Role of GABAA receptors in dorsal raphe nucleus in stress-induced reinstatement of morphine-conditioned place preference in rats

Rationale

The serotonin (5-hydroxytryptamine, 5-HT) system plays an important role in stress-related psychiatric disorders and substance abuse. Our data indicate that stress inhibits the dorsal raphe nucleus (DRN)-5-HT system via stimulation of GABA synaptic activity by the stress neurohormone corticotropin-releasing factor and, more recently, that morphine history sensitizes DRN-5-HT neurons to GABAergic inhibitory effects of stress.

Objectives

We tested the hypothesis that DRN GABA_A receptors contribute to stress-induced reinstatement of morphine-conditioned place preference (CPP).

Methods

First, we tested if activation of GABA_A receptors in the DRN would reinstate morphine CPP. Second, we tested if blockade of GABA_A receptors in the DRN would attenuate swim stress-induced reinstatement of morphine CPP. CPP was induced by morphine (5 mg/kg) in a 4-day conditioning phase followed by a conditioning test. Upon acquiring conditioning criteria, subjects underwent 4 days of extinction training followed by an extinction test. Upon acquiring extinction criteria, animals underwent a reinstatement test. For the first experiment, the GABA_A receptor agonist muscimol (50 ng) or vehicle was injected into the DRN prior to the reinstatement test. For the second experiment, the GABA_A receptor antagonist bicuculline (75 ng) or vehicle was injected into the DRN prior to a forced swim stress, and then, animals were tested for reinstatement of CPP.

Results

Intraraphe injection of muscimol reinstated morphine CPP, while intraraphe injection of bicuculline attenuated swim stress-induced reinstatement.

Conclusions

These data provide evidence that GABA_A receptor-mediated inhibition of the serotonergic DRN contributes to stress-induced reinstatement of morphine CPP.     

Effects of the kappa opioid receptor antagonist, norbinaltorphimine, on stress and drug-induced reinstatement of nicotine-conditioned place preference in mice

Rationale

Several studies implicate stress as a risk factor for the development and maintenance of drug addictive behaviors and drug relapse. Kappa opioid receptor (KOR) antagonists have been shown to attenuate behavioral responses to stress and stress-induced reinstatement of cocaine and ethanol seeking and preference.

Objectives

In the current study, we determined whether the selective KOR antagonist, norbinaltorphimine (nor-BNI), would block stress-induced reinstatement of nicotine preference.

Methods

Adult Institute of Cancer Research mice were conditioned with 0.5 mg/kg nicotine, injected subcutaneously (s.c.) for 3 days and tested in the nicotine-conditioned place preference (CPP) model. After 3 days extinction, nor-BNI (10 mg/kg, s.c.) was administered 16 h prior to a priming dose of nicotine (0.1 mg/kg, s.c.), and mice were tested in the CPP model for nicotine-induced reinstatement of CPP. A separate group of mice was subjected to a 2-day modified forced swim test (FST) paradigm to induce stress after 3 days extinction from CPP. Mice were given vehicle or nor-BNI (10 mg/kg, s.c.) 16 h prior to each FST session.

Results

Nor-BNI pretreatment significantly attenuated stress-induced reinstatement of nicotine-CPP, but had no effect on nicotine-primed reinstatement.

Conclusions

Blockade of KORs by selective antagonists attenuates stress-induced reinstatement of nicotine-CPP. Overall, the kappa opioid system may serve as a therapeutic target for suppressing multiple signaling processes which contribute to maintenance of smoking, smoking relapse, and drug abuse in general.     

Chronic psychosocial stress causes delayed extinction and exacerbates reinstatement of ethanol-induced conditioned place preference in mice

Rationale

We have shown previously, using an animal model of voluntary ethanol intake and ethanol-conditioned place preference (EtOH-CPP), that exposure to chronic psychosocial stress induces increased ethanol intake and EtOH-CPP acquisition in mice.

Objective

Here, we examined the impact of chronic subordinate colony (CSC) exposure on EtOH-CPP extinction, as well as ethanol-induced reinstatement of CPP.

Methods

Mice were conditioned with saline or 1.5 g/kg ethanol and were tested in the EtOH-CPP model. In the first experiment, the mice were subjected to 19 days of chronic stress, and EtOH-CPP extinction was assessed during seven daily trials without ethanol injection. In the second experiment and after the EtOH-CPP test, the mice were subjected to 7 days of extinction trials before the 19 days of chronic stress. Drug-induced EtOH-CPP reinstatement was induced by a priming injection of 0.5 g/kg ethanol.

Results

Compared to the single-housed colony mice, CSC mice exhibited increased anxiety-like behavior in the elevated plus maze (EPM) and the open field tests. Interestingly, the CSC mice showed delayed EtOH-CPP extinction. More importantly, CSC mice showed increased alcohol-induced reinstatement of the EtOH-CPP behavior.

Conclusion

Taken together, this study indicates that chronic psychosocial stress can have long-term effects on EtOH-CPP extinction as well as drug-induced reinstatement behavior and may provide a suitable model to study the latent effects of chronic psychosocial stress on extinction and relapse to drug abuse.     

Assessment of the impact of pattern of cocaine dosing schedule during conditioning and reconditioning on magnitude of cocaine CPP, extinction, and reinstatement

Rationale and objective

We sought to examine the impact of differing cocaine administration schedules and dosing on the magnitude of cocaine conditioned place preference (CPP), extinction, and stress- and cocaine-induced reinstatement of CPP.

Methods

First, in C57Bl/6J mice, we investigated whether total cocaine administration or pattern of drug exposure could influence the magnitude of cocaine CPP by conditioning mice with a fixed-low dose (F_L; 7.5 mg/kg; total of 30 mg/kg), a fixed-high dose (F_H; 16 mg/kg; total of 64 mg/kg), or an ascending dosing schedule (Asc; 2, 4, 8, and 16 mg/kg; total of 30 mg/kg). Next, we investigated if cocaine or saline is more effective at extinguishing preference by reconditioning mice with either a descending dosing schedule (Desc; 8, 4, 2, and 1 mg/kg) or saline. Finally, we examined if prior conditioning and reconditioning history alters stress (~2–3-min forced swim test) or cocaine-induced (3.5 mg/kg) reinstatement.

Results

We replicated and extended findings by Itzhak and Anderson (Addict. Biol. 17(4): 706–16, 2011) demonstrating that Asc conditioning produces a greater CPP than either the F_L or F_H conditioning schedules. The magnitude of extinction expressed was similar in the Desc reconditioned and saline groups. Moreover, only the saline, and not the Desc reconditioned mice, showed stress and cocaine-induced reinstatement of CPP.

Conclusions

Our results suggest that the schedule of cocaine administration during conditioning and reconditioning can have a significant influence on the magnitude of CPP and extinction of preference and the ability of cocaine or a stressor to reinstate CPP.     

Beta-2 adrenergic receptors mediate stress-evoked reinstatement of cocaine-induced conditioned place preference and increases in CRF mRNA in the bed nucleus of the stria terminalis in mice

Rationale

Understanding the mechanisms responsible for stress-induced relapse is important for guiding treatment strategies aimed at minimizing the contribution of stress to addiction. Evidence suggests that these mechanisms involve interactions between noradrenergic systems and the neuropeptide corticotropin-releasing factor (CRF).

Objectives

The interaction between β-adrenergic receptors (ARs) and CRF as it relates to the reinstatement of cocaine-conditioned reward in response to a stressor was examined in mice. We hypothesized that β₂-ARs are required for stress-induced activation of CRF pathways responsible for reinstatement.

Methods

Stress-induced relapse was examined based on the re-establishment of cocaine-induced conditioned place preference (CPP; 4?×?15 mg/kg cocaine, i.p.) after extinction using forced swim (6 min at 22 °C) or an injection of the β₂-AR agonist, clenbuterol (4 mg/kg, i.p.). The CRF-R1 antagonist antalarmin (10 mg/kg, i.p.) or the β₂-AR antagonist ICI-118,551 (1 mg/kg, i.p.) were given 30 min prior to reinstating stimuli. Quantitative PCR was conducted in dissected bed nucleus of the stria terminalis (BNST) and amygdala, putative sources of CRF that contribute to reinstatement, to examine the effects of ICI-118,551 on swim-induced increases in CRF messenger RNA (mRNA) in mice with a cocaine history.

Results

Pretreatment with ICI-118,551 or antalarmin blocked swim-induced reinstatement of CPP. Reinstatement by clenbuterol was also blocked by antalarmin. ICI-118,551 pretreatment prevented swim-induced increases in CRF mRNA in the BNST. Effects in the amygdala were not observed.

Conclusions

These findings indicate that, during stress, norepinephrine, via β₂-ARs, either directly or indirectly activates CRF-releasing neurons in the BNST that interface with motivational neurocircuitry to induce reinstatement of cocaine-conditioned reward.     

Involvement of insular muscarinic cholinergic receptors in morphine-induced conditioned place preference in rats

Rationale

Drug addiction represents a pathological usurpation of neural processes involved in learning and memory. Retrieval of drug-related memories can result in drug craving and relapse. Recently, the insula was identified as part of the neuronal circuit responsible for the processing of drug memory; however, its precise role remains unclear.

Objective

To investigate the involvement of insular muscarinic acetylcholine receptors (mAChRs) in the processing of drug memory.

Method

The morphine-induced conditioned place preference (CPP) was used to assess drug memory. All rats were first trained with morphine to establish the CPP. Sub-groups of these rats were used for contextual cue-induced CPP reinstatement. Other sub-groups of rats underwent extinction of the CPP, and 5 m/kg morphine was used for priming-induced CPP reinstatement. Microinjection of mAChR antagonists or agonists into the insula was performed prior to the CPP tests in order to evaluate their effect on CPP expression.

Results

Insular microinjections of the nonselective mAChR antagonist, scopolamine, and the M₁ antagonist, pirenzepine, significantly inhibited CPP expression in both contextual cue- and priming-induced CPP reinstatement; the M₁ agonist, MCN-A-343, and the M₄ antagonist, tropicamide, enhanced CPP expression. The M₄ agonist, LY2033298, inhibited CPP expression. The M₂ antagonist, methoctramine, and M₃ antagonist, 4-DAMP, had no effect on CPP expression.

Conclusion

Our results demonstrate that insular mAChRs play a role in the processing of drug memory. M₁ and M₄ mAChRs work paradoxically; M₁ activation and M₄ inhibition attenuate the expression of drug memory, while M₁ inhibition and M₄ activation augment the expression of drug memory.     

Reinstatement of cocaine seeking induced by drugs, cues, and stress in adolescent and adult rats

Rationale

In human and animal studies, adolescence marks a period of increased vulnerability to the initiation and subsequent abuse of drugs. Adolescents may be especially vulnerable to relapse, and a critical aspect of drug abuse is that it is a chronically relapsing disorder. However, little is known of how vulnerability factors such as adolescence are related to conditions that induce relapse, triggered by the drug itself, drug-associated cues, or stress.

Objective

The purpose of this study was to compare adolescent and adult rats on drug-, cue-, and stress-induced reinstatement of cocaine-seeking behavior.

Methods

On postnatal days 23 (adolescents) and 90 (adults), rats were implanted with intravenous catheters and trained to lever press for i.v. infusions of cocaine (0.4 mg/kg) during two daily 2-h sessions. The rats then self-administered i.v. cocaine for ten additional sessions. Subsequently, visual and auditory stimuli that signaled drug delivery were unplugged, and rats were allowed to extinguish lever pressing for 20 sessions. Rats were then tested on cocaine-, cue-, and yohimbine (stress)-induced cocaine seeking using a within-subject multicomponent reinstatement procedure.

Results

Results indicated that adolescents had heightened cocaine seeking during maintenance and extinction compared to adults. During reinstatement, adolescents (vs adults) responded more following cocaine- and yohimbine injections, while adults (vs adolescents) showed greater responding following presentations of drug-associated cues.

Conclusion

These results demonstrated that adolescents and adults differed across several measures of drug-seeking behavior, and adolescents may be especially vulnerable to relapse precipitated by drugs and stress.     

Rhodiola rosea L. extract and its active compound salidroside antagonized both induction and reinstatement of nicotine place preference in mice

Rationale

Conventional pharmacological treatments for drug addiction aim to reduce three most important aspects: withdrawal syndrome, craving, and relapse. Pharmacological treatments currently available for the treatment of tobacco smoking are able to alleviate withdrawal symptoms but are not sufficiently effective in reducing craving and rarely effective to prevent relapse. Rhodiola rosea L., a well-known traditional oriental medicine with anxiolytic, antidepressive, antistress, and adaptogenic properties, has been recently shown to be effective in the prevention and treatment of nicotine-withdrawal symptoms.

Objectives

The present study used the conditioned place preference (CPP) model to systematically investigate, in mice, the effects of a R. rosea L. extract (RHO) and its active compound salidroside (SDS), on the reinforcing properties of nicotine and their efficacy in the vulnerability to reinstatement.

Methods

To study the effects on the rewarding properties of nicotine, RHO (10, 15, and 20 mg/kg) and SDS (0.2 mg/kg) were tested both in the acquisition and expression of CPP induced by nicotine injection (0.5 mg/kg). Moreover, the efficacy of RHO and SDS in preventing relapse induced by nicotine priming (0.1 mg/kg, s.c.) and by restraint stress was also evaluated.

Results

Results showed the ability of RHO and salidroside to significantly reduce the rewarding properties of nicotine at all doses tested. RHO and SDS also suppressed both priming- and stress-induced reinstatement of CPP.

Conclusions

The present study showed the positive effects of R. rosea L. in reducing rewarding properties and preventing relapse to nicotine and evidenced the important role of salidroside in the effects of the extract.     

The acute effects of glucose ingestion on attentional control in fasting healthy older adults

Rationale

Modafinil (Provigil®) is a wake-promoting drug characterized by cognitive enhancing abilities. Recent clinical data have supported the use of modafinil for treatment of chronic psychostimulant addiction and relapse prevention.

Materials and methods

We used an intravenous methamphetamine (meth) self-administration procedure to assess the dose-dependent effects of modafinil on reinstatement following abstinence and after extinction on conditioned-cue and meth-primed reinstatement of meth seeking.

Results

Modafinil attenuated active lever responding in multiple reinstatement conditions—context-induced, conditioned cue, and meth prime. The most pronounced and consistent effect was on meth-primed reinstatement, and modafinil did not reinstate meth seeking when tested alone.

Discussion

These findings support clinical findings in humans that modafinil may be an effective therapeutic agent for the prevention of relapse in abstinent meth users.     

The facilitative effects of d-cycloserine on extinction of a cocaine-induced conditioned place preference can be long lasting and resistant to reinstatement

Rationale and objective

The N-methyl-d-aspartate receptor agonist, d-cycloserine (DCS), accelerates extinction of a cocaine-induced conditioned place preference (CPP) when given after daily extinction tests. Here, we studied the effects of DCS in rats given spaced-extinction sessions at 3- or 7-day intervals using two different extinction procedures.

Materials and methods

Rats were trained on a CPP (four cocaine, 10 mg/kg, i.p., and four saline pairings with one of two compartments). Immediately following the CPP test and all extinction tests (days 4, 7, 10, and 24, experiment 1), DCS (15 mg/kg, i.p.) or saline was administered. In experiment 2, extinction was conducted by exposing rats to the drug-paired cues for 2 or 20 min, three times, at 7-day intervals followed immediately by DCS or saline. After extinction, tests for retention and cocaine-induced reinstatement were given.

Results

In experiment 1, rats given DCS lost the cocaine CPP after one extinction trial, an effect that persisted for 2 weeks after the last DCS injection and that was resistant to cocaine-induced reinstatement. In experiment 2, extinction was facilitated by DCS compared to saline when rats received 2-min exposures to the conditioned stimulus. Longer 20-min exposures minus/plus repeated testing led to retention of extinction in both groups regardless of DCS treatment.

Conclusions

Extinction of appetitive conditioning is facilitated by DCS after 1–3 post-spaced trial injections, and retention is lasting and resistant to reinstatement. The facilitative effects appear early in extinction, but when extinction procedures are intensive, DCS appears to have no additional benefit.     

Cannabis intoxication inhibits avoidance action tendencies: a field study in the Amsterdam coffee shops

Rationale

Astrocytes play an integral role in modulating synaptic transmission and plasticity, both key mechanisms underlying addiction. However, while astrocytes are capable of releasing chemical transmitters that can modulate neuronal function, the role of these gliotransmitters in mediating behaviors associated with drugs of abuse has been largely unexplored.

Objectives

The objective of the present study was to utilize mice with astrocytes that lack the ability to release chemical transmitters to evaluate the behavioral consequence of impaired gliotransmission on cocaine-related behaviors. These mice have previously been used to examine the role of gliotransmission in sleep homeostasis; however, no studies to date have utilized them in the study of addictive behaviors.

Methods

Mice expressing a dominant-negative SNARE protein selectively in astrocytes (dnSNARE mice) were tested in a variety of behavioral paradigms examining cocaine-induced behavioral plasticity. These paradigms include locomotor sensitization, conditioned place preference followed by cocaine-induced reinstatement of CPP, and cocaine self-administration followed by cue-induced reinstatement of cocaine-seeking behavior.

Results

Wild-type and dnSNARE mice demonstrated no significant differences in the development or maintenance of locomotor sensitization. While there were non-significant trends for reduced CPP following a low dose of cocaine, drug-induced reinstatement of CPP is completely blocked in dnSNARE mice. Similarly, while dnSNARE mice demonstrated a non-significant trend toward reduced cocaine self-administration compared with wild-type mice, dnSNARE mice do not demonstrate cue-induced reinstatement in this paradigm.

Conclusions

Gliotransmission is necessary for reinstatement of drug-seeking behaviors by cocaine or associated cues.     

Persistent reduction of cocaine seeking by pharmacological manipulation of adenosine A1 and A2A receptors during extinction training in rats

Rationale

Adenosine receptor stimulation and blockade have been shown to modulate a variety of cocaine-related behaviors.

Objectives

These studies identify the direct effects of adenosine receptor stimulation on cocaine seeking during extinction training and the persistent effects on subsequent reinstatement to cocaine seeking.

Methods

Rats self-administered cocaine on a fixed ratio one schedule in daily sessions over 3 weeks. Following a 1-week withdrawal, the direct effects of adenosine receptor modulation were tested by administering the adenosine A₁ receptor agonist, N⁶-cyclopentyladenosine (CPA, 0.03 and 0.1 mg/kg), the adenosine A_2A agonist, CGS 21680 (0.03 and 0.1 mg/kg), the presynaptic adenosine A_2A receptor antagonist, SCH 442416 (0.3, 1, and 3 mg/kg), or vehicle prior to each of six daily extinction sessions. The persistent effects of adenosine receptor modulation during extinction training were subsequently tested on reinstatement to cocaine seeking induced by cues, cocaine, and the dopamine D₂ receptor agonist, quinpirole.

Results

All doses of CPA and CGS 21680 impaired initial extinction responding; however, only CPA treatment during extinction produced persistent impairment in subsequent cocaine- and quinpirole-induced seeking. Dissociating CPA treatment from extinction did not alter extinction responding or subsequent reinstatement. Administration of SCH 442416 had no direct effects on extinction responding but produced dose-dependent persistent impairment of cocaine- and quinpirole-induced seeking.

Conclusions

These findings demonstrate that adenosine A₁ or A_2A receptor stimulation directly impair extinction responding. Interestingly, adenosine A₁ receptor stimulation or presynaptic adenosine A_2A receptor blockade during extinction produces lasting changes in relapse susceptibility.     

The effects of varied extinction procedures on contingent cue-induced reinstatement in Sprague-Dawley rats

Rationale

Cue exposure therapy, which attempts to limit relapse by reducing reactivity to cocaine-paired cues through repeated exposures, has had limited success.

Objectives

The current experiments examined cocaine cue-induced anxiogenesis and investigated whether a model of cue exposure therapy would reduce reinstatement of cocaine seeking in rats with a history of cocaine self-administration.

Methods

Male rats experienced daily intravenous cocaine self-administration. Rats then experienced exposure to either the self-administration context or the context plus noncontingent presentations of cocaine-paired cues. Immediately following exposure, anxiety-like behavior was measured using elevated plus maze and defensive burying tests. In a second group of rats, self-administration was followed by 7 days of exposure to the context, context + noncontingent cue exposure, lever extinction, or cue + lever extinction. All animals then underwent two contingent cue-induced reinstatement tests separated by 7 days of lever extinction.

Results

Exposure to noncontingent cocaine-paired cues in the self-administration context increased anxiety-like behavior on the defensive burying test. Animals that experienced lever + cue extinction displayed the least cocaine seeking on the first reinstatement test, and lever extinction reduced cocaine seeking below context exposure or context + noncontingent cue exposure. All animals had similar levels of cocaine seeking on the second reinstatement test.

Conclusion

Noncontingent cue exposure causes anxiety, and noncontingent cue and context exposure are less effective at reducing contingent cue-induced reinstatement than lever or lever + cue extinction. These data indicate that active extinction of the drug-taking response may be critical for reduction of relapse proclivity in former cocaine users.     

Cues predicting drug or food reward restore morphine-induced place conditioning in mice lacking delta opioid receptors

Rationale

The exact role of delta opioid receptors in drug-induced conditioned place preference (CPP) remains debated. Under classical experimental conditions, morphine-induced CPP is decreased in mice lacking delta opioid receptors (Oprd1 ^?/?). Morphine self-administration, however, is maintained, suggesting that drug-context association rather than drug reward is deficient in these animals.

Objectives

This study further examined the role of delta opioid receptors in mediating drug-cue associations, which are necessary for the expression of morphine-induced CPP.

Methods

We first identified experimental conditions under which Oprd1 ^?/? mice are able to express CPP to morphine (5, 10 or 20 mg/kg) in a drug-free state and observed that, in this paradigm, CPP was dependent on circadian time conditions. We then took advantage of this particularity to assess the ability of various cues (internal or discrete), predicting either drug or food reward, to restore CPP induced by morphine (10 mg/kg) in Oprd1 ^?/? mice in conditions under which they normally fail to express CPP.

Results

We found that presentation of circadian, drug or auditory cues, predicting morphine or food reward, restored morphine CPP in Oprd1 ^?/? mice, which then performed as well as control mice.

Conclusions

This study reveals that, in contrast to spatial cues, internal or discrete morphine-predicting stimuli permit full expression of morphine CPP in Oprd1 ^?/? mice. Delta receptors, therefore, appear to play a crucial role in modulating spatial contextual cue-related responses. This activity may be critical when context gains control over behavior, as is the case for context-induced relapse in drug abuse.     

The reinstatement model of drug relapse: recent neurobiological findings, emerging research topics, and translational research

Background and rationale

Results from many clinical studies suggest that drug relapse and craving are often provoked by acute exposure to the self-administered drug or related drugs, drug-associated cues or contexts, or certain stressors. During the last two decades, this clinical scenario has been studied in laboratory animals by using the reinstatement model. In this model, reinstatement of drug seeking by drug priming, drug cues or contexts, or certain stressors is assessed following drug self-administration training and subsequent extinction of the drug-reinforced responding.

Objective

In this review, we first summarize recent (2009–present) neurobiological findings from studies using the reinstatement model. We then discuss emerging research topics, including the impact of interfering with putative reconsolidation processes on cue- and context-induced reinstatement of drug seeking, and similarities and differences in mechanisms of reinstatement across drug classes. We conclude by discussing results from recent human studies that were inspired by results from rat studies using the reinstatement model.

Conclusions

Main conclusions from the studies reviewed highlight: (1) the ventral subiculum and lateral hypothalamus as emerging brain areas important for reinstatement of drug seeking, (2) the existence of differences in brain mechanisms controlling reinstatement of drug seeking across drug classes, (3) the utility of the reinstatement model for assessing the effect of reconsolidation-related manipulations on cue-induced drug seeking, and (4) the encouraging pharmacological concordance between results from rat studies using the reinstatement model and human laboratory studies on cue- and stress-induced drug craving.     

Effects of the beta-lactam antibiotic ceftriaxone on nicotine withdrawal and nicotine-induced reinstatement of preference in mice

Rationale

Several studies suggest that repeated nicotine administration causes alterations in glutaminergic transmission that may play an important role in developing and maintaining nicotine addiction. Chronic nicotine administration in rats decreases the expression of the glutamate transporter-1 (GLT-1) and cysteine–glutamate exchanger (system x_C?) in the nucleus accumbens. We hypothesized that ceftriaxone, a GLT-1 and system x_C? activator, would decrease murine behavioral aspects of nicotine dependence.

Objective

This study aimed to investigate the effect of repeated ceftriaxone administration on the behavioral effects of nicotine using mouse models of conditioned reward and withdrawal.

Method

Using male ICR mice, the ability of repeated ceftriaxone injections to modulate the development and reinstatement of a nicotine-conditioned place preference (CPP) was evaluated. Additionally, nicotine withdrawal-associated signs were assessed. These included both physical (somatic signs and hyperalgesia) and affective (anxiety-related behaviors) withdrawal signs in mice. Finally, the effects of ceftriaxone on nicotine-induced antinociception and hypothermia after acute nicotine injection were measured.

Result

Ceftriaxone had no effect on the development of nicotine preference but significantly attenuated nicotine-induced reinstatement of CPP. Furthermore, ceftriaxone reversed all nicotine withdrawal signs measured in mice.

Conclusion

Altogether, these findings show that a β-lactam antibiotic reduces nicotine withdrawal and nicotine-seeking behavior. Our results suggest that the documented efficacy of ceftriaxone against cocaine and morphine dependence-related behaviors effects extends to nicotine.     

Effects of inhibitory GABA-active neurosteroids on cocaine seeking and cocaine taking in rats

Rationale

Several compounds that potentiate GABA-induced inhibitory currents also decrease stress, anxiety and addiction-related behaviors. Because of the well-established connection between stress and addiction, compounds that reduce stress-induced responses might be efficacious in treating addiction. Since endogenous neurosteroids such as allopregnanolone may function in a manner similar to benzodiazepines to reduce HPA axis activation and anxiety following stressful stimuli, we hypothesized that exogenously applied neurosteroids would reduce cocaine reinforcement in two animal models.

Methods

Male Wistar rats were trained to self-administer cocaine and food under a concurrent alternating operant schedule of reinforcement. Two separate groups of rats were trained to self-administer cocaine or food pellets and were then exposed to similar cue-induced reinstatement paradigms. Both groups of rats were pretreated with various doses of neurosteroids.

Results

Allopregnanolone and 3α-hydroxy-3β-methyl-17β-nitro-5α-androstane (R6305-7, a synthetic neurosteroid) were ineffective in selectively decreasing cocaine relative to food self-administration. On the other hand, both allopregnanolone and R6305-7 significantly decreased the cue-induced reinstatement of extinguished cocaine seeking, confirmed by one-way ANOVA.

Conclusions

These results suggest that neurosteroids may be effective in reducing the relapse to cocaine use without affecting ongoing cocaine self-administration.     

Effects of prenatal immune activation and peri-adolescent stress on amphetamine-induced conditioned place preference in the rat

Rationale

Addiction is a disease of learning and memory, as learning processes underlying acquisition, extinction, and reinstatement of drug-paired associations play central roles in addiction. Early developmental stress enhances risk for drug problems in adulthood. Environmental factors influencing learning and memory processes relevant to addiction remain incompletely characterized.

Objectives

To determine effects of prenatal immune activation and developmental stress on conditioned place preference to amphetamine, and reversal learning.

Methods

Pregnant Sprague-Dawley rats were injected with polyinosinic:polycytidylic acid (poly I:C) or vehicle on gestational day 14. Half of the male offspring received 2?h of restraint stress at post-natal day 35. Behavioral testing was performed in adulthood.

Results

Restraint stress inhibited acquisition of place preference to low-dose amphetamine (0.5?mg/kg), while poly I:C treatment had no measurable effect on place preference acquisition. In contrast, drug-induced reinstatement of preference for drug-paired chamber was enhanced in offspring of poly I:C-treated dams [F(1,25)?=?5.31, p?=?0.03]. Performance on a Morris water maze reversal learning task was impaired in poly I:C offspring. Reversal learning performance was correlated with place preference reinstatement in non-stressed (r ²?=?0.42, p?=?0.0095), but not stressed rats (r ² =0.04, p?=?0.49).

Conclusions

Prenatal immune activation enhances drug-induced reinstatement of conditioned place preference. These data demonstrate longstanding impact on behaviors with potential influence on risk for drug relapse as a consequence of prenatal immune activation. Further study is needed to determine clinical and epidemiological consequences of similar exposures in human populations.     

The rapid hydrolysis of chlordiazepoxide to demoxepam may affect the outcome of chronic osmotic minipump studies

Background

In chronic studies, the classical benzodiazepine chlordiazepoxide (CDP) is often the preferred drug because, unlike other benzodiazepines, it is soluble in water. However, rapid CDP hydrolysis in solution has been described. This would diminish plasma levels in chronic minipump studies and introduce the corelease of active compounds.

Methods

Therefore, the present study aimed to explore the putative hydrolysis of CDP in aqueous solution over time and to identify the hydrolysis products. Moreover, we aimed to characterize the hydrolysis products for their in vitro (³H-flunitrazepam binding and oocyte electrophysiology) and in vivo (stress-induced hyperthermia paradigm) GABA_A receptor potency.

Results

CDP in solution hydrolyzed to the ketone structure demoxepam which was confirmed using mass spectrometry. The hydrolysis was concentration dependent (first-order kinetics) and temperature dependent. CDP exerted greater potency compared to demoxepam in vitro (increased activity at GABA_A receptors containing α₁ subunits) and in vivo (stress-induced hyperthermia), although ³H-flunitrazepam binding was comparable.

Conclusions

The classical benzodiazepine CDP is rapidly hydrolyzed in solution to the active compound demoxepam which possesses a reduced activity at the GABA_A receptor. Chronic studies that use CDP in aqueous solution should thus be interpreted with caution. It is therefore important to consider drug stability in chronic minipump applications.