Cannabinoid 1 receptor blockade in the dorsal hippocampus prevents the reinstatement but not acquisition of morphine-induced conditioned place preference in rats

Dysregulation of the endogenous cannabinoid system following opioid exposure

Rates of opioid-related deaths and overdoses in the United States are at record-high levels. Thus, novel neurobiological targets for the treatment of OUD are greatly needed. Given the close interaction between the endogenous opioid system and the endocannabinoid system (ECS), targeting the ECS may have therapeutic potential in OUD. The various components of the ECS, including cannabinoid receptors, their lipid-derived endogenous ligands (endocannabinoids [eCBs]), and the related enzymes, present potential targets for developing new medications in OUD treatment. The purpose of this paper is to review the clinical and preclinical literature on the dysregulation of the ECS after exposure to opioids. We review the evidence of ECS dysregulation across various study types, exposure protocols, and measurement protocols and summarize the evidence for dysregulation of ECS components at specific brain regions. Preclinical research has shown that opioids disrupt various ECS components that are region-specific. However, the results in the literature are highly heterogenous and sometimes contradictory, possibly due to variety of different methods used. Further research is needed before a confident conclusion could be made on how exposure to opioids can affect ECS components in various brain regions.

Endocannabinoids and addiction memory: Relevance to methamphetamine/morphine abuse

AIM

This review aims to summarise the role of endocannabinoid system (ECS), incluing cannabinoid receptors and their endogenous lipid ligands in the modulation of methamphetamine (METH)/morphine-induced memory impairments.

METHODS

Here, we utilized the results from researches which have investigated regulatory role of ECS (including cannabinoid receptor agonists and antagonists) on METH/morphine-induced memory impairments.

RESULTS

Among the neurotransmitters, glutamate and dopamine seem to play a critical role in association with the ECS to heal the drug-induced memory damages. Also, the amygdala, hippocampus, and prefrontal cortex are three important brain regions that participate in both drug addiction and memory task processes, and endocannabinoid neurotransmission have been investigated.

CONCLUSION

ECS can be regarded as a treatment for the side effects of METH and morphine, and their memory-impairing effects.

The distinct roles of various neurotransmitters in modulating methamphetamine-induced conditioned place preference in relevant brain regions in mice

OBJECTIVES

Previous studies have shown that methamphetamine (METH) can induce complex adaptive changes in the reward system in the brain, including the changes in the content of neurotransmitters in the signal transduction pathway. However, how the changes of various neurotransmitters in relevant brain reward circuits contribute to METH-induced conditioned place preference (CPP) remains unclear.

METHODS

In this study, first, we designed an animal model of METH-induced CPP. Then we used liquid chromatography-mass spectrometry (LC-MS) to simultaneously determine the contents of various neurotransmitters - dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), 5-hydroxyindole acetic acid (5-HIAA), glutamic acid (Glu) and glutamine (Gln) - in different brain regions of the prefrontal cortex (PFc), nucleus accumbens (NAc), caudate-putamen (CPu) and hippocampus (Hip), which are believed to be relevant to the drug's reward effect.

RESULTS

The results of the behavioral experiment suggested that 1.0 mg/kg METH could induce obvious CPP in mice. The results about various neurotransmitters showed that: DA significantly increased in NAc in the METH group; Glu increased significantly in the METH group in PFc and NAc and Gln increased significantly in the METH group in PFc.

CONCLUSIONS

These results suggested that the neurotransmitters of DA, Glu and Gln may work together and play important roles in METH-induced CPP in relevant brain reward circuits, especially in PFc and NAc. These findings therefore could help to advance the comprehensive understanding of the neurochemic and psychopharmacologic properties of METH in reward effect, which is important for future improvements in the treatment of drug addiction.

Genetic Modulation of Initial Sensitivity to Δ9-Tetrahydrocannabinol (THC) Among the BXD Family of Mice

Cannabinoid receptor 1 activation by the major psychoactive component in cannabis, Δ9-tetrahydrocannabinol (THC), produces motor impairments, hypothermia, and analgesia upon acute exposure. In previous work, we demonstrated significant sex and strain differences in acute responses to THC following administration of a single dose (10 mg/kg, i.p.) in C57BL/6J (B6) and DBA/2J (D2) inbred mice. To determine the extent to which these differences are heritable, we quantified acute responses to a single dose of THC (10 mg/kg, i.p.) in males and females from 20 members of the BXD family of inbred strains derived by crossing and inbreeding B6 and D2 mice. Acute THC responses (initial sensitivity) were quantified as changes from baseline for: 1. spontaneous activity in the open field (mobility), 2. body temperature (hypothermia), and 3. tail withdrawal latency to a thermal stimulus (antinociception). Initial sensitivity to the immobilizing, hypothermic, and antinociceptive effects of THC varied substantially across the BXD family. Heritability was highest for mobility and hypothermia traits, indicating that segregating genetic variants modulate initial sensitivity to THC. We identified genomic loci and candidate genes, including Ndufs2, Scp2, Rps6kb1 or P70S6K, Pde4d, and Pten, that may control variation in THC initial sensitivity. We also detected strong correlations between initial responses to THC and legacy phenotypes related to intake or response to other drugs of abuse (cocaine, ethanol, and morphine). Our study demonstrates the feasibility of mapping genes and variants modulating THC responses in the BXDs to systematically define biological processes and liabilities associated with drug use and abuse.

The role of cannabinoid 1 receptor in the nucleus accumbens on tramadol induced conditioning and reinstatement

AIMS

Previous investigations demonstrated that tramadol, as a painkiller, similar to morphine induces tolerance and dependence. Furthermore, the cannabinoid receptor 1 (CB1R) located in the nucleus accumbens (NAc) plays a critical role in morphine-induced conditioning. Therefore, the main objective of this study was to evaluate the role of NAc CB1R in tramadol induced conditioning and reinstatement.

MAIN METHODS

In the present experiment, the effect of NAc CB1 receptors on tramadol induced conditioning was tested by microinjecting of arachidonylcyclopropylamide (ACPA, CB1R agonist) and AM 251 (CB1R inverse agonist) in the NAc during tramadol-induced conditioning in the adult male Wistar rats. In addition, the role of NAc CB1R in the reinstatement was also evaluated by injecting ACPA and AM 251 after a 10-days extinction period.

KEY FINDINGS

The obtained data revealed that the administration of tramadol (1,2, and 4 mg/kg, ip) dose-dependently produced conditioned place preference (CPP). Moreover, intra-NAc administration of ACPA (0.25, 0.5, and 1 μg/rat) dose-dependently induced conditioning, while the administration of AM-251 (30, 60, and 120 ng/rat) induced a significant aversion. In addition, the administration of a non-effective dose of AM251 during tramadol conditioning inhibited conditioning induced by tramadol. On the other hand, the administration of ACPA after extinction induced a significant reinstatement. Notably, the locomotor activity did not change among groups.

SIGNIFICANCE

Previous studies have shown that tramadol-induced CPP occurs through μ-opioid receptors. The data obtained in the current study indicated that CB1R located in the NAc is involved in mediating conditioning induced by tramadol. Besides, CB1R also plays a vital role in the reinstatement of tramadol-conditioned animals. It might be due to the effect of opioids on enhancing the level of CB1R.

Endogenous opiates and behavior: 2017

This paper is the fortieth consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2017 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides and receptors as well as effects of opioid/opiate agonists and antagonists. The review is subdivided into the following specific topics: molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors (1), the roles of these opioid peptides and receptors in pain and analgesia in animals (2) and humans (3), opioid-sensitive and opioid-insensitive effects of nonopioid analgesics (4), opioid peptide and receptor involvement in tolerance and dependence (5), stress and social status (6), learning and memory (7), eating and drinking (8), drug abuse and alcohol (9), sexual activity and hormones, pregnancy, development and endocrinology (10), mental illness and mood (11), seizures and neurologic disorders (12), electrical-related activity and neurophysiology (13), general activity and locomotion (14), gastrointestinal, renal and hepatic functions (15), cardiovascular responses (16), respiration and thermoregulation (17), and immunological responses (18).

Removal of microglial-specific MyD88 signaling alters dentate gyrus doublecortin and enhances opioid addiction-like behaviors

Drugs of abuse promote a potent immune response in central nervous system (CNS) via the activation of microglia and astrocytes. However, the molecular mechanisms underlying microglial activation during addiction are not well known. We developed and functionally characterized a novel transgenic mouse (Cx3cr1-CreBT^tg/0:MyD88^f/f [Cre^tg/0]) wherein the immune signaling adaptor gene, MyD88, was specifically deleted in microglia. To test the downstream effects of loss of microglia-specific MyD88 signaling in morphine addiction, Cre^tg/0 and Cre^0/0 mice were tested for reward learning, extinction, and reinstatement using a conditioned place preference (CPP) paradigm. There were no differences in drug acquisition, but Cre^tg/0 mice had prolonged extinction and enhanced reinstatement compared to Cre^0/0 controls. Furthermore, morphine-treated Cre^tg/0 mice showed increased doublecortin (DCX) signal relative to Cre^0/0 control mice in the hippocampus, indicative of increased number of immature neurons. Additionally, there was an increase in colocalization of microglial lysosomal marker CD68 with DCX⁺cells in morphine-treated Cre^tg/0 mice but not in Cre^0/0 or drug-naїve mice, suggesting a specific role for microglial MyD88 signaling in neuronal phagocytosis in the hippocampus. Our results show that MyD88 deletion in microglia may negatively impact maturing neurons within the adult hippocampus and thus reward memories, suggesting a novel protective role for microglia in opioid addiction.

Common neurocircuitry mediating drug and fear relapse in preclinical models

BACKGROUND

Comorbidity of anxiety disorders, stressor- and trauma-related disorders, and substance use disorders is extremely common. Moreover, therapies that reduce pathological fear and anxiety on the one hand, and drug-seeking on the other, often prove short-lived and are susceptible to relapse. Considerable advances have been made in the study of the neurobiology of both aversive and appetitive extinction, and this work reveals shared neural circuits that contribute to both the suppression and relapse of conditioned responses associated with trauma or drug use.

OBJECTIVES

The goal of this review is to identify common neural circuits and mechanisms underlying relapse across domains of addiction biology and aversive learning in preclinical animal models. We focus primarily on neural circuits engaged during the expression of relapse.

KEY FINDINGS

After extinction, brain circuits involving the medial prefrontal cortex and hippocampus come to regulate the expression of conditioned responses by the amygdala, bed nucleus of the stria terminalis, and nucleus accumbens. During relapse, hippocampal projections to the prefrontal cortex inhibit the retrieval of extinction memories resulting in a loss of inhibitory control over fear- and drug-associated conditional responding.

CONCLUSIONS

The overlapping brain systems for both fear and drug memories may explain the co-occurrence of fear and drug-seeking behaviors.