Oligodendrocyte responses to buprenorphine uncover novel and opposing roles of μ-opioid- and nociceptin/orphanin FQ receptors in cell development: implications for drug addiction treatment during pregnancy

Investigating the neurobiology of maternal opioid use disorder and prenatal opioid exposure using brain organoid technology

Over the past two decades, Opioid Use Disorder (OUD) among pregnant women has become a major global public health concern. OUD has been characterized as a problematic pattern of opioid use despite adverse physical, psychological, behavioral, and or social consequences. Due to the relapsing-remitting nature of this disorder, pregnant mothers are chronically exposed to exogenous opioids, resulting in adverse neurological and neuropsychiatric outcomes. Collateral fetal exposure to opioids also precipitates severe neurodevelopmental and neurocognitive sequelae. At present, much of what is known regarding the neurobiological consequences of OUD and prenatal opioid exposure (POE) has been derived from preclinical studies in animal models and postnatal or postmortem investigations in humans. However, species-specific differences in brain development, variations in subject age/health/background, and disparities in sample collection or storage have complicated the interpretation of findings produced by these explorations. The ethical or logistical inaccessibility of human fetal brain tissue has also limited direct examinations of prenatal drug effects. To circumvent these confounding factors, recent groups have begun employing induced pluripotent stem cell (iPSC)-derived brain organoid technology, which provides access to key aspects of cellular and molecular brain development, structure, and function in vitro. In this review, we endeavor to encapsulate the advancements in brain organoid culture that have enabled scientists to model and dissect the neural underpinnings and effects of OUD and POE. We hope not only to emphasize the utility of brain organoids for investigating these conditions, but also to highlight opportunities for further technical and conceptual progress. Although the application of brain organoids to this critical field of research is still in its nascent stages, understanding the neurobiology of OUD and POE via this modality will provide critical insights for improving maternal and fetal outcomes.

Neurocognitive Functions After 6-Month Buprenorphine (Naloxone)-Based Opioid Agonist Maintenance Treatment: A Controlled Prospective Study

BACKGROUND

Medications for opioid use disorder (OUD) may influence neurocognitive functions. Inadequate power, confounders, and practice effects limit the validity of the existing research. We examined the change in cognitive functions in patients with OUD at 6-month buprenorphine (naloxone) posttreatment and compared the cognitive performance of the buprenorphine-treated group with control subjects.

METHODS

We recruited 498 patients with OUD within a week of initiating buprenorphine. Assessments were done twice-at baseline and 6 months. Those abstinent from illicit opioids and adherent to treatment (n = 199) underwent follow-up assessments. Ninety-eight non-substance-using control subjects were recruited from the community. The neurocognitive assessments comprised the Wisconsin Card Sorting Test, Iowa Gambling Task, Trail-Making Tests A and B (TMT-A and TMT-B), and verbal and visual N-Back Test. We controlled for potential effect modifiers.

RESULTS

Twenty-five of the 32 test parameters significantly improved with 6 months of buprenorphine treatment; 20 parameters withstood corrections for multiple comparisons (P < 0.001). The improved test domains spread across cognitive tests: Wisconsin Card Sorting Test (perseverative errors and response, categories completed, conceptual responses), TMTs (time to complete), verbal and visual N-Back Tests (hits, omission, and total errors). After treatment, OUD (vs control subjects) had less perseverative response and error (P < 0.001) and higher conceptual response (P = 0.004) and took lesser time to complete TMT-A (P < 0.001) and TMT-B (P = 0.005). The baseline neurocognitive functions did not differ between those who retained and those who discontinued the treatment.

CONCLUSION

Cognitive functions improve in patients with OUD on buprenorphine. This improvement is unlikely to be accounted for by the practice effect, selective attrition, and potential confounders.

Morphine exposure and prematurity affect flash visual evoked potentials in preterm infants

Objective

The present study aimed to explore first the impact of perinatal risk factors on flash-VEP waves and morphology in a group of preterm infants studied at term equivalent age (TEA). Second, to correlate VEP morphology with neurological outcome at 2 years corrected age (CA).

Methods

Infants with a gestational age (GA) at birth <32 weeks, without major brain injury, were enrolled. Multivariate regression analyses were performed, and the models were run separately for each dependent variable N2, P2, N3 latencies and P2 amplitude. Logistic regression was applied to study N4 component (present/absent) and VEP morphology (regular/irregular). The predictors were GA, bronchopulmonary dysplasia (BPD), postmenstrual age at VEP registration, cumulative morphine and fentanyl dose, and painful procedures. Lastly, linear regression models were performed to assess the relation between the Bayley-III cognitive and motor scores at 2 years CA and VEP morphology, in relation to GA, BPD, painful procedures and cumulative morphine dose.

Results

Eighty infants were enrolled. Morphine was the predictor of N2 (R2 = 0.09, p = 0.006), P2 (R2 = 0.11, p = 0.002), and N3 (R2 = 0.13, p = 0.003) latencies. Younger GA was associated with lower amplitude (R2 = 0.05, p = 0.029). None of the independent variables predicted the presence of N4 component, nor VEP morphology in the logistic analysis. VEP morphology was not associated with cognitive and motor scores at 2 years.

Conclusions

Morphine treatment and prematurity were risk factors for altered VEPs parameters at TEA. In our cohort VEP morphology did not predict neurological outcome.

Significance

Morphine administration should be evaluated according to potential risks and benefits, and dosage individually accustomed, according to pain and comfort scores, considering the possible risk for neurodevelopmental impairment.

Decreased myelin-related gene expression in the nucleus accumbens during spontaneous neonatal opioid withdrawal in the absence of long-term behavioral effects in adult outbred CFW mice

Prenatal opioid exposure is a major health concern in the United States, with the incidence of neonatal opioid withdrawal syndrome (NOWS) escalating in recent years. NOWS occurs upon cessation of in utero opioid exposure and is characterized by increased irritability, disrupted sleep patterns, high-pitched crying, and dysregulated feeding. The main pharmacological strategy for alleviating symptoms is treatment with replacement opioids. The neural mechanisms mediating NOWS and the long-term neurobehavioral effects are poorly understood. We used a third trimester-approximate model in which neonatal outbred pups (Carworth Farms White; CFW) were administered once-daily morphine (15 mg/kg, s.c.) from postnatal day (P) day 1 through P14 and were then assessed for behavioral and transcriptomic adaptations within the nucleus accumbens (NAc) on P15. We also investigated the long-term effects of perinatal morphine exposure on adult learning and reward sensitivity. We observed significant weight deficits, spontaneous thermal hyperalgesia, and altered ultrasonic vocalization (USV) profiles following repeated morphine and during spontaneous withdrawal. Transcriptome analysis of NAc from opioid-withdrawn P15 neonates via bulk mRNA sequencing identified an enrichment profile consistent with downregulation of myelin-associated transcripts. Despite the neonatal behavioral and molecular effects, there were no significant long-term effects of perinatal morphine exposure on adult spatial memory function in the Barnes Maze, emotional learning in fear conditioning, or in baseline or methamphetamine-potentiated reward sensitivity as measured via intracranial self-stimulation. Thus, the once daily third trimester-approximate exposure regimen, while inducing NOWS model traits and significant transcriptomic effects in neonates, had no significant long-term effects on adult behaviors.

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.

Decreased myelin-related gene expression in the nucleus accumbens during spontaneous neonatal opioid withdrawal in the absence of long-term behavioral effects in adult outbred CFW mice

Prenatal opioid exposure is a major health concern in the United States, with the incidence of neonatal opioid withdrawal syndrome (NOWS) escalating in recent years. NOWS occurs upon cessation of in utero opioid exposure and is characterized by increased irritability, disrupted sleep patterns, high-pitched crying, and dysregulated feeding. The main pharmacological strategy for alleviating symptoms is treatment with replacement opioids. The neural mechanisms mediating NOWS and the long-term neurobehavioral effects are poorly understood. We used a third trimester-approximate model in which neonatal outbred pups (Carworth Farms White; CFW) were administered once-daily morphine (15 mg/kg, s.c.) from postnatal day (P) day 1 through P14 and were then assessed for behavioral and transcriptomic adaptations within the nucleus accumbens (NAc) on P15. We also investigated the long-term effects of perinatal morphine exposure on adult learning and reward sensitivity. We observed significant weight deficits, spontaneous thermal hyperalgesia, and altered ultrasonic vocalization (USV) profiles following repeated morphine and during spontaneous withdrawal. Transcriptome analysis of NAc from opioid-withdrawn P15 neonates via bulk mRNA sequencing identified an enrichment profile consistent with downregulation of myelin-associated transcripts. Despite the neonatal behavioral and molecular effects, there were no significant long-term effects of perinatal morphine exposure on adult spatial memory function in the Barnes Maze, emotional learning in fear conditioning, or in baseline or methamphetamine-potentiated reward sensitivity as measured via intracranial self-stimulation. Thus, the once daily third trimester-approximate exposure regimen, while inducing NOWS model traits and significant transcriptomic effects in neonates, had no significant long-term effects on adult behaviors.

HIGHLIGHTS

We replicated some NOWS model traits via 1x-daily morphine (P1-P14).We found a downregulation of myelination genes in nucleus accumbens on P15.There were no effects on learning/memory or reward sensitivity in adults.

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.

Role of Brain Modulators in Neurodevelopment: Focus on Autism Spectrum Disorder and Associated Comorbidities

Autism spectrum disorder (ASD) and associated neurodevelopmental disorders share similar pathogenesis and clinical features. Pathophysiological changes in these diseases are rooted in early neuronal stem cells in the uterus. Several genetic and environmental factors potentially perturb neurogenesis and synaptogenesis processes causing incomplete or altered maturation of the brain that precedes the symptomology later in life. In this review, the impact of several endogenous neuromodulators and pharmacological agents on the foetus during pregnancy, manifested on numerous aspects of neurodevelopment is discussed. Within this context, some possible insults that may alter these modulators and therefore alter their role in neurodevelopment are high-lighted. Sometimes, a particular insult could influence several neuromodulator systems as is supported by recent research in the field of ASD and associated disorders. Dopaminergic hy-pothesis prevailed on the table for discussion of the pathogenesis of schizophrenia (SCH), atten-tion-deficit hyperactivity disorder (ADHD) and ASD for a long time. However, recent cumulative evidence suggests otherwise. Indeed, the neuromodulators that are dysregulated in ASD and comorbid disorders are as diverse as the causes and symptoms of this disease. Additionally, these neuromodulators have roles in brain development, further complicating their involvement in comorbidity. This review will survey the current understanding of the neuromodulating systems to serve the pharmacological field during pregnancy and to minimize drug-related insults in pa-tients with ASD and associated comorbidity disorders, e.g., SCH or ADHD.

Inhibition of Oligodendrocyte Apoptosis in the Prelimbic Medial Prefrontal Cortex Prevents Fentanyl-induced Hyperalgesia in Rats

Opioid-induced hyperalgesia (OIH) is a problem associated with prolonged use of opioids in chronic pain management, and its effective treatment has been hampered by lack of mechanistic evidence. Oligodendrocytes have recently been linked with several pain-related diseases; however, little is known its role in OIH. The prelimbic medial prefrontal cortex (PL-mPFC) has emerged as a significant center of pain regulation, and is rich in oligodendrocytes. Herein we explored the effect of oligodendrocyte apoptosis of PL-mPFC on OIH. Using a fentanyl-induced rat model of OIH and proteomics analysis of the PL-mPFC, we observed a downregulation in 5 types of myelin-related proteins originating from oligodendrocytes; this was further verified by western blotting. Meanwhile, cleaved-caspase 3 (an apoptosis marker) was increased, whereas the oligodendrocyte precursor cell (OPC) marker NG2 remained unchanged. These results suggest that downregulated myelin-related proteins may be associated with oligodendrocyte apoptosis rather than a reduction in their generating source, and immunohistochemistry confirmed this hypothesis. Behaviorally, prophylactic blockade of oligodendrocyte apoptosis by microinjection of z-DEVD-fmk into the PL-mPFC prevented fentanyl-induced mechanical and thermal hyperalgesia, but downregulated myelin basic protein (mbp) gradually recovered in 12 h. We suggest that OIH may be primed in part via oligodendrocyte apoptosis in the PL-mPFC. PERSPECTIVE: In this study we showed that oligodendrocyte apoptosis in the PL-mPFC is a key trigger for fentanyl-induced hyperalgesia. Targeting oligodendrocyte apoptosis in the PL-mPFC may prevented hyperalgesia priming induced by fentanyl.

Cognitive Dysfunction After Analgesia and Sedation: Out of the Operating Room and Into the Pediatric Intensive Care Unit

In the midst of concerns for potential neurodevelopmental effects after surgical anesthesia, there is a growing awareness that children who require sedation during critical illness are susceptible to neurologic dysfunctions collectively termed pediatric post-intensive care syndrome, or PICS-p. In contrast to healthy children undergoing elective surgery, critically ill children are subject to inordinate neurologic stress or injury and need to be considered separately. Despite recognition of PICS-p, inconsistency in techniques and timing of post-discharge assessments continues to be a significant barrier to understanding the specific role of sedation in later cognitive dysfunction. Nonetheless, available pediatric studies that account for analgesia and sedation consistently identify sedative and opioid analgesic exposures as risk factors for both in-hospital delirium and post-discharge neurologic sequelae. Clinical observations are supported by animal models showing neuroinflammation, increased neuronal death, dysmyelination, and altered synaptic plasticity and neurotransmission. Additionally, intensive care sedation also contributes to sleep disruption, an important and overlooked variable during acute illness and post-discharge recovery. Because analgesia and sedation are potentially modifiable, understanding the underlying mechanisms could transform sedation strategies to improve outcomes. To move the needle on this, prospective clinical studies would benefit from cohesion with regard to datasets and core outcome assessments, including sleep quality. Analyses should also account for the wide range of diagnoses, heterogeneity of this population, and the dynamic nature of neurodevelopment in age cohorts. Much of the related preclinical evidence has been studied in comparatively brief anesthetic exposures in healthy animals during infancy and is not generalizable to critically ill children. Thus, complementary animal models that more accurately "reverse translate" critical illness paradigms and the effect of analgesia and sedation on neuropathology and functional outcomes are needed. This review explores the interactive role of sedatives and the neurologic vulnerability of critically ill children as it pertains to survivorship and functional outcomes, which is the next frontier in pediatric intensive care.

Endogenous and exogenous opioid effects on oligodendrocyte biology and developmental brain myelination

The elevated presence of opioid receptors and their ligands throughout the developing brain points to the existence of maturational functions of the endogenous opioid system that still remain poorly understood. The alarmingly increasing rates of opioid use and abuse underscore the urgent need for clear identification of those functions and the cellular bases and molecular mechanisms underlying their physiological roles under normal and pathological conditions. This review is focused on current knowledge on the direct and indirect regulatory roles that opioids may have on oligodendrocyte development and their generation of myelin, a complex insulating membrane that not only facilitates rapid impulse conduction but also participates in mechanisms of brain plasticity and adaptation. Information is examined in relation to the importance of endogenous opioid function, as well as direct and indirect effects of opioid analogues, which like methadone and buprenorphine are used in medication-assisted therapies for opioid addiction during pregnancy and pharmacotherapy in neonatal abstinence syndrome. Potential opioid effects are also discussed regarding late myelination of the brain prefrontal cortex in adolescents and young adults. Such knowledge is fundamental for the design of safer pharmacological interventions for opioid abuse, minimizing deleterious effects in the developing nervous system.

Neonatal opioid exposure: public health crisis and novel neuroinflammatory disease

Substance use, specifically the use of prescription and non-prescription opioids among pregnant women, is a major public health issue and chief contributor to the opioid crisis. The prevalence of Neonatal Opioid Withdrawal Syndrome has risen 5-fold in the past decade, and is a well-recognized consequence of perinatal opioid exposure. By contrast, the long-term damage to the developing brain from opioid medications is just beginning to be recognized as a serious concern. Published data suggest that opioid exposure commencing in utero negatively affects the maturation of the neural-immune system, and trajectory of central nervous system development. Methadone induces peripheral immune hyper-reactivity, lasting structural and microstructural brain injury, and significant deficits in executive function and cognitive control in adult animals following in utero exposure. Thus, to address the cascading public health crisis stemming from the multitude of infants with in utero opioid exposure who will grow up with altered neurodevelopmental trajectories, rigorous preclinical, mechanistic studies are required. Such studies will define the long-term sequelae of prenatal opioid exposure in an effort to develop appropriate and targeted interventions. Specifically, the development of novel fluid, neuroimaging and biobehavioral biomarkers will be the most useful to aid in early identification and treatment of opioid exposed infants with the greatest risk of poor clinical outcomes. These studies will be essential to understand how in utero insults determine brain structure and function in adulthood, and what targeted interventions will be required to improve long-term outcomes in the countless children being born exposed to opioids each year.

Endogenous opioid peptides and brain development: Endomorphin-1 and Nociceptin play a sex-specific role in the control of oligodendrocyte maturation and brain myelination

The generation of fully functional oligodendrocytes, the myelinating cells of the central nervous system, is preceded by a complex maturational process. We previously showed that the timing of oligodendrocyte differentiation and rat brain myelination were altered by perinatal exposure to buprenorphine and methadone, opioid analogs used for the management of pregnant addicts. Those observations suggested the involvement of the μ-opioid receptor (MOR) and the nociceptin/orphanin FQ receptor (NOR). However, it remained to be determined if these receptors and their endogenous ligands could indeed control the timing of myelination under normal physiological conditions of brain development. We now found that the endogenous MOR ligand endomorphin-1 (EM-1) exerts a striking stimulatory action on cellular and morphological maturation of rat pre-oligodendrocytes, but unexpectedly, these effects appear to be restricted to the cells from the female pups. Critically, this stimulation is abolished by coincubation with the endogenous NOR ligand nociceptin. Furthermore, NOR antagonist treatment of 9-day-old female pups results in accelerated brain myelination. Interestingly, the lack of sex-dependent differences in developmental brain levels of EM-1 and nociceptin, or oligodendroglial expression of MOR and NOR, suggests that the observed sex-specific responses may be highly dependent on important intrinsic differences between the male and female oligodendrocytes. The discovery of a significant effect of EM-1 and nociceptin in the developing female oligodendrocytes and brain myelination, underscores the need for further studies investigating brain sex-related differences and their implications in opioid use and abuse, pain control, and susceptibility and remyelinating capacity in demyelinating disease as multiple sclerosis.

Opioid system influences gut-brain axis: Dysbiosis and related alterations

Opioid drugs are widely used to treat chronic pain, but their misuse can lead to tolerance, dependence, and addiction and have created a significant public health problem. In addition, food-derived opioid peptides, known as exorphins, like gluten exorphins have been shown to have harmful effects in certain pathologies like celiac disease, for example. Several studies support the involvement of the opioid system in the development of disorders such as autism spectrum syndrome. Moreover, bidirectional communication between the intestine and brain has been shown to be altered in various neurodegenerative diseases including Alzheimer´s and Parkinson´s. The presence of opioid receptors in both the digestive tract and the central nervous system (CNS) suggests that opioid drugs and exorphins may modulate the gut-brain axis. Morphine, for example, has shown a dysbiotic effect on the bacterial microbiota in addition to inducing an increase in intestinal permeability facilitating bacterial translocation. Furthermore, certain components of bacteria can modify the expression of opioid receptors at the central level increasing sensitivity to pain. Strategies based on use of probiotics have resulted in improvements in symptoms of autism and Parkinson´s disease. In this manuscript, we review the role of the opioid system in disorders and CNS pathologies and the involvement of the gut-brain axis.

Clinical and basic research investigations into the long-term effects of prenatal opioid exposure on brain development

Coincident with the opioid epidemic in the United States has been a dramatic increase in the number of children born with neonatal abstinence syndrome (NAS), a form of withdrawal resulting from opioid exposure during pregnancy. Many research efforts on NAS have focused on short-term care, including acute symptom treatment and weaning of the infants off their drug dependency prior to authorizing their release. However, investigations into the long-term effects of prenatal opioid exposure (POE) on brain development, from the cellular to the behavioral level, have not been as frequent. Given the importance of the perinatal period for human brain development, opioid-induced disturbances in the formation and function of nascent synaptic networks and glia have the potential to impact brain connectivity and cognition long after the drug supply is cutoff shortly after birth. In this review, we will summarize the current state of NAS research, bringing together findings from human studies and preclinical animal models to highlight what is known about how POE can induce significant, prolonged deficits in brain structure and function. With rates of NAS continuing to rise, particularly in regions that already face substantial socioeconomic challenges, we speculate as to the most promising avenues for future research to alleviate this growing multigenerational threat.

Potential Neurodevelopmental Effects of Pediatric Intensive Care Sedation and Analgesia: Repetitive Benzodiazepine and Opioid Exposure Alters Expression of Glial and Synaptic Proteins in Juvenile Rats

Sedatives are suspected contributors to neurologic dysfunction in PICU patients, to whom they are administered during sensitive neurodevelopment. Relevant preclinical modeling has largely used comparatively brief anesthesia in infant age-approximate animals, with insufficient study of repetitive combined drug administration during childhood. We hypothesized that childhood neurodevelopment is selectively vulnerable to repeated treatment with benzodiazepine and opioid. We report a preclinical model of combined midazolam and morphine in early childhood age-approximate rats.

Single-Cell RNA-Seq Uncovers a Robust Transcriptional Response to Morphine by Glia

Molecular and behavioral responses to opioids are thought to be primarily mediated by neurons, although there is accumulating evidence that other cell types play a prominent role in drug addiction. To investigate cell-type-specific opioid responses, we performed single-cell RNA sequencing (scRNA-seq) of the nucleus accumbens of mice following acute morphine treatment. Differential expression analysis uncovered unique morphine-dependent transcriptional responses by oligodendrocytes and astrocytes. We examined the expression of selected genes, including Cdkn1a and Sgk1, by FISH, confirming their induction by morphine in oligodendrocytes. Further analysis using RNA-seq of FACS-purified oligodendrocytes revealed a large cohort of morphine-regulated genes. The affected genes are enriched for roles in cellular pathways intimately linked to oligodendrocyte maturation and myelination, including the unfolded protein response. Altogether, our data illuminate the morphine-dependent transcriptional response by oligodendrocytes and offer mechanistic insights into myelination defects associated with opioid abuse.

A review on neuroimaging studies of genetic and environmental influences on early brain development

The past decades witnessed a surge of interest in neuroimaging study of normal and abnormal early brain development. Structural and functional studies of normal early brain development revealed massive structural maturation as well as sequential, coordinated, and hierarchical emergence of functional networks during the infancy period, providing a great foundation for the investigation of abnormal early brain development mechanisms. Indeed, studies of altered brain development associated with either genetic or environmental risks emerged and thrived. In this paper, we will review selected studies of genetic and environmental risks that have been relatively more extensively investigated-familial risks, candidate risk genes, and genome-wide association studies (GWAS) on the genetic side; maternal mood disorders and prenatal drug exposures on the environmental side. Emerging studies on environment-gene interactions will also be reviewed. Our goal was not to perform an exhaustive review of all studies in the field but to leverage some representative ones to summarize the current state, point out potential limitations, and elicit discussions on important future directions.

N/OFQ-NOP System in Peripheral and Central Immunomodulation

Classical opioids (μ: mu, MOP; δ: delta, DOP and κ: kappa, KOP) variably affect immune function; they are immune depressants and there is good clinical evidence in the periphery. In addition, there is evidence for a central role in the control of a number of neuropathologies, e.g., neuropathic pain. Nociceptin/Orphanin FQ (N/OFQ) is the endogenous ligand for the N/OFQ peptide receptor, NOP; peripheral and central activation can modulate immune function. In the periphery, NOP activation generally depresses immune function, but unlike classical opioids this is in part driven by NOP located on circulating immune cells. Peripheral activation has important implications in pathologies like asthma and sepsis. NOP is expressed on central neurones and glia where activation can modulate glial function. Microglia, as resident central 'macrophages', increase/infiltrate in pain and following trauma; these changes can be reduced by N/OFQ. Moreover, the interaction with other glial cell types such as the ubiquitous astrocytes and their known cross talk with microglia open a wealth of possibilities for central immunomodulation. At the whole animal level, clinical ligands with wide central and peripheral distribution have the potential to modulate immune function, and defining the precise nature of that interaction is important in mitigating or even harnessing the adverse effect profile of these important drugs.

A Monoclonal Antibody against 6-Acetylmorphine Protects Female Mice Offspring from Adverse Behavioral Effects Induced by Prenatal Heroin Exposure

Escalating opioid use among fertile women has increased the number of children being exposed to opioids during fetal life. Furthermore, accumulating evidence links prenatal opioid exposure, including opioid maintenance treatment, to long-term negative effects on cognition and behavior, and presses the need to explore novel treatment strategies for pregnant opioid users. The present study examined the potential of a monoclonal antibody (mAb) targeting heroin's first metabolite, 6-acetylmorphine (6-AM), in providing fetal protection against harmful effects of prenatal heroin exposure in mice. First, we examined anti-6-AM mAb's ability to block materno-fetal transfer of active metabolites after maternal heroin administration. Next, we studied whether maternal mAb pretreatment could prevent adverse effects in neonatal and adolescent offspring exposed to intrauterine heroin (3 × 1.05 mg/kg). Anti-6-AM mAb pretreatment of pregnant dams profoundly reduced the distribution of active heroin metabolites to the fetal brain. Furthermore, maternal mAb administration prevented hyperactivity and drug sensitization in adolescent female offspring prenatally exposed to heroin. Our findings demonstrate that passive immunization with a 6-AM-specific antibody during pregnancy provides fetal neuroprotection against heroin metabolites, and thereby prevents persistent adverse behavioral effects in the offspring. An immunotherapeutic approach to protect the fetus against long-term effects of prenatal drug exposure has not been reported previously, and should be further explored as prophylactic treatment of pregnant heroin users susceptible to relapse.

A Novel Role for Oligodendrocyte Precursor Cells (OPCs) and Sox10 in Mediating Cellular and Behavioral Responses to Heroin

Opiate abuse and addiction have become a worldwide epidemic with great societal and financial burdens, highlighting a critical need to understand the neurobiology of opiate addiction. Although several studies have focused on drug-dependent changes in neurons, the role of glia in opiate addiction remains largely unstudied. RNA sequencing pathway analysis from the prefrontal cortex (PFC) of male rats revealed changes in several genes associated with oligodendrocyte differentiation and maturation following heroin self-administration. Among these genes changed was Sox10, which is regulated, in part, by the chromatin remodeler BRG1/SMARCA4. To directly test the functional role of Sox10 in mediating heroin-induced behavioral plasticity, we selectively overexpressed Sox10 and BRG1 in the PFC. Overexpression of either Sox10 or BRG1 decreased the motivation to obtain heroin infusions in a progressive ratio test without altering the acquisition or maintenance of heroin self-administration. These data demonstrate a critical, and perhaps compensatory, role of Sox10 and BRG1 in oligodendrocytes in regulating the motivation for heroin.

Novel role of the nociceptin system as a regulator of glutamate transporter expression in developing astrocytes

Our previous results showed that oligodendrocyte development is regulated by both nociceptin and its G-protein coupled receptor, the nociceptin/orphanin FQ receptor (NOR). The present in vitro and in vivo findings show that nociceptin plays a crucial conserved role regulating the levels of the glutamate/aspartate transporter GLAST/EAAT1 in both human and rodent brain astrocytes. This nociceptin-mediated response takes place during a critical developmental window that coincides with the early stages of astrocyte maturation. GLAST/EAAT1 upregulation by nociceptin is mediated by NOR and the downstream participation of a complex signaling cascade that involves the interaction of several kinase systems, including PI-3K/AKT, mTOR, and JAK. Because GLAST is the main glutamate transporter during brain maturation, these novel findings suggest that nociceptin plays a crucial role in regulating the function of early astrocytes and their capacity to support glutamate homeostasis in the developing brain.

Pharmacotherapy for Neonatal Abstinence Syndrome: Choosing the Right Opioid or No Opioid at All

Neonatal abstinence syndrome (NAS) from in utero opioid exposure has reached epidemic levels in the United States. Although nonpharmacologic therapies form the foundation of care, many neonates require pharmacotherapy. Morphine represents the most widely used first-line agent and effectively treats the symptoms of withdrawal. However, methadone or buprenorphine may facilitate earlier discharge. Although phenobarbital is traditionally used when opioids fail, clonidine may be a more appropriate adjunctive agent to minimize negative neurodevelopmental impact. Consideration of the available data allows hospitals to generate effective pharmacologic strategies to manage NAS while further research continues.

Opiate Drugs with Abuse Liability Hijack the Endogenous Opioid System to Disrupt Neuronal and Glial Maturation in the Central Nervous System

The endogenous opioid system, comprised of multiple opioid neuropeptide and receptor gene families, is highly expressed by developing neural cells and can significantly influence neuronal and glial maturation. In many central nervous system (CNS) regions, the expression of opioid peptides and receptors occurs only transiently during development, effectively disappearing with subsequent maturation only to reemerge under pathologic conditions, such as with inflammation or injury. Opiate drugs with abuse liability act to modify growth and development by mimicking the actions of endogenous opioids. Although typically mediated by μ-opioid receptors, opiate drugs can also act through δ- and κ-opioid receptors to modulate growth in a cell-type, region-specific, and developmentally regulated manner. Opioids act as biological response modifiers and their actions are highly contextual, plastic, modifiable, and influenced by other physiological processes or pathophysiological conditions, such as neuro-acquired immunodeficiency syndrome. To date, most studies have considered the acute effects of opiates on cellular maturation. For example, activating opioid receptors typically results in acute growth inhibition in both neurons and glia. However, with sustained opioid exposure, compensatory factors become operative, a concept that has been largely overlooked during CNS maturation. Accordingly, this article surveys prior studies on the effects of opiates on CNS maturation, and also suggests new directions for future research in this area. Identifying the cellular and molecular mechanisms underlying the adaptive responses to chronic opiate exposure (e.g., tolerance) during maturation is crucial toward understanding the consequences of perinatal opiate exposure on the CNS.

Cellular and network-level adaptations to in utero methadone exposure along the ventral respiratory column in the neonate rat

Neonatal abstinence syndrome (NAS) occurs in babies chronically exposed to opioids during pregnancy. NAS shares features with opioid withdrawal symptoms seen in adults, including autonomic dysregulation. Here, the effect of low-dose in utero methadone (MTD) exposure on respiration-modulated networks along the ventral respiratory column (VRC) in ventrolateral medulla was investigated in the neonate Sprague-Dawley rat. MTD was administered via drinking water (3mg/kg/day in drinking water of the mother E7-E21). Lower expression levels of myelin-associated proteins phosphorylated axonal neurofilament subunit H (pNFH), 2',3'-Cyclicnucleotide 3'-phosphodiesterase (CNPase) and myelin basic protein (MBP), in MTD-exposed pups compared to controls at P3, P6 and P10 indicated MTD transport across the placenta. We investigated whether in utero MTD exposure led to network-level excitability changes consistent with tolerance, and also probed for changes in endogenous opioid modulation of respiratory networks. To this end, high-speed (45.5Hz) optical recordings of respiratory network activity in control and MTD-exposed neonate (P0-P2) pups before and during administration of the μ-opioid receptor antagonist naloxone (NAL; 10μM) were carried out. Spike rate was estimated from optical traces via deconvolution, and coupling between all neuron pairs in recorded networks was quantified using the normalized transfer entropy (NTE). Recordings of local networks along the VRC, together with recordings of respiratory output from ventral root C1 did not reveal changes in respiratory activity at the system level, but cellular and network changes in MTD-exposed pups were consistent with the development of opioid tolerance. MTD-exposed pups were found to have i. higher neuronal firing rates; ii. higher covariance between neuronal activity and motor output; iii. more bidirectionally and unidirectionally coupled neurons, and fewer uncoupled neurons; iv. stronger coupling and shorter integration times between network constituents. The μ-opioid receptor antagonist NAL did not alter system-level function. The correlation between the activity of neurons caudal to -400μm and motor output was significantly reduced in control animals following NAL. In both control and MTD-exposed pups, the relative number of neurons whose correlation with motor output increased following NAL followed a rostrocaudal gradient along the VRC, with fewer neurons caudally, and more neurons rostrally. The up-regulation of coupling strength, firing rate and coefficient of variation between neurons and motor output following in utero opioid exposure suggests that these networks may contribute to NAS in infants born to opioid-dependent mothers.

Systematic Review of Pharmacological Properties of the Oligodendrocyte Lineage

Oligodendrogenesis and oligodendrocyte precursor maturation are essential processes during the course of central nervous system development, and lead to the myelination of axons. Cells of the oligodendrocyte lineage are generated in the germinal zone from migratory bipolar oligodendrocyte precursor cells (OPCs), and acquire cell surface markers as they mature and respond specifically to factors which regulate proliferation, migration, differentiation, and survival. Loss of myelin underlies a wide range of neurological disorders, some of an autoimmune nature—multiple sclerosis probably being the most prominent. Current therapies are based on the use of immunomodulatory agents which are likely to promote myelin repair (remyelination) indirectly by subverting the inflammatory response, aspects of which impair the differentiation of OPCs. Cells of the oligodendrocyte lineage express and are capable of responding to a diverse array of ligand-receptor pairs, including neurotransmitters and nuclear receptors such as γ-aminobutyric acid, glutamate, adenosine triphosphate, serotonin, acetylcholine, nitric oxide, opioids, prostaglandins, prolactin, and cannabinoids. The intent of this review is to provide the reader with a synopsis of our present state of knowledge concerning the pharmacological properties of the oligodendrocyte lineage, with particular attention to these receptor-ligand (i.e., neurotransmitters and nuclear receptor) interactions that can influence oligodendrocyte migration, proliferation, differentiation, and myelination, and an appraisal of their therapeutic potential. For example, many promising mediators work through Ca²⁺ signaling, and the balance between Ca²⁺ influx and efflux can determine the temporal and spatial properties of oligodendrocytes (OLs). Moreover, Ca²⁺ signaling in OPCs can influence not only differentiation and myelination, but also process extension and migration, as well as cell death in mature mouse OLs. There is also evidence that oligodendroglia exhibit Ca²⁺ transients in response to electrical activity of axons for activity-dependent myelination. Cholinergic antagonists, as well as endocannabinoid-related lipid-signaling molecules target OLs. An understanding of such pharmacological pathways may thus lay the foundation to allow its leverage for therapeutic benefit in diseases of demyelination.

Opiate addiction therapies and HIV-1 Tat: interactive effects on glial [Ca²⁺]i, oxyradical and neuroinflammatory chemokine production and correlative neurotoxicity

Few preclinical studies have compared the relative therapeutic efficacy of medications used to treat opiate addiction in relation to neuroAIDS. Here we compare the ability of methadone and buprenorphine, and the prototypic opiate morphine, to potentiate the neurotoxic and proinflammatory ([Ca²⁺]i, ROS, H2O2, chemokines) effects of HIV-1 Tat in neuronal and/or mixed-glial co-cultures. Repeated observations of neurons during 48 h exposure to combinations of Tat, equimolar concentrations (500 nM) of morphine, methadone, or buprenorphine exacerbated neurotoxicity significantly above levels seen with Tat alone. Buprenorphine alone displayed marked neurotoxicity at 500 nM, prompting additional studies of its neurotoxic effects at 5 nM and 50 nM concentrations ± Tat. In combination with Tat, buprenorphine displayed paradoxical, concentration-dependent, neurotoxic and neuroprotective actions. Buprenorphine neurotoxicity coincided with marked elevations in [Ca²⁺]i, but not increases in glial ROS or chemokine release. Tat by itself elevated the production of CCL5/RANTES, CCL4/MIP-1β, and CCL2/MCP-1. Methadone and buprenorphine alone had no effect, but methadone interacted with Tat to further increase production of CCL5/RANTES. In combination with Tat, all drugs significantly increased glial [Ca²⁺]i, but ROS was only significantly increased by co-exposure with morphine. Taken together, the increases in glial [Ca²⁺]i, ROS, and neuroinflammatory chemokines were not especially accurate predictors of neurotoxicity. Despite similarities, opiates displayed differences in their neurotoxic and neuroinflammatory interactions with Tat. Buprenorphine, in particular, was partially neuroprotective at a low concentration, which may result from its unique pharmacological profile at multiple opioid receptors. Overall, the results reveal differences among addiction medications that may impact neuroAIDS.

Extended access nicotine self-administration with periodic deprivation increases immature neurons in the hippocampus

RATIONALE

Limited access nicotine self-administration decreases hippocampal neurogenesis, providing a mechanism for the deleterious effects of nicotine on hippocampal neuronal plasticity. However, recent studies have shown that limited access nicotine self-administration does not exhibit key features of nicotine dependence such as motivational withdrawal and increased motivation for nicotine after deprivation.

OBJECTIVES

The present study used extended access nicotine self-administration (0.03 mg/kg/infusion, 21 h/day, 4 days) with intermittent periods of deprivation (3 days) for 14 weeks, to test the hypothesis that this model enhances nicotine seeking and produces distinct responses in hippocampal neurogenesis when compared with limited access (1 h/day, 4 days) intake. Animals in the extended access group were either perfused prior to or following their final deprivation period, whereas animals in the limited access group were perfused after their last session.

RESULTS

Limited- and extended access nicotine self-administration with periodic deprivation did not affect proliferation and differentiation of oligodendrocyte progenitors in the medial prefrontal cortex (mPFC). Conversely, extended access nicotine self-administration with periodic deprivation enhanced proliferation and differentiation of hippocampal neural progenitors. Furthermore, in the hippocampus, the number of differentiating NeuroD-labeled cells strongly and positively correlated with enhanced nicotine seeking in rats that experienced extended access nicotine self-administration.

CONCLUSIONS

These findings demonstrate that extended versus limited access to nicotine self-administration differentially affects the generation of new oligodendroglia and new neurons during adulthood. The increases in the number of differentiating cells in extended access nicotine self-administering rats may consequently contribute to aberrant hippocampal neurogenesis and may contribute to maladaptive addiction-like behaviors dependent on the hippocampus.

Buprenorphine, methadone, and morphine treatment during pregnancy: behavioral effects on the offspring in rats

Methadone and buprenorphine are widely used for treating people with opioid dependence, including pregnant women. Prenatal exposure to opioids has devastating effects on the development of human fetuses and may induce long-term physical and neurobehavioral changes during postnatal maturation. This study aimed at comparing the behavioral outcomes of young rats prenatally exposed to buprenorphine, methadone, and morphine. Pregnant Sprague-Dawley rats were administered saline, morphine, methadone, and buprenorphine during embryonic days 3-20. The cognitive function, social interaction, anxiety-like behaviors, and locomotor activity of offsprings were examined by novel object recognition test, social interaction test, light-dark transition test, elevated plus-maze, and open-field test between 6 weeks and 10 weeks of age. Prenatal exposure to methadone and buprenorphine did not affect locomotor activity, but significantly impaired novel object recognition and social interaction in both male and female offsprings in the same manner as morphine. Although prenatal exposure to methadone or buprenorphine increased anxiety-like behaviors in the light-dark transition in both male and female offsprings, the effects were less pronounced as compared to that of morphine. Methadone affected elevated plus-maze in both sex, but buprenorphine only affected the female offsprings. These findings suggest that buprenorphine and methadone maintenance therapy for pregnant women, like morphine, produced detrimental effects on cognitive function and social behaviors, whereas the offsprings of such women might have a lower risk of developing anxiety disorders.

Minocycline enhances the effectiveness of nociceptin/orphanin FQ during neuropathic pain

Nociceptin/orphanin FQ (N/OFQ) antinociception, which is mediated selectively by the N/OFQ peptide receptor (NOP), was demonstrated in pain models. In this study, we determine the role of activated microglia on the analgesic effects of N/OFQ in a rat model of neuropathic pain induced by chronic constriction injury (CCI) to the sciatic nerve. Repeated 7-day administration of minocycline (30 mg/kg i.p.), a drug that affects microglial activation, significantly reduced pain in CCI-exposed rats and it potentiates the analgesic effects of administered N/OFQ (2.5-5 μg i.t.). Minocycline also downregulates the nerve injury-induced upregulation of NOP protein in the dorsal lumbar spinal cord. Our in vitro study showed that minocycline reduced NOP mRNA, but not protein, level in rat primary microglial cell cultures. In [(35)S]GTPγS binding assays we have shown that minocycline increases the spinal N/OFQ-stimulated NOP signaling. We suggest that the modulation of the N/OFQ system by minocycline is due to the potentiation of its neuronal antinociceptive activity and weakening of the microglial cell activation. This effect is beneficial for pain relief, and these results suggest new targets for the development of drugs that are effective against neuropathic pain.

The opioid system and brain development: effects of methadone on the oligodendrocyte lineage and the early stages of myelination

Oligodendrocytes express opioid receptors throughout development, but the role of the opioid system in myelination remains poorly understood. This is a significant problem as opioid use and abuse continue to increase in two particular populations: pregnant addicts (in whom drug effects could target early myelination in the fetus and newborn) and adolescents and young adults (in whom late myelination of 'higher-order' regions takes place). Maintenance treatments for opioid addicts include the long-lasting opioids methadone and buprenorphine. Similar to our previous findings on the effects of buprenorphine, we have now found that early myelination in the developing rat brain is also altered by perinatal exposure to therapeutic doses of methadone. Pups exposed to this drug exhibited elevated brain levels of the 4 major splicing variants of myelin basic protein, myelin proteolipid protein, and myelin-oligodendrocyte glycoprotein. Consistent with the enrichment and function of these proteins in mature myelin, analysis of the corpus callosum in these young animals also indicated an elevated number of axons with already highly compacted myelin sheaths. Moreover, studies in cultured cells showed that methadone exerts direct effects at specific stages of the oligodendrocyte lineage, stimulating the proliferation of progenitor cells while on the other hand accelerating the maturation of the more differentiated but still immature preoligodendrocytes. While the long-term effects of these observations remain unknown, accelerated or increased oligodendrocyte maturation and myelination could both disrupt the complex sequence of synchronized events leading to normal connectivity in the developing brain. Together with our previous observations on the effects of buprenorphine, the present findings further underscore a crucial function of the endogenous opioid system in the control of oligodendrocyte development and the timing of myelination. Interference with these regulatory systems by opioid use or maintenance treatments could disrupt the normal process of brain maturation at critical stages of myelin formation.

Interactions of HIV and drugs of abuse: the importance of glia, neural progenitors, and host genetic factors

Considerable insight has been gained into the comorbid, interactive effects of HIV and drug abuse in the brain using experimental models. This review, which considers opiates, methamphetamine, and cocaine, emphasizes the importance of host genetics and glial plasticity in driving the pathogenic neuron remodeling underlying neuro-acquired immunodeficiency syndrome and drug abuse comorbidity. Clinical findings are less concordant than experimental work, and the response of individuals to HIV and to drug abuse can vary tremendously. Host-genetic variability is important in determining viral tropism, neuropathogenesis, drug responses, and addictive behavior. However, genetic differences alone cannot account for individual variability in the brain "connectome." Environment and experience are critical determinants in the evolution of synaptic circuitry throughout life. Neurons and glia both exercise control over determinants of synaptic plasticity that are disrupted by HIV and drug abuse. Perivascular macrophages, microglia, and to a lesser extent astroglia can harbor the infection. Uninfected bystanders, especially astroglia, propagate and amplify inflammatory signals. Drug abuse by itself derails neuronal and glial function, and the outcome of chronic exposure is maladaptive plasticity. The negative consequences of coexposure to HIV and drug abuse are determined by numerous factors including genetics, sex, age, and multidrug exposure. Glia and some neurons are generated throughout life, and their progenitors appear to be targets of HIV and opiates/psychostimulants. The chronic nature of HIV and drug abuse appears to result in sustained alterations in the maturation and fate of neural progenitors, which may affect the balance of glial populations within multiple brain regions.

Glial abnormalities in substance use disorders and depression: does shared glutamatergic dysfunction contribute to comorbidity?

OBJECTIVES

Preclinical and clinical research in neuropsychiatric disorders, particularly mood and substance use disorders, have historically focused on neurons; however, glial cells-astrocytes, microglia, and oligodendrocytes - also play key roles in these disorders.

METHODS

Peer-reviewed PubMed/Medline articles published through December 2012 were identified using the following keyword combinations: glia, astrocytes, oligodendrocytes/glia, microglia, substance use, substance abuse, substance dependence, alcohol, opiate, opioid, cocaine, psychostimulants, stimulants, and glutamate.

RESULTS

Depressive and substance use disorders are highly comorbid, suggesting a common or overlapping aetiology and pathophysiology. Reduced astrocyte cell number occurs in both disorders. Altered glutamate neurotransmission and metabolism - specifically changes in the levels/activity of transporters, receptors, and synaptic proteins potentially related to synaptic physiology - appear to be salient features of both disorders. Glial cell pathology may also underlie the pathophysiology of both disorders via impaired astrocytic production of neurotrophic factors. Microglial/neuroinflammatory pathology is also evident in both depressive and substance use disorders. Finally, oligodendrocyte impairment decreases myelination and impairs expression of myelin-related genes in both substance use and depressive disorders.

CONCLUSIONS

Glial-mediated glutamatergic dysfunction is a common neuropathological pathway in both substance use and depression. Therefore, glutamatergic neuromodulation is a rational drug target in this comorbidity.

Endogenous opiates and behavior: 2012

This paper is the thirty-fifth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2012 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior (Section 2), and the roles of these opioid peptides and receptors in pain and analgesia (Section 3); stress and social status (Section 4); tolerance and dependence (Section 5); learning and memory (Section 6); eating and drinking (Section 7); alcohol and drugs of abuse (Section 8); sexual activity and hormones, pregnancy, development and endocrinology (Section 9); mental illness and mood (Section 10); seizures and neurologic disorders (Section 11); electrical-related activity and neurophysiology (Section 12); general activity and locomotion (Section 13); gastrointestinal, renal and hepatic functions (Section 14); cardiovascular responses (Section 15); respiration and thermoregulation (Section 16); and immunological responses (Section 17).

The role of orphanin FQ/nociceptin in neuroplasticity: relationship to stress, anxiety and neuroinflammation

The neuropeptide, orphanin FQ/nociceptin (OFQ/N or simply, nociceptin), is expressed in both neuronal and non-neuronal tissue, including the immune system. In the brain, OFQ/N has been investigated in relation to stress, anxiety, learning and memory, and addiction. More recently, it has also been found that OFQ/N influences glial cell functions, including oligodendrocytes, astrocytes, and microglial cells. However, this latter research is relatively small, but potentially important, when observations regarding the relationship of OFQ/N to stress and emotional functions is taken into consideration and integrated with the growing evidence for its involvement in cells that mediate inflammatory events. This review will first provide an overview and understanding of how OFQ/N has been implicated in the HPA axis response to stress, followed by an understanding of its influence on natural and learned anxiety-like behavior. What emerges from an examination of the literature is a neuropeptide that appears to counteract anxiogenic influences, but paradoxically, without attenuating HPA axis responses generated in response to stress. Studies utilized both central administration of OFQ/N, which was shown to activate the HPA axis, as well as antagonism of NOP-R, the OFQ/N receptor. In contrast, antagonist or transgenic OFQ/N or NOP-R knockout studies, showed augmentation of HPA axis responses to stress, suggesting that OFQ/N may be needed to control the magnitude of the HPA axis response to stress. Investigations of behavior in standard exploratory tests of anxiogenic behavior (eg., elevated plus maze) or learned fear responses have suggested that OFQ/N is needed to attenuate fear or anxiety-like behavior. However, some discrepant observations, in particular, those that involve appetitive behaviors, suggest a failure of NOP-R deletion to increase anxiety. However, it is also suggested that OFQ/N may operate in an anxiolytic manner when initial anxiogenic triggers (eg., the neuropeptide CRH) are initiated. Finally, the regulatory functions of OFQ/N in relation to emotion-related behaviors may serve to counteract potential neuroinflammatory events in the brain. This appears to be evident within the glial cell environment of the brain, since OFQ/N has been shown to reduce the production of proinflammatory cellular and cytokine events. Given that both OFQ/N and glial cells are activated in response to stress, it is possible that there is a possible convergence of these two systems that has important repercussions for behavior and neuroplasticity.

Buprenorphine use in pregnant opioid users: a critical review

Pregnancy in opioid users poses a number of problems to treating physicians. Most guidelines recommend maintenance treatment to manage opioid addiction in pregnancy, with methadone being the gold standard. More recently, buprenorphine has been discussed as an alternate medication. The use and efficacy of buprenorphine in pregnancy is still controversial. This article reviews the current database on the basis of a detailed and critical literature search performed in MEDLINE (206 counts). Most of the relevant studies (randomised clinical trials and one national cohort sample) were published in the last 2 years and mainly compared buprenorphine with methadone. Some studies are related to maternal outcomes, others to foetal, neonatal or older child outcomes. With respect to maternal outcomes, most studies suggest that buprenorphine has similar effects to methadone. Very few data from small studies discuss an effect of buprenorphine on neurodevelopment of the foetus. Neonatal abstinence syndrome is common in infants of both buprenorphine- and methadone-maintained mothers. As regards neonatal outcomes, buprenorphine has the same clinical outcome as methadone, although some newer studies suggest that it causes fewer withdrawal symptoms. Since hardly any studies have investigated the combination of buprenorphine with naloxone (which has been suggested to possibly have teratogenic effects) in pregnant women, a switch to buprenorphine monotherapy is recommended in women who become pregnant while receiving the combination product. These novel findings indicate that buprenorphine is emerging as a first-line treatment for pregnant opioid users.

Gestational nicotine exposure modifies myelin gene expression in the brains of adolescent rats with sex differences

Myelination defects in the central nervous system (CNS) are associated with various psychiatric disorders, including drug addiction. As these disorders are often observed in individuals prenatally exposed to cigarette smoking, we tested the hypothesis that such exposure impairs central myelination in adolescence, an important period of brain development and the peak age of onset of psychiatric disorders. Pregnant Sprague Dawley rats were treated with nicotine (3 mg kg(-1) per day; gestational nicotine (GN)) or gestational saline via osmotic mini pumps from gestational days 4-18. Both male and female offsprings were killed on postnatal day 35 or 36, and three limbic brain regions, the prefrontal cortex (PFC), caudate putamen and nucleus accumbens, were removed for measurement of gene expression and determination of morphological changes using quantitative real-time PCR (qRT-PCR) array, western blotting and immunohistochemical staining. GN altered myelin gene expression at both the mRNA and protein levels, with striking sex differences. Aberrant expression of myelin-related transcription and trophic factors was seen in GN animals, which correlated highly with the alterations in the myelin gene expression. These correlations suggest that these factors contribute to GN-induced alterations in myelin gene expression and also indicate abnormal function of oligodendrocytes (OLGs), the myelin-producing cells in the CNS. It is unlikely that these changes are attributable solely to an alteration in the number of OLGs, as the cell number was changed only in the PFC of GN males. Together, our findings suggest that abnormal brain myelination underlies various psychiatric disorders and drug abuse associated with prenatal exposure to cigarette smoke.