Gestational buprenorphine exposure: Effects on pregnancy, development, neonatal opioid withdrawal syndrome, and behavior in a translational rodent model

The effects of buprenorphine and morphine during pregnancy: Impact of exposure length on maternal brain, behavior, and offspring neurodevelopment

The escalating incidence of opioid-related issues among pregnant women in the United States underscores the critical necessity to understand the effects of opioid use and Medication for Opioid Use Disorders (MOUDs) during pregnancy. This research employed a translational rodent model to examine the impact of gestational exposure to buprenorphine (BUP) or morphine on maternal behaviors and offspring well-being. Female rats received BUP or morphine before conception, representing established use, with exposure continuing until postnatal day 2 or discontinued on gestational day 19 to mimic treatment cessation before birth. Maternal behaviors - including care, pup retrieval, and preference - as well as hunting behaviors and brain neurotransmitter levels were assessed. Offspring were evaluated for mortality, weight, length, milk bands, surface righting latency, withdrawal symptoms, and brain neurotransmitter levels. Our results reveal that regardless of exposure length (i.e., continued or discontinued), BUP resulted in reduced maternal care in contrast to morphine-exposed and control dams. Opioid exposure altered brain monoamine levels in the dams and offspring, and was associated with increased neonatal mortality, reduced offspring weight, and elevated withdrawal symptoms compared to controls. These findings underscore BUP's potential disruption of maternal care, contributing to increased pup mortality and altered neurodevelopmental outcomes in the offspring. This study calls for more comprehensive research into prenatal BUP exposure effects on the maternal brain and infant development with the aim to mitigate adverse outcomes in humans exposed to opioids during pregnancy.

Effects of prenatal exposure to methadone or buprenorphine and maternal separation on anxiety-like behavior in rats

BACKGROUND

The use of medications for opioid use disorder such as methadone or buprenorphine is increasing among pregnant women. However, long-term effects of this treatment on the children's health are not well understood. A key challenge is distinguishing the effects of opioid exposure from other confounding factors associated with human opioid use, such as reduced maternal care. In this study, we therefore used a multi-risk factor design to examine anxiety-like behavior in rats prenatally exposed to methadone or buprenorphine, with or without maternal separation the first two weeks after birth.

METHODS

Female Sprague Dawley rats were exposed to methadone (10mg/kg/day), buprenorphine (1mg/kg/day) or sterile water throughout gestation. Half of the offspring in each litter experienced maternal separation for 3h per day from postnatal day 2 to 12. Male and female offspring (6-9 weeks) were tested in the open field, light-dark transition and elevated plus maze tests to assess anxiety-like behavior.

RESULTS

Offspring exposed to buprenorphine and not subjected to maternal separation displayed increased anxiety-like behavior in 3 out of 6 outcomes in the light-dark transition and elevated plus maze tests. Maternal separation did not exacerbate, but rather diminished this behavior. Males and females responded differently to methadone, with a trend towards reduced anxiety for males and increased anxiety for females.

CONCLUSIONS

Prenatal exposure to methadone or buprenorphine may increase the risk of developing anxiety-like behavior later in life, but the effect depends on specific subgroup characteristics. Further research is required to draw definitive conclusions.

Advances in animal models of prenatal opioid exposure

Neonatal opioid withdrawal syndrome (NOWS) is a growing public health concern. The complexity of in utero opioid exposure in clinical studies makes it difficult to investigate underlying mechanisms that could ultimately inform early diagnosis and treatments. Clinical studies are unable to dissociate the influence of maternal polypharmacy or the environment from direct effects of in utero opioid exposure, highlighting the need for effective animal models. Early animal models of prenatal opioid exposure primarily used the prototypical opioid, morphine, and opioid exposure that was often limited to a narrow period during gestation. In recent years, the number of preclinical studies has grown rapidly. Newer models utilize both prescription and nonprescription opioids and vary the onset and duration of opioid exposure. In this review, we summarize novel prenatal opioid exposure models developed in recent years and attempt to reconcile results between studies while critically identifying gaps within the current literature.

Opioid-induced dysbiosis of maternal gut microbiota during gestation alters offspring gut microbiota and pain sensitivity

There has been a rapid increase in neonates born with a history of prenatal opioid exposure. How prenatal opioid exposure affects pain sensitivity in offspring is of interest, as this may perpetuate the opioid epidemic. While few studies have reported hypersensitivity to thermal pain, potential mechanisms have not been described. This study posits that alterations in the gut microbiome may underly hypersensitivity to pain in prenatally methadone-exposed 3-week-old male offspring, which were generated using a mouse model of prenatal methadone exposure. Fecal samples collected from dams and their offspring were subjected to 16s rRNA sequencing. Thermal and mechanical pain were assessed using the tail flick and Von Frey assays. Transcriptomic changes in whole brain samples of opioid or saline-exposed offspring were investigated using RNA-sequencing, and midbrain sections from these animals were subjected to qPCR profiling of genes related to neuropathic and inflammatory pain pathways. Prenatal methadone exposure increased sensitivity to thermal and mechanical pain and elevated serum levels of IL-17a. Taxonomical analysis revealed that prenatal methadone exposure resulted in significant alterations in fecal gut microbiota composition, including depletion of Lactobacillus, Bifidobacterium, and Lachnospiracea sp and increased relative abundance of Akkermansia, Clostridium sensu stricto 1, and Lachnoclostridium. Supplementation of the probiotic VSL#3 in dams rescued hypersensitivity to thermal and mechanical pain in prenatally methadone-exposed offspring. Similarly, cross-fostering prenatally methadone-exposed offspring to control dams also attenuated hypersensitivity to thermal pain in opioid-exposed offspring. Modulation of the maternal and neonatal gut microbiome with probiotics resulted in transcriptional changes in genes related to neuropathic and immune-related signaling in whole brain and midbrain samples of prenatally methadone-exposed offspring. Together, our work provides compelling evidence of the gut-brain-axis in mediating pain sensitivity in prenatally opioid-exposed offspring.

Maternal care behavior and physiology moderate offspring outcomes following gestational exposure to opioids

The opioid epidemic has resulted in a drastic increase in gestational exposure to opioids. Opioid-dependent pregnant women are typically prescribed medications for opioid use disorders ("MOUD"; e.g., buprenorphine [BUP]) to mitigate the harmful effects of abused opioids. However, the consequences of exposure to synthetic opioids, particularly BUP, during gestation on fetal neurodevelopment and long-term outcomes are poorly understood. Further, despite the known adverse effects of opioids on maternal care, many preclinical and clinical studies investigating the effects of gestational opioid exposure on offspring outcomes fail to report on maternal care behaviors. Considering that offspring outcomes are heavily dependent upon the quality of maternal care, it is important to evaluate the effects of gestational opioid exposure in the context of the mother-infant dyad. This review compares offspring outcomes after prenatal opioid exposure and after reduced maternal care and integrates this information to potentially identify common underlying mechanisms. We explore whether adverse outcomes after gestational BUP exposure are due to direct effects of opioids in utero, deficits in maternal care, or a combination of both factors. Finally, suggestions for improving preclinical models of prenatal opioid exposure are provided to promote more translational studies that can help to improve clinical outcomes for opioid-dependent mothers.

Transcriptomic profiling of reward and sensory brain areas in perinatal fentanyl exposed juvenile mice

Use of the synthetic opioid fentanyl increased ~300% in the last decade, including among women of reproductive ages. Adverse neonatal outcomes and long-term behavioral disruptions are associated with perinatal opioid exposure. Our previous work demonstrated that perinatal fentanyl exposed mice displayed enhanced negative affect and somatosensory circuit and behavioral disruptions during adolescence. However, little is known about molecular adaptations across brain regions that underlie these outcomes. We performed RNA sequencing across three reward and two sensory brain areas to study transcriptional programs in perinatal fentanyl exposed juvenile mice. Pregnant dams received 10 μg/ml fentanyl in the drinking water from embryonic day 0 (E0) through gestational periods until weaning at postnatal day 21 (P21). RNA was extracted from nucleus accumbens (NAc), prelimbic cortex (PrL), ventral tegmental area (VTA), somatosensory cortex (S1) and ventrobasal thalamus (VBT) from perinatal fentanyl exposed mice of both sexes at P35. RNA sequencing was performed, followed by analysis of differentially expressed genes (DEGs) and gene co-expression networks. Transcriptome analysis revealed DEGs and gene modules significantly associated with exposure to perinatal fentanyl in a sex-wise manner. The VTA had the most DEGs, while robust gene enrichment occurred in NAc. Genes enriched in mitochondrial respiration were pronounced in NAc and VTA of perinatal fentanyl exposed males, extracellular matrix (ECM) and neuronal migration enrichment were pronounced in NAc and VTA of perinatal fentanyl exposed males, while genes associated with vesicular cycling and synaptic signaling were markedly altered in NAc of perinatal fentanyl exposed female mice. In sensory areas from perinatal fentanyl exposed females, we found alterations in mitochondrial respiration, synaptic and ciliary organization processes. Our findings demonstrate distinct transcriptomes across reward and sensory brain regions, with some showing discordance between sexes. These transcriptome adaptations may underlie structural, functional, and behavioral changes observed in perinatal fentanyl exposed mice.

An Examination of the Complex Pharmacological Properties of the Non-Selective Opioid Modulator Buprenorphine

The goal of this review is to provide a recent examination of the pharmacodynamics as well as pharmacokinetics, misuse potential, toxicology, and prenatal consequences of buprenorphine. Buprenorphine is currently a Schedule III opioid in the US used for opioid-use disorder (OUD) and as an analgesic. Buprenorphine has high affinity for the mu-opioid receptor (MOR), delta (DOR), and kappa (KOR) and intermediate affinity for the nociceptin (NOR). Buprenorphine's active metabolite, norbuprenorphine, crosses the blood-brain barrier, is a potent metabolite that attenuates the analgesic effects of buprenorphine due to binding to NOR, and is responsible for the respiratory depressant effects. The area under the concentration curves are very similar for buprenorphine and norbuprenorphine, which indicates that it is important to consider this metabolite. Crowding sourcing has identified a buprenorphine street value (USD 3.95/mg), indicating some non-medical use. There have also been eleven-thousand reports involving buprenorphine and minors (age < 19) at US poison control centers. Prenatal exposure to clinically relevant dosages in rats produces reductions in myelin and increases in depression-like behavior. In conclusion, the pharmacology of this OUD pharmacotherapy including the consequences of prenatal buprenorphine exposure in humans and experimental animals should continue to be carefully evaluated.

Buprenorphine reduces somatic withdrawal in a mouse model of early-life morphine exposure

The rising prevalence of early-life opioid exposure has become a pressing public health issue in the U.S. Neonates exposed to opioids in utero are at risk of experiencing a constellation of postpartum withdrawal symptoms commonly referred to as neonatal opioid withdrawal syndrome (NOWS). Buprenorphine (BPN), a partial agonist at the mu-opioid receptor (MOR) and antagonist at the kappa-opioid receptor (KOR), is currently approved to treat opioid use disorder in adult populations. Recent research suggests that BPN may also be effective in reducing withdrawal symptoms in neonates who were exposed to opioids in utero. We sought to determine whether BPN attenuates somatic withdrawal in a mouse model of NOWS. Our findings indicate that the administration of morphine (10mg/kg, s.c.) from postnatal day (PND) 1-14 results in increased somatic symptoms upon naloxone-precipitated (1mg/kg, s.c.) withdrawal. Co-administration of BPN (0.3mg/kg, s.c.) from PND 12-14 attenuated symptoms in morphine-treated mice. On PND 15, 24h following naloxone-precipitated withdrawal, a subset of mice was examined for thermal sensitivity in the hot plate test. BPN treatment significantly increased response latency in morphine-exposed mice. Lastly, neonatal morphine exposure elevated mRNA expression of KOR, and reduced mRNA expression of corticotropin-releasing hormone (CRH) in the periaqueductal gray when measured on PND 14. Altogether, this data provides support for the therapeutic effects of acute low-dose buprenorphine treatment in a mouse model of neonatal opioid exposure and withdrawal.

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'.

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.

Gestational buprenorphine exposure disrupts dopamine neuron activity and related behaviors in adulthood

Opioid misuse among pregnant women is rapidly increasing in the United States. The number of maternal opioid-related diagnoses increased by 131% in the last ten years, resulting in an increased number of infants exposed to opioids in utero and a subsequent increase in infants developing neonatal abstinence syndrome (NAS). The most prescribed treatment to combat maternal opioid use disorder is buprenorphine, a partial μ-opioid receptor agonist and κ-opioid receptor antagonist. Buprenorphine treatment effectively reduces NAS but has been associated with disrupted cortical development and neurodevelopmental consequences in childhood. Less is known about the long-term neurodevelopmental consequences following buprenorphine exposure in utero Previous research has shown that gestational buprenorphine exposure can induce anxiety- and depressive-like phenotypes in adult rats, suggesting that exposure to buprenorphine in utero may render individuals more susceptible to psychiatric illness in adulthood. A common pathology observed across multiple psychiatric illnesses is dopamine system dysfunction. Here, we administered the highly-abused opioid, oxycodone (10 mg/kg, i.p.) or a therapeutic used to treat opioid use disorder, buprenorphine (1 mg/kg, i.p) to pregnant Sprague Dawley rats from gestational day 11 through 21, then examined neurophysiological alterations in the mesolimbic dopamine system and dopamine-dependent behaviors in adult offspring. We found that gestational exposure to buprenorphine or oxycodone increases dopamine neuron activity in adulthood. Moreover, prenatal buprenorphine exposure disrupts the afferent regulation of dopamine neuron activity in the ventral tegmental area (VTA). Taken together, we posit that gestational buprenorphine or oxycodone exposure can have profound effects on the mesolimbic dopamine system in adulthood.Significance StatementThe opioid epidemic in the United States is a growing problem that affects people from all demographics, including pregnant women. In 2017, nearly 21,000 pregnant women reported misusing opioids during pregnancy, which can lead to many physiological and neurodevelopmental complications in infants. To combat illicit opioid use during pregnancy, buprenorphine is the priority treatment option, as it reduces illicit opioid use and alleviates symptoms of neonatal abstinence syndrome in infants. However, less is known about the long-term neurophysiological consequences of in utero opioid or buprenorphine exposure. Here, we demonstrate that both oxycodone and buprenorphine exposure, in utero, can result in aberrant dopamine system function in adult rats. These results provide evidence of potential long-lasting effects of opioid exposure during development.

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.

Opioid withdrawal behavior in spiny mice: A novel preclinical model of neonatal opioid withdrawal syndrome (NOWS)

As the opioid epidemic continues to grow, opioid use among pregnant women is increasing significantly. This has led to a steady rise in the number of infants born with neonatal opioid withdrawal syndrome (NOWS). Although short-term withdrawal symptoms associated with NOWS are well characterized, there are many gaps in our understanding of the short and long-term effects of prenatal opioid exposure. Current animal models of NOWS are limited by shortened gestational periods, large litter sizes, and primary organogenesis occurring after birth. This often leads to postnatal treatment to mimic drug exposure during third-trimester development. Using the unique rodent species Acomys cahirinus, more commonly known as spiny mice, which have an extended 40-day gestation period, small litter sizes, and increased in utero organogenesis we aim to study the short-term effects of prenatal morphine exposure by assessing withdrawal behavior. To model maternal opioid use, dams were treated daily with morphine (10 and 30 mg/kg S.C.) beginning on gestation day 19 until the day of birth; this resulted in a cumulative exposure of 19-21 days. Withdrawal behaviors for each pup were recorded daily between postnatal days 0-7 (PND 0-7). Our study found that prenatal morphine exposure in spiny mice led to an increase in withdrawal behavior throughout the early postnatal period and validated the use of this species as a novel pre-clinical model of NOWS. We are hopeful this rodent model will further our understanding of the short and long-term consequences of prenatal opioid exposure on neurodevelopment and behavior.

Maternal continuous oral oxycodone self-administration alters pup affective/social communication but not spatial learning or sensory-motor function

BACKGROUND

The broad use/misuse of prescription opioids during pregnancy has resulted in a surge of infants with Neonatal Opioid Withdrawal Syndrome (NOWS). Short-term irritability and neurological complications are its hallmarks, but the long-term consequences are unknown.

METHODS

A newly-developed preclinical model of oxycodone self-administration enables adult female rats to drink oxycodone (∼10/mg/kg/day) before and during pregnancy, and after delivery, and to maintain normal liquid intake, titrate dosing, and avoid withdrawal.

RESULTS

Oxycodone was detected in the serum of mothers and pups. Growth parameters in dams and pups and litter mass and size were similar to controls. There were no differences in paw retraction latency to a thermal stimulus between Oxycodone and Control pups at postnatal (PN) 2 or PN14. Oxycodone and Control pups had similar motor coordination, cliff avoidance, righting time, pivoting, and olfactory spatial learning from PN3 through PN13. Separation-induced ultrasonic vocalizations at PN8 revealed higher call frequency in Oxycodone pups relative to Control pups (p<0.031; Cohen's d=1.026). Finally, Oxycodone pups displayed withdrawal behaviors (p's<0.029; Cohen's d's>0.806), and Oxycodone males only vocalized more than Control pups in the first minute of testing (p's<0.050; Cohen's d's>.866). Significant effects were corroborated by estimation plots.

CONCLUSIONS

Our rat model of oral oxycodone self-administration in pregnancy shows exacerbated affect/social communication in pups in a sex-dependent manner but spared cognition and sensory-motor behaviors. This preclinical model reproduces selective aspects of human opioid use during pregnancy, enabling longitudinal analysis of how maternal oxycodone changes emotional behavior in the offspring.

Opioid use during pregnancy can impair maternal behavior and the Maternal Brain Network: A literature review

Opioid Use Disorder (OUD) is a global epidemic also affecting women of reproductive age. A standard form of pharmacological treatment for OUD is Opioid Maintenance Therapy (OMT) and buprenorphine has emerged as the preferred treatment for pregnant women with OUD relative to methadone. However, the consequences of BUP exposure on the developing Maternal Brain Network and mother-infant dyad are not well understood. The maternal-infant bond is dependent on the Maternal Brain Network, which is responsible for the dynamic transition from a "nulliparous brain" to a "maternal brain". The Maternal Brain Network consists of regions implicated in maternal care (e.g., medial preoptic area, nucleus accumbens, ventral pallidum, ventral tegmentum area) and maternal defense (e.g., periaqueductal gray). The endogenous opioid system modulates many of the neurochemical changes in these areas during the transition to motherhood. Thus, it is not surprising that exogenous opioid exposure during pregnancy can be disruptive to the Maternal Brain Network. Though less drastic than misused opioids, OMTs may not be without risk of disrupting the neural and molecular structures of the Maternal Brain Network. This review describes the Maternal Brain Network as a framework for understanding how pharmacological differences in exogenous opioid exposure can disrupt the onset and maintenance of the maternal brain and summarizes opioid and OMT (in particular buprenorphine) use in the context of pregnancy and maternal behavior. This review also highlights future directions for evaluating exogenous opioid effects on the Maternal Brain Network in the hopes of raising awareness for the impact of the opioid crisis not only on exposed infants, but also on mothers and subsequent mother-infant bonds.

Maternal Opioid Exposure Culminates in Perturbed Murine Neurodevelopment and Hyperactive Phenotype in Adolescence

Opioid use by women during pregnancy has risen dramatically since 2004, accompanied by a striking increase in the prevalence of neonatal opioid withdrawal syndrome (NOWS) and other long-term neurological deficits. However, the mechanisms underlying the impact of prenatal opioid exposure on fetal neurodevelopment are largely unknown. To translate from the clinical presentation, we developed a novel mouse model to study the neurodevelopmental consequences of maternal opioid use and management. Female mice were treated with oxycodone (OXY) before mating to mimic opioid use disorder (OUD) in humans. Following pregnancy confirmation, dams were switched to buprenorphine (BUP) via oral administration, simulating medication management of OUD (MOUD) in pregnant women. Here, we document critical changes in fetal brain development including reduced cortical thickness, altered corticogenesis, and ventriculomegaly in embryos from dams that were treated with opioids before and throughout pregnancy. Maternal care giving behavior was slightly altered without affecting gross growth of offspring. However, adolescent offspring exposed to maternal opioid use during pregnancy exhibited hyperactivity in late adolescence. Remarkably, we also show increased generation of dopaminergic neurons within the ventral tegmental area (VTA) of mice exposed to prenatal opioids. These data provide critical evidence of teratogenic effects of opioid use during pregnancy and suggest a causal relationship between maternal opioid use and neurodevelopmental/behavioral anomalies in adolescence.

Prenatal methadone exposure disrupts behavioral development and alters motor neuron intrinsic properties and local circuitry

Despite the rising prevalence of methadone treatment in pregnant women with opioid use disorder, the effects of methadone on neurobehavioral development remain unclear. We developed a translational mouse model of prenatal methadone exposure (PME) that resembles the typical pattern of opioid use by pregnant women who first use oxycodone then switch to methadone maintenance pharmacotherapy, and subsequently become pregnant while maintained on methadone. We investigated the effects of PME on physical development, sensorimotor behavior, and motor neuron properties using a multidisciplinary approach of physical, biochemical, and behavioral assessments along with brain slice electrophysiology and in vivo magnetic resonance imaging. Methadone accumulated in the placenta and fetal brain, but methadone levels in offspring dropped rapidly at birth which was associated with symptoms and behaviors consistent with neonatal opioid withdrawal. PME produced substantial impairments in offspring physical growth, activity in an open field, and sensorimotor milestone acquisition. Furthermore, these behavioral alterations were associated with reduced neuronal density in the motor cortex and a disruption in motor neuron intrinsic properties and local circuit connectivity. The present study adds to the limited body of work examining PME by providing a comprehensive, translationally relevant characterization of how PME disrupts offspring physical and neurobehavioral development.

Automated quantification of opioid withdrawal in neonatal rat pups using Ethovision® XT software

Chronic prenatal exposure to opioids often causes fetal opioid dependence that leads to neonatal opioid withdrawal syndrome (NOWS) shortly after delivery. Rat models of NOWS often require quantifying neonatal withdrawal behaviors using time-consuming, labor-intensive manual scoring methods. The goal of this study was to automate quantification of opioid withdrawal in neonatal rat pups. Accordingly, we used the animal behavior software Ethovision® XT to analyze archived videos of rat pups subjected to precipitated opioid withdrawal testing on postnatal day 0. We compared results obtained from Ethovision® XT with those previously obtained from manual scoring. Two endpoints reported by Ethovision® XT, Distance Moved (cm) and Movement Duration (s), had strong positive linear relationships with manually derived global withdrawal scores (GWS; R² > 0.73). Sensitivity and specificity of each endpoint to discriminate presence and absence of low-grade withdrawal were assessed by receiver operator characteristic curve analysis, which indicated that Distance Moved and Movement Duration had excellent accuracy (AUC > 0.90). Finally, we analyzed main and interaction effects of prenatal treatment (with vehicle or mu opioid receptor full agonists) and postnatal challenge (with saline or an opioid receptor antagonist) on each endpoint and determined they were similar for the manual and automated methods. These results show that Ethovision® XT software can reliably quantify opioid withdrawal in neonatal rat pups with non-inferiority to manual scoring even in videos that were not originally purposed and optimized for Ethovision® XT analysis. This faster and less labor-intensive method of analysis is expected to accelerate progress in preclinical studies of NOWS.

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

The opioid crisis has resulted in an unprecedented number of neonates born with prenatal opioid exposure (POE); however, the long-term effects of POE on offspring behavior and neurodevelopment remain relatively unknown. The advantages and disadvantages of the various preclinical POE models developed over the last several decades are discussed in the context of clinical and translational relevance. Although considerable and important variability exists among preclinical models of POE, the examination of these preclinical models has revealed that opioid exposure during the prenatal period contributes to maladaptive behavioral development as offspring mature including an altered responsiveness to rewarding drugs and increased pain response. The present review summarizes key findings demonstrating the impact of POE on offspring drug self-administration (SA), drug consumption, the reinforcing properties of drugs, drug tolerance, and other reward-related behaviors such as hypersensitivity to pain. Potential underlying molecular mechanisms which may contribute to this enhanced addictive phenotype in POE offspring are further discussed with special attention given to key brain regions associated with reward including the striatum, prefrontal cortex (PFC), ventral tegmental area (VTA), hippocampus, and amygdala. Improvements in preclinical models and further areas of study are also identified which may advance the translational value of findings and help address the growing problem of POE in clinical populations.

Characterization of the intergenerational impact of in utero and postnatal oxycodone exposure

Prescription opioid abuse during and after pregnancy is a rising public health concern. While earlier studies have documented that offspring exposed to opioids in utero have impaired neurodevelopment, a significant knowledge gap remains in comparing the overall development between offspring exposed in utero and postnatally. Adding a layer of complexity is the role of heredity in the overall development of these exposed offspring. To fill in these important knowledge gaps, the current study uses a preclinical rat model mimicking oxycodone (oxy) exposure in utero (IUO) and postnatally (PNO) to investigate comparative and intergenerational effects in the two different treatment groups. While significant phenotypic attributes were observed with the two treatments and across the two generations, RNA sequencing revealed alterations in the expression of key synaptic genes in the two exposed groups in both generations. RNA sequencing and post validation of genes using RT-PCR highlighted the differential expression of several neuropeptides associated with the hypocretin system, a system recently implicated in addiction. Further, behavior studies revealed anxiety-like behaviors and social deficits that persisted even in the subsequent generations in the two treatment groups. To summarize, our study for the first time reveals a new line of investigation on the potential risks associated with oxy use during and after pregnancy, specifically the disruption of neurodevelopment and intergenerational impact on behavior.

The association of cannabis use late in pregnancy with engagement and retention in perinatal substance use disorder care for opioid use disorder: A cohort comparison

BACKGROUND

Prenatal use of cannabis and opioids are increasing and very concerning. Engagement and retention in comprehensive, perinatal substance use disorder (PSUD) care are associated with better outcomes for mothers and babies. We compared the characteristics and engagement in care among women with opioid use disorder who used cannabis late in pregnancy versus those who didn't.

METHODS

The primary outcome, "overall engagement and retention in PSUD care" included: utilization of substance use treatment prenatally, negative screening/toxicology at delivery (excluding cannabis), and attendance at expected prenatal and postpartum visits. Cannabis use late in pregnancy was objectively assessed at delivery via maternal urine drug screen and/or neonatal meconium/cord toxicology. Between-group comparisons utilized chi square, t-test or Mann-Whitney. Associations were assessed using Spearman Rho and two multivariate, binary logistic regressions for cannabis use and the primary outcome.

RESULTS

18.0% (85/472) consumed cannabis late in pregnancy. Women of color, younger women, and those diagnosed with concurrent cannabis use disorder were more likely to consume cannabis. Engagement and retention in PSUD care was not associated with cannabis use, but rather, with prescribed pharmacotherapy for psychiatric disorders. The use of prescribed buprenorphine+naloxone was associated with cannabis avoidance late in pregnancy.

CONCLUSIONS

Cannabis use late in pregnancy, compared to none, did not impact engagement and retention in our PSUD program. Adjunctive psychotropic medication and/or buprenorphine+naloxone prescription were associated with cannabis avoidance suggesting the use and interactions of pharmacotherapies in an opioid dependent population is complex. A shared decision-making process during PSUD care is warranted.

Prenatal exposure to methadone or buprenorphine impairs cognitive performance in young adult rats

BACKGROUND

Concerns have been raised about the use of opioid maintenance treatment (OMT) during pregnancy and negative effects for the offspring. While neonatal outcomes and short-term effects are relatively well described, studies examining long-term effects in adolescents and adults are absent. The aim of the present study was to examine effects on learning and memory in young adult rats prenatally exposed to methadone or buprenorphine.

METHODS

Female rats were implanted with a 28-day osmotic minipump delivering methadone (10 mg/kg/day), buprenorphine (1 mg/kg/day) or vehicle 5 days prior to mating. To examine possible effects on cognitive functioning, young adult offspring were included in three different behavioral tests that examine recognition memory, nonspatial, and spatial learning and memory. In addition, offspring growth and maternal behavior after birh were investigated.

RESULTS

Prenatal exposure to methadone or buprenorphine caused impaired recognition memory and nonspatial reference learning and memory in young adult rats compared with the vehicle-treated group. Methadone-exposed offspring, but not the buprenorphine-exposed, also showed reduced long-term spatial memory. We did not observe any changes in maternal behavior or offspring growth after prenatal exposure to methadone or buprenorphine, suggesting that the impaired cognitive functioning is due to the opioid exposure rather than reduced maternal caregiving.

CONCLUSION

The present findings of long-term cognitive impairments in methadone- and buprenorphine-exposed offspring points to a negative impact of OMT on neurobiological development.