Long-term opiate effects on amphetamine-induced dopamine release in the nucleus accumbens core and conditioned place preference

Medications Development for Treatment of Opioid Use Disorder

This review describes methods for preclinical evaluation of candidate medications to treat opioid use disorder (OUD). The review is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effectiveness, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and effects of candidate medications. Effects of opioid medications and vaccines on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications (e.g., G-protein-biased μ-opioid agonists), and (2) continued development of nonopioid medications (e.g., clonidine) that might serve as adjunctive agents to current opioid medications.

Effects of nucleus accumbens amphetamine administration on performance in a delay discounting task

Chronic administration of cocaine can cause pronounced and enduring cognitive alterations such as increases in impulsive choice. Chronic cocaine can also result in enhanced dopamine (DA) release in the nucleus accumbens (NAc) in response to reward-related cues. It is possible that this enhanced DA release in the NAc is a mechanism by which cocaine increases impulsive choice. To date, however, the specific role of DA in the NAc in impulsive choice is unclear. To begin to address this, rats received acute microinjections of the indirect DA agonist amphetamine directly into the NAc prior to testing in a delay discounting task in which rats chose between a small, immediate and a large, delayed food reward. When delays to the large reward increased within test sessions, amphetamine increased choice of the large reward. When delays decreased within test sessions, however, amphetamine decreased choice of the large reward. These findings suggest that, rather than specifically mediating impulsive choice, DA neurotransmission in the NAc is necessary for flexible adaptation of choice strategies in the presence of shifting reward contingencies. These results further indicate that enhancements in NAc DA release likely do not account for lasting increases in impulsive choice caused by chronic cocaine.

Psychometric properties, validity, and reliability of the Temporal Experience of Pleasure Scale state version in an opioid-dependent sample

BACKGROUND

Individuals with substance dependence commonly experience anhedonia. Theories of anhedonia distinguish between anticipatory and consummatory reward deficits, with the Temporal Experience of Pleasure Scale (TEPS) the first self-report scale to separately measure these two constructs. Several psychometric studies have analysed the trait version of the TEPS, but the state version of the TEPS has not been previously validated.

METHODS

We examined the psychometric properties of the state version of the TEPS in 121 individuals with opiate dependence (81% Australian-born), to confirm its 2-factor structure and examine the internal consistency, convergent and divergent validity, test-retest reliability, and performance as a state measure.

RESULTS

Confirmation of the 2-factor solution required removal of two items and allowing correlation between residuals of three pairs of highly-similar items. The resulting consummatory and anticipatory scales correlated strongly with each other (r=.76), suggesting poor divergent validity between them. Nevertheless, the scale showed good internal consistency (Chronbach's α: anticipatory=.90; consummatory=.84; total=.92), convergent (TEPS total and Snaith-Hamilton Pleasure Scale r=-.76) and divergent validity (-.38<r<-.10 for measures of negative affect, anxiety, and alexithymia) with other psychological measures, and test-retest reliability. Changes in TEPS scores between baseline and 1-month follow-up correlated well with changes in scores on other state anhedonia and positive affect measures, suggesting that the TEPS state version functions well as a state measure.

CONCLUSION

In opioid-dependent participants, the TEPS state version appeared to have good validity as a measure of state anhedonia. However, evidence for its ability to distinguish between consummatory and anticipatory anhedonia was weak.

The role of the aversive effects of drugs in self-administration: assessing the balance of reward and aversion in drug-taking behavior

Since the first experimental demonstration that a drug of abuse supports instrumental behavior, drugs have been discussed in the context of their rewarding effects, which are assumed to drive and maintain drug-taking behavior. Indeed, drug reward has been fundamental in the formulation of most models of drug use, abuse, and addiction. Over the last several decades, however, drugs of abuse have been increasingly recognized as complex pharmacological compounds producing multiple stimulus effects, not all of which are rewarding. The aversive effects of such drugs, for example, have been described by a number of researchers working in the field, although few attempts have been made to investigate the role of these aversive effects in drug taking. The present paper offers a historical perspective on the view that drugs of abuse are complex pharmacological compounds with multiple stimulus effects. In doing so, we argue that the discussion of drug reward only may be insufficient in accounting for drug taking and we present evidence for the theoretical position that both the rewarding and the aversive effects of drugs should be taken into consideration in ongoing attempts to model drug-taking behavior. The present review summarizes several decades of research characterizing the aversive effects of major drugs of abuse, as well as more recent studies seeking to assess directly the role of drug aversion in drug taking.

Medications development for opioid abuse

Here we describe methods for preclinical evaluation of candidate medications to treat opioid abuse and dependence. Our perspective is founded on the propositions that (1) drug self-administration procedures provide the most direct method for assessment of medication effects, (2) procedures that assess choice between opioid and nondrug reinforcers are especially useful, and (3) the states of opioid dependence and withdrawal profoundly influence both opioid reinforcement and the effects of candidate medications. Effects of opioid medications on opioid choice in nondependent and opioid-dependent subjects are reviewed. Various nonopioid medications have also been examined, but none yet have been identified that safely and reliably reduce opioid choice. Future research will focus on (1) strategies for increasing safety and/or effectiveness of opioid medications, and (2) continued development of nonopioids such as inhibitors of endocannabinoid catabolic enzymes or inhibitors of opioid-induced glial activation.

Neonatal quinpirole treatment enhances locomotor activation and dopamine release in the nucleus accumbens core in response to amphetamine treatment in adulthood

Neonatal quinpirole treatment to rats produces long-term increases in D(2) receptor sensitivity that persists throughout the animal's lifetime, a phenomenon referred to as D(2) priming. Male and female Sprague-dawley rats were administered quinpirole (1 mg kg(-1)) or saline from postnatal days (P)1-11. At P60, all animals were given an injection of quinpirole (100 microg kg(-1)), and results showed that rats neonatally treated with quinpirole demonstrated enhanced yawning in response to quinprole, verifying D(2) receptor priming because yawning is a D(2) receptor mediated event. Beginning 1-3 days later, locomotor sensitization was tested through administration of d-amphetamine (1 mg kg(-1)) or saline every other day over 14 days, and horizontal activity and turning behavior were analyzed. Findings indicated that D(2)-priming enhanced horizontal activity in response to amphetamine in females compared to males at Days 1 and 4 of locomotor sensitization testing, and D(2)-priming enhanced turning in response to amphetamine. Seven to ten days after sensitization was complete, microdialysis of the NAcc core was performed using a cumulative dosing regimen of amphetamine (0.1-3.0 mg kg(-1)). D(2)-primed rats administered amphetamine demonstrated a 500% increase in accumbal DA overflow compared to control rats administered amphetamine. Additionally, amphetamine produced a significant increase in NE overflow compared to controls, but this was unaffected by D(2) priming. These results indicate that D(2) receptor priming as is produced by neonatal quinpirole treatment robustly enhances behavioral activation and accumbal DA overflow in response to amphetamine, which may underlie increases in psychostimulant use and abuse within the psychotic population where increased D(2) receptor sensitivity is a hallmark.

Roles of hippocampal NMDA receptors and nucleus accumbens D1 receptors in the amphetamine-produced conditioned place preference in rats

There are glutamatergic projections from the hippocampus to the nucleus accumbens (NAc), which regulate DA transmission in this structure. To be precise, the ventral hippocampal (VH) glutamatergic neurons project to the nucleus accumbens shell region (NAcSh), whereas the dorsal hippocampus (DH) sends glutamatergic projections to the nucleus accumbens core region (NAcC). This study investigates the roles of hippocampal N-methyl-D-aspartate (NMDA) glutamate receptors and NAc type 1 dopamine receptor (D1) in amphetamine-produced conditioned place preference (AMPH-CPP) in rats. Our earlier reports showed that AMPH-CPP results in the enhancement of hippocampal CaMKII activity and it can be impaired by NMDA antagonist (AP5). In this study AMPH-CPP did not alter the NAc CaMKII activity, although AMPH-CPP was impaired by a blockade of D1 receptors (SCH23390) during conditioning. Moreover, inactivation of hippocampal area (dorsal hippocampus or ventral hippocampus) impaired AMPH-CPP, but its effect was diminished by the activation of D1 receptors in accumbal region (NAc core or NAc shell). By inactivating both DH and NAc core resulted in the disruption of rat's CPP expression. However, the impaired CPP expression was recovered during the next testing session, suggesting the disruption of CPP expression was a short term effect. Moreover, the disruption of CPP expression was not exhibited if NAc core was not inactivated. Interestingly, the rats that received activation in VH but an inactivation in NAc shell before testing show impaired CPP expression compared to those received inactivation in both VH and NAc shell. DH activation plus an inactivation in NAc core before testing show a significantly higher rate of the weakening of AMPH-CPP expression. Similarly, an activation of VH plus an inactivation of NAc shell before testing also show a statistically significant lower CPP score on tests 3 and 4. These results, taken together, indicate that NMDA receptor activation in DH and VH have different enhancing effects on the AMPH-CPP as their innervations onto the different NAc regions are essential for AMPH-CPP establishment. If the deterioration of AMPH-CPP expression (or extinction process) resembles the formation of new learning, then this active process might have been facilitated by the hippocampal NMDA receptor activations during testing.

Measuring reward with the conditioned place preference (CPP) paradigm: update of the last decade

Conditioned place preference (CPP) continues to be one of the most popular models to study the motivational effects of drugs and non-drug treatments in experimental animals. This is obvious from a steady year-to-year increase in the number of publications reporting the use this model. Since the compilation of the preceding review in 1998, more than 1000 new studies using place conditioning have been published, and the aim of the present review is to provide an overview of these recent publications. There are a number of trends and developments that are obvious in the literature of the last decade. First, as more and more knockout and transgenic animals become available, place conditioning is increasingly used to assess the motivational effects of drugs or non-drug rewards in genetically modified animals. Second, there is a still small but growing literature on the use of place conditioning to study the motivational aspects of pain, a field of pre-clinical research that has so far received little attention, because of the lack of appropriate animal models. Third, place conditioning continues to be widely used to study tolerance and sensitization to the rewarding effects of drugs induced by pre-treatment regimens. Fourth, extinction/reinstatement procedures in place conditioning are becoming increasingly popular. This interesting approach is thought to model certain aspects of relapse to addictive behavior and has previously almost exclusively been studied in drug self-administration paradigms. It has now also become established in the place conditioning literature and provides an additional and technically easy approach to this important phenomenon. The enormous number of studies to be covered in this review prevented in-depth discussion of many methodological, pharmacological or neurobiological aspects; to a large extent, the presentation of data had to be limited to a short and condensed summary of the most relevant findings.

Endogenous opiates and behavior: 2004

This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.

Activations of c-fos/c-jun signaling are involved in the modulation of hypothalamic superoxide dismutase (SOD) and neuropeptide Y (NPY) gene expression in amphetamine-mediated appetite suppression

Amphetamine (AMPH) is known as an anorectic agent. The mechanism underlying the anorectic action of AMPH has been attributed to its inhibitory action on hypothalamic neuropeptide Y (NPY), an appetite stimulant in the brain. This study was aimed to examine the molecular mechanisms behind the anorectic effect of AMPH. Results showed that AMPH treatment decreased food intake, which was correlated with changes of NPY mRNA level, but increased c-fos, c-jun and superoxide dismutase (SOD) mRNA levels in hypothalamus. To determine if c-fos or c-jun was involved in the anorectic response of AMPH, infusions of antisense oligonucleotide into the brain were performed at 1 h before daily AMPH treatment in freely moving rats, and the results showed that c-fos or c-jun knockdown could block this anorectic response and restore NPY mRNA level. Moreover, c-fos or c-jun knockdown could partially block SOD mRNA level that might involve in the modulation of NPY gene expression. It was suggested that c-fos/c-jun signaling might involve in the central regulation of AMPH-mediated feeding suppression via the modulation of NPY gene expression.

Selegiline modifies the extinction of responding following morphine self-administration, but does not alter cue-induced reinstatement, reacquisition of morphine reinforcement, or precipitated withdrawal

Selegiline is an irreversible inhibitor of monoamine oxidase (MAO) with psychostimulant and neuroprotective effects which can prevent decreases in dopamine efflux that follow opiate withdrawal. The present study evaluated effects of selegiline treatment on morphine-seeking behavior and morphine reinforcement in Wistar rats (n = 26). In additional animals (n = 30), the ability of single doses of selegiline to modify naloxone-precipitated withdrawal was determined. After pretreatment with noncontingent morphine to establish opiate dependence, rats acquired self-administration of intravenous morphine. Daily intravenous treatment with saline or 2.0mg kg(-1) doses of selegiline was then initiated and continued over 14 days during extinction, reinstatement, and reacquisition of morphine self-administration. To reduce the potential for psychostimulant effects, selegiline was administered approximately 1h following self-administration, extinction, or reinstatement sessions. In some animals (n = 23), effects of saline or selegiline administration on locomotor activity were determined following extinction sessions. Daily selegiline treatment decreased the number of ratios completed and increased response latency during extinction, without modifying these measures during reinstatement or reacquisition of morphine self-administration. Chronic selegiline treatment increased locomotor activity recorded between 4 and 7h after selegiline administration on day 7 of extinction, but otherwise did not alter locomotor activity. Pretreatment with single, 2.0mg kg(-1) doses of selegiline did not modify naloxone-precipitated withdrawal. In conclusion, pretreatment with selegiline produced only a small decrease in responding during extinction of morphine self-administration and did not modify cue-induced reinstatement of morphine-seeking behavior, reacquisition or morphine reinforcement, or precipitated withdrawal.

Effects of high-dose selegiline on morphine reinforcement and precipitated withdrawal in dependent rats

Selegiline is an irreversible inhibitor of monoamine oxidase (MAO) with psychostimulant and neuroprotective effects. Several lines of evidence suggest that treatment with selegiline at doses that exceed levels required for inhibition of MAO can produce distinct pharmacologic effects. The purpose of this study was to evaluate the effects of chronic treatment with high-dose selegiline on extinction responding, cue-induced reinstatement, morphine reinforcement and naloxone-precipitated withdrawal. After pretreatment with noncontingent morphine to establish opiate dependence, rats acquired self-administration of 3.2 mg/kg per injection of morphine under a progressive ratio schedule. Daily treatment with saline or 6.4 mg/kg per day of selegiline was then administered over extinction, reinstatement and re-acquisition of morphine self-administration. To enhance or diminish the potential for psychostimulant effects, selegiline was administered either immediately prior to (pre-session) or 1 h following (post-session) extinction, reinstatement and self-administration sessions. Pre-session selegiline decreased the number of ratios completed on days 2, 3 and 4 of extinction, and decreased morphine self-administration during all four re-acquisition sessions. When administered at the same dose level, post-session selegiline decreased responding on the fourth extinction session, and was ineffective in modifying re-acquisition of self-administration. Selegiline administered by either schedule did not modify cue-induced reinstatement. Daily treatment with 6.4 mg/kg per day of selegiline did not modify self-administration of food under a progressive ratio schedule. Acute treatment with single, 6.4 mg/kg doses of selegiline attenuated naloxone-induced increases in ptosis and global withdrawal score, but did not modify any other sign of withdrawal or global withdrawal score calculated without ratings of ptosis. In conclusion, high-dose selegiline can attenuate extinction responding and morphine-reinforced behavior, and these effects may be mediated by psychostimulant metabolites.

Chronic opiate treatment enhances both cocaine-reinforced and cocaine-seeking behaviors following opiate withdrawal

After chronic exposure to psychostimulants or opiates, self-administration or conditioned place preference with either class is increased (sensitized). Cross-sensitization of conditioned place preference, i.e., enhancement of psychostimulant-induced preferences after exposure to opiates, has also been described, but increases in cocaine self-administration after morphine pretreatment have not been reported. The present study evaluated effects of chronic morphine treatment on cocaine reinforcement. Opiate dependence was established in Wistar rats by administration of morphine as a constant infusion that was gradually increased to a dose of 50mg/kg per day over a 1-week period. Immediately after discontinuation of chronic morphine treatment, animals were allowed to acquire cocaine self-administration under a simple fixed-ratio schedule (FR-1), and were subsequently advanced to a progressive ratio schedule. Acquisition of cocaine self-administration under the FR-1 did not differ in saline- and morphine-pretreated animals. For cocaine self-administration under a progressive ratio schedule measured at 5 or more days after the onset of opiate withdrawal, chronic pretreatment with morphine increased the number of ratios completed, augmented final response requirements, and produced a more stable pattern of cocaine self-administration. Responding was also increased in morphine-pretreated animals during an initial extinction session. These results show that chronic opiate treatment can enhance both cocaine-reinforced and cocaine-seeking behaviors following opiate withdrawal. A similar effect may occur in human patients who discontinue methadone or other forms of replacement therapy for opiate abuse, and may contribute to relapse involving use of cocaine or other psychostimulants.