Amphetamine-induced Conditioned Place Preference Research Articles

The anterior insula and its projection to amygdala nuclei modulate the abstinence-exacerbated expression of conditioned place preference

RationaleRelapse into substance use is often triggered by exposure to drug-related environmental cues. The magnitude of drug seeking depends on the duration of abstinence, a phenomenon known as the incubation of drug craving. Clinical and preclinical research shows that the insular cortex is involved in substance use disorders and cue-induced drug seeking. However, the role of the insula on memory retrieval and motivational integration for cue-elicited drug seeking remains to be determined.ObjectivesWe investigated the role of the anterior insular cortex (aIC) and its glutamatergic projection to amygdala nuclei (aIC-AMY) on the expression of conditioned place preference (CPP) during early and late abstinence.MethodsMale adult C57BL/6J mice underwent amphetamine-induced CPP, and their preference was tested following 1 or 14 days of abstinence. aIC and aIC-AMY functional role in CPP expression was assessed at both abstinence periods by employing optogenetic silencing and behavioral pharmacology.ResultsCompared to a single day, an exacerbated preference for the amphetamine-paired context was observed after 14 days of abstinence. Photoinhibition of either aIC or aIC-AMY projection reduced CPP expression following late but not early abstinence. Similarly, the antagonism of aIC NMDA receptors reduced CPP expression after 14 days of abstinence but not 1 day.ConclusionsThese results suggest that aIC and its glutamatergic output to amygdala nuclei constitute critical neurobiological substrates mediating enhanced motivational cue reactivity during the incubation of amphetamine craving rather than contextual memory recall. Moreover, cortical NMDA receptor signaling may become sensitized during abstinence, ultimately modulating disproportioned drug seeking.

GPR55 activation prevents amphetamine-induced conditioned place preference and decrease the amphetamine-stimulated inflammatory response in the ventral hippocampus in male rats

Inflammatory response in the Central Nervous System (CNS) induced by psychostimulants seems to be a crucial factor in the development and maintenance of drug addiction. The ventral hippocampus (vHp) is part of the reward system involved in substance addiction and expresses abundant G protein-coupled receptor 55 (GPR55). This receptor modulates the inflammatory response in vitro and in vivo, but there is no information regarding its anti-inflammatory effects and its impact on psychostimulant consumption. The aim of the present study was to investigate whether vHp GPR55 activation prevents both the inflammatory response induced by amphetamine (AMPH) in the vHp and the AMPH-induced conditioned place preference (A-CPP). Wistar adult male rats with a bilateral cannula into the vHp or intact males were subjected to A-CPP (5 mg/kg). Upon the completion of A-CPP, the vHp was dissected to evaluate IL-1β and IL-6 expression through RT-PCR, Western blot and immunofluorescence. Our results reveal that AMPH induces both A-CPP and an increase of IL-1β and IL-6 in the vHp. The GPR55 agonist lysophosphatidylinositol (LPI, 10 μM) infused into the vHp prevented A-CPP and the AMPH-induced IL-1β increase. CID 16020046 (CID, 10 μM), a selective GPR55 antagonist, abolished LPI effects. To evaluate the effect of the inflammatory response, lipopolysaccharide (LPS, 5 μg/μl) was infused bilaterally into the vHp during A-CPP acquisition. LPS strengthened A-CPP and increased IL-1β/IL-6 mRNA and protein levels in the vHp. LPS also increased CD68, Iba1, GFAP and vimentin expression. All LPS-induced effects were blocked by LPI. Our results suggest that GPR55 activation in the vHp prevents A-CPP while decreasing the local neuro-inflammatory response. These findings indicate that vHp GPR55 is a crucial factor in preventing the rewarding effects of AMPH due to its capacity to interfere with proinflammatory responses in the vHp.

Chronic risperidone administration leads to greater amphetamine-induced conditioned place preference

Risperidone is an atypical antipsychotic drug used increasingly in children to manage symptoms of ADHD and conduct disorder. In rats, developmental risperidone administration is accompanied by increased locomotor activity during adulthood, as well as heightened sensitivity to the locomotor stimulating effects of amphetamine. This study compared sensitivity to the rewarding effects of amphetamine, as measured by conditioned place preference (CPP), between groups of rats administered chronic risperidone (3.0 mg/kg, s.c.) during development (postnatal days 14–42) or adulthood (postnatal days 77–105). Locomotor activity in a novel test cage and amphetamine-induced CPP were measured beginning three and four weeks, respectively, after the final risperidone injection. Female rats administered risperidone early in life were more active than any other group tested. Previous risperidone administration enhanced amphetamine CPP regardless of sex, and this effect appeared more prominent in the developmentally treated group. The density of forebrain dopamine transporters, a primary target of amphetamine, was also quantified in rats administered risperidone early in life and found to be reduced in the medial anterior, posterior, and ventral caudate nucleus. These results suggest that chronic risperidone treatment modifies later locomotor activity and sensitivity to the reinforcing effects of amphetamine, perhaps via a mechanism related to decreased forebrain dopamine transporter density.

Concomitant D1 and D2 dopamine receptor agonist infusion in prelimbic cortex is required to foster extinction of amphetamine-induced conditioned place preference

Dopamine (DA) in medial prefrontal cortex is crucial in extinction of aversive or appetitive experiences. Although attention has been mostly focused on the infralimbic area of prefrontal cortex, a role of the prelimbic (PL) area has been envisaged pointing to DA transmission in the extinction of drug conditioned behavior. Evidence shows that DA exerts its action also via both D1 and D2 receptor subtypes.Here we investigated the effects of D1 and D2 receptor agonist microinfusion in the PL cortex of C57BL/6J mice on expression and extinction of amphetamine-induced conditioned place preference (CPP), in order to ascertain the effects of selective vs concomitant receptor subtypes stimulation.SKF38393 and Quinpirole were used at doses not impairing expression of amphetamine-induced CPP on the day of infusion. Acute infusion of each agonist alone did not affect extinction in subsequent days in comparison with Vehicle-treated mice, while concomitant infusion of both agonists produced a clear-cut advance of extinction of preference for the compartment previously paired with amphetamine.These results show that concomitant stimulation of D1 and D2 receptors in PL is required to foster extinction suggesting a synergic action between receptors or a heteromeric receptor involvement.

Cannabidiol Treatment Might Promote Resilience to Cocaine and Methamphetamine Use Disorders: A Review of Possible Mechanisms.

Currently, there are no approved pharmacotherapies for addiction to cocaine and other psychostimulant drugs. Several studies have proposed that cannabidiol (CBD) could be a promising treatment for substance use disorders. In the present work, the authors describe the scarce preclinical and human research about the actions of CBD on the effects of stimulant drugs, mainly cocaine and methamphetamine (METH). Additionally, the possible mechanisms underlying the therapeutic potential of CBD on stimulant use disorders are reviewed. CBD has reversed toxicity and seizures induced by cocaine, behavioural sensitization induced by amphetamines, motivation to self-administer cocaine and METH, context- and stress-induced reinstatement of cocaine and priming-induced reinstatement of METH seeking behaviours. CBD also potentiated the extinction of cocaine- and amphetamine-induced conditioned place preference (CPP), impaired the reconsolidation of cocaine CPP and prevented priming-induced reinstatement of METH CPP. Observational studies suggest that CBD may reduce problems related with crack-cocaine addiction, such as withdrawal symptoms, craving, impulsivity and paranoia (Fischer et al., 2015). The potential mechanisms involved in the protective effects of CBD on addiction to psychostimulant drugs include the prevention of drug-induced neuroadaptations (neurotransmitter and intracellular signalling pathways changes), the erasure of aberrant drug-memories, the reversion of cognitive deficits induced by psychostimulant drugs and the alleviation of mental disorders comorbid with psychostimulant abuse. Further, preclinical studies and future clinical trials are necessary to fully evaluate the potential of CBD as an intervention for cocaine and methamphetamine addictive disorders.

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

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

Amphetamine-induced Conditioned Place Preference and Changes in mGlu1/5 Receptor Expression and Signaling in the Rat Medial Prefrontal Cortex

The medial prefrontal cortex (mPFC) is implicated in the rewarding effect of psychostimulants, although molecular mechanisms underlying the rewarding properties of stimulants in this region are poorly understood. Group I metabotropic glutamate (mGlu) receptors (mGlu1/5 subtypes) are believed to be critical in this event. We thus in this study investigated changes in mGlu1/5 receptor expression and function in the rat mPFC in response to conditioned place preference (CPP) induced by amphetamine. Repeated amphetamine administration (2.5 mg/kg, once daily on alternate days for 10 days) induced reliable CPP. In the mPFC, surface expression of mGlu5 receptors was elevated in rats after amphetamine conditioning. mGlu5 receptors were also increased at synaptic and extrasynaptic sites in amphetamine-conditioned rats. Expression of mGlu1 receptors was stable in surface and synaptic compartments, while it was elevated in the extrasynaptic location. In mPFC neurons, the mGlu1/5 agonist-stimulated phosphoinositide signaling pathway was upregulated in its efficacy following amphetamine conditioning. The mGlu1/5 agonist-stimulated Src kinase phosphorylation was also augmented in rats treated with amphetamine. These results demonstrate the sensitivity of mPFC mGlu1/5 receptors to amphetamine-induced CPP. Amphetamine conditioning results in the upregulation of mGlu1/5 receptor expression at subcellular and/or subsynaptic levels and mGlu1/5-mediated postreceptor signaling in mPFC neurons.

Prenatal ethanol exposure increases risk of psychostimulant addiction

Prenatal ethanol exposure (PE) causes many cognitive and behavioral deficits including increased drug addiction risk, demonstrated by enhanced ethanol intake and behavioral phenotypes associated with addiction risk. Additionally, preclinical studies show that PE persistently changes the function of dopaminergic neurons in the ventral tegmental area, a major neural substrate for addiction, and alters these neurons’ responses to psychostimulants. Accordingly, PE could also lead to increased risk of addiction to drugs of abuse, other than ethanol. In the present study, addiction risk was examined utilizing paradigms of amphetamine conditioned place preference (CPP) and intravenous self-administration. Ethanol was administered to pregnant dams via intragastric gavage (6 g/kg, during gestational days 8–20). Behavioral tests were conducted in adult male offspring. Amphetamine at a low dose (0.3 mg/kg, i.p.) induced CPP in PE but not control rats, whereas at a higher dose (0.6 mg/kg, i.p.) both groups acquired CPP. There was no group difference in amphetamine-induced CPP reinstatement. Furthermore, PE rats self-administered more amphetamine at a low dose (0.02 mg/kg/infusion) than controls, while no group differences were observed at a higher dose (0.1 mg/kg/infusion). Rats with PE also exhibited greater reactivity to contextual drug cues after extended abstinence and amphetamine-induced reinstatement of drug seeking. These results support that PE persistently leads to increased psychostimulant addiction risk later in life, manifested in many elements of addictive behavior following limited psychostimulant exposure. The observations provide insights into prevention strategies for drug addiction in individuals with fetal alcohol spectrum disorders.

Sleep deprivation precipitates the development of amphetamine-induced conditioned place preference in rats

Sleep deprivation (SD) and amphetamine use are commonly associated conditions. SD shares similar neurobiological effects with psychostimulants, playing an important role in drug addiction, especially through conditioning manipulations. The aim of the present study was to investigate the effects of SD on the development of amphetamine-induced conditioned place preference (CPP) in a protocol with a reduced number of conditioning sessions. Male adult Wistar rats were submitted to 4 conditioning sessions (2 sessions/day) in the CPP apparatus, half with saline (non-drug-paired compartment) and half with 2 mg/kg amphetamine (drug-paired compartment) after control (home-cage maintained) or SD (6 h gentle handling method) conditions. Control animals did not express a preference for the amphetamine-paired compartment, showing that 2 conditioning sessions with the drug were not sufficient to establish CPP. On the other hand, animals submitted to SD during the conditioning sessions expressed a preference for the amphetamine-paired compartment, which was maintained across the entire test session. SD precipitated the development of CPP to amphetamine, showing that lack of sleep can contribute to the establishment of a conditioning between the drug effect and environmental cues.

Constitutive Ret signaling leads to long-lasting expression of amphetamine-induced place conditioning via elevation of mesolimbic dopamine

Addictive drugs enhance dopamine release in the striatum, which can lead to compulsive drug-seeking after repeated exposure. Glial cell line-derived neurotrophic factor (GDNF) is an important regulator of midbrain dopamine neurons, and may play a mechanistic role in addiction-related behaviors. To elucidate the components of GDNF-signaling that contribute to addiction-related behaviors of place preference and its extinction, we utilized two genetically modified GDNF mouse models in an amphetamine-induced conditioned place preference (CPP) paradigm and evaluated how the behavioral findings correlate with dopamine signaling in the dorsal and ventral striatum. We utilized two knock-in mouse strains to delineate contributions of GDNF and Ret signaling using MEN2B mice (constitutively active GDNF receptor Ret), and GDNF hypermorphic mice (enhanced endogenous GDNF expression). The duration of amphetamine-induced CPP was greatly enhanced in MEN2B mice, but not in the GDNF hypermorphic mice. The enhanced duration of CPP was correlated with increased tyrosine hydroxylase (TH) expression and dopamine content in the ventral striatum. Together, our results suggest that downstream components of GDNF signaling, in this case Ret, may mediate persistent drug-seeking behavior through increased TH expression and dopamine levels in the mesolimbic dopamine neurons.

Single Prazosin Infusion in Prelimbic Cortex Fosters Extinction of Amphetamine-Induced Conditioned Place Preference.

Exposure to drug-associated cues to induce extinction is a useful strategy to contrast cue-induced drug seeking. Norepinephrine (NE) transmission in medial prefrontal cortex has a role in the acquisition and extinction of conditioned place preference induced by amphetamine. We have reported recently that NE in prelimbic cortex delays extinction of amphetamine-induced conditioned place preference (CPP). A potential involvement of α1-adrenergic receptors in the extinction of appetitive conditioned response has been also suggested, although their role in prelimbic cortex has not been yet fully investigated. Here, we investigated the effects of the α1-adrenergic receptor antagonist prazosin infusion in the prelimbic cortex of C57BL/6J mice on expression and extinction of amphetamine-induced CPP. Acute prelimbic prazosin did not affect expression of amphetamine-induced CPP on the day of infusion, while in subsequent days it produced a clear-cut advance of extinction of preference for the compartment previously paired with amphetamine (Conditioned stimulus, CS). Moreover, prazosin-treated mice that had extinguished CS preference showed increased mRNA expression of brain-derived neurotrophic factor (BDNF) and post-synaptic density 95 (PSD-95) in the nucleus accumbens shell or core, respectively, thus suggesting that prelimbic α1-adrenergic receptor blockade triggers neural adaptations in subcortical areas that could contribute to the extinction of cue-induced drug-seeking behavior. These results show that the pharmacological blockade of α1-adrenergic receptors in prelimbic cortex by a single infusion is able to induce extinction of amphetamine-induced CPP long before control (vehicle) animals, an effect depending on contingent exposure to retrieval, since if infused far from or after reactivation it did not affect preference. Moreover, they suggest strongly that the behavioral effects depend on post-treatment neuroplasticity changes in corticolimbic network, triggered by a possible “priming” effect of prazosin, and point to a potential therapeutic power of the antagonist for maladaptive memories.

Chloramphenicol decreases CB1 receptor expression in the nucleus accumbens and prefrontal cortex and prevents amphetamine-induced conditioned place preference in rats

Drug dependence seems to involve a learning and memory process. Since learning and memory depend on protein synthesis, drug dependence may depend on protein synthesis, too. Drug-induced reward is a crucial effect for the development of drug-dependence. We used chloramphenicol (CAP, a protein synthesis inhibitor), to evaluate its effects on amphetamine (amph)-seeking behavior, on CB1R expression and on protein synthesis in general, in specific areas of the brain. Two groups of Wistar adult male rats were subjected to amph-induced conditioned place preference (CPP). Rats in group 1 received amph and were kept in the chamber for 30min. Once this period elapsed, they received a subcutaneous injection of saline (veh) and were returned to their home-cage. Rats in group 2 were also treated with amph but received CAP (150mg/kgsc) instead of saline. Once CPP was evaluated rats were sacrificed and the prefrontal cortex (PFC), the nucleus accumbens (NAcc) and the hippocampus (Hipp) were isolated and prepared for CB1R Western blot analysis. A vivarium reared group of rats was added as a non-experimentally manipulated control group. Results indicate that group 1 developed CPP while increasing CB1R expression in the NAcc. Group 2 did not develop CPP, had lower CB1R expression in the PFC and lacked the CB1R increase in the NAcc observed in the amph+veh group. These results support the notion that among the underlying mechanisms for amph-seeking reward is an increase in CB1R, further supporting an interaction between dopamine/endocannabinoids in CPP learning.

Inhibition of Wnt signalling dose-dependently impairs the acquisition and expression of amphetamine-induced conditioned place preference

The mechanisms by which dopaminergic neurotransmission in the nucleus accumbens (NAc) is involved in incentive learning produced by rewarding stimuli remain unclear. Recently, Wnt signalling has been implicated in synaptic plasticity and learning and memory. Functional interactions between Wnt and dopamine (DA) signalling has been demonstrated using in vitro and tissue physiology approaches, however there remains a lack of in vivo research into the involvement of Wnt in DA-mediated learning in behaving animals. The present study assessed the role of Wnt signalling in DA-mediated incentive learning using the conditioned place preference (CPP) paradigm. We hypothesized that inhibition of Wnt with intra-NAc microinjections of Wnt palmitoylation inhibitor IWP-2 will dose-dependently block the acquisition and expression of amphetamine (AMPH)-induced CPP in rats. Intra-NAc IWP-2 (0.001, 0.05, 1.0 but not 0.0001μg/0.5μl/side) prior to conditioning with AMPH (20.0μg/0.5μl/side) blocked acquisition of CPP. Intra-NAc IWP-2 (0.05, 0.5, 1.0 but not 0.001μg/0.5μl/side) during test following conditioning with AMPH blocked expression but at a higher dose than was need to block acquisition. Sensitization of locomotor activity to AMPH was observed during conditioning and this effect was blocked in groups given IWP-2 prior to AMPH. However, intra-NAc IWP-2 during conditioning did not block the locomotor stimulant effects of AMPH. These results implicate Wnt in DA-mediated incentive learning and suggest that Wnt signalling may be more important for the acquisition of CPP then for its expression. However, mechanisms by which Wnt and DA signalling pathways interact to influence DA-mediated reward-related learning remain to be elucidated.

The effects of d-govadine on conditioned place preference with d-amphetamine or food reward

Tetrahydroprotoberberines (THPB) have a high affinity for dopamine (DA) D1 and D2 receptors and may provide a novel treatment for drug addiction. We assessed the effects of the THPB d-govadine on the acquisition, expression, extinction and reinstatement of d-amphetamine-(1.5mg/kg, i.p.) induced conditioned place preference (CPP). Furthermore, the effects of d-govadine on conditioned association between contextual stimuli and a natural reward were examined using food-induced CPP. In separate experiments, rats received d-govadine (0, 0.5 or 1.0mg/kg, i.p.) before a) each d-amphetamine injection during conditioning, b) expression of amphetamine-induced CPP, c) each extinction session, d) amphetamine-induced reinstatement of CPP, or e) placement into a compartment containing food during conditioning. Although d-govadine had no effect on acquisition of amphetamine CPP, treatment with d-govadine during acquisition dose-dependently extinguished a preference for the amphetamine-associated context more quickly than vehicle treatment. Moreover, d-govadine treatment facilitated the extinction of amphetamine CPP when given repeatedly throughout the extinction phase. Although the expression of amphetamine CPP was not affected by d-govadine administered prior to the expression test, amphetamine-induced reinstatement of CPP following an extinction period was blocked by d-govadine (1.0mg/kg). The intermediate dose of d-govadine blocked the acquisition of food CPP, whereas the high dose facilitated extinction of this preference as compared to vehicle-treated animals. Therefore, d-govadine attenuates the maintenance of conditioned associations between contextual stimuli and amphetamine or food reward, as well as amphetamine-induced reinstatement of drug seeking behaviour. As such, d-govadine may be a candidate for further development as a pharmacological treatment of psychostimulant drug dependence.

Central & peripheral glucagon-like peptide-1 receptor signaling differentially regulate addictive behaviors

Recent data implicate glucagon-like peptide-1 (GLP-1), a potent anorexigenic peptide released in response to nutrient intake, as a regulator for the reinforcing properties of food, alcohol and psychostimulants. While, both central and peripheral mechanisms mediate effects of GLP-1R signaling on food intake, the extent to which central or peripheral GLP-1R signaling regulates reinforcing properties of drugs of abuse is unknown. Here, we examined amphetamine reinforcement, alcohol intake and hedonic feeding following peripheral administration of EX-4 (a GLP-1 analog) in FLOX and GLP-1R KDNestin (GLP-1R selectively ablated from the central nervous system) mice (n=13/group). First, the effect of EX-4 pretreatment on the expression of amphetamine-induced conditioned place preference (Amp-CPP) was examined in the FLOX and GLP-1R KDNestin mice. Next, alcohol intake (10% v/v) was evaluated in FLOX and GLP-1R KDNestin mice following saline or EX-4 injections. Finally, we assessed the effects of EX-4 pretreatment on hedonic feeding behavior. Results indicate that Amp-CPP was completely blocked in the FLOX mice, but not in the GLP-1R KDNestin mice following EX-4 pretreatment. Ex-4 pretreatment selectively blocked alcohol consumption in the FLOX mice, but was ineffective in altering alcohol intake in the GLP-1R KDNestin mice. Notably, hedonic feeding was partially blocked in the GLP-1R KDNestin mice, whereas it was abolished in the FLOX mice. The present study provides critical insights regarding the nature by which GLP-1 signaling controls reinforced behaviors and underscores the importance of both peripheral and central GLP-1R signaling for the regulation of addictive disorders.

Norepinephrine in prelimbic cortex delays extinction of amphetamine-induced conditioned place preference.

Drug-associated cues exposure to induce extinction is a useful strategy to contrast cue-induced drug seeking. Treatments aimed at reducing motivational properties of cues are considered highly promising since they could decrease their ability to induce drug-conditioned behaviors. Norepinephrine (NE) in the medial prefrontal cortex (mPFC) is critical for attribution of motivational salience to highly salient stimuli, suggesting a major role in prelimbic (PL) mpFC to modulate the motivational properties of drug-related cues, invigorating them, and consequently, delaying extinction. To investigate if NE in PL fosters the maintenance of drug-seeking behavior, we assessed its role on amphetamine-induced conditioned place preference (CPP). Moreover, to affirm the specificity of NE in PL, we also assessed the role of NE in the infralimbic (IL) mPFC. The effects of selective NE depletion in the PL or in the IL of C57BL/6J mice were assessed on the expression of amphetamine-induced CPP before and after extinction procedure. NE-depleted mice in PL extinguished preference for Amph-paired chamber long before sham animals. By contrast, IL-depleted animals maintained place preference for more than 4 weeks after the procedure of extinction, having at that moment interrupted the test. Inactivation of NE in PL cortex blunts amphetamine-induced CPP, thus fostering extinction and showing to be critical for the maintenance of conditioned Amph-seeking behavior. Opposite effects of NE depletion in IL, seemingly in agreement with literature on extinction, are discussed in terms of balance of activity between PL and IL in extinction.

Influence of neonatal tactile stimulation on amphetamine preference in young rats: Parameters of addiction and oxidative stress

This study investigated the influence of neonatal handling on amphetamine-induced conditioned place preference (CPP), as well as the consequent anxiety-like symptoms and oxidative status related to drug abstinence in young rats. Male pups were exposed to tactile stimulation (TS) or neonatal isolation (NI) for 10min every day from postnatal day one (PND1) to PND21. After being weaned (PND22), pups were separated by handling type until PND40, when treatment with amphetamine (AMPH-4mg/kg/mL ip, for 8days) or vehicle (NaCl 0.9% ip, 1mL/Kg) in CPP started. AMPH-conditioning evoked drug-preference (in 24h and 96h) and abstinence symptoms in unhandled (UH) animals, followed by oxidative damage in the cortex, hippocampus and striatum. TS showed beneficial influence, as observed by the decreased drug-preference (24 and 96h) in relation to UH and NI, showing no abstinence symptoms in this last period, as observed by the reduced anxiety-like symptoms. The oxidative status indicated a protective influence of TS on brain tissues: lower lipid peroxidation (LP) and reduced protein carbonylation (PC) in the cortex, hippocampus and striatum. Furthermore, TS also increased antioxidant defenses in brain tissues and blood: i) increased plasma levels of vitamin C; ii) increased activity of catalase (CAT) and iii) higher levels of glutathione (GSH) in red blood cells (RBC). Moreover, there were positive correlations of AMPH-CPP with PC and LP levels in all the brain areas assessed. In summary, TS modifies AMPH-preference in the CPP paradigm, reducing drug abstinence behaviors, and stimulating the antioxidant defense system, thus protecting the brain areas closely related to addiction in young rats. Studies about TS and addiction in animal models should be extended to the molecular level.

Amphetamine reward in food restricted mice lacking the melanin-concentrating hormone receptor-1

Chronic food restriction (FR) and maintenance of low body weight have long been known to increase the rewarding and motor-activating effects of addictive drugs. However, the neurobiological mechanisms through which FR potentiates drug reward remain largely unknown. Melanin-concentrating hormone (MCH) signaling could be one of these mechanisms since this peptide is involved in energy homeostasis and modulates mesolimbic dopaminergic transmission. The purpose of the present study was to test this hypothesis by investigating the impact of FR on amphetamine reward in wild-type (WT) and knockout mice lacking the melanin-concentrating hormone receptor-1 (MCHR1-KO). The rewarding effects of amphetamine (0.75–2.25mg/kg, i.p.) were measured with the conditioned place preference (CPP) technique. The food of the mice was restricted to maintain their body weight at 80–85% of their free-feeding (FF) weight throughout the entire CPP experiment. Locomotor activity of the animals was recorded during the conditioning sessions. Our results show that locomotion of all the food-restricted mice treated with saline or amphetamine increased over the sessions whatever the genotype. On the place preference test, the amplitude of CPP induced by 0.75mg/kg amphetamine was higher in food restricted WT mice than in free-fed WT mice and food restricted MCHR1-KO mice. However, FR did not affect amphetamine reward in MCHR1-KO mice. The present results indicate that MCH signaling could be involved in the ability of FR to increase amphetamine-induced CPP.

Glucocorticoid receptor gene inactivation in dopamine-innervated areas selectively decreases behavioral responses to amphetamine

The meso-cortico-limbic system, via dopamine release, encodes the rewarding and reinforcing properties of natural rewards. It is also activated in response to abused substances and is believed to support drug-related behaviors. Dysfunctions of this system lead to several psychiatric conditions including feeding disorders and drug addiction. These disorders are also largely influenced by environmental factors and in particular stress exposure. Stressors activate the corticotrope axis ultimately leading to glucocorticoid hormone (GCs) release. GCs bind the glucocorticoid receptor (GR) a transcription factor ubiquitously expressed including within the meso-cortico-limbic tract. While GR within dopamine-innervated areas drives cocaine's behavioral responses, its implication in responses to other psychostimulants such as amphetamine has never been clearly established. Moreover, while extensive work has been made to uncover the role of this receptor in addicted behaviors, its contribution to the rewarding and reinforcing properties of food has yet to be investigated. Using mouse models carrying GR gene inactivation in either dopamine neurons or in dopamine-innervated areas, we found that GR in dopamine responsive neurons is essential to properly build amphetamine-induced conditioned place preference and locomotor sensitization. c-Fos quantification in the nucleus accumbens further confirmed defective neuronal activation following amphetamine injection. These diminished neuronal and behavioral responses to amphetamine may involve alterations in glutamate transmission as suggested by the decreased MK801-elicited hyperlocomotion and by the hyporeactivity to glutamate of a subpopulation of medium spiny neurons. In contrast, GR inactivation did not affect rewarding and reinforcing properties of food suggesting that responding for natural reward under basal conditions is preserved in these mice.

Medial prefrontal cortex inactivation attenuates the diurnal rhythm in amphetamine reward

Psychostimulant reward, as assessed via the conditioned place preference (CPP) paradigm, exhibits a daily rhythm with peaks in the late dark and early light periods, and a nadir near the light-to-dark transition. While this diurnal rhythm is correlated with neural activity in several corticolimbic structures, the brain regions mediating this behavioral rhythm remain unknown. Here, we examine the role of the ventral medial prefrontal cortex (mPFC). The effects of excitotoxic mPFC lesions on daily rhythms in amphetamine CPP were examined at previously observed peak (zeitgeber time [ZT] 23) and nadir times (ZT11). mPFC lesions encompassing the prelimbic and infralimbic subregions increased the CPP for amphetamine at the nadir time, thereby eliminating the daily rhythm in amphetamine reward. To examine the effects of transient mPFC inactivation, rats received intra-mPFC infusions of GABA receptor agonists during the acquisition or expression phases of CPP testing. Inactivation of the ventral mPFC at either of these phases also eliminated the daily rhythm in amphetamine-induced CPP via an increase in drug-paired chamber dwell time at the baseline nadir. Together, these results indicate that the ventral mPFC plays a critical role in mediating the diurnal rhythm in amphetamine CPP during both the acquisition and expression of learned reward–context associations. Moreover, as the loss of rhythmicity occurs via an increase at the nadir point, these results suggest that excitatory output from the ventral mPFC normally inhibits context-elicited reward seeking prior to the light-to-dark transition.