Characterization of the dopamine receptor system in adult rhesus monkeys exposed to cocaine throughout gestation

Mass Spectrometry-Based Proteome Profiling of Extracellular Vesicles Derived from the Cerebrospinal Fluid of Adult Rhesus Monkeys Exposed to Cocaine throughout Gestation

Cocaine use disorder has been reported to cause transgenerational effects. However, due to the lack of standardized biomarkers, the effects of cocaine use during pregnancy on postnatal development and long-term neurobiological and behavioral outcomes have not been investigated thoroughly. Therefore, in this study, we examined extracellular vesicles (EVs) in adult (~12 years old) female and male rhesus monkeys prenatally exposed to cocaine (n = 11) and controls (n = 9). EVs were isolated from the cerebrospinal fluid (CSF) and characterized for the surface expression of specific tetraspanins, concentration (particles/mL), size distribution, and cargo proteins by mass spectrometry (MS). Transmission electron microscopy following immunogold labeling for tetraspanins (CD63, CD9, and CD81) confirmed the successful isolation of EVs. Nanoparticle tracking analyses showed that the majority of the particles were <200 nm in size, suggesting an enrichment for small EVs (sEV). Interestingly, the prenatally cocaine-exposed group showed ~54% less EV concentration in CSF compared to the control group. For each group, MS analyses identified a number of proteins loaded in CSF-EVs, many of which are commonly listed in the ExoCarta database. Ingenuity pathway analysis (IPA) demonstrated the association of cargo EV proteins with canonical pathways, diseases and disorders, upstream regulators, and top enriched network. Lastly, significantly altered proteins between groups were similarly characterized by IPA, suggesting that prenatal cocaine exposure could be potentially associated with long-term neuroinflammation and risk for neurodegenerative diseases. Overall, these results indicate that CSF-EVs could potentially serve as biomarkers to assess the transgenerational adverse effects due to prenatal cocaine exposure.

Environmental influence on the preclinical evaluation of substance use disorder therapeutics

Substance use disorders (SUD) develop as a result of complex interactions between the environment, the subject, and the drug of abuse. Preclinical basic research investigating each of these tripartite components of SUD individually has resulted in advancements in our fundamental knowledge regarding the progression from drug abuse to SUD and severe drug addiction and the underlying behavioral and neurobiological mechanisms. How these complex interactions between the environment, the subject, and the drug of abuse impact the effectiveness of candidate or clinically used medications for SUD has not been as extensively investigated. The focus of this chapter will address the current state of our knowledge how these environmental, subject, and pharmacological variables have been shown to impact candidate or clinical SUD medication evaluation in preclinical research using drug self-administration procedures as the primary dependent measure. The results discussed in this chapter highlight the importance of considering environmental variables such as the schedule of reinforcement, concurrent availability of alternative nondrug reinforcers, and experimental housing conditions in the context of SUD therapeutic evaluation. The thesis of this chapter is that improved understanding of environmental variables in the context of SUD research will facilitate the utility of preclinical drug self-administration studies in the evaluation and development of candidate SUD therapeutics.

Utility of Nonhuman Primates in Substance Use Disorders Research

Substance use disorders (i.e., drug addiction) constitute a global and insidious public health issue. Preclinical biomedical research has been invaluable in elucidating the environmental, biological, and pharmacological determinants of drug abuse and in the process of developing innovative pharmacological and behavioral treatment strategies. For more than 70 years, nonhuman primates have been utilized as research subjects in biomedical research related to drug addiction. There are already several excellent published reviews highlighting species differences in both pharmacodynamics and pharmacokinetics between rodents and nonhuman primates in preclinical substance abuse research. Therefore, the aim of this review is to highlight three advantages of nonhuman primates as preclinical substance abuse research subjects. First, nonhuman primates offer technical advantages in experimental design compared to other laboratory animals that afford unique opportunities to promote preclinical-to-clinical translational research. Second, these technical advantages, coupled with the relatively long lifespan of nonhuman primates, allows for pairing longitudinal drug self-administration studies and noninvasive imaging technologies to elucidate the biological consequences of chronic drug exposure. Lastly, nonhuman primates offer advantages in the patterns of intravenous drug self-administration that have potential theoretical implications for both the neurobiological mechanisms of substance use disorder etiology and in the drug development process of pharmacotherapies for substance use disorders. We conclude with potential future research directions in which nonhuman primates would provide unique and valuable insights into the abuse of and addiction to novel psychoactive substances.

Cocaine-induced neurodevelopmental deficits and underlying mechanisms

Exposure to drugs early in life has complex and long-lasting implications for brain structure and function. This review summarizes work to date on the immediate and long-term effects of prenatal exposure to cocaine. In utero cocaine exposure produces disruptions in brain monoamines, particularly dopamine, during sensitive periods of brain development, and leads to permanent changes in specific brain circuits, molecules, and behavior. Here, we integrate clinical studies and significance with mechanistic preclinical studies, to define our current knowledge base and identify gaps for future investigation. Birth Defects Research (Part C) 108:147-173, 2016. © 2016 Wiley Periodicals, Inc.

Evaluation of the Reinforcing Effect of Quetiapine, Alone and in Combination with Cocaine, in Rhesus Monkeys

There are several case reports of nonmedicinal quetiapine abuse, yet there are very limited preclinical studies investigating quetiapine self-administration. The goal of this study was to investigate the reinforcing effects of quetiapine alone and in combination with intravenous cocaine in monkeys. In experiment 1, cocaine-experienced female monkeys (N = 4) responded under a fixed-ratio (FR) 30 schedule of food reinforcement (1.0-g banana-flavored pellets), and when responding was stable, quetiapine (0.003-0.1 mg/kg per injection) or saline was substituted for a minimum of five sessions; there was a return to food-maintained responding between doses. Next, monkeys were treated with quetiapine (25 mg, by mouth, twice a day) for approximately 30 days, and then the quetiapine self-administration dose-response curve was redetermined. In experiment 2, male monkeys (N = 6) self-administered cocaine under a concurrent FR schedule with food reinforcement (three food pellets) as the alternative to cocaine (0.003-0.3 mg/kg per injection) presentation. Once choice responding was stable, the effects of adding quetiapine (0.03 or 0.1 mg/kg per injection) to the cocaine solution were examined. In experiment 1, quetiapine did not function as a reinforcer, and chronic quetiapine treatment did not alter these effects. In experiment 2, cocaine choice increased in a dose-dependent fashion. The addition of quetiapine to cocaine resulted in increases in low-dose cocaine choice and number of cocaine injections in four monkeys, while not affecting high-dose cocaine preference. Thus, although quetiapine alone does not have abuse potential, there was evidence of enhancement of the reinforcing potency of cocaine. These results suggest that the use of quetiapine in cocaine-addicted patients should be monitored.

Differential effects of the dopamine D3 receptor antagonist PG01037 on cocaine and methamphetamine self-administration in rhesus monkeys

The dopamine D3 receptor (D3R) has been shown to mediate many of the behavioral effects of psychostimulants associated with high abuse potential. This study extended the assessment of the highly selective D3R antagonist PG01037 on cocaine and methamphetamine (MA) self-administration to include a food-drug choice procedure. Eight male rhesus monkeys (n=4/group) served as subjects in which complete cocaine and MA dose-response curves were determined daily in each session. When choice was stable, monkeys received acute and five-day treatment of PG01037 (1.0-5.6 mg/kg, i.v.). Acute administration of PG01037 was effective in reallocating choice from cocaine to food and decreasing cocaine intake, however, tolerance developed by day 5 of treatment. Up to doses that disrupted responding, MA choice and intake were not affected by PG01037 treatment. PG01037 decreased total reinforcers earned per session and the behavioral potency was significantly greater on MA-food choice compared to cocaine-food choice. Furthermore, the acute efficacy of PG01037 was correlated with the sensitivity of the D3/D2R agonist quinpirole to elicit yawning. These data suggest (1) that efficacy of D3R compounds in decreasing drug choice is greater in subjects with lower D3R, perhaps suggesting that it is percent occupancy that is the critical variable in determining efficacy and (2) differences in D3R activity in chronic cocaine vs. MA users. Although tolerance developed to the effects of PG01037 treatment on cocaine choice, tolerance did not develop to the disruptive effects on food-maintained responding. These findings suggest that combination treatments that decrease cocaine-induced elevations in DA may enhance the efficacy of D3R antagonists on cocaine self-administration.

Identifying Medication Targets for Psychostimulant Addiction: Unraveling the Dopamine D3 Receptor Hypothesis

The dopamine D3 receptor (D3R) is a target for developing medications to treat substance use disorders. D3R-selective compounds with high affinity and varying efficacies have been discovered, providing critical research tools for cell-based studies that have been translated to in vivo models of drug abuse. D3R antagonists and partial agonists have shown especially promising results in rodent models of relapse-like behavior, including stress-, drug-, and cue-induced reinstatement of drug seeking. However, to date, translation to human studies has been limited. Herein, we present an overview and illustrate some of the pitfalls and challenges of developing novel D3R-selective compounds toward clinical utility, especially for treatment of cocaine abuse. Future research and development of D3R-selective antagonists and partial agonists for substance abuse remains critically important but will also require further evaluation and development of translational animal models to determine the best time in the addiction cycle to target D3Rs for optimal therapeutic efficacy.

Prenatal drug exposure to illicit drugs alters working memory-related brain activity and underlying network properties in adolescence

The persistence of effects of prenatal drug exposure (PDE) on brain functioning during adolescence is poorly understood. We explored neural activation to a visuospatial working memory (VSWM) versus a control task using functional magnetic resonance imaging (fMRI) in adolescents with PDE and a community comparison group (CC) of non-exposed adolescents. We applied graph theory metrics to resting state data using a network of nodes derived from the VSWM task activation map to further explore connectivity underlying WM functioning. Participants (ages 12-15 years) included 47 adolescents (27 PDE and 20 CC). All analyses controlled for potentially confounding differences in birth characteristics and postnatal environment. Significant group by task differences in brain activation emerged in the left middle frontal gyrus (BA 6) with the CC group, but not the PDE group, activating this region during VSWM. The PDE group deactivated the culmen, whereas the CC group activated it during the VSWM task. The CC group demonstrated a significant relation between reaction time and culmen activation, not present in the PDE group. The network analysis underlying VSWM performance showed that PDE group had lower global efficiency than the CC group and a trend level reduction in local efficiency. The network node corresponding to the BA 6 group by task interaction showed reduced nodal efficiency and fewer direct connections to other nodes in the network. These results suggest that adolescence reveals altered neural functioning related to response planning that may reflect less efficient network functioning in youth with PDE.

Developmental consequences of fetal exposure to drugs: what we know and what we still must learn

Most drugs of abuse easily cross the placenta and can affect fetal brain development. In utero exposures to drugs thus can have long-lasting implications for brain structure and function. These effects on the developing nervous system, before homeostatic regulatory mechanisms are properly calibrated, often differ from their effects on mature systems. In this review, we describe current knowledge on how alcohol, nicotine, cocaine, amphetamine, Ecstasy, and opiates (among other drugs) produce alterations in neurodevelopmental trajectory. We focus both on animal models and available clinical and imaging data from cross-sectional and longitudinal human studies. Early studies of fetal exposures focused on classic teratological methods that are insufficient for revealing more subtle effects that are nevertheless very behaviorally relevant. Modern mechanistic approaches have informed us greatly as to how to potentially ameliorate the induced deficits in brain formation and function, but conclude that better delineation of sensitive periods, dose-response relationships, and long-term longitudinal studies assessing future risk of offspring to exhibit learning disabilities, mental health disorders, and limited neural adaptations are crucial to limit the societal impact of these exposures.

Effects of quetiapine treatment on cocaine self-administration and behavioral indices of sleep in adult rhesus monkeys

RATIONALE

Clinical literature suggests a link between substance abuse and sleep disturbances. Quetiapine, an atypical antipsychotic, has shown efficacy in treating sleep disturbances, with clinical studies showing promise for quetiapine as a treatment for cocaine abuse.

OBJECTIVE

The goal of this study was to examine the effects of quetiapine on cocaine self-administration and behavioral indices of sleep in monkeys.

METHODS

Seven adult male rhesus monkeys, fitted with Actical® activity monitors, were trained to respond under a choice paradigm of food (1.0-g pellets) and cocaine (0.003-0.3 mg/kg per injection) presentation. First, monkeys received acute pretreatment (45 min) with quetiapine (25-75 mg, p.o.) prior to choice sessions; three cocaine doses were studied in combination with quetiapine. Next, the effect of chronic (14-16 days) quetiapine treatment (25-250 mg, p.o., BID) was examined in combination with the lowest preferred cocaine dose (≥80 % cocaine choice). Behavioral indices of sleep, based on activity measures obtained during lights-out, were recorded throughout the study.

RESULTS

Acute quetiapine decreased cocaine choice in four of the seven monkeys. Chronic quetiapine treatment resulted in initial decreases in cocaine choice, but tolerance developed to these effects. Acute doses of quetiapine did not improve sleep efficiency the following night nor did chronic quetiapine. The first night after discontinuing quetiapine treatment resulted in significant decreases in sleep efficiency and increases in nighttime activity.

CONCLUSIONS

These findings do not offer support for the use of quetiapine as a monotherapy for treatment of cocaine abuse nor as an adjunct therapy to treat sleep disturbances associated with stimulant abuse.

PET studies in nonhuman primate models of cocaine abuse: translational research related to vulnerability and neuroadaptations

The current review highlights the utility of positron emission tomography (PET) imaging to study the neurobiological substrates underlying vulnerability to cocaine addiction and subsequent adaptations following chronic cocaine self-administration in nonhuman primate models of cocaine abuse. Environmental (e.g., social rank) and sex-specific influences on dopaminergic function and sensitivity to the reinforcing effects of cocaine are discussed. Cocaine-related cognitive deficits have been hypothesized to contribute to high rates of relapse and are described in nonhuman primate models. Lastly, the long-term consequences of cocaine on neurobiology are discussed. PET imaging and longitudinal, within-subject behavioral studies in nonhuman primates have provided a strong framework for designing pharmacological and behavioral treatment strategies to aid drug-dependent treatment seekers. Non-invasive PET imaging will allow for individualized treatment strategies. Recent advances in radiochemistry of novel PET ligands and other imaging modalities can further advance our understanding of stimulant use on the brain. This article is part of the Special Issue Section entitled 'Neuroimaging in Neuropharmacology'.

Further characterization of quinpirole-elicited yawning as a model of dopamine D3 receptor activation in male and female monkeys

The dopamine (DA) D3 receptor (D3R) has been associated with impulsivity, pathologic gambling, and drug addiction, making it a potential target for pharmacotherapy development. Positron emission tomography studies using the D3R-preferring radioligand [(11)C]PHNO ([(11)C](+)-propyl-hexahydro-naphtho-oxazin) have shown higher binding potentials in drug abusers compared with control subjects. Preclinical studies have examined D3R receptor activation using the DA agonist quinpirole and the unconditioned behavior of yawning. However, the relationship between quinpirole-elicited yawning and D3R receptor availability has not been determined. In Experiment 1, eight drug-naive male rhesus monkeys were scanned with [(11)C]PHNO, and the ability of quinpirole (0.01-0.3 mg/kg i.m.) to elicit yawning was examined. Significant positive (globus pallidus) and negative (caudate nucleus, putamen, ventral pallidum, and hippocampus) relationships between D3R receptor availability and quinpirole-induced yawns were noted. Experiment 2 replicated earlier findings that a history of cocaine self-administration (n = 11) did not affect quinpirole-induced yawning and extended this to examine monkeys (n = 3) with a history of methamphetamine (MA) self-administration and found that monkeys with experience self-administering MA showed greater potency and significantly higher quinpirole-elicited yawning compared with controls. Finally, quinpirole-elicited yawning was studied in drug-naive female monkeys (n = 6) and compared with drug-naive male monkeys (n = 8). Sex differences were noted, with quinpirole being more potent and eliciting significantly more yawns in males compared with females. Taken together these findings support the use of quinpirole-elicited yawning as a behavioral tool for examining D3R activation in monkeys and that both drug history and sex may influence individual sensitivity to the behavioral effects of D3R compounds.

Multisite, randomized, double-blind, placebo-controlled pilot clinical trial to evaluate the efficacy of buspirone as a relapse-prevention treatment for cocaine dependence

OBJECTIVE

To evaluate the potential efficacy of buspirone as a relapse-prevention treatment for cocaine dependence.

METHOD

A randomized, double-blind, placebo-controlled, 16-week pilot trial was conducted at 6 clinical sites between August 2012 and June 2013. Adult crack cocaine users meeting DSM-IV-TR criteria for current cocaine dependence who were scheduled to be in inpatient/residential substance use disorder (SUD) treatment for 12-19 days when randomized and planning to enroll in local outpatient treatment through the end of the active treatment phase were randomized to buspirone titrated to 60 mg/d (n = 35) or placebo (n = 27). All participants received psychosocial treatment as usually provided by the SUD treatment programs in which they were enrolled. Outcome measures included maximum days of continuous cocaine abstinence (primary), proportion of cocaine use days, and days to first cocaine use during the outpatient treatment phase (study weeks 4-15) as assessed by self-report and urine drug screens.

RESULTS

There were no significant treatment effects on maximum continuous days of cocaine abstinence or days to first cocaine use. In the female participants (n = 23), there was a significant treatment-by-time interaction effect (χ²₁ = 15.26, P < .0001), reflecting an increase in cocaine use by those receiving buspirone, relative to placebo, early in the outpatient treatment phase. A similar effect was not detected in the male participants (n = 39; χ²₁ = 0.14, P = .70).

CONCLUSIONS

The results suggest that buspirone is unlikely to have a beneficial effect on preventing relapse to cocaine use and that buspirone for cocaine-dependent women may worsen their cocaine use outcomes.

TRIAL REGISTRATION

ClinicalTrials.gov identifier: NCT01641159.

The relationship between cocaine self-administration and actigraphy-based measures of sleep in adult rhesus monkeys

RATIONALE

Clinical trials show that chronic cocaine users suffer from sleep disturbances and preclinical research has shown that acute sleep deprivation increases the rate of cocaine self-administration in rats.

OBJECTIVE

This study examined the effect of cocaine self-administration on behavioral indices of sleep and alternatively the effect of sleep disruption on cocaine-maintained responding by rhesus monkeys.

METHODS

Seven adult rhesus monkeys, fitted with Actical® activity monitors, were trained to respond under a concurrent choice paradigm with food (three 1.0-g pellets) and cocaine (0.003-0.3 mg/kg) or saline presentation. For each monkey, the lowest preferred dose of cocaine (>80% cocaine choice) was determined. Activity data were analyzed during lights out (2000-0600) to determine sleep efficiency, sleep latency, and total activity counts. Subsequently, the monkeys' sleep was disrupted (every hour during lights-out period) the night prior to food-cocaine choice sessions.

RESULTS

Self-administration of the preferred dose of cocaine resulted in a significant decrease in sleep efficiency, with a significant increase in total lights-out activity. Sleep disruption significantly altered behavioral indices of sleep, similar to those seen following cocaine self-administration. However, sleep disruption did not affect cocaine self-administration under concurrent choice conditions.

CONCLUSIONS

Based on these findings, cocaine self-administration does appear to disrupt behavioral indices of sleep, although it remains to be determined if treatments that improve sleep measures can affect future cocaine taking.

Developmental and behavioral consequences of prenatal cocaine exposure: a review

Substance use among pregnant women continues to be a major public health concern, posing potential risk to their drug-exposed children as well as burdens on society. This review is intended to discuss the most recent literature regarding the association between in utero cocaine exposure and developmental and behavioral outcomes from birth through adolescence across various domains of functioning (growth, neurobiology, intelligence, academic achievement, language, executive functioning, behavioral regulation and psychopathology). In addition, methodological limitations, associated biological, sociodemographic and environmental risk factors and future directions in this area of research are discussed. Given the large number of exposed children in the child welfare system and the increased need for medical, mental health and special education services within this population, more definitively documenting associations between prenatal cocaine exposure and later child outcomes is essential in order to be able to prospectively address the many significant public health, economic and public policy implications.

Lack of abuse potential in a highly selective dopamine D3 agonist, PF-592,379, in drug self-administration and drug discrimination in rats

Dopamine D3-preferring agonists are commonly used to treat Parkinson's disease and restless leg syndrome; however, laboratory animal studies suggest that they may possess a moderate abuse potential. These studies aimed to compare the highly selective, full D3 agonist PF-592,379 to the less selective D3 agonist 7-OH-DPAT, and the indirect dopamine agonist cocaine in drug self-administration and discrimination assays. Although rats readily acquired high rates of fixed ratio (FR)1 responding for cocaine, experimentally naive rats failed to acquire responding when 7-OH-DPAT or PF-592,379 was made available during an 18-session acquisition period. Cocaine also maintained dose-dependent levels of responding when available under a FR5 or a progressive ratio (PR) schedule of reinforcement. Although 7-OH-DPAT maintained modest levels of responding when substituted under a FR5, it failed to maintain significant levels of PR responding. PF-592,379 maintained saline-like rates of responding when substituted under FR5 or PR schedules of reinforcement. Similar behavioral profiles were observed in cocaine discrimination assays, with 7-OH-DPAT partially substituting for cocaine, and PF-592,379 producing saline-like effects over a wide range of doses. Together, the results of these studies predict that highly selective D3 agonists, such as PF-592,379, will have low abuse potential in humans.

Medication discovery for addiction: translating the dopamine D3 receptor hypothesis

The dopamine D3 receptor (D3R) has been investigated as a potential target for medication development to treat substance use disorders (SUDs) with a particular focus on cocaine and methamphetamine. Currently, there are no approved medications to treat cocaine and methamphetamine addiction and thus developing pharmacotherapeutics to complement existing behavioral strategies is a fundamental goal. Novel compounds with high affinity and D3R selectivity have been evaluated in numerous animal models of drug abuse and favorable outcomes in nonhuman primate models of self-administration and relapse have provided compelling evidence to advance these agents into the clinic. One approach is to repurpose drugs that share the D3R mechanism and already have clinical utility, and to this end buspirone has been identified as a viable candidate for clinical trials. A second, but substantially more resource intensive and risky approach involves the development of compounds that exclusively target D3R, such as GSK598809 and PG 619. Clinical investigation of these drugs or other novel D3R-selective agents will provide a better understanding of the role D3R plays in addiction and whether or not antagonists or partial agonists that are D3R selective are effective in achieving abstinence in this patient population.

Memory ability and hippocampal volume in adolescents with prenatal drug exposure

The objective of the present study was to examine the influence of prenatal drug exposure (PDE) on memory performance and supporting brain structures (i.e., hippocampus) during adolescence. To achieve this goal, declarative memory ability and hippocampal volume were examined in a well-characterized sample of 138 adolescents (76 with a history of PDE and 62 from a non-exposed comparison group recruited from the same community, mean age=14 years). Analyses were adjusted for: age at time of the assessments, gender, IQ, prenatal exposure to alcohol and tobacco, and indices of early childhood environment (i.e., caregiver depression, potential for child abuse, and number of caregiver changes through 7 years of age). Results revealed that adolescents with a history of PDE performed worse on the California Verbal Learning Test-Child Version (CVLT-C), and story recall from the Children's Memory Scale (CMS), and had larger hippocampal volumes, even after covariate adjustment. Hippocampal volume was negatively correlated with memory performance on the CVLT-C, with lower memory scores associated with larger volumes. These findings provide support for long-term effects of PDE on memory function and point to neural mechanisms that may underlie these outcomes.

Contributions of neuroimaging to understanding sex differences in cocaine abuse

A consistent observation in drug abuse research is that males and females show differences in their response to drugs of abuse. In order to understand the neurobiology underlying cocaine abuse and effective treatments, it is important to consider the role of sex differences. Sex hormones have been investigated in both behavioral and molecular studies, but further evidence addressing drug abuse and dependence in both sexes would expand our knowledge of sex differences in response to drugs of abuse. Neuroimaging is a powerful tool that can offer insight into the biological bases of these differences and meet the challenges of directly examining drug-induced changes in brain function. As such, neuroimaging has drawn much interest in recent years. Specifically, positron emission tomography (PET), single photon emission computed tomography (SPECT), and magnetic resonance imaging (MRI) technology have emerged as effective noninvasive approaches for human and animal models. Studies have revealed sex-specific changes in patterns of brain activity in response to acute cocaine injection and after prolonged cocaine use. SPECT and PET studies have demonstrated changes in the dopamine transporter but are less clear on other components of the dopaminergic system. This review highlights contributions of neuroimaging toward understanding the role of sex differences in the drug abuse field, specifically regarding cocaine, and identifies relevant questions that neuroimaging can effectively address.

Behavioral sensitization to cocaine in rats: evidence for temporal differences in dopamine D3 and D2 receptor sensitivity

RATIONALE

Cocaine-induced changes in D(2) receptors have been implicated in the expression of sensitized behavioral responses and addiction-like behaviors; however, the influence of D(3) receptors is less clear.

OBJECTIVES

To characterize the effects of repeated cocaine administration on the sensitivity of rats to D(2)- and D(3)-mediated behaviors, as well as the binding properties of ventral striatal D(2)-like and D(3) receptors.

METHODS

Pramipexole was used to assess the sensitivity of rats to D(3)/D(2) agonist-induced yawning, hypothermia, and locomotor activity, 24 h, 72 h, 10, 21, and 42 days after repeated cocaine or saline administration. The locomotor effects of cocaine (42 day) and the binding properties of ventral striatal D(2)-like and D(3) receptors (24 h and 42 days) were also evaluated.

RESULTS

Cocaine-treated rats displayed an enhanced locomotor response to cocaine, as well as a progressive and persistent leftward/upward shift of the ascending limb (72 h-42 day) and leftward shift of the descending limb (42 days) of the pramipexole-induced yawning dose-response curve. Cocaine treatment also decreased B (max) and K (d) for D(2)-like receptors and increased D(3) receptor binding at 42 days. Cocaine treatment did not change pramipexole-induced hypothermia or locomotor activity or yawning induced by cholinergic or serotonergic agonists.

CONCLUSIONS

These studies suggest that temporal differences exist in the development of cocaine-induced sensitization of D(3) and D(2) receptors, with enhancements of D(3)-mediated behavioral effects observed within 72 h and enhancements of D(2)-mediated behavioral effects apparent 42 days after cocaine. These findings highlight the need to consider changes in D(3) receptor function when thinking about the behavioral plasticity that occurs during abstinence from cocaine use.

Influence of cocaine history on the behavioral effects of Dopamine D(3) receptor-selective compounds in monkeys

Although dopamine D(3) receptors have been associated with cocaine abuse, little is known about the consequences of chronic cocaine on functional activity of D(3) receptor-preferring compounds. This study examined the behavioral effects of D(3) receptor-selective 4-phenylpiperazines with differing in vitro functional profiles in adult male rhesus monkeys with a history of cocaine self-administration and controls. In vitro assays found that PG 619 (N-(3-hydroxy-4-(4-(2-methoxyphenyl)piperazin-1-yl)butyl)-4-(pyridin-2-yl)benzamide HCl) was a potent D(3) antagonist in the mitogenesis assay, but a fully efficacious agonist in the adenylyl cyclase assay, NGB 2904 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)-9H-fluorene-2-carboxamide HCl) was a selective D(3) antagonist, whereas CJB 090 (N-(4-(4-(2,3-dichlorophenyl)piperazin-1-yl)butyl)-4-(pyridin-2-yl)benzamide HCl) exhibited a partial agonist profile in both in vitro assays. In behavioral studies, the D(3) preferential agonist quinpirole (0.03-1.0 mg/kg, i.v.) dose-dependently elicited yawns in both groups of monkeys. PG 619 and CJB 090 elicited yawns only in monkeys with an extensive history of cocaine, whereas NGB 2904 did not elicit yawns, but did antagonize quinpirole and PG 619-elicited yawning in cocaine-history monkeys. In another experiment, doses of PG 619 that elicited yawns did not alter response rates in monkeys self-administering cocaine (0.03-0.3 mg/kg per injection). Following saline extinction, cocaine (0.1 mg/kg) and quinpirole (0.1 mg/kg), but not PG 619 (0.1 mg/kg), reinstated cocaine-seeking behavior. When given before a cocaine prime, PG 619 decreased cocaine-elicited reinstatement. These findings suggest that (1) an incongruence between in vitro and in vivo assays, and (2) a history of cocaine self-administration can affect in vivo efficacy of D(3) receptor-preferring compounds PG 619 and CJB 090, which appear to be dependent on the behavioral assay.

Behavioral characterization of adult male and female rhesus monkeys exposed to cocaine throughout gestation

RATIONALE

In utero cocaine exposure has been associated with alterations in the dopamine (DA) system in monkeys. However, the behavioral outcomes of prenatal cocaine exposure in adulthood are poorly understood.

OBJECTIVES

To assess several behavioral measures in 14-year-old rhesus monkeys exposed to cocaine in utero and controls (n = 10 per group).

MATERIALS AND METHODS

For these studies, two unconditioned behavioral tasks, novel object reactivity and locomotor activity, and two conditioned behavioral tasks, response extinction and delay discounting, were examined. In addition, cerebrospinal fluid (CSF) samples were analyzed for concentrations of the monoamine metabolites homovanillic acid (HVA) and 5-hydroxyindole acetic acid (5-HIAA).

RESULTS

No differences in CSF concentrations of 5-HIAA and HVA, latencies to touch a novel object or locomotor activity measures were observed between groups or sexes. However, prenatally cocaine-exposed monkeys required a significantly greater number of sessions to reach criteria for extinction of food-reinforced behavior than control monkeys. On the delay-discounting task, male prenatally cocaine-exposed monkeys switched preference from the larger reinforcer to the smaller one at shorter delay values than male control monkeys; no differences were observed in females.

CONCLUSIONS

These findings suggest that prenatal cocaine exposure results in long-term neurobehavioral deficits that are influenced by sex of the individual.