Withdrawal from chronic administration of cocaine decreases delta opioid receptor signaling and increases anxiety- and depression-like behaviors in the rat

Prenatal and postnatal cocaine exposure enhances the anxiety- and depression-like behaviors in rats during cocaine withdrawal

Prenatal drug exposure is a public health problem, which results in profound behavioral problems during childhood and adolescence, mainly represented by an increase in the risk of cocaine abuse at an early age. In rodents, prenatal and postnatal cocaine exposure enhanced locomotor activity and cocaine- or nicotine-induced locomotor sensitization. Various authors consider that the adverse emotional states (anxiety and depression) that occur during cocaine withdrawal are the main factors that precipitate, relapse, and increase chronic cocaine abuse, which could increase the risk of relapse of cocaine abuse. Therefore, the objective of this study was to characterize anxiety- and depression-like behaviors at different times (30, 60, 90, and 120 days) of cocaine withdrawal in rats born to females exposed prenatally and postnatally to cocaine. A group of pregnant female Wistar rats were administered daily from day GD0 to GD21 with cocaine (cocaine preexposure group), and another group of pregnant female rats was administered daily with saline (saline preexposure group). Of the litters resulting from the cocaine-pre-exposed and saline-pre-exposed pregnant female groups, only the male rats were used for the recording of the anxiety- and depression-like behaviors at different times (30, 60, 90, and 120 days) of cocaine withdrawal The study found that prenatal and postnatal cocaine exposure dose-dependent enhanced anxiety- and depression-like behaviors. This suggests that prenatal and postnatal cocaine exposure can result in enhanced vulnerability to cocaine abuse in young and adult humans.

Impact of Mephedrone on Fear Memory in Adolescent Rats: Involvement of Matrix Metalloproteinase-9 (MMP-9) and N-Methyl-D-aspartate (NMDA) Receptor

Treatment of Post-Traumatic Stress Disorder (PTSD) is complicated by the presence of drug use disorder comorbidity. Here, we examine whether conditioned fear (PTSD model) modifies the rewarding effect of mephedrone and if repeated mephedrone injections have impact on trauma-related behaviors (fear sensitization, extinction, and recall of the fear reaction). We also analyzed whether these trauma-induced changes were associated with exacerbation in metalloproteinase-9 (MMP-9) and the GluN2A and GluN2B subunits of N-methyl-D-aspartate (NMDA) glutamate receptor expression in such brain structures as the hippocampus and basolateral amygdala. Male adolescent rats underwent trauma exposure (1.5 mA footshock), followed 7 days later by a conditioned place preference training with mephedrone. Next, the post-conditioning test was performed. Fear sensitization, conditioned fear, anxiety-like behavior, extinction acquisition and relapse were then assessed to evaluate behavioral changes. MMP-9, GluN2A and GluN2B were subsequently measured. Trauma-exposed rats subjected to mephedrone treatment acquired a strong place preference and exhibited impairment in fear extinction and reinstatement. Mephedrone had no effect on trauma-induced MMP-9 level in the basolateral amygdala, but decreased it in the hippocampus. GluN2B expression was decreased in the hippocampus, but increased in the basolateral amygdala of mephedrone-treated stressed rats. These data suggest that the modification of the hippocampus and basolateral amygdala due to mephedrone use can induce fear memory impairment and drug seeking behavior in adolescent male rats.

GIRK channel activity in prelimbic pyramidal neurons regulates the extinction of cocaine conditioned place preference in male mice

Drug-induced neuroadaptations in the prefrontal cortex (PFC) have been implicated in drug-associated memories that motivate continued drug use. Chronic cocaine exposure increases pyramidal neuron excitability in the prelimbic subregion of the PFC (PL), an adaptation that has been attributed in part to a suppression of inhibitory signalling mediated by the GABA_B receptor (GABA_B R) and G protein-gated inwardly rectifying K⁺ (GIRK/Kir3) channels. Although reduced GIRK channel activity in PL pyramidal neurons enhances the motor-stimulatory effect of cocaine in mice, the impact on cocaine reward and associated memories remains unclear. Here, we employed Cre- and CRISPR/Cas9-based viral manipulation strategies to evaluate the impact of GIRK channel or GABA_B R ablation in PL pyramidal neurons on cocaine-induced conditioned place preference (CPP) and extinction. Neither ablation of GIRK channels nor GABA_B R impacted the acquisition of cocaine CPP. GIRK channel ablation in PL pyramidal neurons, however, impaired extinction of cocaine CPP in male but not female mice. Since ablation of GIRK channels but not GABA_B R increased PL pyramidal neuron excitability, we used a chemogenetic approach to determine if acute excitation of PL pyramidal neurons impaired the expression of extinction in male mice. While acute chemogenetic excitation of PL pyramidal neurons induced locomotor hyperactivity, it did not impair the extinction of cocaine CPP. Lastly, we found that persistent enhancement of GIRK channel activity in PL pyramidal neurons accelerated the extinction of cocaine CPP. Collectively, our findings show that the strength of GIRK channel activity in PL pyramidal neurons bi-directionally regulates cocaine CPP extinction in male mice.

Brain systems in cocaine abstinence-induced anxiety-like behavior in rodents: A review

Cocaine use disorder (CUD) is a significant public health issue that generates substantial personal, familial, and economic burdens. Still, there are no FDA-approved pharmacotherapies for CUD. Cocaine-dependent individuals report anxiety during withdrawal, and alleviation of anxiety and other negative affective states may be critical for maintaining drug abstinence. However, the neurobiological mechanisms underlying abstinence-related anxiety in humans or anxiety-like behavior in rodents are not fully understood. This review summarizes investigations regarding anxiety-like behavior in mice and rats undergoing cocaine abstinence, as assessed using four of the most common anxiety-related assays: the elevated plus (or its derivative, the elevated zero) maze, open field test, light-dark transition test, and defensive burying task. We first summarize available evidence that cocaine abstinence generates anxiety-like behavior that persists throughout protracted abstinence. Then, we examine investigations concerning neuropeptide, neurotransmitter, and neuromodulator systems in cocaine abstinence-induced anxiety-like behavior. Throughout, we discuss how differences in sex, rodent strain, cocaine dose and dosing strategy and abstinence duration interact to generate anxiety-like behavior.

Responsivity of serotonin transporter knockout rats to short and long access to cocaine: modulation of the glutamate signaling in the nucleus accumbens shell

Background and Purpose

It has been well established that glutamate in the nucleus accumbens (NAc) plays a critical role in the motivation to take drugs of abuse. We have previously demonstrated that rats with ablation of the serotonin transporter (SERT^−/− rats) show increased cocaine intake reminiscent of compulsivity.

Experimental Approach

By comparing SERT^−/− to SERT^+/+ rats, we investigated whether SERT deletion influences glutamate homeostasis under control conditions as well as after short access (ShA: 1 h per session) or long access (LgA: 6 h per session) to cocaine self‐administration. Rats were killed at 24 h after the last self‐administration session for ex vivo molecular analyses of the main determinants of the glutamate system, including transporters (vesicular and glial), receptors (main post‐synaptic subunits of NMDA and AMPA receptors together with the metabotropic subunit mGLUR5), and scaffolding proteins (SAP102, SAP97, and GRIP) in the NAc shell (sNAc)

Key Results

In cocaine‐naive animals, SERT deletion was associated with changes indicative for a reduction in glutamate signalling. ShA and LgA exposure led to a further dysregulation of the glutamatergic synapse.

Conclusion

SERT deletion may render the glutamatergic synapses of the NAc shell more responsive to both ShA and LgA intake of cocaine.

Cannabidiol prevents several of the behavioral alterations related to cocaine addiction in mice

Cocaine dependence is a highly prevalent disease in modern society and lacks an effective treatment. Cannabidiol (CBD), a major non-psychoactive constituent of Cannabis sativa, has been shown to be a promising tool in the management of some neuropsychiatric disorders, including cocaine abuse. However, its therapeutic effects on the behavioral outcomes related to cocaine addiction remain unclear. The present research evaluates the effects of CBD (30, 60 and 120 mg/kg; injected intraperitoneally) on the acquisition, expression, extinction and reinstatement of cocaine (10 mg/kg)-induced conditioned place preference (CPP; Study 1); cocaine (25 mg/kg)-induced locomotor stimulation (Study 2); and cocaine withdrawal symptoms (Study 3) in male C57BL/6 J mice. The results show that CBD does not possess motivational properties in itself and does not modify the acquisition, expression or extinction of cocaine-induced CPP. Interestingly, when administered during the extinction phase of the cocaine-induced CPP, CBD (30 and 60 mg/kg) prevented priming-induced reinstatement of CPP. Moreover, CBD abolished cocaine-induced hyperactivity without altering the spontaneous locomotion of the animals. Furthermore, CBD (120 mg/kg) reduced the memory deficits induced by cocaine withdrawal in the object recognition test, though it did not reverse depressive-like symptoms measured in the tail suspension test. Overall, our data suggest that CBD can prevent the development of cocaine addiction, and, when administered during cocaine abstinence, may be of help in avoiding relapse to drug-seeking and in ameliorating the memory disturbances provoked by chronic consumption of cocaine.

Exercise Pills for Drug Addiction: Forced Moderate Endurance Exercise Inhibits Methamphetamine-Induced Hyperactivity through the Striatal Glutamatergic Signaling Pathway in Male Sprague Dawley Rats

Physical exercise reduces the extent, duration, and frequency of drug use in drug addicts during the drug initiation phase, as well as during prolonged addiction, withdrawal, and recurrence. However, information about exercise-induced neurobiological changes is limited. This study aimed to investigate the effects of forced moderate endurance exercise training on methamphetamine (METH)-induced behavior and the associated neurobiological changes. Male Sprague Dawley rats were subjected to the administration of METH (1 mg/kg/day, i.p.) and/or forced moderate endurance exercise (treadmill running, 21 m/min, 60 min/day) for 2 weeks. Over the two weeks, endurance exercise training significantly reduced METH-induced hyperactivity. METH and/or exercise treatment increased striatal dopamine (DA) levels, decreased p(Thr308)-Akt expression, and increased p(Tyr216)-GSK-3β expression. However, the phosphorylation levels of Ser9-GSK-3β were significantly increased in the exercise group. METH administration significantly increased the expression of NMDAr1, CaMKK2, MAPKs, and PP1 in the striatum, and exercise treatment significantly decreased the expression of these molecules. Therefore, it is apparent that endurance exercise inhibited the METH-induced hyperactivity due to the decrease in GSK-3β activation by the regulation of the striatal glutamate signaling pathway.

Repeated cocaine exposure prior to fear conditioning induces persistency of PTSD-like symptoms and enhancement of hippocampal and amygdala cell density in male rats

Pre- and post-trauma drug use can interfere with recovery from post-traumatic stress disorder (PTSD). However, the biological underpinnings of this interference are poorly understood. Here we examined the effect of pre-fear conditioning cocaine self-administration on PTSD-like symptoms in male rats, and defined impairment of fear extinction as difficulty to recover from PTSD. We also examined cell density changes in brain regions suspected of being involved in resistance to PTSD recovery. Before footshock stress testing, rats were trained to self-administer cocaine during 20 consecutive days, after which they were exposed to footshocks, while other rats continued to self-administer cocaine until the end of the experiment. Upon assessment of three PTSD-like symptoms (fear during situational reminders, anxiety-like behavior, and impairment of recognition memory) and fear extinction learning and memory, changes in cell density were measured in the medial prefrontal cortex, hippocampus, and amygdala. Results show that pre-footshock cocaine exposure did not affect fear during situational reminders. Fear conditioning did not lead to an increase in cocaine consumption. However, in footshock stressed rats, cocaine induced a reduction of anxiety-like behavior, an aggravation of recognition memory decline, and an impairment of extinction memory. These behavioral alterations were associated with increased cell density in the hippocampal CA1, CA2, and CA3 regions and basolateral amygdala, but not in the medial prefrontal cortex. Our findings suggest that enhancement of cell density in the hippocampus and amygdala may be changes associated with drug use, interfering with PTSD recovery.

Long access to cocaine self-administration dysregulates the glutamate synapse in the nucleus accumbens core of serotonin transporter knockout rats

Background and Purpose

It is well established that the nucleus accumbens and glutamate play a critical role in the motivation to take drugs of abuse. We have previously demonstrated that rats with ablation of the serotonin (5‐HT) transporter (SERT^−/− rats) show increased cocaine intake reminiscent of compulsivity.

Experimental Approach

By comparing SERT^−/− to SERT^+/+ rats, we set out to explore whether SERT deletion influences glutamate neurotransmission under control conditions as well as after short access (1 h/session) or long access (6 h/session) to cocaine self‐administration.

Key Results

Rats were killed at 24 h after the final self‐administration session for ex vivo molecular analyses of the glutamate system (vesicular and glial transporters, post‐synaptic subunits of NMDA and AMPA receptors and their related scaffolding proteins). Such analyses were undertaken in the nucleus accumbens core. In cocaine‐naïve animals, SERT deletion evoked widespread abnormalities in markers of glutamatergic neurotransmission that, overall, indicate a reduction of glutamate signalling. These results suggest that 5‐HT is pivotal for the maintenance of accumbal glutamate homeostasis. We also found that SERT deletion altered glutamate homeostasis mainly after long access, but not short access, to cocaine.

Conclusion and Implications

Our findings reveal that SERT deletion may sensitize the glutamatergic synapses of the nucleus accumbens core to the long access but not short access, intake of cocaine.

LINKED ARTICLES

This article is part of a themed issue on New discoveries and perspectives in mental and pain disorders. To view the other articles in this section visit http://onlinelibrary.wiley.com/doi/10.1111/bph.v179.17/issuetoc

Increased negative affect when combining early-life maternal deprivation with adolescent, but not adult, cocaine exposure in male rats: regulation of hippocampal FADD

RATIONALE

Besides early drug initiation during adolescence, another vulnerability factor associated with increased risk for substance abuse later in life is early-life stress. One way of assessing such combined risk is by evaluating the emergence of increased negative affect during withdrawal (i.e., linked to persistence in drug seeking).

OBJECTIVES

To compare the impact of maternal deprivation with cocaine exposure at different ages on affective-like behavior and hippocampal neuroplasticity regulation.

METHODS

Maternal deprivation was performed in whole-litters of Sprague-Dawley rats (24 h, PND 9-10). Cocaine (15 mg/kg, 7 days, i.p.) was administered in adolescence (PND 33-39) or adulthood (PND 64-70). Changes in affective-like behavior were assessed by diverse tests across time (forced-swim, open field, novelty-suppressed feeding, sucrose preference). Hippocampal multifunctional FADD protein (balance between cell death and plasticity) was evaluated by Western blot.

RESULTS

Exposing rats to either maternal deprivation or adolescent cocaine did not modulate affective-like behavior immediately during adolescence, but increased negative affect in adulthood. Maternal deprivation combined with adolescent cocaine advanced the negative impact to adolescence. Adult cocaine exposure alone and/or in combination with maternal deprivation did not induce any behavioral changes at the time-points analyzed. FADD regulation might participate in the neural adaptations taking place in the hippocampus in relation to the observed behavioral changes.

CONCLUSIONS

Adolescence is a more vulnerable period, as compared to adulthood, to the combined impact of cocaine and early maternal deprivation, thus suggesting that the accumulation of stress early in life can anticipate the negative behavioral outcome associated with drug consumption.

Cocaine Self-administration Regulates Transcription of Opioid Peptide Precursors and Opioid Receptors in Rat Caudate Putamen and Prefrontal Cortex

The brain opioid system plays an important role in cocaine reward. Altered signaling in the opioid system by chronic cocaine exposure contributes to cocaine-seeking and taking behavior. The current study investigated concurrent changes in the gene expression of multiple components in rat brain opioid system following cocaine self-administration. Animals were limited to 40 infusions (1.5 mg/kg/infusion) within 6 h per day for five consecutive days. We then examined the mRNA levels of opioid receptors including mu (Oprm), delta (Oprd), and kappa (Oprk), and their endogenous opioid peptide precursors including proopiomelanocortin (Pomc), proenkephalin (Penk), prodynorphin (Pdyn) in the dorsal striatum (CPu) and the prefrontal cortex (PFC) 18 h after the last cocaine infusion. We found that cocaine self-administration significantly increased the mRNA levels of Oprm and Oprd in both the CPu and PFC, but had no effect on Oprk mRNA levels in either brain region. Moreover, cocaine had a greater influence on the mRNA levels of opioid peptide precursors in rat CPu than in the PFC. In the CPu, cocaine self-administration significantly increased the mRNA levels of Penk and Pdyn and abolished the mRNA levels of Pomc. In the PFC, cocaine self-administration only increased Pdyn mRNA levels without changing the mRNA levels of Pomc and Penk. These data suggest that cocaine self-administration influences the expression of multiple genes in the brain opioid system, and the concurrent changes in these targets may underlie cocaine-induced reward and habitual drug-seeking behavior.

Sex differences in the effect of the FKBP5 inhibitor SAFit2 on anxiety and stress-induced reinstatement following cocaine self-administration

Cocaine use and withdrawal prompt stress system responses. Stress and the negative affective state produced by cocaine withdrawal are major triggers for relapse. FKBP5 is a co-chaperone of the glucocorticoid receptor and regulates HPA axis negative feedback. The role of FKBP5 in cocaine-related behaviors has not been studied. The FKBP5 inhibitor SAFit2 was used to examine the role of FKBP5 in anxiety-like behavior during early cocaine withdrawal and in stress-induced reinstatement following cocaine self-administration in male and female rats. Withdrawal from cocaine self-administration resulted in heightened anxiety-like behavior in female rats, which was significantly attenuated by SAFit2 administration. SAFit2 pretreatment prior to stress-induced reinstatement to cocaine seeking significantly reduced active lever presses of males. In female rats, SAFit2 administration prevented stress-induced reinstatement for rats in metestrus or diestrus, but not proestrus or estrus phases at the time of reinstatement. These data suggest an important role for FKBP5 in stress-related behaviors following cocaine self-administration, particularly in females.

Increased relapse to cocaine-seeking in a genetic model for depression

The greatest difficulty in treating cocaine addiction is the enormous rates of relapse, which occur despite immense negative consequences. Relapse risks are even greater in addicts with comorbid depression, perhaps because they use drugs to alleviate depressive symptoms. Only a few preclinical studies have examined this comorbidity, mostly exploring depressive-like effects following drug exposure. We examined rats from two different depression-like models: (a) chronic-mild-stress (CMS), which respond to antidepressant medications and (b) depressed-rat-line (DRL), a genetic model of selective breeding, which is less responsive to antidepressant medications. We tested addictive behaviors in a cocaine self-administration procedure, including the "conflict model," where drug-seeking and relapse encounter adverse consequences: an electrified grid in front of the drug-delivering lever. Following behavioral testing, we explored a potential association between behavioral outcomes and protein expression of brain-derived neurotrophic factor (BDNF). We found that DRL rats self-administer more cocaine compared with both CMS and controls, while CMS and control groups did not differ significantly. Notably, DRL but not CMS rats, displayed higher rates of relapse than controls, and expressed higher levels of BDNF in the prelimbic cortex (PLC). Potential translation of these results suggest that medication-resistant depressed patients tend to consume more drugs and are more susceptible to relapse. The increase in PLC BDNF levels is consistent with previous rat models of depression, and concomitantly, with its suggested role in promoting cocaine-seeking.

Regulation of CRF mRNA in the Rat Extended Amygdala Following Chronic Cocaine: Sex Differences and Effect of Delta Opioid Receptor Agonism

BACKGROUND

Cocaine withdrawal activates stress systems. Females are more vulnerable to relapse to cocaine use and more sensitive to withdrawal-induced negative affect. Delta opioid receptors modulate anxiety-like behavior during cocaine withdrawal in rats. This study measured the time course of gene regulation of one of the main stress peptides, corticotropin-releasing factor (CRF), and its type 1 receptor in male and female rats as well as the ability of the delta opioid receptor agonist SNC80 to normalize cocaine withdrawal-induced changes in CRF mRNA.

METHODS

Rats were injected with cocaine or saline 3 times daily for 14 days. Brains were collected 30 minutes, 24 hours, 48 hours, 7 days, and 14 days following the last injection. The paraventricular nucleus of the hypothalamus, central amygdala, and bed nucleus of the stria terminalis were processed for quantitative reverse transcriptase PCR measurement of CRF and CRFR1 mRNA. Additional rats received SNC80 during early cocaine withdrawal, and CRF mRNA was measured in the central amygdala.

RESULTS

CRF mRNA was elevated in the central amygdala at 24 hours and the paraventricular nucleus at 48 hours of cocaine withdrawal in males and females. Significant sex differences in cocaine-induced CRF upregulation were found in the bed nucleus of the stria terminalis at 30 minutes and 24 hours. SNC80 administration attenuated the increase in CRF mRNA in the central amygdala of female rats only.

CONCLUSIONS

CRF mRNA regulation during cocaine withdrawal is sex, time, and brain region dependent. Administration of a delta opioid receptor agonist during early withdrawal may ameliorate stress-related negative affect in females by abrogating the induction of CRF mRNA.

Effects of cocaine base paste on anxiety-like behavior and immediate-early gene expression in nucleus accumbens and medial prefrontal cortex of female mice

RATIONALE

Cocaine base paste (CBP) is an illegal drug of abuse usually consumed by adolescents in a socio-economically vulnerable situation. Repeated drug use targets key brain circuits disrupting the processes that underlie emotions and cognition. At the basis of such neuroadaptations lie changes in the expression of immediate-early genes (IEGs). Nevertheless, changes in transcriptional regulation associated with CBP consumption remain unknown.

OBJECTIVES

We aimed to describe behavioral phenotype related to locomotion, anxiety-like behavior, and memory of CBP-injected mice and to study IEGs expression after an abstinence period.

METHODS

Five-week-old female CF-1 mice were i.p. injected daily with vehicle or CBP (40 mg/kg) for 10 days and subjected to a 10-day period of abstinence. Open field and novel object recognition tests were used to evaluate locomotion and anxiety-like behaviors and recognition memory, respectively, during chronic administration and after abstinence. After abstinence, prefrontal cortex (mPFC) and nucleus accumbens (NAc) were isolated and gene expression analysis performed through real-time PCR.

RESULTS

We found an increase in locomotion and anxiety-like behavior during CBP administration and after the abstinence period. Furthermore, the CBP group showed impaired recognition memory after abstinence. Egr1, FosB, ΔFosB, Arc, Bdnf, and TrkB expression was upregulated in CBP-injected mice in NAc and FosB, ΔFosB, Arc, and Npas4 expression was downregulated in mPFC. We generated an anxiety score and found positive and negative correlations with IEGs expression in NAc and mPFC, respectively.

CONCLUSION

Our results suggest that chronic CBP exposure induced alterations in anxiety-like behavior and recognition memory. These changes were accompanied by altered IEGs expression.

Transgenerational influence of parental morphine exposure on pain perception, anxiety-like behavior and passive avoidance memory among male and female offspring of Wistar rats

Accumulating evidence suggests that epigenetic mechanisms play an important role in the formation and maintenance of memory within the brain. Moreover, the effect of parental drug-exposure before gestation on behavioral state of offspring has been little studied. The main objective of the current study is to evaluate the effect of parental morphine exposure on avoidance memory, morphine preference and anxiety-like behavior of offspring. The total of 32 males and 32 females were used for mating. The animals were treated with morphine. The offspring according to their parental morphine treatment was divided into four groups (n=16) including paternally treated, maternally treated, both of parents treated and naïve animals. The pain perception, anxiety-like behavior, and avoidance memory were evaluated in the offspring. In the current study, the total of 256 offspring was used for the experiments (4 tasks × 4 groups of offspring × 8 female offspring × 8 male offspring). The finding revealed that the avoidance memory and visceral pain were reduced significantly in male and female offspring with at least one morphine-treated parent. Moreover, anxiety-like behavior was reduced significantly in the male offspring with at least one morphine-treated parent. While anxiety-like behavior was increased significantly in female offspring that were treated by morphine either maternally or both of parents. The data revealed that the endogenous opioid system may be altered in the offspring of morphine-treated parent(s), and epigenetic role could be important. However, analysis of variance signified the important role of maternal inheritance.

Cocaine treatment before pregnancy differentially affects the anxiety and brain glucose metabolism of lactating rats if performed during adulthood or adolescence

Cocaine exposure disrupts the maternal behavior of lactating rats, yet it is less known whether it alters the affective changes that accompany motherhood. As the long-term action of cocaine on anxiety varies according to the developmental stage of the individuals, this study aimed to compare the effect of a chronic treatment with cocaine to adult and adolescent non-pregnant females on their anxiety-like behavior and basal brain metabolic activity during lactation. Thus, adult and adolescent virgin rats were exposed to cocaine (0.0 or 15.0 mg/kg ip) during 10 days and were mated four days later. Anxiety behavior was evaluated on postpartum days 3-4 in the elevated plus maze test, and the basal brain glucose metabolism was determined on postpartum days 7-9 by means of [¹⁸F] fluorodeoxyglucose positron emission tomography. Cocaine treatment during adulthood increased the anxiety-like behavior of lactating females whereas its administration during adolescence decreased it. Also, the basal glucose metabolism of the medial prefrontal cortex differed between lactating females treated with cocaine during adulthood and adolescence. These differential effects of cocaine, according to the age at which the drug was administered, support the idea that the adolescent and adult brains have a distinct susceptibility to this drug, which leads to divergent long-term changes in the neural circuits that regulate anxiety during lactation.

Alleviation of diazepam-induced conditioned place preference and its withdrawal-associated neurobehavioral deficits following pre-exposure to enriched environment in rats

Diazepam is one of the widely prescribed sedative drugs for the treatment of anxiety and sleep disorders. However, its continuous use can induce addiction, tolerance, and withdrawal symptoms and, therefore, the pharmacological use of diazepam is restricted. Exposure to enriched environment can reduce the addiction to stimulants including amphetamine, cocaine, and nicotine. However, the protective effect of enriched environment against preference of sedative drugs is not yet investigated. This study, therefore, determined the effects of enriched environment to prevent diazepam-preference using conditioned place preference (CPP) paradigm. Adult rats were reared in social (n = 12) or physically (n = 12) enriched environment for four weeks. Each group was then sub-divided into two groups and were administered either saline (Control; n = 6) or diazepam (1 mg/kg; n = 6) on alternate days for thirteen days. During the administration of diazepam, the CPP was conducted to monitor drug preference on 5th, 9th and 13th day of experiment. It was observed that the diazepam administration significantly (p < .01) induced preference in rats. Neurobehavioral deficits including hypolocomotor activity, depression-like behavior, impaired learning and memory functions were also observed after 24 h of drug abstinence. Exposure to enriched environment significantly reduced diazepam-preference and other neurobehavioral deficits. This study provides preliminary evidence to highlight the importance of enriched environment in the attenuation of diazepam-preference.

Chronic cocaine administration upregulates FKBP5 in the extended amygdala of male and female rats

BACKGROUND

Dysregulation of glucocorticoid receptors has been implicated in addiction and stress-related disorders. FKBP5 is a co-chaperone of the glucocorticoid receptor and regulates receptor sensitivity. While FKBP5 is known to be involved in mood- and stress-related disorders, less is known regarding FKBP5 and cocaine abuse. This study investigated the regulation of FKBP5 expression in the extended amygdala and paraventricular nucleus of the hypothalamus, regions important in the control of stress-responses and HPA axis function, following chronic and acute cocaine administration.

METHODS

Adult male and female rats received saline or cocaine three times per day for 1 or 14 days. Brain tissue was collected 30 min, 24 h, 48 h, 7 days or 14 days following the final injection. FKBP5 mRNA was measured by qRT-PCR in the central nucleus of the amygdala (CeA), bed nucleus of the stria terminalis (BNST) and paraventricular nucleus (PVN).

RESULTS

FKBP5 mRNA levels were significantly elevated as a result of chronic cocaine administration in both males and females in the PVN and BNST 30 min and 24 h after the final injection. In females, FKBP5 was also elevated in the CeA. Following acute cocaine, FKBP5 gene expression was unaltered except for elevated levels in the BNST of females 24 h later.

CONCLUSIONS

These results demonstrate that FKBP5 mRNA is regulated by cocaine administration. Increased FKBP5 expression may play a role in the dysregulation of the stress axis following chronic cocaine exposure, contributing to the negative affective symptoms of cocaine withdrawal.

Mirtazapine attenuates anxiety- and depression-like behaviors in rats during cocaine withdrawal

BACKGROUND

Anxiety and depression, key symptoms of the cocaine withdrawal syndrome in human addicts, are considered the main factors that precipitate relapse in chronic cocaine addiction. Preclinical studies have found that rodents exposed to different withdrawal periods show an increase in anxiety and depressive-like behavior. Mirtazapine - a tetracyclic medication - is used primarily to treat depression and, sometimes, anxiety. It has also successfully improved withdrawal symptoms in drug-dependent patients.

AIM

This study sought to determine whether chronic dosing of mirtazapine during cocaine withdrawal reduced depression- and anxiety-like behaviors that characterize cocaine withdrawal in animals.

METHODS

Cocaine pre-treated Wistar rats were subjected to a 60-day cocaine withdrawal period during which depression- and anxiety-like behaviors were evaluated in open field tests (OFT), the elevated plus-maze (EPM), the light-dark box test (LDT), the forced swimming test (FST) and spontaneous locomotor activity (SLA).

RESULTS

We found that chronic dosing with different doses of mirtazapine (30 and 60 mg/kg) decreased depression- and anxiety-like behaviors induced by different doses of cocaine (10, 20 and 40 mg/kg) during the 60-day cocaine withdrawal.

INTERPRETATION

Our results suggest that the pharmacological effect of mirtazapine on its target sites of action (α₂-adrenergic and 5-HT_2A and 5-HT₃ receptors) within the brain may improve depression- and anxiety-like behaviors for long periods.

CONCLUSION

Therefore, the findings support the use of mirtazapine as a potentially effective therapy to reduce anxiety and depressive-like behavior during cocaine withdrawal.

Targeting opioid dysregulation in depression for the development of novel therapeutics

Since the serendipitous discovery of the first class of modern antidepressants in the 1950's, all pharmacotherapies approved by the Food and Drug Administration for major depressive disorder (MDD) have shared a common mechanism of action, increased monoaminergic neurotransmission. Despite the widespread availability of antidepressants, as many as 50% of depressed patients are resistant to these conventional therapies. The significant length of time required to produce meaningful symptom relief with these medications, 4-6 weeks, indicates that other mechanisms are likely involved in the pathophysiology of depression which may yield more viable targets for drug development. For decades, no viable candidate target with a different mechanism of action to that of conventional therapies proved successful in clinical studies. Now several exciting avenues for drug development are under intense investigation. One of these emerging targets is modulation of endogenous opioid tone. This review will evaluate preclinical and clinical evidence pertaining to opioid dysregulation in depression, focusing on the role of the endogenous ligands endorphin, enkephalin, dynorphin, and nociceptin/orphanin FQ (N/OFQ) and their respective receptors, mu (MOR), delta (DOR), kappa (KOR), and the N/OFQ receptor (NOP) in mediating behaviors relevant to depression and anxiety. Finally, putative opioid based antidepressants that are under investigation in clinical trials, ALKS5461, JNJ-67953964 (formerly LY2456302 and CERC-501) and BTRX-246040 (formerly LY-2940094) will be discussed. This review will illustrate the potential therapeutic value of targeting opioid dysregulation in developing novel therapies for MDD.

Adolescent cocaine exposure enhanced negative affect following drug re-exposure in adult rats: Attenuation of c-Fos activation

BACKGROUND

The goal of the present study was to utilize the adolescent drug experience as an emerging vulnerability factor for developing psychiatric comorbidities in adulthood that could, in turn, help to elucidate and/or hypothesize possible mechanisms contributing to higher relapse rates.

OUTCOMES

The current results showed that adolescent cocaine exposure (15 mg/kg, intraperitoneally, seven days) during early-mid adolescence (postnatal days 33-39) enhanced negative affect in adulthood, by increasing behavioral despair following drug re-exposure and by increasing anhedonia. Thus, these behavioral data provided a good model to further ascertain the long-term cellular and molecular adaptations that might take place in the brain in response to adolescent cocaine exposure as well as the impact of drug re-exposure in adulthood. In this regard, the results showed that adolescent cocaine exposure did not modulate cell proliferation (Ki-67+ cells) or c-Fos protein activation in the dentate gyrus region of the hippocampus, but attenuated c-Fos activation in the dorsal striatum.

CONCLUSIONS

These results proved that a history of cocaine exposure during adolescence increased the vulnerability to induce negative affect (i.e. emergence of psychiatric comorbidity) in adulthood while it decreased neuronal activation in the dorsal striatum. Interestingly, these effects were only observed following cocaine re-exposure in adulthood, suggesting that avoiding drug contact in adulthood could prevent the long-term negative effects induced by adolescent cocaine.

Involvement of opioid system in behavioral despair induced by social isolation stress in mice

Social isolation stress (SIS) as a type of chronic stress could induce depressive- and anxiety-like behaviors. Our study evaluates the role of opioid system on negative behavioral impacts of SIS in male NMRI mice. We investigated effects of morphine, a nonselective opioid receptor (OR) agonist, naltrexone (NLX), an OR antagonist, naltrindole (NLT), a delta opioid receptor (DOR) antagonist, SNC80, a DOR agonist, U-69593, a kappa opioid receptor (KOR) agonist, nor-Binaltorphimine, a selective KOR antagonist and cyprodime hydrochloride a selective mu opioid receptor (MOR) antagonist on depressive- and anxiety-like behaviors. Using RT-PCR we evaluated ORs gene expression in mice brain. Our findings showed that SIS induced anxiety- and depressive-like behavior in the forced swimming test, open field test, splash test and hole-board test. Moreover, administration of SNC-80 significantly mitigated anxiety- and depressive-like behaviors. NLT decreased grooming-activity in the splash test. Excitingly, administration of agents affecting KOR failed to alter the negative effects of SIS. RT-PCR demonstrated that MOR and KOR gene expression decreased in socially isolated mice; however, SIS did not affect DORs expression. Our findings suggest that SIS at least in part, probably via altering endogenous opioids particularly MORs and KORs but not DORs mediated negative impacts on behavior; also, it could be concluded that DORs might be considered as a novel target for studying depression and anxiety.

Epigenetic mechanisms associated with addiction-related behavioural effects of nicotine and/or cocaine: implication of the endocannabinoid system

The addictive use of nicotine (NC) and cocaine (COC) continues to be a major public health problem, and their combined use has been reported, particularly during adolescence. In neural plasticity, commonly induced by NC and COC, as well as behavioural plasticity related to the use of these two drugs, the involvement of epigenetic mechanisms, in which the reversible regulation of gene expression occurs independently of the DNA sequence, has recently been reported. Furthermore, on the basis of intense interactions with the target neurotransmitter systems, the endocannabinoid (ECB) system has been considered pivotal for eliciting the effects of NC or COC. The combined use of marijuana with NC and/or COC has also been reported. This article presents the addiction-related behavioural effects of NC and/or COC, based on the common behavioural/neural plasticity and combined use of NC/COC, and reviews the interacting role of the ECB system. The epigenetic processes inseparable from the effects of NC and/or COC (i.e. DNA methylation, histone modifications and alterations in microRNAs) and the putative therapeutic involvement of the ECB system at the epigenetic level are also discussed.

Binge-pattern cocaine administration causes long-lasting behavioral hyperarousal but does not enhance vulnerability to single prolonged stress in rats

Cocaine use disorder and post-traumatic stress disorder (PTSD) commonly co-occur. This could be due to vulnerability to post-traumatic symptoms conferred by previous exposure to cocaine. Therefore, we combined chronic binge-pattern cocaine with a model of psychological trauma (single prolonged stress) to determine whether the behavioral effects of psychological trauma are enhanced in cocaine-sensitized individuals. Adult male Sprague Dawley rats received 14 days of cocaine (15mg/kg/injection) or saline in a binge pattern (3 injections per day, 1h apart). Seven days after the last injection animals were exposed to traumatic stress or a control procedure. Seven days after stress, activity and anxiety-like behaviors were measured. Binge-pattern cocaine increased locomotor activity in the open field and elevated plus maze, and both cocaine and SPS exposure increased the rapidity with which rats moved through grooming sequences. Neither binge-pattern cocaine nor SPS increased anxiety-like behaviors, and no interactions were found between binge-pattern cocaine exposure and SPS exposure. A behavioral phenotype categorization approach demonstrated that cocaine-exposed groups expressed a high incidence of hyperactivity-like symptoms. These results suggest that binge-pattern cocaine exposure causes a long-lasting hyper-exploratory phenotype but does not make individuals more vulnerable to a later traumatic stress exposure.

Synthetic cathinones and stereochemistry: S enantiomer of mephedrone reduces anxiety- and depressant-like effects in cocaine- or MDPV-abstinent rats

BACKGROUND AND PURPOSE

The neuropharmacological profile of the synthetic cathinone mephedrone (MEPH) is influenced by stereochemistry. Both MEPH enantiomers are monoamine transporter substrates, but R-MEPH is primarily responsible for rewarding effects of MEPH as it produces greater locomotor activation and intracranial self-stimulation than S-MEPH. S-MEPH is a 50-fold more potent 5-HT releaser than R-MEPH and does not place preference in rats. MEPH is also structurally similar to the cathinone derivative bupropion, an antidepressant and smoking cessation medication, suggesting MEPH has therapeutic and addictive properties.

METHODS

We tested the hypothesis that S-MEPH reduces anxiety- and depression-like behaviors in rats withdrawn from chronic cocaine or methylenedioxypyrovalerone (MDPV) using the elevated plus maze (EPM) and forced swim test (FST), respectively. Rats were tested 48-h after a binge-like paradigm (3×/day for 10days in 1-h intervals) of cocaine (10mg/kg), MDPV (1mg/kg) or saline. In vitro studies assessed the receptor binding and activity of S-MEPH.

KEY RESULTS

Rats withdrawn from chronic cocaine or MDPV displayed an increase in anxiety- and depression-like behaviors that was antagonized by treatment with S-MEPH (10, 30mg/kg). S-MEPH displayed affinity, but not agonist activity, for 5-HT₂ receptors (2A-2C) and showed negligible affinity for dopaminergic, adrenergic and nicotinic receptors.

CONCLUSION AND IMPLICATION

S-MEPH attenuated withdrawal behaviors following chronic cocaine or MDPV, perhaps through 5-HT release and/or 5-HT₂ receptor interactions. The present data suggest S-MEPH may be a possible structural and pharmacological template to develop maintenance therapy for acute anxiety and depression during early withdrawal from psychostimulant abuse.

Differential behavioral and molecular alterations upon protracted abstinence from cocaine versus morphine, nicotine, THC and alcohol

Unified theories of addiction are challenged by differing drug-seeking behaviors and neurobiological adaptations across drug classes, particularly for narcotics and psychostimulants. We previously showed that protracted abstinence to opiates leads to despair behavior and social withdrawal in mice, and we identified a transcriptional signature in the extended amygdala that was also present in animals abstinent from nicotine, Δ9-tetrahydrocannabinol (THC) and alcohol. Here we examined whether protracted abstinence to these four drugs would also share common behavioral features, and eventually differ from abstinence to the prototypic psychostimulant cocaine. We found similar reduced social recognition, increased motor stereotypies and increased anxiety with relevant c-fos response alterations in morphine, nicotine, THC and alcohol abstinent mice. Protracted abstinence to cocaine, however, led to strikingly distinct, mostly opposing adaptations at all levels, including behavioral responses, neuronal activation and gene expression. Together, these data further document the existence of common hallmarks for protracted abstinence to opiates, nicotine, THC and alcohol that develop within motivation/emotion brain circuits. In our model, however, these do not apply to cocaine, supporting the notion of unique mechanisms in psychostimulant abuse.

Disruption of GluA2 phosphorylation potentiates stress responsivity

Cocaine addiction is characterized by persistent craving and addicts frequently relapse even after long periods of abstinence. Exposure to stress can precipitate relapse in humans and rodents. Stress and drug use can lead to common alterations in synaptic plasticity and these commonalities may contribute to the ability of stress to elicit relapse. These common changes in synaptic plasticity are mediated, in part, by alterations in the trafficking and stabilization of AMPA receptors. Exposure to both cocaine and stress can lead to alterations in protein kinase C-mediated phosphorylation of GluA2 AMPA subunits and thus alter the trafficking of GluA2-containing AMPARs. However, it is not clear what role AMPAR trafficking plays in the interactions between stress and cocaine. The current study utilized a mouse with a point mutation within the GluA2 subunit c-terminus resulting in a disruption of PKC-mediated GluA2 phosphorylation to examine stress responsivity. Although no differences were seen in the response to a forced swim stress in naïve mice, GluA2 K882A knock-in mice exhibited an increased stress response following cocaine self-administration. Furthermore, we demonstrated that disrupting GluA2 phosphorylation increases vulnerability to stress-induced reinstatement of both cocaine seeking and cocaine-conditioned reward. Finally, GluA2 K882A knock-in mice exhibit an increased vulnerability to social defeat as indicated by increased social avoidance. Taken together these results indicate that disrupting GluA2 phosphorylation leads to increased responsivity to acute stress following cocaine exposure and increased vulnerability to chronic stress. These results highlight the GluA2 phosphorylation site as a novel target for the stress-related disorders.

Adolescent Exposure to the Synthetic Cannabinoid WIN 55212-2 Modifies Cocaine Withdrawal Symptoms in Adult Mice

Chronic cannabinoid consumption is an increasingly common behavior among teenagers and has been shown to cause long-lasting neurobehavioral alterations. Besides, it has been demonstrated that cocaine addiction in adulthood is highly correlated with cannabis abuse during adolescence. Cocaine consumption and subsequent abstinence from it can cause psychiatric symptoms, such as psychosis, cognitive impairment, anxiety, and depression. The aim of the present research was to study the consequences of adolescent exposure to cannabis on the psychiatric-like effects promoted by cocaine withdrawal in adult mice. We pre-treated juvenile mice with the cannabinoid CB1 receptor agonist WIN 55212-2 (WIN) and then subjected them to a chronic cocaine treatment during adulthood. Following these treatments, animals were tested under cocaine withdrawal in the following paradigms: pre-pulse inhibition, object recognition, elevated plus maze, and tail suspension. The long-term psychotic-like actions induced by WIN were not modified after cocaine cessation. Moreover, the memory impairments induced by cocaine withdrawal were not altered by previous adolescent WIN intake. However, WIN pre-treatment prevented the anxiogenic effects observed after cocaine abstinence, and led to greater depressive-like symptoms following cocaine removal in adulthood. This study is the first to show the long-lasting behavioral consequences of juvenile exposure to WIN on cocaine withdrawal in adult mice.

Molecular Pharmacology of δ-Opioid Receptors

Opioids are among the most effective analgesics available and are the first choice in the treatment of acute severe pain. However, partial efficacy, a tendency to produce tolerance, and a host of ill-tolerated side effects make clinically available opioids less effective in the management of chronic pain syndromes. Given that most therapeutic opioids produce their actions via µ-opioid receptors (MOPrs), other targets are constantly being explored, among which δ-opioid receptors (DOPrs) are being increasingly considered as promising alternatives. This review addresses DOPrs from the perspective of cellular and molecular determinants of their pharmacological diversity. Thus, DOPr ligands are examined in terms of structural and functional variety, DOPrs' capacity to engage a multiplicity of canonical and noncanonical G protein-dependent responses is surveyed, and evidence supporting ligand-specific signaling and regulation is analyzed. Pharmacological DOPr subtypes are examined in light of the ability of DOPr to organize into multimeric arrays and to adopt multiple active conformations as well as differences in ligand kinetics. Current knowledge on DOPr targeting to the membrane is examined as a means of understanding how these receptors are especially active in chronic pain management. Insight into cellular and molecular mechanisms of pharmacological diversity should guide the rational design of more effective, longer-lasting, and better-tolerated opioid analgesics for chronic pain management.

Adolescent but not adult ethanol binge drinking modulates cocaine withdrawal symptoms in mice

Background

Ethanol (EtOH) binge drinking is an increasingly common behavior among teenagers that induces long-lasting neurobehavioral alterations in adulthood. An early history of EtOH abuse during adolescence is highly correlated with cocaine addiction in adulthood. Abstinence of cocaine abuse can cause psychiatric symptoms, such as anxiety, psychosis, depression, and cognitive impairments. This study assessed the consequences of adolescent exposure to EtOH on the behavioral alterations promoted by cocaine withdrawal in adulthood.

Methods

We pretreated juvenile (34–47 days old) or adult (68–81 days old) mice with EtOH (1.25 g/kg) following a binge-drinking pattern. Then, after a three-week period without drug delivery, they were subjected to a chronic cocaine treatment in adulthood and tested under cocaine withdrawal by the ensuing paradigms: open field, elevated plus maze, prepulse inhibition, tail suspension test, and object recognition. Another set of mice were treated with the same EtOH binge-drinking procedure during adolescence and were tested immediately afterwards under the same behavioral paradigms.

Results

Adolescent EtOH pretreatment undermined the anxiogenic effects observed after cocaine abstinence, reduced prepulse inhibition, and increased immobility scores in the tail suspension test following cocaine withdrawal. Moreover, the memory deficits evoked by these substances when given separately were enhanced in cocaine-withdrawn mice exposed to EtOH during adolescence. EtOH binge drinking during adolescence also induced anxiety, depressive symptoms, and memory impairments when measured immediately afterwards. In contrast, neither EtOH nor cocaine alone or in combination altered any of these behaviors when given in adulthood.

Conclusions

EtOH binge drinking induces short- and long-term behavioral alterations and modulates cocaine withdrawal symptoms when given in adolescent mice.

Long-lasting memory deficits in mice withdrawn from cocaine are concomitant with neuroadaptations in hippocampal basal activity, GABAergic interneurons and adult neurogenesis

Cocaine addiction disorder is notably aggravated by concomitant cognitive and emotional pathology that impedes recovery. We studied whether a persistent cognitive/emotional dysregulation in mice withdrawn from cocaine holds a neurobiological correlate within the hippocampus, a limbic region with a key role in anxiety and memory but that has been scarcely investigated in cocaine addiction research. Mice were submitted to a chronic cocaine (20 mg/kg/day for 12 days) or vehicle treatment followed by 44 drug-free days. Some mice were then assessed on a battery of emotional (elevated plus-maze, light/dark box, open field, forced swimming) and cognitive (object and place recognition memory, cocaine-induced conditioned place preference, continuous spontaneous alternation) behavioral tests, while other mice remained in their home cage. Relevant hippocampal features [basal c-Fos activity, GABA⁺, parvalbumin (PV)⁺ and neuropeptide Y (NPY)⁺ interneurons and adult neurogenesis (cell proliferation and immature neurons)] were immunohistochemically assessed 73 days after the chronic cocaine or vehicle protocol. The cocaine-withdrawn mice showed no remarkable exploratory or emotional alterations but were consistently impaired in all the cognitive tasks. All the cocaine-withdrawn groups, independent of whether they were submitted to behavioral assessment or not, showed enhanced basal c-Fos expression and an increased number of GABA⁺ cells in the dentate gyrus. Moreover, the cocaine-withdrawn mice previously submitted to behavioral training displayed a blunted experience-dependent regulation of PV⁺ and NPY⁺ neurons in the dentate gyrus, and neurogenesis in the hippocampus. Results highlight the importance of hippocampal neuroplasticity for the ingrained cognitive deficits present during chronic cocaine withdrawal.

Study of the effects of controlled morphine administration for treatment of anxiety, depression and cognition impairment in morphine-addicted rats

Background:

Morphine dependency usually results in undesired outcomes such as anxiety, depression, and cognitive alterations. In this study, morphine was used to manage morphine dependence-induced anxiety, depression, and learning and memory disturbances.

Materials and Methods:

Forty rats were divided equally into five groups. Group 1 received saline for 21 days. Groups 2–5 were dependent by increasing administration of morphine (15–45 mg/kg) for 7 days. For the next 14 days, morphine was administered as the following regimen: Group 2: once daily; 45 mg/kg (positive controls), Group 3: the same dose with an increasing interval (6 h longer than the previous intervals each time), Group 4: the same dose with an irregular intervals (12, 24, 36 h intervals interchangeably), and Group 5: decreasing doses once daily (every time 2.5 mg/kg less than the former dosage). On days 22–26, elevated plus maze (EPM), open field test (OFT), forced swim test (FST), and tail suspension test (TST) were performed to investigate anxiety level and depression in animals. Between 17^th and 21^st days, Morris water maze (MWM) was used to evaluate the spatial learning and memory.

Results:

Chronic morphine administration caused depression and anxiety as observed by FST, EPM, and TST and decreased motor activity in OFT and caused impairment in learning and memory performance in MWM. Treatment with our protocol as increasing interval, irregular interval, and decreasing dosage of morphine caused marked reduction in depression, anxiety, and improved cognition performance compared with positive control group; and attenuated motor deficits in morphine-dependent rats, remarkably.

Conclusions:

Change in dosage regimens of morphine can reduce morphine-induced anxiety, depression, and cognitive impairments.

Localization of the delta opioid receptor and corticotropin-releasing factor in the amygdalar complex: role in anxiety

It is well established that central nervous system norepinephrine (NE) and corticotropin-releasing factor (CRF) systems are important mediators of behavioral responses to stressors. More recent studies have defined a role for delta opioid receptors (DOPR) in maintaining emotional valence including anxiety. The amygdala plays an important role in processing emotional stimuli, and has been implicated in the development of anxiety disorders. Activation of DOPR or inhibition of CRF in the amygdala reduces baseline and stress-induced anxiety-like responses. It is not known whether CRF- and DOPR-containing amygdalar neurons interact or whether they are regulated by NE afferents. Therefore, this study sought to better define interactions between the CRF, DOPR and NE systems in the basolateral (BLA) and central nucleus of the amygdala (CeA) of the male rat using anatomical and functional approaches. Irrespective of the amygdalar subregion, dual immunofluorescence microscopy showed that DOPR was present in CRF-containing neurons. Immunoelectron microscopy confirmed that DOPR was localized to both dendritic processes and axon terminals in the BLA and CeA. Semi-quantitative dual immunoelectron microscopy analysis of gold-silver labeling for DOPR and immunoperoxidase labeling for CRF revealed that 55 % of the CRF neurons analyzed contained DOPR in the BLA while 67 % of the CRF neurons analyzed contained DOPR in the CeA. Furthermore, approximately 41 % of DOPR-labeled axon terminals targeted BLA neurons that expressed CRF while 29 % of DOPR-labeled axon terminals targeted CeA neurons that expressed CRF. Triple label immunofluorescence microscopy revealed that DOPR and CRF were co-localized in common cellular profiles that were in close proximity to NE-containing fibers in both subregions. These anatomical results indicate significant interactions between DOPR and CRF in this critical limbic region and reveal that NE is poised to regulate these peptidergic systems in the amygdala. Functional studies were performed to determine if activation of DOPR could inhibit the anxiety produced by elevation of NE in the amygdala using the pharmacological stressor yohimbine. Administration of the DOPR agonist, SNC80, significantly attenuated elevated anxiogenic behaviors produced by yohimbine as measured in the rat on the elevated zero maze. Taken together, results from this study demonstrate the convergence of three important systems, NE, CRF, and DOPR, in the amygdala and provide insight into their functional role in modulating stress and anxiety responses.

Resveratrol fails to affect cocaine conditioned place preference behavior, but alleviates anxiety-like behaviors in cocaine withdrawn rats

RATIONALE

Resveratrol participates in regulating abnormal behaviors in psychostimulant-exposed animals.

OBJECTIVES

To examine effects of resveratrol on relapse and anxiety-like behaviors in cocaine withdrawn rats and to investigate possible molecular mechanisms underlying resveratrol effects in hippocampus (HP) and prefrontal cortex (PFC).

METHODS

Conditioned place preference (CPP) assay and elevated plus maze (EPM) test were used to examine cocaine CPP behavior and anxiety-like behaviors in rats, respectively. Resveratrol was administrated to cocaine withdrawn rats. Levels of MDA, GSH and SOD were examined to evaluate oxidative status, and levels of IL-6, IL-1β and TNF α were measured to examine inflammatory status and levels of caspase-3 and BAX was examined to evaluate apoptotic status in HP and PFC. SIRT expression was also examined here.

RESULTS

Resveratrol did not affect cocaine CPP behaviors, but attenuated anxiety-like behaviors in cocaine withdrawn rats. Levels of MDA and TNFα in PFC, and levels of MDA, SOD, GSH, IL-6, IL-1β, TNFα, caspase-3 and BAX in HP, but not SIRT1 expression in both regions were significantly changed during cocaine withdrawal period. Except SOD, resveratrol reversed above neurochemical changes induced by cocaine withdrawal. Furthermore, RSV induced a greater upregulation of SIRT1 expression in PFC in cocaine withdrawn rats than that in saline controls.

CONCLUSIONS

Current findings suggest that resveratrol may influence behaviors in cocaine withdrawn rats. Oxidative stress, inflammation, apoptosis, and SIRT1 signaling pathway in HP or PFC might be involved in mediating effects of RSV on behaviors in cocaine withdrawn rats.

Synergistic antidepressant-like effects between a kappa opioid antagonist (LY2444296) and a delta opioid agonist (ADL5859) in the mouse forced swim test

Kappa opioid (KOP) receptor antagonists and delta opioid (DOP) receptor agonists have antidepressant-like effects in animal tests and may be useful for treatment-resistant depression in humans. In this study, we examined whether the combination of a KOP receptor antagonist and a DOP receptor agonist would produce a better than additive effect (i.e. synergy). LY2444296 is a short-acting selective nonpeptide KOP receptor antagonist. ADL5859 is a selective nonpeptide DOP receptor agonist which does not produce seizures and EEG disturbances. Each compound and combinations of the two were examined in the forced swim test (FST) one h post injection, a screening test for antidepressant-like effect, in male adult C57BL/6J mice (Jackson Lab). LY2444296 [subcutaneous (s.c.) injection] at 10 and 30mg/kg, but not 3mg/kg, significantly decreased immobility time in a dose-dependent manner. Intraperitoneal (i.p.) injections of ADL5859 also reduced immobility time dose-dependently at doses of 3 and 10mg/kg, but not at 1mg/kg. An analysis was conducted using the method of Tallarida and Raffa (2010), which employed dose equivalence. The relative potency of the drugs was determined to be LY2444296: ADL5859=1:0.28, which was the dose ratio for combination studies. Six combinations of the two compounds were tested in mice at a fixed dose ratio. We found that LY2444296 and ADL5859 yielded significant synergistic effects for the antidepressant-like effect at the combined dose ranging from 3.84mg/kg to 9.0mg/kg. ADL5859 (10mg/kg), LY2444296 (30mg/kg) and their combined dose (3.84mg/kg) had no effects on locomotor activities. Since the two drugs have distinct pharmacological profiles, such a synergism will allow use of lower doses of both drugs to achieve desired antidepressant effects with fewer side effects.

Substance use modulates stress reactivity: Behavioral and physiological outcomes

Drug addiction is a major public health concern in the United States costing taxpayers billions in health care costs, lost productivity and law enforcement. However, the availability of effective treatment options remains limited. The development of novel therapeutics will not be possible without a better understanding of the addicted brain. Studies in both clinical and preclinical models indicate that chronic drug use leads to alterations in the body and brain's response to stress. Dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis may shed light on the ability of stress to increase vulnerability to relapse. Further, within both the HPA axis and limbic brain regions, corticotropin-releasing factor (CRF) is critically involved in the brain's response to stress. Alterations in both central and peripheral CRF activity seen following chronic drug use provide a mechanism by which substance use can alter stress reactivity, thus mediating addictive phenotypes. While many reviews have focused on how stress alters drug-mediated changes in physiology and behavior, the goal of this review is to focus on how substance use alters responses to stress.

Strain and cocaine-induced differential opioid gene expression may predispose Lewis but not Fischer rats to escalate cocaine self-administration

The aim of the present study was to investigate alterations in gene expression of opioid system components induced by extended access (18 h) cocaine self-administration and to determine the impact of genetic background in the vulnerability to escalate cocaine intake. Comparing two inbred rat strains, we previously reported that Lewis rats progressively escalated cocaine consumption compared to Fischer rats, in a new translational model of intravenous cocaine self-administration, which included 14 sessions of 18-h operant sessions in which rats were allowed to select the cocaine unit dose to self-administer. We compare here Fischer and Lewis rats in the gene expression of endogenous opioid peptides (Pomc, Penk, Pdyn) and cognate receptors (Oprm, Oprk and Oprd) in reward-related brain regions, after exposure to either cocaine self-administration or yoked-saline, in the aforementioned translational paradigm. We performed a correlation analysis between the mRNA level, found in the Dorsal Striatum (DS), Nucleus accumbens (NAcc) shell and core respectively, and individual cocaine intake. Our findings show that the gene expression of all the aforementioned opioid genes exhibit strain-dependent differences in the DS, in absence of cocaine exposure. Also, different strain-specific cocaine-induced mRNA expression of Oprm and Oprk was found in DS. Only few differences were found in the ventral parts of the striatum. Moreover, gene expression level of Pdyn, Penk, Oprk, and Oprm in the DS was significantly correlated with cocaine intake only in Fischer rats. Overall, these data shed light on potential genetic differences which may predispose of subjects to initiate and escalate cocaine consumption.

The Effects of 4-Methylethcathinone on Conditioned Place Preference, Locomotor Sensitization, and Anxiety-Like Behavior: A Comparison with Methamphetamine

BACKGROUND

4-Methylethcathinone is a drug that belongs to the second generation of synthetic cathinones, and recently it has been ranked among the most popular "legal highs". Although it has similar in vitro neurochemical actions to other drugs such as cocaine, the behavioral effects of 4-methylethcathinone remain to be determined.

METHODS

The addictive potential and locomotor potentiation by 4-methylethcathinone were investigated in rats using the conditioned place preference and sensitization paradigm. Methamphetamine was used as a positive control. Because synthetic cathinones can have psychological effects, we also examined anxiety-like behavior using the elevated plus maze.

RESULTS

A conditioning dose of 10 mg/kg 4-methylethcathinone was able to induce conditioned place preference and reinstatement (following 2 weeks of withdrawal). Acute or repeated injections of 4-methylethcathinone at 3 or 10mg/kg failed to alter locomotor activity. At 30 mg/kg, however, acute 4-methylethcathinone increased locomotor activity compared with saline, while chronic 4-methylethcathinone induced a delayed and attenuated sensitization compared with methamphetamine. Additionally, repeated daily injections of 4-methylethcathinone (30 mg/kg) reduced, whereas methamphetamine increased time spent by rats in the open arm of an elevated plus maze compared with saline injections. Interestingly, a 2-week withdrawal period following chronic injections of 4-methylethcathinone or methamphetamine increased time spent in the open arm in all rats.

CONCLUSIONS

The rewarding properties of 4-methylethcathinone were found to be dissociated from its effects on locomotor activity. Additionally, chronic 4-methylethcathinone use may trigger abnormal anxious behaviors. These behavioral effects caused by 4-methylethcathinone appear to last even after a withdrawal period.

Cocaine-induced locomotor sensitization in rats correlates with nucleus accumbens activity on manganese-enhanced MRI

A long-standing goal of substance abuse research has been to link drug-induced behavioral outcomes with the activity of specific brain regions to understand the neurobiology of addiction behaviors and to search for drug-able targets. Here, we tested the hypothesis that cocaine produces locomotor (behavioral) sensitization that correlates with increased calcium channel-mediated neuroactivity in brain regions linked with drug addiction, such as the nucleus accumbens (NAC), anterior striatum (AST) and hippocampus, as measured using manganese-enhanced MRI (MEMRI). Rats were treated with cocaine for 5 days, followed by a 2-day drug-free period. The following day, locomotor sensitization was quantified as a metric of cocaine-induced neuroplasticity in the presence of manganese. Immediately following behavioral testing, rats were examined for changes in calcium channel-mediated neuronal activity in the NAC, AST, hippocampus and temporalis muscle, which was associated with behavioral sensitization using MEMRI. Cocaine significantly increased locomotor activity and produced behavioral sensitization compared with saline treatment of control rats. A significant increase in MEMRI signal intensity was determined in the NAC, but not AST or hippocampus, of cocaine-treated rats compared with saline-treated control rats. Cocaine did not increase signal intensity in the temporalis muscle. Notably, in support of our hypothesis, behavior was significantly and positively correlated with MEMRI signal intensity in the NAC. As neuronal uptake of manganese is regulated by calcium channels, these results indicate that MEMRI is a powerful research tool to study neuronal activity in freely behaving animals and to guide new calcium channel-based therapies for the treatment of cocaine abuse and dependence.

Evaluating Exercise as a Therapeutic Intervention for Methamphetamine Addiction-Like Behavior

The need for effective treatments for addiction and dependence to the illicit stimulant methamphetamine in primary care settings is increasing, yet no effective medications have been FDA approved to reduce dependence [1]. This is partially attributed to the complex and dynamic neurobiology underlying the various stages of addiction [2]. Therapeutic strategies to treat methamphetamine addiction, particularly the relapse stage of addiction, could revolutionize methamphetamine addiction treatment. In this context, preclinical studies demonstrate that voluntary exercise (sustained physical activity) could be used as an intervention to reduce methamphetamine addiction. Therefore, it appears that methamphetamine disrupts normal functioning in the brain and this disruption is prevented or reduced by engaging in exercise. This review discusses animal models of methamphetamine addiction and sustained physical activity and the interactions between exercise and methamphetamine behaviors. The review highlights how methamphetamine and exercise affect neuronal plasticity and neurotoxicity in the adult mammalian striatum, hippocampus, and prefrontal cortex, and presents the emerging mechanisms of exercise in attenuating intake and in preventing relapse to methamphetamine seeking in preclinical models of methamphetamine addiction.

Sex differences in morphine-induced behavioral sensitization and social behaviors in ICR mice

Gender and genetic strain are two prominent variants that influence drug abuse. Although certain sex-related behavioral responses have been previously characterized in ICR mice, little is known about the effects of sex on morphine-induced behavioral responses in this outbred strain. Therefore, in this study, we investigated the sex differences of morphine-induced locomotion, anxiety-like and social behaviors in ICR mice. After morphine or saline exposure for four consecutive days (twice daily), increased locomotion, more time spent in the central area, as well as attenuated rearing and self-grooming behaviors were found in morphine-treated females in an open field; no differences were found in locomotion and the time spent in the central area between male and female controls. When interacting with the same-sex individuals, female controls were engaged in more social investigation, following, body contacting and self-grooming behaviors than controls; morphine exposure reduced contacting and self-grooming behaviors in females; in contrast, these effects were not found in males. These results indicate that female ICR mice are more prosocial and are more susceptible to morphine exposure than males.

Hippocampal cell fate regulation by chronic cocaine during periods of adolescent vulnerability: Consequences of cocaine exposure during adolescence on behavioral despair in adulthood

Given that adolescence represents a critical moment for shaping adult behavior and may predispose to disease vulnerability later in life, the aim of this study was to find a vulnerable period during adolescence in which hippocampal cell fate regulation was altered by cocaine exposure, and to evaluate the long-term consequences of a cocaine experience during adolescence in affecting hippocampal plasticity and behavioral despair in adulthood. Study I: Male rats were treated with cocaine (15mg/kg, i.p.) or saline for 7 consecutive days during adolescence (early post-natal day (PND) 33-39, mid PND 40-46, late PND 47-53). Hippocampal plasticity (i.e., cell fate regulation, cell genesis) was evaluated 24h after the last treatment dose during the course of adolescence (PND 40, PND 47, PND 54). Study II: The consequences of cocaine exposure during adolescence (PND 33-39 or PND 33-46; 7 or 14days) were measured in adulthood at the behavioral (i.e., forced swim test, PND 62-63) and molecular (hippocampal cell markers, PND 64) levels. Chronic cocaine during early adolescence dysregulated FADD forms only in the hippocampus (HC), as compared to other brain regions, and during mid adolescence, impaired cell proliferation (Ki-67) and increased PARP-1 cleavage (a cell death maker) in the HC. Interestingly, chronic cocaine exposure during adolescence did not alter the time adult rats spent immobile in the forced swim test. These results suggest that this paradigm of chronic cocaine administration during adolescence did not contribute to the later manifestation of behavioral despair (i.e., one pro-depressive symptom) as measured by the forced swim test in adulthood.

Enkephalin analog, cyclo[N(ε),N(β)-carbonyl-D-Lys(2),Dap(5)] enkephalinamide (cUENK6), inhibits the ethanol withdrawal-induced anxiety-like behavior in rats

An analog of enkephalin, cyclo[N(ε),N(β)-carbonyl-D-Lys(2),Dap(5)] enkephalinamide (cUENK6), is predominantly a functional agonist of μ-opioid receptors (MOPr) and, to a lesser extent, of δ-opioid receptors (DOPr) in vitro. The aim of the present study was to determine whether cUENK6 could affect ethanol withdrawal-induced anxiety-like behavior in the elevated plus maze (EPM) test in rats. An anxiety-like effect of withdrawal was predicted to occur in the EPM test 24 h after the last ethanol administration (2 g/kg, intraperitoneally [i.p.]; 15% w/v once daily for 9 days). Ethanol withdrawal decreased the percent of time spent by rats in the open arms and the percent of open-arms entries. cUENK6 (0.25 nmol), given by intracerebroventricular (i.c.v.) injection, significantly reversed these anxiety-like effects of ethanol withdrawal and elevated the percent of time spent by rats in the open arms and the percent of open-arms entries. These effects of cUENK6 were significantly inhibited by the DOPr antagonist naltrindole (NTI) (5 nmol, i.c.v.), but not by the MOPr antagonist β-funaltrexamine (β-FNA) (5 nmol, i.c.v.). The preferential DOPr agonist [Leu(5)]-enkephalin (LeuEnk) (2.7 and 5.4 nmol, i.c.v.) and the MOPr agonist morphine (6.5 and 13 nmol, i.c.v.) reduced the anxiety-like effects of ethanol withdrawal. cUENK6 at the dose of 0.25 nmol did not disturb locomotor activity in the EPM, in contrast to cUENK6 at the dose of 0.5 nmol, and morphine at 6.5 and 13 nmol. However, similarly to LeuEnk, cUENK6 induced the anxiolytic-like effects in naïve rats. Thus, our study suggests that cUENK6 reduced ethanol withdrawal-induced anxiety-like behavior by activation of δ-opioid receptors rather than μ-opioid receptors.

Differences in cocaine-induced place preference persistence, locomotion and social behaviors between C57BL/6J and BALB/cJ mice

C57BL/6J and BALB/cJ mice display significant differences in sociability and response to drugs, but the phenotypic variability of their susceptibility to cocaine is still not well known. In this study, the differences between these two mice strains in the persistence of cocaine-induced conditioned place preference (CPP), as well as the locomotion and social behaviors after the 24-hour withdrawal from a four-day cocaine (20 mg/kg/day) administration were investigated. The results showed that the cocaine-induced CPP persisted over two weeks in C57BL/6J mice, while it diminished within one week among BALB/cJ mice. After 24-hours of cocaine withdrawal, high levels of locomotion as well as low levels of social interaction and aggressive behavior were found in C57BL/6J mice, but no significant changes were found in BALB/cJ mice, indicating that cocaine-induced CPP persistence, locomotion and social behavior are not consistent between these two strains, and that overall C57BL/6J mice are more susceptible to cocaine than BALB/cJ mice at the tested doses.

Dorsal raphe 5-HT(2C) receptor and GABA networks regulate anxiety produced by cocaine withdrawal

The serotonin system is intimately linked to both the mediation of anxiety and long-term effects of cocaine, potentially through interaction of inhibitory 5-HT2C receptor and gamma-aminobutyric acid (GABA) networks. This study characterized the function of the dorsal raphe (DR) 5-HT2C receptor and GABA network in anxiety produced by chronic cocaine withdrawal. C57BL/6 mice were injected with saline or cocaine (15 mg/kg) 3 times daily for 10 days, and tested on the elevated plus maze 30 min, 25 h, or 7 days after the last injection. Cocaine-withdrawn mice showed heightened anxiety-like behavior at 25 h of withdrawal, as compared to saline controls. Anxiety-like behavior was not different when mice were tested 30 min or 7 days after the last cocaine injection. Electrophysiology data revealed that serotonin cells from cocaine-withdrawn mice exhibited increased GABA inhibitory postsynaptic currents (IPSCs) in specific DR subregions dependent on withdrawal time (25 h or 7 d), an effect that was absent in cells from non-withdrawn mice (30 min after the last cocaine injection). Increased IPSC activity was restored to baseline levels following bath application of the 5-HT2C receptor antagonist, SB 242084. In a separate cohort of cocaine-injected mice at 25 h of withdrawal, both global and intra-DR blockade of 5-HT2C receptors prior to elevated plus maze testing attenuated anxiety-like behavior. This study demonstrates that DR 5-HT2C receptor blockade prevents anxiety-like behavior produced by cocaine withdrawal, potentially through attenuation of heightened GABA activity, supporting a role for the 5-HT2C receptor in mediating anxiety produced by cocaine withdrawal.

Stress rapidly dysregulates the glutamatergic synapse in the prefrontal cortex of cocaine-withdrawn adolescent rats

Although several lines of evidence have shown that chronic cocaine use is associated with stress system dysregulation, the underlying neurochemical mechanisms are still elusive. To investigate whether the rapid stress-induced response of the glutamatergic synapse was influenced by a previous history of cocaine, rats were exposed to repeated cocaine injections during adolescence [from postnatal day (PND) 28-42], subjected to a single swim stress (5 minutes) three days later (PND 45) and sacrificed 15 minutes after the end of this stressor. Critical determinants of glutamatergic homeostasis were measured in the medial prefrontal cortex (mPFC) whereas circulating corticosterone levels were measured in the plasma. Exposure to stress in saline-treated animals did not show changes in the crucial determinants of the glutamatergic synapse. Conversely, in cocaine-treated animals, stress dynamically altered the glutamatergic synapse by: (1) enhancing the presynaptic vesicular mediators of glutamate release; (2) reducing the transporters responsible for glutamate clearance; (3) increasing the postsynaptic responsiveness of the N-methyl-D-aspartate subunit GluN1; and (4) causing hyperresponsive spines as evidenced by increased activation of the postsynaptic cdc42-Pak pathway. These findings indicate that exposure to cocaine during adolescence sensitizes mPFC glutamatergic synapses to stress. It is suggested that changes in glutamatergic signaling may contribute to the increased sensitivity to stress observed in cocaine users. Moreover, glutamatergic processes may play an important role in stress-induced reinstatement of cocaine seeking.

Serotonergic responses to stress are enhanced in the central amygdala and inhibited in the ventral hippocampus during amphetamine withdrawal

Withdrawal from amphetamine increases anxiety and reduces the ability to cope with stress, which are factors that are believed to contribute to drug relapse. Stress-induced serotonergic transmission in the central nucleus of the amygdala is associated with anxiety states and fear. Conversely, stress-induced increases in ventral hippocampal serotonin (5-HT) levels have been linked to coping mechanisms. The goal of this study was to investigate the neurobiological changes induced by amphetamine that contribute to stress sensitivity during withdrawal. We tested the hypothesis that limbic serotonergic responses to restraint stress would be altered in male Sprague-Dawley rats chronically pretreated with amphetamine (2.5 mg/kg, intraperitoneal) and then subjected to 2 weeks of withdrawal. Amphetamine withdrawal resulted in increased stress-induced behavioral arousal relative to control treatment, suggesting that drug withdrawal induced greater sensitivity to the stressor. When microdialysis was used to determine the effects of restraint on extracellular 5-HT, stress-induced increases in 5-HT levels were abolished in the ventral hippocampus and augmented in the central amygdala during amphetamine withdrawal. Reverse dialysis of the glucocorticoid receptor antagonist mifepristone into the ventral hippocampus blocked the stress-induced increase in 5-HT levels in saline-pretreated rats, suggesting that glucocorticoid receptors mediate stress-induced increases in 5-HT levels in the ventral hippocampus. However, mifepristone had no effect on stress-induced increases in 5-HT levels in the central amygdala, indicating that stress increases 5-HT levels in this region independently of glucocorticoid receptors. During amphetamine withdrawal, the absence of stress-induced increases in ventral hippocampal 5-HT levels combined with enhanced stress-induced serotonergic responses in the central amygdala may contribute to drug relapse by decreasing stress-coping ability and heightening stress responsiveness.

Individual differences in cocaine addiction: maladaptive behavioural traits

Cocaine use leads to addiction in only a subset of individuals. Understanding the mechanisms underlying these individual differences in the transition from cocaine use to cocaine abuse is important to develop treatment strategies. There is agreement that specific behavioural traits increase the risk for addiction. As such, both high impulsivity and high anxiety have been reported to predict (compulsive) cocaine self-administration behaviour. Here, we set out a new view explaining how these two behavioural traits may affect addictive behaviour. According to psychological and psychiatric evolutionary views, organisms flourish well when they fit (match) their environment by trait and genotype. However, under non-fit conditions, the need to compensate the failure to deal with this environment increases, and, as a consequence, the functional use of rewarding drugs like cocaine may also increase. It suggests that neither impulsivity nor anxiety are bad per se, but that the increased risk to develop cocaine addiction is dependent on whether behavioural traits are adaptive or maladaptive in the environment to which the animals are exposed. This 'behavioural (mal)adaptation view' on individual differences in vulnerability to cocaine addiction may help to improve therapies for addiction.