Relapse of methamphetamine-seeking behavior in C57BL/6J mice demonstrated by a reinstatement procedure involving intravenous self-administration

Impaired extinction of operant cocaine in a genetic mouse model of schizophrenia risk

BACKGROUND

Individuals with schizophrenia have high rates of comorbid substance use problems. One potential explanation for this comorbidity is similar neuropathophysiology in substance use and schizophrenia, which may arise from shared genetic risk factors between the two disorders. Here we investigated if genetic risk for schizophrenia could affect drug reward and reinforcement for cocaine in an established mouse model of genetic risk for schizophrenia, the neuregulin 1 transmembrane domain heterozygous (Nrg1 TM HET) mouse.

METHODS

We examined drug-induced locomotor sensitization and conditioned place preference for several cocaine doses (5, 10, 20, 30 mg/kg) in male adult Nrg1 TM HET and wild-type-like (WT) littermates. We also investigated intravenous self-administration of and motivation for cocaine (doses 0.1, 0.5, 1 mg/kg/infusion), as well as extinction and cue-induced reinstatement of cocaine. In a follow-up experiment, we examined self-administration, extinction and cue-induced reinstatement of a natural reward, oral sucrose.

RESULTS

Cocaine preference was similar between Nrg1 TM HET mice and WT littermates at all doses tested. Locomotor sensitization to cocaine was not affected by Nrg1 genotype at any dose. Although self-administration and motivation for cocaine was unaffected, extinction of cocaine self-administration was impaired in Nrg1 TM HET compared to WT controls, and cue-induced reinstatement was greater in Nrg1 mutants in the middle of the reinstatement session. Sucrose self-administration and extinction thereof was not affected by genotype, but inactive lever responding was elevated during cue-induced reinstatement for operant sucrose in Nrg1 TM HET mice compared to WTs.

DISCUSSION

These results suggest impaired response inhibition for cocaine in Nrg1 TM HET mice and suggests Nrg1 mutation may contribute to behaviours which can limit control over cocaine use.

Intracerebroventricular microinjection of the 5-HT1F receptor agonist LY 344864 inhibits methamphetamine conditioned place preference reinstatement in rats

Relapse following a prolonged period of drug cessation is a key barrier in the treatment of methamphetamine (METH) addiction, for which pharmacological treatment exhibits little efficacy. Previous studies have suggested that this process involves alterations in levels of serotonin (5-HT) in the brain. Although the 5-HT1F receptor has been implicated in the reward pathway, its physiological functions remain unknown. In the present study, we examined the effect of the 5-HT1F agonist LY 344864 on the reinstatement of METH-seeking behavior in rats using a conditioned place preference (CPP) paradigm. The CPP paradigm was first used to determine the effective doses of LY and METH. Four groups were then conditioned with METH (5 mg/kg; i.p.), while the sham group received saline. METH-induced CPP was subsequently extinguished. On the 13th day of extinction, the rats received either METH (0, 1, or 2.5 mg/kg; i.p.) plus vehicle or priming METH plus LY (2 μg/5 μL; i.c.v.). On reinstatement day, preference scores were calculated as the difference in time spent in the drug-paired and vehicle-paired compartments. Rats conditioned with the lowest effective dose of METH (5 mg/kg) exhibited significant differences in pre- and post-testing preference scores. Preference scores were significantly higher in the saline + METH group than in the control group. Furthermore, preference scores were significantly higher in rats that had received priming METH treatment, and pre-treatment with LY significantly attenuated the reinstatement of METH-seeking behavior. These findings suggest that future studies should evaluate the therapeutic potential of 5-HT1F agonists for preventing relapse in individuals with METH addiction.

Intravenous cocaine self-administration in a panel of inbred mouse strains differing in acute locomotor sensitivity to cocaine

RATIONALE

Initial sensitivity to drugs of abuse often predicts subsequent use and abuse, but this relationship is not always observed in human studies. Moreover, studies examining the relationship between initial locomotor sensitivity and the rewarding and reinforcing effects of drugs in animal models have also been equivocal. Understanding the relationship between initial drug effects and propensity to continue use, potentially resulting in the development of a substance use disorder, may help to identify key targets for prevention and treatment.

OBJECTIVES

We examined intravenous cocaine self-administration in a set of mouse strains that were previously identified to be at the phenotypic extremes for cocaine-induced locomotor activation to determine if initial locomotor sensitivity predicted acquisition, extinction, dose response, or progressive ratio (PR) breakpoint.

METHODS

We selected eight inbred mouse strains based on locomotor sensitivity to 20 mg/kg cocaine. These strains, designated as low and high responders, were tested in an intravenous self-administration paradigm that included acquisition of 0.5 mg/(kg*inf) under a FR1 schedule, extinction, re-acquisition, dose response to 0.125, 0.25, 0.5, 1, and 2 mg/(kg*inf), and progressive ratio.

RESULTS

We observed overall differences in self-administration behavior between high and low responders. Low responders self-administered less cocaine and had lower breakpoints under the PR schedule. However, we also observed strain differences within each group. Self-administration in the low responder, LG/J, more closely resembled the behavior of the high-responding group, and the high responder, P/J, had self-administration behavior that more closely resembled the low-responding group.

CONCLUSIONS

We conclude that acute cocaine-induced locomotor activation does predict self-administration behavior, but in a strain-specific manner. These data support the idea that genetic background influences the relationship among addiction-related behaviors.

Insular neural system controls decision-making in healthy and methamphetamine-treated rats

Patients suffering from neuropsychiatric disorders such as substance-related and addictive disorders exhibit altered decision-making patterns, which may be associated with their behavioral abnormalities. However, the neuronal mechanisms underlying such impairments are largely unknown. Using a gambling test, we demonstrated that methamphetamine (METH)-treated rats chose a high-risk/high-reward option more frequently and assigned higher value to high returns than control rats, suggestive of changes in decision-making choice strategy. Immunohistochemical analysis following the gambling test revealed aberrant activation of the insular cortex (INS) and nucleus accumbens in METH-treated animals. Pharmacological studies, together with in vivo microdialysis, showed that the insular neural system played a crucial role in decision-making. Moreover, manipulation of INS activation using designer receptor exclusively activated by designer drug technology resulted in alterations to decision-making. Our findings suggest that the INS is a critical region involved in decision-making and that insular neural dysfunction results in risk-taking behaviors associated with altered decision-making.

Methamphetamine self-administration in mice decreases GIRK channel-mediated currents in midbrain dopamine neurons

BACKGROUND

Methamphetamine is a psychomotor stimulant with abuse liability and a substrate for catecholamine uptake transporters. Acute methamphetamine elevates extracellular dopamine, which in the midbrain can activate D2 autoreceptors to increase a G-protein gated inwardly rectifying potassium (GIRK) conductance that inhibits dopamine neuron firing. These studies examined the neurophysiological consequences of methamphetamine self-administration on GIRK channel-mediated currents in dopaminergic neurons in the substantia nigra and ventral tegmental area.

METHODS

Male DBA/2J mice were trained to self-administer intravenous methamphetamine. A dose response was conducted as well as extinction and cue-induced reinstatement. In a second study, after at least 2 weeks of stable self-administration of methamphetamine, electrophysiological brain slice recordings were conducted on dopamine neurons from self-administering and control mice.

RESULTS

In the first experiment, ad libitum-fed, nonfood-trained mice exhibited a significant increase in intake and locomotion following self-administration as the concentration of methamphetamine per infusion was increased (0.0015-0.15mg/kg/infusion). Mice exhibited extinction in responding and cue-induced reinstatement. In the second experiment, dopamine cells in both the substantia nigra and ventral tegmental area from adult mice with a history of methamphetamine self-administration exhibited significantly smaller D2 and GABAB receptor-mediated currents compared with control mice, regardless of whether their daily self-administration sessions had been 1 or 4 hours. Interestingly, the effects of methamphetamine self-administration were not present when intracellular calcium was chelated by including BAPTA in the recording pipette.

CONCLUSIONS

Our results suggest that methamphetamine self-administration decreases GIRK channel-mediated currents in dopaminergic neurons and that this effect may be calcium dependent.

Dopamine D1 and D3 receptors mediate reconsolidation of cocaine memories in mouse models of drug self-administration

Memories of drug experience and drug-associated environmental cues can elicit drug-seeking and taking behaviors in humans. Disruption of reconsolidation of drug memories dampens previous memories and therefore may provide a useful way to treat drug abuse. We and others previously demonstrated that dopamine D1 and D3 receptors play differential roles in acquiring cocaine-induced behaviors. Moreover, D3 receptors contribute to the reconsolidation of cocaine-induced conditioned place preference. In the present study, we examined effects of manipulating D1 or D3 receptors on reconsolidation of cocaine memories in mouse models of drug self-administration. We found that pharmacological blockade of D1 receptors or a genetic mutation of the D3 receptor gene attenuated reconsolidation that lasted for at least 1week after the memory retrieval. In contrast, with no memory retrieval, pharmacological antagonism of D1 receptors or the D3 receptor gene mutation did not significantly affect reconsolidation of cocaine memories. Pharmacological blockade of D3 receptors also attenuated reconsolidation in wild-type mice that lasted for at least 1week after the memory retrieval. These results suggest that D1 and D3 receptors and related signaling mechanisms play key roles in reconsolidation of cocaine memories in mice, and that these receptors may serve as novel targets for the treatment of cocaine abuse in humans.

Intrastriatal gene delivery of GDNF persistently attenuates methamphetamine self-administration and relapse in mice

Relapse of drug abuse after abstinence is a major challenge to the treatment of addicts. In our well-established mouse models of methamphetamine (Meth) self-administration and reinstatement, bilateral microinjection of adeno-associated virus vectors expressing GDNF (AAV-Gdnf) into the striatum significantly reduced Meth self-administration, without affecting locomotor activity. Moreover, the intrastriatal AAV-Gdnf attenuated cue-induced reinstatement of Meth-seeking behaviour in a sustainable manner. In addition, this manipulation showed that Meth-primed reinstatement of Meth-seeking behaviour was reduced. These findings suggest that the AAV vector-mediated Gdnf gene transfer into the striatum is an effective and sustainable approach to attenuate Meth self-administration and Meth-associated cue-induced relapsing behaviour and that the AAV-mediated Gdnf gene transfer in the brain may be a valuable gene therapy against drug dependence and protracted relapse in clinical settings.

The metabotropic glutamate 5 receptor modulates extinction and reinstatement of methamphetamine-seeking in mice

Methamphetamine (METH) is a highly addictive psychostimulant with no therapeutics registered to assist addicts in discontinuing use. Glutamatergic dysfunction has been implicated in the development and maintenance of addiction. We sought to assess the involvement of the metabotropic glutamate 5 receptor (mGlu5) in behaviours relevant to METH addiction because this receptor has been implicated in the actions of other drugs of abuse, including alcohol, cocaine and opiates. mGlu5 knockout (KO) mice were tested in intravenous self-administration, conditioned place preference and locomotor sensitization. Self-administration of sucrose was used to assess the response of KO mice to a natural reward. Acquisition and maintenance of self-administration, as well as the motivation to self-administer METH was intact in mGlu5 KO mice. Importantly, mGlu5 KO mice required more extinction sessions to extinguish the operant response for METH, and exhibited an enhanced propensity to reinstate operant responding following exposure to drug-associated cues. This phenotype was not present when KO mice were tested in an equivalent paradigm assessing operant responding for sucrose. Development of conditioned place preference and locomotor sensitization were intact in KO mice; however, conditioned hyperactivity to the context previously paired with drug was elevated in KO mice. These data demonstrate a role for mGlu5 in the extinction and reinstatement of METH-seeking, and suggests a role for mGlu5 in regulating contextual salience.

Dissociable role of tumor necrosis factor alpha gene deletion in methamphetamine self-administration and cue-induced relapsing behavior in mice

RATIONALE

During the development of addiction, addictive drugs induce transient and long-lasting changes in the brain including expression of endogenous molecules and alteration of morphological structure. Of the altered endogenous molecules, some facilitate but others slow the development of drug addiction. Previously, we have reported that tumor necrosis factor alpha (TNF-α) is a critical molecule among endogenous anti-addictive modulators using animal models of drug-conditioned place preference and drug discrimination.

OBJECTIVES

Does targeted deletion of the TNF-α gene in mice affect methamphetamine (METH) self-administration, motivation to self-administer METH, cue-induced reinstatement of METH-seeking behavior, and food reinforcement or seeking behavior?

METHODS

Both METH self-administration and reinstatement of drug-seeking behavior and food self-delivery and food-seeking behavior were measured in TNF-α (-/-) and wild-type mice.

RESULTS

There were an upward shift of dose responses to METH self-administration under a fixed ratio schedule of reinforcement and higher breaking points under a progressive ratio schedule of reinforcement in TNF-α knockout (TNF-α (-/-)) mice as compared with wild-type mice. There was no significant difference in cue-induced reinstatement of METH-seeking behavior, food-maintained operant behavior, motivation to natural food, and cue-induced food-seeking behavior between TNF-α (-/-) and wild-type mice.

CONCLUSION

TNF-α affects METH self-administration and motivation to self-administer METH but contributes to neither METH-associated cue-induced relapsing behavior nor food reward and food-seeking behavior. TNF-α may be explored for use as a diagnostic biomarker for the early stage of drug addiction.

Ceftriaxone upregulates the glutamate transporter in medial prefrontal cortex and blocks reinstatement of methamphetamine seeking in a condition place preference paradigm

Glutamate signaling plays an essential role in drug-seeking behavior. Using reinstatement of conditioned place preference (CPP), we determined whether ceftriaxone, a β-lactam antibiotic known to increase the expression and activity of the glutamate transporter (EAAT₂) on glial cells, blocks methamphetamine-triggered reinstatement of CPP. Rats acquired methamphetamine CPP following 7 consecutive days of conditioning, during which each animal received pairings of alternating morning methamphetamine (2.5 mg/kg, IP) and afternoon saline (IP). Animals showing CPP were successfully extinguished with repeated twice daily saline administration over a 7-day period. Ceftriaxone (200 mg/kg, IP) was administered (vs. saline) once a day for 7 days during the extinction period. Upon successful extinction, animals received a single dose of methamphetamine (2.5 mg/kg, IP) for reinstatement and were tested for CPP one day later. Using real time PCR, EAAT₂ mRNA levels in the nucleus accumbens (NAc) and medial prefrontal cortex (mPFC) were quantified in response to ceftriaxone. Ceftriaxone blocked methamphetamine-triggered reinstatement of CPP and significantly increased EAAT₂ mRNA levels in the mPFC, with a trend towards significance in the NAc. In conclusion, Ceftriaxone modulated the expression of the glutamate transporter in a critical region of the cortico-striatal addiction circuitry and attenuated drug-seeking behavior in rats. Further research is needed to test the efficacy of compounds targeting the EAAT₂ in human methamphetamine-dependent users.

Nicotine-taking and nicotine-seeking in C57Bl/6J mice without prior operant training or food restriction

The ability to examine genetically engineered mice in a chronic intravenous (IV) nicotine self-administration paradigm will be a powerful tool for investigating the contribution of specific genes to nicotine reinforcement and more importantly, to relapse behavior. Here we describe a reliable model of nicotine-taking and -seeking behavior in male C57BL/6J mice without prior operant training or food restriction. Mice were allowed to self-administer either nicotine (0.03mg/kg/infusion) or saline in 2-h daily sessions under fixed ratio 1 (FR1) followed by FR2 schedules of reinforcement. In the nicotine group, a dose-response curve was measured after the nose-poke behavior stabilized. Subsequently, nose-poke behavior was extinguished and ability of cue presentations, priming injections of nicotine, or intermittent footshock to reinstate responding was assessed in both groups. C57BL/6J mice given access to nicotine exhibited high levels of nose-poke behavior and self-administered a high number of infusions as compared to mice given access to saline. After this acquisition phase, changing the unit-dose of nicotine resulted in a flat dose-response curve for nicotine-taking and subsequently reinstatement of nicotine-seeking behavior was achieved by both nicotine-associated light cue presentation and intermittent footshock. Nicotine priming injections only triggered significant reinstatement on the second consecutive day of priming. In contrast, mice previously trained to self-administer saline did not increase their responding under those conditions. These results demonstrate the ability to produce nicotine-taking and nicotine-seeking behavior in naive C57BL/6J mice without both prior operant training and food restriction. Future work will utilize these models to evaluate nicotine-taking and relapsing behavior in genetically-altered mice.

Intrathecal cocaine delivery enables long-access self-administration with binge-like behavior in mice

RATIONALE

Long-access intravenous drug self-administration shows diurnal alterations in drug intake, with escalation and binge patterns, in rats. A similar long-access model in mice would allow the use of genetically modified animals to better understand the molecular mechanisms underlying drug addiction and relapse. However, attempts to transfer this model to mice have been less successful, mainly because of technical difficulties with long-term maintenance of the indwelling catheter implanted into small veins.

OBJECTIVES

We devised an intrathecal probe implanted in the supracerebellar cistern as an alternative for intravenous drug administration to address this challenge and allow continuous, chronic drug self-administration in mice.

RESULTS

We found that mice readily self-administered intrathecal infusions of cocaine as a drug reward, and, under daily 24-h access conditions, animals exhibited a binge-like behavior comparable to rats.

CONCLUSIONS

This innovation enables a full analysis of long-access drug self-administration behavior in mice not possible with intravenous administration.

Patterns of responding differentiate intravenous nicotine self-administration from responding for a visual stimulus in C57BL/6J mice

RATIONALE

Testing genetically engineered mice in a reliable nicotine self-administration procedure could provide important insights into the molecular mechanisms underlying nicotine reinforcement.

OBJECTIVES

We assessed operant responding for intravenous nicotine infusions in C57BL/6J male mice under a fixed-ratio 3 schedule of reinforcement in which a visual cue was contingently associated with drug delivery.

METHODS/RESULTS

Acquisition, dose-response function, extinction, and cue-induced reinstatement of operant behavior were characterized. Low nicotine doses (0.001-0.06 mg/kg/infusion) elicited response rates similar to those supported by saline, whereas a higher dose (0.1 mg/kg/infusion) decreased responding. Using an identical procedure to assess cocaine self-administration in an independent group of mice yielded an inverted U-shaped dose-response curve. Other mice trained to respond exclusively for the visual stimulus earned a similar number of reinforcers as mice self-administering saline or low nicotine doses, although with a lower selectivity for the active lever and their response rates were sensitive to the discontinuation and resumption of cue light presentation. Finally, patterns of responding for nicotine, cocaine, or the visual stimulus alone were analyzed using frequency distributions of inter-response intervals and extended return maps. These analyses revealed unique properties of nicotine, which dose-dependently delayed the first response post-timeout and increased the regularity of lever pressing activity.

CONCLUSIONS

Nicotine did not enhance the reinforcing properties of the visual cue paired with drug delivery. Interestingly, however, patterns of responding could differentiate nicotine self-administration from responding for a visual stimulus or saline and indicated that nicotine functioned as a salient stimulus driving highly regular operant behavior.

Operant sensation seeking engages similar neural substrates to operant drug seeking in C57 mice

Novelty and sensation seeking have been associated with elevated drug intake in human and animal studies, suggesting overlap in the circuitry mediating these behaviors. In this study, we found that C57Bl/6J mice readily acquired operant responding for dynamic visual stimuli, a phenomenon we term operant sensation seeking (OSS). Like operant studies using other reinforcers, mice responded on fixed and progressive ratio schedules, were resistant to extinction, and had sustained responding with extended access. We also found that OSS, like psychostimulant self-administration, is sensitive to disruption of dopamine signaling. Low doses of the dopamine antagonist cis-flupenthixol increased active lever responding, an effect reported for psychostimulant self-administration. Additionally, D1-deficient mice failed to acquire OSS, although they readily acquired lever pressing for food. Finally, we found that one common measure of novelty seeking, locomotor activity in a novel open field, did not predict OSS performance. OSS may have predictive validity for screening compounds for use in the treatment of drug addiction. In addition, we also discuss the potential relevance of this animal model to the field of behavioral addictions.

New operant model of nicotine-seeking behaviour in mice

Nicotine addiction represents a major health problem in the world with dramatic socio-economic consequences. Recent studies using genetically modified mice have provided a better understanding of the neurobiological mechanisms involved in nicotine responses. However, the study of nicotine addiction requires sophisticated behavioural models that are still not fully developed in mice. Here, we report the validation of a new reliable operant model of nicotine-seeking behaviour in mice. C57BL/6 mice were trained to self-administer nicotine (0.03 mg/kg per infusion) under a fixed ratio 1 schedule of reinforcement for 10 d. A light cue was contingently associated with the nicotine infusion. After reaching the acquisition criteria of nicotine self-administration, mice were exposed to extinction sessions similar to the self-administration training except that nicotine was not available and the associated cues were not presented. Nicotine-seeking behaviour was then reinstated by exposure to nicotine-associated environment cues, a priming injection of nicotine or stress, the three main conditions leading to nicotine relapse in humans. The exposure to the cues associated with nicotine infusion was the most effective stimulus reinstating nicotine-seeking behaviour in 90% of mice. A priming injection of nicotine (0.18 mg/kg) produced nicotine reinstatement in 30% of the animals, whereas stress exposure (0.22 mA footshock) reinstated nicotine-seeking behaviour in 50% of mice. The validation of this new model of nicotine-seeking behaviour and reinstatement in mice provides an important tool to help clarify the genetic and neurochemical bases of nicotine addiction.

Racemic gamma vinyl-GABA (R,S-GVG) blocks methamphetamine-triggered reinstatement of conditioned place preference

Preventing relapse poses a significant challenge to the successful management of methamphetamine (METH) dependence. Although no effective medication currently exists for its treatment, racemic gamma vinyl-GABA (R,S-GVG, vigabatrin) shows enormous potential as it blocks both the neurochemical and behavioral effects of a variety of drugs, including METH, heroin, morphine, ethanol, nicotine, and cocaine. Using the reinstatement of a conditioned place preference (CPP) as an animal model of relapse, the present study specifically investigated the ability of an acute dose of R,S-GVG to block METH-triggered reinstatement of a METH-induced CPP. Animals acquired a METH CPP following a 20-day-period of conditioning, in which they received 10 pairings of alternating METH and saline injections. During conditioning, rats were assigned to one of four METH dosage groups: 1.0, 2.5, 5.0, or 10.0 mg/kg (i.p., n = 8/group). Animals in all dosage groups demonstrated a robust and consistent CPP. This CPP was subsequently extinguished in each dosage group with repeated saline administration. Upon extinction, all groups reinstated following an acute METH challenge. On the following day, an acute dose of R,S-GVG (300 mg/kg, i.p.) was administered 2.5 h prior to an identical METH challenge. R,S-GVG blocked METH-triggered reinstatement in all four groups. Given that drug re-exposure may potentiate relapse to drug-seeking behavior, the ability of R,S-GVG to block METH-triggered reinstatement offers further support for its use in the successful management of METH dependence.

Endogenous modulators for drug dependence

Drug addiction/dependence is defined as a chronically relapsing disorder that is characterized by compulsive drug taking, inability to limit intake, and intense drug cravings. The positive reinforcing/rewarding effects of drugs primarily depend on the mesocorticolimbic dopamine system innervating the nucleus accumbens while the craving for drugs is associated with activation of the prefrontal cortex. The chronic intake of drugs causes homeostatic molecular and functional changes in synapses, which may be critically associated with the development of drug dependence. Recent studies have demonstrated that various cytokines and proteinases are produced in the brain on treatment with drugs of abuse, and play a role in drug dependence. These endogenous modulators of drug dependence are classified into two groups, pro-addictive and anti-addictive factors. The former including basic fibroblast growth factor, brain-derived neurotrophic factor, tissue plasminogen activator, matrix metalloproteinase (MMP)-2 and MMP-9 act to potentiate the rewarding effects of drugs, while the latter such as tumor necrosis factor-alpha and glial cell line-derived neurotrophic factor reduce the reward. These findings suggest that an imbalance between pro-addictive and anti-addictive factors contributes to the development and relapse of drug dependence. Furthermore, targeting these endogenous modulators would provide new therapeutic approaches to the treatment of drug dependence.

Mouse model of relapse to the abuse of drugs: procedural considerations and characterizations

To identify genetic risk factors involved in relapse to the abuse of drugs in humans, it is essential for researchers to develop a reliable mouse model of relapse by extending well-established extinction-reinstatement procedures in rats. Because of technical difficulties such as the relatively short duration of catheter patency in mice, few reports are available on the characterization of extinction-reinstatement behavior in wild-type and genetically engineered mutant mice. In this review, efforts are made to describe practical considerations during the establishment of extinction-reinstatement procedure in mice, including drug-primed, cue-induced, and stress-triggered reinstatement of previously extinguished drug-seeking behavior. Next, attention will be given to some characteristics of extinction-reinstatement behavior in mice. The present review might provide a new impetus in the exploration of genetic risk factors involved in relapse to drug dependence/addiction in humans using extinction-reinstatement procedures in widely available mutant mice.

Comparison of systemic and local methamphetamine treatment on acetylcholine and dopamine levels in the ventral tegmental area in the mouse

Acetylcholine (ACh) is an important mediator of dopamine (DA) release and the behavioral reinforcing characteristics of drugs of abuse in the mesocorticolimbic pathway. Within the ventral tegmental area (VTA), the interaction of DA with ACh appears to be integral in mediating motivated behaviors. However, the effects of methamphetamine on VTA ACh and DA release remain poorly characterized. The current investigation performed microdialysis to evaluate the effects of methamphetamine on extracellular levels of ACh and DA. Male C57BL/6J mice received an i.p. injection (saline, 2 mg/kg, or 5 mg/kg) and an intra-VTA infusion (vehicle, 100 microM or 1 mM) of methamphetamine. Locally perfused methamphetamine resulted in no change in extracellular ACh compared with vehicle, but caused a strong, immediate and dose-dependent increase in extrasynaptic DA levels (1240% and 2473% of baseline, respectively) during the 20-min pulse perfusion. An i.p. injection of methamphetamine increased extrasynaptic DA to 275% and 941% of baseline (2 mg/kg and 5 mg/kg, respectively). Systemic methamphetamine significantly increased ACh levels up to 275% of baseline for 40-60 min (2 mg/kg) and 397% of baseline for 40-160 min (5 mg/kg) after injection. ACh remained elevated above baseline for 2-3 h post injection, depending on the methamphetamine dose. Methamphetamine-induced locomotor activity was dose-dependently correlated with extrasynaptic VTA ACh, but not DA levels. These data suggest that methamphetamine acts in the VTA to induce a robust and short-lived increase in extracellular DA release but acts in an area upstream from the VTA to produce a prolonged increase in ACh release in the VTA. We conclude that methamphetamine may activate a recurrent loop in the mesocorticolimbic DA system to stimulate pontine cholinergic nuclei and produce a prolonged ACh release in the VTA.

Developmental lead exposure alters methamphetamine self-administration in the male rat: acquisition and reinstatement

The rate of acquisition of drug self-administration and the return to drug seeking are important elements of the overall drug profile, and are essential factors in understanding risks associated with drug abuse. Experiment 1 examined the effects of perinatal (gestation/lactation) lead exposure on adult rates of acquisition of intravenous (i.v.) methamphetamine self-administration. Experiment 2 investigated the effects of perinatal lead exposure on drug-maintained responding in a reinstatement (relapse) paradigm. In Experiment 1, female rats were gavaged daily with 0 or 16 mg lead for 30 days prior to breeding with nonexposed males. Lead exposure continued through gestation and lactation and was discontinued at weaning (postnatal day [PND] 21). Male rats born to control or lead-exposed dams were tested daily as adults in an acquisition paradigm that incorporated both Pavlovian and operant components. An initial 3-h autoshaping period preceded a 3-h self-administration period. For 35 daily training sessions i.v. methamphetamine infusions [inf] (0.02 mg/kg) were paired with the extension and retraction of a lever (autoshaping), while inf occurred during self-administration only when a lever press was executed (FR-1). In Experiment 2 animals developmentally exposed to lead were trained on an FR-2 to self-administer methamphetamine (0.04 mg/kg/inf) and then placed on an extinction schedule prior to receiving intraperitoneal (i.p.) priming injections of saline, 0.50, 1.00, or 1.50 mg/kg methamphetamine. The findings from Experiment 1 showed that acquisition was delayed in rats born to lead-exposed dams gavaged daily with 16 mg lead throughout gestation and lactation when a 0.02-mg/kg/inf of methamphetamine served as the reinforcement outcome. Additional data from Experiment 2 indicated priming cues (injections of methamphetamine [i.p.]) administered after extinction were less likely to occasion a return to drug seeking (relapse) in the 16-mg group relative to the 0-mg control group. These results suggest perinatal lead exposure alters patterns of methamphetamine self-administration during the adult cycle.

Effect of drug-paired exteroceptive stimulus presentations on methamphetamine reinstatement in rats

The purpose of the present study was to examine the impact of drug-paired cues on methamphetamine reinstatement. Three groups of rats were trained to self-administer 0.1 mg/kg/infusion methamphetamine. Each methamphetamine infusion was accompanied by a 6 s flashing light+tone stimulus (cues). After training, the groups were then given 12, daily extinction sessions either with or without response-contingent drug-paired cues and then tested for 1 mg/kg i.p. methamphetamine priming-induced reinstatement either with or without cues. Methamphetamine priming significantly reinstated drug-appropriate responding regardless of whether response-contingent cues were omitted during both extinction and testing, presented during both extinction and testing, or omitted during extinction but presented during reinstatement testing. The group in which cues were omitted during extinction and presented during reinstatement exhibited significantly greater reinstatement than did the other two groups. A separate group of rats was also tested demonstrating that response-contingent presentation of previously methamphetamine-paired cues alone, without methamphetamine priming, significantly reinstated drug-appropriate responding. These data show that methamphetamine priming produces a robust reinstatement effect which can be influenced by drug-paired cues.

Effect of cannabinoid CB1 receptor antagonist SR141716A and CB1 receptor knockout on cue-induced reinstatement of Ensure and corn-oil seeking in mice

The cannabinoid CB1 receptor antagonist SR141716A decreases cue-induced reinstatement of sucrose and drug seeking in rats. Reinstatement behavior is not well characterized in C57Bl/6 mice, including CB1 receptor knockout mice generated on a C57Bl/6 background. In the present study, male C57Bl/6, CB1 knockout (CB1 KO), and wild-type littermate (WT) mice were trained to respond for the sweet reinforcer Ensure or corn oil. Responding was maintained on a fixed ratio 1 (FR1) schedule of reinforcement for 10 days, and then extinguished by the removal of the reinforcer and associated cues. Subsequently, the effect of either pretreatment with SR141716A or CB1 receptor knockout on cue-induced reinstatement of Ensure or corn-oil seeking was assessed. Both 1.0 and 3.0 mg/kg SR141716A decreased reinstatement of Ensure seeking in C57Bl/6 mice. A tenfold higher dose of SR141716A (10.0 mg/kg) was required to attenuate reinstatement behavior in C57Bl/6 mice responding for corn oil, suggesting that CB1 receptors may be selectively involved in the neurobiology underlying reinstatement of responding for some food reinforcers but not others. Whereas CB1 receptor antagonism selectively attenuated reinstatement of responding for Ensure, genetic deletion of the CB1 receptor produced only a trend in decreasing reinstatement of Ensure seeking, and did not attenuate reinstatement of corn-oil seeking. Baseline differences in levels of operant responding were also observed in WT vs CB1 KO mice maintained by Ensure and corn oil. This and other possible reasons for the observed discrepancy between pharmacological blockade vs genetic invalidation of the CB1 receptor on reinstatement of Ensure seeking are discussed.

Behavioral genetic contributions to the study of addiction-related amphetamine effects

Amphetamines, including methamphetamine, pose a significant cost to society due to significant numbers of amphetamine-abusing individuals who suffer major health-related consequences. In addition, methamphetamine use is associated with heightened rates of violent and property-related crimes. The current paper reviews the existing literature addressing genetic differences in mice that impact behavioral responses thought to be relevant to the abuse of amphetamine and amphetamine-like drugs. Summarized are studies that used inbred strains, selected lines, single-gene knockouts and transgenics, and quantitative trait locus (QTL) mapping populations. Acute sensitivity, neuroadaptive responses, rewarding and conditioned effects are among those reviewed. Some gene mapping work has been accomplished, and although no amphetamine-related complex trait genes have been definitively identified, translational work leading from results in the mouse to studies performed in humans is beginning to emerge. The majority of genetic investigations have utilized single-gene knockout mice and have concentrated on dopamine- and glutamate-related genes. Genes that code for cell support and signaling molecules are also well-represented. There is a large behavioral genetic literature on responsiveness to amphetamines, but a considerably smaller literature focused on genes that influence the development and acceleration of amphetamine use, withdrawal, relapse, and behavioral toxicity. Also missing are genetic investigations into the effects of amphetamines on social behaviors. This information might help to identify at-risk individuals and in the future to develop treatments that take advantage of individualized genetic information.

The cannabinoid CB1 receptor antagonist AM251 does not modify methamphetamine reinstatement of responding

Cannabinoid CB(1) receptor antagonists can decrease methamphetamine self-administration. This study examined whether the CB(1) receptor antagonist AM251 [N-(piperidin-1-yl)-5-(4-indophonyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide] modifies reinstatement in rats that previously self-administered methamphetamine. Rats (n=10) self-administered methamphetamine (0.1 mg/kg/infusion) under a fixed ratio 2 schedule. Non-contingent methamphetamine (0.01-1.78 mg/kg, i.v.) yielded responding for saline (reinstatement) that was similar to responding for self-administered methamphetamine. AM251 (0.032-0.32, i.v.) did not affect methamphetamine-induced reinstatement but significantly attenuated Delta(9)-tetrahydrocannabinol (2.0 mg/kg, i.p.)-induced hypothermia. These data fail to support a role for endogenous cannabinoids or cannabinoid CB(1) receptors in reinstatement and, therefore, relapse to stimulant abuse.

Enduring vulnerability to reinstatement of methamphetamine‐seeking behavior in glial cell line‐derived neurotrophic factor mutant mice

Genetic factors are considered to play an important role in drug dependence/addiction including the development of drug dependence and relapse. With the use of a model of drug self-administration in mutant mice, several specific genes and proteins have been identified as potentially important in the development of drug dependence. In contrast, little is known about the role of specific genes in enduring vulnerability to relapse, a clinical hallmark of drug addiction. Using a mouse model of reinstatement, which models relapse of drug-seeking behavior in addicts, we provide evidence that a partial reduction in the expression of the glial cell line-derived neurotrophic factor (GDNF) potentiates methamphetamine (METH) self-administration, enhances motivation to take METH, increases vulnerability to drug-primed reinstatement, and prolongs cue-induced reinstatement of extinguished METH-seeking behavior. In contrast, there was no significant difference in novelty responses, METH-stimulated hyperlocomotion and locomotor sensitization, food-reinforced operant behavior and motivation, or reinstatement of food-seeking behavior between GDNF heterozygous knockout mice and wild-type littermates. These findings suggest that GDNF may be associated with enduring vulnerability to reinstatement of METH-seeking behavior and a potential target in the development of therapies to control relapse.

Reinforcing effects of morphine are reduced in tissue plasminogen activator-knockout mice

Tissue plasminogen activator (tPA) plays a key role in neuroplasticity. We have recently demonstrated that the tPA-plasmin system is involved in the rewarding effects of drugs of abuse by regulating the release of dopamine in the nucleus accumbens. In the present study, we investigated whether tPA is involved in the reinforcing properties of morphine in a paradigm of drug self-administration. Eight-week-old tPA knockout and wild-type control mice were subjected to a single 24-h session of morphine self-administration under a fixed ratio (FR) 2 or a progressive ratio (PR) schedule of reinforcement after eight daily 30-min sessions of nose-poke training. tPA knockout mice responded significantly more often for morphine self-administration in a dose-dependent manner as compared with wild-type control mice. Under the PR schedule of morphine reinforcement, however, tPA knockout mice showed a lower breaking point than wild-type control mice. There was no significant difference in food-reinforced operant behavior, breaking points to food pellets, and saline self-administration between the two genotypes. The increased responding in tPA knockout mice under the FR2 schedule was significantly attenuated by the dopamine D1 receptor antagonist SCH23390 (0.3 mg/kg), whereas SCH23390, at a dose range of 0.03-2.0 mg/kg, demonstrated biphasic effects on morphine self-administration in wild-type control mice. Our findings suggest that the reinforcing effects of morphine are reduced in tPA knockout mice. Modulation of the tPA system in the brain may be a potential target against drugs of abuse.

Transient drug-primed but persistent cue-induced reinstatement of extinguished methamphetamine-seeking behavior in mice

It is essential to develop animal models to study the role of genetic factors in the relapse of drug-seeking behavior in genetically engineered mutant mice. This paper reports a typical model of drug-primed and cue-induced reinstatement of extinguished methamphetamine (METH)-seeking behavior in mice. C57BL/6J mice were trained to self-administer METH (0.1mg/kg/infusion) by poking their nose into an active hole under a fixed ratio schedule in daily 3-h sessions. After acquiring stable METH self-administration behavior, the mice were subjected to extinction training in the absence of both METH and METH-associated cues. Once the active nose-poking responses were extinguished, drug-primed and cue-induced reinstatement were investigated according to a within-subjects design. A priming injection of METH reliably reinstated the extinguished drug-seeking behavior in the absence of both METH and METH-associated cues. Interestingly, the drug-primed METH-seeking behavior disappeared within 2 months after withdrawal from METH, while cue-induced reinstatement of extinguished METH-seeking behavior lasted for at least 5 months after the withdrawal. A correlation study revealed that drug-primed, but not cue-induced, reinstatement behavior was positively correlated with the total amount of METH taken by individuals during METH self-administration. In conclusion, our findings suggest that the present reinstatement procedure for mouse model of relapse is useful and reliable, and different neural mechanisms may be involved in drug-primed and cue-induced METH-seeking behavior.

Intravenous Drug Self-administration in Mice: Practical Considerations

Chronic intravenous drug self-administration in rodents is a useful procedure for predicting the abuse liability of novel drugs in humans, for evaluating candidate treatments for drug abuse and dependence, and for studying the biological basis of addiction. Despite the technical challenge in achieving chronic self-administration behavior in the mouse species, researchers are increasingly using genetically engineered mice to investigate the role of specific genes in abuse-related effects of drugs. This review focuses on recent technical innovations as well as theoretical considerations for comparing intravenous (i.v.) drug self-administration behavior between mouse strains, including mice with targeted mutations. Part I of the present article describes techniques for successfully conducting self-administration studies in mice, including advantages, disadvantages and possible implications of employing various experimental approaches. Part II provides a review of recent data that address how the genetic background on which mutations are expressed may influence results from gene-targeting studies.