Study of morphine-induced dependence in gonadectomized male and female mice

Estradiol and Mu opioid-mediated reward: The role of estrogen receptors in opioid use

Opioid use and opioid use disorder are characterized by sex and gender differences, and some of these differences may be mediated by differences in the hormonal milieu within and across individuals. This review focuses on the role of ovarian hormones, and particularly estradiol, on the endogenous mu opioid receptor system. There is an abundance of data indicating that estradiol influences the activity of endogenous mu opioid peptides, the activation of mu opioid receptors, and the internalization and desensitization of mu opioid receptors. These effects have functional consequences on behaviors mediated by endogenous mu opioid receptor activity and on sensitivity to mu opioid agonists and antagonists. Recent behavioral data suggest these consequences extend to mu opioid reward, and preclinical studies report that estradiol decreases self-administration of mu opioid receptor agonists across a range of experimental conditions. Data collected in human laboratory studies suggest that estradiol may have functionally similar effects in clinical populations, and thus estrogen receptors may be a potential target in the development of novel therapeutics. This review summarizes data from cellular assays to clinical trials to explore how estradiol influences mu opioid receptor activity, as well as potential ways in which estrogen receptors may be targeted to address the problems of opioid use.

Modulation of morphine physical dependence and discriminative stimulus effects by ovarian hormones: Role of estradiol

Ovarian hormones influence the activity of endogenous opioids, and exogenous administration of estradiol reduces opioid intake and opioid seeking in animal models of opioid reward and reinforcement. The purpose of this study was to examine the effects of ovarian hormones on the discriminative stimulus effects of morphine and naloxone-precipitated opioid withdrawal. To this end, separate groups of ovariectomized female rats were trained to discriminate the stimulus effects of either 3.0 or 10 mg/kg morphine, and substitution tests were conducted with estradiol or progesterone alone and in combination with morphine. At the conclusion of discrimination testing, rats were treated chronically with estradiol, progesterone, or their combination, and challenged with naloxone to measure opioid-like withdrawal symptoms. Finally, the effects of estradiol, progesterone, and their combination were examined on naloxone-precipitated withdrawal in morphine-dependent rats. Neither estradiol nor progesterone substituted for the morphine discriminative stimulus, but estradiol significantly increased the potency of morphine in rats trained to discriminate 10 mg/kg but not 3 mg/kg morphine. When administered chronically, neither hormone nor their combination produced an opioid-like withdrawal syndrome following a naloxone challenge. Acute administration of estradiol, but not progesterone or a combination of estradiol and progesterone, significantly reduced naloxone-precipitated weight loss in morphine-dependent rats. These data indicate that estradiol influences the behavioral effects of morphine, possibly by increasing endogenous tone at mu opioid receptors.

Sex differences in opioid receptor mediated effects: Role of androgens

An abundance of data indicates there are sex differences in endogenous opioid peptides and opioid receptors, leading to functional differences in sensitivity to opioid receptor mediated behaviors between males and females. Many of these sex differences are mediated by the effects of gonadal hormones on the endogenous opioid system. Whereas much research has examined the role of ovarian hormones on opioid receptor mediated endpoints, comparatively less research has examined the role of androgens. This review describes what is currently known regarding the influence of androgens on opioid receptor mediated endpoints and how androgens may contribute to sex differences in these effects. The review also addresses the clinical implications of androgenic modulation of opioid receptor mediated behaviors and suggests future lines of research for preclinical and clinical investigators. We conclude that further investigation into androgenic modulation of opioid receptor mediated effects may lead to new options for addressing conditions such as chronic pain and substance use disorders.

Exposure to smoke from high- but not low-nicotine cigarettes leads to signs of dependence in male rats and potentiates the effects of nicotine in female rats

Nicotine is only mildly rewarding, but after becoming dependent, it is difficult to quit smoking. The goal of these studies was to determine if low-nicotine cigarettes are less likely to cause dependence and enhance the reinforcing effects of nicotine than regular high-nicotine cigarettes. Male and female rats were exposed to tobacco smoke with a low or high nicotine level for 35 days. It was investigated if smoke exposure affects the development of dependence, anxiety- and depressive-like behavior, and nicotine-induced behavioral sensitization. Smoke exposure did not affect locomotor activity in a small open field or sucrose preference. Mecamylamine precipitated somatic withdrawal signs in male rats exposed to smoke with a high level of nicotine, but not in male rats exposed to smoke with a low level of nicotine or in females. After cessation of smoke exposure, there was a small decrease in sucrose preference in the male rats, which was not observed in the females. Cessation of smoke exposure did not affect anxiety-like behavior in the large open field or the elevated plus maze test. Female rats displayed less anxiety-like behavior in both these tests. Repeated treatment with nicotine increased locomotor activity, rearing, and stereotypies. Prior exposure to smoke with a high level of nicotine increased nicotine-induced rearing in the females. These findings indicate that exposure to smoke with a low level of nicotine does not lead to dependence and does not potentiate the effects of nicotine. Exposure to smoke with a high level of nicotine differently affects males and females.

Effects of Urtica dioica hydro-alcoholic extract on blood serum glucose and lipid profiles of female Wistar rats with long-term estrogen deficiency

In this study, the effects of Urtica dioica hydro-alcoholic extract were investigated on the blood glucose and lipid profiles of female ovariectomized and non-ovariectomized rats. In total, 32 adult female rats were divided into four groups (eight each) including control and ovariectomy groups as well as non-ovariectomy and ovariectomy groups treated with 200 mg kg^-1 of Urtica dioica extract orally in the last five weeks of the study starting from the week 56^th. The duration of the study was 60 weeks. Glucose, serum lipid profiles and pancreatic pathological alterations were determined in these groups at the end of experiment. Serum glucose, triglyceride (TG), very-low-density lipoprotein (VLDL), and TG/high-density lipoprotein (HDL) ratio indicated a significant increase in the healthy female rats under treatment with Urtica dioica extract compared to others. The TG, cholesterol, HDL, low-density lipoprotein (LDL) and VLDL showed a significant increase in menopaused rats compared to others. The interaction of consuming Urtica dioica extract and ovariectomy caused significant decreases in glucose, TG, VLDL, HDL/LDL ratio and TG/HDL ratio. Consumption of Urtica dioica extract by non-menopaused rats damaged the beta cells in Langerhans islets. Results of the present study revealed that the consumption of Urtica dioica extract is not beneficial and has diabetogenic effects in female non-ovariectomized rats compared to ovariectomized ones.

Genistein modulation of seizure: involvement of estrogen and serotonin receptors

Genistein, a major source of phytoestrogen exposure for humans and animals, has been shown to mediate neuroprotection in Alzheimer's disease and status epilepticus. In the present study, we investigated the effect of genistein on pentylenetetrazole-induced seizures in ovariectomized mice and the possible involvement of estrogenic and serotonergic pathways in the probable effects of genistein. Intraperitoneal (i.p.) administration of genistein (10 mg/kg) significantly increased the seizure threshold 30 min prior to induction of seizures 14 days after ovariectomy surgery. Administration of fulvestrant (1 mg/kg, i.p.), an estrogen receptor antagonist, completely reversed the anticonvulsant effect of genistein (10 mg/kg) in ovariectomized mice. Administration of the antagonist of serotonin receptor (5-HT3), tropisetron (10 mg/kg, i.p.), eliminated the anticonvulsant effect of genistein, whereas co-administration of m-chlorophenylbiguanide (5-HT3 receptor agonist; 1 mg/kg) and a non-effective dose of genistein (5 mg/kg) increased the seizure threshold. To conclude, it seems that estrogenic/serotonergic systems might be involved in the anticonvulsant properties of genistein.

17α-ethinyl estradiol attenuates depressive-like behavior through GABAA receptor activation/nitrergic pathway blockade in ovariectomized mice

OBJECTIVES

This study was performed to investigate the antidepressant-like effect of 17α-ethinyl estradiol (EE2) in ovariectomized (OVX) mice and the possible role of nitrergic and gamma aminobutyric acid (GABA)ergic pathways in this paradigm.

METHODS

Bilateral ovariectomy was performed in female mice, and different doses of EE2 were intraperitoneally injected either alone or combined with GABAA agonist, diazepam, GABAA antagonist, flumazenil, non-specific nitric oxide synthase (NOS) inhibitor, N(ω)-nitro-L-arginine methyl ester (L-NAME), specific nNOS inhibitor, 7-nitroindazole (7-NI), a nitric oxide (NO) precursor, L-arginine, and selective PDE5I, sildenafil. After locomotion assessment, immobility times were recorded in the forced swimming test (FST) and tail suspension test (TST). Moreover, hippocampal nitrite concentrations were measured in the examined groups.

RESULTS

Ten days after ovariectomy, a significant prolonged immobility times were observed. EE2 (0.3 and 1μg/kg and 0.03, 0.1, and 1mg/kg) caused antidepressant-like activity in OVX mice in FST and TST. Diazepam (1 and 5mg/kg), L-NAME (30mg/kg), and 7-NI (100mg/kg) significantly reduced the immobility times. Co-administration of minimal and sub-effective doses of EE2 and diazepam (0.3μg/kg and 0.5mg/kg, respectively) exerted a significant antidepressant-like effect. The same effect was observed in combination of minimal and sub-effective doses of EE2 and either L-NAME or 7-NI. Moreover, combination of minimal and sub-effective doses of EE2, diazepam either L-NAME, or 7-NI emphasized the significant robust antidepressant-like activity.

CONCLUSIONS

The study has demonstrated that lowest dose of EE2 exerts a significant antidepressant-like behavior. It is suggested that suppression of NO system, as well as GABAA activation, may be responsible for antidepressant-like activity of EE2 in OVX mice. Moreover, GABAA activation may inhibit nitrergic pathway.

Pioglitazone potentiates development of morphine-dependence in mice: possible role of NO/cGMP pathway

Peroxizome proliferator-activated receptor gamma (PPARγ) is highly expressed in the central nervous system where it modulates numerous gene transcriptions. Nitric oxide synthase (NOS) expression could be modified by simulation of PPARγ which in turn activates nitric oxide (NO)/soluble guanylyl-cyclase (sGC)/cyclic guanosine mono phosphate (cGMP) pathway. It is well known that NO/cGMP pathway possesses pivotal role in the development of opioid dependence and this study is aimed to investigate the effect of PPARγ stimulation on opioid dependence in mice as well as human glioblastoma cell line. Pioglitazone potentiated naloxone-induced withdrawal syndrome in morphine dependent mice in vivo. While selective inhibition of PPARγ, neuronal NOS or GC could reverse the pioglitazone-induced potentiation of morphine withdrawal signs; sildenafil, a phosphodiesterase-5 inhibitor amplified its effect. We also showed that nitrite levels in the hippocampus were significantly elevated in pioglitazone-treated morphine dependent mice. In the human glioblastoma (U87) cell line, rendered dependent to morphine, cAMP levels did not show any alteration after chronic pioglitazone administration while cGMP measurement revealed a significant rise. We were unable to show a significant alteration in neuronal NOS mRNA expressions by pioglitazone in mice hippocampus or U87 cells. Our results suggest that pioglitazone has the ability to enhance morphine-dependence and to augment morphine withdrawal signs. The possible pathway underlying this effect is through activation of NO/GC/cGMP pathway.

Estradiol reduces depressive-like behavior through inhibiting nitric oxide/cyclic GMP pathway in ovariectomized mice

Estradiol decline has been associated with depressive-like behavior in female mice and NO has been suggested to play a major role in the pathogenesis of major depression. This study was conducted to investigate the antidepressant-like effects of acute estradiol administration in female ovariectomized (OVX) mice and the possible role of nitric oxide (NO)/cyclic GMP (cGMP) pathway. To this end, bilateral ovariectomy was performed in female mice and different doses of estradiol were injected alone or in combination with non-specific NO synthase (NOS) inhibitor (L-NAME), selective neural NOS (nNOS) inhibitor (7-NI), an NO precursor (L-arginine) or selective phosphodiesterase type 5 inhibitor (sildenafil). The duration of immobility was recorded in the forced swimming test (FST) to assess the depressive behavior. Moreover, hippocampal levels of NO were determined in select groups. 10 days following the procedure, OVX mice showed significantly prolonged immobility time in comparison with the sham group. Estradiol (3, 10, and 30 μg/kg, s.c.), when injected 1 h prior to FST, exerted antidepressant-like effects in OVX mice. Both L-NAME (30 mg/kg, i.p.), and 7-NI (50 mg/kg, i.p.) significantly reduced the immobility times of OVX mice. Administration of a sub-effective dose of L-NAME (10mg/kg), 15 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) had a robust antidepressant-like effect in OVX mice. Also a sub-effective dose of 7-NI (25 mg/kg), 30 min after a sub-effective dose of estradiol (1 μg/kg, s.c.) showed antidepressant-like effect in OVX mice. Both the NO precursor L-arginine (750 mg/kg, i.p.) and the cGMP-specific phosphodiesterase type 5 inhibitor sildenafil (5 mg/kg, i.p.), 30 min before estradiol treatment, prevented the antidepressant-like effect of a potent dose of estradiol (10 μg/kg, s.c.) in OVX mice. The present findings suggest that suppression of the NO synthase/NO/cGMP pathway may be involved in the antidepressant-like effects of estradiol in OVX mice.

Social influences on plasma testosterone levels in morphine withdrawn adolescent mice and their drug-naïve cage-mates

Opioid administration in males results in opioid-induced androgen deficiency which persists throughout the treatment. In adults, this quickly reverses once opioid administration is suspended. However, less is known about the duration of the effect following drug discontinuation in adolescents. Given the significant implications to sexual maturation in adolescent males, this study examined plasma testosterone levels in both morphine withdrawn mice and their drug-naïve (saline-injected) cage-mates as compared to drug-naïve mice housed physically and visually separate from the morphine-treated mice ('saline only'). Consistent with the literature, plasma testosterone levels in morphine withdrawn adults were reduced on withdrawal day 1 (WD1) and returned to baseline levels by WD9. No significant effects were observed in their saline cage-mates. In the adolescents, no significant differences were observed on WD1 between the morphine withdrawn mice, their saline cage-mates, and the saline only mice - all of which had significantly lower plasma testosterone levels than adults. By WD9, testosterone levels in the saline only adolescent mice had reached adult levels. Notably, plasma testosterone levels were reduced in both the morphine withdrawn adolescent mice and their saline cage-mates, as compared to saline only mice. The effect was not a drug effect per se, given that reduced plasma testosterone levels were not observed in individually housed morphine withdrawn mice. Moreover, our results also suggest that these social effects are not solely explained by stress. These results have numerous implications to the short term and long term health of both adolescents requiring pain management and of adolescent drug addicts.

Sex differences in opioid analgesia, hyperalgesia, tolerance and withdrawal: central mechanisms of action and roles of gonadal hormones

This article reviews sex differences in opiate analgesic and related processes as part of a Special Issue in Hormones and Behavior. The research findings on sex differences are organized in the following manner: (a) systemic opioid analgesia across mu, delta and kappa opioid receptor subtypes and drug efficacy at their respective receptors, (b) effects of the activational and organizational roles of gonadal steroid hormones and estrus phase on systemic analgesic responses, (c) sex differences in spinal opioid analgesia, (d) sex differences in supraspinal opioid analgesia and gonadal hormone effects, (e) the contribution of genetic variance to analgesic sex differences, (f) sex differences in opioid-induced hyperalgesia, (g) sex differences in tolerance and withdrawal-dependence effects, and (h) implications for clinical therapies.