Prenatal Hypoxia Triggers a Glucocorticoid-Associated Depressive-like Phenotype in Adult Rats, Accompanied by Reduced Anxiety in Response to Stress.

Fetal hypoxia and maternal stress frequently culminate in neuropsychiatric afflictions in life. To replicate this condition, we employed a model of prenatal severe hypoxia (PSH) during days 14-16 of rat gestation. Subsequently, both control and PSH rats at 3 months old were subjected to episodes of inescapable stress to induce learned helplessness (LH). The results of the open field test revealed an inclination towards depressive-like behavior in PSH rats. Following LH episodes, control (but not PSH) rats displayed significant anxiety. LH induced an increase in glucocorticoid receptor (GR) levels in extrahypothalamic brain structures, with enhanced nuclear translocation in the hippocampus (HPC) observed both in control and PSH rats. However, only control rats showed an increase in GR nuclear translocation in the amygdala (AMG). The decreased GR levels in the HPC of PSH rats correlated with elevated levels of hypothalamic corticotropin-releasing hormone (CRH) compared with the controls. However, LH resulted in a reduction of the CRH levels in PSH rats, aligning them with those of control rats, without affecting the latter. This study presents evidence that PSH leads to depressive-like behavior in rats, associated with alterations in the glucocorticoid system. Notably, these impairments also contribute to increased resistance to severe stressors.

The Prenatal Hypoxic Pathology Associated with Maternal Stress Predisposes to Dysregulated Expression of the chrna7 Gene and the Subsequent Development of Nicotine Addiction in Adult Offspring.

INTRODUCTION: Previous studies have shown that fetal hypoxia predisposes individuals to develop addictive disorders in adulthood. However, the specific impact of maternal stress, mediated through glucocorticoids and often coexisting with fetal hypoxia, is not yet fully comprehended. METHODS: To delineate the potential effects of these pathological factors, we designed models of prenatal severe hypoxia (PSH) in conjunction with maternal stress and prenatal intrauterine ischemia (PII). We assessed the suitability of these models for our research objectives by measuring HIF1α levels and evaluating the glucocorticoid neuroendocrine system. To ascertain nicotine dependence, we employed the conditioned place aversion test and the startle response test. To identify the key factor implicated in nicotine addiction associated with PSH, we employed techniques such as Western blot, immunohistochemistry, and correlational analysis between chrna7 and nr3c1 genes across different brain structures. RESULTS: In adult rats exposed to PSH and PII, we observed increased levels of HIF1α in the hippocampus (HPC). However, the PSH group alone exhibited reduced glucocorticoid receptor levels and disturbed circadian glucocorticoid rhythms. Additionally, they displayed signs of nicotine addiction in the conditioned place aversion and startle response tests. We also observed elevated levels of phosphorylated DARPP-32 protein in the nucleus accumbens (NAc) indicated compromised glutamatergic efferent signaling. Furthermore, there was reduced expression of α7 nAChR, which modulates glutamate release, in the medial prefrontal cortex (PFC) and HPC. Correlation analysis revealed strong associations between chrna7 and nr3c1 expression in both brain structures. CONCLUSION: Perturbations in the glucocorticoid neuroendocrine system and glucocorticoid-dependent gene expression of chrna7 associated with maternal stress response to hypoxia in prenatal period favor the development of nicotine addiction in adulthood.

Oxidative stress accompanies HIF1-dependent impairment of glucose metabolism in the hippocampus of adult rats survived prenatal severe hypoxia.

INTRODUCTION: Many socially significant diseases are associated with prenatal developmental disorders. Previously, we showed the pathological role of hypoxia-inducible factor HIF1 in post-hypoxic reoxygenation. This study aimed to investigate the effect of prenatal severe hypoxia (PSH) on HIF1α protein expression as well as on HIF1-dependent activity of the pentose phosphate pathway (PPP) and anaerobic glycolysis in the hippocampus (HPC) of offspring that reached adulthood. METHODS: PSH was induced during the critical period of fetal hippocampal formation on gestation days 14-16 in a hypobaric chamber (180 Torr, 5% oxygen, 3 hours). Subsequent studies were conducted on both the HPC of adult control and PSH rats under normal conditions, as well as in response to severe hypobaric hypoxia (SH) or psycho-emotional stress ("learned helplessness" model, LH). We evaluated HIF1α protein levels using both immunohistochemistry and western blotting techniques. The amount of glucose-6-phosphate dehydrogenase (G6PD) was also determined by western blotting. Colorimetric enzymatic assays were employed to analyze enzymatic activity of lactate dehydrogenase (LDH), the concentration of lactate, NADPH, reduced glutathione (GSHred), and malonic dialdehyde (MDA). RESULTS: We showed that PSH caused a stable increase in the content of HIF1α protein in the HPC, which was accompanied by an increase in the efficiency of anaerobic glycolysis. This was confirmed by increased LDH activity and lactate concentration. At the same time, the amounts of G6PD, NADPH, and reduced glutathione decreased in the HPC of PSH rats, whereas the concentration of MDA, an oxidative stress marker, exceeded the control values. In a series of experiments using the LH or SH stress, it was shown that in the HPC of control rats, there was an increase in the amount of HIF1α in response to stress, which was also accompanied by more efficient anaerobic glycolysis and decreased of PPP-dependent NADPH production, similar to the intact PSH rats. In PSH rats, emotional stress resulted in higher HIF1α levels without affecting glycolysis or PPP. CONCLUSION: Therefore, the increased content and activity of the transcription factor HIF1α in the HPC of adult rats exposed to prenatal hypoxia leads to an imbalance between glycolysis and PPP, which is accompanied by oxidative stress.

Prenatal Hypoxia-Induced Adverse Reaction to Mild Stress is Associated with Depressive-Like Changes in the Glucocorticoid System of Rats.

The effects of prenatal hypoxia on neurodevelopment are predominantly associated with impaired maternal glucocorticoid stimulation of the fetus, which is "imprinted" in altered sensitivity of glucocorticoid reception in brain structures of offspring and can affect brain plasticity during lifespan. This study aimed to investigate response of the brain glucocorticoid system to mild stress (MS) in adult rats that survived prenatal severe hypoxia (PSH) on embryonic days 14-16. In response to MS the control (but not PSH) rats demonstrate increased corticosterone levels, a decrease in exploratory activity and increased anxiety. In the raphe nuclei of adult PSH rats the expression of glucocorticoid receptors (GR) is increased without changes in serotonin levels in comparison with the control. MS induces a decrease in GR expression accompanied by up-regulation of tryptophan hydroxylase 2 (tph2) and down-regulation of monoamine oxidase A (maoa) transcription in the raphe nuclei of both control and PSH groups. PSH also causes significant deviations in GR expression and GR-dependent transcription in the hippocampus, the medial prefrontal cortex, but not in the amygdala of rats. However, in response to MS, PSH rats demonstrate mild changes in their activity, while in control animals the MS-induced activity of the glucocorticoid system in these brain structures is similar to intact PSH animals. Impaired activity of the glucocorticoid system in the extrahypothalamic brain structures of PSH rats is accompanied by increase in the hypothalamic corticotropin-releasing hormone (CRH) levels in comparison with the control regardless of MS. Synthesis of proopiomelanocortin (POMC) and release of adrenocorticotropic hormone (ACTH) into the blood are decreased in response to MS in the pituitary of control rats, which demonstrates a negative glucocorticoid feedback mechanism. Meanwhile, in the pituitary of PSH rats reduced POMC levels were found regardless of MS. Thus, prenatal hypoxia causes depression-like patterns in the brain glucocorticoid system with adverse reaction to mild stressors.

Prenatal Hypoxia Affects Nicotine Consumption and Withdrawal in Adult Rats via Impairment of the Glutamate System in the Brain.

The role of damaging factors in the prenatal period as a basis for drug addiction in offspring is of great interest. In this study, we aim at deciphering the effects and possible mechanisms of prenatal severe hypoxia (PSH) on predisposition to nicotine addiction in adult rats. In PSH rats, we found an increasing tendency to nicotine consumption in the two-bottle choice test. After 2 weeks of chronic treatment with nicotine via osmotic minipump (9 mg/kg per day), we assessed the symptoms of withdrawal in the conditioned place aversion test after mecamylamine (an antagonist of nicotinic acetylcholine receptors, nAChR) treatment. We showed that the mecamylamine-precipitated withdrawal aversion was stronger in the PSH group than in the control group. This suggests that PSH acts as a predisposing factor for developing nicotine addiction in adulthood. PSH rats also demonstrated an increased level of phosphorylated DARPP-32 protein (known as the relay for dopamine and glutamate signaling) at 34 threonine (pThr34DARPP-32) in relation to its total amount in the nucleus accumbens of the striatum (NAc). Meanwhile, no changes in both the content of dopamine in the mesolimbic pathway and the first type of dopamine receptors (DAR1) in NAc were found. The increased rate of DARPP-32 phosphorylation in adult PSH rats might result from excessive glutamatergic stimulation of the dopaminergic (DA) neurons of the ventral tegmental area (VTA) caused by activation of presynaptic nAChR by nicotine. This hypothesis is supported by the observed increase in VGluT2-positive terminals to Nurr1-positive neuronal bodies in VTA in PSH animals. Thus, the altered glutamate signaling phenotype might play a significant role in the development of PSH-related nicotine addiction.

Prenatal Hypoxia Induces Premature Aging Accompanied by Impaired Function of the Glutamatergic System in Rat Hippocampus.

Prenatal hypoxia is among leading causes of progressive brain pathologies in postnatal life. This study aimed to analyze the characteristics of the hippocampal glutamatergic system and behavior of rats in early (2 weeks), adult (3 months) and advanced (18 months) postnatal ontogenesis after exposure to prenatal severe hypoxia (PSH, 180 Torr, 5% O2, 3 h) during the critical period in the formation of the hippocampus (days 14-16 of gestation). We have shown an age-dependent progressive decrease in the hippocampal glutamate levels, a decrease of the neuronal cell number in the CA1 hippocampal region, as well as impairment of spatial long-term memory in the Morris water navigation task. The gradual decrease of glutamate was accompanied by decreased expression of the genes that mediate glutamate metabolism and recycling in the hippocampus. That deficiency apparently correlated with an increase of the metabotropic glutamate receptor type 1 (mGluR1) and synaptophysin expression. Generation of the lipid peroxidation products in the hippocampus of adult rats subjected to prenatal severe hypoxia (PSH rats) was not increased compared to the control animals when tested in a model of glutamate excitotoxicity induced by severe hypoxia. This demonstrates that excessive glutamate sensitivity in PSH rats does not compensate for glutamate deficiency. Our results show a significant contribution of the glutamate system dysfunction to age-associated decrease of this mediator, cognitive decline, and early neuronal loss in PSH rats.

Long-Term Effects of Prenatal Severe Hypoxia on Central and Peripheral Components of the Glucocorticoid System in Rats.

INTRODUCTION: Prenatal hypoxia is a risk factor for the development of numerous neurological disorders. It is known that the maternal stress response to hypoxia determines the epigenetic impairment of the perinatal expression of glucocorticoid receptors (GR) in the hippocampus of the progeny, but so far no detailed study of how this affects the functional state of the glucocorticoid system during further ontogenesis has been performed. OBJECTIVE: The goal of the present study was to examine the long-term effects of the prenatal hypoxia on the functioning of the glucocorticoid system throughout life. METHODS: Prenatal severe hypobaric hypoxia (PSH) was induced in the critical period of embryonic hippocampal formation on days 14-16 of gestation in a hypobaric chamber (180 Torr, 5% oxygen, 3 h). The activity of central (hippocampus) and peripheral (liver) components of the glucocorticoid system was assessed in 1-day-old (newborn), 2-week-old (juvenile), 3-month-old (adult), and 18-month-old (aged) male rats. RESULTS: The PSH resulted in continuously elevated baseline corticosterone blood levels in the adult and aged rats. The chronic elevation of the corticosterone levels was accompanied by a progressive deficit of the GR expression in the liver, increased hepatic glycogen content, dysregulated glucose-6-phosphatase activity, and eventually hypoglycemia. Elevated corticosterone appears to result from the impairment of the mechanisms of glucocorticoid negative feedback since a substantial decrease in both the total number of GR and their nuclear localization was observed already in the hippocampus of newborn rat pups and persisted throughout life. Corresponding stable hippocampal downregulation of GR-dependent genes was observed as well. Suppression of the maternal glucocorticoid stress response to hypoxia by metyrapone injection to pregnant rats prior to each hypoxic challenge considerably reduced corticosterone over-response to hypoxia and prevented reduced hippocampal GR. CONCLUSIONS: Our findings demonstrate that in progeny a deficit of hippocampal GR resulting from maternal glucocorticoid response to hypoxia remains stable throughout life and is accompanied by severe disturbances of baseline glucocorticoid levels and its peripheral reception. Negative consequences of PSH can be prevented by injection with an inhibitor of corticosterone synthesis (metyrapone) to pregnant females undergoing hypoxia.