Conditioned Place Preference Paradigm Research Articles

Establishment of a social conditioned place preference paradigm for the study of social reward in female mice

Social interactions can be and often are rewarding. The effect of social contact strongly depends on circumstances, and the reward may be driven by varied motivational processes, ranging from parental or affiliative behaviors to investigation or aggression. Reward associated with nonreproductive interactions in rodents is measured using the social conditioned place preference (sCPP) paradigm, where a change in preference for an initially neutral context confirms reinforcing effects of social contact. Here, we revised the sCPP method and reexamined social reward in adult female mice. Contrary to earlier studies, we found that robust rewarding effects of social contact could be detected in adult (14-week-old) female C57BL/6 mice when the sCPP task was refined to remove confounding factors. Strikingly, the rewarding effects of social interaction were only observed among female siblings who remained together from birth. Contact with same-age nonsiblings was not rewarding even after 8 weeks of cohousing. Other factors critical for the social reward effect in the sCPP paradigm included the number of conditioning sessions and the inherent preference for contextual cues. Thus, we show that social interaction is rewarding in adult female mice, but this effect strictly depends on the familiarity of the interaction partners. Furthermore, by identifying confounding factors, we provide a behavioral model to study the mechanisms underlying the rewarding effects of nonreproductive social interaction in adult mice.

Cannabidiol treatment prevents drug reinstatement and the molecular alterations evoked by amphetamine on receptors and enzymes from dopaminergic and endocannabinoid systems in rats

In psychostimulant drug addiction, relapse is the most concerning outcome to be managed, considering there is no approved treatment for this neuropsychiatric condition. Here, we investigated the effects of the CBD treatment on the relapse behavior triggered by stress, after being submitted to the amphetamine (AMPH)-induced conditioned place preference (CPP) in rats. To elucidate the mechanisms of action underlying the CBD treatment, we evaluated the neuroadaptations on dopaminergic and endocannabinoid targets in the ventral striatum (VS) and ventral tegmental area (VTA) of the brain. Animals received d,l-AMPH (4 mg/kg, i.p.) or vehicle in the CPP paradigm for 8 days. Following the first CPP test, animals were treated with CBD (10 mg/kg, i.p.) or its vehicle for 5 days and subsequently submitted to forced swim stress protocol to induce AMPH-CPP relapse. Behavioral findings showed that CBD treatment prevented AMPH-reinstatement, also exerting anxiolytic activity. At the molecular level, in the VTA, CBD restored the CB1R levels decreased by AMPH-exposure, increased NAPE-PLD, and decreased FAAH levels. In the VS, the increase of D1R and D2R, as well as the decrease of DAT levels induced by AMPH were restored by CBD treatment. The current outcomes evidence a substantial preventive action of the CBD on the AMPH-reinstatement evoked by stress, also involving neuroadaptations in both dopaminergic and endocannabinoid systems in brain areas closely involved in the addiction. Although further studies are needed, these findings support the therapeutic potential of CBD in AMPH-relapse prevention.

Evaluation of drug seeking behavior on nicotine conditioned place preference in zebrafish

Seeking of drugs is commonly evaluated in a specific environment for assessing drug preference. However, cognitive strategies involved in drug seeking are mostly unknown. To assess the strength of environmental cues that can be associated with nicotine in the zebrafish brain reward circuitry, we have designed herein a modified conditioned place preference (CPP) paradigm. This task was devised to identify salient environmental cues relevant for strong nicotine–environment association and drug seeking induction. During test sessions, background colors of the CPP tank chambers were shifted and preference for colors associated to nicotine was assessed. We have compared several tank designs and different compartment colors. Our findings indicated that zebrafish seeking behavior was strongly dependent on compartment color shades. Combination of red and yellow environments, which were preferred and avoided compartments, respectively, was the most effective design presenting the highest CPP-score. Interestingly, animals that stayed for longer periods in the environment conditioned to nicotine during a first testing interval were also able to follow the background color shade conditioned to nicotine to the other compartment immediately after background colors were relocated between compartments. During a second testing period, zebrafish also stayed for longer periods in the colored compartment paired to nicotine during conditioning. These findings suggest that under salient environmental conditions, zebrafish voluntarily followed a shifting visual cue previously associated with nicotine delivery. Furthermore, our findings indicate that zebrafish exhibit spatial associative learning and memory, which generates a repertoire of conspicuous locomotor behaviors induced by nicotine preference in the CPP task.

Tactile Stimulation in Adult Rats Modulates Dopaminergic Molecular Parameters in the Nucleus accumbens Preventing Amphetamine Relapse.

Amphetamine (AMPH) is a psychostimulant drug frequently related to addiction, which is characterized by functional and molecular changes in the brain reward system, favoring relapse development, and pharmacotherapies have shown low effectiveness. Considering the beneficial influences of tactile stimulation (TS) in different diseases that affect the central nervous system (CNS), here we evaluated if TS applied in adult rats could prevent or minimize the AMPH-relapse behavior also accessing molecular neuroadaptations in the nucleus accumbens (NAc). Following AMPH conditioning in the conditioned place preference (CPP) paradigm, male rats were submitted to TS (15-min session, 3 times a day, for 8 days) during the drug abstinence period, which were re-exposed to the drug in the CPP paradigm for additional 3 days for relapse observation and molecular assessment. Our findings showed that besides AMPH relapse, TS prevented the dopamine transporter (DAT), dopamine 1 receptor (D1R), tyrosine hydroxylase (TH), mu opioid receptor (MOR) increase, and AMPH-induced delta FosB (ΔFosB). Based on these outcomes, we propose TS as a useful tool to treat psychostimulant addiction, which is subsequent to clinical studies; it could be included in detoxification programs together with pharmacotherapies and psychological treatments already conventionally established.

Quetiapine attenuates the acquisition of morphine-induced conditioned place preference and reduces ERK phosphorylation in the hippocampus and cerebral cortex

ABSTRACT Background: Quetiapine is an atypical antipsychotic that antagonizes dopamine and serotonin receptors. It has been suggested that quetiapine can be used to treat substance use disorders, including opioid use disorder. Opioids modulate dopaminergic functions associated with conditioned reinforcement and these effects can be measured via the conditioned place preference (CPP) paradigm. Opioids’ unconditioned effects are regulated by several proteins, including extracellular signal-regulated kinase (ERK) and cAMP-responsive element-binding (CREB). Objective: To assess the effect of quetiapine on morphine-induced CPP and motor activity levels, and on the levels of ERK and CREB proteins in the hippocampus and cerebral cortex. Methods: 42 male rats were exposed to a CPP protocol, in which they underwent a conditioning paradigm with saline, quetiapine (40 mg/kg), morphine (10 mg/kg), morphine plus quetiapine (10, 20, or 40 mg/kg), or morphine plus memantine (7.5 mg/kg, a positive control drug) (n = 6 per group). The rats were tested for CPP and exploratory activity. Levels of ERK and CREB proteins in the hippocampus and cerebral cortex were also measured. Results: Quetiapine co-administered with morphine inhibited morphine-induced CPP [F (6, 70) = 11.67, p < .001] and morphine’s effects on motor activity (p < .001). Morphine enhanced ERK phosphorylation in the hippocampus (p < .001) and cerebral cortex (p < .001), an effect inhibited by quetiapine. Conclusion: Quetiapine attenuates morphine-induced CPP and locomotion and these effects are associated with a reduction of ERK phosphorylation in the hippocampus and cerebral cortex. These results suggest that quetiapine should be further explored as a potential treatment for opioid use disorder.

NIH HEAL Initiative: National Institute of Neurological Disorders and Stroke Preclinical Program for Non-Addictive Pain Therapeutic Development

The National Institutes of Health Helping to End Addiction Long-term, or NIH HEAL Initiative aims to focus efforts on advancing scientific solutions to stem the opioid crisis, improving prevention and treatment of opioid misuse/addiction, and enhancing pain management. NINDS is charged with accelerating the discovery and development of new non-addictive pharmacologic and non-pharmacologic pain therapeutics as part of the HEAL Initiative. PSPP provides researchers from academia and industry, within the US and internationally, an efficient, rigorous, one-stop in vivo resource to screen and profile therapeutic candidates including small molecules, biologics, natural products, and devices for the treatment of pain. Under PSPP direction, preclinical testing is performed by a National Institute of Neurological Disorders and Stroke (NINDS) contract facility, PsychoGenics Inc., in a blinded and confidential manner at no cost to the PSPP participants. Participant assets are evaluated in a suite of in vivo pain-related models, for example, chemotherapy-induced neuropathic pain, osteoarthritis pain, and headache. In these models, PSPP uses both evoked (e.g., paw withdrawal threshold, acetone) and non-evoked (e.g., dynamic weight bearing) endpoints to rigorously assess efficacy of the asset in both male and female animals. Importantly, abuse liability is also assessed using a conditioned place preference paradigm or using intravenous self-administration. A key feature of the PSPP is the flexibility to continuously acquire and validate innovative models and endpoints that more closely represent human pain conditions. Notably, in addition to enabling evaluation of small molecules, biologics and natural products, models and endpoints can be appropriately adapted or incorporated to assess devices. We will describe the advances made to date towards establishing program goals of evaluating assets in a rigorous and reproducible manner.

Ethanol Antiallodynia and Reward Seeking in Mice with Spared Nerve Injury

Clinical data suggests that both men and women with chronic pain are more likely to develop alcohol use disorder, to relapse after a period of abstinence, and to report using alcohol to manage chronic pain. These data led to the hypothesis that alcohol-related behaviors are different in those experiencing chronic pain. To test this hypothesis, the analgesic effect of multiple doses of ethanol (0.5, 1, 2 g/kg i.p.) on male and female mice with spared nerve injury (SNI) was investigated using Von Frey and dynamic weight bearing assays. A conditioned place preference (CPP) paradigm was then used to model ethanol seeking after nerve injury. Findings indicate that SNI reduced mechanical thresholds, increased weight bearing on the contralateral hindpaw, and decreased paw print area on the ipsilateral hindpaw. In male SNI mice, all three doses of ethanol fully reversed mechanical hypersensitivity, while in female mice only the highest dose (2.0 g/kg) was fully antiallodynic. Additionally, the highest dose was analgesic in Sham animals in both male and female mice. In the CPP experiments, conditioning with 0.5 g/kg ethanol induced a modest CPP for the ethanol-paired chamber in SNI and Sham male mice. Further, following extinction, painful stimulation reinstated ethanol-seeking behavior only in SNI mice. These data suggest that the analgesic effects of alcohol are distinct in male and female mice and that animals in chronic pain may be more sensitive to stress-induced reinstatement when pain is the stressor. Ongoing work is focused on characterizing ethanol CPP in female mice and investigating neural correlates of ethanol analgesia and reward in mice in chronic pain.

The Effect of Spared Nerve Injury on Ethanol Reward Seeking and Reinstatement

Alcohol use disorder (AUD) and chronic pain are complex and debilitating conditions that are difficult to treat, lead to enormous economic costs, and excessive suffering. The difficulty in developing new treatments for AUD is partially due to the lack of consideration given to the wide array of factors that drive alcohol intake. Clinical data suggest that both men and women with chronic pain are more likely to develop alcohol use disorder and report using alcohol to deal with chronic pain. Additionally, it has been shown that self‐report of chronic pain correlates with alcohol relapse after a period of abstinence. These data led to the hypothesis that neural mechanisms that contribute to alcohol related behaviors are different in individuals that are also experiencing chronic pain. To test this hypothesis, we used a conditioned place preference (CPP) paradigm to model ethanol seeking in male and female rodents that had undergone either a spared nerve injury (SNI) model of chronic pain or a sham surgery. To determine a dose of ethanol that may be selectively rewarding to injured animals, we first tested the analgesic effects of multiple doses of ethanol on pain‐related behaviors in SNI and Sham mice. The higher doses of 1.0g/kg and 2.0g/kg (i.p.) of ethanol were anti‐allodynic in SNI mice and analgesic in sham mice. However, we found that the lower dose 0.5 g/kg of ethanol was able to fully reverse mechanical hypersensitivity in SNI animals, while not influencing mechanical thresholds in sham mice. Thus, we conditioned mice using 0.5g/kg of ethanol. We found this dose induced a modest conditioned place preference for the ethanol‐paired chamber in both SNI and Sham male mice. Mice then underwent extinction training for 1 week, during which time animals were exposed to the CPP apparatus without receiving any ethanol. To investigate relapse‐related behavior, we then tested whether painful stimulation would reinstate ethanol seeking behavior. We found that threshold hindpaw stimulation was able to reinstate ethanol seeking behavior in SNI, but not sham animals. This suggests that animals in chronic pain may associate alcohol with pain relief or that chronic pain animals may be more sensitive to stress induced reinstatement when pain is the stressor. We also tested the effect of drug induced reinstatement and found no differences between SNI and Sham mice, leading us to believe that differences found in pain induced reinstatement were selective to that modality. Ongoing work is aimed at determining the effect of ethanol on weight bearing behavior as well as the effect of chronic pain on ethanol seeking and relapse‐related behavior in female mice.

An extended amygdala-midbrain circuit controlling cocaine withdrawal-induced anxiety and reinstatement.

SUMMARYAlthough midbrain dopamine (DA) circuits are central to motivated behaviors, our knowledge of how experience modifies these circuits to facilitate subsequent behavioral adaptations is limited. Here we demonstrate the selective role of a ventral tegmental area DA projection to the amygdala (VTADA→amygdala) for cocaine-induced anxiety but not cocaine reward or sensitization. Our rabies virus-mediated circuit mapping approach reveals a persistent elevation in spontaneous and task-related activity of inhibitory GABAergic cells from the bed nucleus of the stria terminalis (BNST) and downstream VTADA→amygdala cells that can be detected even after a single cocaine exposure. Activity in BNSTGABA→midbrain cells is related to cocaine-induced anxiety but not reward or sensitization, and silencing this projection prevents development of anxiety during protracted withdrawal after cocaine administration. Finally, we observe that VTADA→amygdala cells are strongly activated after a challenge exposure to cocaine and that activity in these cells is necessary and sufficient for reinstatement of cocaine place preference.

Localizing circuits of cocaine contextual memories

Addiction is characterized by compulsive drug seeking and taking behaviors. Cravings triggered by the presence of environmental cues that were once associated to drug use are a main contributor of relapse and once these drug‐cue memories are formed they are difficult to erase. Addictive drugs like cocaine engage molecular pathways of associate learning, in which recall of an established memory is followed by its reconsolidation, strengthening that memory. The reactivation period is a critical time wherein memories are labile and vulnerable to behavioral and pharmacological interference. Given the widespread negative impact of drug use in our society, it is of great importance to understand the mechanisms underlying drug seeking behaviors to generate effective preventions and treatments. The goal of this study is to elucidate the neural substrate in the nucleus accumbens crucial for the maintenance of cocaine contextual memories, and explore neural plasticity involved. Designer receptors exclusively activated by designer drugs (DREADDs) were used to inhibit neurons at the nucleus accumbens. To accomplish this, adult male mice underwent bilateral intracranial injections of an inhibitory DREADD followed by a cocaine conditioned place preference paradigm. Nucleus accumbens neurons were inhibited via systemic injection of clozapine N‐oxide immediately following reactivation of cocaine contextual memory, and mice were re‐tested for place preference 72 hours and 7 days later. A separate cohort of mice underwent the same cocaine conditioned place preference paradigm, 24 hours post preference testing animals were returned to the cocaine context in a drug‐free state to reactivate cocaine memories. Sixty minutes after, brains were collected and prepared for quantitative RT‐PCR to measure activity‐regulated cytoskeleton‐associate protein (Arc) mRNA. To evaluate the functional plasticity in medium spiny neurons at the nucleus accumbens, upon reconsolidation of cocaine contextual memories, we utilized the fosTRAP2‐Ai14 mouse model. A cohort of male and female fosTRAP2‐Ai14 mice underwent cocaine conditioned place preference exactly as in the previous experiment and brains collected 9 days after recall of cocaine contextual memory and 4‐hydroxytamoxifen induction. Dendritic spine density of fosTRAP cells activated by recall of cocaine context were analyzed. Results show that chemogenetic inhibition of the nucleus accumbens immediately following reactivation of cocaine contextual memory significantly reduced a once established preference for the cocaine context. Furthermore, Arc mRNA expression is upregulated at the nucleus accumbens following exposure to the prior cocaine‐paired context. Finally, we show a significant increase in dendritic spine density in medium spiny neurons at the nucleus accumbens following recall of cocaine context. These findings suggest the nucleus accumbens is important for the reconsolidation of cocaine contextual memories and exhibits dendritic neuroplastic changes upon reconsolidation of cocaine memories.

The D2-like Dopamine Receptor Agonist Quinpirole Microinjected Into the Ventral Pallidum Dose-Dependently Inhibits the VTA and Induces Place Aversion.

BackgroundThe ventral pallidum (VP) is a dopaminoceptive forebrain structure regulating the ventral tegmental area (VTA) dopaminergic population activity. We have recently demonstrated that in the VP, the D2-like dopamine (DA) receptor agonist quinpirole dose dependently facilitates memory consolidation in inhibitory avoidance and spatial learning. According to our hypothesis, quinpirole microinjected into the VP can modulate the VTA DAergic activity and influence motivation and learning processes of rats.MethodsQuinpirole was microinjected at 3 different doses into the VP of male rats, and controls received vehicle. Single unit recordings were employed to assess VTA DAergic activity. To investigate the possible reinforcing or aversive effect of quinpirole in the VP, the conditioned place preference paradigm was used.ResultsOur results showed that intra-VP quinpirole microinjection regulates VTA DAergic neurons according to an inverted U-shaped dose-response curve. The largest dose of quinpirole decreased the population activity and strongly reduced burst activity of the DAergic neurons in the first hour after its application. In contrast, the 2 smaller doses increased DA population activity, but their effect started with a delay 1 hour after their microinjection. The CPP experiments revealed that the largest dose of quinpirole in the VP induced place aversion in the rats. Furthermore, the largest dose of quinpirole induced an acute locomotor activity reduction, while the medium dose led to a long-duration increase in locomotion.ConclusionsIn summary, quinpirole dose dependently regulates VTA DAergic activity as well as the motivation and motor behavior of the rats at the level of the VP.

Encoding of Environmental Cues in Central Amygdala Neurons during Foraging.

To successfully forage in an environment filled with rewards and threats, animals need to rely on familiar structures of their environment that signal food availability. The central amygdala (CeA) is known to mediate a panoply of consummatory and defensive behaviors, yet how specific activity patterns within CeA subpopulations guide optimal choices is not completely understood. In a paradigm of appetitive conditioning in which mice freely forage for food across a continuum of cues, we found that two major subpopulations of CeA neurons, Somatostatin-positive (CeASst) and protein kinase Cδ-positive (CeAPKCδ) neurons, can assign motivational properties to environmental cues. Although the proportion of food responsive cells was higher within CeASst than CeAPKCδ neurons, only the activities of CeAPKCδ, but not CeASst, neurons were required for learning of contextual food cues. Our findings point to a model in which CeAPKCδ neurons may incorporate stimulus salience together with sensory features of the environment to encode memory of the goal location.SIGNIFICANCE STATEMENT The CeA has a very important role in the formation of memories that associate sensory information with aversive or rewarding representation. Here, we used a conditioned place preference paradigm, where freely moving mice learn to associate external cues with food availability, to investigate the roles of CeA neuron subpopulations. We found that CeASst and CeAPKCδ neurons encoded environmental cues during foraging but only the activities of CeAPKCδ neurons were required for learning of contextual food cues.

Brief Maternal Separation Inoculates Against the Effects of Social Stress on Depression-Like Behavior and Cocaine Reward in Mice

Exposure to intermittent repeated social defeat (IRSD) increases the vulnerability of mice to the rewarding effects of cocaine in the conditioned place preference (CPP) paradigm. According to the “inoculation of stress” hypothesis, a brief period of maternal separation (MS) can provide protection against the negative effects of IRSD. The aim of the present study was to assess whether exposure to a brief episode of MS prevents the subsequent short-term effects of IRSD on depression- and anxiety-like behaviors and to explore its long-term effects on cocaine CPP in mice. Four groups of male C57BL/6 mice were employed; two groups were separated from their mother [6 h on postnatal day (PND) 9], while the other two groups were not (controls). On PND 47, 50, 53 and 56, mice that had experienced MS were exposed to social defeat in the cage of an aggressive resident mouse (MS + IRSD group) or were allowed to explore an empty cage (MS + EXPL group). The same procedure was performed with control mice that had not experienced MS (CONTROL + IRSD and CONTROL + EXPL groups). On PND57-58, all the mice performed the elevated plus maze and the hole-board, social interaction and splash tests. Three weeks after the last episode of defeat, all the mice underwent the CPP procedure with cocaine (1 mg/kg). Irrespective of whether or not MS had taken place, a reduction in open arms measures, dips, and social interaction was observed in mice that experienced IRSD. A higher latency of grooming and acquisition of cocaine-induced CPP were observed only in mice exposed to IRSD alone (CONTROL + IRSD). These results suggest that exposure to a brief episode of stress early in life increases the subsequent resilience of animals to the effects of social stress on vulnerability to cocaine.

Lateral Hypothalamic Orexin Neurons Mediate the Reward Effects of Pain Relief Induced by Electroacupuncture.

The reward of pain relief caused by acupuncture has been found to be clinically significant. However, the molecular mechanisms underlying acupuncture-induced reward of pain relief in chronic pain remain unclear and have not been analyzed in suitable preclinical models. Here, we investigated whether acupuncture could potentially induce the reward of pain relief and orexin neuronal signaling in the lateral hypothalamus (LH) and exhibit a possible role in electroacupuncture (EA)-induced reward in spared nerve injury (SNI) rats. Therefore, by using conditioned place preference (CPP) paradigm, we noticed that EA induced the preference for cues associated with EA-induced pain relief in the early, but not late, phase of chronic pain. These observations were different from the immediate antihyperalgesic effects of EA. c-Fos/orexin double labeling revealed that EA stimulation on 14 days but not on 28 days after SNI modeling activated greater numbers of c-Fos positive orexin neurons in the LH after the CPP test. Moreover, the administration of an orexin-A antagonist in the LH significantly blocked the reward effects of pain relief induced by EA. Furthermore, by using cholera toxin b subunit combined with c-Fos detection, we found that the orexin circuit from the LH to the nucleus accumbens (NAc) shell was significantly activated after EA induced CPP. Microinjection of the orexin antagonist into the NAc shell substantially attenuated the CPP induced by EA. Intravenous injection of low-dose orexin-A together with EA resulted in significantly greater antihyperalgesia effects and CPP scores. Together, these findings clearly demonstrated that LH orexin signaling could potentially play a critical role in the reward effects of pain relief induced by acupuncture. The observations of the present study extended our understanding of orexin signaling in the LH and its role in EA-induced reward, providing new insights into the mechanisms of acupuncture analgesia.

Differences in the Alcohol Preference Assessment of Shy and Bold Zebrafish.

Individuals differ in their preference for alcohol and propensity to develop alcoholism, where the behavioral profile, such as the bold-shy axis, plays an important role for such a difference. However, literature is limited and conflicting on the causes and consequences of this relationship. Translational studies using animal models, such as zebrafish, can help identify behavioral traits that predispose individuals to drink alcohol compulsively. Here, the preference for alcohol was investigated in two distinct traits in zebrafish: shy and bold. For this purpose, fish were separated into shy and bold traits and then a conditioned place preference paradigm was used, a strategy that allows the rewarding effects from alcohol to be assessed by the ability to enhance the animal’s preference for an environment that initially was not preferred. It was found that bold zebrafish actively searched for the environment that was paired to alcohol after one acute exposure, whereas, shy fish changed their place preference even without alcohol administration, showing that the conditioned place preference protocol, given the short amount time to assess place preference, is not ample enough for shy fish to choose. Our results show that behavioral profiles must be considered in further studies since differences between shy and bold individuals on preference behavior can strongly interfere in the assessment of drug preference, mainly when using the conditioned place preference paradigm.

Neuropsychopharmacology of Emerging Drugs of Abuse: meta- and para-Halogen-Ring-Substituted α-PVP ("flakka") Derivatives.

Changes in the molecular structure of synthetic cathinones has led to an increase in the number of novel emerging drugs in the illicit drug market at an unprecedented rate. Unfortunately, little is known about the neuropsychopharmacology of recently emerged halogen-substituted α-PVP derivatives. Thus, the aim of this study was to investigate the role of para- and meta-halogen (F-, Cl-, and Br-) substitutions on the in vitro, in silico, and in vivo effects of α-pyrrolidinopentiophenone (α-PVP) derivatives. HEK293 cells expressing the human dopamine or serotonin transporter (hDAT and hSERT) were used for the uptake inhibition and transporter affinity assays. Molecular docking was used to model the interaction mechanism against DAT. Swiss CD-1 mice were used for the horizontal locomotor activity, open field test, and conditioned place preference paradigm. All compounds demonstrated potent DA uptake inhibition and higher DAT selectivity than cocaine. Meta-substituted cathinones showed higher DAT/SERT ratios than their para- analogs, which correlates with an increased psychostimulant effect in vivo and with different meta- and para-in silico interactions at DAT. Moreover, all compounds induced rewarding and acute anxiogenic effects in mice. In conclusion, the present study demonstrates the role of meta- and para-halogen substitutions in the mechanism of action and provides the first evidence of the rewarding and anxiety-like properties of halogenated α-PVP derivatives.

Effects of electrical stimulation and temporary inactivation of basolateral amygdala on morphine-induced conditioned place preference in rats

In the present study, to evaluate the role of the basolateral amygdala (BLA) in morphine addiction, the BLA was stimulated electrically, or inactivated temporarily using lidocaine. The electrical stimulation (ES) was delivered to BLA with low or high intensities (LI or HI: 25 or 150 µA, respectively), and five minutes before morphine administration with effective or ineffective doses, lidocaine was microinjected into the BLA. Using a 5-day conditioned place preference (CPP) paradigm, the dependence on morphine was evaluated. The results showed that LI-ES of BLA induced CPP in both the acquisition and expression phases, in the control and the ineffective dose of morphine groups. HI-ES had no effect on CPP acquisition but induced aversion in the expression, with both effective and ineffective doses of morphine. Inactivation of BLA using lidocaine, inhibited morphine-induced CPP in both acquisition and expression phases. The results of the present study indicate the prominent role of BLA in morphine addiction and dependence. Considering the contradictory results of different intensities of ES, it can be inferred that there are different neural circuits in this area of the brain, in relation to the reward responses.

Rabbits can be conditioned in a food-induced place preference paradigm

The conditioned place preference (CPP) paradigm has been employed in behavioral studies to investigate the responses to an environment where a reinforcing event occurs. It is applied to reveal incentive motivational responses to reward-related stimuli. It is standardized and widely applied in mice and rats, two of the most common species of laboratory animals. However, no studies using the CPP protocol have been performed in rabbits, even though this animal model is commonly used in pharmacological and behavioral research. There are important physiological and behavioral differences between rodents and rabbits. For example, rodents are spontaneous ovulators while rabbits are induced ovulators. In addition, lactation in the rabbit is circadian, which is unique among mammals. The present investigation aims to establish whether rabbits can be conditioned by using a food-induced CPP protocol in subjects with caloric restriction. Adult female rabbits were subjected to a three-compartment CPP protocol. The food produced place preference, demonstrating for the first time that rabbits can be conditioned using the CPP paradigm opening a new field of opportunities for behavioral studies of positive affective states in a species with important behavioral and physiological differences from rodents.

Effects of imidazoline agents in a rat conditioned place preference model of addiction

Agmatine (AG), idazoxan (IDZ), and efaroxan (EFR) are imidazoline receptor ligands with beneficial effects in central nervous system disorders. The present study aimed to evaluate the interaction between AG, IDZ, and EFR with an opiate, tramadol (TR), in a conditioned place preference (CPP) paradigm. In the experiment, we used five groups with 8 adult male Wistar rats each. During the condition session, on days 2, 4, 6, and 8, the rats received the drugs (saline, or TR, or IDZ and TR, or EFR and TR, or AG and TR) and were placed in their least preferred compartment. On days 1, 3, 5, and 7, the rats received saline in the preferred compartment. In the preconditioning, the preferred compartment was determined. In the postconditioning, the preference for one of the compartments was reevaluated. TR increased the time spent in the non-preferred compartment. AG decreased time spent in the TR-paired compartment. EFR, more than IDZ, reduced the time spent in the TR-paired compartment, but without statistical significance. AG reversed the TR-induced CPP, while EFR and IDZ only decreased the time spent in the TR-paired compartment, without statistical significance.

Insulin replacement prevents the acquisition but not the expression of morphine-induced conditioned place preference in streptozotocin-induced diabetic rats

Insulin receptors have distributed in all brain regions, including the nucleus Accumbens (NAc), and where is implicated in the reward properties of drugs. It is well known that insulin signaling can regulate dopamine release. Therefore, in the present study, we tried to examine the effect of insulin replacement on the acquisition and expression of morphine-induced conditioned place preference (CPP) in diabetic rats. Forty-eight male Wistar rats were divided into two non-diabetic (Naïve) and diabetic groups rendered by a single injection of streptozotocin (STZ). These groups separately received insulin (10U/kg) or saline (1 ml/kg) one hour prior to morphine administration (5mg/kg;s.c.) during conditioning days (acquisition phase) or post-conditioning day (expression phase) in the CPP paradigm. In this paradigm, conditioning score (CS) and locomotion activity were recorded by Ethovision. The STZ-induced diabetic rats displayed higher CS compared to naïve rats (P<0.05). This effect was abolished in all diabetic rats that received insulin during conditioning days but not the expression phase. This study has provided evidence that insulin plays a modulatory role in morphine-induced CPP, and insulin replacement during the acquisition phase could reduce the rewarding properties of morphine in diabetes conditions through a possible modulating effect on dopamine release in the NAc region.