Regulation of learned fear expression through the MgN-amygdala pathway.

Heightened fear responding is characteristic of fear- and anxiety-related disorders, including post-traumatic stress disorder. Neural plasticity in the amygdala is essential for both initial fear learning and fear expression, and strengthening of synaptic connections between the medial geniculate nucleus (MgN) and amygdala is critical for auditory fear learning. However, very little is known about what happens in the MgN-amygdala pathway during fear recall and extinction, in which conditional fear decreases with repeated presentations of the auditory stimulus alone. In the present study, we found that optogenetic inhibition of activity in the MgN-amygdala pathway during fear retrieval and extinction reduced expression of conditional fear. While this effect persisted for at least two weeks following pathway inhibition, it was specific to the context in which optogenetic inhibition occurred, linking MgN-BLA inhibition to facilitation of extinction-like processes. Reduced fear expression through inhibition of the MgN-amygdala pathway was further characterized by similar synaptic expression of GluA1 and GluA2 AMPA receptor subunits compared to what was seen in controls. Inhibition also decreased CREB phosphorylation in the amygdala, similar to what has been reported following auditory fear extinction. We then demonstrated that this effect was reduced by inhibition of GluN2B-containing NMDA receptors. These results demonstrate a new and important role for the MgN-amygdala pathway in extinction-like processes, and show that suppressing activity in this pathway results in a persistent decrease in fear behavior.

Hypericum perforatum L. prevents the acquisition of and promotes resilience against stress-induced reinstatement of the conditioned place preference induced by cocaine.

Cocaine use disorder is a serious problem worldwide, and there are no approved medications for its treatment. A novel approach to the treatment of drug addiction is the use of natural products, and, in this context, preclinical evidence suggests that Hypericum perforatum L. (Hypericum) is effective against alcohol and other substance use disorders. We hypothesised that Hypericum could also be useful as a treatment for cocaine use disorder, and so we set out to test its effectiveness in a mice model of cocaine addiction. In the first experiment we evaluated its effects on the acquisition of cocaine-induced conditioned place preference (CPP). Adult male mice were conditioned with cocaine (25 mg/kg), cocaine with Hypericum (75, 150 or 300 mg/kg) or the plant extract alone (300 mg/kg). In the second experiment, we tested the effects of Hypericum on stress-induced reinstatement of cocaine CPP. All the mice were conditioned with cocaine (25 mg/kg) and, after extinction of CPP, the reinstating effects of social defeat (alone or with 75, 150 or 300 mg/kg of Hypericum) were evaluated. All the doses of Hypericum prevented the acquisition of cocaine-induced CPP. Furthermore, the plant extract dose-dependently reduced the reinstating effects of social defeat. Therefore, Hypericum is effective in reducing the rewarding effects of cocaine and prevents the stress-induced reinstatement of cocaine CPP in mice. The mechanisms underlying these positive effects of Hypericum perforatum L. need to be determined by future research. Our results endorse Hypericum as a natural treatment for cocaine dependence.

Brd4 participates in epigenetic regulation of the extinction of remote auditory fear memory.

BACKGROUND: Inaccurate fear memories can be maladaptive and potentially portrait a core symptomatic dimension of fear adaptive disorders such as post-traumatic stress disorder (PTSD), which is generally characterized by an intense and enduring memory for the traumatic events. Evidence exists in support of epigenetic regulation of fear behavior. Brd4, a member of the bromodomain and extra-terminal domain (BET) protein family, serves as a chromatin "reader" by binding to histones in acetylated lysine residues, and hence promotes transcriptional activities. However, less is known whether Brd4 participates in modulating cognitive activities especially memory formation and extinction. Here we provide evidence for a role of Brd4 in modulation of auditory fear memory. Auditory fear conditioning resulted in a biphasic Brd4 activation in the anterior cingulate cortex (ACC) and hippocampus of adult mice. Thus, Brd4 phosphorylation occurred 6 h and 3-14 days, respectively, after auditory fear conditioning. Systemic inhibition of Brd4 with a BET inhibitor, JQ1, impaired the extinction of remote (i.e., 14 days after conditioning) fear memory. Further, conditional Brd4 knockout in excitatory neurons of the forebrain impaired remote fear extinction as observed in the JQ1-treated mice. Herein, we identified that Brd4 is essential for extinction of remote fear in rodents. These results thus indicate that Brd4 potentially plays a role in the pathogenesis of PTSD.

Effects of Compound 511 on BDNF-TrkB Signaling in the Mice Ventral Tegmental Area in Morphine-Induced Conditioned Place Preference.

Compound 511 (511) is specially developed for opioid addiction treatment based on the Ancient Chinese drug rehabilitation literature, and its composition has profound effects in the treatment of drug addiction in various clinical trials and animal experiments. The effect of 511 on the rewarding properties of morphine and craving responses and its potential mechanisms remain unclear. Here, we have applied a conditioned place preference (CPP) paradigm in mice to measure morphine-induced rewarding effects under the treatment of 511. Then we used the RNA sequencing strategy to screen its potential mechanisms. In our research, firstly, we found 511 could decrease CPP score, locomotor activity, self-administration, jumping behavior, weight loss, wet-dog shakes, and stereotyped behavior. Then the brain VTA region tissues were performed mRNA sequencing to detect potential mechanisms. We found the brain-derived neurotrophic factor (BDNF) and tropomyosin-related kinase B (TrkB) were downregulated in morphine-induced CPP, whereas the decreased BDNF and TrkB were reversed after 511 treatment. We retested the levels of BDNF and TrkB using qRT-PCR and Western blot and found the similar results to mRNA sequencing. It has been widely reported that BDNF-TrkB signaling in the VTA is involved in multiple facets of addiction, including reward and motivation, so we focused on the BDNF-TrkB signaling to investigate the anti-addiction mechanisms of 511 in morphine addiction mice. We studied the downstream pathway of BDNF-TrkB and the soma size of dopaminergic neurons. The results showed 511 could increase the phosphorylation levels of PI3K and AKT, which were decreased in morphine-induced CPP. Simultaneously, 511 could decrease the level of PLCγ1 and the phosphorylation levels of ERK and S6K, which were increased in morphine-induced CPP. In addition, 511 also enlarged the soma size of VTA dopaminergic neurons, which was reduced in morphine-induced CPP. Hence, our research indicated 511 maybe mediate the BDNF-TrkB signaling in VTA to improve morphine addiction behavior.

Cross-reinstatement of mitragynine and morphine place preference in rats.

Kratom is a medicinal plant that exhibits promising results as an opiate substitute. However, there is little information regarding the abuse profile of its main psychoactive constituent, mitragynine (MG), particularly in relapse to drug abuse. Using the place conditioning procedure as a model of relapse, this study aims to evaluate the ability of MG to induce conditioned place preference (CPP) reinstatement in rats. To evaluate the cross-reinstatement effects, MG and morphine were injected to rats that previously extinguished a morphine- or MG-induced CPP. Following a CPP acquisition induced by either MG (10 and 30 mg/kg, i.p.) or morphine (10 mg/kg, i.p.), rats were subjected to repeated CPP extinction sessions. A low dose priming injection of MG or morphine produced a reinstatement of the previously extinguished CPP. In the second experiment of this study, a priming injection of morphine (1, 3 and 10 mg/kg, i.p.) dose-dependently reinstated an MG-induced CPP. Likewise, a priming injection of MG (3, 10 and 30 mg/kg, i.p.) was able to dose-dependently reinstate a morphine-induced CPP. The present study demonstrates a cross-reinstatement effect between MG and morphine, thereby suggesting a similar interaction in their rewarding motivational properties. The findings from this study also suggesting that a priming exposure to kratom and an opioid may cause relapse for a previously abused drug.

Inhibition of monoacylglycerol lipase reduces nicotine reward in the conditioned place preference test in male mice.

Nicotine, the primary psychoactive component in tobacco, plays a major role in the initiation and maintenance of tobacco dependence and addiction, a leading cause of preventable death worldwide. An essential need thus exists for more effective pharmacotherapies for nicotine-use cessation. Previous reports suggest that pharmacological and genetic blockade of CB1 receptors attenuate nicotine reinforcement and reward; while exogenous agonists enhanced these abuse-related behaviors. In this study, we utilized complementary genetic and pharmacologic approaches to test the hypothesis that increasing the levels of the endocannabinoid 2-arachindonoylglycerol (2-AG), will enhance nicotine reward by stimulating neuronal CB1 receptors. Contrary to our hypothesis, we found that inhibition of monoacylglycerol lipase (MAGL), the primary catabolic enzyme of 2-AG, attenuates nicotine conditioned place preference (CPP) in mice, through a non-CB1 receptor-mediated mechanism. MAGL inhibition did not alter palatable food reward or Lithium Chloride (LiCl) aversion. In support of our findings, repeated MAGL inhibition did not induce a reduction in CB1 brain receptor levels or hinder function. To explore the potential mechanism of action, we investigated if MAGL inhibition affected other fatty acid levels in our CPP paradigm. Indeed, MAGL inhibition caused a concomitant decrease in arachidonic acid (AA) levels in various brain regions of interest, suggesting an AA cascade-dependent mechanism. This idea is supported by dose-dependent attenuation of nicotine preference by the selective COX-2 inhibitors valdecoxib and LM-4131. Collectively, these findings, along with our reported studies on nicotine withdrawal, suggest that inhibition of MAGL represents a promising new target for the development of pharmacotherapies to treat nicotine dependence.

Convolvulus pluricaulis extract can modulate synaptic plasticity in rat brain hippocampus.

The memory-boosting property of Indian traditional herb, Convolvulus pluricaulis, has been documented in literature; however, its effect on synaptic plasticity has not yet been reported. Two important forms of synaptic plasticity known to be involved in the processes of memory formation are long-term potentiation (LTP) and long-term depression (LTD). In the present study, the effect of C. pluricaulis plant extract on LTP and LTD were evaluated. The adult male Wistar rats were fed orally with 250, 500 and 1000 mg/kg of this extract for 4 weeks and the effect was determined on LTP and LTD in the Schaffer collaterals of the hippocampal cornu ammonis region CA1. We found that the 500 mg/kg dose of the extract could significantly enhance LTP compared to the vehicle treated ones. Moreover, the same dose could also reduce LTD while used in a separate set of animals. Also, a fresh group of animals treated with the effective dose (500 mg/kg) of plant extract were examined for memory retention in two behavioral platforms namely, contextual fear conditioning (CFC) and novel object recognition test (NORT). Increased fear response to the conditioned stimulus and enhanced recognition of objects were observed in CFC and NORT, respectively, both indicating strengthening of memory. Following up, ex-vivo electrophysiology experiments were performed with the active single molecule scopoletin, present in C. pluricaulis extract and similar patterns in synaptic plasticity changes were obtained. These findings suggest that prolonged treatment of C. pluricaulis extract, at a specific dose in healthy animals, can augment memory functions by modulating hippocampal plasticity.

Hypobaric hypoxia induced fear and extinction memory impairment and effect of Ginkgo biloba in its amelioration: Behavioral, neurochemical and molecular correlates.

Regulated fear and extinction memory is essential for balanced behavioral response. Limbic brain regions are susceptible to hypobaric hypoxia (HH) and are putative target for fear extinction deficit and dysregulation. The present study aimed to examine the effect of HH and Ginkgo biloba extract (GBE) on fear and extinction memory with the underlying mechanism. Adult male Sprague-Dawley rats were evaluated for fear extinction and anxious behavior following GBE administration during HH exposure. Blood and tissue (PFC, hippocampus and amygdala) samples were collected for biochemical, morphological and molecular studies. Results revealed deficit in contextual and cued fear extinction following 3 days of HH exposure. Increased corticosterone, glutamate with decreased GABA level was found with marked pyknosis, decrease in apical dendritic length and number of functional spines. Decline in mRNA expression level of synaptic plasticity genes and immunoreactivity of BDNF, synaptophysin, PSD95, spinophilin was observed following HH exposure. GBE administration during HH exposure improved fear and extinction memory along with decline in anxious behavior. It restored corticosterone, glutamate and GABA levels with an increase in apical dendritic length and number of functional spines with a reduction in pyknosis. It also improved mRNA expression level and immunoreactivity of neurotrophic and synaptic proteins. The present study is the first which demonstrates fear extinction deficit and anxious behavior following HH exposure. GBE administration ameliorated fear and extinction memory dysregulation by restoration of neurotransmitter levels, neuronal pyknosis and synaptic connections along with improved neurotrophic and synaptic protein expressions.

Effects of oxytocin administration and conditioned oxytocin on brain activity: An fMRI study.

It has been demonstrated that secretion of several hormones can be classically conditioned, however, the underlying brain responses of such conditioning have never been investigated before. In this study we aimed to investigate how oxytocin administration and classically conditioned oxytocin influence brain responses. In total, 88 females were allocated to one of three groups: oxytocin administration, conditioned oxytocin, or placebo, and underwent an experiment consisting of three acquisition and three evocation days. Participants in the conditioned group received 24 IU of oxytocin together with a conditioned stimulus (CS) during three acquisition days and placebo with the CS on three evocation days. The oxytocin administration group received 24 IU of oxytocin and the placebo group received placebo during all days. On the last evocation day, fMRI scanning was performed for all participants during three tasks previously shown to be affected by oxytocin: presentation of emotional faces, crying baby sounds and heat pain. Region of interest analysis revealed that there was significantly lower activation in the right amygdala and in two clusters in the left superior temporal gyrus in the oxytocin administration group compared to the placebo group in response to observing fearful faces. The activation in the conditioned oxytocin group was in between the other two groups for these clusters but did not significantly differ from either group. No group differences were found in the other tasks. Preliminary evidence was found for brain activation of a conditioned oxytocin response; however, despite this trend in the expected direction, the conditioned group did not significantly differ from other groups. Future research should, therefore, investigate the optimal timing of conditioned endocrine responses and study whether the findings generalize to other hormones as well.

Conditioned taste avoidance induced by the combination of heroin and cocaine: Implications for the use of speedball.

Speedball (heroin + cocaine) is a prevalent drug combination among intravenous drug users. Although its use is generally discussed to be a function of changes in the rewarding effects of either or both drugs, changes in the aversive effects of either drug may also be impacted (weakened) by the combination. To address this latter possibility and its potential role in the use of speedball, the present studies examined the interaction of cocaine and heroin in taste avoidance conditioning. In Experiment 1, male Sprague-Dawley rats were given access to a novel saccharin solution and then injected with either vehicle or heroin (3.2 mg/kg, IP) followed immediately by various doses of cocaine (10, 18 or 32 mg/kg, SC). At the two lowest doses of cocaine, only animals injected with the drug combination (H + C) displayed a taste avoidance relative to control subjects (taste avoidance was induced with both the combination and the high dose of cocaine). At no dose did animals injected with the combination of heroin and cocaine drink more than animals injected with cocaine alone. In Experiment 2, male Sprague-Dawley rats were similarly treated but injected with vehicle or cocaine (10 mg/kg) followed by injections of various doses of heroin (1.8, 3.2, 5.6 or 10 mg/kg). At the three highest doses of heroin, only animals injected with the drug combination (C + H) displayed significant avoidance relative to control subjects (no avoidance was evident with the combination of cocaine and the low dose of heroin). At no dose did animals injected with the combination of cocaine and heroin drink more than animals injected with heroin alone. Together, these results suggest that the aversive effects of heroin and cocaine are not attenuated by co-administration by cocaine and heroin, respectively. The importance of this for the use of speedball was discussed.

Strain differences in muscarinic cholinergic receptor antagonism of fat intake and acquisition and expression of fat-conditioned flavor preferences in male BALB/c, C57BL/6 and SWR mice.

Murine strain differences occur for both intakes of and preferences for sugars and fats. Previous studies demonstrated that the muscarinic cholinergic receptor antagonist, scopolamine (SCOP) more potently reduced sucrose and saccharin intakes in inbred C57BL/6 and BALB/c than SWR mice, sucrose-conditioned flavor preferences (CFP) expression in BALB/c, but not C57BL/6 or SWR mice, and sucrose-CFP acquisition in BALB/c relative to SWR and C57BL/6 mice. Although fat intake and fat-CFP are observed in all three strains, strain-specific effects were previously observed following dopamine D1, opiate and NMDA receptor antagonism of sweet and fat intake and CFP. The present study investigated whether muscarinic receptor antagonism differentially affected fat (Intralipid) intake and preferences in these strains by examining whether SCOP altered fat (Intralipid) intake and fat-CFP expression and acquisition in BALB/c, C57BL/6 and SWR mice. SCOP (0.1-10 mg/kg) significantly reduced Intralipid (5%) intake in all three strains across 2 h. In fat-CFP expression experiments, food-restricted mice consumed one flavored (conditioned stimulus (CS)+, 5 sessions) Intralipid (5%) solution and a differently-flavored (CS-, 5 sessions) Intralipid (0.5%) solution. Two-bottle CS choice tests with the two flavors mixed in 0.5% Intralipid occurred following vehicle and two SCOP doses (1, 5 mg/kg). SCOP elicited small, but significant reductions in fat-CFP expression in BALB/c and C57BL/6, but not SWR mice. In fat-CFP acquisition experiments, separate groups of BALB/c, C57BL/6 and SWR mice were treated prior to the ten acquisition training sessions with vehicle or two SCOP (2.5, 5 mg/kg) doses followed by six two-bottle choice tests without injections. SCOP eliminated fat-CFP acquisition in all three strains. Thus, muscarinic receptor signaling mediates learning, and to a lesser degree maintenance of fat-CFP while maximally inhibiting fat intake in the three strains.

Mapping the estrous cycle to context-specific extinction memory.

In Pavlovian renewal paradigms, intact female rats have previously failed to exhibit renewal of appetitive behavior after extinction. However, when treated with exogenous estradiol, female rats exhibit robust renewal behavior. The current study aims to investigate whether the estrous cycle can influence renewal of appetitive behaviors and activity in brain areas known to support the renewal effect. We further aimed to examine whether the estrous cycle would similarly affect renewal of two different types of appetitive behaviors. We first establish that rats in the proestrous stage of the estrous cycle during extinction exhibit elevated renewal behavior compared with rats in either metestrous/diestrous stages, and only rats in proestrus during extinction training (but not during the renewal test) exhibit elevated renewal behavior. Furthermore, we show that this estrous cycle dependent effect on renewal only applies to the conditioned approach behavior toward the food delivery site but not the conditioned approach behavior toward the light cue associated with food delivery. Finally, we examined FOS activity within the prelimbic and infralimbic areas of the medial prefrontal cortex, the dorsal and ventral hippocampal formation, the paraventricular nucleus of the thalamus, the nucleus accumbens, and areas of the amygdala. Particularly in the hippocampus and amygdala, FOS expression which corresponded to the behavioral differences between groups was observed. Results from this study suggest that context information processing may vary as a function of endogenous female hormones across the gonadal hormone cycle and that encoding and retrieval of this information is accomplished in a state-specific manner. (PsycINFO Database Record (c) 2019 APA, all rights reserved).

Cocaine-induced behavioral sensitization is greater in adolescent than in adult mice and heightens cocaine-induced conditioned place preference in adolescents.

Adolescents are more sensitive than adults to the neural and behavioral effects of psychostimulants, and exhibit greater vulnerability to drug abuse, dependence or relapse into these conditions. We have reported that cocaine pretreatment during adolescence promotes the expression of behavioral sensitization to a greater extent than when the pretreatment occurs at adulthood. Behavioral sensitization has been associated to the transition from drug use to addiction and is postulated to indicate heightened sensitivity to the appetitive motivational effects of drugs. The relationship between behavioral sensitization and conventional measures of drug reward, such as conditioned place preference (CPP), has yet to be thoroughly investigated, and little is known about age-related differences in this phenomenon. The present study tested cocaine-induced CPP in adolescent and adult mice exposed to cocaine (or vehicle) pretreatment, either in an intermittent or "binge" (i.e., heavy cocaine use on a single occasion, which increases the likelihood of experiencing cocaine-related problems) fashion. Cocaine administration induced behavioral sensitization to a greater extent in adolescent than in adult mice. Cocaine-induced CPP was fairly similar in vehicle pretreated adolescent and adult mice, yet greater in adolescent vs. adults after cocaine-induced sensitization. The results confirmed the higher sensitivity of adolescent mice to cocaine-induced behavioral sensitization and suggest its association with greater sensitivity to cocaine's rewarding effects.

Omega-3 decreases D1 and D2 receptors expression in the prefrontal cortex and prevents amphetamine-induced conditioned place preference in rats.

Amphetamine (AMPH) abuse is a serious public health problem due to the high addictive potential of this drug, whose use is related to severe brain neurotoxicity and memory impairments. So far, therapies for psychostimulant addiction have had limited efficacy. Omega-3 polyunsaturated fatty acids (n-3 PUFA) have shown beneficial influences on the prevention and treatment of several diseases that affect the central nervous system. Here, we assessed the influence of fish oil (FO), which is rich in n-3 PUFA, on withdrawal and relapse symptoms following re-exposure to AMPH. Male Wistar rats received d,l-AMPH or vehicle in the conditioned place preference (CPP) paradigm for 14 days. Then, half of each experimental group was treated with FO (3 g/kg, p.o.) for 14 days. Subsequently, animals were re-exposed to AMPH-CPP for three additional days, in order to assess relapse behavior. Our findings have evidenced that FO prevented relapse induced by AMPH reconditioning. While FO prevented AMPH-induced oxidative damages in the prefrontal cortex, molecular assays allowed us to observe that it was also able to modulate dopaminergic cascade markers (DAT, TH, VMAT-2, D1R and D2R) in the same brain area, thus preventing AMPH-induced molecular changes. To the most of our knowledge, this is the first study to show a natural alternative tool which is able to prevent psychostimulant relapse following drug withdrawal. This non-invasive and healthy nutraceutical may be considered as an adjuvant treatment in detoxification clinics.

Conditioned stimulus presentations alter anxiety level in fear-conditioned mice.

It is generally believed that fear is rapidly triggered by a distinct cue while anxiety onset is less precise and not associated with a distinct cue. Although it has been claimed that both processes can be measured with certain independence of each other, it is unclear how exactly they differ. In this study, we measured anxiety in mice that received discriminative fear conditioning using behavioral, heart rate and calcium (Ca2+) responses in the ventral hippocampal CA1 (vCA1) neurons. We found that the occurrence of fear significantly interfered with anxiety measurements under various conditions. Diazepam reduced basal anxiety level but had no effect during the presentation of conditioned stimulus (CS). Injection of an inhibitory peptide of PKMzeta (ZIP) into the basolateral amygdala almost entirely abolished CS-triggered fear expression and reduced anxiety to basal level. Heart rate measures suggested a small reduction in anxiety during CS-. Calcium responses in the lateral hypothalamus-projecting vCA1 neurons showed a steady decay during CS suggesting a reduced anxiety. Thus, under our experimental conditions, CS presentations likely reduce anxiety level in the fear-conditioned mice.

Choline ameliorates adult learning deficits and reverses epigenetic modification of chromatin remodeling factors related to adolescent nicotine exposure.

Earlier initiation of smoking correlates with higher risk of nicotine dependence, mental health problems, and cognitive impairments. Additionally, exposure to nicotine and/or tobacco smoke during critical developmental periods is associated with lasting epigenetic modifications and altered gene expression. This study examined whether adolescent nicotine exposure alters adult hippocampus-dependent learning, involving persistent changes in hippocampal DNA methylation and if choline, a dietary methyl donor, would reverse and mitigate these alterations. Mice were chronically treated with nicotine (12.6 mg/kg/day) starting at post-natal day 23 (pre-adolescent), p38 (late adolescent), or p54 (adult) for 12 days followed by a 30-day period during which they consumed either standard chow or chow supplemented with choline (9 g/kg). Mice then were tested for fear-conditioning and dorsal hippocampi were dissected for whole genome methylation and selected gene expression analyses. Nicotine exposure starting at p21 or p38, but not p54, disrupted adult hippocampus-dependent fear conditioning. Choline supplementation ameliorated these deficits. 462 genes in adult dorsal hippocampus from mice exposed to nicotine as adolescents showed altered promoter methylation that was reversed by choline supplementation. Gene network analysis revealed that chromatin remodeling genes were the most enriched category whose methylation was altered by nicotine and reversed by choline dietary supplementation. Two key chromatin remodeling genes, Smarca2 and Bahcc1, exhibited inversely correlated changes in methylation and expression due to nicotine exposure; this was reversed by choline. Our findings support a role for epigenetic modification of hippocampal chromatin remodeling genes in long-term learning deficits induced by adolescent nicotine and their amelioration by dietary choline supplementation.

Effect of Yulangsan Polysaccharide on the Reinstatement of Morphine-Induced Conditioned Place Preference in Sprague-Dawley Rats.

We previously reported that Yulangsan polysaccharide (YLSP), which was isolated from the root of Millettia pulchra Kurz, attenuates withdrawal symptoms of morphine dependence by regulating the nitric oxide pathway and modulating monoaminergic neurotransmitters. In this study, we investigated the effects and mechanism of YLSP on the reinstatement of morphine-induced conditioned place preference (CPP) in rats. A CPP procedure was employed to assess the behavior of rats, and indicators of serum and four brain regions (nucleus accumbens, ventral tegmental area, hippocampus and prefrontal cortex) were determined to explore its underlying mechanism. YLSP inhibited priming morphine-induced reinstatement of CPP in a dose-dependent manner. YLSP markedly reduced nitric oxide and nitric oxide synthase levels in the brain. Moreover, YLSP significantly decreased the dopamine and norepinephrine levels in the serum and brain. Furthermore, YLSP significantly decreased cyclic adenosine monophosphate (cAMP) and cyclic guanosine monophosphate (cGMP) concentrations, inhibited the expression of dopamine D1 receptors and cAMP response element binding protein mRNA, and improved the expression of dopamine D2 receptor mRNA in the four brain regions. Our findings indicated that YLSP could inhibit the reinstatement of morphine-induced CPP possibly by modulating the NO-cGMP and D1R-cAMP signaling pathways.

Behavioural and computational methods reveal differential effects for how delayed and rapid onset antidepressants effect decision making in rats.

Major depressive disorder (MDD) is one of the most prevalent psychiatric disorders. Until the recent discovery of the rapid onset antidepressant action of ketamine, pharmacological treatments for MDD were limited to conventional antidepressant drugs with delayed clinical efficacy. Using a judgement bias task, this study has investigated whether the temporal differences observed in patients would be reflected in affective biases and decision making behaviour in rodents. The diffusion model was also used to investigate the underlying decision making processes. Positive biases were induced in this task over timeframes that mirror the rapid versus delayed antidepressant efficacy of the drugs in clinical populations. Diffusion modelling revealed that the antidepressants tested also have different effects on decision making processes, suggesting they may act through different neurobiological substrates. This combination of behaviour and computational modelling may provide a useful approach to further investigate the mechanisms underlying rapid antidepressant effect and assess potential new treatments.

Electroacupuncture suppresses morphine reward-seeking behavior: Lateral hypothalamic orexin neurons implicated.

The orexin system specifically located in the lateral hypothalamus (LH) has been shown to play a unique role in reward seeking, drug relapse, and addiction. In this study, we investigated the effects of electroacupuncture (EA) on morphine conditioned place preference (CPP), reinstatement of extinguished CPP, and the expression of orexin in the LH. A two-chamber CPP model was used to measure the rewarding properties of morphine. 2Hz EA at points BL23 and ST36 was carried out for 30min daily before morphine injection on three conditioning days. The extinguished CPP was reinstated by systemic morphine injection. Immunohistochemistry was used to detect orexin-positive nuclei in the LH. The findings indicated that the expression of morphine-induced CPP can be effectively suppressed by EA. EA suppressed orexin-positive nuclei in the LH compared with morphine-conditioned rats. A combination of EA and orexin A antagonist (10mg/kg, i.p.) produced a significant decrease in the morphine reinstatement scores. The results indicate the possibility that orexin may be involved in the acupuncture effect on drug-seeking behavior and thereby has an important role in modulating acupuncture. The synergetic use of a protocol consisting of EA and low-dose orexin A antagonist may provide a novel treatment strategy for drug reward seeking and relapse.

Pharmacological sensitivity of reflexive and nonreflexive outcomes as a correlate of the sensory and affective responses to visceral pain in mice.

Pain encompasses both sensory and affective dimensions which can be differentially modulated by drugs. Here, we compare the pharmacological sensitivity of the sensory and affective responses using acetic acid-induced abdominal writhings (sensory-reflexive outcome) and acetic acid-induced depression of reward seeking behaviour (RSB, affective-nonreflexive outcome) to a highly palatable food in mice. We found that the expression of RSB critically depends on factors such as sex and previous knowledge and type of the food stimulus. Intraperitoneal administration of acetic acid (iAA) produced a long-lasting (beyond the resolution of writhing behaviour) and concentration-dependent decrease on both appetitive-approach and consummatory dimensions of RSB. Ibuprofen and diclofenac were much more potent in reversing AA-induced changes in RSB: latency to eat (ED50 = 2 and 0.005 mg/kg, intraperinoneally, respectively) and amount consumed (ED50 = 11 and 0.1 mg/kg) than in AA-induced writhing (ED50 = 123 and 60 mg/kg). Morphine and duloxetine inhibited the writhing response (ED50 = 0.8 and 6 mg/kg, respectively) but not the AA-induced changes in RSB. Caffeine was ineffective in both AA-induced writhing and RSB changes. Overall, this study characterized a preclinical mouse model of hedonic deficits induced by pain that can be used to assess affective responses as well as complementary classic reflexive approaches in the evaluation of candidate analgesics.