Opiate-associated contextual memory formation and retrieval are differentially modulated by dopamine D1 and D2 signaling in hippocampal-prefrontal connectivity

The epigenetically regulated PP1α expression by KDM1A may contribute to oxycodone conditioned place preference in mice

The lysine-specific demethylase 1 (KDM1A) is reported to be a regulator in learning and memory. However, the effect of KDM1A in oxycodone rewarding memory has yet to be studied. In our study, rewarding memory was assessed by using conditioned place preference (CPP) in male mice. Next generation sequencing and chromatin immunoprecipitation-PCR were used to explore the molecular mechanisms. Oxycodone significantly decreased PP1α mRNA and protein levels in hippocampal neurons. Oxycodone significantly increased KDM1A and H3K4me1 levels, while significantly decreased H3K4me2 levels in a time- and dose-dependent manner. Behavioral data demonstrated that intraperitoneal injection of ORY-1001 (KDM1A inhibitor) or intra-hippocampal injection of KDM1A siRNA/shRNA blocked the acquisition and expression of oxycodone CPP and facilitated the extinction of oxycodone CPP. The decrease of PP1α was markedly blocked by the injection of ORY-1001 or KDM1A siRNA/shRNA. Oxycodone-induced enhanced binding of CoRest with KDM1A and binding of CoRest with the PP1α promoter was blocked by ORY-1001. The level of H3K4me2 demethylation was also decreased by the treatment. The results suggest that oxycodone-induced upregulation of KDM1A via demethylation of H3K4me2 promotes the binding of CoRest with the PP1α promoter, and the subsequent decrease in PP1α expression in hippocampal neurons may contribute to oxycodone reward.

Chronic stress dysregulates the Hippo/YAP/14-3-3η pathway and induces mitochondrial damage in basolateral amygdala in a mouse model of depression

Rationale: Recent evidence highlights the pivotal role of mitochondrial dysfunction in mood disorders, but the mechanism involved remains unclear. We studied whether the Hippo/YAP/14-3-3η signaling pathway mediates mitochondrial abnormalities that result in the onset of major depressive disorder (MDD) in a mouse model. Methods: The ROC algorithm was used to identify a subpopulation of mice that were exposed to chronic unpredictable mild stress (CUMS) and exhibited the most prominent depressive phenotype (Dep). Electron microscopy, biochemical assays, quantitative PCR, and immunoblotting were used to evaluate synaptic and mitochondrial changes in the basolateral amygdala (BLA). RNA sequencing was used to explore changes in the Hippo pathway and downstream target genes. In vitro pharmacological inhibition and immunoprecipitation was used to confirm YAP/14-3-3η interaction and its role in neuronal mitochondrial dysfunction. We used virus-mediated gene overexpression and knockout in YAP transgenic mice to verify the regulatory effect of the Hippo/YAP/14-3-3η pathway on depressive-like behavior. Results: Transcriptomic data identified a large number of genes and signaling pathways that were specifically altered from the BLA of Dep mice. Dep mice showed notable synaptic impairment in BLA neurons, as well as mitochondrial damage characterized by abnormal mitochondrial morphology, compromised function, impaired biogenesis, and alterations in mitochondrial marker proteins. The Hippo signaling pathway was activated in Dep mice during CUMS, and the transcriptional regulatory activity of YAP was suppressed by phosphorylation of its Ser127 site. 14-3-3η was identified as an important co-regulatory factor of the Hippo/YAP pathway, as it can respond to chronic stress and regulate cytoplasmic retention of YAP. Importantly, the integrated Hippo/YAP/14-3-3η pathway mediated neuronal mitochondrial dysfunction and depressive behavior in Dep mice. Conclusion: The integrated Hippo/YAP/14-3-3η pathway in the BLA neuron is critical in mediating depressive-like behaviors in mice, suggesting a causal role for this pathway in susceptibility to chronic stress-induced depression. This pathway therefore may present a therapeutic target against mitochondrial dysfunction and synaptic impairment in MDD.

Repeated Use of Morphine Induces Anxiety by Affecting a Proinflammatory Cytokine Signaling Pathway in the Prefrontal Cortex in Rats

We examined the role of toll-like receptors (TLRs) and proinflammatory cytokine signaling pathways in the prefrontal cortex (PFC) in anxiety-like behaviors after repeated use of morphine. Morphine (10 mg/kg) was used twice daily for 8 days to induce morphine dependence in male Wistar rats. On day 8, opioid dependence was confirmed by measuring naloxone-precipitated withdrawal signs. On days 1 and 8, anxiety-like behaviors were evaluated using a light/dark box test. Expression of TLR1 and 4, proinflammatory cytokines, and some of the downstream signaling molecules was also evaluated in the bilateral PFC at mRNA and protein levels following morphine dependence. The results revealed that morphine caused anxiolytic-like effects on day 1 while induced anxiety following 8 days of repeated injection. On day 8, a significant decrease in TLR1 expression was detected in the PFC in morphine-dependent rats, but TLR4 remained unaffected. Repeated morphine injection significantly increased IL1-β, TNFα, and IL6 expression, but decreased IL1R and TNFR at mRNA and protein levels except for IL6R at the protein level in the PFC. The p38α mitogen-activated protein (MAP) kinase expression significantly increased but the JNK3 expression decreased in the PFC in morphine-dependent rats. Repeated injection of morphine also significantly increased the NF-κB expression in the PFC. Further, significant increases in Let-7c, mir-133b, and mir-365 were detected in the PFC in morphine-dependent rats. We conclude that TLR1 and proinflammatory cytokines signaling pathways in the PFC are associated with the anxiogenic-like effects of morphine following its chronic use in rats via a MAP kinase/NF-κB pathway.

Cdc42 signaling regulated by dopamine D2 receptor correlatively links specific brain regions of hippocampus to cocaine addiction

BACKGROUND

Hippocampus plays critical roles in drug addiction. Cocaine-induced modifications in dopamine receptor function and the downstream signaling are important regulation mechanisms in cocaine addiction. Rac regulates actin filament accumulation while Cdc42 stimulates the formation of filopodia and neurite outgrowth. Based on the region specific roles of small GTPases in brain, we focused on the hippocampal subregions to detect the regulation of Cdc42 signaling in long-term morphological and behavioral adaptations to cocaine.

METHODS

Genetically modified mouse models of Cdc42, dopamine receptor D1 (D1R) and D2 (D2R) and expressed Cdc42 point mutants that are defective in binding to and activation of its downstream effector molecules PAK and N-WASP were generated, respectively, in CA1 or dentate gyrus (DG) subregion.

RESULTS

Cocaine induced upregulation of Cdc42 signaling activity. Cdc42 knockout or mutants blocked cocaine-induced increase in spine plasticity in hippocampal CA1 pyramidal neurons, leading to a decreased conditional place preference (CPP)-associated memories and spatial learning and memory in water maze. Cdc42 knockout or mutants promoted cocaine-induced loss of neurogenesis in DG, leading to a decreased CPP-associated memories and spatial learning and memory in water maze. Furthermore, by using D1R knockout, D2R knockout, and D2R/Cdc42 double knockout mice, we found that D2R, but not D1R, regulated Cdc42 signaling in cocaine-induced neural plasticity and behavioral changes.

CONCLUSIONS

Cdc42 acts downstream of D2R in the hippocampus and plays an important role in cocaine-induced neural plasticity through N-WASP and PAK-LIMK-Cofilin, and Cdc42 signaling pathway correlatively links specific brain regions (CA1, dentate gyrus) to cocaine-induced CPP behavior.

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.

A comparison of reinforcing effectiveness and drug-seeking reinstatement of 2-fluorodeschloroketamine and ketamine in self-administered rats

2-Fluorodeschloroketamine (2F-DCK), a structural analog of ketamine, has been reported to cause impaired consciousness, agitation, and hallucination in abuse cases. It has similar reinforcing and discriminative effects as ketamine. However, the reinforcing efficacy and drug-seeking reinstatement of this analog have not been clarified to date. In this study, the effectiveness of 2F-DCK and ketamine was compared using a behavioral economics demand curve. The reinstatement of 2F-DCK- and ketamine-seeking behaviors induced by either conditioned cues or self-priming was also analyzed. Rats were intravenously self-administered 2F-DCK and ketamine at a dose of 0.5 mg/kg/infusion under a reinforcing schedule of fixed ratio 1 (FR1) with 4 h of daily training for at least 10 consecutive days. The elasticity coefficient parameter α and the essential value of the demand curve in the two groups were similar. Both groups of rats showed significant drug-seeking behavior induced either by conditional cues or by 2F-DCK and ketamine priming. Moreover, the α parameter was inversely related to the degree of reinstatement induced by cues or drug priming in both groups. In total, the expression levels of brain-derived neurotrophic factor (BDNF) and phosphorylated cAMP response element-binding protein (p-CREB) in the nucleus accumbens in both extinguished and reinstated rats were significantly lower than those in the control. The expression of total Akt, glycogen synthase kinase (GSK)-3β, mammalian target of rapamycin (mTOR), and extracellular signal-related kinase (ERK) also decreased, but p-Akt, p-GSK-3β, p-mTOR, and p-ERK levels increased in both extinguished and reinstated rats. This is the first study to demonstrate that 2F-DCK has similar reinforcing efficacy, effectiveness, and post-withdrawal cravings as ketamine after repeated use. These data suggest that the downregulation of CREB/BDNF and the upregulation of the Akt/mTOR/GSK-3β signaling pathway in the nucleus accumbens may be involved in ketamine or 2F-DCK relapse.

Basolateral Amygdala SIRT1/PGC-1α Mitochondrial Biogenesis Pathway Mediates Morphine Withdrawal-Associated Anxiety in Mice

BACKGROUND

Anxiety is a negative emotion that contributes to craving and relapse during drug withdrawal. Sirtuins 1 (SIRT1) has been reported to be critical in both negative emotions and drug addiction. However, it remains incompletely elucidated whether SIRT1 is involved in morphine withdrawal-associated anxiety.

METHODS

We established a mouse model of anxiety-like behaviors induced by morphine withdrawal and then detected neuronal activity with immunofluorescence and mitochondrial morphology with electron microscopy, mitochondrial DNA contents with quantitative real-time PCR, and mitochondrial function with the ATP content detection kit and the Mitochondrial Complex IV Activity Kit in the basolateral amygdala (BLA). The mitochondrial molecules were detected by western blot. Then we used virus-mediated downregulation and overexpression of SIRT1 in BLA to investigate the effect of SIRT1 on anxiety and mitochondrial function. Finally, we examined the effects of pharmacological inhibition of SIRT1 on anxiety and mitochondrial function.

RESULTS

We found that BLA neuronal activity, mitochondrial function, and mtDNA content were significantly higher in morphine withdrawal mice. Furthermore, the expression levels of mitochondrial molecules increased in BLA cells. Virus-mediated downregulation of SIRT1 in BLA prevented anxiety-like behaviors in morphine withdrawal mice, whereas overexpression of SIRT1 in BLA facilitated anxiety-like behaviors in untreated mice through the SIRT1/ peroxisome proliferator activated receptor gamma coactivator 1-alpha pathway. Intra-BLA infusion of selective SIRT1 antagonist EX527 effectively ameliorated anxiety-like behaviors and mitochondrial dysfunction in mice with morphine withdrawal.

CONCLUSION

Our results implicate a causal role for SIRT1 in the regulation of anxiety through actions on mitochondrial biogenesis. Inhibitors targeting SIRT1 may have therapeutic potential for the treatment of opioid withdrawal-associated anxiety.

Anxiety and cognitive-related effects of Δ 9-tetrahydrocannabinol (THC) are differentially mediated through distinct GSK-3 vs. Akt-mTOR pathways in the nucleus accumbens of male rats

RATIONALE

Δ⁹-tetrahydrocannabinol (THC) is the primary psychoactive compound in cannabis and is responsible for cannabis-related neuropsychiatric side effects, including abnormal affective processing, cognitive and sensory filtering deficits and memory impairments. A critical neural region linked to the psychotropic effects of THC is the nucleus accumbens shell (NASh), an integrative mesocorticolimbic structure that sends and receives inputs from multiple brain areas known to be dysregulated in various disorders, including schizophrenia and anxiety-related disorders. Considerable evidence demonstrates functional differences between posterior vs. anterior NASh sub-regions in the processing of affective and cognitive behaviours influenced by THC. Nevertheless, the neuroanatomical regions and local molecular pathways responsible for these psychotropic effects are not currently understood.

OBJECTIVES

The objectives of this study were to characterize the effects of intra-accumbens THC in the anterior vs. posterior regions of the NASh during emotional memory formation, sensorimotor gating and anxiety-related behaviours.

METHODS

We performed an integrative series of translational behavioural pharmacological studies examining anxiety, sensorimotor gating and fear-related associative memory formation combined with regionally specific molecular signalling analyses in male Sprague Dawley rats.

RESULTS

We report that THC in the posterior NASh causes distortions in emotional salience attribution, impaired sensory filtering and memory retention and heightened anxiety, through a glycogen-synthase-kinase-3 (GSK-3)-β-catenin dependent signalling pathway. In contrast, THC in the anterior NASh produces anxiolytic effects via modulation of protein kinase B (Akt) phosphorylation states.

CONCLUSIONS

These findings reveal critical new insights into the neuroanatomical and molecular mechanisms associated with the differential neuropsychiatric side effects of THC in dissociable nucleus accumbens sub-regions.

Effects of heroin self-administration and forced withdrawal on the expression of genes related to the mTOR network in the basolateral complex of the amygdala of male Lewis rats

RATIONALE

The development of substance use disorders involves long-lasting adaptations in specific brain areas that result in an elevated risk of relapse. Some of these adaptations are regulated by the mTOR network, a signalling system that integrates extracellular and intracellular stimuli and modulates several processes related to plasticity. While the role of the mTOR network in cocaine- and alcohol-related disorders is well established, little is known about its participation in opiate use disorders.

OBJECTIVES

To use a heroin self-administration and a withdrawal protocol that induce incubation of heroin-seeking in male rats and study the associated effects on the expression of several genes related to the mTOR system and, in the specific case of Rictor, its respective translated protein and phosphorylation.

RESULTS

We found that heroin self-administration elicited an increase in the expression of the genes Igf1r, Igf2r, Akt2 and Gsk3a in the basolateral complex of the amygdala, which was not as evident at 30 days of withdrawal. We also found an increase in the expression of Rictor (a protein of the mTOR complex 2) after heroin self-administration compared to the saline group, which was occluded at the 30-day withdrawal period. The activation levels of Rictor, measured by the phosphorylation rate, were also reduced after heroin self-administration, an effect that seemed more apparent in the protracted withdrawal group.

CONCLUSIONS

These results suggest that heroin self-administration under extended access conditions modifies the expression profile of activators and components of the mTOR complexes and show a putative irresponsive mTOR complex 2 after withdrawal from heroin use.

α-Conotoxin TxIB Inhibits Development of Morphine-Induced Conditioned Place Preference in Mice via Blocking α6β2* Nicotinic Acetylcholine Receptors

Morphine, the main component of opium, is a commonly used analgesic in clinical practice, but its abuse potential limits its clinical application. Nicotinic acetylcholine receptors (nAChRs) in the mesolimbic circuitry play an important role in the rewarding effects of abused drugs. Previous studies have showed that α6β2* (* designated other subunits) nAChRs are mainly distributed in dopaminergic neurons in the midbrain area, which regulates the release of dopamine. So α6β2* nAChRs are regarded as a new target to treat drug abuse. α-Conotoxin TxIB was discovered in our lab, which is the most selective ligand to inhibit α6β2* nAChRs only. Antagonists of α6β2* nAChRs decreased nicotine, cocaine, and ethanol rewarding effects previously. However, their role in morphine addiction has not been reported so far. Thus, it is worth evaluating the effect of α-conotoxin TxIB on the morphine-induced conditioned place preference (CPP) and its behavioral changes in mice. Our results showed that TxIB inhibited expression and acquisition of morphine-induced CPP and did not produce a rewarding effect by itself. Moreover, repeated injections of TxIB have no effect on learning, memory, locomotor activity, and anxiety-like behavior. Therefore, blocking α6/α3β2β3 nAChRs inhibits the development of morphine-induced CPP. α-Conotoxin TxIB may be a potentially useful compound to mitigate the acquisition and/or retention of drug-context associations.

Spatiotemporal expression of Rap1 and Ras mediates the acquisition and reinstatement of methamphetamine-induced conditioned place preference in mice via extracellular signal-regulated kinase activation

Drug addiction is a chronic recurrent brain disease characterized by compulsive drug use and a high tendency to relapse. We previously reported that the Ras-extracellular signal-regulated kinase (ERK)-ΔFosB pathway in the caudate putamen (CPu) was involved in methamphetamine-induced behavioral sensitization. Rap1, as an antagonist of Ras originally, was found to participate in neuronal synaptic plasticity recently, but the role of Rap1 in methamphetamine addiction is unclear. First, in this study, we constructed the acquisition, extinction and reinstatement of methamphetamine-induced conditioned place preference (CPP) in mice, respectively. Then, protein levels of Rap1, Ras and pERK/ERK in the prefrontal cortex (PFc), CPu and hippocampus of CPP mice on three phases were detected. We found that protein levels of Rap1, Ras and pERK/ERK in the CPu were significantly increased after repeated methamphetamine administration, as well as Rap1 and pERK/ERK in the hippocampus. However, protein levels of Rap1 and pERK/ERK in the CPu were decreased on the reinstatement of CPP mice. Therefore, Rap1 and Ras in the CPu and Rap1 in the hippocampus may participate in the regulation of the acquisition of methamphetamine-induced CPP in mice by activating ERK. Moreover, Rap1-ERK cascade in the CPu contributes to both the acquisition and reinstatement of methamphetamine-induced CPP in mice.

Endogenous opiates and behavior: 2019

This paper is the forty-second consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2019 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).

Glutamatergic Systems and Memory Mechanisms Underlying Opioid Addiction

Glutamate is the main excitatory neurotransmitter in the brain and is of critical importance for the synaptic and circuit mechanisms that underlie opioid addiction. Opioid memories formed over the course of repeated drug use and withdrawal can become powerful stimuli that trigger craving and relapse, and glutamatergic neurotransmission is essential for the formation and maintenance of these memories. In this review, we discuss the mechanisms by which glutamate, dopamine, and opioid signaling interact to mediate the primary rewarding effects of opioids, and cover the glutamatergic systems and circuits that mediate the expression, extinction, and reinstatement of opioid seeking over the course of opioid addiction.

Association study of Catechol-o-methyltransferase and Alpha-1-adrenergic receptor gene polymorphisms with multiple phenotypes of heroin use disorder

Heroin use disorder is a chronic relapsing brain disease containing multiple phenotypes. These phenotypes vary among heroin users and might be influenced by genetic factors. Single-nucleotide polymorphisms (SNPs) of catechol-O-methyltransferase (COMT) and alpha-1-adrenergic receptor (ADRA1A) genes are associated with heroin use disorder. However, it has not been clarified which phenotypes of heroin use disorder are related to these genes. To address this question, we recruited 801 unrelated heroin users and divided them into different subgroups according to four important phenotypes of heroin use disorder. Then 7 SNPs in the functional region of these genes were systematically screened and genotyped using a SNaPshot assay. We found that the A allele of ADRA1A rs1048101 was associated with a shorter duration of transition from first use to addiction. Subjects with the C allele of ADRA1A rs3808585 were more susceptible to memory impairment after heroin use disorder. Subjects with the G allele of COMT rs769224 were more likely to take a higher dose of heroin every day. Our study confirmed the association between polymorphisms of COMT and ADRA1A with those specific phenotypes of heroin use disorder, which will be instructive for the precise treatment of the disease.

Valence processing in the PFC: Reconciling circuit-level and systems-level views

An essential component in animal behavior is the ability to process emotion and dissociate among positive and negative valence in response to a rewarding or aversive stimulus. The medial prefrontal cortex (mPFC)-responsible for higher order executive functions that include cognition, learning, and working memory; and is also involved in sociability-plays a major role in emotional processing and control. Although the amygdala is widely regarded as the "emotional hub," the mPFC encodes for context-specific salience and elicits top-down control over limbic circuitry. The mPFC can then conduct behavioral responses, via cortico-striatal and cortico-brainstem pathways, that correspond to emotional stimuli. Evidence shows that abnormalities within the mPFC lead to sociability deficits, working memory impairments, and drug-seeking behavior that include addiction and compulsive disorders; as well as conditions such as anhedonia. Recent studies investigate the effects of aberrant salience processing on cortical circuitry and neuronal populations associated with these behaviors. In this chapter, we discuss mPFC valence processing, neuroanatomical connections, and physiological substrates involved in mPFC-associated behavior. We review neurocomputational and theoretical models such as "mixed selectivity," that describe cognitive control, attentiveness, and motivational drives. Using this knowledge, we describe the effects of valence imbalances and its influence on mPFC neural pathways that contribute to deficits in social cognition, while understanding the effects in addiction/compulsive behaviors and anhedonia.

Dynamic Changes of Cytoskeleton-Related Proteins Within Reward-Related Brain Regions in Morphine-Associated Memory

Drug-induced memory engages complex and dynamic processes and is coordinated at multiple reward-related brain regions. The spatiotemporal molecular mechanisms underlying different addiction phases remain unknown. We investigated the role of β-actin, as well as its potential modulatory protein activity-regulated cytoskeletal-associated protein (Arc/Arg3.1) and extracellular signal-regulated kinase (ERK), in reward-related associative learning and memory using morphine-induced conditioned place preference (CPP) in mice. CPP was established by alternate morphine (10 mg/kg) injections and extinguished after a 10-day extinction training, while the withdrawal group failed to extinguish without training. In the nucleus accumbens (NAc), morphine enhanced the level of β-actin and Arc only during extinction, while p-ERK1/2 was increased during both CPP acquisition and extinction phases. In the dorsal hippocampus, morphine induced an upregulation of p-ERK only during extinction, while p-β-actin was elevated during both CPP establishment and extinction. In the dorsal hippocampus, Arc was elevated during CPP formation and suppressed during extinction. Compared with the NAc and dorsal hippocampus, dynamic changes in the medial prefrontal cortex (mPFC) and caudate putamen (CPu) were not very significant. These results suggested region-specific changes of p-β-actin, Arc/Arg3.1, and p-ERK1/2 protein during establishment and extinction phases of morphine-induced CPP. These findings unveiled a spatiotemporal molecular regulation in opiate-induced plasticity.

Dual-specificity phosphatase 15 (DUSP15) in the nucleus accumbens is a novel negative regulator of morphine-associated contextual memory

Drug relapse among addicts often occurs due to the learned association between drug-paired cues and the rewarding effects of these drugs, such as morphine. Contextual memory associated with morphine has a central role in maintenance and relapse. We showed that morphine-conditioned place preference (CPP) activates extracellular-regulated protein kinase (ERK) in the nucleus accumbens (NAc). The main enzymes that mediate ERK dephosphorylation are members of the dual-specificity phosphatase (DUSP) superfamily. It is unclear which members regulate the morphine CPP-induced activation of ERK. After screening, DUSP15 was found to be decreased during both morphine CPP expression and the reinstatement period. Intra-NAc infusions of AAV-DUSP15 (overexpression) not only prevented the expression of morphine-induced CPP but also facilitated extinction, inhibited reinstatement, and abolished ERK activation. However, after repeated morphine exposure and withdrawal in mice, there was no change in the expression of p-ERK and DUSP15, and the overexpression of DUSP15 in the NAc did not improve the impaired spatial memory or anxiety-like behaviour induced by morphine. Together, these findings indicate that DUSP15 not only prevents the expression of drug-paired contextual memory but also promotes the extinction of existing addiction memories, thus providing a novel therapeutic target for the treatment of drug addiction.

The Projection From Ventral CA1, Not Prefrontal Cortex, to Nucleus Accumbens Core Mediates Recent Memory Retrieval of Cocaine-Conditioned Place Preference

Drug-paired cues inducing memory retrieval by expressing drug-seeking behaviors present a major challenge to drug abstinence. How neural circuits coordinate for drug memory retrieval remains unclear. Here, we report that exposure of the training chamber where cocaine-conditioned place preference (CPP) was performed increased neuronal activity in the core of nucleus accumbens (AcbC), ventral CA1 (vCA1), and medial prefrontal cortex (mPFC), as shown by elevated pERK and c-Fos levels. Chemogenetic inhibition of neuronal activity in the vCA1 and AcbC, but not mPFC, reduced the time spent in the cocaine-paired compartment, suggesting that the vCA1 and AcbC are required for the retrieval of cocaine-CPP memory and are key nodes recruited for cocaine memory storage. Furthermore, chemogenetic inhibition of the AcbC-projecting vCA1 neurons, but not the AcbC-projecting mPFC neurons, decreased the expression of cocaine-CPP. Optogenetic inhibition of the vCA1–AcbC projection, but not the mPFC–AcbC projection, also reduced the preference for the cocaine-paired compartment. Taken together, the cue-induced natural recall of cocaine memory depends on vCA1–AcbC circuits. The connectivity from the vCA1 to the AcbC may store the information of the cue–cocaine reward association critically required for memory retrieval. These data thus provide insights into the neural circuit basis of retrieval of drug-related memory.

The role of the mTOR pathway in models of drug-induced reward and the behavioural constituents of addiction

BACKGROUND

Exposure to drugs of abuse induces neuroadaptations in critical nodes of the so-called reward systems that are thought to mediate the transition from controlled drug use to the compulsive drug-seeking that characterizes addictive disorders. These neural adaptations are likely to require protein synthesis, which is regulated, among others, by the mechanistic target of the rapamycin kinase (mTOR) signalling cascade.

METHODS

We have performed a narrative review of the literature available in PubMed about the involvement of the mTOR pathway in drug-reward and addiction-related phenomena.

AIMS

The aim of this study was to review the underlying architecture of this complex intracellular network and to discuss the alterations of its components that are evident after exposure to drugs of abuse. The aim was also to delineate the effects that manipulations of the mTOR network have on models of drug reward and on paradigms that recapitulate some of the psychological components of addiction.

RESULTS

There is evidence for the involvement of the mTOR pathway in the acute and rewarding effects of drugs of abuse, especially psychostimulants. However, the data regarding opiates are scarce. There is a need to use sophisticated animal models of addiction to ascertain the real role of the mTOR pathway in this pathology and not just in drug-mediated reward. The involvement of this pathway in behavioural addictions and impulsivity should also be studied in detail in the future.

CONCLUSIONS

Although there is a plethora of data about the modulation of mTOR by drugs of abuse, the involvement of this signalling pathway in addictive disorders requires further research.

Effects of brief inhibition of the ventral tegmental area dopamine neurons on the cocaine seeking during abstinence

Preclinical studies strongly suggest that cocaine seeking depends on the neuronal activity of the ventral tegmental area (VTA) and phasic dopaminergic (DA) signaling. Notably, VTA pharmacological inactivation or dopamine receptor blockade in the forebrain may induce behavioral inhibition in general and acute aversive states in particular, thus reducing cocaine seeking indirectly. Such artifacts hinder successful translation of these findings in clinical studies and practice. Here, we aimed to evaluate if dynamic VTA manipulations effectively reduce cocaine seeking. We used male tyrosine hydroxylase (TH) IRES-Cre⁺ rats along with optogenetic tools to inhibit directly and briefly VTA DA neurons during conditioned stimulus (CS)-induced cocaine seeking under extinction conditions. The behavioral effects of optogenetic inhibition were also assessed in the real-time dynamic place aversion, conditioned place aversion, and CS-induced food-seeking tests. We found that brief and nondysphoric/nonsedative pulses of VTA photo-inhibition (1 s every 9 s, ie, for 10% of time) attenuated CS-induced cocaine seeking under extinction conditions in rats expressing archaerhodopsin selectively on the TH⁺ neurons. Furthermore, direct inhibition of the VTA DA activity reduced CS-induced cocaine seeking 24 hours after photo-modulation. Importantly, such effect appears to be selective for cocaine seeking as similar inhibition of the VTA DA activity had no effect on CS-induced food seeking. Thus, briefly inhibiting VTA DA activity during CS-induced cocaine seeking drastically and selectively reduces seeking without behavioral artifacts such as sedation or dysphoria. Our results point to the therapeutic possibilities of coupling nonpharmacologic treatments with extinction training in reducing cocaine addiction.

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.

Pre-exposure of adolescent mice to morphine results in stronger sensitization and reinstatement of conditioned place preference than pre-exposure to hydrocodone

BACKGROUND

Opioids are commonly prescribed to treat moderate-to-severe pain. However, their use can trigger the development of opioid use disorder. A major problem in treating opioid use disorder remains the high rate of relapse.

AIM

The purpose of this study was to determine whether there are differences among opioids in their ability to trigger relapse after pre-exposure during adolescence.

METHODS

On postnatal day 33, mice were examined for the acute locomotor response to saline, morphine, or hydrocodone (5 mg/kg). They were administered with the corresponding opioid or saline during postnatal days 34-38 (20 mg/kg) and 40-44 (40 mg/kg). On postnatal day 45, they were recorded for the development of locomotor sensitization (5 mg/kg). Starting on postnatal day 55, mice were examined for the acquisition (1, 5, 10, 20, and 40 mg/kg), extinction, and drug-induced reinstatement (1, 2.5, and 5 mg/kg) of conditioned place preference.

RESULTS

There were no significant differences in the acute locomotor response to morphine and hydrocodone. Morphine induced significantly stronger locomotor sensitization as compared to hydrocodone. Pre-exposure to morphine, but not hydrocodone, sensitized the acquisition of conditioned place preference. There were no significant differences in extinction rates. Mice pre-exposed to morphine reinstate conditioned place preference after priming with a 1 mg/kg dose. In contrast, higher priming doses were required for reinstatement in all other experimental groups.

CONCLUSIONS

Adolescent mice administered with morphine develop greater sensitization to its effects and subsequently reinstate conditioned place preference more readily than mice administered with hydrocodone. This suggests higher risk for relapse after pre-exposure to morphine during adolescence as compared to hydrocodone.

Improvement of Petroselinum crispum on Morphine Toxicity in Prefrontal Cortex in Rats

Background:

Petroselinum crispum (P. Crispum) is an associate of the umbelliferae family with several therapeutic attributes. Morphine is known as a major risk factor in the development of functional disorder of several organs.

Objective:

This study was designed to evaluate the effects of P. Crispum extract against morphine-induced damage to the brain prefrontal cortex (PC) of rats.

Materials and Methods:

In this experimental study, 64 Wistar male rats were randomly assigned to 8 groups: Sham group, Morphine group, P. Crispum groups (50, 100, and 150 mg/kg), and Morphine + P. Crispum groups. Daily intraperitoneal treatment applied for 20 days. Ferric reducing/antioxidant power method was hired to determine the total antioxidant capacity (TAC). The number of dendritic spines was investigated by Golgi staining technique. Cresyl violet staining method was used to determine the number of neurons in the PC region. Furthermore, Griess technique was used to determine the level of serum nitrite oxide.

Results:

Morphine administration increased nitrite oxide levels and decreased TAC, density of neuronal dendritic spines and neurons compared to the sham group significantly (P < 0.05). In whole doses of the P. Crispum and Morphine + P. Crispum groups, the number of neurons and neuronal dendritic spines increased significantly while nitrite oxide level and TAC decreased compared to the morphine group (P < 0.05).

Conclusion:

It seems that the administration of P. Crispum extract protects the animals against oxidative stress and nitrite oxide, also improves some PC parameters including the number of neurons, and dendritic spines because of the morphine application.

Decreased Neuronal Excitability in Medial Prefrontal Cortex during Morphine Withdrawal is associated with enhanced SK channel activity and upregulation of small GTPase Rac1

Rationale: Neuroadaptations in the medial prefrontal cortex (mPFC) and Nucleus Accumbens (NAc) play a role in the disruption of control-reward circuits in opioid addiction. Small Conductance Calcium-Activated Potassium (SK) channels in the mPFC have been implicated in neuronal excitability changes during morphine withdrawal. However, the mechanism that modulates SK channels during withdrawal is still unknown.

Methods: Rats were exposed for one week to daily morphine injections (10 mg·kg^-1 s.c.) followed by conditional place preference (CPP) assessment. One week after withdrawal, electrophysiological, morphological and molecular biological methods were applied to investigate the effects of morphine on SK channels in mPFC, including infralimbic (IL), prelimbic (PrL) cortices and NAc (core and shell). We verified the hypothesis that Rac1, a member of Rho family of small GTPases, implicated in SK channel regulation, modulate SK channel neuroadaptations during opiate withdrawal.

Results: One week after morphine withdrawal, the neuronal excitability of layer 5 pyramidal neurons in IL was decreased, but not in PrL. Whereas, the excitability was increased in NAc-shell, but not in NAc-core. In mPFC, the expression of the SK3 subunit was enhanced after one-week of withdrawal compared to controls. In the IL, Rac1 signaling was increased during withdrawal, and the Rac1 inhibitor NSC23766 disrupted SK current, which increased neuronal firing. Suppression of Rac1 inhibited morphine-induced CPP and expression of SK channels in IL.

Conclusions: These findings highlight the potential value of SK channels and the upstream molecule Rac1, which may throw light on the therapeutic mechanism of neuromodulation treatment for opioid dependence.

Glycogen synthase kinase-3 signaling in cellular and behavioral responses to psychostimulant drugs

Glycogen synthase kinase-3 (GSK-3) is a serine/threonine kinase implicated in numerous physiological processes and cellular functions through its ability to regulate the function of many proteins, including transcription factors and structural proteins. GSK-3β has been demonstrated to function as a regulator of multiple behavioral processes induced by drugs of abuse, particularly psychostimulant drugs. In this review, we provide an overview of the regulation of GSK-3β activity produced by psychostimulants, and the role of GSK-3β signaling in psychostimulant-induced behaviors including drug reward, associative learning and memory which play a role in the maintenance of drug-seeking. Evidence supports the conclusion that GSK-3β is an important component of the actions of psychostimulant drugs and that GSK-3β is a valid target for developing novel therapeutics. Additional studies are required to examine the role of GSK-3β in distinct cell types within the mesolimbic and memory circuits to further elucidate the mechanisms related to the acquisition, consolidation, and recall of drug-related memories, and potentially countering neuroadaptations that reinforce drug-seeking behaviors that maintain drug dependence.

Effect of morphine exposure on novel object memory of the offspring: The role of histone H3 and ΔFosB

It has been demonstrated that alteration in histone acetylation in the regions of the brain involved in the reward which may have an important role in morphine addiction. It is well established that epigenetic changes prior to birth influence the function and development of the brain. The current study was designed to evaluate changes in novel object memory, histone acetylation and ΔFosB in the brain of the offspring of morphine-withdrawn parents. Male and female Wistar rats received morphine orally for 21 following days. After ten days of abstinent, they were prepared for mating. The male offspring of the first parturition were euthanized on postnatal days 5, 21, 30 and 60. The novel object recognition (NOR) test was performed on adult male offspring. The amount of acetylated histone H3 and ΔFosB were evaluated in the prefrontal cortex (PFC) and hippocampus using western blotting. Obtained results indicated that the discrimination index in the NOR test was decreased in the offspring of morphine-withdrawn parents as compared with morphine-naïve offspring. In addition, the level of acetylated histone H3 was decreased in the PFC and hippocampus in the offspring of morphine-withdrawn parents during lifetime (postnatal days 5, 21, 30 and 60). In the case of ΔFosB, it also decreased in these regions in the morphine-withdrawn offspring. These results demonstrated that parental morphine exposure affects NOR memory, and decreased the level of histone H3 acetylation and ΔFosB in the PFC and hippocampus. Taken together, the effect of morphine might be transmitted to the next generation even after stop consuming morphine.

Dopamine D1 receptor-mediated activation of the ERK signaling pathway is involved in the osteogenic differentiation of bone mesenchymal stem cells

BACKGROUND

Osteogenic differentiation of bone mesenchymal stem cells (BMSCs) is regulated by numerous signaling pathways. Dopamine (DA), a neurotransmitter, has previously been demonstrated to induce new bone formation by stimulating the receptors on BMSCs, but the essential mediators of DA-induced osteogenic signaling remain unclear.

METHODS

In this work, we evaluated the influence of both dopamine D1 and D2 receptor activation on BMSC osteogenic differentiation. Gene and protein expression of osteogenic-related markers were tested. The direct binding of transcriptional factor, Runx2, to those markers was also investigated. Additionally, cellular differentiation-associated signaling pathways were evaluated.

RESULTS

We showed that the expression level of the D1 receptor on BMSCs increased during osteogenic differentiation. A D1 receptor agonist, similar to DA, induced the osteogenic differentiation of BMSCs, and this phenomenon was effectively inhibited by a D1 receptor antagonist or by D1 receptor knockdown. Furthermore, the suppression of protein kinase A (PKA), an important kinase downstream of the D1 receptor, successfully inhibited DA-induced BMSC osteogenic differentiation and decreased the phosphorylation of ERK1/2. Compared with P38, MAPK, and JNK, DA mainly induced the phosphorylation of ERK1/2 and led to the upregulation of Runx2 transcriptional activity, thus facilitating BMSC osteogenic differentiation. On the other hand, an ERK1/2 inhibitor could reverse these effects.

CONCLUSIONS

Taken together, these results suggest that ERK signaling may play an essential role in coordinating the DA-induced osteogenic differentiation of BMSCs by D1 receptor activation.

Glycogen Synthase Kinase 3β in the Ventral Hippocampus is Important for Cocaine Reward and Object Location Memory

The ventral hippocampus is a component of the neural circuitry involved with context-associated memory for reward and generation of appropriate behavioral responses to context. Glycogen synthase kinase 3 beta (GSK3β) has been linked to the maintenance of synaptic plasticity, contextual memory retrieval, and is involved in the reconsolidation of cocaine-associated contextual memory. In this study, the effects of targeted downregulation of GSK3β in the ventral hippocampus were examined on a series of behavioral tests for assessing drug reward-context association and non-reward related memory. The Cre/loxP site-specific recombination system was used to knockdown GSK3β through bilateral stereotaxic delivery of an adeno-associated virus expressing Cre-recombinase (AAV-Cre) into the ventral hippocampus of adult mice homozygous for a floxed GSK3β allele. GSK3β floxed mice injected with AAV-Cre had a loss of 56-75% of GSK3β in the ventral hippocampus and displayed diminished development of cocaine conditioned place preference, but not morphine place preference as compared with wild-type mice injected with AAV-Cre or GSK3β floxed mice injected with a control virus, AAV-GFP. Impaired object location memory was observed in mice with GSK3β downregulation in the ventral hippocampus, but novel object recognition remained intact. These results indicate that GSK3β signaling in the ventral hippocampus is differentially involved in the formation of place-drug reward association dependent upon drug class. Additionally, ventral hippocampal GSK3β signaling is important in detection of discrete spatial cues, but not recognition memory for objects.

Reversal of oxycodone conditioned place preference by oxytocin: Promoting global DNA methylation in the hippocampus

Repeated exposure to the opioid agonist, oxycodone, can lead to addiction. Accumulating evidence has shown that oxytocin (OT), a neurohypophyseal neuropeptide, could reduce the abuse potential of drugs. Recent studies suggest that epigenetic regulation through DNA methylation are involved in neuroadaptations. The current study was conducted to investigate the effects of OT on oxycodone conditioned place preference (CPP) and the epigenetic mechanism of OT in the hippocampus. For induction of CPP, oxycodone (3.0 mg/kg, i. p.) was administrated to male Sprague-Dawley rats once every other day during an eight-day conditioning phase. Global 5-methylcytosine (5-mC) level was determined based on CPP procedure, including acquisition, expression, extinction and reinstatement. We also measured mRNA levels of DNA methyltransferases (Dnmts), ten-eleven translocations (Tets) and synaptic genes (Psd95, Shank2, Gap43, etc.), and determined synaptic density after restraint stress-induced reinstatement of oxycodone CPP. The results showed that OT (2.5 μg, i. c.v.) pretreatment specifically inhibited the CPP acquisition and expression, facilitated the CPP extinction, and abolished restraint stress-induced reinstatement of oxycodone CPP. OT markedly inhibited global 5-mC changes induced by oxycodone CPP in the four phases. Following restraint stress-induced reinstatement of oxycodone CPP, OT significantly increased mRNA levels of Dnmt1, decreased Tet1 mRNA, synaptic proteins and synaptic density in the hippocampus. Our study indicated that reversal of global DNA hypomethylation through OT could significantly attenuate the rewarding effects induced by oxycodone. Our results suggested that OT could be specific manipulation on oxycodone addiction.

Peripubertal stress of male, but not female rats increases morphine-induced conditioned place preference and locomotion in adulthood

Animal studies demonstrate that peripubertal social stress markedly increases the risk for subsequent substance use in adulthood. However, whether non-social stress has a similar long-term impact is not clear, and whether male and female animals show different sensitivity to peripubertal non-social stress has not been examined. In the present study, we addressed these issues by introducing two non-social stressors (elevated platform and predator odor 2,5-Dihydro-2,4,5-trimethylthiazoline) to male and female Wistar rats during adolescence (postnatal days 28-30, 34, 36, 40, and 42), then tested reward-related behaviors during adulthood, including morphine-induced conditioned place preference (CPP, 1 mg/kg morphine or 5 mg/kg morphine) and hyperlocomotor activity (5 mg/kg morphine). We found that adult male rats, but not females who were exposed to peripubertal non-social stressors showed enhanced morphine-induced CPP. Moreover, morphine-induced increase in locomotor activity was also significantly increased in adult male rats, but not in females. These results indicate that peripubertal exposure to repeated non-social stress may enhance sensitivity to the rewarding effects of opioids in adulthood in a sex-dependent manner, with males being even more sensitive than females in this regard.

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.