Prenatal stress increases adult vulnerability to cocaine reward without affecting pubertal anxiety or novelty response

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.

A framework for testing pathways from prenatal stress-responsive hormones to cardiovascular disease risk

Cardiovascular disease (CVD) is a leading cause of death globally, with the prevalence projected to keep rising. Risk factors for adult CVD emerge at least as early as the prenatal period. Alterations in stress-responsive hormones in the prenatal period are hypothesized to contribute to CVD in adulthood, but little is known about relations between prenatal stress-responsive hormones and early precursors of CVD, such as cardiometabolic risk and health behaviors. The current review presents a theoretical model of the relation between prenatal stress-responsive hormones and adult CVD through cardiometabolic risk markers (e.g., rapid catch-up growth, high BMI/adiposity, high blood pressure, and altered blood glucose, lipids, and metabolic hormones) and health behaviors (e.g., substance use, poor sleep, poor diet and eating behaviors, and low physical activity levels). Emerging evidence in human and non-human animal literatures suggest that altered stress-responsive hormones during gestation predict higher cardiometabolic risk and poorer health behaviors in offspring. This review additionally highlights limitations of the current literature (e.g., lack of racial/ethnic diversity, lack of examination of sex differences), and discusses future directions for this promising area of research.

Acute hypoxia exposure following prenatal stress impairs hippocampus and novelty-seeking behavior in adolescent rats

OBJECTIVES

The present study aimed to investigate the effects of acute hypoxia exposure following prenatal stress on the novelty-seeking behavior and hippocampus of adolescent rats.

METHODS

The offspring were divided into prenatal stress (PS) and non-stress (NS) groups. Both groups were exposed to hypoxia on postnatal day 10 (P10) while control groups were undisturbed. Novel object recognition task was performed in each group. Next, brains were collected to examine hippocampus via immunohistochemical and biochemical studies on postnatal day 35 (P35).

RESULTS

PS decreased novelty discrimination and synaptophysin (SYN) expressions in both CA1 and CA3 of the hypoxia group prominently (p < 0.05). Nestin-expressing cells were reduced while vascular endothelial growth factor (VEGF) expression was enhanced in the subgranular zone (SGZ) of PS-hypoxia group (p < 0.05). VEGF enhancement triggered angiogenesis in the CA1 and CA3 significantly (p < 0.05). PS also increased thiobarbituric acid reactive substances (TBARS) levels in the hypoxia group as a result of oxidative stress (p < 0.05).

CONCLUSION

These findings demonstrated that PS exacerbates neurodevelopmental deficits in the hippocampus of acute hypoxia-induced offspring in adolescence.

Early-Life Stress Reprograms Stress-Coping Abilities in Male and Female Juvenile Rats

Prenatal stress (PS) is a major risk factor for the development of emotional disorders in adulthood that may be mediated by an altered hypothalamic-pituitary-adrenal axis response to stress. Although the early onset of stress-related disorders is recognized as a major public health problem, to date, there are relatively few studies that have examined the incidence of early-life stressors in younger individuals. In this study, we assessed PS impact on the stress-coping response of juvenile offspring in behavioral tests and in the induced molecular changes in the hippocampus. Furthermore, we assessed if pregnancy stress could be driving changes in patterns of maternal behavior during early lactation. We found that PS modified stress-coping abilities of both sex offspring. In the hippocampus, PS increased the expression of bdnf-IV and crfr1 and induced sex difference changes on glucocorticoids and BDNF mRNA receptor levels. PS changed the hippocampal epigenetic landscape mainly in male offspring. Stress during pregnancy enhanced pup-directed behavior of stressed dams. Our study indicates that exposure to PS, in addition to enhanced maternal behavior, induces dynamic neurobehavioral variations at juvenile ages of the offspring that should be considered adaptive or maladaptive, depending on the characteristics of the confronting environment. Our present results highlight the importance to further explore risk factors that appear early in life that will be important to allow timely prevention strategies to later vulnerability to stress-related disorders.

Prefrontal cortex nicotinic receptor inhibition by methyllycaconitine impaired cocaine-associated memory acquisition and retrieval

Cocaine administration has been shown to induce plastic changes in the medial prefrontal cortex (mPFC), which could represent a mechanism by which cocaine facilitates the association between cocaine rewarding effects with contextual cues. Nicotinic acetylcholine receptors (nAChRs) in the mPFC have critical roles in cognitive function including attention and memory and are key players in plasticity processes. However, whether nAChRs in the mPFC are required for the acquisition and maintenance of cocaine-associated memories is still unknown. To assess this question, we used the conditioning place preference (CPP) model to study the effect of intra-mPFC infusion of methyllycaconitine, a selective antagonist of α7 nAChRs, on the acquisition, consolidation and expression of cocaine-associated memory in adult rats. Our findings reveal that mPFC α7 nAChRs activation is necessary for the acquisition and retrieval, but not consolidation, of cocaine induced CPP. Moreover, cocaine-induced sensitization during CPP conditioning sessions was abolished by methyllycaconitine infusion in the mPFC. Together, these results identify mPFC α7 nAChRs as critical players involved in both acquiring and retrieving cocaine-associated memories. Considering that drug seeking often depends on the association between drug-paired cues and the rewarding effects of the drug, α7 nAChRs in the mPFC could be considered as potential targets for the prevention or treatment of cocaine use disorder.

Strain differences in maternal neuroendocrine and behavioral responses to stress and the relation to offspring cocaine responsiveness

Early life stress exposure, including prenatal stress (PNS), influences subsequent risk for many disorders, including substance abuse, and these effects interact with genetic factors to determine risk for disease. We previously demonstrated gene X environmental interactions across the BXD recombinant inbred mouse strain panel and their progenitor strains in PNS modulation of cocaine-induced reward and locomotion. Critical to dissecting genetic interactions with PNS is consideration of the modes of stress transmission to the offspring. Both maternal neuroendocrine responses during stress and subsequent maternal-offspring interactions following stress may serve as transmission modes for PNS-induced changes in cocaine responsiveness. Therefore, we characterized the maternal stress response by measuring restraint stress-induced plasma corticosterone (CORT) during gestation as well as effects of restraint stress on dam-pup contact in the first 10 postnatal days in BXD and progenitor mouse strains. Restraint stress interacted with strain to affect plasma CORT levels and dam-pup contact, indicating heritable variation of the maternal stress response. Furthermore, strain-level variance in maternal stress response correlated to the impact on cocaine response exhibited by adult offspring. These findings implicate multiple modes of maternal stress response in alterations of offspring drug responsiveness and indicate that assessment of maternal endocrine and behavioral responses during early life can be utilized to dissect the complex intersection of maternal factors, the response of the offspring and genetics.

Discovery of early life stress interacting and sex-specific quantitative trait loci impacting cocaine responsiveness

BACKGROUND AND PURPOSE

Addiction vulnerability involves complex gene X environment interactions leading to a pathological response to drugs. Identification of the genes involved in these interactions is an important step in understanding the underlying neurobiology and rarely have such analyses examined sex-specific influences. To dissect this interaction, we examined the impact of prenatal stress (PNS) on cocaine responsiveness in male and female mice of the BXD recombinant inbred panel.

EXPERIMENTAL APPROACH

BXD strains were subjected to timed mating and assigned to PNS or control groups. PNS dams were subjected to restraint stress (1-hr restraint, three times daily) starting between embryonic day (E) 11 and 14 and continued until parturition. Adult male and female, control and PNS offspring were tested for locomotor response to initial and repeated cocaine injections (sensitization) as well as cocaine-induced conditioned place preference (CPP).

KEY RESULTS

Strain, PNS, and sex interacted to modulate initial and sensitized cocaine-induced locomotion, as well as CPP. Moreover, a quantitative trait locus (QTL) interacting with PNS regulating initial locomotor response to cocaine (chromosome X, 37.91 to 50.95 Mb) was identified. Also PNS-independent, female-specific QTLs regulating CPP (chromosome 11, 65.50 to 81.31 Mb) and sensitized cocaine-induced locomotion (chromosome 16, 95.79 to 98.32 Mb) were identified. Publicly available mRNA expression data were utilized to identify cis-eQTL and transcript covariation with the behavioural phenotype to prioritize candidate genes; including Aifm1.

CONCLUSIONS AND IMPLICATIONS

These QTL encompass genes that may moderate genetic susceptibility to PNS and interact with sex to determine adult responsiveness to cocaine and addiction vulnerability.

LINKED ARTICLES

This article is part of a themed section on The Importance of Sex Differences in Pharmacology Research. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v176.21/issuetoc.

Neuroendocrine and immune pathways from pre- and perinatal stress to substance abuse

Early life adversity is a documented risk factor for substance abuse and addiction. The pre- and perinatal period (i.e., from implantation, through pregnancy, to 6 months of age) is a critical period marked by high biological plasticity and vulnerability, making perinatal stress a particularly robust form of adversity. The neuroendocrine and immune systems are key mechanisms implicated in the transmission of addiction risk. We review animal and human studies that provide preliminary evidence for links between perinatal stress, neuroendocrine and immune dysregulation, and risk for substance abuse and addiction. A translational neuroscience perspective is employed to elucidate pre- and perinatally-induced biological mechanisms linked to addiction and discuss implications for prevention and intervention efforts. Significant evidence supports associations between pre- and perinatal stress and dysregulation of the hypothalamic-pituitary-adrenal axis and immune systems as well as links between neuroendocrine/immune functioning and addiction risk. More work is needed to explicitly examine the interplay between pre- and perinatal stress and neuroendocrine/immune disruptions that together heighten substance abuse risk. Future work is needed to fully understand how pre- and perinatal stress induces biological alterations to predispose individuals to higher risk for addiction. Such knowledge will strengthen theoretically-driven and empirically-supported prevention efforts for substance abuse and addiction.