Prenatal morphine exposure suppresses mineralocorticoid receptor-dependent basal synaptic transmission and synaptic plasticity in the lateral perforant path in adult male rats

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'.

Morphine Perinatal Exposure Induces Long-Lasting Negative Emotional States in Adult Offspring Rodents

Psychoactive substances during pregnancy and lactation is a key problem in contemporary society, causing social, economic, and health disturbance. In 2010, about 30 million people used opioid analgesics for non-therapeutic purposes, and the prevalence of opioids use during pregnancy ranged from 1% to 21%, representing a public health problem. This study aimed to evaluate the long-lasting neurobehavioral and nociceptive consequences in adult offspring rats and mice exposed to morphine during intrauterine/lactation periods. Pregnant rats and mice were exposed subcutaneously to morphine (10 mg/kg/day) during 42 consecutive days (from the first day of pregnancy until the last day of lactation). Offspring were weighed on post-natal days (PND) 1, 5, 10, 15, 20, 30, and 60, and behavioral tasks (experiment 1) or nociceptive responses (experiment 2) were assessed at 75 days of age (adult life). Morphine-exposed female rats displayed increased spontaneous locomotor activity. More importantly, both males and female rats perinatally exposed to morphine displayed anxiety- and depressive-like behaviors. Morphine-exposed mice presented alterations in the nociceptive responses on the writhing test. This study showed that sex difference plays a role in pain threshold and that deleterious effects of morphine during pre/perinatal periods are nonrepairable in adulthood, which highlights the long-lasting clinical consequences related to anxiety, depression, and nociceptive disorders in adulthood followed by intrauterine and lactation morphine exposure.

Prenatal methadone exposure impairs adolescent cognition and GABAergic neurodevelopment in a novel rat model of maternal methadone treatment

Methadone maintenance treatment (MMT) is the most common treatment for opioid-dependent pregnant women worldwide. Despite its widespread use, MMT is associated with a variety of adverse neurodevelopmental outcomes in exposed offspring, particularly cognitive impairments. The neurobiological abnormalities underlying these cognitive impairments are, however, poorly understood. This is, in part, due to a lack of animal models that represents the standard of care that methadone is administered in the clinic, with inconsistencies in the timing, doses and durations of treatment. Here we describe the characterisation of a clinically relevant rat model of MMT in which the long-term behavioural and neurobiological effects of prenatal methadone exposure can be assessed in adolescent offspring. Female Sprague-Dawley rats were treated orally with an ascending methadone dosage schedule (5, 10, 15, 20, 25 and 30 mg/kg/day), self-administered in drinking water prior to conception, throughout gestation and lactation. Pregnancy success, maternal gestational weight gain, litter survival and size were not significantly altered in methadone-exposed animals. Methadone-exposed offspring body and brain weights were significantly lower at birth. Novel object recognition tests performed at adolescence revealed methadone-exposed offspring had impaired recognition memory. Furthermore, the rewarded T-maze alternation task demonstrated that methadone-exposed female, but not male, offspring also exhibit working memory and learning deficits. Immunoblots of the adolescent prefrontal cortex and hippocampus showed methadone-exposed offspring displayed reduced levels of mature BDNF, in addition to the GABAergic proteins, GAD67 and parvalbumin, in a sex- and brain region-specific fashion. This rat model closely emulates the clinical scenario in which methadone is administered to opioid-dependent pregnant woman and provides evidence MMT can cause cognitive impairments in adolescent offspring that may be underlined by perturbed neurodevelopment of the GABAergic system.

Perinatal Fentanyl Exposure Leads to Long-Lasting Impairments in Somatosensory Circuit Function and Behavior

One consequence of the opioid epidemic are lasting neurodevelopmental sequelae afflicting adolescents exposed to opioids in the womb. A translationally relevant and developmentally accurate preclinical model is needed to understand the behavioral, circuit, network, and molecular abnormalities resulting from this exposure. By employing a novel preclinical model of perinatal fentanyl exposure, our data reveal that fentanyl has several dose-dependent, developmental consequences to somatosensory function and behavior. Newborn male and female mice exhibit signs of withdrawal and sensory-related deficits that extend at least to adolescence. As fentanyl exposure does not affect dams' health or maternal behavior, these effects result from the direct actions of perinatal fentanyl on the pups' developing brain. At adolescence, exposed mice exhibit reduced adaptation to sensory stimuli, and a corresponding impairment in primary somatosensory (S1) function. In vitro electrophysiology demonstrates a long-lasting reduction in S1 synaptic excitation, evidenced by decreases in release probability, NMDA receptor-mediated postsynaptic currents, and frequency of miniature excitatory postsynaptic currents (mEPSCs), as well as increased frequency of miniature inhibitory postsynaptic currents (mIPSCs). In contrast, anterior cingulate cortical neurons exhibit an opposite phenotype, with increased synaptic excitation. Consistent with these changes, electrocorticograms (ECoGs) reveal suppressed ketamine-evoked γ oscillations. Morphologic analysis of S1 pyramidal neurons indicate reduced dendritic complexity, dendritic length, and soma size. Further, exposed mice exhibited abnormal cortical mRNA expression of key receptors involved in synaptic transmission and neuronal growth and development, changes that were consistent with the electrophysiological and morphologic changes. These findings demonstrate the lasting sequelae of perinatal fentanyl exposure on sensory processing and function.SIGNIFICANCE STATEMENT This is the first study to show that exposure to fentanyl in the womb results in behavioral, circuitry, and synaptic effects that last at least to adolescence. We also show, for the first time, that this exposure has different, lasting effects on synapses in different cortical areas.

Perinatal Fentanyl Exposure Leads to Long-Lasting Impairments in Somatosensory Circuit Function and Behavior

One consequence of the opioid epidemic are lasting neurodevelopmental sequelae afflicting adolescents exposed to opioids in the womb. A translationally relevant and developmentally accurate preclinical model is needed to understand the behavioral, circuit, network, and molecular abnormalities resulting from this exposure. By employing a novel preclinical model of perinatal fentanyl exposure, our data reveal that fentanyl has several dose-dependent, developmental consequences to somatosensory function and behavior. Newborn male and female mice exhibit signs of withdrawal and sensory-related deficits that extend at least to adolescence. As fentanyl exposure does not affect dams' health or maternal behavior, these effects result from the direct actions of perinatal fentanyl on the pups' developing brain. At adolescence, exposed mice exhibit reduced adaptation to sensory stimuli, and a corresponding impairment in primary somatosensory (S1) function. In vitro electrophysiology demonstrates a long-lasting reduction in S1 synaptic excitation, evidenced by decreases in release probability, NMDA receptor-mediated postsynaptic currents, and frequency of miniature excitatory postsynaptic currents (mEPSCs), as well as increased frequency of miniature inhibitory postsynaptic currents (mIPSCs). In contrast, anterior cingulate cortical neurons exhibit an opposite phenotype, with increased synaptic excitation. Consistent with these changes, electrocorticograms (ECoGs) reveal suppressed ketamine-evoked γ oscillations. Morphologic analysis of S1 pyramidal neurons indicate reduced dendritic complexity, dendritic length, and soma size. Further, exposed mice exhibited abnormal cortical mRNA expression of key receptors involved in synaptic transmission and neuronal growth and development, changes that were consistent with the electrophysiological and morphologic changes. These findings demonstrate the lasting sequelae of perinatal fentanyl exposure on sensory processing and function.SIGNIFICANCE STATEMENT This is the first study to show that exposure to fentanyl in the womb results in behavioral, circuitry, and synaptic effects that last at least to adolescence. We also show, for the first time, that this exposure has different, lasting effects on synapses in different cortical areas.

Modeling prenatal opioid exposure in animals: Current findings and future directions

The past decade has seen a drastic rise in the number of infants exposed to opioids in utero. It is unclear what lasting effect this exposure may have on these children. Animal models of prenatal opioid exposure may provide insight into potential areas of vulnerability. The present review summarizes the findings across animal models of prenatal opioid exposure, including exposure to morphine, methadone, buprenorphine, and oxycodone. Details regarding the drug, doses, and duration of treatment, as well as key findings, are summarized in tables with associated references. Finally, significant gaps in the current preclinical literature and future directions are discussed.

Are changes in excitability in the hippocampus of adult male rats induced by prenatal methamphetamine exposure or stress?

Prenatal stress and drug exposure induce permanent alterations of the brain. Even though different brain structures are involved, alterations almost always refer to the hippocampus. The aim of this study was to investigate the excitability of hippocampal slices in low-magnesium epilepsy model of prenatally methamphetamine (MA, 5mg/kg sc.) or saline (sc., stress model) exposed animals in adult male rats. The second aim was to investigate, if a low dose of MA (1ml/kgs.c.) administered in adulthood changes the hippocampal activity of these animals. Adult Wistar male rats were divided into groups according to their prenatal treatment (C - naïve control; Sa - saline; MA - MA administration). One half of the animals was treated with a challenge dose of MA (1mg/kg sc.) 45min before hippocampal slices were cut. The activity of 350μ thick transversal slices of CA1 hippocampi was recorded (latencies of the first epileptiform discharge and the regular epileptiform activity) and evaluated in ACSF with low-magnesium concentration. Effects of prenatal exposure: The highest excitability was found in the Sa (prenatally stressed) group in respect to C and MA groups. This group developed also the highest number of seizure-like events. In addition, the prenatally MA treated group had also higher excitability than C group. Effects of the MA challenge dose: The challenge dose decreased the excitability of prenatally SA- exposed group. To conclude, even a mild prenatal stress significantly increases hippocampal excitability in adulthood and a challenge dose of MA is able to dampen it.

Dynamic regulation of NMDAR function in the adult brain by the stress hormone corticosterone

Stress and corticosteroids dynamically modulate the expression of synaptic plasticity at glutamatergic synapses in the developed brain. Together with alpha-amino-3-hydroxy-methyl-4-isoxazole propionic acid receptors (AMPAR), N-methyl-D-aspartate receptors (NMDAR) are critical mediators of synaptic function and are essential for the induction of many forms of synaptic plasticity. Regulation of NMDAR function by cortisol/corticosterone (CORT) may be fundamental to the effects of stress on synaptic plasticity. Recent reports of the efficacy of NMDAR antagonists in treating certain stress-associated psychopathologies further highlight the importance of understanding the regulation of NMDAR function by CORT. Knowledge of how corticosteroids regulate NMDAR function within the adult brain is relatively sparse, perhaps due to a common belief that NMDAR function is stable in the adult brain. We review recent results from our laboratory and others demonstrating dynamic regulation of NMDAR function by CORT in the adult brain. In addition, we consider the issue of how differences in the early life environment may program differential sensitivity to modulation of NMDAR function by CORT and how this may influence synaptic function during stress. Findings from these studies demonstrate that NMDAR function in the adult hippocampus remains sensitive to even brief exposures to CORT and that the capacity for modulation of NMDAR may be programmed, in part, by the early life environment. Modulation of NMDAR function may contribute to dynamic regulation of synaptic plasticity and adaptation in the face of stress, however, enhanced NMDAR function may be implicated in mechanisms of stress-related psychopathologies including depression.

Prenatal morphine exposure attenuates the maintenance of late LTP in lateral perforant path projections to the dentate gyrus and the CA3 region in vivo

Previously we reported that prenatal exposure to morphine twice daily during gestation decreases proenkephalin levels in adult progeny within the brain, including the dentate gyrus, and alters mu and delta opioid receptors in the hippocampal CA3 region. The lateral aspect of the perforant path contains and releases enkephalin-derived opioid peptides, and induction of long-term potentiation (LTP) in lateral perforant path projections to both the dentate gyrus and the hippocampal CA3 region is blocked by antagonists of opioid receptors. Thus LTP induction at these synapses involves opioid receptor activation mediated by the release of proenkephalin-derived opioid peptides with lateral perforant path activation. Here we show in adult behaving animals, neither LTP induction nor the early phase of LTP (E-LTP) maintenance is altered by prenatal morphine exposure in the lateral perforant path projections to the dentate gyrus and the CA3 region. However, maintenance and longevity of late LTP (L-LTP), as reflected in the magnitude of LTP over days, was attenuated in animals prenatally exposed to morphine. In contrast, in medial perforant path projections to the dentate gyrus and CA3 region, both LTP induction and the maintenance of E- and L-LTP were unaffected by prenatal morphine treatment. Thus a brief prenatal exposure to the opiate morphine produces sustained, and possibly permanent, alterations in L-LTP in the opioidergic lateral perforant path projection. This suggests that prenatal morphine exposure disrupts LTP via disruption of opioid mechanisms involved in LTP maintenance or via disruption of opioid receptor activation during LTP induction, which can subsequently alter LTP maintenance.

Effect of parental morphine addiction on hippocampal long-term potentiation in rats offspring

Attention to addiction of women alone for fetus and infant's health has caused the possible role of father's status was less considered, while some developmental impairments including decrease of liter size, weight loss, congenital deficiencies, behavioral disorders, and learning and memory impairments in offspring with addicted father have been reported. In this study the effects of addiction of one or both parents to morphine on male and female offspring hippocampal long-term potentiation (LTP), were assessed. One hundred twenty female and 48 male rats (4-5 months, 250-270 g) were used. Forty females and 16 males were addicted by oral administration of morphine (32 mg/kg twice daily) for 5 days before mating. Then each two males with five females were housed (coupled) per cage as five groups for coupling: (A) addicted females+5% dextrose males (add.F); (B) addicted males+5% dextrose females (add.M); (C) addicted females+addicted males (add.MF); (D) 5% dextrose females+intact males (dex.F); (E) 5% dextrose males+intact females (dex.M). In puberty offspring LTP was induced in hippocampal dentate gyrus by stimulation of perforant path (pp). Changes of population spikes (PS) amplitude and LTP slope at 0, 5, 30, 60 and 120 min were evaluated. Slope of LTP at 30, 60 and 120 min, and amplitude of PS at 60 and 120 min in add.F and add.M offspring were significantly lower than dextrose groups (P<0.01). LTP slope and PS amplitude of male and female offspring did not different between add.F and add.M groups. Our results suggest that both parental and paternal addiction to morphine may cause memory deficiency through reduction of LTP in hippocampus.

CNS Aspects of Prenatal Drug Exposure: Drugs of Abuse, Toxins, and Corticosteroids

Studies of the effects of prenatal exposure (to drugs or environmental factors) on postnatal brain morphology and function have an important role in assessing adverse effects of prenatal administration of corticosteroids in obstetrics, in studying the impairment of the offspring due to maternal drug abuse, as well as in studies of the influence of other environmental factors (such as toxins or stress). Timing, duration, and dose of the prenatal exposure play a significant role in the postnatal expression of the impact. However, data interpretation may be complicated by additional factors. As mixed litters of prenatally exposed subjects are evaluated, significant differences between males and females may occur. Additionally in females, cyclical changes in ovarian steroids may interfere with the effects of prenatal impact. Developmental differences may be also present, and data from infant, juvenile, prepubertal, and adult individuals cannot be simply compared. Finally, prenatal treatment is a stressful event and may present itself as prenatal stress, misguiding the interpretation. Postnatal environmental factors in raising the offspring, such as housing, maternal care, light-dark cycle, and weaning age can also change the data in such a way, which makes comparisons between different research laboratories impossible.

Mifepristone (RU486) inhibits lateral perforant path long‐term potentiation in hippocampal slices from prenatally morphine‐exposed female rats

In brain slices from prenatally saline-exposed female rats during proestrus and diestrus, long-term potentiation (LTP) can be induced in the lateral perforant pathway (LPP). Prenatal morphine exposure suppresses LTP induction in the LPP during proestrus. Here we studied synaptic plasticity in the LPP in slices from female rats prenatally exposed to morphine. Two additional factors were investigated: the role of the estrous cycle and role of glucocorticoid receptors. Hippocampal slices were prepared from adult, prenatally saline- or morphine-exposed female rats. One hour prior to decapitation, vaginal smears were obtained and the rats either in proestrus or diestrus were treated with a non-specific glucocorticoid receptor antagonist mifepristone (RU486) or with a vehicle. LPP was stimulated with high-frequency stimulation. Short-tem plasticity (STP) and the induction and maintenance of long-term potentiation (LTP) were assessed. In all groups of prenatally saline-exposed rats, LTP was induced and maintained with the exception of RU486-treated rats during proestrus where the LTP was induced but not maintained. In prenatally morphine-exposed females in diestrus, both STP and LTP were induced after postnatal vehicle treatment. In morphine-exposed, proestrous females, neither STP nor LTP were induced irrespective of the postnatal treatment. Thus, prenatal morphine exposure suppresses the induction of LTP in the LPP, except during diestrus. Data indicate that the induction and maintenance of LTP in the LPP in hippocampal slices from female rats is multifactorial: ovarian steroids and functionality of glucocorticoid receptors cooperation are necessary for induction and maintenance of the LTP, prenatal morphine exposure interferes with this process possibly by its long-term effects on synaptic plasticity.

Endogenous opiates and behavior: 2003

This paper is the 26th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over a quarter-century of research. It summarizes papers published during 2003 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).