Effects of prenatal ethanol exposure on cognition/behavior and hypothalamic-pituitary-adrenal stress response in adult rats
Creators: name: Kim, Chang Kwon
Publisher: name: University of British Columbia
Year: 2009

description: The maternal consumption of alcohol during pregnancy produces a wide range of abnormalities in the offspring. The main purpose of this thesis was to investigate the (1) cognitive deficits and behavioral abnormalities and (2) hypothalamic-pituitary-adrenal (HPA) stress hyperresponsiveness produced by prenatal ethanol exposure. Sprague-Dawley rats from prenatal ethanol (E), pair-fed (PF) and ad libitum fed control (C) treatment groups were tested as adults. The purpose of the first study was to assess the effects of prenatal ethanol exposure on cognitive and behavioral function. Two memory tasks that placed different cognitive demands on the subject were used: the object-recognition nonrecurring-items delayed-nonmatching-tosample (DNMS) task and the spatial-navigation Morris water maze task. There were no significant effects of prenatal ethanol exposure in performance of the DNMS task at retention delays ranging from 4 to 300 s, or in reacquisition of the task following a 10 week rest period. Furthermore, prenatal ethanol exposure did not produce significant increases in distractibility or response perseveration in the DNMS apparatus. However, when the same rats were tested on the water maze task, prenatal ethanol exposure produced performance deficits. E rats took significantly longer than PF and C rats to find the submerged platform over the course of the training sessions. There are two likely explanations for the differences in performance on these two tasks, that are not mutually exclusive. First, the brain areas underlying spatial cognitive abilities may be more vulnerable to the teratogenic effects of prenatal ethanol exposure than those underlying object-recognition abilities. Second, E animals, which display HPA hyperresponsiveness to stressors, may be differentially responsive to the stress involved in performance of these two tasks. The main purpose of the second study was to determine the mechanism of HPA hyperresponsiveness produced by prenatal ethanol exposure. It tested the hypothesis that decreased corticosteroid receptor densities at HPA feedback sites may be responsible, at least partially, for the deficient feedback inhibition and resultant HPA hyperresponsiveness produced by prenatal ethanol exposure. Densities of both types of corticosteroid receptors, the glucocorticoid receptor (GR) and mineralocorticoid receptor (MR), were measured at the hippocampus, prefrontal cortex, hypothalamus, and anterior pituitary. Furthermore, differential downregulation of corticosteroid receptors following one of two intermittent chronic stress regimens (two of six stressors daily for 18 days), and differential upregulation of receptors 7 days following adrenalectomy (ADX) compared to that at the usual 24 h were examined. Prenatal ethanol exposure did not produce changes in basal or nonstressed corticosteroid receptor densities, nor differentially downregulate hippocampal GRs under conditions of the more stressful Stress Regimen I, or differentially upregulate hippocampal GRs 7 days following ADX. However, there were small changes in hippocampal GRs among E, PF and C rats under the conditions of the milder Stress Regimen II. Given the nature of these changes in receptor densities, however, it would appear that these changes do not play a critical role in mediating the feedback deficits. Thus, the hypothesis that decreased corticosteroid receptor densities, as measured by the whole site cytosolic binding assay, underlie the deficits in feedback inhibition and resultant HPA hyperresponsiveness following prenatal ethanol exposure was not supported. The main purpose of the third study was to test the hypothesis that prenatal ethanol exposure would produce HPA hyperresponsiveness to chronic cold stress (4 °C for 0, 1 and 3 days), and increased sensitization to a novel acute stressor (IP isotonic saline injection) superimposed during the chronic cold stress. Exposure to cold stress resulted in elevated corticosterone (CORT) levels in E males, and elevated adrenocorticotropin (ACTH) levels in E males and females. However, prenatal ethanol exposure did not increase sensitization to the acute stressor, nor affect corticotropin-releasing factor (CRF) and vasopressin (VP) mRNA levels in the parvocellular nucleus (PVN) of the hypothalamus under basal conditions or following chronic cold stress. Thus, although prenatal ethanol exposure produced HPA hyperresponsiveness, it was not observed at all levels of the HPA axis examined or under all experimental conditions. This study extends the finding of HPA hyperresponsiveness following prenatal ethanol exposure to chronic cold stress. This study was also a preliminary exploration of the effects of prenatal ethanol exposure on the hypothalamic-pituitary-thyroid (HPT) response to chronic cold stress. Cold stress increased TRH mRNA levels in both males and females, but there were no signifcant differences among the E, PF and C groups. In addition, a fourth study of this thesis made an important methodological point regarding the use of the gel filtration technique using Sephadex gel beads. Gel filtration is a commonly used method to separate particles based on molecular size, and was used in the corticosteroid receptor assay (second study of this thesis). The measured receptor densities were significantly higher with previously used gel columns compared to new gel columns, and the measured densities became stable after just one use of the columns. The change in measured densities between new versus used gel columns is sizable enough to produce serious confounding of experimental results if attention is not given to whether new or used gel columns are used. It is possible that this feature of Sephadex gel filtration beads may generalize to other types of gel filtration systems.