Postretrieval Microinjection of Baclofen Into the Agranular Insular Cortex Inhibits Morphine-Induced CPP by Disrupting Reconsolidation

Baclofen prevents morphine rewarding effects and associated biochemical alterations in male and female mice

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

Insular cortex subregions have distinct roles in cued heroin seeking after extinction learning and prolonged withdrawal in rats

Evidence indicates that the anterior (aIC), but not posterior (pIC), insular cortex promotes cued reinstatement of cocaine seeking after extinction in rats. It is unknown whether these subregions also regulate heroin seeking and whether such involvement depends on prior extinction learning. To address these questions, we used baclofen and muscimol (BM) to inactivate the aIC or pIC bilaterally during a seeking test after extinction or prolonged withdrawal from heroin. Male Sprague-Dawley rats in the extinction groups underwent 10+ days of heroin self-administration, followed by 6+ days of extinction sessions, and subsequent cued or heroin-primed reinstatement. Results indicate that aIC inactivation increased cued reinstatement of heroin seeking after extinction, whereas pIC inactivation prevented cued reinstatement. To determine whether these effects were extinction-dependent, we conducted a subsequent study using both sexes with prolonged withdrawal. Male and female rats in the withdrawal groups underwent 10+ days of heroin self-administration, followed by cued seeking tests after 1 and 14 days of homecage withdrawal to measure incubation of heroin craving. In this case, the findings indicate that aIC inactivation had no effect on incubation of heroin craving after withdrawal in either sex, whereas pIC inactivation decreased heroin craving only in males. These findings suggest that the aIC and pIC have opposing roles in suppressing vs promoting cued heroin seeking after extinction and that these roles are distinct from those in cocaine seeking. Moreover, the incubation of craving results suggest that new contingency learning is necessary to recruit the aIC in cued heroin seeking.

GABA system in the prefrontal cortex involved in psychostimulant addiction

Drug addiction is a chronic and relapse brain disorder. Psychostimulants such as cocaine and amphetamine are highly addictive drugs. Abuse drugs target various brain areas in the nervous system. Recent studies have shown that the prefrontal cortex (PFC) plays a key role in regulating addictive behaviors. The PFC is made up of excitatory glutamatergic cells and gamma-aminobutyric acid (GABAergic) interneurons. Recently, studies showed that GABA level was related with psychostimulant addiction. In this review, we will introduce the role and mechanism of GABA and γ-aminobutyric acid receptors (GABARs) of the PFC in regulating drug addiction, especially in psychostimulant addiction.

Analysis of the functional role and mRNA expression of GABA B R in the nucleus accumbens of cocaine-addicted rats

BACKGROUND

Drug addiction is a social and medical problem that must be urgently addressed. The nucleus accumbens (NAc) is closely related to addiction-related learning memory, and γ-aminobutyric acid type B receptor (GABA B R) is a potential target for the treatment of drug addiction. However, the role of GABA B R activity levels in the NAc in cocaine addiction is unclear.

METHODS

In this study, we established an animal model of cocaine dependence, modulated the level of GABA B R activity, applied a conditioned place preference assay (CPP) to assess the role of the NAc in reconsolidation of addiction memory, evaluated learning and memory functions by behavioral experiments, examined the expression of GB1, GB2, cyclic adenosine monophosphate response element binding protein (CREB), p-CREB, protein kinase A (PKA), protein kinase (ERK), and Brain-derived neurotrophic factor (BDNF) in the NAc by molecular biology experiments, and screened differentially significantly expressed genes by transcriptome sequencing.

RESULTS

Our study showed that the GABA B receptor agonist baclofen (BLF) had a significant effect on locomotor distance in rats, promoted an increase in GABA levels and significantly inhibited the PKA and ERK1/2/CREB/BDNF signaling pathways. Moreover, transcriptome sequencing showed that GABA B R antagonist intervention identified a total of 21 upregulated mRNAs and 21 downregulated mRNAs. The differentially expressed (DE) mRNA genes were mainly enriched in tyrosine metabolism; however, further study is needed.

CONCLUSION

GABA B R activity in the NAc is involved in the regulation of cocaine addiction and may play an important role through key mRNA pathways.

Impairment of the GABAergic system in the anterior insular cortex of heroin-addicted males

Opioid addiction is a global problem, causing the greatest health burden among drug use disorders, with opioid overdose deaths topping the statistics of fatal overdoses. The multifunctional anterior insular cortex (AIC) is involved in inhibitory control, which is severely impaired in opioid addiction. GABAergic interneurons shape the output of the AIC, where abnormalities have been reported in individuals addicted to opioids. In these neurons, glutamate decarboxylase (GAD) with its isoforms GAD 65 and 67 is a key enzyme in the synthesis of GABA, and research data point to a dysregulation of GABAergic activity in the AIC in opioid addiction. Our study, which was performed on paraffin-embedded brains from the Magdeburg Brain Bank, aimed to investigate abnormalities in the GABAergic function of the AIC in opioid addiction by densitometric evaluation of GAD 65/67-immunostained neuropil. The study showed bilaterally increased neuropil density in layers III and V in 13 male heroin-addicted males compared to 12 healthy controls, with significant U-test P values for layer V bilaterally. Analysis of confounding variables showed that age, brain volume and duration of formalin fixation did not confound the results. Our findings suggest a dysregulation of GABAergic activity in the AIC in opioid addiction, which is consistent with experimental data from animal models and human neuroimaging studies.

Dorsal raphe to basolateral amygdala corticotropin-releasing factor circuit regulates cocaine-memory reconsolidation

Environmental stimuli elicit drug craving and relapse in cocaine users by triggering the retrieval of strong cocaine-related contextual memories. Retrieval can also destabilize drug memories, requiring reconsolidation, a protein synthesis-dependent storage process, to maintain memory strength. Corticotropin-releasing factor (CRF) signaling in the basolateral amygdala (BLA) is necessary for cocaine-memory reconsolidation. We have hypothesized that a critical source of CRF in the BLA is the dorsal raphe nucleus (DR) based on its neurochemistry, anatomical connectivity, and requisite involvement in cocaine-memory reconsolidation. To test this hypothesis, male and female Sprague-Dawley rats received adeno-associated viruses to express Gi-coupled designer receptors exclusively activated by designer drugs (DREADDs) selectively in CRF neurons of the DR and injection cannulae directed at the BLA. The rats were trained to self-administer cocaine in a distinct environmental context then received extinction training in a different context. Next, they were briefly re-exposed to the cocaine-predictive context to destabilize (reactivate) cocaine memories. Intra-BLA infusions of the DREADD agonist deschloroclozapine (DCZ; 0.1 mM, 0.5 µL/hemisphere) immediately after memory reactivation attenuated cocaine-memory strength, relative to vehicle infusion. This was indicated by a selective, DCZ-induced and memory reactivation-dependent decrease in drug-seeking behavior in the cocaine-predictive context in DREADD-expressing males and females at test compared to respective controls. Notably, BLA-projecting DR CRF neurons that exhibited increased c-Fos expression during memory reconsolidation co-expressed the glutamatergic neuronal marker, vesicular glutamate transporter 3. Together, these findings suggest that the DRCRF → BLA circuit is engaged to maintain cocaine-memory strength after memory destabilization, and this phenomenon may be mediated by DR CRF and/or glutamate release in the BLA.

Lycium barbarum polysaccharide mitigated methamphetamine addiction and altered methamphetamine-induced gut microbiota dysbiosis

Methamphetamine (MA) is a highly addictive mental stimulant, and MA abuse remains a significant public health problem worldwide, while effective treatment options are limited. Lycium barbarum polysaccharide (LBP), a major effective component extracted from Lycium barbarum, has potential health-promoting effects on the nervous system; however, its role in MA dependence remains unclear. In this study, the conditioned place preference (CPP) of MA addiction in adult male mice was established to detect changes in gut microbiota profiles after LBP treatment through 16S rRNA gene sequencing. Our results found that LBP administration could alleviate MA-induced CPP and hyperactivity. Interestingly, LBP improved MA-induced gut microbiota dysbiosis by increasing some beneficial autochthonous genus abundances, such as Allobaculum, Gordonibacter, and Ileibacterium. MA exposure induced the co-occurrence network of intestinal microbiota to become weaker and more unstable when compared with the control group, while LBP changed the above effects when compared with the MA group. Bacterial gene function prediction showed that amphetamine addiction, cocaine addiction, and short-chain fatty acid metabolism were enriched. These findings reveal that LBP might regulate MA-induced gut microbiota and behavior changes, which showed potential therapeutic applicability in treating MA addiction by regulating the gut microbiota.

Dorsal Raphe to Basolateral Amygdala Corticotropin-Releasing Factor Circuit Regulates Cocaine-Memory Reconsolidation

Environmental stimuli elicit drug craving and relapse in cocaine users by triggering the retrieval of strong cocainerelated contextual memories. Retrieval can also destabilize drug memories, requiring reconsolidation, a protein synthesis-dependent storage process, to maintain memory strength. Corticotropin-releasing factor (CRF) signaling in the basolateral amygdala (BLA) is necessary for cocainememory reconsolidation. We have hypothesized that a critical source of CRF in the BLA is the dorsal raphe nucleus (DR) based on its neurochemistry, anatomical connectivity, and requisite involvement in cocaine-memory reconsolidation. To test this hypothesis, male and female Sprague-Dawley rats received adeno-associated viruses to express Gi-coupled designer receptors exclusively activated by designer drugs (DREADDs) selectively in CRF neurons of the DR and injection cannulae directed at the BLA. The rats were trained to self-administer cocaine in a distinct environmental context then received extinction training in a different context. They were then briefly reexposed to the cocaine-predictive context to destabilize (reactivate) cocaine memories. Intra-BLA infusions of the DREADD agonist deschloroclozapine (DCZ; 0.1 mM, 0.5 μL/hemisphere) after memory reactivation attenuated cocaine-memory strength, relative to vehicle infusion. This was indicated by a selective, DCZ-induced and memory reactivation-dependent decrease in drug-seeking behavior in the cocaine-predictive context in DREADD-expressing males and females at test compared to respective controls. Notably, BLA-projecting DR CRF neurons that exhibited increased c-Fos expression during memory reconsolidation co-expressed glutamatergic and serotonergic neuronal markers. Together, these findings suggest that the DRCRF → BLA circuit is engaged to maintain cocaine-memory strength after memory destabilization, and this phenomenon may be mediated by DR CRF, glutamate, and/or serotonin release in the BLA.

Synergistic photoactivation of VTA-catecholaminergic and BLA-glutamatergic projections induces long-term potentiation in the insular cortex

The presentation of novel stimuli induces a reliable dopamine release in the insular cortex (IC) from the ventral tegmental area (VTA). The novel stimuli could be associated with motivational and emotional signals induced by cortical glutamate release from the basolateral amygdala (BLA). Dopamine and glutamate are essential for acquiring and maintaining behavioral tasks, including visual and taste recognition memories. In this study, we hypothesize that the simultaneous activation of dopaminergic and glutamatergic projections to the neocortex can underlie synaptic plasticity. High-frequency stimulation of the BLA-IC circuit has demonstrated a reliable long-term potentiation (LTP), a widely acknowledged synaptic plasticity that underlies memory consolidation. Therefore, the concurrent optogenetic stimulation of the insula's glutamatergic and dopaminergic terminal fibers would induce reliable LTP. Our results confirmed that combined photostimulation of the VTA and BLA projections to the IC induces a slow-onset LTP. We also found that optogenetically-induced LTP in the IC relies on both glutamatergic NMDA receptors and dopaminergic D1/D5 receptors, suggesting that the combined effects of these neurotransmitters can trigger synaptic plasticity in the neocortex. Overall, our findings provide compelling evidence supporting the essential role of both dopaminergic and glutamatergic projections in modulating synaptic plasticity within the IC. Furthermore, our results suggest that the synergistic actions of these projections have a pivotal influence on the formation of motivational memories.

Still a "hidden island"? The rodent insular cortex in drug seeking, reward, and risk

The insular cortex (IC) is implicated in risky decision making and drug-seeking behaviors, in a manner dissociable from natural reward seeking. However, evidence from rodent studies of motivated behaviors suggests that the role of the IC is not always consistent across procedures. Moreover, there is evidence of dissociation of function between posterior (pIC) and anterior (aIC) subregions in these behaviors. Under which circumstances, and by which mechanisms, these IC subregions are recruited to regulate motivated behaviors remains unclear. Here, we discuss evidence of rodent pIC and aIC function across drug-related behaviors, natural reward seeking, and decision making under risk and highlight procedural differences that may account for seemingly conflicting findings. Although gaps in the literature persist, we hypothesize that IC activity is broadly important for selection of appropriate behaviors based on learned action-outcome contingencies and that associated risk is sufficient, but not necessary, to recruit the aIC in reward seeking without involving the pIC.

Alterations of RNAs in the insula related to cocaine-induced condition place preference in adolescent mice

Cocaine as a highly addictive psychostimulant can cause changes in the body at the cellular and molecular levels over a long period of time. It reminds us that cocaine may have a potential role in post-transcriptional regulation, but the alteration of insula-expression profile in adolescent cocaine use disorder (CUD) has not been reported. To reveal the mechanisms underlying the post-transcriptional regulation of cocaine, we investigate the transcriptome in the insula of cocaine-induced mice based on high-throughput strand-specific RNA sequencing. We analyzed the alterations of messenger RNA (mRNA) expression profile in the insula of cocaine-induced condition place preference (CPP) mice and then correlated it with microRNAs to reveal their involvement in the formation of cocaine-induced CPP. In this study, a total of 27786 genes were identified, 5750 new genes (novel expressed transcripts of unannotated in the reference genome) were discovered, among which 1,205 were annotated functionally. A total of 198 differentially expressed genes (DEG) that functioned in synaptic transmission, cholinergic, developmental process, neurotransmitter metabolic process, drug catabolism, cellular response to drug, MAP kinase activity, ceramidase activity, and drug resistance were significantly enriched. Further analysis showed that 26045 mRNAs formed 45,208 network-relationship pairs with 1770 microRNAs. In the current study, our work was the first to reveal that alterations of RNAs in the insula, as a core brain region of the neural circuits of interoception, were involved in the process of cocaine-induced CPP of adolescent mice. These findings enrich the biology and expand the molecular regulatory network related to adolescence CUD. They provided the possibility that some DEGs may be used as novel biomarkers for the diagnosis or evaluation of substance use disorder, and also provided clues for elucidating the neurobiological mechanism of substance use disorder.

Endogenous opiates and behavior: 2020

This paper is the forty-third consecutive installment of the annual anthological review of research concerning the endogenous opioid system, summarizing articles published during 2020 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).

Global Cerebral Ischemia in Male Long Evans Rats Impairs Dopaminergic/ΔFosB Signalling in the Mesocorticolimbic Pathway Without Altering Delay Discounting Rates

Global cerebral ischemia (GCI) in rats has been shown to promote exploration of anxiogenic zones of the Elevated-Plus Maze (EPM) and Open Field Test (OFT). This study investigated changes in impulsive choice and/or defensive responses as possible contributors of heightened anxiogenic exploration observed after ischemia. Impulsivity was assessed using delay discounting (DD) paradigms, while the Predator Odour Test (PO) served to assess changes in defensive responses towards a naturally aversive stimulus. Male Long Evans rats underwent 9 days of autoshaping training and 24 days of DD training prior to GCI or sham surgery (n = 9/group). Post-surgery, rats completed the OFT, EPM, and PO, followed by 6 days of DD sessions. Blood droplets served to evaluate corticosterone secretion associated with PO exposure. With impulsivity being regulated through mesocorticolimbic monoaminergic pathways, we also characterised post-ischemic changes in the expression of dopamine D₂ receptors (DRD₂), dopamine transporters (DAT), and 1FosB in the basolateral amygdala (BLA), nucleus accumbens core (NAcC) and shell (NAcS), and ventromedial prefrontal cortex (vmPFC) using immunohistofluorescence. Our findings revealed no impact of GCI on delay discounting rates, while PO approach behaviours were minimally affected. Nonetheless, GCI significantly reduced DRD₂ and ΔFosB-ir in the NAcS and NAcC, respectively, while DAT-ir was diminished in both NAc subregions. Collectively, our findings refine the understanding of cognitive-behavioural and biochemical responses following stroke or cardiac arrest. They support significant alterations to the dopaminergic mesocorticolimbic pathway after ischemia, which are not associated with altered impulsive choice in a DD task but may influence locomotor exploration of the OFT and EPM.

Medial prefrontal cortex Notch1 signalling mediates methamphetamine-induced psychosis via Hes1-dependent suppression of GABAB1 receptor expression

Methamphetamine (METH), a widely abused stimulant drug, induces psychosis in approximately half of abusers; this effect is becoming a major concern for society. Although the Notch1 signalling pathway has been shown to play a part in the pathogenesis of some psychiatric disorders, its role in METH-induced psychosis (MIP) is still unknown. Here, the METH-induced locomotor sensitization model in rodents is considered to represent the underlying neurochemical changes driving psychoses. We found that the Notch1 signalling was downregulated in the medial prefrontal cortex (mPFC) in sensitized mice. Direct genetic and pharmacological manipulations of Notch1 signalling bidirectionally altered METH-induced locomotor sensitization and other MIP-related behaviours through governing neuronal activity in the mPFC. Moreover, Notch1 signalling negatively regulated GABA_B1 receptor expression in the mPFC of METH-sensitized mice through Hes1, a transcriptional repressor in Notch1 signalling. Further, we show that Hes1 can directly bind to the GABA_B1 receptor promoter. Notably, pharmacological regulation of the GABA_B receptor in the mPFC reversed the changes in METH-induced locomotor sensitization caused by the dysfunction of Notch1 signalling. Together, our findings uncover a previously unrecognised Notch1-Hes1-GABA_B1 receptor-dependent mechanism involved in regulating mPFC neuronal activity and behavioural phenotypes in MIP. Our work provides mechanistic insight into the aetiology and pathophysiology of MIP.

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.

Continuous High Frequency Deep Brain Stimulation of the Rat Anterior Insula Attenuates the Relapse Post Withdrawal and Strengthens the Extinction of Morphine Seeking

Deep brain stimulation (DBS) modulates the neuronal activity in specific brain circuits and has been recently considered as a promising intervention for refractory addiction. The insula cortex is the hub of interoception and is known to be involved in different aspects of substance use disorder. In the present study, we investigate the effects of continuous high frequency DBS in the anterior insula (AI) on drug-seeking behaviors and examined the molecular mechanisms of DBS action in morphine-addicted rats. Sprague-Dawley rats were trained to the morphine-conditioned place preference (CPP, day 1-8) followed by bilaterally implanted with DBS electrodes in the AI (Day 10) and recovery (Day 10-15). Continuous high-frequency (HF) -DBS (130 Hz, 150 μA, 90 μs) was applied during withdrawal (Day 16-30) or extinction sessions. CPP tests were conducted on days 16, 30, 40 during withdrawal session and several rats were used for proteomic analysis on day 30. Following the complete extinction, morphine-CPP was reinstated by a priming dose of morphine infusion (2 mg/kg). The open field and novel objective recognition tests were also performed to evaluate the DBS side effect on the locomotion and recognition memory. Continuous HF-DBS in the AI attenuated the expression of morphine-CPP post-withdrawal (Day 30), but morphine addictive behavior relapsed 10 days after the cessation of DBS (Day 40). Continuous HF-DBS reduced the period to full extinction of morphine-CPP and blocked morphine priming-induced recurrence of morphine addiction. HF-DBS in the AI had no obvious effect on the locomotor activity and novel objective recognition and did not cause anxiety-like behavior. In addition, our proteomic analysis identified eight morphine-regulated proteins in the AI and their expression levels were reversely changed by HF-DBS. Continuous HF-DBS in the bilateral anterior insula prevents the relapse of morphine place preference after withdrawal, facilitates its extinction, blocks the reinstatement induced by morphine priming and reverses the expression of morphine-regulated proteins. Our findings suggest that manipulation of insular activity by DBS could be a potential intervention to treat substance use disorder, although future research is warranted.