The effects of prenatal stress on alpha4 beta2 and alpha7 hippocampal nicotinic acetylcholine receptor levels in adult offspring

Abstract

Prenatal stress in humans is associated with psychiatric problems in offspring such as anxiety, depression, and schizophrenia. These same illnesses are also associated with neuronal nicotinic acetylcholine receptor (nAChR) dysfunction. Despite the known associations between prenatal stress exposure and offspring mental illness, and between mental illness and nAChR dysfunction, it is not known whether prenatal stress exposure impacts neuronal nAChRs. Thus, we tested the hypothesis that maternal stress alters the development of hippocampal alpha4 beta2 (α4β2∗) and alpha7 (α7∗) nicotinic receptor levels in adult offspring. Female Sprague-Dawley rats experienced unpredictable variable stressors two to three times daily during the last week of gestation. At weaning (21 days) the offspring of prenatally stressed (PS) and nonstressed (NS) dams were assigned to same-sex PS or NS groups. In young adulthood (56 days), the brains of offspring were collected and adjacent sections processed for quantitative autoradiography using [125I]-epibatidine (α4β2* nicotinic receptor-selective) and [125I]-α-bungarotoxin (α-BTX; α7* nicotinic receptor-selective) ligands. We found that PS significantly increased hippocampal α4β2* nAChRs of males and females in all subfields analyzed. In contrast, only females showed a trend toward PS-induced increases in α7* nAChRs in the dentate gyrus. Interestingly, NS females displayed a significant left-biased lateralization of α7* nAChRs in the laconosum moleculare of area CA1, whereas PS females did not, suggesting that PS interfered with normal lateralization patterns of α7* nAChRs during development. Taken together, our results suggest that PS impacts the development of hippocampal nAChRs, which may be an important link between PS exposure and risk for neuropsychiatric illness.

Keywords: acetylcholine; alpha-bungarotoxin; alpha4 beta2; alpha7; anxiety; asymmetry; depression; epibatidine; gestation; hippocampus; lateralization; maternal; memory; nicotinic; prenatal stress; psychopathology; stress.

Figure 1

Representative photomicrograph of adjacent 12 µm hippocampal sections exposed to (A) I125-epibatadine for visualization of α4β2* nAChRs, and (B) I125-α-bungarotoxin for visualization of α7* nAChRs. (A) Epibatidine binding was found in the alveus, lacunosum moleculare of the CA1 (LMol CA1), lacunosum moleculare of the CA3 (LMol CA3), and the molecular layer of the dentate gyrus (MoDG). (B) a-BTX binding was highest in the CA1, lacunosum moleculare of the CA1 (LMol CA1), the molecular layer of the dentate gyrus (Mo DG), the polymorphic layer of the dentate gyrus (PoDG), and the CA3.

Figure 2

Prenatal stress increases α4β2* nicotinic acetylcholine receptor levels in the hippocampus. Prenatal stress significantly increased epibatidine binding in the following hippocampal subfields: lacunosum moleculare of the CA1 (LMol CA1), lacunosum moleculare of the CA3 (LMol CA3), and the molecular layer of the dentate gyrus (MoDG). No effects of sex or interactions between sex and stress condition were detected. Data expressed as mean ± SEM. Asterisk (*) indicates a significant difference between stressed and nonstressed groups (*p<0.05, **p<0.01, ***p<0.001).

Figure 3

Representative photomicrograph depicting the difference in hippocampal epibatadine binding intensity between prenatally stressed (A) and nonstressed (B) animals.

Figure 4

Prenatal stress and brain hemisphere influence α7* nicotinic acetylcholine receptor levels in the CA1. (A) Lacunosum moleculare of the CA1 (LMol CA1). A significant interaction between brain hemisphere and stress condition was detected such that a significant left-biased lateralization of α-bungarotoxin binding was present in nonstressed (NS) but not prenatally stressed (PS) females. (B) CA1 remaining layers. Both males and females displayed a significant left-biased lateralization of α-bungarotoxin binding. No interactions between brain hemisphere and stress condition were detected for either sex. Data expressed as mean ± SEM. Asterisk (*) indicates a significant difference between left and right hemispheres (**p<0.01, ***p<0.001).

Figure 5

Prenatal stress increases female α7* nicotinic acetylcholine receptor levels in the molecular layer of the dentate gyrus (MoDG) and polymorphic layer of the dentate gyrus (PoDG). (A&B) A trend toward a prenatal stress-induced increase in α-BTX binding was observed in the MoDG and PoDG of females but not males. No effects of brain hemisphere or interactions between brain hemisphere and stress condition were observed in either region. (C) Neither brain hemisphere nor stress condition influenced α-BTX binding in the CA3. Data expressed as mean ± SEM. Cross (†) indicates a difference between prenatally stressed (PS) and nonstressed (NS) females (p<0.1).