A comparative study of morphine treatment regimen prior to mating and during late pregnancy

Maternal morphine intake during pregnancy and lactation affects the circadian clock of rat pups

Early-life morphine exposure causes a variety of behavioural and physiological alterations observed later in life. In the present study, we investigated the effects of prenatal and early postnatal morphine on the maturation of the circadian clockwork in the suprachiasmatic nucleus and the liver, and the rhythm in aralkylamine N-acetyltransferase activity in the pineal gland. Our data suggest that the most affected animals were those born to control, untreated mothers and cross-fostered by morphine-exposed dams. These animals showed the highest mesor and amplitude in the rhythm of Per2, Nr1d1 but not Per1 gene expression in the suprachiasmatic nuclei (SCN) and arrhythmicity in AA-NAT activity in the pineal gland. In a similar pattern to the rhythm of Per2 expression in the SCN, they also expressed Per2 in a higher amplitude rhythm in the liver. Five of seven specific genes in the liver showed significant differences between groups in their expression. A comparison of mean relative mRNA levels suggests that this variability was caused mostly by cross-fostering, animals born to morphine-exposed dams that were cross-fostered by control mothers and vice versa differed from both groups of natural mothers raising offspring. Our data reveal that the circadian system responds to early-life morphine administration with significant changes in clock gene expression profiles both in the SCN and in the liver. The observed differences between the groups suggest that the dose, timing and accompanying stress events such as cross-fostering may play a role in the final magnitude of the physiological challenge that opioids bring to the developing circadian clock.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

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

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

Mothering under the influence: how perinatal drugs of abuse alter the mother-infant interaction

Although drug-abusing women try to moderate their drug and alcohol use during pregnancy, they often relapse at a time when childcare needs are high and maternal bonding is critical to an infant's development. In the clinical setting, the search for the neural basis of drug-induced caregiving deficits is complex due to several intervening variables. Rather, the preclinical studies that control for drug dose and regimen, as well as for gestational and postpartum environment, allow a precise determination of the effects of drugs on maternal behaviour. Given the relevance of the issue, this review will gather reports on the phenotypic correlates of maternal behaviour in preclinical studies, and focus on the detrimental consequences on the mother-infant interaction exerted by the perinatal use of alcohol, nicotine, cannabis, cocaine and stimulants and opiates. The drug-induced disruptions of this maternal repertoire are associated with adverse maternal and infant outcomes. A comprehensive overview will help promote the refinement of the treatment approaches toward maternal drug use disorders and maternal misbehaviour, in favour of augmented parenting resiliency.

μ opioid receptor, social behaviour and autism spectrum disorder: reward matters

The endogenous opioid system is well known to relieve pain and underpin the rewarding properties of most drugs of abuse. Among opioid receptors, the μ receptor mediates most of the analgesic and rewarding properties of opioids. Based on striking similarities between social distress, physical pain and opiate withdrawal, μ receptors have been proposed to play a critical role in modulating social behaviour in humans and animals. This review summarizes experimental data demonstrating such role and proposes a novel model, the μ opioid receptor balance model, to account for the contribution of μ receptors to the subtle regulation of social behaviour. Interestingly, μ receptor null mice show behavioural deficits similar to those observed in patients with autism spectrum disorder (ASD), including severe impairment in social interactions. Therefore, after a brief summary of recent evidence for blunted (social) reward processes in subjects with ASD, we review here arguments for altered μ receptor function in this pathology. This article is part of a themed section on Emerging Areas of Opioid Pharmacology. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v175.14/issuetoc.

Role of steroid hormones and morphine treatment in the modulation of opioid receptor gene expression in brain structures in the female rat

This study determined the effects of acute treatment with morphine on the expression of the Oprm1, Oprk1, and Oprd1 genes (which encode μ, κ, and δ receptors, respectively) in the striatum, hypothalamus, and periaqueductal gray (PAG) in ovariectomized female rats treated with estrogen. Ovariectomized female rats were divided into five equal groups. Two groups received estrogen (50 µg/kg, 54 h before testing) and saline (ES group) or 3.5 mg/kg morphine (EM group) 2 h before euthanasia. The SS group received saline solution 54 and 2 h before the experiments. The SM group received saline 54 h and 3.5 mg/kg morphine 2 h before the experiments. The W group remained undisturbed. The genes expression were evaluated. Oprm1 and Oprk1 expression were activated, respectively, in the hypothalamus and PAG and in the striatum and PAG by morphine only in estrogen-treated animals. Oprd1 expression in the hypothalamus and PAG was activated by morphine in both estrogen-treated and -nontreated animals. The Oprm1 and Oprk1 gene response to morphine might depend on estrogen, whereas the Oprd1 gene response to morphine might not depend on estrogen, supporting the hypothesis of a functional role for ovarian hormones in opioid receptor-mediated functional adaptations in the female brain.

Behavioral effects of perinatal opioid exposure

Opioids are among the world's oldest known drugs used mostly for pain relief, but recreational use is also widespread. A particularly important problem is opioid exposure in females, as their offspring can also be affected. Adverse intrauterine and postnatal environments can affect offspring development and may lead to various disabilities later in life. It is clear that repetitive painful experiences, such as randomly occurring invasive procedures during neonatal intensive care, can permanently alter neuronal and synaptic organization and therefore later behavior. At the same time, analgesic drugs can also be harmful, inducing neuronal apoptosis or withdrawal symptoms in the neonate and behavioral alterations in adulthood. Hence, risk-benefit ratios should be taken into consideration when pain relief is required during pregnancy or in neonates. Recreational use of opioids can also alter many aspects of life. Intrauterine opioid exposure has many toxic effects, inducing poor pregnancy outcomes due to underdevelopment, but it is believed that later negative consequences are more related to environmental factors such as a chaotic lifestyle and inadequate prenatal care. One of the crucial components is maternal care, which changes profoundly in addicted mothers. In substance-dependent mothers, pre- and postnatal care has special importance, and controlled treatment with a synthetic opioid (e.g., methadone) could be beneficial. We aimed to summarize and compare human and rodent data, as it is important to close the gap between scientific knowledge and societal policies. Special emphasis is given to gender differences in the sensitivity of offspring to perinatal opioid exposure.

Behavioral meaningful opioidergic stimulation activates kappa receptor gene expression

The periaqueductal gray (PAG) has been reported to be a location for opioid regulation of pain and a potential site for behavioral selection in females. Opioid-mediated behavioral and physiological responses differ according to the activity of opioid receptor subtypes. The present study investigated the effects of the peripheral injection of the kappa-opioid receptor agonist U69593 into the dorsal subcutaneous region of animals on maternal behavior and on Oprk1 gene activity in the PAG of female rats. Female Wistar rats weighing 200-250 g at the beginning of the study were randomly divided into 2 groups for maternal behavior and gene expression experiments. On day 5, pups were removed at 7:00 am and placed in another home cage that was distant from their mother. Thirty minutes after removing the pups, the dams were treated with U69593 (0.15 mg/kg, sc) or 0.9% saline (up to 1 mL/kg) and after 30 min were evaluated in the maternal behavior test. Latencies in seconds for pup retrieval, grouping, crouching, and full maternal behavior were scored. The results showed that U69593 administration inhibited maternal behavior (P < 0.05) because a lower percentage of kappa group dams showed retrieval of first pup, retrieving all pups, grouping, crouching and displaying full maternal behavior compared to the saline group. Opioid gene expression was evaluated using real-time reverse-transcription polymerase chain reaction (RT-PCR). A single injection of U69593 increased Oprk1 PAG expression in both virgin (P < 0.05) and lactating female rats (P < 0.01), with no significant effect on Oprm1 or Oprd1 gene activity. Thus, the expression of kappa-opioid receptors in the PAG may be modulated by single opioid receptor stimulation and behavioral meaningful opioidergic transmission in the adult female might occur simultaneously to specific changes in gene expression of kappa-opioid receptor subtype. This is yet another alert for the complex role of the opioid system in female reproduction.

Subsequent anxiety-related behavior in rats exposed to low-dose methadone during gestation, lactation or both periods consecutively

In order to assess the long-term behavioral consequences of exposing rats to methadone during gestation, lactation or both periods consecutively, pregnant Wistar dams were provided with drinking water containing approximately 2.39 mg/kg/day methadone. Soon after birth, litters of offspring were assigned to methadone-naïve foster mothers. Half of these foster mothers were then provided with drinking water containing methadone (approximately 2.86 mg/kg/day), while the other half received unadulterated water. Maternal weight gain, pregnancy duration, litter sizes, sex ratios and average pup weights were recorded. Following weaning on postnatal day (PND) 28, individual rats were weighed and inspected for physical abnormalities and stress reactions at PND20, 60 and 120. At these same ages, observations were also made of the rats' behavior in an emergence apparatus, and an open field. Apart from a smaller number of full-term pregnancies, there were no effects of any type of methadone treatment on physical measurements recorded at any age. Nor were there any behavioral effects of gestational methadone experienced on its own. However, methadone experienced during lactation (without gestational exposure) decreased emergence speed at PND30, and for all testing ages combined, increased open-field ambulation (males only), walking, rearing and occupancy of the center of the apparatus. Exposure to methadone during both gestation and lactation decreased emergence latencies at PND30 and, for all ages combined, decreased ambulation (males only), center occupancy and defecation. The subsequent behavioral effects of methadone were largely confined to lactational exposure and, when combined with gestational exposure, suggested increased anxiety.

Morphine-induced changes in opioid sensitivity in postpartum females: a unique progesterone response

Opioid peptides play an important role in maternal behaviour, as well as in physiological and pathological phenomena involving motivation. Daily 3.5 mg/kg doses of morphine from days 17-21 of pregnancy are able to change the expression of maternal behaviour patterns. However, the role of hormones on such opioid behavioural actions remains to be determined. The present study investigated the endocrine responses to this morphine treatment. Corticosterone, progesterone, oestradiol and prolactin serum concentrations were measured after each morphine injection. No significant differences were found in corticosterone, oestradiol or prolactin serum concentrations. The results suggest that the treatment was unable to promote different effects, other than those caused by saline injections. In morphine-treated animals, however, progesterone concentrations were consistently and significantly increased from days 18-20 of treatment. Thus, because this behavioural meaningful opioidergic stimulation during late pregnancy affects progesterone levels, the findings of the present study raise the hypothesis that this hormone may play a role in morphine-induced changes in opioid sensitivity during late pregnancy and early lactation.

Morphine treatment during pregnancy modulates behavioral selection in lactating rats

Previous studies have demonstrated that treatment of postpartum female rats with morphine inhibits maternal behavior and stimulates foraging. Exposure to drugs of abuse may result in a progressive enhancement of their reinforcing effects. Puerperal treatment with morphine leads to reverse tolerance to this drug. The present study investigated whether repeated morphine treatment during late pregnancy may influence the effects of different morphine dosages on behavioral selection in lactating rats. Females were simultaneously exposed to pups and insects, and the choice between taking care of the pups and hunting insects was observed. Female Wistar rats were treated with morphine (3.5 mg/kg/day, subcutaneous [s.c.]) or saline for 5 days beginning on pregnancy day 17. On day 5 of lactation, animals were acutely challenged with morphine (0.5, 1.0, or 1.5 mg/kg, s.c.; MM0.5, MM1.0, and MM1.5 groups, respectively) or saline (MS group) and tested for predatory hunting and maternal behavior. Control groups were pretreated with saline and challenged with morphine (SM0.5, SM1.0, and SM1.5 groups) or saline (SS group). Animals treated with morphine during late pregnancy and acutely challenged with 1.0 mg/kg morphine (MM1.0 group) exhibited significantly decreased maternal behavior and enhanced hunting. This effect was not evident with the 0.5 mg/kg dose. The 1.5 mg/kg morphine dose decreased maternal behavior and increased hunting in both the MM1.5 group and in animals challenged with morphine after previous saline treatment (SM1.5 group). These results provide evidence of plasticity of the opioidergic role in behavioral selection during lactation.

SUBSEQUENTLY ENHANCED CPP TO MORPHINE FOLLOWING CHRONIC BUT NOT ACUTE FOOTSHOCK STRESS ASSOCIATED WITH CORTICOSTERONE MECHANISM IN RATS

The purpose of this study was to determine the morphine-induced place preference in rats pre-exposed to footshock stress and corticosterone (CORT). The authors also studied the involvement of dopamine mechanisms in the CORT-induced place preference. The results showed that chronic footshock or CORT exposure but not acute footshock or CORT exposure similarly potentiated the conditioned place preference to morphine. The CORT-induced conditioned place preference were established only with high and middle dose (5, 3 mg/kg) CORT. The dopamine levels in NAc of rats injected with CORT (5, 3, 1 mg/kg, i.p.) increased significantly. The findings suggest that the increase of dopamine levels in NAc induced by CORT might be the medium between stress and morphine.

Opiate regulation of behavioral selection during lactation

Treatment of postpartum female rats with morphine inhibits maternal behavior. The same type of treatment stimulates foraging in adult animals. The aim of the present study was to investigate, in lactating rats, the functional role of opioid systems in the choice between caring for pups versus hunting insects. Experiment 1 was designed to test how acute morphine treatment with 3.0 mg/kg interferes with choosing between caring for pups versus predatory behavior. Morphine-treated dams decreased maternal behavior while increasing efficiency in hunting insects. The next step was to test the opioid antagonist naloxone in the same context of maternal versus predatory behavior. Naloxone restored maternal care and reduced hunting in morphine-treated rats. Finally, in order to test the role of endogenous opioidergic stimulation in this scenario, lactating rats were treated with the opioid antagonist naloxone alone. Consistently, naloxone treatment induced a decrease in number of insects captured and an increase in the percentage of animals displaying nursing behavior. These results provide important insight into the role of opioidergic transmission in the regulation of behavioral selection during lactation. The present results suggest that endogenous opioids may stimulate hunting by replacing maternal behavior during lactation.

Reproductive experience modifies dopaminergic function, serum levels of prolactin, and macrophage activity in female rats

Reproductive experience (RE), i.e. pregnancy and lactation, induces physiological changes in mammals. Recent data show that neuroimmune interactions are modulated by a diversity of events involving neurotransmitters and neuropeptides. These molecules, particularly dopamine (DA), were reported to mediate the relevant cross talk between immune and neuroendocrine systems. Moreover, DA-mediated regulation of leukocyte function is a reasonable approach to investigate the DA-operated regulatory switch for immune-competent cells, such as macrophages. Therefore, the goals of the present study were to determine the effects of RE on: (1) dopaminergic function through hypothalamic levels of DA, dihydroxyphenylacetic acid (DOPAC), homovanilic acid (HVA), serotonin (5-HT), and 5-hydroxyindole acetic acid (5-HIAA); (2) basal levels of circulating prolactin (PRL); and (3) activity of peritoneal macrophage (phagocytosis and oxidative burst). A total of 16 adult (200-250 g) female Wistar rats were used, divided in two groups: nulliparous and primiparous. Approximately 2-3 weeks after weaning pups from the primiparous group, both groups of rats were tested. The findings indicate that: (1) DOPAC concentrations, DOPAC/DA and HVA+DOPAC/DA ratios decreased in primiparous rats as compared to virgin rats, (2) primiparous rats showed significantly lower serum PRL levels, and (3) phorbol miristate acetate (PMA)-induced oxidative burst was decreased in peritoneal macrophage from primiparous rats as compared to virgin rats. To test the possible positive correlation between serum levels of PRL and the intensity of oxidative burst by peritoneal macrophage, an extra experiment was done with adult virgin female rats treated with domperidone, an antagonist of DA receptors. Domperidone-treated animals showed increased serum levels of PRL and simultaneous increase in peritoneal macrophage oxidative burst. Thus, suggesting an indirect participation of hyperprolactinemia, induced by this treatment in peritoneal macrophage activity of female rats. These results suggest that a previous RE can modulate the activity of dopaminergic hypothalamic systems, while decreasing PRL serum levels and the oxidative burst of peritoneal macrophage. The neurochemical and hormonal RE-induced changes correlate with the immune alterations.

Separation stress, litter size, and the rewarding effects of low-dose morphine in the dams of maternally separated rats

Potential differences in sensitivity to the rewarding effects of morphine as a function of litter separation stress were assessed in post-weaning rat dams. During the first two weeks postnatal, Sprague-Dawley rat litters were subjected to daily 15- or 180-min sessions of dam-pup separation while control litters only experienced twice-weekly animal facility care. One week after weaning, the dams (n=7 per group) underwent a fully unbiased conditioned place preference (CPP) procedure to 1 mg/kg subcutaneous morphine. CPP responses after each conditioning cycle were recorded. Rates of acquisition and asymptotic levels of CPP were comparable in all groups; however, an inverse relationship between litter size and magnitude of morphine CPP was revealed. Although these initial data indicate no differential sensitivity to the rewarding effects of low-dose morphine produced by the stress of litter separation, this assessment of litter size and drug-induced place conditioning in post-weaning litter-separated dams is the first of its kind. Potential effects of other doses, drugs of abuse and post-partum manipulations remain to be evaluated within this emerging etiological model.

Periaqueductal gray cholecystokinin infusions block morphine-induced disruption of maternal behavior

Cholecystokinin (CCK) and opiates interaction is critical for maintaining maternal behavior during lactation. Morphine inhibits while CCK restores maternal behavior. Recently we have shown that periaqueductal gray (PAG) is a region critically involved in the opioidergic blockade of maternal behavior. A critical level of morphine-induced activation of the rostral lateral PAG is required to inhibit maternal behavior in lactating rats. Since central CCK injections reverted morphine-induced inhibition of maternal behavior, we tested whether this peptide would act similarly in the PAG. This hypothesis was confirmed in experiments showing that morphine's inhibitory effect on maternal responsiveness was blocked by 1.0 and 0.2 nmol CCK injections into the rostral PAG, but not in nearby regions of the mesencephalic reticular nucleus. To test for possible compensatory changes the CCK2 receptor due to morphine treatments the expression of CCK2 receptor mRNA was evaluated in the PAG. PAG CCK2 receptor cDNA amplification revealed no difference in morphine treated animals. These results broaden understanding of the role played by CCK in the PAG. This CCK action might not depend on changes in its receptor.

Preliminary study of the effects of morphine treatment on opioid receptor gene expression in brain structures of the female rat

Opioid receptors play an important role in female physiology. They modulate directly and indirectly neuroendocrine phenomena that influence pregnancy maintenance, pain threshold, parturition, lactation, maternal behavior, rewarding and addiction. Thus understanding the gene expression levels of the three major opioid receptors, mu, delta and kappa in different brain regions is essential for investigating dynamic mechanisms of opioidergic transmission. Adult virgin female rats were treated acutely with morphine sulfate (3.5 mg/kg or 20 mg/kg s.c.) or chronically for 5 days (3.5 mg/kg). Rats were killed 1 h after the last injection. In the acute treatment, expression levels for the encoded mu-opioid receptor Oprm1, as detected by reverse transcription-polymerase chain reaction, were significantly decreased in the periaqueductal gray. In chronic treatment, both Oprk1 and Oprm1 expression levels, that encoded kappa and mu-opioid receptor respectively, showed significant decreases in the periaqueductal gray and striatum. Regional changes in opioid receptor gene expression levels might reflect highly specialized roles for these receptors with possible functional meaning for the plasticity of the opioidergic transmission.