Behavioral and biological adaptations underlying neonatal opioid withdrawal syndrome

Opioid-linked overdose death rates have reached unprecedented levels in the United States. The growing incidence of Opioid Use Disorder (OUD) is concomitant with elevated rates of OUD in women during pregnancy and through parturition. Neonates born to mothers with active OUD can develop opioid dependence in utero and display various signs of postnatal withdrawal, a condition termed Neonatal Opioid Withdrawal Syndrome (NOWS). Common symptomatic features of NOWS include sleep disturbances, low birth weight, altered heart and respiratory rates, increased irritability, high-pitched crying, feeding difficulties. Many of these symptomatic presentations are driven by dysregulated function of the autonomic nervous system and hyperirritability of the sympathetic nervous system. Given the increasing incidence of NOWS, there is an alarming lack of knowledge regarding the long-term effects of perinatal opioid exposure on behavioral and neurodevelopmental outcomes. Murine models provide efficient means to understand the neurobiological adaptations impacted by opioid exposure during perinatal neurodevelopment that drive long-term effects on cognitive, social, affective, and reward-related behaviors. We describe a rodent model of third-trimester-equivalent opioid exposure which produces replicable, opioid withdrawal-related phenotypes including robust thermal hyperalgesia and altered ultrasonic vocalization (USV) profiles. We present results from two drug regimens of the model, differing in the schedule of opioid administration (once or twice daily injections of morphine from postnatal day (P) 1-14; 15.0 mg/kg). Beyond hyperalgesia and altered USV profiles, both drug regimens lead to weight loss. Furthermore, both models resulted in transcriptional adaptations within brain regions relevant to opioid dependence and withdrawal. Twice-daily exposure resulted in sex-specific changes in metabolic gene expression in the brainstem, while once-daily exposure resulted in down-regulation of genes related to myelin and dopaminergic circuitry development in the nucleus accumbens. We found minimal evidence for behavioral consequences associated with once-daily morphine exposure during adulthood; there were no significant effects of perinatal morphine on cognitive, reward-related, or fear learning tasks. This could potentially indicate compensatory mechanisms that mitigate the adverse effects of third trimester-equivalent morphine exposure over time. Lastly, we identified epigenetic mechanisms potentially driving dysregulation of normal development within the central nervous system following pre-natal opioid exposure in humans. We analyzed placental samples from pregnancies with opioid exposure and identified gene networks containing altered DNA methylation patterns. Notably, we found enrichment within the ‘integral component of the plasma membrane’ and ‘synapse assembly’ functional networks, indicating potential effects of prenatal opioid exposure on neural connectivity and transmission. Together, the transcriptional adaptations identified in rodent brain tissue and the epigenetic modifications identified in human placental tissue provide novel mechanistic insight as to how perinatal opioid exposure impacts neural and fetal development

Intrauterine Exposure to Maternal Stress Alters Bdnf IV DNA Methylation and Telomere Length in the Brain of Adult Rat Offspring

DNA methylation (addition of methyl groups to cytosines which normally represses gene transcription) and changes in telomere length (TTAGGG repeats on the ends of chromosomes) are two molecular modifications that result from stress and could contribute to the long-term effects of intrauterine exposure to maternal stress on offspring behavioral outcomes. Here, we measured methylation of Brain-derived neurotrophic factor (Bdnf), a gene important in development and plasticity, and telomere length in the brains of adult rat male and female offspring whose mothers were exposed to unpredictable and variable stressors throughout gestation. Males exposed to prenatal stress had greater methylation (Bdnf IV) in the medial prefrontal cortex (mPFC) compared to non-stressed controls. Further, prenatally-stressed males had shorter telomeres than controls in the mPFC. This study provides the first evidence in a rodent model of an association between prenatal stress exposure and subsequent shorter brain telomere length. Together findings indicate a long-term impact of prenatal stress on DNA methylation and telomere biology with relevance for behavioral and health outcomes, and contribute to a growing literature linking stress to intergenerational epigenetic alterations and changes in telomere length

Effect of Prenatal Opioid Exposure on the Human Placental Methylome

Prenatal exposure to addictive drugs can lead to placental epigenetic modifications, but a methylome-wide evaluation of placental DNA methylation changes after prenatal opioid exposure has not yet been performed. Placental tissue samples were collected at delivery from 19 opioid-exposed and 20 unexposed control full-term pregnancies. Placental DNA methylomes were profiled using the Illumina Infinium HumanMethylationEPIC BeadChip. Differentially methylated CpG sites associated with opioid exposure were identified with a linear model using the ‘limma’ R package. To identify differentially methylated regions (DMRs) spanning multiple CpG sites, the ‘DMRcate’ R package was used. The functions of genes mapped by differentially methylated CpG sites and DMRs were further annotated using Enrichr. Differentially methylated CpGs (n = 684, unadjusted p < 0.005 and |∆β| ≥ 0.05) were mapped to 258 genes (including PLD1, MGAM, and ALCS2). Differentially methylated regions (n = 199) were located in 174 genes (including KCNMA1). Enrichment analysis of the top differentially methylated CpG sites and regions indicated disrupted epigenetic regulation of genes involved in synaptic structure, chemical synaptic transmission, and nervous system development. Our findings imply that placental epigenetic changes due to prenatal opioid exposure could result in placental dysfunction, leading to abnormal fetal brain development and the symptoms of opioid withdrawal in neonates

Intracranial self-stimulation and concomitant behaviors following systemic methamphetamine administration in Hnrnph1 mutant mice

RationaleMethamphetamine (MA) addiction is a major public health issue in the USA, with a poorly understood genetic component. We previously identified heterogeneous nuclear ribonucleoprotein H1 (Hnrnph1; H1) as a quantitative trait gene underlying sensitivity to MA-induced behavioral sensitivity. Mice heterozygous for a frameshift deletion in the first coding exon of H1 (H1+/-) showed reduced MA phenotypes including oral self-administration, locomotor activity, dopamine release, and dose-dependent differences in MA conditioned place preference. However, the effects of H1+/- on innate and MA-modulated reward sensitivity are not known.ObjectivesWe examined innate reward sensitivity and facilitation by MA in H1+/- mice via intracranial self-stimulation (ICSS).MethodsWe used intracranial self-stimulation (ICSS) of the medial forebrain bundle to assess shifts in reward sensitivity following acute, ascending doses of MA (0.5-4.0 mg/kg, i.p.) using a within-subjects design. We also assessed video-recorded behaviors during ICSS testing sessions.ResultsH1+/- mice displayed reduced normalized maximum response rates in response to MA. H1+/- females had lower normalized M50 values compared to wild-type females, suggesting enhanced reward facilitation by MA. Finally, regardless of genotype, there was a dose-dependent reduction in distance to the response wheel following MA administration, providing an additional measure of MA-induced reward-driven behavior.ConclusionsH1+/- mice displayed a complex ICSS phenotype following MA, displaying indications of both blunted reward magnitude (lower normalized maximum response rates) and enhanced reward sensitivity specific to H1+/- females (lower normalized M50 values)