The Effects of Fingolimod (FTY720) on Leukocyte Subset Circulation cannot be Behaviourally Conditioned in Rats.

Suppression of immune functions can be elicited by behavioural conditioning using drugs such as cyclosporin A or rapamycin. Nevertheless, little is known about the underlying mechanisms and generalisability of this phenomenon. Against this background, the present study investigated whether the pharmacological properties of fingolimod (FTY720), an immunosuppressive drug widely applied to treat multiple sclerosis, can be conditioned in rats by means of taste-immune associative learning. For this purpose, a conditioned taste avoidance paradigm was used, pairing the presentation of a novel sweet drinking solution (saccharin or sucrose) as conditioned stimulus (CS) with therapeutically effective doses of FTY720 as unconditioned stimulus (US). Subsequent re-exposure to the CS at a later time point revealed that conditioning with FTY720 induced a mild conditioned taste avoidance only when saccharin was employed as CS. However, on an immunological level, neither re-exposure with saccharin nor sucrose altered blood immune cell subsets or splenic cytokine production. Despite the fact that intraperitonally administered FTY720 could be detected in brain regions known to mediate neuro-immune interactions, the present findings show that the physiological action of FTY720 is not inducible by mere taste-immune associative learning. Whether conditioning generalises across all small-molecule drugs with immunosuppressive properties still needs to be investigated with modified paradigms probably using distinct sensory CS. Moreover, these findings emphasize the need to further investigate the underlying mechanisms of conditioned immunomodulation to assess the generalisability and usability of associative learning protocols as supportive therapies in clinical contexts.

Pharmacological manipulations of the dorsomedial and dorsolateral striatum during fear extinction reveal opposing roles in fear renewal.

Systemic manipulations that enhance dopamine (DA) transmission around the time of fear extinction can strengthen fear extinction and reduce conditioned fear relapse. Prior studies investigating the brain regions where DA augments fear extinction focus on targets of mesolimbic and mesocortical DA systems originating in the ventral tegmental area, given the role of these DA neurons in prediction error. The dorsal striatum (DS), a primary target of the nigrostriatal DA system originating in the substantia nigra (SN), is implicated in behaviors beyond its canonical role in movement, such as reward and punishment, goal-directed action, and stimulus-response associations, but whether DS DA contributes to fear extinction is unknown. We have observed that chemogenetic stimulation of SN DA neurons during fear extinction prevents the return of fear in contexts different from the extinction context, a form of relapse called renewal. This effect of SN DA stimulation is mimicked by a DA D1 receptor (D1R) agonist injected into the DS, thus implicating DS DA in fear extinction. Different DS subregions subserve unique functions of the DS, but it is unclear where in the DS D1R agonist acts during fear extinction to reduce renewal. Furthermore, although fear extinction increases neural activity in DS subregions, whether neural activity in DS subregions is causally involved in fear extinction is unknown. To explore the role of DS subregions in fear extinction, adult, male Long-Evans rats received microinjections of either the D1R agonist SKF38393 or a cocktail consisting of GABAA/GABAB receptor agonists muscimol/baclofen selectively into either dorsomedial (DMS) or dorsolateral (DLS) DS subregions immediately prior to fear extinction, and extinction retention and renewal were subsequently assessed drug-free. While increasing D1R signaling in the DMS during fear extinction did not impact fear extinction retention or renewal, DMS inactivation reduced later renewal. In contrast, DLS inactivation had no effect on fear extinction retention or renewal but increasing D1R signaling in the DLS during extinction reduced fear renewal. These data suggest that DMS and DLS activity during fear extinction can have opposing effects on later fear renewal, with the DMS promoting renewal and the DLS opposing renewal. Mechanisms through which the DS could influence the contextual gating of fear extinction are discussed.

Social-Single Prolonged Stress affects contextual fear conditioning in male and female Wistar rats: Molecular insights in the amygdala.

Stress exposure can lead to post-traumatic stress disorder (PTSD) in male and female rats. Social-Single Prolonged Stress (SPS) protocol has been considered a potential PTSD model. This study aimed to pharmacologically validate the Social-SPS as a PTSD model in male and female rats. Male and female Wistar rats (60-day-old) were exposed to Social-SPS protocol and treated with fluoxetine (10 mg/Kg) or saline solution intraperitoneally 24 h before euthanasia. Two cohorts of animals were used; for cohort 1, male and female rats were still undisturbed until day 7 post-Social-SPS exposure, underwent locomotor and conditioned fear behaviors, and were euthanized on day 9. Animals of cohort 2 were subjected to the same protocol but were re-exposed to contextual fear behavior on day 14. Results showed that fluoxetine-treated rats gained less body weight than control and Social-SPS in both sexes. Social-SPS effectively increased the freezing time in male and female rats on day eight but not on day fourteen. Fluoxetine blocked the increase of freezing in male and female rats on day 8. Different mechanisms for fear behavior were observed in males, such as Social-SPS increased levels of glucocorticoid receptors and Beclin-1 in the amygdala. Social-SPS was shown to increase the levels of NMDA2A, GluR-1, PSD-95, and CAMKII in the amygdala of female rats. No alterations were observed in the amygdala of rats on day fourteen. The study revealed that Social-SPS is a potential PTSD protocol applicable to both male and female rats.

No harmful effect of propranolol administered prior to fear memory extinction in rats and humans.

Exposure therapy is an evidence-based treatment option for anxiety-related disorders. Many patients also take medication that could, in principle, affect exposure therapy efficacy. Clinical and laboratory evidence indeed suggests that benzodiazepines may have detrimental effects. Large clinical trials with propranolol, a common beta-blocker, are currently lacking, but several preclinical studies do indicate impaired establishment of safety memories. Here, we investigated the effects of propranolol given prior to extinction training in 9 rat studies (N = 215) and one human study (N = 72). A Bayesian meta-analysis of our rat studies provided strong evidence against propranolol-induced extinction memory impairment during a drug-free test, and the human study found no significant difference with placebo. Two of the rat studies actually suggested a small beneficial effect of propranolol. Lastly, two rat studies with a benzodiazepine (midazolam) group provided some evidence for a harmful effect on extinction memory, i.e., impaired extinction retention. In conclusion, our midazolam findings are in line with prior literature (i.e., an extinction retention impairment), but this is not the case for the 10 studies with propranolol. Our data thus support caution regarding the use of benzodiazepines during exposure therapy, but argue against a harmful effect of propranolol on extinction learning.

Central amygdala contributes to stimulus facilitation and pre-stimulus vigilance during cerebellar learning.

Our previous studies found that the central amygdala (CeA) modulates cerebellum-dependent eyeblink conditioning (EBC) using muscimol inactivation. We also found that CeA inactivation decreases cerebellar neuronal activity during the conditional stimulus (CS) from the start of training. Based on these findings, we hypothesized that the CeA facilitates CS input to the cerebellum. The current study tested the CS facilitation hypothesis using optogenetic inhibition with archaerhodopsin (Arch) and excitation with channelrhodopsin (ChR2) of the CeA during EBC in male rats. Optogenetic manipulations were administered during the 400 ms tone CS or during a 400 ms pre-CS period. As predicted by the CS facilitation hypothesis CeA inhibition during the CS impaired EBC and CeA excitation during the CS facilitated EBC. Unexpectedly, CeA inhibition just prior to the CS also impaired EBC, while CeA excitation during the pre-CS pathway did not facilitate EBC. The results suggest that the CeA contributes to CS facilitation and vigilance during the pre-CS period. These putative functions of the CeA may be mediated through separate output pathways from the CeA to the cerebellum.

Role of amygdala astrocytes in different phases of contextual fear memory.

Growing evidence indicates a critical role of astrocytes in learning and memory. However, little is known about the role of basolateral amygdala complex (BLA-C) astrocytes in contextual fear conditioning (CFC), a paradigm relevant to understand and generate treatments for fear- and anxiety-related disorders. To get insights on the involvement of BLA-C astrocytes in fear memory, fluorocitrate (FLC), a reversible astroglial metabolic inhibitor, was applied at critical moments of the memory processing in order to target the acquisition, consolidation, retrieval and reconsolidation process of the fear memory. Adult Wistar male rats were bilaterally cannulated in BLA-C. Ten days later they were infused with different doses of FLC (0.5 or 1 nmol/0.5 µl) or saline before or after CFC and before or after retrieval. FLC impaired fear memory expression when administered before and shortly after CFC, but not one hour later. Infusion of FLC prior and after retrieval did not affect the memory. Our findings suggest that BLA-C astrocytes are critically involved in the acquisition/early consolidation of fear memory but not in the retrieval and reconsolidation. Furthermore, the extinction process was presumably not affected (considering that peri-retrieval administration could also affect this process).

Generalization of a positive-feature interoceptive morphine occasion setter across the rat estrous cycle.

INTRODUCTION: Interoceptive stimuli elicited by drug administration acquire conditioned modulatory properties of the induction of conditioned appetitive behaviours by exteroceptive cues. This effect may be modeled using a drug discrimination task in which the drug stimulus is trained as a positive-feature (FP) occasion setter (OS) that disambiguates the relation between an exteroceptive light conditioned stimulus (CS) and a sucrose unconditioned stimulus (US). We previously reported that females are less sensitive to generalization of a FP morphine OS than males, so we investigated the role of endogenous ovarian hormones in this difference. METHODS: Male and female rats received intermixed injections of 3.2 mg/kg morphine or saline before each daily training session. Training consisted of 8 presentations of the CS, each followed by access to sucrose on morphine, but not saline sessions. Following acquisiton, rats were tested for generalization of the morphine stimulus to 0, 1.0, 3.2, and 5.4 mg/kg morphine. Female rats were monitored for estrous cyclicity using vaginal cytology throughout the study. RESULTS: Both sexes acquired stable drug discrimination. A gradient of generalization was measured across morphine doses and this behaviour did not differ by sex, nor did it differ across the estrous cycle in females. CONCLUSIONS: Morphine generalization is independent of fluctuations in levels of sex and endogenous gonadal hormones in females under these experimental conditions.

Functional lateralization in the medial prefrontal cortex control of contextual conditioned emotional responses in rats.

A functional lateralization has been reported in control of emotional responses by the medial prefrontal cortex (mPFC). However, a hemisphere asymmetry in involvement of the mPFC in expression of fear conditioning responses has never been reported. Therefore, we investigated whether control by mPFC of freezing and cardiovascular responses during re-exposure to an aversively conditioned context is lateralized. For this, rats had guide cannulas directed to the mPFC implanted bilaterally or unilaterally in the right or left hemispheres. Vehicle or the non-selective synaptic inhibitor CoCl2 was microinjected into the mPFC 10 min before re-exposure to a chamber where the animals had previously received footshocks. A catheter was implanted into the femoral artery before the fear retrieval test for cardiovascular recordings. We observed that bilateral microinjection of CoCl2 into the mPFC reduced both the freezing behavior (enhancing locomotion and rearing) and arterial pressure and heart rate increases during re-exposure to the aversively conditioned context. Unilateral microinjection of CoCl2 into the right hemisphere of the mPFC also decreased the freezing behavior (enhancing locomotion and rearing), but without affecting the cardiovascular changes. Conversely, unilateral synaptic inhibition in the left mPFC did not affect either behavioral or cardiovascular responses during fear retrieval test. Taken together, these results suggest that the right hemisphere of the mPFC is necessary and sufficient for expression of freezing behavior to contextual fear conditioning. However, the control of cardiovascular responses and freezing behavior during fear retrieval test is somehow dissociated in the mPFC, being the former bilaterally processed.

The effects of diazepam on fear extinction in nulliparous and primiparous female rats.

Benzodiazepines undermine the success of exposure therapy in humans with anxiety disorders, and impair the long-term memory of fear extinction (the laboratory basis of exposure therapy) in rodents. However, most rodent studies on fear extinction and benzodiazepines have been conducted in male rodents. In female rodents, the estrous cycle influences the consolidation of fear extinction memories and sensitivity to benzodiazepines. In addition, pregnancy leads to long-term changes in the neurobiological, hormonal, and behavioural features of fear extinction, as well as the responsivity to benzodiazepines. Therefore, the present experiments examined the impact of benzodiazepines on fear extinction in female rats with and without reproductive experience. Age-matched nulliparous (no reproductive experience) and primiparous (one prior reproductive experience; tested one-month post-weaning) rats received fear conditioning to a discrete cue. The next day, rats were administered the benzodiazepine diazepam (2 mg/kg, s.c), or vehicle, prior to or immediately after extinction training. Rats were then tested the next day, drug free, for extinction retention. Similar to previous findings in males, diazepam impaired extinction retention in both nulliparous and primiparous rats when administered either pre- or post-extinction training. These findings may have potential clinical implications as they suggest that benzodiazepine use in conjunction with exposure therapy may undermine long-term treatment success in women with and without reproductive experience, although this remains to be tested in human populations. Moreover, these findings are theoretically important when considered in light of previous studies showing dissociable mechanisms of fear extinction in females pre- versus post-pregnancy.

Attenuated incubation of ethanol-induced conditioned taste aversion in a model of dependence.

RATIONALE: Preclinical studies report attenuated ethanol-induced conditioned taste aversion (CTA) following chronic ethanol exposure, suggesting that tolerance develops to the aversive properties of ethanol. However, these studies are confounded by pre-exposure to the unconditioned stimulus (US; ethanol), which is well known to hinder conditioning. OBJECTIVES: This study was designed to determine whether chronic ethanol exposure produces tolerance to the aversive properties of ethanol in the absence of a US pre-exposure confound. METHODS: CTA was performed in adult male and female Long-Evans rats by pairing 0.1% ingested saccharin with an intraperitoneal injection of ethanol (1.5 or 2.0 g/kg) or saline. Rats were then rendered ethanol dependent using chronic intermittent ethanol (CIE) vapor exposure. Controls were exposed to room air (AIR). The effect of chronic ethanol on CTA expression and reconditioning were examined following vapor exposure. RESULTS: Prior to vapor exposure, both sexes developed CTA to a comparable degree with 2.0 g/kg producing greater CTA than 1.5 g/kg ethanol. Following vapor exposure, AIR controls exhibited an increase in CTA magnitude compared to pre-vapor levels. This effect was largely absent in CIE-exposed rats. Re-conditioning after vapor exposure facilitated increased CTA magnitude to a similar degree in AIR- and CIE-exposed males. In contrast, CTA magnitude was unchanged by re-conditioning in females. CONCLUSIONS: These data suggest that chronic ethanol does not facilitate tolerance to the aversive properties of ethanol but rather attenuates incubation of ethanol-induced CTA. Loss of CTA incubation suggests that CIE exposure disrupts circuits encoding aversion.

Rewarding and reinforcing effects of two dissociative-based new psychoactive substances, deschloroketamine and diphenidine, in mice.

Dissociative-based new psychoactive substances (NPSs) are increasingly available through the Internet, and public health problems related to the recreational use of these substances have been increasing globally. Two such NPSs are deschloroketamine and diphenidine, which are primarily used recreationally as ketamine substitutes. However, there is little scientific evidence to describe the dependence liability of NPSs. This study aimed to evaluate the dependence liability of deschloroketamine and diphenidine via animal behavioral experiments. We evaluated the rewarding and reinforcing effects of these NPSs using the conditioned place preference (CPP) and the self-administration (SA) paradigms in mice. Psychomotor effects and behavioral features of these compounds were assessed by quantifying locomotor activity, stereotypic movements, and dopaminergic neurotransmission. Both deschloroketamine (10 mg/kg) and diphenidine (10-60 mg/kg) produced increased locomotor activation and stereotypy that were similar to the effects of ketamine (10 mg/kg). Both deschloroketamine (10 mg/kg) and diphenidine (10, 20 mg/kg) increased the animals' preference for the drug-paired compartment in the CPP testing. In the SA testing, deschloroketamine (1 mg/kg/infusion) increased the number of active lever presses and the number of infusions received, whereas diphenidine administration (1, 2 mg/kg/infusion) did not alter either of these. Furthermore, both deschloroketamine and diphenidine increased dopamine levels in PC-12 cells. Collectively, the data suggest that deschloroketamine may have both rewarding and reinforcing effects, whereas diphenidine only induced rewarding effect.

Activation of dopamine D2 receptors in the shell of nucleus accumbens triggers conditioned avoidance responses in rats.

Conditioned avoidance responses (CAR) behavior is a classical instrumental response paradigm, which is widely used to study aversive conditioning and defensive motivation behavior. Previous studies have shown that dopamine D1 and D2 receptors are involved in CAR behavior; however, it is unclear in which brain regions that dopamine evokes CAR behavior. The aim of the study is to investigate whether dopamine triggers CAR behavior via activating dopamine D1 or D2 receptors in the shell of nucleus accumbens or dorsolateral striatum. The present study found that infusion of the dopamine D2 receptor agonist quinpirole, but not D1 receptor agonist SKF38393, into the shell of nucleus accumbens evoked CAR behavior in reserpine-treated rats. Whereas, infusion of neither SKF38393 nor quinpirole into the dorsolateral striatum evoked CAR behavior. In addition, infusion of quinpirole into the shell of nucleus accumbens enhanced CAR behavior in the unsuccessful trained rats without affecting the motor function in the balance beam and locomotor tests. In conclusion, activation of dopamine D2, but not D1 receptors in the shell of nucleus accumbens evokes CAR behavior. However, activation of dopamine D1 and D2 receptors in the dorsolateral striatum does not evoke CAR behavior. It is suggested that the shell of nucleus accumbens is the critical brain region for dopamine to invoke CAR behavior, and activation of dopamine D2 receptors in the shell of nucleus accumbens is sufficient and necessary to evoke CAR behavior.

Extended amygdala, conditioned withdrawal and memory consolidation.

Opioid withdrawal can be associated to environmental cues through classical conditioning. Exposure to these cues can precipitate a state of conditioned withdrawal in abstinent subjects, and there are suggestions that conditioned withdrawal can perpetuate the addiction cycle in part by promoting the storage of memories. This review discusses evidence supporting the hypothesis that conditioned withdrawal facilitates memory consolidation by activating a neurocircuitry that involves the extended amygdala. Specifically, the central amygdala, the bed nucleus of the stria terminalis, and the nucleus accumbens shell interact functionally during withdrawal, mediate expression of conditioned responses, and are implicated in memory consolidation. From this perspective, the extended amygdala could be a neural pathway by which drug-seeking behaviour performed during a state of conditioned withdrawal is more likely to become habitual and persistent.

Effect of PPM1F in dorsal raphe 5-HT neurons in regulating methamphetamine-induced conditioned place preference performance in mice.

Methamphetamine (METH), a synthetically produced central nervous system stimulant, is one of the most illicit and addictive drugs worldwide. Protein phosphatase Mg2 + /Mn2 + -dependent 1F F (PPM1F) has been reported to exert multiple biological and cellular functions. Nevertheless, the effects of PPM1F and its neuronal substrates on METH addiction remain unclear. Herein, we first established a METH-induced conditioned place preference (CPP) mouse model. We showed that PPM1F is widely distributed in 5-HT neurons of the dorsal raphe nucleus (DRN), and METH treatment decreased the expression of PPM1F in DRN, which was negatively correlated with METH-induced CPP behaviors. Knockout of PPM1F mediated by adeno-associated virus (AAV) in DRN produced enhanced susceptibility to METH-induced CPP, whereas the overexpression of PPM1F in DRN attenuated METH-induced CPP phenotypes. The expression levels of Tryptophan hydroxylase2 (TPH2) and serotonin transporter (SERT) were down-regulated with a concurrent reduction in 5-hydroxytryptamine (5-HT), tryptophan hydroxylase2 (TPH2)-immunoreactivity neurons and 5-HT levels in DRN of PPM1F knockout mice. In the end, decreased expression levels of PPM1F were found in the blood of METH abusers and METH-taking mice. These results suggest that PPM1F in DRN 5-HT neurons regulates METH-induced CPP behaviors by modulating the key components of the 5-HT neurotransmitter system, which might be an important pathological gene and diagnostic marker for METH-induced addiction.

Evaluation of the effects of quercetin on the rewarding property of ethanol in mice.

BACKGROUND: The flavonoid quercetin has several pharmacological effects on the nervous system. Previous research showed that quercetin has useful influences on some mechanisms that are relevant in drug and substance addiction. Alcohol addiction, also known as alcoholism, is a disorder that influences the population in all walks of life. The purpose of the current study was to investigate whether quercetin affects the acquisition, extinction, and reinstatement of ethanol-induced conditioned place preference (ethanol-CPP) in adolescent mice. METHODS: CPP was established by administration of intraperitoneal (i.p.) ethanol (2.0 g/kg) in a conditioning trial. The mice were pretreated with quercetin (at doses of 10, 30, and 100 mg/kg, i.p.) 30 minutes before each ethanol injection to test the effects of quercetin on the reward properties of ethanol. Ethanol-CPP was extinguished (13-days) by repeated testing, during which conditioned mice were given different doses of quercetin every day. Lastly, efficacy of quercetin in preventing reinstatement of ethanol-CPP triggers was also assessed by the administration of single dose ethanol (0.4 g/kg, i.p.). RESULTS: Quercetin pretreatment attenuated the acquisition and reinstatement. In addition, quercetin administration accelerated the extinction of ethanol-CPP. CONCLUSIONS: In conclusion, these results may cast a novel light on quercetin as an agent that could be potentially useful to attenuate different effects of ethanol and as adjuvant pharmacotherapy for ethanol addiction. However, future studies are needed to demonstrate the detailed underlying mechanisms of quercetin on ethanol addiction.

Intravenous administration of Tat-NR2B9c peptide, a PSD95 inhibitor, attenuates reinstatement of cocaine-seeking behavior in rats.

Cocaine use disorder is a serious, chronic and relapsing disease of the nervous system, for which effective treatments do not yet exist. Recently, the role of the N-methyl-d-aspartate (NMDA) receptor subunit GluN2B has been highlighted in cocaine abstinence followed by extinction training. Since the GluN2B subunit is stabilized at synaptic level by the interaction with its scaffolding protein PSD95, in this study we aimed at investigating efficacy of Tat-NR2B9c peptide, a PSD95 inhibitor, which disrupts the interaction of PSD95 with GluN2B, in the attenuation of cocaine seeking-behavior or cue-induced reinstatement. We found that Tat-NR2B9c, administered intravenously, attenuated the reinstatement of active lever presses induced by a priming dose of cocaine or by drug-associated conditioned stimuli. At the same time, the GluN2B/PSD95 complex levels were decreased in the ventral hippocampus of rats that previously self-administered cocaine injected with Tat-NR2B9c during cocaine- or cue-induced reinstatement. In conclusion, we here provide the first evidence showing that the disruption of the GluN2B/PSD95 complexes during cocaine abstinence followed by extinction training may represent a useful strategy to reduce reinstatement of cocaine-seeking behavior.

The interaction between sexual reward/ deprivation and the acquisition, extinction and reinstatement of morphine-seeking behavior.

Natural rewards and abused drugs affect the function of the common brain's reward system. Interaction between social and drug rewards can change the vulnerability to development of drug addiction. Here, we investigate the effects of sexual experience and sex deprivation on the acquisition, maintenance, and drug prime-induced reinstatement of morphine-seeking behavior in male mice using conditioned place preference (CPP). CPP induced with morphine (3, 5, 7 mg/kg, s.c. for 3 days) lasted for 10 days after cessation of morphine treatment and priming dose of morphine (2 mg/kg, s.c.) reinstated the extinguished CPP. In the post-test phase, sexually experienced animals showed a lower preference for morphine compared to sex-deprived males. In the extinction phase, sex deprivation shortened maintenance time compared to control animals. The preference for morphine in sexually experienced animals did not diminish by the seventeenth extinction day. In both groups, the priming injection of morphine after the extinction period could reinstate the extinguished morphine-induced CPP. Together, these data showed the interaction between sex and drug reward and that sexual behavior -a natural rewarding stimulus- can prolong, whereas sex deprivation can block the maintenance of morphine-seeking behaviors. Sexual experience may induce functional and morphological alterations in brain reward areas particularly the mesolimbic system similar to repeated exposure to abused drugs which can affect morphine-seeking behaviors.

Effects of synthetic cathinone naphyrone in the conditioned place preference test - Evidence of its addictive potential.

Naphyrone, also known as NRG-1, is a novel psychoactive substance (NPS), a cathinone with stimulatory properties available on the grey/illicit drug market for almost a decade. It is structurally related to infamously known powerful stimulants with the pyrovalerone structure, such as alpha-pyrrolidinovalerophenone (α-PVP) or methylenedioxypyrovalerone (MDPV) that are labeled as a cheap replacement for cocaine and other stimulants. Despite the known addictive potential of α-PVP and MDPV, there are no studies directly evaluating naphyrone's addictive potential e.g., in conditioned place preference (CPP) test or using self-administration. Therefore, our study was designed to evaluate the addictive potential in a CPP test in male Wistar rats and compare its effect to another powerful stimulant with a high addictive potential - methamphetamine. Naphyrone increased time spent in the drug-paired compartment with 5 and 20 mg/kg s.c. being significant and 10 mg/kg s.c. reaching the threshold (p = 0.07); the effect was comparable to that of methamphetamine 1.5 mg/kg s.c. The lowest dose, naphyrone 1 mg/kg s.c., had no effect on CPP. Interestingly, no dose response effect was detected. Based on these data, we are able to conclude that naphyrone has an addictive potential and may possess a significant risk to users.

Differential involvement of nucleus tractus solitarius projections and locus coeruleus projections to the basolateral amygdala in morphine-associated memory destabilization.

Drug-related memory can be transiently destabilized by memory retrieval, after which memories are reconsolidated. Neurons in the basolateral amygdala (BLA) that are activated by emotional information may be one of the key mechanisms underlying this destabilization. However, the specific neural circuits underlying this destabilization process remain unknown. Because BLA receives noradrenergic inputs from the nucleus tractus solitarius (NTS) and locus coeruleus (LC), we studied the role of afferent projections into the BLA in the destabilization of morphine self-administration memory in rats. We first showed that morphine (unconditioned stimulus, US) + morphine-associated conditioned stimuli (CS) exposure, rather than CS exposure alone, destabilized morphine self-administration memory. Then, we measured projection-specific activation after the US + CS or CS retrieval test using c-fos (activity marker)-labeling in projection areas. Compared with CS exposure, we found that US + CS exposure induced more neuronal activation in the BLA and NTS but not in the LC. Next, we determined the effects of chemogenetic inactivation or activation of NTS or LC projections to BLA (NTS â†’ BLA or LC â†’ BLA) on this destabilization. We found that NTS â†’ BLA, but not LC â†’ BLA inactivation during memory retrieval, prevented memory destabilization induced by US + CS exposure. Furthermore, NTS â†’ BLA, but not LC â†’ BLA activation during CS retrieval induced destabilization. Thus, our results identify a specific neural circuit underlying the transformation of a stable opiate-associated memory into an unstable memory and subsequently guide reconsolidation.

Ethanol pre-exposure differentially impacts the rewarding and aversive effects of α-pyrrolidinopentiophenone (α-PVP): Implications for drug use and abuse.

RATIONALE: Exposure to a drug can subsequently impact its own reactivity as well as that of other drugs. Given that users of synthetic cathinones, i.e., "bath salts", typically have extensive and varied drug histories, an understanding of the effects of drug history on the behavioral and physiological consequences of synthetic cathiones may be important to their abuse liability. OBJECTIVES: The goal of the current work was to assess the effects of an ethanol pre-exposure on the rewarding and aversive effects of α-PVP. METHODS: Adult male Sprague Dawley rats were exposed to ethanol prior to combined conditioned taste avoidance/conditioned place preference training in which rats were injected with 1.5, 3 or 5 mg/kg of racemic α-PVP or vehicle. Following a 7-day washout period, rats were then tested for thermoregulatory effects of α-PVP using subcutaneous probes to measure body temperature changes over the course of 8 h. This was followed 10 days later by assessments for α-PVP-induced locomotor activity and stereotypies over a 1-h session. RESULTS: α-PVP induced significant dose- and trial-dependent taste avoidance that was significantly attenuated by ethanol history and dose- and time-dependent increases in locomotor activity that were significantly increased by ethanol. α-PVP also induced place preferences and dose- and time-dependent increases in body temperature, but these measures were unaffected by ethanol history. CONCLUSIONS: α-PVP's aversive effects (as measured by taste avoidance) were attenuated, while its rewarding effects (as indexed by place preference conditioning) were unaffected, by ethanol pre-exposure. Such a pattern may indicate increased α-PVP abuse liability, as changes in the balance of aversion and reward may impact overall drug effects and likelihood of drug intake. Future self-administration studies will be necessary to explore this possibility.