Role of Nitric Oxide on Dopamine Release and Morphine-Dependency

Exploring the progression of drug dependence in a methamphetamine self-administration rat model through targeted and non-targeted metabolomics analyses

Persistent neurochemical and biological disturbances resulting from repeated cycles of drug reward, withdrawal, and relapse contribute to drug dependence. Methamphetamine (MA) is a psychostimulant with substantial abuse potential and neurotoxic effects, primarily affecting monoamine neurotransmitter systems in the brain. In this study, we aimed to explore the progression of drug dependence in rat models of MA self-administration, extinction, and reinstatement through targeted and non-targeted metabolomics analyses. Metabolic profiles were examined in rat plasma during the following phases: after 16 days of MA self-administration (Group M); after 16 days of self-administration followed by 14 days of extinction (Group MS); and after self-administration and extinction followed by a reinstatement injection of MA (Group MSM). Each group of MA self-administration, extinction, and reinstatement induces distinct changes in the metabolic pathways, particularly those related to the TCA cycle, arginine and proline metabolism, and arginine biosynthesis. Additionally, the downregulation of glycerophospholipids and sphingomyelins in Group MSM suggests their potential role in MA reinstatement. These alterations may signify the progressive deterioration of these metabolic pathways, possibly contributing to drug dependence following repeated cycles of drug reward, withdrawal, and relapse. These results provide valuable insights into the metabolic changes associated with MA use at various stages, potentially facilitating the discovery of early diagnostic biomarkers and therapeutic targets for MA use disorders.

No significant change of N6 -methyladenosine modification landscape in mouse brain after morphine exposure

OBJECTIVES

N6 -methyladenosine (m6 A) plays a crucial role in regulating neuroplasticity and different brain functions at the posttranscriptional level. However, it remains unknown whether m6 A modification is involved in acute and chronic morphine exposure.

MATERIALS AND METHODS

In this study, we conducted a direct comparison of m6 A levels and mRNA expression of m6 A-associated factors between morphine-treated and nontreated C57BL/6 wild-type mice. We established animal models of both acute and chronic morphine treatment and confirmed the rewarding effects of chronic morphine treatment using the conditioned place preference (CPP) assay. The activation status of different brain regions in response to morphine was assessed by c-fos staining. To assess overall m6 A modification levels, we employed the m6 A dot blot assay, while mRNA levels of m6 A-associated proteins were measured using a quantitative polymerase chain reaction (qPCR) assay. These analyses were performed to investigate whether and how m6 A modification and m6 A-associated protein expression will change following morphine exposure.

RESULTS

The overall m6 A methylation and mRNA levels of m6 A-associated proteins were not significantly altered in brain regions that were either activated or not activated during acute morphine stimulation. Similarly, the overall m6 A modification and mRNA levels of m6 A-associated proteins remained unaffected in several key brain regions associated with reward following chronic morphine exposure.

CONCLUSION

This study showed that the overall m6 A modification level and mRNA expression levels of m6 A-associated factors were not affected after acute and chronic morphine exposure in different brain regions, indicating m6 A modification may not be involved in brain response to morphine exposure.

The reinstatement of the expression phase of morphine-induced conditioned place preference in male Wistar rats under ventral tegmental area stimulation and brief inactivation

Background and purpose

Previous research has found that the electrical stimulation of the ventral tegmental area (VTA) is involved in drug-dependent behaviors and plays a role in reward-seeking. However, the mechanisms remain unknown, especially the effect of electrical stimulation on this area. Therefore, this study aimed to investigate how the electrical stimulation and the temporary inactivation of VTA affect the morphine- dependent behavior in male rats.

Experimental approach

The adult Wistar male rats were anesthetized with ketamine and xylazine. The stimulation electrode (unilaterally) and the microinjection cannula (bilaterally) were implanted into the VTA, stereotaxically. Then, the rats underwent three-day of repeated conditioning with subcutaneous morphine (0.5 or 5 mg/kg) injections, in the conditioned place preference apparatus, followed by four-day forced abstinence, which altered their conditioning response to a morphine (0.5 mg/kg) priming dose on the ninth day. On that day, rats were given high- or low-intensity electrical stimulation or reversible inactivation with lidocaine (0.5 pL/site) in the VTA.

Findings/Results

Results showed that the electrical stimulation of the VTA with the high intensity (150 μA/rat), had a minimal effect on the expression of morphine-induced place conditioning in rats treated with a high dose (5 mg/kg) of morphine. However, the reversible inactivation of the VTA with lidocaine greatly increased place preference in rats treated with a low dose (0.5 mg/kg) of morphine. Additionally, the reinstatement of 0.5 mg/kg morphine-treated rats was observed after lidocaine infusion into the VTA.

Conclusion and implications

These results suggest that VTA electrical stimulation suppresses neuronal activation, but the priming dose causes reinstatement. The VTA may be a potential target for deep brain stimulation-based treatment of intractable disorders induced by substance abuse.

Methadone administered to rat dams during pregnancy and lactation affects the circadian rhythms of their pups

The circadian clock is one of the most important homeostatic systems regulating the majority of physiological functions. Its proper development contributes significantly to the maintenance of health in adulthood. Methadone is recommended for the treatment of opioid use disorders during pregnancy, increasing the number of children prenatally exposed to long-acting opioids. Although early-life opioid exposure has been studied for a number of behavioral and physiological changes observed later in life, information on the relationship between the effects of methadone exposure and circadian system development is lacking. Using a rat model, we investigated the effects of prenatal and early postnatal methadone administration on the maturation of the circadian clockwork in the suprachiasmatic nucleus (SCN) and liver, the rhythm of aralkylamine N-acetyltransferase (AA-NAT) activity in the pineal gland, and gene expression in the livers of 20-day-old rats. Our data show that repeated administration of methadone to pregnant and lactating mothers has significant effect on rhythmic gene expression in the SCN and livers and on the rhythm of AA-NAT in the offspring. Similar to previous studies with morphine, the rhythm amplitudes of the clock genes in the SCN and liver were unchanged or enhanced. However, six of seven specific genes in the liver showed significant downregulation of their expression, compared to the controls in at least one experimental group. Importantly, the amplitude of the AA-NAT rhythm was significantly reduced in all methadone-treated groups. As there is a strong correlation with melatonin levels, this result could be of importance for clinical practice.

Neuroinflammatory Response in Reward-Associated Psychostimulants and Opioids: A Review

Substance abuse is one of the significant problems in social and public health worldwide. Vast numbers of evidence illustrate that motivational and reinforcing impacts of addictive drugs are primarily attributed to their ability to change dopamine signaling in the reward circuit. However, the roles of classic neurotransmitters, especially dopamine and neuromodulators, monoamines, and neuropeptides, in reinforcing characteristics of abused drugs have been extensively investigated. It has recently been revealed that central immune signaling includes cascades of chemokines and proinflammatory cytokines released by neurons and glia via downstream intracellular signaling pathways that play a crucial role in mediating rewarding behavioral effects of drugs. More interestingly, inflammatory responses in the central nervous system modulate the mesolimbic dopamine signaling and glutamate-dependent currents induced by addictive drugs. This review summarized researches in the alterations of inflammatory responses accompanied by rewarding and reinforcing properties of addictive drugs, including cocaine, methamphetamine, and opioids that were evaluated by conditioned place preference and self-administration procedures as highly common behavioral tests to investigate the motivational and reinforcing impacts of addictive drugs. The neuroinflammatory responses affect the rewarding properties of psychostimulants and opioids.

Attenuation of Morphine Dependence by Ganoderma lucidum Extract in Mice

Background: Opioids are the principal drugs of choice for managing acute severe pain; however, physical dependence is still reported as one of the main limiting factors in the clinical application of these drugs. In the present study, the effect of Ganoderma lucidum (G. lucidum) was assessed on morphine dependence in mice. Methods: A 19-day administration schedule was applied to induce morphine dependence in male adult NMRI mice. The mice were given intraperitoneal (i.p.) morphine sulfate once daily in an increasing dose of 10, 20, and 40 mg/kg. Then, G. lucidum hydroalcoholic extract (12.5, 25, and 50 mg/kg, i.p.) was given to the mice from days 10 to 18. Another group of mice received single doses of the extract (50, 100, and 200 mg/kg, i.p.) only on the 19th day. Naloxone (3 mg/kg, i.p.) was used to precipitate withdrawal syndrome. Normal saline and diazepam (0.25 mg/kg) were used as the negative and positive controls, respectively. Results: The administration of single doses of G. lucidum extract (100 and 200 mg/kg, i.p.) significantly decreased the number of jumps, leanings, and diarrhea in mice subjected to morphine dependence. The repeated administration of G. lucidum extract (25 and 50 mg/kg for nine days) significantly attenuated the number of jumps, leanings, and diarrhea in morphine-dependent mice. Conclusions: Overall, G. lucidum extract attenuates induced morphine dependence and inhibits withdrawal syndrome symptoms in mice.

Dopaminergic and nitric oxide systems interact to regulate the electrical activity of neurons in the medial septal nucleus in rats

Research characterizing the neuronal substrate of anxiety has implicated different brain areas, including the medial septal nucleus (m-SEPT). Previous reports indicated a role of dopamine and nitric oxide (NO) in anxiety-related behaviors. In this study, the extracellular single-unit recording was performed from the m-SEPT in adult male albino Wistar rats. Baseline activity was recorded for 5 min, and the post-injection recording was performed for another 5 min after the microinjection of each drug. The results showed that (1) both D1- and D2-like receptor agonists (SKF-38393 and quinpirole) enhanced the firing rate of m-SEPT neurons; (2) both D1- and D2-like antagonists (SCH-23390 and sulpiride) attenuated the firing rate of m-SEPT neurons; (3) L-arginine (NO precursor) increased the firing rate of m-SEPT neurons, but a non-specific NOS inhibitor, L-NAME, elicited no significant alterations; (4) the non-specific NOS inhibitor reversed the enhanced firing rate produced by SKF-38393 and quinpirole; (5) neither of the dopaminergic antagonists changed the enhanced activity resulted from the application of the NO precursor. These results contribute to our understanding of the complex neurotransmitter interactions in the m-SEPT and showed that both dopaminergic and NO neurotransmission are involved in the modulation of the firing rate of neurons in the m-SEPT.

Effects of linagliptin on morphine dependence in larval zebrafish (Danio rerio)

Drug addiction is a chronic, recurrent disease of the central nervous system that leads to the development of comorbidities and premature death. Despite extensive scientific research concerning addiction, no effective method of addiction pharmacotherapy has been known so far. Glucagon-like peptide 1 has been suggested to play a role in the rewarding effect of addictive drugs. Linagliptin is a selective dipeptidyl peptidase-4 inhibitor that suppresses the rapid degradation of endogenous glucagon-like peptide-1. In clinical practice, it is used as an antidiabetic drug, but recent studies have confirmed its role in the activity of the central nervous system. This pilot study was conducted to ascertain whether linagliptin might influence morphine dependence – a locomotor activity test was carried out to assess the intensity of morphine withdrawal symptom. The obtained results clearly confirmed that linagliptin (0.01 and 0.1 mM) reduced the locomotor activity in morphine-dependent larval zebrafish. The undertaken experiments clearly indicates that linagliptin is involved in the addictive effects of morphine, thus, further studies on higher organisms should be carried out.

The Mechanisms Involved in Morphine Addiction: An Overview

Opioid use disorder is classified as a chronic recurrent disease of the central nervous system (CNS) which leads to personality disorders, co-morbidities and premature death. It develops as a result of long-term administration of various abused substances, along with morphine. The pharmacological action of morphine is associated with its stimulation of opioid receptors. Opioid receptors are a group of G protein-coupled receptors and activation of these receptors by ligands induces significant molecular changes inside the cell, such as an inhibition of adenylate cyclase activity, activation of potassium channels and reductions of calcium conductance. Recent data indicate that other signalling pathways also may be involved in morphine activity. Among these are phospholipase C, mitogen-activated kinases (MAP kinases) or β-arrestin. The present review focuses on major mechanisms which currently are considered as essential in morphine activity and dependence and may be important for further studies.

SB-334867 (an Orexin-1 Receptor Antagonist) Effects on Morphine-Induced Sensitization in Mice-a View on Receptor Mechanisms

The present study focused upon the role of SB-334867, an orexin-1 receptor antagonist, in the acquisition of morphine-induced sensitization to locomotor activity in mice. Behavioral sensitization is an enhanced systemic reaction to the same dose of an addictive substance, which assumingly increases both the desire for the drug and the risk of relapse to addiction. Morphine-induced sensitization in mice was achieved by sporadic doses (five injections every 3 days) of morphine (10 mg/kg, i.p.), while a challenge dose of morphine (10 mg/kg) was injected 7 days later. In order to assess the impact of orexin system blockade on the acquisition of sensitization, SB-334867 was administered before each morphine injection, except the morphine challenge dose. The locomotor activity test was performed on each day of morphine administration. Brain structures (striatum, hippocampus, and prefrontal cortex) were collected after behavioral tests for molecular experiments in which mRNA expression of orexin, dopamine, and adenosine receptors was explored by the qRT-PCR technique. Additionally, the mRNA expression of markers, such as GFAP and Iba-1, was also analyzed by the same technique. SB-334867 inhibited the acquisition of morphine-induced sensitization to locomotor activity of mice. Significant alterations were observed in mRNA expression of orexin, dopamine, and adenosine receptors and in the expression of GFAP and Iba-1, showing a broad range of interactions in the mesolimbic system among orexin, dopamine, adenosine, and glial cells during behavioral sensitization. Summing up, the orexin system may be an effective measure to inhibit morphine-induced behavioral sensitization.