Prenatal Opioid Exposure Enhances Responsiveness to Future Drug Reward and Alters Sensitivity to Pain: A Review of Preclinical Models and Contributing Mechanisms

Neurobehavioral Characterization of Perinatal Oxycodone-Exposed Offspring in Early Adolescence

The opioid epidemic has received considerable attention, but the impact on perinatal opioid-exposed (POE) offspring remains underexplored. This study addresses the emerging public health challenge of understanding and treating POE children. We examined two scenarios using preclinical models: offspring exposed to oxycodone (OXY) in utero (IUO) and acute postnatal OXY (PNO). We hypothesized exposure to OXY during pregnancy primes offspring for neurodevelopmental deficits and severity of deficits is dependent on timing of exposure. Notable findings include reduced head size and brain weight in offspring. Molecular analyses revealed significantly lower levels of inflammasome-specific genes in the prefrontal cortex (PFC). Gene Set Enrichment Analysis (GSEA) and Ingenuity Pathway Analysis (IPA) highlighted the enrichment of genes associated with mitochondrial and synapse dysfunction in POE offspring. Western blot analysis validated IPA predictions of mitochondrial dysfunction in PFC-derived synaptosomes. Behavioral studies identified significant social deficits in POE offspring. This study presents the first comparative analysis of acute PNO- and IUO-offspring during early adolescence finding acute PNO-offspring have considerably greater deficits. The striking difference in deficit severity in acute PNO-offspring suggests that exposure to opioids in late pregnancy pose the greatest risk for offspring well-being.

The impact of abstinence from chronic alcohol consumption on the mouse striatal proteome: sex and subregion-specific differences

Alcohol misuse is the third leading preventable cause of death in the world. The World Health Organization currently estimates that 1 in 20 deaths are directly alcohol related. One of the ways in which consuming excessive levels of alcohol can both directly and indirectly affect human mortality and morbidity, is through chronic inflammation. Recently, studies have suggested a link between increased alcohol use and the incidence of neuroinflammatory-related diseases. However, the mechanism in which alcohol potentially influences neuroinflammatory processes is still being uncovered. We implemented an unbiased proteomics exploration of alcohol-induced changes in the striatum, with a specific emphasis on proteins related to inflammation. The striatum is a brain region that is critically involved with the progression of alcohol use disorder. Using mass spectrometry following voluntary alcohol self-administration in mice, we show that distinct protein abundances and signaling pathways in different subregions of the striatum are disrupted by chronic exposure to alcohol compared to water drinking control mice. Further, in mice that were allowed to experience abstinence from alcohol compared to mice that were non-abstinent, the overall proteome and signaling pathways showed additional differences, suggesting that the responses evoked by chronic alcohol exposure are dependent on alcohol use history. To our surprise we did not find that chronic alcohol drinking or abstinence altered protein abundance or pathways associated with inflammation, but rather affected proteins and pathways associated with neurodegeneration and metabolic, cellular organization, protein translation, and molecular transport processes. These outcomes suggest that in this drinking model, alcohol-induced neuroinflammation in the striatum is not a primary outcome controlling altered neurobehavioral function, but these changes are rather mediated by altered striatal neuronal structure and cellular health.

GABA system as the cause and effect in early development

GABA is the primary inhibitory neurotransmitter in the adult brain and through its actions on GABAARs, it protects against excitotoxicity and seizure activity, ensures temporal fidelity of neurotransmission, and regulates concerted rhythmic activity of neuronal populations. In the developing brain, the development of GABAergic neurons precedes that of glutamatergic neurons and the GABA system serves as a guide and framework for the development of other brain systems. Despite this early start, the maturation of the GABA system also continues well into the early postnatal period. In this review, we organize evidence around two scenarios based on the essential and protracted nature of GABA system development: 1) disruptions in the development of the GABA system can lead to large scale disruptions in other developmental processes (i.e., GABA as the cause), 2) protracted maturation of this system makes it vulnerable to the effects of developmental insults (i.e., GABA as the effect). While ample evidence supports the importance of GABA/GABAAR system in both scenarios, large gaps in existing knowledge prevent strong mechanistic conclusions.

Pharmacogenetic landscape of pain management variants among Mediterranean populations

Background

Chronic pain is a major socioeconomic burden in the Mediterranean region. However, we noticed an under-representation of these populations in the pharmacogenetics of pain management studies. In this context, we aimed 1) to decipher the pharmacogenetic variant landscape among Mediterranean populations compared to worldwide populations in order to identify therapeutic biomarkers for personalized pain management and 2) to better understand the biological process of pain management through in silico investigation of pharmacogenes pathways.

Materials and Methods

We collected genes and variants implicated in pain response using the Prisma guidelines from literature and PharmGK database. Next, we extracted these genes from genotyping data of 829 individuals. Then, we determined the variant distribution among the studied populations using multivariate (MDS) and admixture analysis with R and STRUCTURE software. We conducted a Chi2 test to compare the interethnic frequencies of the identified variants. We used SNPinfo web server, miRdSNP database to identify miRNA-binding sites. In addition, we investigated the functions of the identified genes and variants using pathway enrichment analysis and annotation tools. Finally, we performed docking analysis to assess the impact of variations on drug interactions.

Results

We identified 63 variants implicated in pain management. MDS analysis revealed that Mediterranean populations are genetically similar to Mexican populations and divergent from other populations. STRUCTURE analysis showed that Mediterranean populations are mainly composed of European ancestry. We highlighted differences in the minor allele frequencies of three variants (rs633, rs4680, and rs165728) located in the COMT gene. Moreover, variant annotation revealed ten variants with potential miRNA-binding sites. Finally, protein structure and docking analysis revealed that two missense variants (rs4680 and rs6267) induced a decrease in COMT protein activity and affinity for dopamine.

Conclusion

Our findings revealed that Mediterranean populations diverge from other ethnic groups. Furthermore, we emphasize the importance of pain-related pathways and miRNAs to better implement these markers as predictors of analgesic responses in the Mediterranean region.

Developmental outcomes with perinatal exposure (DOPE) to prescription opioids

Researchers have found considerable evidence in the past 20 years that perinatal opioid exposure leads to an increased risk of developmental disorders in offspring that persist into adulthood. The use of opioids to treat pain concerning pregnancy, delivery, and postpartum complications has been rising. As a result, communities have reported a 300-400 % increase in Neonatal Opioid Withdrawal Syndrome (NOWS). NOWS represents the initial stage of several behavioral, phenotypic, and synaptic deficits. This review article summarizes the Developmental Outcomes of Perinatal Exposure (DOPE) to prescription opioids. Moreover, we also seek to connect these findings to clinical research that describes DOPE at multiple stages of life. Since specific mechanisms that underlie DOPE remain unclear, this article aims to provide a framework for conceptualizing across all ages and highlight the implications they may have for longevity.

Perigestational Opioid Exposure Alters Alcohol-Driven Reward Behaviors in Adolescent Rats

Every fifteen minutes, a baby is born in the U.S. experiencing neonatal opioid withdrawal syndrome (NOWS). Since 2004, the rate of NOWS has increased 7-fold. Clinical studies have established intrauterine exposure to drugs of abuse as a risk factor for adverse health outcomes in adult life, including the propensity for future illicit drug use. Despite extensive knowledge about common mechanisms of action in the neural circuitry that drives opioid and alcohol reward, there is little data on the risks that those born with NOWS face regarding alcohol use later in life. Here, we investigate the impact of perigestational opioid exposure (POE) on the mesolimbic reward system of male and female Sprague Dawley rats at postnatal and adolescent ages. Our laboratory has developed a clinically relevant model for morphine exposure spanning pre-conception to the first week of life. Using this model, we found that POE increased alcohol consumption in female rats under noncontingent conditions, and inversely, reduced alcohol consumption in both male and female rats during operant conditioning sessions. Operant responding was also reduced for sucrose, suggesting that the impact of POE on reward-seeking behaviors is not limited to drugs of abuse. Expression of µ-opioid receptors was also significantly altered in the nucleus accumbens and medial habenula, regions previously shown to play a significant role in reward/aversion circuitry.

Significance Statement

Early life exposure to opioids is known to alter future drug behavior in rats. In the present study, female rats exposed to morphine via their mothers throughout and after pregnancy exhibited increased alcohol consumption when allowed to consume freely. During operant conditioning, however, male and female rats exposed to gestational morphine decreased consumption of alcohol as well as sucrose. We also observed that gestational morphine exposure altered µ-opioid receptor expression in reward-related brain regions. Our study provides the first evidence of changes in alcohol-directed reward behavior in a gestational opioid exposure rat model.

Prenatal heroin exposure alters brain morphology and connectivity in adolescent mice

The United States is experiencing a dramatic increase in maternal opioid misuse and, consequently, the number of individuals exposed to opioids in utero. Prenatal opioid exposure has both acute and long-lasting effects on health and wellbeing. Effects on the brain, often identified at school age, manifest as cognitive impairment, attention deficit, and reduced scholastic achievement. The neurobiological basis for these effects is poorly understood. Here, we examine how in utero exposure to heroin affects brain development into early adolescence in a mouse model. Pregnant C57BL/6J mice received escalating doses of heroin twice daily on gestational days 4-18. The brains of offspring were assessed on postnatal day 28 using 9.4 T diffusion MRI of postmortem specimens at 36 μm resolution. Whole-brain volumes and the volumes of 166 bilateral regions were compared between heroin-exposed and control offspring. We identified a reduction in whole-brain volume in heroin-exposed offspring and heroin-associated volume changes in 29 regions after standardizing for whole-brain volume. Regions with bilaterally reduced standardized volumes in heroin-exposed offspring relative to controls include the ectorhinal and insular cortices. Regions with bilaterally increased standardized volumes in heroin-exposed offspring relative to controls include the periaqueductal gray, septal region, striatum, and hypothalamus. Leveraging microscopic resolution diffusion tensor imaging and precise regional parcellation, we generated whole-brain structural MRI diffusion connectomes. Using a dimension reduction approach with multivariate analysis of variance to assess group differences in the connectome, we found that in utero heroin exposure altered structure-based connectivity of the left septal region and the region that acts as a hub for limbic regulatory actions. Consistent with clinical evidence, our findings suggest that prenatal opioid exposure may have effects on brain morphology, connectivity, and, consequently, function that persist into adolescence. This work expands our understanding of the risks associated with opioid misuse during pregnancy and identifies biomarkers that may facilitate diagnosis and treatment.

Prenatal methadone exposure selectively alters protein expression in primary motor cortex: Implications for synaptic function

As problematic opioid use has reached epidemic levels over the past 2 decades, the annual prevalence of opioid use disorder (OUD) in pregnant women has also increased 333%. Yet, how opioids affect the developing brain of offspring from mothers experiencing OUD remains understudied and not fully understood. Animal models of prenatal opioid exposure have discovered many deficits in the offspring of prenatal opioid exposed mothers, such as delays in the development of sensorimotor function and long-term locomotive hyperactivity. In attempt to further understand these deficits and link them with protein changes driven by prenatal opioid exposure, we used a mouse model of prenatal methadone exposure (PME) and preformed an unbiased multi-omic analysis across many sensoriomotor brain regions known to interact with opioid exposure. The effects of PME exposure on the primary motor cortex (M1), primary somatosensory cortex (S1), the dorsomedial striatum (DMS), and dorsolateral striatum (DLS) were assessed using quantitative proteomics and phosphoproteomics. PME drove many changes in protein and phosphopeptide abundance across all brain regions sampled. Gene and gene ontology enrichments were used to assess how protein and phosphopeptide changes in each brain region were altered. Our findings showed that M1 was uniquely affected by PME in comparison to other brain regions. PME uniquely drove changes in M1 glutamatergic synapses and synaptic function. Immunohistochemical analysis also identified anatomical differences in M1 for upregulating the density of glutamatergic and downregulating the density of GABAergic synapses due to PME. Lastly, comparisons between M1 and non-M1 multi-omics revealed conserved brain wide changes in phosphopeptides associated with synaptic activity and assembly, but only specific protein changes in synapse activity and assembly were represented in M1. Together, our studies show that lasting changes in synaptic function driven by PME are largely represented by protein and anatomical changes in M1, which may serve as a starting point for future experimental and translational interventions that aim to reverse the adverse effects of PME on offspring.

Effects of prenatal opioid exposure on synaptic adaptations and behaviors across development

In this review, we focus on prenatal opioid exposure (POE) given the significant concern for the mental health outcomes of children with parents affected by opioid use disorder (OUD) in the view of the current opioid crisis. We highlight some of the less explored interactions between developmental age and sex on synaptic plasticity and associated behavioral outcomes in preclinical POE research. We begin with an overview of the rich literature on hippocampal related behaviors and plasticity across POE exposure paradigms. We then discuss recent work on reward circuit dysregulation following POE. Additional risk factors such as early life stress (ELS) could further influence synaptic and behavioral outcomes of POE. Therefore, we include an overview on the use of preclinical ELS models where ELS exposure during key critical developmental periods confers considerable vulnerability to addiction and stress psychopathology. Here, we hope to highlight the similarity between POE and ELS on development and maintenance of opioid-induced plasticity and altered opioid-related behaviors where similar enduring plasticity in reward circuits may occur. We conclude the review with some of the limitations that should be considered in future investigations. This article is part of the Special Issue on 'Opioid-induced addiction'.

Perinatal Morphine Exposure Leads to Sex-Dependent Executive Function Deficits and Microglial Changes in Mice

Children exposed prenatally to opioids are at an increased risk for behavioral problems and executive function deficits. The prefrontal cortex (PFC) and amygdala (AMG) regulate executive function and social behavior and are sensitive to opioids prenatally. Opioids can bind to toll-like receptor 4 (TLR4) to activate microglia, which may be developmentally important for synaptic pruning. Therefore, we tested the effects of perinatal morphine exposure on executive function and social behavior in male and female mouse offspring, along with microglial-related and synaptic-related outcomes. Dams were injected once daily subcutaneously with saline (n = 8) or morphine (MO; 10 mg/kg; n = 12) throughout pregestation, gestation, and lactation until offspring were weaned on postnatal day 21 (P21). Male MO offspring had impairments in attention and accuracy in the five-choice serial reaction time task, while female MO offspring were less affected. Targeted gene expression analysis at P21 in the PFC identified alterations in microglial-related and TLR4-related genes, while immunohistochemical analysis in adult brains indicated decreased microglial Iba1 and phagocytic CD68 proteins in the PFC and AMG in males, but females had an increase. Further, both male and female MO offspring had increased social preference. Overall, these data demonstrate male vulnerability to executive function deficits in response to perinatal opioid exposure and evidence for disruptions in neuron-microglial signaling.

Alterations of brain microstructures in a mouse model of prenatal opioid exposure detected by diffusion MRI

Growing opioid use among pregnant women is fueling a crisis of infants born with prenatal opioid exposure. A large body of research has been devoted to studying the management of opioid withdrawal during the neonatal period in these infants, but less substantive work has explored the long-term impact of prenatal opioid exposure on neurodevelopment. Using a translationally relevant mouse model of prenatal methadone exposure (PME), the aim of the study is to investigate the cerebral microstructural differences between the mice with PME and prenatal saline exposure (PSE). The brains of eight-week-old male offspring with either PME (n = 15) or PSE (n = 15) were imaged using high resolution in-vivo diffusion magnetic resonance imaging on a 9.4 Tesla small animal scanner. Brain microstructure was characterized using diffusion tensor imaging (DTI) and Bingham neurite orientation dispersion and density imaging (Bingham-NODDI). Voxel-based analysis (VBA) was performed using the calculated microstructural parametric maps. The VBA showed significant (p < 0.05) bilateral alterations in fractional anisotropy (FA), mean diffusivity (MD), axial diffusivity (AD), radial diffusivity (RD), orientation dispersion index (ODI) and dispersion anisotropy index (DAI) across several cortical and subcortical regions, compared to PSE. Particularly, in PME offspring, FA, MD and AD were significantly higher in the hippocampus, dorsal amygdala, thalamus, septal nuclei, dorsal striatum and nucleus accumbens. These DTI-based results suggest widespread bilateral microstructural alterations across cortical and subcortical regions in PME offspring. Consistent with the observations in DTI, Bingham-NODDI derived ODI exhibited significant reduction in PME offspring within the hippocampus, dorsal striatum and cortex. NODDI-based results further suggest reduction in dendritic arborization in PME offspring across multiple cortical and subcortical regions. To our best knowledge, this is the first study of prenatal opioid exposure to examine microstructural organization in vivo. Our findings demonstrate perturbed microstructural complexity in cortical and subcortical regions persisting into early adulthood which could interfere with critical neurodevelopmental processes in individuals with prenatal opioid exposure.

Prenatal opioid exposure inhibits microglial sculpting of the dopamine system selectively in adolescent male offspring

The current opioid epidemic has dramatically increased the number of children who are prenatally exposed to opioids, including oxycodone. A number of social and cognitive abnormalities have been documented in these children as they reach young adulthood. However, little is known about the mechanisms underlying developmental effects of prenatal opioid exposure. Microglia, the resident immune cells of the brain, respond to acute opioid exposure in adulthood. Moreover, microglia are known to sculpt neural circuits during typical development. Indeed, we recently found that microglial phagocytosis of dopamine D1 receptors (D1R) in the nucleus accumbens (NAc) is required for the natural developmental decline in NAc-D1R that occurs between adolescence and adulthood in rats. This microglial pruning occurs only in males, and is required for the normal developmental trajectory of social play behavior. However, virtually nothing is known as to whether this developmental program is altered by prenatal exposure to opioids. Here, we show in rats that maternal oxycodone self-administration during pregnancy leads to reduced adolescent microglial phagocytosis of D1R and subsequently higher D1R density within the NAc in adult male, but not female, offspring. Finally, we show prenatal and adult behavioral deficits in opioid-exposed offspring, including impaired extinction of oxycodone-conditioned place preference in males. This work demonstrates for the first time that microglia play a key role in translating prenatal opioid exposure to changes in neural systems and behavior.

Sex-Dependent Synaptic Remodeling of the Somatosensory Cortex in Mice With Prenatal Methadone Exposure

Rising opioid use among pregnant women has led to a growing population of neonates exposed to opioids during the prenatal period, but how opioids affect the developing brain remains to be fully understood. Animal models of prenatal opioid exposure have discovered deficits in somatosensory behavioral development that persist into adolescence suggesting opioid exposure induces long lasting neuroadaptations on somatosensory circuitry such as the primary somatosensory cortex (S1). Using a mouse model of prenatal methadone exposure (PME) that displays delays in somatosensory milestone development, we performed an un-biased multi-omics analysis and investigated synaptic functioning in the primary somatosensory cortex (S1), where touch and pain sensory inputs are received in the brain, of early adolescent PME offspring. PME was associated with numerous changes in protein and phosphopeptide abundances that differed considerably between sexes in the S1. Although prominent sex effects were discovered in the multi-omics assessment, functional enrichment analyses revealed the protein and phosphopeptide differences were associated with synapse-related cellular components and synaptic signaling-related biological processes, regardless of sex. Immunohistochemical analysis identified diminished GABAergic synapses in both layer 2/3 and 4 of PME offspring. These immunohistochemical and proteomic alterations were associated with functional consequences as layer 2/3 pyramidal neurons revealed reduced amplitudes and a lengthened decay constant of inhibitory postsynaptic currents. Lastly, in addition to reduced cortical thickness of the S1, cell-type marker analysis revealed reduced microglia density in the upper layer of the S1 that was primarily driven by PME females. Taken together, our studies show the lasting changes on synaptic function and microglia in S1 cortex caused by PME in a sex-dependent manner.

Prenatal opioid exposure reprograms the behavioural response to future alcohol reward

As the opioid crisis has continued to grow, so has the number of infants exposed to opioids during the prenatal period. A growing concern is that prenatal exposure to opioids may induce persistent neurological changes that increase the propensity for future addictions. Although alcohol represents the most likely addictive substance that the growing population of prenatal opioid exposed will encounter as they mature, no studies to date have examined the effect of prenatal opioid exposure on future sensitivity to alcohol reward. Using a recently developed mouse model of prenatal methadone exposure (PME), we investigated the rewarding properties of alcohol and alcohol consumption in male and female adolescent PME and prenatal saline exposed (PSE) control animals. Conditioned place preference to alcohol was disrupted in PME offspring in a sex-dependent manner with PME males exhibiting resistance to the rewarding properties of alcohol. Repeated injections of alcohol revealed enhanced sensitivity to the locomotor-stimulating effects of alcohol specific to PME females. PME males consumed significantly more alcohol over 4 weeks of alcohol access relative to PSE males and exhibited increased resistance to quinine-adulterated alcohol. Further, a novel machine learning model was developed to employ measured differences in alcohol consumption and drinking microstructure to reliably predict prenatal exposure. These findings indicate that PME alters the sensitivity to alcohol reward in adolescent mice in a sex-specific manner and suggests prenatal opioid exposure may induce persistent effects on reward neurocircuitry that can reprogram offspring behavioural response to alcohol later in life.

The distinct roles of various neurotransmitters in modulating methamphetamine-induced conditioned place preference in relevant brain regions in mice

OBJECTIVES

Previous studies have shown that methamphetamine (METH) can induce complex adaptive changes in the reward system in the brain, including the changes in the content of neurotransmitters in the signal transduction pathway. However, how the changes of various neurotransmitters in relevant brain reward circuits contribute to METH-induced conditioned place preference (CPP) remains unclear.

METHODS

In this study, first, we designed an animal model of METH-induced CPP. Then we used liquid chromatography-mass spectrometry (LC-MS) to simultaneously determine the contents of various neurotransmitters - dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), 5-hydroxyindole acetic acid (5-HIAA), glutamic acid (Glu) and glutamine (Gln) - in different brain regions of the prefrontal cortex (PFc), nucleus accumbens (NAc), caudate-putamen (CPu) and hippocampus (Hip), which are believed to be relevant to the drug's reward effect.

RESULTS

The results of the behavioral experiment suggested that 1.0 mg/kg METH could induce obvious CPP in mice. The results about various neurotransmitters showed that: DA significantly increased in NAc in the METH group; Glu increased significantly in the METH group in PFc and NAc and Gln increased significantly in the METH group in PFc.

CONCLUSIONS

These results suggested that the neurotransmitters of DA, Glu and Gln may work together and play important roles in METH-induced CPP in relevant brain reward circuits, especially in PFc and NAc. These findings therefore could help to advance the comprehensive understanding of the neurochemic and psychopharmacologic properties of METH in reward effect, which is important for future improvements in the treatment of drug addiction.

Prenatal exposure to morphine impairs attention and impulsivity in adult rats

RATIONALE

An alarming number of neonates born with prenatal exposure to morphine has resulted from the opioid epidemic; however, the long-term effects of prenatal opioid exposure on offspring behavior remain relatively unknown. In this study, we evaluated whether prenatal exposure to the mu opioid receptor agonist, morphine, has enduring effects on cognitive functions in adult life.

METHODS

On embryonic days 11-18 (E11-E18), female pregnant rats were injected subcutaneously with either morphine or saline twice daily. Adult male offspring that was prenatally exposed to saline or morphine was trained in the 5-choice serial reaction time test (5-CSRTT) to test their cognitive abilities under baseline conditions. Next, these rats were treated with saline (1 ml/kg), naloxone (1 mg/kg), and acute morphine (1, 3, 5 mg/kg), subcutaneously, once daily and following drug challenges rats were tested in the 5-CSRTT. Meanwhile, behavioral performance on training days between opioid drug challenges were analyzed to monitor possible drug-induced shifts in baseline performance. As a final experiment in order to investigate subchronic exposure to morphine, rats were injected with 5 mg/kg morphine for 5 days and then naloxone in the last day of the experiment (day 6).

RESULTS

Firstly, during acquisition of a stable baseline in the training phase, rats prenatally exposed to morphine showed delayed learning of the task demands. Furthermore, under baseline responding the rats prenatally exposed to morphine showed declined inhibitory control demonstrated by increased impulsive and compulsive-like responding compared to rats prenatally exposed to saline. Moreover, acute and subchronic morphine challenges in the rats prenatally exposed to morphine caused a deficit in visuospatial attention in comparison with saline treatment as well as the rats prenatally exposed to saline. These effects were abolished by naloxone.

CONCLUSION

The current findings indicate a direct causal effect of prenatal morphine exposure on inhibitory control and task learning later in life, as well as deficits in attention following morphine exposure in adulthood.

Prenatal opioid exposure and vulnerability to future substance use disorders in offspring

The heightened incidence of opioid use during pregnancy has resulted in unprecedented rates of neonates prenatally exposed to opioids. Prenatal opioid exposure (POE) results in significantly adverse medical, developmental, and behavioral outcomes in offspring. Of growing interest is whether POE contributes to future vulnerability to substance use disorders. The effects of POE on brain development is difficult to assess in humans, as the timing, dose, and route of drug exposure together with complex genetic and environmental factors affect susceptibility to addiction. Preclinical models of POE have allowed us to avoid methodological difficulties and confounding factors of POE in humans. Here, we review the effects of maternal opioid exposure on the developing brain with an emphasis on the neurobiological basis of drug addiction and on preclinical models of POE and their limitations. These studies have indicated that POE increases self-administration of drugs, reward-driven behaviors in the conditioned place paradigm, and locomotor sensitization. While addiction is multifaceted and vulnerability to drug addiction is still inconclusive in human studies of prenatally exposed infants, animal studies do provide a noteworthy corroboration of negative behavioral outcomes.