Neurobiological mechanisms of the reinstatement of drug-conditioned place preference

Blunted food conditioned place preference-like behavior in adolescent-stressed male hamsters

Social stress during adolescence results in long lasting weight gain, obesity, and enhanced food hoarding behavior in hamsters. We wanted to determine whether stress also enhanced conditioned place preference-like behavior (CPP-like) for food reward, as would be expected from studies with substances like cocaine. Our experimental animals were exposed daily to aggressive adults for two weeks in early puberty, while also trained to explore a V-shaped maze containing a food reward at one end. They were tested for CPP-like behavior on the last day of social stress. Our results showed that while stress enhanced weight gain, food intake, food efficiency, and body fat, it caused a reduction of Place Preference as compared to controls. In fact, the correlated relationship between Place Preference and body fat was inverted by stress exposure: while it was positively correlated in controls, it was mildly negatively correlated in stressed hamsters. These unexpected data illustrate the extent of adaptive behavior in foraging animals once a resource has become untrustworthy.

Regulator of G protein signaling 6 (RGS6) in dopamine neurons promotes EtOH seeking, behavioral reward, and susceptibility to relapse

Mesolimbic dopamine (DA) transmission is believed to play a critical role in mediating reward responses to drugs of abuse, including alcohol (EtOH). The neurobiological mechanisms underlying EtOH-seeking behavior and dependence are not fully understood, and abstinence remains the only effective way to prevent alcohol use disorders (AUDs). Here, we developed novel RGS6fl/fl; DAT-iCreER mice to determine the role of RGS6 in DA neurons on EtOH consumption, reward, and relapse behaviors. We found that RGS6 is expressed in DA neurons in both human and mouse ventral tegmental area (VTA), and that RGS6 loss in mice upregulates DA transporter (DAT) expression in VTA DA neuron synaptic terminals. Remarkably, loss of RGS6 in DA neurons significantly reduced EtOH consumption, preference, and reward in a manner indistinguishable from that seen in RGS6-/- mice. Strikingly, RGS6 loss from DA neurons before or after EtOH behavioral reward is established significantly reduced (~ 50%) re-instatement of reward following extinguishment, demonstrating distinct roles of RGS6 in promoting reward and relapse susceptibility to EtOH. These studies identify DA neurons as the locus of RGS6 action in promoting EtOH consumption, preference, reward, and relapse. RGS6 is unique among R7 RGS proteins in promoting rather than suppressing behavioral responses to drugs of abuse and to modulate EtOH behavioral reward. This is a result of RGS6's pre-synaptic actions that we hypothesize promote VTA DA transmission by suppressing GPCR-Gαi/o-DAT signaling in VTA DA neurons. These studies identify RGS6 as a potential therapeutic target for behavioral reward and relapse to EtOH.

N-acetylcysteine attenuates accumbal core neuronal activity in response to morphine in the reinstatement of morphine CPP in morphine extinguished rats

Numerous studies have suggested that N-acetylcysteine (NAC), has the potential to suppress drug craving in people with substance use disorder and reduce drug-seeking behaviors in animals. The nucleus accumbens (NAc) plays a crucial role in the brain's reward system, with the nucleus accumbens core (NAcore) specifically implicated in compulsive drug seeking and relapse. In this study, we aimed to explore the impact of subchronic NAC administration during the extinction period and acute NAC administration on the electrical activity of NAcore neurons in response to a priming dose of morphine in rats subjected to extinction from morphine-induced place preference (CPP).We conducted single-unit recordings in anesthetized rats on the reinstatement day, following the establishment of morphine-induced conditioned place preference (7 mg/kg, s.c., 3 days), and subsequent drug-free extinction. In the subchronically NAC-treated groups, rats received daily injections of either NAC (50 mg/kg; i.p.) or saline during the extinction period. On the reinstatement day, we recorded the spontaneous activity of NAcore neurons for 15 min, administered a priming dose of morphine, and continued recording for an additional 45 min. While morphine excited most recorded neurons in saline-treated rats, it failed to alter firing rates in NAC-treated rats that had received NAC during the extinction period. For acutely NAC-treated animals, we recorded the baseline activity of NAcore neurons for 10 min before administering a single injection of either NAC (50 mg/kg; i.p.) or saline in rats with no treatment during the extinction. Following 30 min of recording and a priming dose of morphine (1 mg/kg, s.c.), the recording continued for an additional 30 min. The firing activity of NAcore neurons did not show significant changes after morphine or NAC injection. In conclusion, our findings emphasize that daily NAC administration during the extinction period significantly attenuates the morphine-induced increase in firing rates of NAcore neurons during the reinstatement of morphine CPP. However, acute NAC injection does not produce the same effect. These results suggest that modulating glutamate transmission through daily NAC during extinction may effectively inhibit the morphine place preference following the excitatory effects of morphine on NAcore neurons.

Δ9-Tetrahydrocannabinol Vapor Exposure Produces Conditioned Place Preference in Male and Female Rats

Background: The use of place conditioning procedures and drug vapor exposure models can increase our understanding of the rewarding and aversive effects of vaped cannabis products. Currently there are limited data on the conditioned rewarding effects of vaporized Δ9-tetrahydrocannabinol (THC), the primary psychoactive constituent of cannabis in rats, and no studies to date examining sex differences. Methods: Male and female Sprague-Dawley rats (N=96; 12 per sex/group) underwent place conditioning sessions immediately after exposure to THC or vehicle (propylene glycol [PG]) vapor. Locomotor activity was measured by beam breaks during conditioning sessions. THC vapor-conditioned rats received one of three THC vapor exposure amounts (low: 5 puffs of 100 mg/mL THC, medium: 5 puffs of 200 mg/mL THC, or high: 10 puffs of 200 mg/mL THC) and matched vehicle vapor (PG) exposure on alternate days for 16 daily sessions. A "no THC" control group of vehicle-conditioned rats received only PG vapor exposure each day. After the 8th and 16th conditioning sessions, untreated rats were tested for conditioned place preference (CPP) or aversion (CPA). Next, extinction tests and a THC vapor-primed reinstatement test were conducted. Results: THC vapor produced CPP and locomotor effects in an exposure dependent manner, and some sex differences were observed. Low THC vapor exposure did not produce CPP in males or females. Medium THC vapor exposure produced CPP in males, but not females. High THC vapor exposure produced CPP in both males and females. Medium and high THC vapor exposure amounts produced hyperactivity in female rats, but not male rats. CPP was more resistant to extinction in females than males. THC vapor reexposure (i.e., drug-prime) after extinction did not result in reinstatement of CPP for either sex. Conclusion: This study demonstrates conditioned rewarding effects of THC vapor in both male and female rats and provides evidence for sex differences in amounts of THC vapor that produce CPP and in time to extinction. CPA was not observed at any of the THC vapor exposure amounts tested. These data provide a foundation for future exploration of the conditioned effects of cannabis constituents and extracts using vapor exposure models.

Associative memory neurons of encoding multi-modal signals are recruited by neuroligin-3-mediated new synapse formation

The joint storage and reciprocal retrieval of learnt associated signals are presumably encoded by associative memory cells. In the accumulation and enrichment of memory contents in lifespan, a signal often becomes a core signal associatively shared for other signals. One specific group of associative memory neurons that encode this core signal likely interconnects multiple groups of associative memory neurons that encode these other signals for their joint storage and reciprocal retrieval. We have examined this hypothesis in a mouse model of associative learning by pairing the whisker tactile signal sequentially with the olfactory signal, the gustatory signal, and the tail-heating signal. Mice experienced this associative learning show the whisker fluctuation induced by olfactory, gustatory, and tail-heating signals, or the other way around, that is, memories to multi-modal associated signals featured by their reciprocal retrievals. Barrel cortical neurons in these mice become able to encode olfactory, gustatory, and tail-heating signals alongside the whisker signal. Barrel cortical neurons interconnect piriform, S1-Tr, and gustatory cortical neurons. With the barrel cortex as the hub, the indirect activation occurs among piriform, gustatory, and S1-Tr cortices for the second-order associative memory. These associative memory neurons recruited to encode multi-modal signals in the barrel cortex for associative memory are downregulated by neuroligin-3 knockdown. Thus, associative memory neurons can be recruited as the core cellular substrate to memorize multiple associated signals for the first-order and the second-order of associative memories by neuroligin-3-mediated synapse formation, which constitutes neuronal substrates of cognitive activities in the field of memoriology.

Regulator of G protein signaling 6 (RGS6) in ventral tegmental area (VTA) dopamine neurons promotes EtOH seeking, behavioral reward and susceptibility to relapse

Mesolimbic dopamine (DA) transmission is believed to play a critical role in mediating reward responses to drugs of abuse, including alcohol (EtOH). EtOH is the most abused substance worldwide with chronic consumption often leading to the development of dependence and abuse. Unfortunately, the neurobiological mechanisms underlying EtOH-seeking behavior and dependence are not fully understood, and abstinence remains the only effective way to prevent alcohol use disorders (AUDs). Here, we developed novel RGS6 fl/fl ; DAT-iCreER mice to determine the role of RGS6 in VTA DA neurons on EtOH consumption and reward behaviors. We found that RGS6 is expressed in DA neurons in both human and mouse VTA, and that RGS6 loss in mice upregulates DA transporter (DAT) expression in VTA DA neuron synaptic terminals. Remarkably, loss of RGS6 in VTA DA neurons significantly reduced EtOH consumption, preference, and reward in a manner indistinguishable from that seen in RGS6 -/- mice. Strikingly, RGS6 loss from VTA DA neurons before or after EtOH behavioral reward is established significantly reduced (∼50%) re-instatement of reward following extinguishment, demonstrating distinct roles of RGS6 in promoting reward and relapse susceptibility to EtOH. These studies illuminate a critical role of RGS6 in the mesolimbic circuit in promoting EtOH seeking, reward, and reinstatement. We propose that RGS6 functions to promote DA transmission through its function as a negative modulator of GPCR-Gα i/o -DAT signaling in VTA DA neurons. These studies identify RGS6 as a potential therapeutic target for behavioral reward and relapse to EtOH.

Bile acids modulate reinstatement of cocaine conditioned place preference and accumbal dopamine dynamics without compromising appetitive learning

Psychostimulants target the dopamine transporter (DAT) to elicit their psychomotor actions. Bile acids (BAs) can also bind to DAT and reduce behavioral responses to cocaine, suggesting a potential therapeutic application of BAs in psychostimulant use disorder. Here, we investigate the potential of BAs to decrease drug-primed reinstatement when administered during an abstinence phase. To do this, after successful development of cocaine-associated contextual place preference (cocaine CPP), cocaine administration was terminated, and animals treated with vehicle or obeticholic acid (OCA). When preference for the cocaine-associated context was extinguished, mice were challenged with a single priming dose of cocaine, and reinstatement of cocaine-associated contextual preference was measured. Animals treated with OCA demonstrate a significantly lower reinstatement for cocaine CPP. OCA also impairs the ability of cocaine to reduce the clearance rate of electrically stimulated dopamine release and diminishes the area under the curve (AUC) observed with amperometry. Furthermore, the AUC of the amperometric signal positively correlates with the reinstatement index. Using operant feeding devices, we demonstrate that OCA has no effect on contextual learning or motivation for natural rewards. These data highlight OCA as a potential therapeutic for cocaine use disorder.

An ethogram analysis of cutaneous thermal pain sensitivity and oxycodone reward-related behaviors in rats

Inter-relationships between pain sensitivity, drug reward, and drug misuse are of considerable interest given that many analgesics exhibit misuse potential. Here we studied rats as they underwent a series of pain- and reward-related tests: cutaneous thermal reflex pain, induction and extinction of conditioned place preference to oxycodone (0.56 mg/kg), and finally the impact of neuropathic pain on reflex pain and reinstatement of conditioned place preference. Oxycodone induced a significant conditioned place preference that extinguished throughout repeated testing. Correlations identified of particular interest included an association between reflex pain and oxycodone-induced behavioral sensitization, and between rates of behavioral sensitization and extinction of conditioned place preference. Multidimensional scaling analysis followed by k-clustering identified three clusters: (1) reflex pain, rate of behavioral sensitization and rate of extinction of conditioned place preference (2) basal locomotion, locomotor habituation, acute oxycodone-stimulated locomotion and rate of change in reflex pain during repeated testing, and (3) magnitude of conditioned place preference. Nerve constriction injury markedly enhanced reflex pain but did not reinstate conditioned place preference. These results suggest that high rates of behavioral sensitization predicts faster rates of extinction of oxycodone seeking/reward, and suggest that cutaneous thermal reflex pain may be predictive of both.

The transcriptional response to acute cocaine is inverted in male mice with a history of cocaine self-administration and withdrawal throughout the mesocorticolimbic system

A large body of work has demonstrated that cocaine-induced changes in transcriptional regulation play a central role in the onset and maintenance of cocaine use disorder. An underappreciated aspect of this area of research, however, is that the pharmacodynamic properties of cocaine can change depending on an organism's previous drug-exposure history. In this study, we utilized RNA sequencing to characterize how the transcriptome-wide effects of acute cocaine exposure were altered by a history of cocaine self-administration and long-term withdrawal (30 days) in the ventral tegmental area (VTA), nucleus accumbens (NAc), and prefrontal cortex (PFC) in male mice. First, we found that the gene expression patterns induced by a single cocaine injection (10 mg/kg) were discordant between cocaine-naïve mice and mice in withdrawal from cocaine self-administration. Specifically, the same genes that were upregulated by acute cocaine in cocaine-naïve mice were downregulated by the same dose of cocaine in mice undergoing long-term withdrawal; the same pattern of opposite regulation was observed for the genes downregulated by initial acute cocaine exposure. When we analyzed this dataset further, we found that the gene expression patterns that were induced by long-term withdrawal from cocaine self-administration showed a high degree of overlap with the gene expression patterns of acute cocaine exposure - even though animals had not consumed cocaine in 30 days. Interestingly, cocaine re-exposure at this withdrawal time point reversed this expression pattern. Finally, we found that this pattern was similar across the VTA, PFC, NAc, and within each brain region the same genes were induced by acute cocaine, re-induced during long-term withdrawal, and reversed by cocaine re-exposure. Together, we identified a longitudinal pattern of gene regulation that is conserved across the VTA, PFC, and NAc, and characterized the genes constituting this pattern in each brain region.

Oleoylethanolamide attenuates cocaine-primed reinstatement and alters dopaminergic gene expression in the striatum

The lipid oleoylethanolamide (OEA) has been shown to affect reward-related behavior. However, there is limited experimental evidence about the specific neurotransmission systems OEA may be affecting to exert this modulatory effect. The aim of this study was to evaluate the effects of OEA on the rewarding properties of cocaine and relapse-related gene expression in the striatum and hippocampus. For this purpose, we evaluated male OF1 mice on a cocaine-induced CPP procedure (10 mg/kg) and after the corresponding extinction sessions, we tested drug-induced reinstatement. The effects of OEA (10 mg/kg, i.p.) were evaluated at three different timepoints: (1) Before each cocaine conditioning session (OEA-C), (2) Before extinction sessions (OEA-EXT) and (3) Before the reinstatement test (OEA-REINST). Furthermore, gene expression changes in dopamine receptor D1 gene, dopamine receptor D2 gene, opioid receptor µ, cannabinoid receptor 1, in the striatum and hippocampus were analyzed by qRT-PCR. The results obtained in the study showed that OEA administration did not affect cocaine CPP acquisition. However, mice receiving different OEA treatment schedules (OEA-C, OEA-EXT and OEA-REINST) failed to display drug-induced reinstatement. Interestingly, the administration of OEA blocked the increase of dopamine receptor gene D1 in the striatum and hippocampus caused by cocaine exposure. In addition, OEA-treated mice exhibited reduced striatal dopamine receptor gene D2 and cannabinoid receptor 1. Together, these findings suggest that OEA may be a promising pharmacological agent in the treatment of cocaine use disorder.

Natural Polyphenols-Resveratrol, Quercetin, Magnolol, and β-Catechin-Block Certain Aspects of Heroin Addiction and Modulate Striatal IL-6 and TNF-α

We have examined the effects of four different polyphenols in attenuating heroin addiction using a conditioned place preference (CPP) paradigm. Adult male Sprague Dawley rats received heroin (alternating with saline) in escalating doses starting from 10 mg/kg, i.p. up to 80 mg/kg/d for 14 consecutive days. The rats were treated with distilled water (1 mL), quercetin (50 mg/kg/d), β-catechin (100 mg/kg/d), resveratrol (30 mg/kg/d), or magnolol (50 mg/kg/d) through oral gavage for 7 consecutive days, 30 min before heroin administration, starting on day 8. Heroin withdrawal manifestations were assessed 24 h post last heroin administration following the administration of naloxone (1 mg/kg i.p). Heroin CPP reinstatement was tested following a single dose of heroin (10 mg/kg i.p.) administration. Striatal interleukin 6 (IL-6) and tumor necrosis factor alpha (TNF-α) were quantified (ELISA) after naloxone-precipitated heroin withdrawal. Compared to the vehicle, the heroin-administered rats spent significantly more time in the heroin-paired chamber (p < 0.0001). Concomitant administration of resveratrol and quercetin prevented the acquisition of heroin CPP, while resveratrol, quercetin, and magnolol blocked heroin-triggered reinstatement. Magnolol, quercetin, and β-catechin blocked naloxone-precipitated heroin withdrawal and increased striatal IL-6 concentration (p < 0.01). Resveratrol administration was associated with significantly higher withdrawal scores compared to those of the control animals (p < 0.0001). The results of this study show that different polyphenols target specific behavioral domains of heroin addiction in a CPP model and modulate the increase in striatal inflammatory cytokines TNF-α and IL-6 observed during naloxone-precipitated heroin withdrawal. Further research is needed to study the clinical utility of polyphenols and to investigate the intriguing finding that resveratrol enhances, rather than attenuates naloxone-precipitated heroin withdrawal.

Mitragynine, a primary constituent of kratom reinstates morphine-seeking behaviour in rats

Mitragynine (MG) is a pharmacologically active alkaloid derived from the leaves of Mitragyna speciosa Korth (Kratom). This plant has sparked significant interest as a potential alternative treatment for managing opioid dependence and withdrawal due to its opioid-like pharmacological effects. However, whether MG exposure would trigger opioid-seeking behaviour following abstinence has not been investigated. The present study examined the effects of MG priming on morphine-seeking behaviour in rats. Male Sprague-Dawley rats were initially trained to intravenously self-administer morphine (0.5 mg/kg/infusion) under a fixed ratio-3 schedule of reinforcement. Removal of both morphine infusions and drug-associated cues led to the subsequent extinction of the drug-seeking behaviour. Tests of reinstatement were made following exposure to a randomised order of intraperitoneal injections of MG (3, 10 and 30 mg/kg), morphine (5 mg/kg) and vehicle. Significant levels of drug-seeking behaviour were observed following extended access to morphine self-administration, which was extinguished following removal of morphine and cues indicative of morphine-seeking behaviour, supporting the relapse model. The present finding demonstrated that MG priming in a dose of 10 mg/kg resulted in the reinstatement of morphine-seeking behaviour, whereas the higher MG dose (30 mg/kg) tested suppressed the seeking response. This study indicated that exposure to a low MG dose may increase the likelihood of relapsing to opioids, suggesting that the potential of MG as a treatment for opioid management merits further scientific assessment of its ability to trigger relapse to opioid abuse.

Endocannabinoid system as a therapeutic target for psychostimulants relapse: A systematic review of preclinical studies

The mechanism behind the reinstament of psychostimulant, as a major obstacle in addiction treatment is not fully understood. Controversial data are available in the literature concerning the role of the endocannabinoid (eCB) system in regulating the relapse to psychostimulant addiction in preclinical studies. The current systematic review aims to evaluate eCB modulators' effect in the reinstatement of commonly abused psychostimulants, including cocaine, amphetamine, methamphetamine, and 3,4-methylenedioxymethamphetamine. By searching the PubMed, Web of Science, and Scopus databases, studies were selected. Then the studies^, quality was evaluated by the SYRCLE risk of bias tool. The results have still been limited to preclinical studies. Thirty-nine articles that employed self-administration and CPP as the most prevalent animal models of addiction were selected. This data indicates that cannabinoid receptor 1 antagonists and some cannabinoid receptor 2 agonists could suppress the reinstatement of cocaine and methamphetamine addiction in a dose-dependent manner. However, only AM251 was efficient to block the reinstatement of 3,4-methylenedioxymethamphetamine. In conclusion, cannabinoid receptor 1 antagonists and some cannabinoid receptor 2 agonists may have curative potential in the relapse of psychostimulant abuse. However, time, dose, and route of administration are crucial factors in their inhibitory impacts.

High Morphine Use Disorder Susceptibility Is Predicted by Impaired Learning Ability in Mice

An obvious reason for substance uses disorders (SUDs) is drug craving and seeking behavior induced by conditioned context, which is an abnormal solid context memory. The relationship between susceptibility to SUD and learning ability remains unclear in humans and animal models. In this study, we found that susceptibility to morphine use disorder (MUD) was negatively correlated with learning ability in conditioned place preference (CPP) in C57 mice. By using behavioral tests, we identified the FVB mouse as learning impaired. In addition, we discovered that learning-relevant proteins, such as the glutamate receptor subunits GluA1, NR1, and NR2A, were decreased in FVB mice. Finally, we assessed the context learning ability of FVB mice using the CPP test and priming. We found that FVB mice had lower learning performance with respect to normal memory but higher performance of morphine-reinstatement memory. Compared to C57 mice, FVB mice are highly sensitive to MUDs. Our results suggest that SUD susceptibility is predicted by impaired learning ability in mice; therefore, learning ability can play a simple and practical role in identifying high-risk SUD groups.

Rapastinel accelerates loss of withdrawal signs after repeated morphine and blunts relapse to conditioned place preference

The purpose of the present study was to evaluate the efficacy of rapastinel, an allosteric modulator of NMDA receptor function, to accelerate the loss of opioid withdrawal symptoms and blunt or prevent relapse to morphine conditioned place preference (CPP) in rats. Two studies were conducted. In study 1, adult and adolescent male and female rats were treated with increasing doses of morphine (5 mg/kg, bid to 25 mg/kg bid) for 5 days. On day 6 animals were treated with naloxone (1 mg/kg) and withdrawal was assessed. They were then treated with saline or rapastinel (5 mg/kg) on days 6 and 8, and withdrawal was assessed on day 9. Rapastinel treated animals exhibited significantly lower levels of withdrawal signs on day 9. No sex or age differences were observed. In Study 2, CPP for morphine was established in adult rats (males and females) by 4 daily pairings with saline and morphine (am/pm alternation). They were tested for CPP on day 5, and then treated with rapastinel (5 mg/kg) or saline daily on days 6-10 of extinction. On day 11 they received a final dose of rapastinel or saline followed by extinction trial. On day 12, animals received 1 mg/kg of morphine and were tested for relapse. Rapastinel did not affect extinction of CPP, but rapastinel-treated animals spent significantly less time in the previously morphine-paired side than saline-treated animals during the relapse trial. These findings of accelerated loss of withdrawal signs and blunted relapse to CPP suggest that rapastinel could provide an adjunctive therapy for opioid dependence during initiation of pharmacotherapy for opioid dependence.

Aerobic exercise as a promising nonpharmacological therapy for the treatment of substance use disorders

Despite the prevalence and public health impact of substance use disorders (SUDs), effective long-term treatments remain elusive. Aerobic exercise is a promising, nonpharmacological treatment currently under investigation as a strategy for preventing drug relapse. Aerobic exercise could be incorporated into the comprehensive treatment regimens for people with substance abuse disorders. Preclinical studies of SUD with animal models have shown that aerobic exercise diminishes drug-seeking behavior, which leads to relapse, in both male and female rats. Nevertheless, little is known regarding the effects of substance abuse-induced cellular and physiological adaptations believed to be responsible for drug-seeking behavior. Accordingly, the overall goal of this review is to provide a summary and an assessment of findings to date, highlighting evidence of the molecular and neurological effects of exercise on adaptations associated with SUD.

Cognitive profile of male mice exposed to a Ketogenic Diet

In recent years, nutritional interventions for different psychiatric diseases have gained increasing attention, such as the ketogenic diet (KD). This has led to positive effects in neurological disorders such as Parkinson's disease, addiction, autism or epilepsy. The neurobiological mechanisms through which these effects are induced and the effects in cognition still warrant investigation, and considering that other high-fat diets (HFD) can lead to cognitive disturbances that may affect the results achieved, the main aim of the present work was to evaluate the effects of a KD to determine whether it can induce such cognitive effects. A total of 30 OF1 male mice were employed to establish the behavioral profile of mice fed a KD by testing anxiety behavior (Elevated Plus Maze), locomotor activity (Open Field), learning (Hebb Williams Maze), and memory (Passive Avoidance Test). The results revealed that the KD did not affect locomotor activity, memory or hippocampal-dependent learning, as similar results were obtained with mice on a standard diet, albeit with increased anxiety behavior. We conclude that a KD is a promising nutritional approach to apply in research studies, given that it does not cause cognitive alterations.

The distinct roles of various neurotransmitters in modulating methamphetamine-induced conditioned place preference in relevant brain regions in mice

OBJECTIVES

Previous studies have shown that methamphetamine (METH) can induce complex adaptive changes in the reward system in the brain, including the changes in the content of neurotransmitters in the signal transduction pathway. However, how the changes of various neurotransmitters in relevant brain reward circuits contribute to METH-induced conditioned place preference (CPP) remains unclear.

METHODS

In this study, first, we designed an animal model of METH-induced CPP. Then we used liquid chromatography-mass spectrometry (LC-MS) to simultaneously determine the contents of various neurotransmitters - dopamine (DA), norepinephrine (NE), 5-hydroxytryptamine (5-HT), 5-hydroxyindole acetic acid (5-HIAA), glutamic acid (Glu) and glutamine (Gln) - in different brain regions of the prefrontal cortex (PFc), nucleus accumbens (NAc), caudate-putamen (CPu) and hippocampus (Hip), which are believed to be relevant to the drug's reward effect.

RESULTS

The results of the behavioral experiment suggested that 1.0 mg/kg METH could induce obvious CPP in mice. The results about various neurotransmitters showed that: DA significantly increased in NAc in the METH group; Glu increased significantly in the METH group in PFc and NAc and Gln increased significantly in the METH group in PFc.

CONCLUSIONS

These results suggested that the neurotransmitters of DA, Glu and Gln may work together and play important roles in METH-induced CPP in relevant brain reward circuits, especially in PFc and NAc. These findings therefore could help to advance the comprehensive understanding of the neurochemic and psychopharmacologic properties of METH in reward effect, which is important for future improvements in the treatment of drug addiction.

Resilience to the effects of social stress on vulnerability to developing drug addiction

We review the still scarce but growing literature on resilience to the effects of social stress on the rewarding properties of drugs of abuse. We define the concept of resilience and how it is applied to the field of drug addiction research. We also describe the internal and external protective factors associated with resilience, such as individual behavioral traits and social support. We then explain the physiological response to stress and how it is modulated by resilience factors. In the subsequent section, we describe the animal models commonly used in the study of resilience to social stress, and we focus on the effects of chronic social defeat (SD), a kind of stress induced by repeated experience of defeat in an agonistic encounter, on different animal behaviors (depression- and anxiety-like behavior, cognitive impairment and addiction-like symptoms). We then summarize the current knowledge on the neurobiological substrates of resilience derived from studies of resilience to the effects of chronic SD stress on depression- and anxiety-related behaviors in rodents. Finally, we focus on the limited studies carried out to explore resilience to the effects of SD stress on the rewarding properties of drugs of abuse, describing the current state of knowledge and suggesting future research directions.

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.

What Have We Learned (or Expect to) From Analysis of Murine Genetic Models Related to Substance Use Disorders?

The tremendous public health problem created by substance use disorders (SUDs) presents a major opportunity for mouse genetics. Inbred mouse strains exhibit substantial and heritable differences in their responses to drugs of abuse (DOA) and in many of the behaviors associated with susceptibility to SUD. Therefore, genetic discoveries emerging from analysis of murine genetic models can provide critically needed insight into the neurobiological effects of DOA, and they can reveal how genetic factors affect susceptibility drug addiction. There are already indications, emerging from our prior analyses of murine genetic models of responses related to SUDs that mouse genetic models of SUD can provide actionable information, which can lead to new approaches for alleviating SUDs. Lastly, we consider the features of murine genetic models that enable causative genetic factors to be successfully identified; and the methodologies that facilitate genetic discovery.

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.

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

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

Contrasting effects of the α7 nicotinic receptor antagonist methyllycaconitine in different rat models of heroin reinstatement

BACKGROUND

α7 Nicotinic acetylcholine receptors are implicated in the reinstatement of drug-seeking, an important component of relapse. We showed previously that the α7 nicotinic acetylcholine receptor antagonist, methyllycaconitine, specifically attenuated morphine-primed reinstatement of conditioned place preference in rodents and this effect was mediated in the ventral hippocampus.

AIMS

The purpose of this study was to evaluate α7 nicotinic acetylcholine receptor antagonism in reinstatement of the conditioned place preference for the more widely abused opioid, heroin, and to compare the effect of α7 nicotinic acetylcholine receptor blockade on reinstatement of heroin-seeking and heroin self-administration in an intravenous self-administration model of addictive behaviour.

METHODS

Rats were trained to acquire heroin conditioned place preference or heroin self-administration; both followed by extinction of responding. Methyllycaconitine or saline was given prior to reinstatement of drug-primed conditioned place preference, or drug-prime plus cue-induced reinstatement of intravenous self-administration, using two protocols: without delivery of heroin in response to lever pressing to model heroin-seeking, or with heroin self-administration, using fixed and progressive ratio reward schedules, to model relapse.

RESULTS

Methyllycaconitine had no effect on acquisition of heroin conditioned place preference or lever-pressing for food rewards. Methyllycaconitine blocked reinstatement of heroin-primed conditioned place preference. Methyllycaconitine did not prevent drug-prime plus cue-induced reinstatement of heroin-seeking, reinstatement of heroin self-administration, or diminish the reinforcing effect of heroin.

CONCLUSIONS

The α7 nicotinic acetylcholine receptor antagonist, methyllycaconitine, prevented reinstatement of the opioid conditioned place preference, consistent with a role for α7 nicotinic acetylcholine receptors in the retrieval of associative memories of drug liking. The lack of effect of methyllycaconitine in heroin-dependent rats in two intravenous self-administration models suggests that α7 nicotinic acetylcholine receptors do not play a role in later stages of heroin abuse.

Binge eating and psychostimulant addiction

Many of the various factors, characteristics, and variables involved in the addictive process can determine an individual’s vulnerability to develop drug addiction. Hedonic eating, based on pleasure rather than energy needs, modulates the same reward circuits, as do drugs of abuse. According to the last report of the World Health Organization, the worldwide obesity rate has more than doubled since 1980, reaching especially critical levels in children and young people, who are overexposed to high-fat, high-sugar, energy-dense foods. Over the past few decades, there has been an increase in the number of studies focused on how eating disorders can lead to the development of drug addiction and on the comorbidity that exists between the two disorders. Herein, we review the most recent research on the subject, focusing especially on animal models of binge eating disorders and drug addiction. The complex profile of patients with substance use and binge eating disorders requires an integrated response to dually diagnosed patients. Nutritional patterns should be considered an important variable in the treatment of substance use disorders, and future studies need to focus on specific treatments and interventions in individuals who show a special vulnerability to shift from one addiction to the other.

The role of hippocampal glial glutamate transporter (GLT-1) in morphine-induced behavioral responses

Opioid abuse modifies synaptic plasticity, which leads to behavioral changes, such as morphine dependence, but the mechanism remains poorly understood. Glial cells play an important role in the modulation of synaptic plasticity and are involved in addictive-like behaviors. The indisputable role of glutamate in opiate addiction has been shown. Astrocytes, a type of glial cells, which are integral functional elements of synapses, modulate the concentration of glutamate in the synaptic space. One of the most important mechanisms for glutamate concentration regulation is its uptake from the synaptic cleft. In this study, we evaluated the role of hippocampal glial glutamate transporter (GLT-1) in morphine dependence. Male rats received subcutaneous (s.c.) morphine sulfate (10 mg/kg) at an interval of 12 h for 9 days. In order to activate GLT-1, animals received an intrahippocampal injection of ceftriaxone (0.5 mmol/0.5 μl) in the CA1 region of the hippocampus, 30 min before each morphine administration. Rats were assessed for morphine dependence by monitoring naloxone hydrochloride-induced morphine withdrawal. Our results showed that hippocampal microinjection of ceftriaxone, as an activator of GLT-1, reduced some signs of morphine withdrawal, such as activity, diarrhea, head tremor, freezing, and ptosis. It seems that hippocampal GLT-1 can be affected by chronic morphine administration and involved in morphine dependence. Therefore, its activation may reduce morphine side effects by reducing hippocampal glutamate.

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.

Systemic administration of N-acetylcysteine during the extinction period and on the reinstatement day decreased the maintenance of morphine rewarding properties in the rats

Many animal studies and early clinical trials suggested that N-acetylcysteine (NAC) may benefit addiction treatment. The present study tried to evaluate whether chronic administration of systemic NAC during the extinction period and acute administration of systemic NAC on the reinstatement day could reduce the maintenance of the morphine rewarding properties in the conditioned place preference (CPP) paradigm in the rats. Ninety-six adult male Wistar rats (190-220 g) were examined with morphine (7 mg/kg; sc) and saline (1 mL/kg; sc) during the 3-day conditioning phase in the CPP paradigm. After the acquisition of morphine CPP, different doses of NAC were daily administered during the extinction period (5, 10, 25, and 50 mg/kg; ip), or 30 min before the CPP test on the reinstatement day (2, 5, 10, 25, and 50 mg/kg; ip). Conditioning score and locomotor activity were recorded by the video tracking system and Ethovision software after acquisition on the post-conditioning day, the extinction period, and reinstatement day. Daily NAC administration in high doses (25 and 50 mg/kg; ip) reduced extinction-responding compared with the vehicle-control group during the extinction period. Although a single injection of NAC in doses 10, 25, 50 mg/kg decreased the reinstatement of morphine-induced CPP, two lower doses (2 and 5 mg/kg) could not significantly reduce the CPP scores. These are the first data suggesting that NAC's application during the extinction period could attenuate the morphine reward-associated behaviors in the rats. Moreover, NAC could inhibit the reinstatement of morphine CPP, which adds to the growing appreciation that the NAC may have potential therapeutic use in combating morphine dependence. It can be consistent with the hypothesis of the involvement of the glutamatergic system in the pathophysiology of addiction.

Linalool attenuates acquisition and reinstatement and accelerates the extinction of nicotine-induced conditioned place preference in male mice

Background: Nicotine is the addictive agent in tobacco products. The monoterpene linalool is the main ingredient in the essential oils of various aromatic plants. It has previously been demonstrated that linalool has beneficial effects on some mechanisms that are important in drug addiction.Objectives: The goal of the current study was to investigate the effect of linalool on nicotine-induced conditioned place preference (CPP) in male mice.Methods: CPP was induced by administering intraperitoneal (i.p.) injection of nicotine (0.5 mg/kg) during the conditioning phase. The effects of nicotinic acetylcholine receptor partial agonist varenicline and linalool on the rewarding characteristics of nicotine were tested in mice with administration of linalool (12.5, 25, and 50 mg/kg, i.p.), varenicline (2 mg/kg, i.p.) or saline 30 minutes before nicotine injection. CPP was extinguished by repeated testing, during which conditioned mice were administered varenicline and linalool every day. One day after the last extinction trial, mice that received linalool, varenicline or saline 30 minutes before a priming injection of nicotine (0.1 mg/kg, i.p.) were immediately tested for reinstatement of CPP.Results: Linalool attenuated nicotine acquisition (50 mg/kg, p < .01) and reinstatement (25 and 50 mg/kg, respectively p < .05, p < .01) and accelerated the extinction of nicotine-induced CPP (50 mg/kg, p < .05). Linalool exhibited similar effects on the reference drug varenicline in the CPP phases.Conclusion: These results suggest that linalool may be helpful as an adjuvant for the treatment of nicotine use disorder.

Resveratrol impairs acquisition, reinstatement and precipitates extinction of alcohol-induced place preference in mice

OBJECTIVE

Alcohol abuse causes several neurological disorders. Resveratrol is a natural polyphenol that occurs as a phytoalexin. In different studies, it has been investigated that resveratrol has positive effects on various mechanisms that are important in drug addiction or substance use disorder. The objective of the present study was to examine the effect of resveratrol on alcohol-induced conditioned place preference (CPP) in mice.

METHODS

CPP was induced by intraperitoneal (i.p.) administration of ethanol (2 g/kg) in an 8-day conditioning program. The influence of reference drug, acamprosate and resveratrol on the rewarding properties of ethanol was tested in mice given treatment of acamprosate (300 mg/kg, i.p.) and resveratrol (25, 50, and 75 mg/kg, i.p.) 30 minutes prior to ethanol administration. Once established, CPP was extinguished by repeated testing, through which conditioned mice were administered acamprosate, various doses of resveratrol or saline daily. Subsequently, the potency of acamprosate and resveratrol in preventing reinstatement of CPP provoked by priming with low-dose ethanol (0.4 g/kg, i.p.) was also evaluated.

RESULTS

The present findings confirm that resveratrol impairs acquisition, reinstatement and precipitates the extinction of preference for alcohol-induced CPP. Resveratrol presented a similar effect in the CPP phases to the acamprosate.

CONCLUSIONS

The effect of resveratrol on ethanol-induced CPP in mice demonstrated for the first time. As a conclusion, these findings may shed light on the fact that resveratrol can be utilized as an agent which is potentially beneficial to prevent the various harmful effects of ethanol, however, more research is needed to completely elucidate this attribute.

Bidirectional role of acupuncture in the treatment of drug addiction

Drug addiction is a chronically relapsing disorder, affecting people from all walks of life. Studies of acupuncture effects on drug addiction are intriguing in light of the fact that acupuncture can be used as a convenient therapeutic intervention for treating drug addiction by direct activation of brain pathway. The current review aims to discuss the neurobiological mechanisms underlying acupuncture's effectiveness in the treatment of drug addiction, on the basis of two different theories (the incentive sensitization theory and the opponent process theory) that have seemingly opposite view on the role of the mesolimbic reward pathways in mediating compulsive drug-seeking behavior. This review provides evidence that acupuncture may reduce relapse to drug-seeking behavior by regulating neurotransmitters involved in drug craving modulation via somatosensory afferent mechanisms. Also, acupuncture normalizes hyper-reactivity or hypoactivity of the mesolimbic dopamine system in these opposed processes in drug addiction, suggesting bidirectional role of acupuncture in regulation of drug addiction. This proposes that acupuncture may reduce drug craving by correcting both dysfunctions of the mesolimbic dopamine pathway.

Misuse and dependence of dimenhydrinate: A mixed studies systematic review

BACKGROUND

Dimenhydrinate (DMH) is an antihistamine used to treat nausea and vomiting. Although widely available in pharmacies as an over the counter medication, there have been reports of potential DMH tolerance and dependence and a possible euphoric potential accompanying heavy use (>100 mg/day). Despite the potential for misuse, there is a gap in the literature concerning patterns, characteristics, and potential mechanisms of DMH misuse.

AIMS

This review aimed to synthesize evidence on the pharmacology, clinical effects, and management of DMH misuse and dependence to inform clinical decision making and relevant drug policy.

METHODS

We conducted a systematic review in accordance with the PRISMA guidelines and using Cochrane collaboration methods. We searched seven databases from their inception through July 2019. To be included in the review, studies needed to measure or focus on one or more dimensions of morbidity or mortality related to the misuse of DMH. Quantitative, qualitative and mixed-method studies were included in order to capture the breadth of possible studies. Studies were excluded if they did not fit into the conceptual framework of the study of if they focused primarily on the misuse of other substances. A narrative synthesis of study findings was pursued given the limited capacity for a quantitative meta-analysis.

FINDINGS

We identified 24 studies, which described a range of neuropsychiatric sequelae related to DMH consumption, including seizures, psychosis, depression, intoxication (resembling anticholinergic syndrome) and withdrawal. The sedative and euphoric properties, readily available nature, and low cost of DMH appear to facilitate DMH dependence, which were more commonly reported among individuals who had concurrent psychiatric disorders, displaying symptoms such as low motivation, poor concentration, and delirium. The overall quality of studies identified by this review was low-largely because the majority of studies were case reports or review articles, with few intervention or cohort studies.

CONCLUSIONS

There is some evidence to suggest the existence of DMH-related syndromes involving intoxication, withdrawal, and dependence, more commonly among long-term, heavy DMH consumers. However, higher quality studies are needed to confirm preliminary findings that there may be a biological basis for such syndromes.

Neuroinflammatory and behavioral susceptibility profile of mice exposed to social stress towards cocaine effects

Using the social defeat (SD) model, numerous studies have shown that stressed mice display an enhanced response to the motivational effects of cocaine in the self-administration (SA) and conditioned-place preference (CPP) paradigms. However, not all subjects exposed to stress express its harmful effects. Some are particularly susceptible to the deleterious effects of repeated SD, while resilient mice successfully cope with stressful experiences and display adjusted psychological functioning after stress. Vulnerability to develop stress-related disorders, such as depression, has been linked to coping strategies and more recently to individual differences in the immune system. However, no studies have evaluated if coping strategies and immune system reactivity to social stress experiences can also predict susceptibility to stress-induced enhancement of the cocaine response. We evaluated cocaine response in socially defeated mice in the CPP and SA paradigms. To evaluate neuroimmune reactivity to stress the pro-inflammatory cytokine IL-6 and the chemokine CX3CL1 were measured in the striatum and hippocampus. Behavioral phenotype during and after SD episodes was also evaluated. Our results showed that susceptible mice to the depressive-like behaviors effects of stress showed increased conditioned rewarding effects of cocaine in the CPP. In addition, susceptible mice displayed passive-reactive coping behavior during social stress episodes and more pronounced changes in neuroinflammatory markers after the last SD episode, which lasted for one month. Although the complex mechanisms underlying susceptibility or resilience to social stress are still unclear, our results point to multiple adaptive stress responses expressed at different phenotypic levels.

Effects of processed Aconiti tuber on the extinction and reinstatement of morphine-induced conditioned place preference in rats

AIM OF THE STUDY

To investigate the effect of processed Aconiti tuber (PAT) administered during or after the time of conditioned place preference (CPP) training on the extinction and reinstatement of morphine-priming CPP in rats. The dynorphin level in rats' nucleus accumbens (NAc) is detected as a target of the Dynorphin/Kappa Opioid Receptor (KOR) system for the possible mechanism.

MATERIALS AND METHODS

Eight groups of rats were subcutaneously (s.c.) injected with morphine (10mg/kg) (on days 2,4,6,8) or saline (1ml/kg) (on days 3,5,7,9) alternately for 8 days. Five groups, including groups (Mor + Water, Mor + PAT (1.0/3.0g/kg) (S) and Sal + PAT(1.0/3.0g/kg)), were orally given distilled water or PAT 1.0 or 3.0 g/kg daily on days 1-8 during CPP training while other three groups, including groups (Sal + Water and Mor + PAT (1.0/3.0g/kg)(P), were given distilled water or PAT daily from day 10 until CPP was extinct. Morphine 1mg/kg (s.c.) was used to reinstate the extinct CPP and the CPP scores were recorded. The dynorphin concentration in nucleus accumbens (NAc) was assayed by radioimmunoassay after the last CPP measurement.

RESULTS

1) The CPP extinction shortened in Mor + PAT (1.0/3.0 g/kg) (S) groups but extended in Mor + PAT (1.0/3.0 g/kg)(P) groups. 2) Morphine-priming CPP did not change either in Mor + PAT (1.0/3.0 g/kg) (S) or Mor + PAT (1.0/3.0 g/kg)(P) groups. 3) The dynorphin concentration in NAc increased either in Mor + PAT (1.0/3.0 g/kg)(S) or Mor + PAT (1.0/3.0 g/kg)(P) groups.

CONCLUSIONS

1) PAT shortened the extinction from morphine induced CPP when administrated before CPP acquisition, whereas it extended the extinction when administrated after CPP formation. 2) PAT administrated during or after CPP training did not affect morphine-priming reinstatement of morphine induced CPP. 3) Dynorphin/KOR system might be a target to regulate morphine-induced CPP extinction but not reinstatement.

Instrumental and Pavlovian Mechanisms in Alcohol Use Disorder

Purpose of Review

Current theories of alcohol use disorders (AUD) highlight the importance of Pavlovian and instrumental learning processes mainly based on preclinical animal studies. Here, we summarize available evidence for alterations of those processes in human participants with AUD with a focus on habitual versus goal-directed instrumental learning, Pavlovian conditioning, and Pavlovian-to-instrumental transfer (PIT) paradigms.

Recent Findings

The balance between habitual and goal-directed control in AUD participants has been studied using outcome devaluation or sequential decision-making procedures, which have found some evidence of reduced goal-directed/model-based control, but little evidence for stronger habitual responding. The employed Pavlovian learning and PIT paradigms have shown considerable differences regarding experimental procedures, e.g., alcohol-related or conventional reinforcers or stimuli.

Summary

While studies of basic learning processes in human participants with AUD support a role of Pavlovian and instrumental learning mechanisms in the development and maintenance of drug addiction, current studies are characterized by large variability regarding methodology, sample characteristics, and results, and translation from animal paradigms to human research remains challenging. Longitudinal approaches with reliable and ecologically valid paradigms of Pavlovian and instrumental processes, including alcohol-related cues and outcomes, are warranted and should be combined with state-of-the-art imaging techniques, computational approaches, and ecological momentary assessment methods.

Oxytocin Signaling as a Target to Block Social Defeat-Induced Increases in Drug Abuse Reward

There is huge scientific interest in the neuropeptide oxytocin (OXT) due to its putative capacity to modulate a wide spectrum of physiological and cognitive processes including motivation, learning, emotion, and the stress response. The present review seeks to increase the understanding of the role of OXT in an individual’s vulnerability or resilience with regard to developing a substance use disorder. It places specific attention on the role of social stress as a risk factor of addiction, and explores the hypothesis that OXT constitutes a homeostatic response to stress that buffers against its negative impact. For this purpose, the review summarizes preclinical and clinical literature regarding the effects of OXT in different stages of the addiction cycle. The current literature affirms that a well-functioning oxytocinergic system has protective effects such as the modulation of the initial response to drugs of abuse, the attenuation of the development of dependence, the blunting of drug reinstatement and a general anti-stress effect. However, this system is dysregulated if there is continuous drug use or chronic exposure to stress. In this context, OXT is emerging as a promising pharmacotherapy to restore its natural beneficial effects in the organism and to help rebalance the functions of the addicted brain.

Bulleyaconitine A Inhibits Morphine-Induced Withdrawal Symptoms, Conditioned Place Preference, and Locomotor Sensitization Via Microglial Dynorphin A Expression

Bulleyaconitine A (BAA), a C19-diterpenoid alkaloid, has been prescribed as a nonnarcotic analgesic to treat chronic pain over four decades in China. The present study investigated its inhibition in morphine-induced withdrawal symptoms, conditioned place preference (CPP) and locomotor sensitization, and then explored the underlying mechanisms of actions. Multiple daily injections of morphine but not BAA up to 300 μg/kg/day into mice evoked naloxone-induced withdrawal symptoms (i.e., shakes, jumps, genital licks, fecal excretion and body weight loss), CPP expression, and locomotor sensitization. Single subcutaneous BAA injection (30–300 μg/kg) dose-dependently and completely attenuated morphine-induced withdrawal symptoms, with ED₅₀ values of 74.4 and 105.8 μg/kg in shakes and body weight loss, respectively. Subcutaneous BAA (300 μg/kg) also totally alleviated morphine-induced CPP acquisition and expression and locomotor sensitization. Furthermore, subcutaneous BAA injection also specifically stimulated dynorphin A expression in microglia but not astrocytes or neurons in nucleus accumbens (NAc) and hippocampal, measured for gene and protein expression and double immunofluorescence staining. In addition, subcutaneous BAA-inhibited morphine-induced withdrawal symptoms and CPP expression were totally blocked by the microglial metabolic inhibitor minocycline, dynorphin A antiserum, or specific KOR antagonist GNTI, given intracerebroventricularly. These results, for the first time, illustrate that BAA attenuates morphine-induced withdrawal symptoms, CPP expression, and locomotor sensitization by stimulation of microglial dynorphin A expression in the brain, suggesting that BAA may be a potential candidate for treatment of opioids-induced physical dependence and addiction.

Microinjection of the BDNF receptor antagonist ANA-12 into the nucleus accumbens and medial-prefrontal cortex attenuates morphine-induced reward memory, and alterations of BDNF levels and apoptotic cells in rats

This study was designed to examine the effects of intra- nucleus accumbens (NAc) of BDNF receptor antagonist ANA-12 on the acquisition and expression and intra- medial-prefrontal cortex (mPFC) of ANA-12 on the extinction and reinstatement of morphine-induced conditioned place preference (CPP) and also BDNF levels and apoptotic neurons in the NAc and mPFC of rats. In this study, adult male Wistar rats (200-250 g) were used. Two separate cannulas were inserted bilaterally into the NAc and/or mPFC. ANA-12 (3 μg/0.5 μl/side) was injected into the NAc and/or mPFC to evaluate the rewarding effects of morphine using a CPP paradigm. Then, the levels of BDNF and apoptotic in the NAc and mPFC were assessed at the end of each treatment phase using ELISA and TUNEL methods, respectively. All of vehicle-treated rats following morphine CPP showed the increase of BDNF levels and apoptotic neurons in the NAc and mPFC. ANA-12 significantly attenuated the acquisition and expression of morphine-induced CPP, BDNF levels and apoptotic neurons in the NAc during the acquisition, but not the expression phase. Also, ANA-12 significantly facilitated the extinction, but no effect on reinstatement of morphine CPP, and decreased BDNF levels and apoptotic neurons in the mPFC during the extinction, but not the reinstatement. We conclude that blocking TrkB with ANA-12 showed therapeutic effects on morphine-associated reward memory and neuronal death in the NAc and mPFC induced by morphine CPP. Thus, the BDNF-TrkB signaling may be important in the acquisition, expression, extinction, but not the reinstatement of morphine CPP.

Conditioned Place Preference (CPP) in Rats: From Conditioning to Reinstatement Test

Opioid addiction in humans is a chronically relapsing disorder characterized by discontinuous periods of drug use and abstinence resulting in dependence. With time, the probability of falling into renewed drug consumption becomes particularly high and constitutes a considerable problem in the management of opioid addicts. Opioid addiction represents an important health concern and animal models have been crucial in understanding the neurobiology and pathophysiology of this complex disease. Although animal models of addiction do not fully reproduce the human condition, they do permit investigation of specific elements of the process as well as identification of potential therapeutic targets. In this chapter, we provide a step-by-step description of the morphine-conditioned place preference (CPP) model that represents a useful preclinical animal model extensively used to study the rewarding/aversive effect of drugs.

Sex differences in pregabalin-seeking like behavior in a conditioned place preference paradigm

Substance abuse is a chronic, relapsing disorder characterized by compulsive drug use regardless of negative consequences. Incremental increases in pregabalin abuse have been observed in Saudi Arabia and throughout the world. In previous studies, the potential for pregabalin abuse with escalating doses of the drug (30, 60, 90, and 120 mg/kg) were investigated in male mice. Notably, researchers have argued that women may exhibit a greater tendency to consume drugs without a prescription to alleviate stress and depression. Moreover, female subjects are more prone to impulsivity in drug intake or abuse than their male counterparts. Therefore, in the present study, we compared the potential for pregabalin abuse between male and female mice using a conditioned place preference paradigm. Male and female BALB/c mice were divided into four groups based on the pregabalin dose administered (30, 60, 90, or 120 mg/kg, intraperitoneal). Preference scores were then calculated and compared between male and female mice in each dosage group. Interestingly, preference scores were significantly higher in female mice than in male mice at dosages of 30 and 120 mg/kg. These findings indicate that female mice may be more prone to pregabalin abuse and tolerance than male mice. These results might be helpful to the healthcare providers and policymakers to consider these sex differences in choosing therapeutic plans and consider alternatives to the misused prescription medications.

Increased Response to 3,4-Methylenedioxymethamphetamine (MDMA) Reward and Altered Gene Expression in Zebrafish During Short- and Long-Term Nicotine Withdrawal

An interactive effect between nicotine and 3,4-methylenedioxymethamphetamine (MDMA) has been reported but the mechanism underlying such interaction is not completely understood. This study used zebrafish to explore gene expression changes associated with altered sensitivity to the rewarding effects of MDMA following 2-week exposure to nicotine and 2-60 days of nicotine withdrawal. Reward responses to MDMA were assessed using a conditioned place preference (CPP) paradigm and gene expression was evaluated using quantitative real-time PCR of mRNA from whole brain samples from drug-treated and control adult zebrafish. Zebrafish pre-exposed for 2 weeks to nicotine showed increased conditioned place preference in response to low-dose, 0.1 mg/kg, MDMA compared to un-exposed fish at 2, 7, 30 and 60 days withdrawal. Pre-exposure to nicotine for 2 weeks induced a significant increase of c-Fos and vasopressin receptor expression but a decrease of D₃ dopaminergic and oxytocin receptor expression at 2 days of withdrawal. C-Fos mRNA increased also at 7, 30, 60 days of withdrawal. Nicotine pre-exposed zebrafish submitted to MDMA-induced CPP showed an increase in expression of p35 at day 2, α4 at day 30, vasopressin at day 7 and D₃ dopaminergic receptor at day 7, 30 and 60. These gene alterations could account for the altered sensitivity to the rewarding effects of MDMA in nicotine pre-exposed fish, suggesting that zebrafish have an altered ability to modulate behaviour as a function of reward during nicotine withdrawal.

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.

Cannabinoid receptor modulation changes the accumbal neuronal responses to morphine in the reinstatement of morphine-induced conditioned place preference

The nucleus accumbens (NAc) is a central component of the brain reward system. It has been known that most of the drugs of abuse such as opioids and cannabinoids affect the NAc. Although cannabinoids can modulate different stages of morphine encounter such as the reinstatement of morphine-induced conditioned place preference (CPP), there is no evidence for the NAc neurons' response to prove it. That is why the present study was designed. The procedure was as follows: The rats were entered to CPP by sc 5 mg/kg morphine in three consecutive days. During the extinction period or in the reinstatement phase, icv WIN 55,212-2 (10mM/5 μL dimethyl sulfoxide [DMSO] 10%) or AM251 (0.5mM/5-μL DMSO 10%) was infused in separate groups. Also, the NAc neurons' response to cannabinoid modulation in reinstatement to morphine was investigated by extracellular single unit recording. As a result, the cannabinoid in the reinstatement phase decreased the NAc neuronal activity. The CB1 receptor inhibition during the extinction period increased the NAc firing rate after ip 1 mg/kg morphine. Also, the inhibition of this receptor in the reinstatement phase increased the NAc neurons' firing rate. The inhibitory effect of cannabinoid on the NAc neuronal activity in the reinstatement has indicated the possible potency of cannabinoid to induce reinstatement of morphine-induced CPP alone and in the absence of a priming dose of morphine. Also, the different effects of the CB1 agonist during the extinction period in the reinstatement phase suggest different mechanisms underlying these two parts.

Drug-Induced Conditioned Place Preference and Its Practical Use in Substance Use Disorder Research

The conditioned place preference (CPP) paradigm is a well-established model utilized to study the role of context associations in reward-related behaviors, including both natural rewards and drugs of abuse. In this review article, we discuss the basic history, various uses, and considerations that are tied to this technique. There are many potential takeaway implications of this model, including negative affective states, conditioned drug effects, memory, and motivation, which are all considered here. We also discuss the neurobiology of CPP including relevant brain regions, molecular signaling cascades, and neuromodulatory systems. We further examine some of our prior findings and how they integrate CPP with self-administration paradigms. Overall, by describing the fundamentals of CPP, findings from the past few decades, and implications of using CPP as a research paradigm, we have endeavored to support the case that the CPP method is specifically advantageous for studying the role of a form of Pavlovian learning that associates drug use with the surrounding environment.

Deep brain stimulation of the orbitofrontal cortex prevents the development and reinstatement of morphine place preference

The orbitofrontal cortex (OFC) is involved in compulsive drug seeking and drug relapse. Its involvement in cue-, context-, and stress-induced reinstatement of drug seeking has also been confirmed in animal models. Deep brain stimulation (DBS) was proposed to be an effective intervention for patients with treatment-refractory addiction. Therefore, in the present study, we investigated the potential efficacy of DBS in the OFC for controlling addictive-like behaviors in rats. Rats were bilaterally implanted with electrodes in the OFC and trained to the morphine conditioned place preference (CPP; 3, 5, and 7 mg/kg). High-frequency (HF; 130 Hz) or low-frequency (LF; 13 Hz) DBS-like stimulation was applied during the conditioning (40 minutes, once daily, 3 days) or extinction (20 minutes, once daily, 6-10 days) trials. Following the extinction, morphine preference was reinstated by a priming dose of morphine (2 mg/kg). When applied during the conditioning phase, HF-DBS significantly decreased preference for the morphine-associated context. HF-DBS during the extinction phase of morphine CPP reduced the number of days to full extinction of morphine preference and prevented morphine priming-induced recurrence of morphine preference. LF-DBS did not change any of these addictive behaviors. HF-DBS had no significant effect on novel object recognition memory. In conclusion, HF-DBS of the OFC prevented morphine preference, facilitated extinction of morphine preference, and blocked drug priming-induced reinstatement of morphine seeking. These findings may indicate a potential applicability of DBS in the treatment of relapse to drug use. Further studies will be necessary to assess the translatability of these findings to the clinic.

Cross-reinstatement between 3,4-methylenedioxypyrovalerone (MDPV) and cocaine using conditioned place preference

3,4-Methylenedioxypyrovalerone (MDPV) is a new psychoactive substance (NPS) considered to be a cocaine-like psychostimulant. The substitution of an established illicit drug as cocaine with an NPS is a pattern of use reported among drug users. The aim of this study was to investigate the relationship between cocaine and MDPV in the reinstatement of the conditioned place preference (CPP) paradigm, in order to establish whether there is cross-reinstatement between the two psychostimulants. Four experimental groups of male OF1 mice were subjected to the CPP paradigm: MDPV-MDPV, Cocaine-Cocaine, Cocaine-MDPV, and MDPV-Cocaine. The first drug refers to the substance with which the animals were conditioned (cocaine 10 mg/kg or MDPV 2 mg/kg) and the s to the substance with which preference was reinstated. In parallel, G9a, ΔFosB, CB1 receptor, CDK5, Arc and c-Fos were determined in ventral striatum. MDPV induced CPP at doses from 1 to 4 mg/kg. Although 2 mg/kg MDPV induced a stronger psychostimulant effect than 10 mg/kg cocaine, both doses seemed to be equivalent in their rewarding properties. However, memories associated with MDPV required more time to be extinguished. MDPV and cocaine restore drug-seeking behavior with respect to each other, although relapse into drug-taking is always more pronounced with the conditioning drug. The fact that MDPV-treated mice show increased ΔFosB protein levels correlates with its longer extinction time and points to the activation of neuroplasticity mechanisms that persist for at least 12 days. Moreover, in these animals, a priming-dose of cocaine can trigger significant neuroplasticity, implying a high vulnerability to cocaine abuse.

Melanin-concentrating hormone in rat nucleus accumbens or lateral hypothalamus differentially impacts morphine and food seeking behaviors

BACKGROUND

Identifying neural substrates that are differentially affected by drugs of abuse and natural rewards is key to finding a target for an efficacious treatment for substance abuse. Melanin-concentrating hormone is a polypeptide with an inhibitory effect on the mesolimbic dopamine system. Here we test the hypothesis that melanin-concentrating hormone in the lateral hypothalamus and nucleus accumbens shell is differentially involved in the regulation of morphine and food-rewarded behaviors.

METHODS

Male Sprague-Dawley rats were trained with morphine (5.0 mg/kg, subcutaneously) or food pellets (standard chow, 10-14 g) to induce a conditioned place preference, immediately followed by extinction training. Melanin-concentrating hormone (1.0 µg/side) or saline was infused into the nucleus accumbens shell or lateral hypothalamus before the reinstatement primed by morphine or food, and locomotor activity was simultaneously monitored. As the comparison, melanin-concentrating hormone was also microinjected into the nucleus accumbens shell or lateral hypothalamus before the expression of food or morphine-induced conditioned place preference.

RESULTS

Microinfusion of melanin-concentrating hormone into the nucleus accumbens shell (but not into the lateral hypothalamus) prevented the reinstatement of morphine conditioned place preference but had no effect on the reinstatement of food conditioned place preference. In contrast, microinfusion of melanin-concentrating hormone into the lateral hypothalamus (but not in the nucleus accumbens shell) inhibited the reinstatement of food conditioned place preference but had no effect on the reinstatement of morphine conditioned place preference.

CONCLUSIONS

These results suggest a clear double dissociation of melanin-concentrating hormone in morphine/food rewarding behaviors and melanin-concentrating hormone in the nucleus accumbens shell. Melanin-concentrating hormone could be a potential target for therapeutic intervention for morphine abuse without affecting natural rewards.