (20.9% O2). All the stressors significantly and differentially increased CRH and corticotropin-releasing factor receptor type 1 (CRHR1) expression but decreased corticotropin-releasing factor receptor type 2 (CRHR2) in the paraventricular nucleus of the hypothalamus (PVN), enhanced CRHR1 mRNA and CRHR2 mRNA expression in the anterior pituitary, and increased plasma adrenocorticotropic hormone (ACTH) and corticosterone (CORT) levels and adrenal weight in adult male offspring aged 120 days. Furthermore, norepinephrine (NE) and dopamine (DA) levels significantly increased in the locus coeruleus (LC), while the percentage of entries into the open arms of the elevated-plus maze test (EPM) markedly declined. In all the above effects, the combination-induced effect was stronger than each stressor alone. Confocal imaging showed a rich colocalization of CRHR1 with CRH or urocortin I (Ucn I), and CRHR2 with CRH or urocortin III (Ucn III) in the PVN, and CRHR1 with CRH in the LC in EPM-tested groups. In conclusion, IH or R alone or both in combination during gestation sensitize the HPA axis and induce anxiety-like behavior of the adult male offspring, and the combined effects are significantly great than IH or R alone. The CRH-NE neural circuit between the PVN and LC through CRH receptor driving might partly be involved in the effects. The differential colocalization of CRH with CRHR1 might be the neural basis of these effects.