Pharmacokinetic aspects of naloxone-precipitated morphine withdrawal in male and female prepubertal mice

BACLOFEN PREVENTS MORPHINE REWARDING EFFECTS AND ASSOCIATED BIOCHEMICAL ALTERATIONS IN MALE AND FEMALE MICE

Previous studies from our laboratory have shown sex differences in the behavioral, molecular, and neurochemical manifestations of morphine withdrawal and they were related to an increased sensitivity to morphine effects in males. In addition, we observed an interaction between the GABAergic and opioid systems that could also be sex-dependent. Baclofen, a GABAB receptor agonist, prevented the somatic expression and the molecular and neurochemical changes induced by morphine withdrawal syndrome in mice. On the contrary, little is known about baclofen effects in the rewarding properties of morphine in male and female mice. The present study aimed to explore the effect of baclofen (1, 2 and 3 mg/kg, i.p.) pretreatment in the rewarding effects induced by morphine (7 mg/kg, s.c.) and its effect on c-Fos and brain-derived neurotrophic factor (BDNF) expression induced by the rewarding properties of morphine in prepubertal male and female mice. Baclofen (2 mg/kg) pretreatment prevented the rewarding effects of morphine only in male mice, while baclofen (3 mg/kg) reduced these effects in both sexes. Moreover, the rewarding effects of morphine were associated with a decrease of BDNF and c-Fos expression cingulate cortex, nucleus accumbens shell, cornu ammonis 1 (CA1), and cornu ammonis 3 (CA3) areas of the hippocampus only in male mice. In addition, baclofen pretreatment prevented these changes in BDNF, but not in c-Fos expression. In conclusion, our results show that GABAB receptors have a regulatory role in the rewarding effects of morphine that could be of interest for a potential future therapeutic application in opioid use disorders.

Theophylline reverses oxycodone's but not fentanyl's respiratory depression in mice while caffeine is ineffective against both opioids

RATIONALE

The opioid epidemic remains a pressing public health crisis in the United States. Most of these overdose deaths are a result of lethal respiratory depression. In recent years the increasing incidence of opioid-involved overdose deaths has been driven by fentanyl, which is more resistant to adequate reversal by naloxone (NARCAN ®) than semi-synthetic or classical morphinan predecessors like oxycodone and heroin. For this and other reasons (e.g., precipitating withdrawal) non-opioidergic pharmacotherapies to reverse opioid-depressed respiration are needed. Methylxanthines are a class of stimulant drugs including caffeine and theophylline which exert their effects primarily via adenosine receptor antagonism. Evidence suggests methylxanthines can stimulate respiration by enhancing neural activity in respiratory nuclei in the pons and medulla independent of opioid receptors. This study aimed to determine whether caffeine and theophylline can stimulate respiration in mice when depressed by fentanyl and oxycodone.

METHODS

Whole-body plethysmography was used to characterize fentanyl and oxycodone's effects on respiration and their reversal by naloxone in male Swiss Webster mice. Next, caffeine and theophylline were tested for their effects on basal respiration. Finally, each methylxanthine was evaluated for its ability to reverse similar levels of respiratory depression induced by fentanyl or oxycodone.

RESULTS AND CONCLUSIONS

Oxycodone and fentanyl dose-dependently reduced respiratory minute volume (ml/min; MVb) that was reversible by naloxone. Caffeine and theophylline each significantly increased basal MVb. Theophylline, but not caffeine, completely reversed oxycodone-depressed respiration. In contrast, neither methylxanthine elevated fentanyl-depressed respiration at the doses tested. Despite their limited efficacy for reversing opioid-depressed respiration when administered alone, the methylxanthines safety, duration, and mechanism of action supports further evaluation in combination with naloxone to augment its reversal of opioid-depressed respiration.

Divergent profiles of fentanyl withdrawal and associated pain in mice and rats

Opioid abuse has devastating effects on patients, their families, and society. Withdrawal symptoms are severely unpleasant, prolonged, and frequently hinder recovery or lead to relapse. The sharp increase in abuse and overdoses arising from the illicit use of potent and rapidly-acting synthetic opioids, such as fentanyl, highlights the urgency of understanding the withdrawal mechanisms related to these drugs. Progress is impeded by inconsistent reports on opioid withdrawal in different preclinical models. Here, using rats and mice of both sexes, we quantified withdrawal behaviors during spontaneous and naloxone-precipitated withdrawal, following two weeks of intermittent fentanyl exposure. We found that both mice and rats lost weight during exposure and showed increased signs of distress during spontaneous and naloxone precipitated withdrawal. However, these species differed in their expression of withdrawal associated pain, a key contributor to relapse in humans. Spontaneous or ongoing pain was preferentially expressed in rats in both withdrawal conditions, while no change was observed in mice. In contrast, withdrawal associated thermal hyperalgesia was found only in mice. These data suggest that rats and mice diverge in how they experience withdrawal and which aspects of the human condition they most accurately model. These differences highlight each species' strengths as model systems and can inform experimental design in studies of opioid withdrawal.

Review of addiction risk potential associated with adolescent opioid use

Adolescence is a critical period of development with robust behavioral, morphological, hormonal, and neurochemical changes including changes in brain regions implicated in the reinforcing effects of drugs such as opioids. Here we examine the preclinical and, where appropriate complementary clinical literature, for the behavioral and neurological changes induced by adolescent opioid exposure/use and their long-term consequences during adulthood. Adolescent opioid exposure results in a widened biphasic shift in reinforcement with increased impact of positive rewarding aspects during initial use and profound negative reinforcement during adulthood. Females may have enhanced vulnerability due to fast onset of antinociceptive tolerance and reduced severity of somatic withdrawal symptoms during adolescence. Overall, adolescent opioid exposure, be it legally prescribed protracted intake or illicit consumption, results in significant and prolonged consequences of increased opioid reward concomitant with reduced analgesic efficacy and exacerbated somatic withdrawal severity during opioid use/exposure in adulthood. These findings are highly relevant to physicians, parents, law makers, and the general public as adolescent opioid exposure/misuse results in heightened risk for substance use disorders.

The influence of opioid dependence on salt consumption and related psychological parameters in mice and humans

BACKGROUND

The consumption of dietary salt (NaCl) is controlled by neuronal pathways that are modulated by endogenous opioid signalling. The latter is disrupted by chronic use of exogenous opioid receptor agonists, such as morphine. Therefore, opioid dependence may influence salt consumption, which we investigated in two complimentary studies in humans and mice.

METHODS

Human study: three groups were recruited: i. Individuals who are currently opioid dependent and receiving opioid substitution treatment (OST); ii. Previously opioid dependent individuals, who are currently abstinent, and; iii. Healthy controls with no history of opioid dependence. Participants tasted solutions containing different salt concentrations and indicated levels of salt 'desire', salt 'liking', and perceptions of 'saltiness'. Mouse study: preference for 0.1 M versus 0.2 M NaCl and overall levels of salt consumption were recorded during and after chronic escalating morphine treatment.

RESULTS

Human study: Abstinent participants' 'desire' for and 'liking' of salt was shifted towards more highly concentrated salt solutions relative to control and OST individuals. Mouse study: Mice increased their total salt consumption during morphine treatment relative to vehicle controls, which persisted for 3 days after cessation of treatment. Preference for 'low' versus 'high' concentrations of salt were unchanged.

CONCLUSION

These findings suggest a possible common mechanistic cross-sensitization to salt that is present in both mice and humans and builds our understanding of how opioid dependence can influence dietary salt consumption. This research may help inform better strategies to improve the diet and overall wellbeing of the growing number of individuals who develop opioid dependence.

Sex differences in the pharmacology of itch therapies-a narrative review

BACKGROUND

Chronic itch is the most common skin-related condition, associated with a high psychosocial and economic burden. In recent years, increasing evidence of sex differences in the perception, clinical presentation and treatment requirements of itch points towards potential benefits when using sex-adapted therapies. It is well-known that body composition, absorption, metabolism, elimination and adverse drug reactions (ADRs) differ between sexes, but only little is known about the impact of sex in the pharmacology of itch treatments, which could help to rationalise sex-adapted treatment strategies.

AIM

To evaluate and review sex effects in the pharmacokinetics and /-dynamics of drugs used to treat itch.

METHODS

In this narrative review we performed a PubMed and MEDLINE (Ovid) search using the terms (itch OR pruritus) AND (gender OR sex) AND (drug OR medication OR pharmacokinetics OR pharmacodynamics). Additional searches were performed for the topical and systemic drugs recommended by the European Guideline on Chronic Pruritus.

RESULTS

We found numerous reports with variable levels of evidence of sex effects with respect to the pharmacokinetics and/or pharmacodynamics of 14 drug classes used for the treatment of itch, including a total of 19 systemic and 3 topical drugs. Women seem to present higher plasma levels of several drugs used in itch treatment, including tri- and tetracyclic antidepressants (e.g. doxepin, amitriptyline, mirtazapine), serotonin reuptake inhibitors (e.g. paroxetine, sertraline, fluoxetine), immunosuppressive drugs (e.g. cyclosporine, mycophenolate mofetil), serotonin receptor antagonists (e.g. ondansetron) and betablockers (e.g. propranolol). Adverse drug reactions (ADRs) were generally more common in women. Being female was reported to be an independent risk factor for QTc-prolongation associated with antihistamines and tetracyclic antidepressants. Additionally, women seem to be more prone to sedative effects of antihistamines, and to suffer from a higher frequency as well as severity of side effects with systemic calcineurin inhibitors, opioid agonists, and opioid antagonists. Women were also sensitised more often to topically applied drugs. Of note, apart from only one experimental study with capsaicin, none of these reports were designed specifically to assess the effect of sex (and gender) in the treatment of itch.

DISCUSSION/CONCLUSION

Our review supports previous reports that sex is of importance in the pharmacokinetics and /-dynamics of several drugs used to treat itch although those drugs were mostly evaluated for non-itch indications. However, the results are limited by methodological limitations evident in most studies such as underrepresentation of women in clinical trials. This emphasises the need to study the impact of sex (and gender) in future itch trials to yield better outcomes and prevent ADRs in both sexes.

Sex differences in affective response to opioid withdrawal during adolescence

Drug withdrawal is suggested to play a role in precipitating mood disorders in individuals with familial predisposition. Age-related differences in affective responses to withdrawal might explain the increased risk of mental illnesses when drug use begins during adolescence. Recently we observed that, in contrast to adult male mice, adolescent males exhibited a decrease in immobility in the forced swim test on the third day of withdrawal, as compared with controls. Thus, the present study examined forced swim test behaviors of adolescent female mice during opioid withdrawal. Similar to the male study, adolescent female mice were injected with two morphine regimens which differed in dosage. Three and nine days following discontinuation of morphine administration, forced swim test immobility time and locomotion were evaluated. In contrast to males, which exhibited a decrease in immobility, no significant differences in immobility were observed in female adolescents undergoing withdrawal as compared with saline-injected controls. This sex difference in forced swim test behaviors was not due to changes in overall motor activity, since differences in locomotion were not observed in either male or female adolescent mice. Thus, this study demonstrates sex differences in forced swim test behavior during opioid withdrawal. Forced swim test behaviors are classically used to evaluate mood in rodents, thus this study suggests that opioid withdrawal might affect mood differentially across sexes.

Endogenous opiates and behavior: 2007

This paper is the thirtieth consecutive installment of the annual review of research concerning the endogenous opioid system. It summarizes papers published during 2007 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, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Different affective response to opioid withdrawal in adolescent and adult mice

AIMS

Drug withdrawal is suggested to play a role in precipitating mood disorders in individuals with familial predisposition. Age-related differences in affective responses to withdrawal might explain the increased risk of mental illnesses when drug use begins during adolescence. Since there is a lack of animal research examining the effects of opioid withdrawal during adolescence, the present study examined whether there are age-related differences in affective responses to opioid withdrawal.

MAIN METHODS

Adolescent and adult mice were injected with two different morphine regimens, namely low and high, which differed in the dosage. Three and nine days following discontinuation of morphine administration, immobility time in the forced swim test (FST) and locomotion (total distance traveled) were evaluated.

KEY FINDINGS

On withdrawal day 3 (WD3), adolescent mice exhibited a decrease in immobility as compared to controls. No significant differences in immobility were observed on withdrawal day 9 (WD9). This effect on FST behaviors was not due to changes in overall motor activity, since no differences in locomotion were observed on either WD3 or WD9 in adolescent mice. In adults, no differences in either FST or locomotor behaviors were observed on WD3. As expected, on WD9, adult mice exhibited an increase in immobility and a decrease in locomotion.

SIGNIFICANCE

This study demonstrates age-dependent differences in both FST scores and locomotor behaviors during opioid withdrawal. FST behaviors are classically used to evaluate mood in rodents, thus this study suggests that opioid withdrawal might affect mood differentially across age.