Prenatal stress and adult drug-seeking behavior: interactions with genes and relation to nondrug-related behavior

Preventive putative effect of agmatine on cognitive and molecular outcomes in ventral tegmental area of male offspring following physical and psychological prenatal stress

Prenatal stress (PS) results from a maternal experience of stressful events during pregnancy, which has been associated with an increased risk of behavioral disorders including substance abuse and anxiety in the offspring. PS is known to result in heightened dopamine release in the ventral tegmental area (VTA), in part through the effects of corticotropin-releasing hormone, which directly excites dopaminergic cells. It has recently been suggested that agmatine plays a role in modulating anxiety-like behaviors. In this study, we investigated whether agmatine could reduce negative cognitive outcomes in male mice prenatally exposed to psychological/physical stress, and whether this could be associated with molecular changes in VTA. Agmatine (37.5 mg/kg) was administrated 30 min prior to PS induction in pregnant Swiss mice. Male offspring were evaluated in a series of behavioral and molecular assays. Findings demonstrated that agmatine reduced the impairment in locomotor activity induced by both psychological and physical PS. Agmatine also decreased heightened conditioned place preference to morphine seen in PS offspring. Moreover, agmatine ameliorated the anxiety-like behavior and drug-seeking behavior induced by PS in the male offspring. Molecular effects were seen in VTA as the enhanced brain-derived neurotrophic factor (BDNF) induced by PS in the VTA was reduced by agmatine. Behavioral tests indicate that agmatine exerts a protective effect on PS-induced impairments in male offspring, which could be due in part to agmatine-associated molecular alterations in the VTA. Taken together, our data suggest that prenatal treatment with agmatine exerts protective effect against negative consequences of PS on the development of affective circuits in the offspring.

Influence of Prevalence of Psychoactive Substance Use in Mexican Municipalities on Early Childhood Development

Children's early development is influenced by characteristics of the child, family, and environment, including exposure to substance abuse. The aim was to examine the association of early childhood development (ECD) with the prevalence of psychoactive substance use in Mexican municipalities. We obtained ECD data from the 2015 Survey of Boys, Girls, and Women (ENIM, for its Spanish acronym), measured with the ECD Index. The prevalence of psychoactive substance use was estimated at the municipal level, using the 2016 National Survey of Drug, Alcohol, and Tobacco Use (ENCODAT, for its Spanish acronym). Multilevel logistic models were fitted to evaluate the association between drug use and inadequacies in ECD overall and in four specific ECD domains: socio-emotional, literacy-numeric, learning, and physical. Inadequate ECD was directly associated with illegal drug use (OR = 1.10; 95% CI: 1.03, 1.17). For the specific ECD domains, inadequate socio-emotional development was directly associated with illegal drug use (OR = 1.08; 95% CI: 1.01, 1.15). These findings suggest that exposure to illegal drug use may influence ECD, and especially can lead to socio-emotional problems, although this cannot be considered the unanimous determinant of the problems presented. The implementation of evidence-based interventions to prevent drug abuse is necessary.

Hyperexcitability of VTA dopaminergic neurons in male offspring exposed to physical or psychological prenatal stress

Prenatal stress (PS) exposure leads to cognitive and behavioral alterations in offspring including an increased risk of substance abuse and anxiety disorders. Signalling from dopamine (DA) neurons of the ventral tegmental area (VTA) in the mesoaccumbal and mesocortical pathways plays a vital role in drug dependency and anxiety behavior. To provide further knowledge about the changes in drug seeking behavior and anxiety behaviors in prenatally stressed mice, we conducted ex vivo investigations in VTA brain slices of adult male PS offspring to evaluate the effects of two types of PS (physical vs. psychological) on activity of DA neurons. Elevated plus maze (EPM) was used to assess anxiety-like behaviors and conditioned place preference (CPP) was used to evaluate drug reinforcing effects in mice. An increased anxiety-like behavior and preference to morphine was observed in prenatally stressed mice. PS VTA DA cells exhibited greater I_h current and a higher frequency and amplitude of sEPSCs, which were consistent with a greater degree of pre- or postsynaptic excitability of the VTA. This was confirmed by lower rheobase and lower firing thresholds in PS VTA neurons, as well as increases in spontaneous firing frequency. When taken together, these data suggest that alterations in VTA DA neurons in this mouse model of prenatal stress might be associated with later life alterations in drug seeking and anxiety-like behaviors through their role in mesocortical and mesoaccumbal pathways.

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.

Negative consequences of early-life adversity on substance use as mediated by corticotropin-releasing factor modulation of serotonin activity

Early-life adversity is associated with increased risk for substance abuse in later life, with women more likely to report past and current stress as a mediating factor in their substance use and relapse as compared to men. Preclinical models of neonatal and peri-adolescent (early through late adolescence) stress all support a direct relationship between experiences of early-life adversity and adult substance-related behaviors, and provide valuable information regarding the underlying neurobiology. This review will provide an overview of these animal models and how these paradigms alter drug and alcohol consumption and/or seeking in male and female adults. An introduction to the corticotropin-releasing factor (CRF) and serotonin systems, their development and their interactions at the level of the dorsal raphe will be provided, illustrating how this particular stress system is sexually dimorphic, and is well positioned to be affected by stressors early in development and throughout maturation. A model for CRF-serotonin interactions in the dorsal raphe and how these influence dopaminergic activity within the nucleus accumbens and subsequent reward-associated behaviors will be provided, and alterations to the activity of this system following early-life adversity will be identified. Overall, converging findings suggest that early-life adversity has long-term effects on the functioning of the CRF-serotonin system, highlighting a potentially important and targetable mediator linking stress to addiction. Future work should focus on identifying the exact mechanisms that promote long-term changes to the expression and activity of CRF receptors in the dorsal raphe. Moreover, it is important to clarify whether similar neurobiological mechanisms exist for males and females, given the sexual dimorphism both in CRF receptors and serotonin indices in the dorsal raphe and in the behavioral outcomes of early-life adversity.

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Early life stress increases risk for substance abuse in adulthood.

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Stress and drugs increase CRF which alters serotonin release in the brain.

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CRF₂ receptor expression in the dorsal raphe is altered by early life stress.

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Resultant changes to serotonin output facilitates dopamine in the accumbens.

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CRF₂-sertotonin-dopamine interactions may link early life stress with substance abuse.

Prenatal stress and genetic risk: How prenatal stress interacts with genetics to alter risk for psychiatric illness

Risk for neuropsychiatric disorders is complex and includes an individual's internal genetic endowment and their environmental experiences and exposures. Embryonic development captures a particularly complex period, in which genetic and environmental factors can interact to contribute to risk. These environmental factors are incorporated differently into the embryonic brain than postnatal one. Here, we comprehensively review the human and animal model literature for studies that assess the interaction between genetic risks and one particular environmental exposure with strong and complex associations with neuropsychiatric outcomes-prenatal maternal stress. Gene-environment interaction has been demonstrated for stress occurring during childhood, adolescence, and adulthood. Additional work demonstrates that prenatal stress risk may be similarly complex. Animal model studies have begun to address some underlying mechanisms, including particular maternal or fetal genetic susceptibilities that interact with stress exposure and those that do not. More specifically, the genetic underpinnings of serotonin and dopamine signaling and stress physiology mechanisms have been shown to be particularly relevant to social, attentional, and internalizing behavioral changes, while other genetic factors have not, including some growth factor and hormone-related genes. Interactions have reflected both the diathesis-stress and differential susceptibility models. Maternal genetic factors have received less attention than those in offspring, but strongly modulate impacts of prenatal stress. Priorities for future research are investigating maternal response to distinct forms of stress and developing whole-genome methods to examine the contributions of genetic variants of both mothers and offspring, particularly including genes involved in neurodevelopment. This is a burgeoning field of research that will ultimately contribute not only to a broad understanding of psychiatric pathophysiology but also to efforts for personalized medicine.

Sex differences in prenatal stress effects on cocaine pursuit in rats

Disruption of early-life ontogeny has severe and persistent consequences for the health of the developing organism. Both clinical and preclinical findings indicate that such interference can be caused by maternal stress during the gestation period (prenatal stress [PS]). In rats, PS facilitates the rewarding and neurochemical-stimulating effects of drugs, suggesting that PS may represent a risk factor for drug abuse in humans. Very little, however, is known about its effects in females, even though sex differences in drug susceptibility have been well documented in no PS (NPS) controls. Thus, we tested for independent effects and interactions between maternal restraint stress during the last week of gestation and sex on drug use with an extended regimen of drug self-administration. Male and female rats were provided daily access to a large but controlled amount of cocaine for seven weeks. Drug pursuit during the final week was used to indicate susceptibility to developing an addiction-like phenotype, based on reports that drug use becomes increasingly compulsive-like after weeks of testing. Overall, females satisfied more addiction-like criteria than males, and the same was true for PS rats when compared to NPS controls. In addition, sex and PS interacted to disproportionately promote drug pursuit of females with a history of PS. These results indicate that sex differences in drug susceptibility persist with continued drug exposure, and that PS widens this difference by more severely affecting females. In all, PS may be a risk factor for drug addiction in humans, and to a greater extent in women vs. men.

Cocaína durante la gestación y conducta materna postparto en ratones

El abuso materno de cocaína durante la gestación se relaciona con negligencia, maltrato y perturbación del vínculo madre- hijo, lo que incide directamente en el desarrollo de los infantes; por esto, las diversas problemáticas neuroconductuales de los hijos de padres drogodependientes podrían atribuirse a la inadecuada conducta materna o a la exposición prenatal a la droga. El objetivo de esta investigación fue analizar los efectos de la administración crónica de cocaína durante la gestación en la conducta materna postparto de ratones. Para esto se asignaron aleatoriamente 21 ratones CD1 hembras gestantes para la administración de solución salina y cocaína (25 mg/kg/día y 50 mg/kg/día), desde el octavo hasta el día veintiuno de gestación. Después del parto, durante 20 días (15 minutos diarios), se registró individualmente la frecuencia de presentación de 16 índices de conducta materna mediante un etograma. Se encontró que la cocaína afectó levemente la frecuencia de la conducta materna, aunque posiblemente afecte otros parámetros como la latencia, duración y secuencia de esta conducta.  

Influences of prenatal and postnatal stress on adult hippocampal neurogenesis: the double neurogenic niche hypothesis

Adult hippocampal neurogenesis (AHN) is involved in learning, memory, and stress, and plays a significant role in neurodegenerative and psychiatric disorders. As an age-dependent process, AHN is largely influenced by changes that occur during the pre- and postnatal stages of brain development, and constitutes an important field of research. This review examines the current knowledge regarding the regulators of AHN and the influence of prenatal and postnatal stress on later AHN. In addition, a hypothesis is presented suggesting that each kind of stress influences a specific neurogenic pool, developmental or postnatal, that later becomes a precursor with important repercussions for AHN. This hypothesis is referred to as "the double neurogenic niche hypothesis." Discovering what receptors, transcription factors, or genes are specifically activated by different stressors is proposed as an essential line of future research in the field. Such knowledge shall constitute an important starting point toward the goal of modifying AHN in neurodegenerative or psychiatric diseases.