Effects of prenatal ethanol exposure on regulation of basal hypothalamic-pituitary-adrenal activity and hippocampal 5-HT1A receptor mRNA levels in female rats across the estrous cycle

Abstract

Prenatal ethanol exposure, like other early adverse experiences, is known to alter hypothalamic-pituitary-adrenal (HPA) activity in adulthood. The present study examined the modulatory effects of the gonadal hormones on basal HPA regulation and serotonin Type 1A receptor (5-HT(1A)) mRNA levels in adult female rats prenatally exposed to ethanol (E) compared to that in females from pair-fed (PF) and ad libitum-fed control (C) conditions. We demonstrate, for the first time, long-lasting consequences of prenatal ethanol exposure for basal corticosterone (CORT) regulation and basal levels of hippocampal mineralocorticoid (MR), glucocorticoid (GR) and serotonin Type 1A (5-HT(1A)) receptor mRNA, as a function of estrous cycle stage: (1) basal CORT levels were higher in E compared to C females in proestrus but lower in E and PF compared to C females in estrus; (2) there were no differences among groups in basal levels of adrenocorticotropin (ACTH), estradiol or progesterone; (3) hippocampal MR mRNA levels were decreased in E compared to PF and C females across the estrus cycle, with the greatest effects in proestrus, whereas E (but not PF or C) females had higher hippocampal GR mRNA levels in proestrus than in estrous and diestrus; (4) 5-HT(1A) mRNA levels were increased in E compared to PF and C females in diestrus. That alterations were revealed as a function of estrous cycle stage suggests a role for the ovarian steroids in mediating the adverse effects of ethanol. Furthermore, it appears that ethanol-induced nutritional effects may play a role in mediating at least some of the effects observed. The resetting of HPA activity by early environmental events could be one mechanism linking early life experiences with long-term health consequences. Thus, changes in basal CORT levels, a shift in the MR/GR balance and alterations in 5-HT(1A) receptor mRNA could have important clinical implications for understanding the secondary disabilities, such as an increased incidence of depression, in children with FASD.

Figure 1

Basal plasma levels of corticosterone [CORT] (A), adrenocorticotropic hormone [ACTH] (B), estradiol (C) and progesterone (D) in adult females rats prenatally exposed to ethanol (E), pair-fed (PF) and controls (C). Data represents mean ±SEM of 4–22 rats per group. (A) in proestrus: E>C, * p<0.05 and PF>C, trend # p=0.07; in estrus: E=PFdiestrus, **** p<0.00001 and proestrus >estrus, trend # p=0.057; in proestrus PF>C, * p<0.05; for E females only: proestrus>diestrus, * p<0.01; (D) diestrus>estrus=proestrus, *** p<0.001; in proestrus: PF>E=C, * p<0.05.

Figure 2

Autoradiograms represent the in situ hybridization signal within rat hippocampus in adult female rats for: (A) MR mRNA; (B) GR mRNA and (C) 5HT_1A mRNA. Hippocampal subfields: CA1, CA2, CA3 and dentate gyrus - DG.

Figure 3

MR mRNA in the hippocampal subfields (CA1, CA2, CA3 and DG) in adult female rats prenatally exposed to ethanol (E), pair-fed (PF) and controls (C) across the estrous cycle; (A) proestrus; (B) estrus and (C) diestrus. Data represents mean ±SEM of 4–12 brains per group. (A) in proestrus: E

Figure 4

GR mRNA in the hippocampal subfields (CA1, CA2, CA3 and DG) in adult female rats prenatally exposed to ethanol (E), pair-fed (PF) and controls (C) across the estrous cycle; (A) proestrus; (B) estrus and (C) diestrus. Data represents mean ±SEM of 4–12 brains per group. Only in E females GR mRNA levels were higher in proestrus then in estrus in diestrus (proestrus>estrus =diestrus), *p<0.05.

Figure 5

5HT_1A mRNA in the hippocampal subfields (CA1, CA2, CA3 and DG) in adult female rats prenatally exposed to ethanol (E), pair-fed (PF) and controls (C) across the estrous cycle. Data represents mean ± SEM of 4–12 brains per group. (B) estrus: in CA3 and DG: PF>C, *p<0.05 and PF>E, trend p=0.06; (C) in diestrus E>C=PF in CA3, trend # p=0.06 and E>C=PF in DG, * p<0.05.