Molecular and neuronal plasticity mechanisms in the amygdala-prefrontal cortical circuit: implications for opiate addiction memory formation

The secondary visual cortex mediated the enhancement of associative learning on methamphetamine self-administration behaviors

RATIONALE

Methamphetamine addiction is a persistent and intractable pathological learning and memory, whereas no approved therapeutics is available. However, few attentions have been paid to how associative learning participates in the formation of intractable memory related to drug addiction OBJECTIVES AND METHODS: To investigate the role of associative learning in methamphetamine addiction and the underlying neurobiological mechanism, methamphetamine self-administration, oral sucrose self-administration, chemogenetic neuromanipulation, and fiber photometry in mice were performed in this study.

RESULTS

We reported that associative learning increased methamphetamine-induced self-administration, but not oral sucrose self-administration. In addition, the enhancement of methamphetamine-induced self-administration was independent of more methamphetamine consumption, and remained with higher drug-taking and motivation in the absence of visual cues, suggesting the direct effects of the associative learning that enhanced methamphetamine-induced self-administration. Moreover, chemogenetic inactivation of the secondary visual cortex (V2) reduced the enhancement of the drug-taking induced by associative learning but did not alter sucrose-taking. Further fiber photometry of V2 neurons demonstrated that methamphetamine-associative learning elicits V2 neuron excitation, and sucrose-associative learning elicits V2 neuron inhibition.

CONCLUSIONS

Therefore, this study reveals the neurobiological mechanism of V2 excitability underlying how associative learning participates in the formation of intractable memory related to drug addiction, and gives evidence to support V2 as a promising target for stimulation therapy for methamphetamine addiction.

Formation of chronic morphine withdrawal memories requires C1QL3-mediated regulation of PSD95 in the mouse basolateral amygdala

Chronic morphine withdrawal memory formation is a complex process influenced by various molecular mechanisms. In this study, we aimed to investigate the contributions of the basolateral amygdala (BLA) and complement component 1, q subcomponent-like 3 (C1QL3), a secreted and presynaptically targeted protein, to the formation of chronic morphine (repeat dosing of morphine) withdrawal memory using conditioned place aversion (CPA) and chemogenetic methods. We conducted experiments involving the inhibition of the BLA during naloxone-induced withdrawal to assess its impact on CPA scores, providing insights into the significance of the BLA in the chronic morphine memory formation process. We also examined changes in C1ql3/C1QL3 expression within the BLA following conditioning. Immunofluorescence analysis revealed the colocalization of C1QL3 and the G protein-coupled receptor, brain-specific angiogenesis inhibitor 3 (BAI3) in the BLA, supporting their involvement in synaptic development. Moreover, we downregulated C1QL3 expression in the BLA to investigate its role in chronic morphine withdrawal memory formation. Our findings revealed that BLA inhibition during naloxone-induced withdrawal led to a significant reduction in CPA scores, confirming the critical role of the BLA in this memory process. Additionally, the upregulation of C1ql3 expression within the BLA postconditioning suggested its participation in withdrawal memory formation. The colocalization of C1QL3 and BAI3 in the BLA further supported their involvement in synaptic development. Furthermore, downregulation of C1QL3 in the BLA effectively hindered chronic morphine withdrawal memory formation, emphasizing its pivotal role in this process. Notably, we identified postsynaptic density protein 95 (PSD95) as a potential downstream effector of C1QL3 during chronic morphine withdrawal memory formation. Blocking PSD95 led to a significant reduction in the CPA score, and it appeared that C1QL3 modulated the ubiquitination-mediated degradation of PSD95, resulting in decreased PSD95 protein levels. This study underscores the importance of the BLA, C1QL3 and PSD95 in chronic morphine withdrawal memory formation. It provides valuable insights into the underlying molecular mechanisms, emphasizing their significance in this intricate process.

Estrogen receptor beta signaling enhances extinction memory recall for heroin-conditioned cues in a sex- and region-specific manner

Return to use, or relapse, is a major challenge in the treatment of opioid use disorder (OUD). Relapse can be precipitated by several factors, including exposure to drug-conditioned cues. Identifying successful treatments to mitigate cue-induced relapse has been challenging, perhaps due to extinction memory recall (EMR) deficits. Previously, inhibition of estradiol (E2) signaling in the basolateral amygdala (BLA) impaired heroin-cue EMR. This effect was recapitulated by antagonism of BLA estrogen receptors (ER) in a sex-specific manner such that blocking ERα in males, but ERβ in females, impaired EMR. However, it is unclear whether increased E2 signaling, in the BLA or systemically, enhances heroin-cue EMR. We hypothesized that ERβ agonism would enhance heroin-cue EMR in a sex- and region-specific manner. To determine the capacity of E2 signaling to improve EMR, we pharmacologically manipulated ERβ across several translationally designed experiments. First, male and female rats acquired heroin or sucrose self-administration. Next, during a cued extinction session, we administered diarylpropionitrile (DPN, an ERβ agonist) and tested anxiety-like behavior on an open field. Subsequently, we assessed EMR in a cue-induced reinstatement test and, finally, measured ERβ expression in several brain regions. Across all experiments, females took more heroin and sucrose than males and had greater responses during heroin-cued extinction. Administration of DPN in the BLA enhanced EMR in females only, driven by ERβ's impacts on memory consolidation. Interestingly, however, systemic DPN administration improved EMR for heroin cues in both sexes across several different tests, but did not impact sucrose-cue EMR. Immunohistochemical analysis of ERβ expression across several different brain regions showed that females only had greater expression of ERβ in the basal nucleus of the BLA. Here, in several preclinical experiments, we demonstrated that ERβ agonism enhances heroin-cue EMR and has potential utility in combatting cue-induced relapse.

The Orexin/Hypocretin System, the Peptidergic Regulator of Vigilance, Orchestrates Adaptation to Stress

The orexin/hypocretin neuropeptide family has emerged as a focal point of neuroscientific research following the discovery that this family plays a crucial role in a variety of physiological and behavioral processes. These neuropeptides serve as powerful neuromodulators, intricately shaping autonomic, endocrine, and behavioral responses across species. Notably, they serve as master regulators of vigilance and stress responses; however, their roles in food intake, metabolism, and thermoregulation appear complementary and warrant further investigation. This narrative review provides a journey through the evolution of our understanding of the orexin system, from its initial discovery to the promising progress made in developing orexin derivatives. It goes beyond conventional boundaries, striving to synthesize the multifaceted activities of orexins. Special emphasis is placed on domains such as stress response, fear, anxiety, and learning, in which the authors have contributed to the literature with original publications. This paper also overviews the advancement of orexin pharmacology, which has already yielded some promising successes, particularly in the treatment of sleep disorders.

Inhibition of Estradiol Signaling in the Basolateral Amygdala Impairs Extinction Memory Recall for Heroin-Conditioned Cues in a Sex-Specific Manner

INTRODUCTION

Relapse is a major treatment barrier for opioid use disorder. Environmental cues become associated with the rewarding effects of opioids and can precipitate relapse, even after numerous unreinforced cue presentations, due to deficits in extinction memory recall (EMR). Estradiol (E2) modulates EMR of fear-related cues, but it is unknown whether E2 impacts EMR of reward cues and what brain region(s) are responsible for E2s effects. Here, we hypothesize that inhibition of E2 signaling in the basolateral amygdala (BLA) will impair EMR of a heroin-associated cue in both male and female rats.

METHODS

We pharmacologically manipulated E2 signaling to characterize the role of E2 in the BLA on heroin-cue EMR. Following heroin self-administration, during which a light/tone cue was co-presented with each heroin infusion, rats underwent cued extinction to extinguish the conditioned association between the light/tone and heroin. During extinction, E2 signaling in the BLA was blocked by an aromatase inhibitor or specific estrogen receptor (ER) antagonists. The next day, subjects underwent a cued test to assess heroin-cue EMR.

RESULTS

In both experiments, females took more heroin than males (mg/kg) and had higher operant responding during cued extinction. Inhibition of E2 synthesis in the BLA impaired heroin-cue EMR in both sexes. Notably, E2s actions are mediated by different ER mechanisms, ERα in males but ERβ in females.

CONCLUSIONS

This study is the first to demonstrate a behavioral role for centrally-produced E2 in the BLA and that E2 also impacts EMR of reward-associated stimuli in both sexes.

Curcumin attenuates morphine dependence by modulating μ-opioid receptors and glial cell-activated neuroinflammation in rat

In recent years, the association between neuroinflammation and opioid dependence has attracted considerable attention. Curcumin, a component of the Curcuma longa, has been shown to act as a suppressor of glial cells and inflammatory cytokines. The main goal of this study was to explore the attenuating effects of curcumin on morphine dependence with a focus on neuroinflammation and μ-opioid receptors in the rat prefrontal cortex. To induce morphine dependence in male Wistar rats, morphine was administered i.p. once daily for 18 days in an escalating dose of 10, 20, and 40 mg/kg. Curcumin (2.5, 5, and 10 mg/kg, i.p.) was given from the days 10th to 18th. Immunofluorescence staining and ELISA methods were used to evaluate glial cells activity and inflammatory cytokines levels, respectively. Western blotting was used to evaluate the expression of μ-opioid receptors. The administration of curcumin (2.5, 5, and 10 mg/kg) for 9 days significantly attenuated the symptoms of morphine withdrawal syndrome. The prefrontal cortex concentration of TNF-α and IL-6 was also reduced by curcumin (2.5, 5, and 10 mg/kg) significantly. Furthermore, curcumin decreased the number of Iba1 and GFAP positive cells in morphine-dependent rats. Moreover, the expression of μ-opioid receptors was significantly reduced by curcumin (10 mg/kg). The results of this study demonstrate that curcumin attenuates morphine dependence in rats through an inhibitory effect on neuroinflammation and a decrease in the expression of μ-opioid receptors in the prefrontal cortex.

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.

Control of fear by discrete prefrontal GABAergic populations encoding valence-specific information

Neurons activated by learning have been ascribed the unique potential to encode memory, but the functional contribution of discrete cell types remains poorly understood. In particular, it is unclear whether learning engages specific GABAergic interneurons and, if so, whether they differ functionally from interneurons recruited by other experiences. Here, we show that fear conditioning activates a heterogeneous neuronal population in the medial prefrontal cortex (mPFC) that is largely comprised of somatostatin-expressing interneurons (SST-INs). Using intersectional genetic approaches, we demonstrate that fear-learning-activated SST-INs exhibit distinct circuit properties and are selectively reactivated to mediate cue-evoked memory expression. In contrast, an orthogonal population of SST-INs activated by morphine experience exerts opposing control over fear and supports reward-like motivational effects. These results outline an important role for discrete subsets of GABAergic cells in emotional learning and point to an unappreciated capacity for functional specialization among SST-INs.

Involvement of the ERK signaling pathways in the NAc in propofol-seeking behavior induced by cues in rats

Propofol, an intravenous short-acting anesthetic, has the potential to induce craving and relapse. Accumulated evidence demonstrates that extracellular signal-regulated kinase (ERK) plays an essential role in drug reward and relapse. In the previous study, we demonstrated that the ERK signaling pathways in the Nucleus accumbens (NAc) were involved in propofol reward. However, the role of the ERK signaling pathways in propofol relapse is still unknown. We first trained rats to self-administer propofol for 14 days, then evaluated propofol-seeking behavior of relapse induced by a contextual cues and conditioned cues after 14-day withdrawal. Meanwhile, MEK inhibitor U0126 was used to investigate the role of the ERK signal pathways in propofol-seeking behavior induced by contextual cues and conditioned cues. Results showed that the number of active nose-poke responses in propofol-seeking behavior induced by conditioned cues was much higher compared to contextual cues. U0126 (5.0 μg/side, Lateral Ventricle (LV)) pretreatment significantly decreased the active responses induced by conditioned cues, which was associated with a large decline in the expression of p-ERK in the NAc. Moreover, microinjectionofU0126 (2.0 μg/side) in the NAc also attenuated the active responses of propofol-seeking behavior. Additionally, microinjections with U0126 in the LV (5.0 μg/side) or NAc (2.0 μg/side) both failed to alter sucrose self-administration or locomotor activity of rats. Therefore, we conclude that ERK phosphorylation in the NAc maybe involved in propofol relapse.

ERK-Directed Phosphorylation of mGlu5 Gates Methamphetamine Reward and Reinforcement in Mouse

Methamphetamine (MA) is a highly addictive psychomotor stimulant drug. In recent years, MA use has increased exponentially on a global scale, with the number of MA-involved deaths reaching epidemic proportions. There is no approved pharmacotherapy for treating MA use disorder, and we know relatively little regarding the neurobiological determinants of vulnerability to this disease. Extracellular signal-regulated kinase (ERK) is an important signaling molecule implicated in the long-lasting neuroadaptations purported to underlie the development of substance use disorders, but the role for this kinase in the propensity to develop addiction, particularly MA use disorder, is uncharacterized. In a previous MA-induced place-conditioning study of C57BL/6J mice, we characterized mice as MA-preferring, -neutral, or -avoiding and collected tissue from the medial prefrontal cortex (mPFC). Using immunoblotting, we determined that elevated phosphorylated ERK expression within the medial prefrontal cortex (mPFC) is a biochemical correlate of the affective valence of MA in a population of C57BL/6J mice. We confirmed the functional relevance for mPFC ERK activation for MA-induced place-preference via site-directed infusion of the MEK inhibitor U0126. By contrast, ERK inhibition did not have any effect upon MA-induced locomotion or its sensitization upon repeated MA treatment. Through studies of transgenic mice with alanine point mutations on T1123/S1126 of mGlu5 that disrupt ERK-dependent phosphorylation of the receptor, we discovered that ERK-dependent mGlu5 phosphorylation normally suppresses MA-induced conditioned place-preference (MA-CPP), but is necessary for this drug’s reinforcing properties. If relevant to humans, the present results implicate individual differences in the capacity of MA-associated cues/contexts to hyper-activate ERK signaling within mPFC in MA Use Disorder vulnerability and pose mGlu5 as one ERK-directed target contributing to the propensity to seek out and take MA.

Conditioned aversive memory associated with morphine withdrawal increases brain-derived neurotrophic factor in dentate gyrus and basolateral amygdala

Morphine has been shown to increase the expression of brain-derived neurotrophic factor (BDNF) in the brain. However, little is known about the effect of conditioned naloxone-precipitated morphine withdrawal on BDNF and its precursor protein, proBDNF. We used the conditioned place aversion (CPA) paradigm to evaluate the role of corticotropin-releasing factor (CRF)/CRF1 receptor signaling on the BDNF expression and corticosterone plasma levels after CPA expression and extinction. Male mice were rendered dependent on morphine and injected acutely with naloxone before paired to confinement in a naloxone-associated compartment. The expression of BDNF and proBDNF in the dentate gyrus (DG) and basolateral amygdala (BLA) was measured in parallel with the corticosterone plasma levels with and without CRF1 receptor blockade. Mice subjected to conditioned naloxone-induced morphine withdrawal showed an increased expression of BDNF (in DG and BLA) in parallel with an enhancement of corticosterone plasma levels. These results demonstrated that BDNF expression together with the increased activity of hypothalamic-pituitary-adrenocortical (HPA) axis are critical to the acquisition of aversive memory. However, we have observed a decrease in corticosterone plasma levels and BDNF expression after CPA extinction reaffirming the importance of BDNF in the maintenance of aversive memory. In addition, the pre-treatment with the CRF1 receptor antagonist CP-154 526 before naloxone conditioning session impaired morphine withdrawal-induced aversive memory acquisition, the increased corticosterone plasma levels, and the expression of BDNF observed after CPA expression in the DG and BLA. Altogether, present results are suggesting a clear connection between HPA axis and BDNF in the formation and extinction of aversive memory.

Sign-tracking behavior is difficult to extinguish and resistant to multiple cognitive enhancers

The attribution of incentive-motivational value to drug-related cues underlies relapse and craving in drug addiction. One method of addiction treatment, cue-exposure therapy, utilizes repeated presentations of drug-related cues in the absence of drug (i.e., extinction learning); however, its efficacy has been limited due to an incomplete understanding of extinction and relapse processes after cues have been imbued with incentive-motivational value. To investigate this, we used a Pavlovian conditioned approach procedure to screen for rats that attribute incentive-motivational value to reward-related cues (sign-trackers; STs) or those that do not (goal-trackers; GTs). In Experiment 1, rats underwent Pavlovian extinction followed by reinstatement and spontaneous recovery tests. For comparison, a separate group of rats underwent PCA training followed by operant conditioning, extinction, and tests of reinstatement and spontaneous recovery. In Experiment 2, three cognitive enhancers (sodium butyrate, D-cycloserine, and fibroblast growth factor 2) were administered following extinction training to facilitate extinction learning. STs but not GTs displayed enduring resistance to Pavlovian, but not operant, extinction and were more susceptible to spontaneous recovery. In addition, none of the cognitive enhancers tested affected extinction learning. These results expand our understanding of extinction learning by demonstrating that there is individual variation in extinction and relapse processes and highlight potential difficulties in applying extinction-based therapies to drug addiction treatment in the clinic.

Acute Tramadol-Induced Cellular Tolerance and Dependence of Ventral Tegmental Area Dopaminergic Neurons: An In Vivo Electrophysiological Study

Introduction

Ventral Tegmental Area (VTA) is a core region of the brainstem that contributes to different vital bio-responses such as pain and addiction. The Dopaminergic (DA) cellular content of VTA has major roles in different functions. This study aims to evaluate the cellular effect of tramadol on the putative VTA-DA neurons.

Methods

Wistar rats were assigned into three groups of control, sham, and tramadol-treated. The animals were anesthetized and their VTA-DA neuronal activity was obtained under controlled stereotaxic operation. The firing rate of the neurons was extracted according to principal component analysis by Igor Pro software and analyzed statistically considering P<0.05 as significant. Tramadol (20 mg/kg) was infused intraperitoneally.

Results

Overall, 121 putative VTA-DA neurons were isolated from all groups. In tramadol-treated rats, the inhibition of the neuronal firing was proposed as tolerance and the excitation period as dependence or withdrawal. The Mean±SD inhibition time lasted up to 50.34±10.17 minutes and 31% of neurons stopped firing and silenced after 24±3 min on average but the remaining neurons lowered their firing up to 43% to 67% of their baseline firing. All neurons showed the excitation period, lasted about 56.12±15.30 min, and the firing of neurons increased from 176% to 244% of their baseline or pre-injection period.

Conclusion

The tolerance and dependence effects of tramadol are related to the changes in the neuronal firing rate at the putative VTA-DA neurons. The acute injection of tramadol can initiate neuroadaptation on the opioid and non-opioid neurotransmission to mediate these effects.

Alkylphenol inverse agonists of HCN1 gating: H-bond propensity, ring saturation and adduct geometry differentially determine efficacy and potency

BACKGROUND AND PURPOSE

In models of neuropathic pain, inhibition of HCN1 is anti-hyperalgesic. 2,6-di-iso-propyl phenol (propofol) and its non-anesthetic congener, 2,6-di-tert-butyl phenol, inhibit HCN1 channels by stabilizing closed state(s).

EXPERIMENTAL APPROACH

Using in vitro electrophysiology and kinetic modeling, we systematically explore the contribution of ligand architecture to alkylphenol-channel coupling.

KEY RESULTS

When corrected for changes in hydrophobicity (and propensity for intra-membrane partitioning), the decrease in potency upon 1-position substitution (NCO∼OH >> SH >>> F) mirrors the ligands' H-bond acceptor (NCO > OH > SH >>> F) but not donor profile (OH > SH >>> NCO∼F). H-bond elimination (OH to F) corresponds to a ΔΔG of ∼4.5 kCal mol^-1 loss of potency with little or no disruption of efficacy. Substitution of compact alkyl groups (iso-propyl, tert-butyl) with shorter (ethyl, methyl) or more extended (sec-butyl) adducts disrupts both potency and efficacy. Ring saturation (with the obligate loss of both planarity and π electrons) primarily disrupts efficacy.

CONCLUSIONS AND IMPLICATIONS

A hydrophobicity-independent decrement in potency at higher volumes suggests the alkylbenzene site has a volume of ≥800 ų. Within this, a relatively static (with respect to ligand) H-bond donor contributes to initial binding with little involvement in generation of coupling energy. The influence of π electrons/ring planarity and alkyl adducts on efficacy reveals these aspects of the ligand present towards a face of the channel that undergoes structural changes during opening. The site's characteristics suggest it is "druggable"; introduction of other adducts on the ring may generate higher potency inverse agonists.

Prefrontal-accumbens opioid plasticity: Implications for relapse and dependence

In addiction, an individual's ability to inhibit drug seeking and drug taking is thought to reflect a pathological strengthening of drug-seeking behaviors or impairments in the capacity to control maladaptive behavior. These processes are not mutually exclusive and reflect drug-induced modifications within prefrontal cortical and nucleus accumbens circuits, however unlike psychostimulants such as cocaine, far less is known about the temporal, anatomical, and cellular dynamics of these changes. We discuss what is known regarding opioid-induced adaptations in intrinsic membrane physiology and pre-/postsynaptic neurotransmission in principle pyramidal and medium spiny neurons in the medial prefrontal cortex and nucleus accumbens from electrophysiological studies and explore how circuit specific adaptations may contribute to unique facets of opioid addiction.

Effect of a 5-HT1D receptor agonist on the reinstatement phase of the conditioned place preference test and hippocampal long-term potentiation in methamphetamine-treated rats

Methamphetamine (METH)-seeking relapse is associated with memory and synaptic plasticity changes. Serotonin is a key neuromodulator in this process. While there is a known distribution of 5-HT_1D receptors in reward and memory areas, such as the hippocampus, its physiological function is currently unknown. Here, we evaluated effect of a 5-HT_1D receptor agonist, PNU142633, on the reinstatement of METH-seeking behavior and long-term potentiation. Rats were implanted with a cannula into lateral ventricle, then treated with saline or METH (5 mg/kg) during the acquisition phase of the conditioned place preference (CPP) test. On day 13 of the extinction phase, METH groups were divided into four groups: METH (0: saline, 1, or 2.5 (priming METH) mg/kg; i.p.) + vehicle (5 µl/rat) or a priming dose of METH (2.5 mg/kg; i.p.) + PNU (2 µg/5 µl; i.c.v.) and their preference scores were calculated on reinstatement day (day 14). Immediately following this, electrophysiology was performed to assay the field excitatory postsynaptic potential (fEPSP) slope and population spike (PS) amplitude between groups. The results showed that CPP induction by METH gradually declined to extinction on days 12 and 13. A priming METH treatment significantly increased preference for the METH-paired chamber when compared with other groups, but pre-treatment with PNU significantly attenuated this effect. PS amplitude and fEPSP slopes in vehicle + priming METH rats were greater when compared with other groups. Furthermore, PNU attenuated the priming METH-induced increase in PS amplitude. These findings suggest that PNU can decrease synaptic transmission and prevent METH reinstatement in rats.

MicroRNA-219 alleviates glutamate-induced neurotoxicity in cultured hippocampal neurons by targeting calmodulin-dependent protein kinase II gamma

Septic encephalopathy is a frequent complication of sepsis, but there are few studies examining the role of microRNAs (miRs) in its pathogenesis. In this study, a miR-219 mimic was transfected into rat hippocampal neurons to model miR-219 overexpression. A protective effect of miR-219 was observed for glutamate-induced neurotoxicity of rat hippocampal neurons, and an underlying mechanism involving calmodulin-dependent protein kinase II γ (CaMKIIγ) was demonstrated. miR-219 and CaMKIIγ mRNA expression induced by glutamate in hippocampal neurons was determined by quantitative real-time reverse transcription-polymerase chain reaction (qRT-PCR). After neurons were transfected with miR-219 mimic, effects on cell viability and apoptosis were measured by 3-(4,5-dimethylthiazolyl-2)-2,5-diphenyltetrazolium bromide (MTT) assay and flow cytometry. In addition, a luciferase reporter gene system was used to confirm CaMKIIγ as a target gene of miR-219. Western blot assay and rescue experiments were also utilized to detect CaMKIIγ expression and further verify that miR-219 in hippocampal neurons exerted its effect through regulation of CaMKIIγ. MTT assay and qRT-PCR results revealed obvious decreases in cell viability and miR-219 expression after glutamate stimulation, while CaMKIIγ mRNA expression was increased. MTT, flow cytometry, and caspase-3 activity assays showed that miR-219 overexpression could elevate glutamate-induced cell viability, and reduce cell apoptosis and caspase-3 activity. Moreover, luciferase CaMKIIγ-reporter activity was remarkably decreased by co-transfection with miR-219 mimic, and the results of a rescue experiment showed that CaMKIIγ overexpression could reverse the biological effects of miR-219. Collectively, these findings verify that miR-219 expression was decreased in glutamate-induced neurons, CaMKIIγ was a target gene of miR-219, and miR-219 alleviated glutamate-induced neuronal excitotoxicity by negatively controlling CaMKIIγ expression.

The involvement of CRF1 receptor within the basolateral amygdala and dentate gyrus in the naloxone-induced conditioned place aversion in morphine-dependent mice

Drug withdrawal-associated aversive memories trigger relapse to drug-seeking behavior. Corticotrophin-releasing factor (CRF) is an important mediator of the reinforcing properties of drugs of abuse. However, the involvement of CRF1 receptor (CRF1R) in aversive memory induced by opiate withdrawal has yet to be elucidated. We used the conditioned-place aversion (CPA) paradigm to evaluate the role of CRF1R on opiate withdrawal memory acquisition, along with plasticity-related processes that occur after CPA within the basolateral amygdala (BLA) and dentate gyrus (DG). Male mice were rendered dependent on morphine and injected acutely with naloxone before paired to confinement in a naloxone-associated compartment. The CPA scores as well as the number of TH-positive neurons (in the NTS-A2 noradrenergic cell group), and the expression of the transcription factors Arc and pCREB (in the BLA and DG) were measured with and without CRF1R blockade. Mice subjected to conditioned naloxone-induced morphine withdrawal robustly expressed CPA. Pre-treatment with the selective CRF1R antagonist CP-154,526 before naloxone conditioning session impaired morphine withdrawal-induced aversive memory acquisition. CP-154,526 also antagonized the enhanced number of TH-positive neurons in the NTS-A2 that was seen after CPA. Increased Arc expression and Arc-pCREB co-localization were seen in the BLA after CPA, which was not modified by CP-154,526. In the DG, CPA was accompanied by a decrease of Arc expression and no changes in Arc-pCREB co-localization, whereas pre-treatment with CP-154,526 induced an increase in both parameters. These results indicate that CRF-CRF1R pathway could be a critical factor governing opiate withdrawal memory storage and retrieval and might suggest a role for TH-NA pathway in the effects of withdrawal on memory. Our results might indicate that the blockade of CRF1R could represent a promising pharmacological treatment strategy approach for the attenuation of the relapse to drug-seeking/taking behavior triggered by opiate withdrawal-associated aversive memories.

Fear Memory Recall Potentiates Opiate Reward Sensitivity through Dissociable Dopamine D1 versus D4 Receptor-Dependent Memory Mechanisms in the Prefrontal Cortex

Disturbances in prefrontal cortical (PFC) dopamine (DA) transmission are well established features of psychiatric disorders involving pathological memory processing, such as post-traumatic stress disorder and opioid addiction. Transmission through PFC DA D4 receptors (D4Rs) has been shown to potentiate the emotional salience of normally nonsalient emotional memories, whereas transmission through PFC DA D1 receptors (D1Rs) has been demonstrated to selectively block recall of reward- or aversion-related associative memories. In the present study, using a combination of fear conditioning and opiate reward conditioning in male rats, we examined the role of PFC D4/D1R signaling during the processing of fear-related memory acquisition and recall and subsequent sensitivity to opiate reward memory formation. We report that PFC D4R activation potentiates the salience of normally subthreshold fear conditioning memory cues and simultaneously potentiates the rewarding effects of systemic or intra-ventral tegmental area (VTA) morphine conditioning cues. In contrast, blocking the recall of salient fear memories with intra-PFC D1R activation, blocks the ability of fear memory recall to potentiate systemic or intra-VTA morphine place preference. These effects were dependent upon dissociable PFC phosphorylation states involving calcium-calmodulin-kinase II or extracellular signal-related kinase 1-2, following intra-PFC D4 or D1R activation, respectively. Together, these findings reveal new insights into how aberrant PFC DAergic transmission and associated downstream molecular signaling pathways may modulate fear-related emotional memory processing and concomitantly increase opioid addiction vulnerability.SIGNIFICANCE STATEMENT Post-traumatic stress disorder is highly comorbid with addiction. In this study, we use a translational model of fear memory conditioning to examine how transmission through dopamine D1 or D4 receptors, in the prefrontal cortex (PFC), may differentially control acquisition or recall of fear memories and how these mechanisms might regulate sensitivity to the rewarding effects of opioids. We demonstrate that PFC D4 activation not only controls the salience of fear memory acquisition, but potentiates the rewarding effects of opioids. In contrast, PFC D1 receptor activation blocks recall of fear memories and prevents potentiation of opioid reward effects. Together, these findings demonstrate novel PFC mechanisms that may account for how emotional memory disturbances might increase the addictive liability of opioid-class drugs.

Maladaptive Sexual Behavior Following Concurrent Methamphetamine and Sexual Experience in Male Rats is Associated with Altered Neural Activity in Frontal Cortex

The use of psychostimulants is often associated with hypersexuality, and psychostimulant users have identified the effects of drug on sexual behavior as a reason for further use. It was previously demonstrated in male rats that methamphetamine (Meth), when administered concurrently with sexual behavior results in impairment of inhibition of sexual behavior in a conditioned sex aversion (CSA) paradigm where mating is paired with illness. This is indicative of maladaptive sex behavior following Meth and sex experience. The present study examined the neural pathways activated during inhibition of sexual behavior in male rats and the effects of concurrent Meth and sexual behavior on neural activity, using ERK phosphorylation (pERK). First, exposure to conditioned aversive stimuli in males trained to inhibit sexual behavior in the CSA paradigm increased pERK expression in medial prefrontal (mPFC), orbitofrontal cortex (OFC) and areas in striatum and amygdala. Second, effects of concurrent Meth and sex experience were tested in males that were exposed to four daily sessions of concurrent Meth (1 mg/kg) or saline and mating and subsequently exposed to CSA one week after last treatment. Meth and mating-treated males showed significant impairment of inhibition of mating, higher pERK expression under baseline conditions, and disrupted pERK induction by exposure to the conditioned aversive stimuli in mPFC and OFC. These alterations of pERK occurred in CaMKII-expressing neurons, suggesting changes in efferent projections of these areas. Altogether, these data show that concurrent Meth and mating experience causes maladapative sexual behavior that is associated with alterations in neural activation in mPFC and OFC.

Glutamate transporter type 3 participates in maintaining morphine-induced conditioned place preference

Glutamate transporters (EAAT) have been implicated in the drug addiction behavior. We determined whether EAAT type 3 (EAAT3) played a role in morphine addiction. Six- to eight-week-old EAAT3 knockout (EAAT3^-/-) mice and their wild-type littermates received 3 intraperitoneal injections of 10mg/kg morphine, each on an alternative day, to induce conditioned place preference (CPP). Two days after the place preference returned to baseline, mice received 2.5mg/kg morphine to induce reinstatement. Some mice received intraperitoneal injection of 4mg/kg riluzole, an EAAT activator, 30min before morphine or saline injection. Hippocampus, medial prefrontal cortex, nucleus accumbens and ventral tegmental area were harvested for Western analysis 24h after the last dose of morphine was injected. Morphine induced CPP in wild-type and EAAT3^-/- mice. Gender is not a statistically significant factor to influence this behavior. This conditioned behavior extinguished after morphine administration was stopped for 8-9days in wild-type mice, while this extinction occurred 6days after discontinuation of morphine injection in EAAT3^-/- mice. A small dose of morphine similarly reinstated the conditioned behavior in the wild-type and EAAT3^-/- mice. Riluzole abolished morphine-induced CPP during the initial place preference. Morphine increased EAAT3 expression in the plasma membrane of medial prefrontal cortex, nucleus accumbens and ventral tegmental area but did not affect EAAT3 expression in the hippocampus. These results suggest that EAAT3 delays the extinction of morphine-induced CPP. EAAT activation may prevent the formation of morphine-induced CPP.