Research Findings - Intramural Research

Development and Plasticity Section, Cellular Neurobiology Research Branch

Transcriptional Profiling in the Human Prefrontal Cortex: Evidence for Two Activational States Associated with Cocaine Abuse CNS-focused cDNA microarrays were used to examine gene expression profiles in dorsolateral prefrontal cortex (dlPFC, Area 46) from seven individual sets of age- and post-mortem interval-matched male cocaine abusers and controls. The presence of cocaine and related metabolites was confirmed by gas chromatography-mass spectrometry. Sixty-five transcripts were differentially expressed, indicating alterations in energy metabolism, mitochondria and oligodendrocyte function, cytoskeleton and related signaling, and neuronal plasticity. There was evidence for two distinct states of transcriptional regulation, with increases in gene expression predominating in subjects testing positive for a metabolite indicative of recent 'crack' cocaine abuse and decreased expression profiles in the remaining cocaine subjects. This pattern was confirmed by quantitative polymerase chain reaction for select transcripts. These data suggest that cocaine abuse targets a distinct subset of genes in the dlPFC, resulting in either a state of acute activation in which increased gene expression predominates, or a relatively destimulated, refractory phase. Lehrmann, E., Oyler, J., Vawter, M.P., Hyde, T.M., Kolachana, B., Kleinman, J.E., Huestis, M.A., Becker, K.G., and Freed, W.J. Pharmacogenomics, 3, pp. 27-40, 2003.

5-Hydroxytryptamine 1A Receptor Activation Protects Against N-Methyl-D-aspartate-induced Apoptotic Cell Death in Striatal and Mesencephalic Cultures Apoptosis and glutamate-mediated excitotoxicity may play a role in the pathogenesis of Parkinson's disease (PD) and toxic effect of drugs of abuse such as amphetamines. We investigated whether stimulation of the 5-hydroxytryptamine 1A (5-HT1A) receptor attenuates N-methyl-D-aspartate- (NMDA) and 1-methyl-4-phenylpyridinium (MPP(+))-induced apoptotic cell death. A brief exposure (20 min) of M213-2O striatal cells to NMDA or glutamate produced a delayed increase in caspase-3 activity and DNA fragmentation. NMDA-induced caspase-3 activity and DNA fragmentation were almost completely blocked by the 5-HT1A agonists 8-hydroxy-2-(di-n-propylamino)-tetralin (8-OH-DPAT) and (R)-5-fluoro-8 hydroxy-2-(dipropylamino)-tetralin (R-UH-301). Similarly, increases in caspase-3 activity and DNA fragmentation in rat primary mesencephalic neurons after exposure to NMDA and glutamate were almost completely inhibited by 8-OH-DPAT. This neuroprotective effect of 8-OH-DPAT was reversed by WAY 100635. Furthermore, 8-OH-DPAT and blocked apoptotic cell death in primary mesencephalic neurons that were exposed to the toxin MPP(+). Together, these results suggest that 5-HT1A receptor stimulation may be a promising pharmacological approach in the development of neuroprotective agents. Madhavan, L., Freed, W.J., Anantharam, V., and Kanthasamy, A.G. Journal of Pharmacology and Experimental Therapeutics, 304, pp. 913-923, 2003.

Nerve Growth Factor-induced Neurite Sprouting in PC12 Cells Involves Sigma-1 Receptors: Implications for Antidepressants One theory concerning the action of antidepressants relates to the drugs' ability to induce an adaptive plasticity in neurons such as neurite sprouting. Certain antidepressants are known to bind to sigma-1 receptors (Sig-1R) with high affinity. Sig-1R are dynamic endoplasmic reticulum proteins that are highly concentrated at the tip of growth cones in cultured cells. In this study, IRP researchers tested the hypotheses that Sig-1R might participate in the neurite sprouting and that antidepressants with Sig-1R affinity may promote the neuronal sprouting via Sig-1R. The prototypic Sig-1R agonist (+)-pentazocine [(+)PTZ], as well as the Sig-1R-active antidepressants imipramine and fluvoxamine, although ineffective by themselves, were found to enhance the nerve growth factor (NGF)-induced neurite sprouting in PC12 cells in a dose-dependent manner. A Sig-1R antagonist N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE100) blocked the enhancements caused by these Sig-1R agonists. In separate experiments, IRP investigators found that NGF dose and time dependently increased Sig-1R in PC12 cells. Chronic treatment of cells with (+)PTZ, imipramine, or fluvoxamine also increased Sig-1R. These latter results suggested that NGF induces the neurite sprouting by increasing Sig-1R. Indeed, the overexpression of Sig-1R per se in PC12 cells enhanced the NGF-induced neurite sprouting. Furthermore, antisense deoxyoligonucleotides directed against Sig-1R attenuated the NGF-induced neurite sprouting. When taken together, these results indicate that Sig-1R plays an important role in the NGF-induced neurite sprouting and that certain antidepressants may facilitate neuronal sprouting in the brain via Sig-1R. Takebayashi, M., Hayashi, T., and Su, T.P. Journal of Pharmacology and Experimental Therapeutics, 303(3), pp. 1227-1237, 2002.

Chronic [D-Ala(2), D-Leu(5)]enkephalin Treatment Increases the Nerve Growth Factor in Adult Mouse Brain The delta opioid peptide [D-Ala(2), D-Leu(5)]enkephalin (DADLE) has been shown to enhance the survival of dopaminergic neurons. Here, IRP scientists found that chronic treatment with DADLE caused a significant increase in nerve growth factor (NGF) in the hippocampus and the midbrain of adult albino Swiss (CD-1) mice, but not in the striatum or frontal cortex. Glia-derived neurotrophic factor (GDNF) was not significantly affected. Thus, the neuroprotective action of DADLE may be mediated in part by NGF. Hayashi, T., and Su, T.P. European Journal of Pharmacology, 464, pp. 237-239, 2003.

Molecular Neuropsychiatry Section, Cellular Neurobiology Research Branch

Methadone Treatment Induces Attenuation of Cerebrovascular Deficits Associated with the Prolonged Abuse of Cocaine and Heroin Opiate replacement therapy has been useful in reducing heroin use and in keeping patients in treatment programs. However, neuropsychological and neurophysiological effects of this treatment regimen have not been evaluated systematically. To determine whether methadone treatment reduces the magnitude of cerebral blood flow alternations in polysubstance (heroin and cocaine) abusers, IRP scientists compared blood flow parameters in control subjects (n=26), polysubstance abusers (n=28) maintained on methadone for 24 weeks, and polysubstance abusers (n=22) who were not seeking treatment. Blood flow velocity was recorded from the anterior and middle cerebral arteries using transcranial Doppler sonography on an outpatient visit. The pulsatility index, a measure of cerebrovascular resistance, was significantly (p<0.05) increased in both groups of polysubstance abusers compared to control subjects. Increased pulsatility in the two groups of substance abusers suggests constriction of the small cortical arteries. Nevertheless, the methadone-maintained polysubstance abusers had significantly lower pulsatility values than the nontreatment substance-abusing group. These findings suggest that maintenance on methadone might have significant beneficial neurovascular effects on this population of patients. Herning, R.I., Better, W.E., Tate, K., Umbricht, A., Preston, K.L., and Cadet, J.L. Neuropsychopharmacology, 28, pp. 562-568, 2003.

Preclinical Pharmacology Section/Behavioral Neuroscience Branch

Glutamate mGlu5-Adenosine A2A-Dopamine D2 Receptor Interactions in the Striatum: Implications for Drug Therapy in Neuropsychiatric Disorders and Drug Abuse There is growing evidence for the existence of not only homomeric, but also functional heteromeric receptor complexes, particularly involving G protein coupled receptors (GPCRs). These include adenosine A2A-dopamine D2 and adenosine A2A-glutamate mGlu5 receptor complexes. The role of these receptor complexes in receptor function seems to be multiple, involving hetero-modulation of ligand recognition, signalling and trafficking. The preferential localization of A2A-D2 and A2A-mGlu5 receptor complexes is in the dendritic spines of striatopallidal GABAergic neurons. Results obtained from behavioral and in vivo microdialysis experiments have shown an important role of mGlu5-A2A-D2 receptor interactions in the modulation of the function of the striatopallidal GABAergic neurons. The striatopallidal GABAergic neurons play a key role in the pathophysiology of basal ganglia disorders, like Parkinson's disease, and comprise a common pathway for the rewarding effects of opiates and psychostimulants and for the antipsychotic effects of neuroleptics. The formation of receptor complexes modifies the single receptor transducing characteristics and leads to the appearance of "emergent properties". Thus, the study of mGlu5-A2A-D2 receptor interactions in the striatum reveals new properties of these GPCRs and gives indications for a new rational approach for drug therapy in neuropsychiatric disorders and drug addiction. Ferre, S., Ciruela, F., Woods, A.S., Canals, M., Burgueno, J., Marcellino, D., Karz-Kubicha, M., Hope, B.T., Morales, M., Popoli, P., Goldberg, S.R., Fuxe, F., Luis, C., Franco, R. and Agnati, L. Curr. Med. Chem.-Central Nervous System Agents, 3, pp. 1-26, 2003.

Second-order Schedules of Drug Self-administration in Animals On a second-order schedule, a subject responds according to one schedule (the unit schedule) for a brief presentation of a stimulus such as a light. Responding by the subject on this unit schedule is then reinforced according to another schedule of reinforcement. Second-order schedules of drug injection allow the study of more complex behavioral sequences than do simple schedules and may more accurately reflect the human drug-abuse situation. Much of the early work in this area used primates as subjects and focused on the behavioral variables controlling responding. It was shown that long sequences of behavior could be maintained on second-order schedules with relatively infrequent injections of drug and that the second-order, brief-stimulus presentations were critical to the acquisition and maintenance of responding. Also, the continued presentation of the brief stimulus in extinction often led to prolonged extinction behavior. These studies clearly showed that environmental stimuli greatly influence drug self-administration behavior under second-order schedules. The focus of much of the more recent work with second-order schedules has been on the evaluation of pharmacological treatments for drug addiction, both as antagonist and substitution therapies. Both types of potential therapies have shown promise in these preclinical models of addictive behavior. The recent extension of second-order self-administration studies to rats as subjects has facilitated the investigation of neural mechanisms involved in this behavior. While this use of second-order schedules is a relatively recent phenomenon, significant contributions have already been made in identifying neural mechanisms critical to second-order schedule drug self-administration. This active area of research holds great promise for delineating specific brain regions critical to different aspects of drug addiction. Schindler, C.W., Panlilio, L.V. and Goldberg S.R. Psychopharmacology, 163, pp. 327-344, 2002.

Cognition and Pharmacology Section, Neuroimaging Research Branch

Cognitive Mechanisms of Nicotine on Visual Attention Nicotine is known to improve performance on a range of cognitive tasks, notably attention and to a lesser extent, working memory in both humans and animals, which could contribute to smoking maintenance by improving concentration. As such, understanding nicotine's neurobiological and cognitive mechanisms may help explain both its addictive properties and potential therapeutic applications. To this end, functional magnetic resonance imaging (fMRI) was used to determine the neural substrates of nicotine's effects on a sustained attention (rapid visual information-processing) task. Task performance activated specific bilateral frontal, parietal, thalamic, occipital and cerebellar regions previously associated with sustained attention and working memory, with additional strong task-induced activations in the anterior insula and caudate. Decreased activation in left frontal, anterior and posterior cingulate, insula and left parahippocampal regions were also seen. Along with subtle behavioral deficits, mildly abstinent smokers showed less task-induced brain activation in the parietal cortex and caudate than did non-smokers. Application of a 21 mg nicotine patch to smokers improved task performance in smokers and increased task-induced BOLD activation in attention-related areas bilaterally including the parietal cortex, thalamus and caudate, while nicotine induced a generalized increase in occipital cortex activity. The nicotine patch also prevented the decline in mood ratings that followed task performance in smokers with placebo patch. Nicotine administration further deactivated some of the brain regions deactivated by the task, suggesting that nicotine improves attention in smokers by enhancing activation in areas traditionally associated with visual attention, arousal and motor activation in order to specifically focus attentional resources on task demands. Lawrence, N.S., Ross, T.J. and Stein, E.A. Neuron, 36, pp. 539-548, 2002.

Neuropsychopharmacology Section, Behavioral Neuroscience Research Branch

Dopamine D3 Receptor Antagonists as Potential Anti-craving and Anti-relapse Medications for Treatment of Addiction IRP investigators have determined that acute blockade of the dopamine D3 receptor in the rat brain (which is neuroanatomically restricted to the mesolimbic dopamine system, implicated in drug-induced reward and drug-seeking behavior) dose-dependently attenuates cocaine-enhanced brain-stimulation reward, acquisition of cocaine-induced conditioned cue preference, expression of cocaine-induced conditioned cue preference, acquisition of heroin-induced conditioned cue preference, expression of heroin-induced conditioned cue preference, and cocaine-triggered relapse to cocaine-seeking behavior in animals pharmacologically detoxified and behaviorally extinguished from their intravenous cocaine-taking behavior. These findings suggest that dopamine D3 receptor antagonists are worthy of further investigation as potential anti-craving and anti-relapse medications for the treatment of drug abuse. Ashby, C.R. Jr., Paul, M., Gardner, E.L., Heidbreder, C.A., and Hagan, J.J. Synapse, 48, pp. 154-156, 2003.

Anatomically Focal Mild Electrical Stimulation of the Brain Triggers Drug-seeking Behavior, A Way to Map the "Relapse" Circuits of the Brain Brain IRP scientists have determined that anatomically focal mild electrical stimulation of specific sites deep within the brain triggers relapse to drug-seeking behavior in animals pharmacologically detoxified and behaviorally extinguished from their intravenous drug-taking behavior. In this way, they have begun to anatomically map out the "relapse" circuits of the brain. They have also determined that these "relapse" circuits of the brain correspond to the brain areas that are activated in humans during drug-craving. They have further determined that these "relapse" circuits in the brain use the brain chemical glutamate as their synaptic transmitter. These findings suggest that compounds acting on the glutamate neurotransmitter system of the brain are worthy of further investigation as potential anti-craving and anti-relapse medications for the treatment of drug abuse. Hayes, R.J., Vorel, S.R., Spector, J., Liu, X., and Gardner, E.L. Psychopharmacology, electronic publication ahead of print, January 24, 2003 [PMID 12545331].

Neurobiology of Relapse Section, Behavioral Neuroscience Research Branch

Time-dependent Increases in Brain-derived Neurotrophic Factor (BDNF) Protein Levels Within the Mesolimbic Dopamine System Following Withdrawal from Cocaine: Implications for Incubation of Cocaine Craving Using a rat model of drug craving, IRP scientists found that the responsiveness to cocaine cues progressively increases or incubates over the first 60 days of cocaine withdrawal. Here investigators studied whether alterations in BDNF protein levels within the mesolimbic dopamine system are associated with this incubation phenomenon. BDNF is involved in synaptic plasticity and was found to enhance responding for cues associated with natural rewards. Rats were trained to lever-press for intravenous cocaine or oral sucrose for 6-hours/day for 10 days; each earned reward was paired with a tone-light cue. Resumption of lever-pressing behavior was then assessed on days 1, 30 or 90 of reward withdrawal. First, resistance to extinction was assessed during 6 hours wherein lever presses were not reinforced and the cue was absent. Second, cue-induced reinstatement was assessed after extinction during 1 h wherein responding led to cue presentations. Other rats were sacrificed without testing on days 1, 30, and 90 of reward withdrawal and BDNF and nerve growth factor (NGF) protein levels were measured in the ventral tegmental area (VTA), accumbens and amygdala. Lever pressing during extinction and cue-induced reinstatement tests of cocaine craving progressively increased following cocaine withdrawal. Time-dependent changes also were observed during the tests for sucrose craving, with maximal responding on day 30. BDNF, but not NGF, levels in the VTA, accumbens and amygdala progressively increased following cocaine, but not sucrose, withdrawal. Time-dependent increases in BDNF levels may lead to synaptic modifications that underlie enhanced responsiveness to cocaine cues after prolonged withdrawal periods. Grimm, J.W., Lu, L., Hayashi, T., Su, T.P., Hope, B.T. and Shaham, Y. The Journal of Neuroscience, 23, pp. 742-747, 2003.

Treatment Section, Clinical Pharmacology & Therapeutics Research Branch

Effects of Opioid Detoxification on Withdrawal and Pain in Hospitalized Heroin-Dependent AIDS Patients With the growing role of intravenous drug use in the transmission of HIV infection, HIV-infected patients frequently present with comorbid opioid dependence. Yet, few empirical evaluations of the efficacy and consequences of opioid detoxification medications in medically ill HIV-infected patients have been reported. In a randomized, double blind clinical trial, IRP scientists evaluated the impact of three medications on the signs and symptoms of withdrawal and on pain severity in heroin-dependent HIV-infected patients (N=55) hospitalized for medical reasons on an inpatient AIDS service. Patients received a 3-day pharmacologic taper with intramuscular buprenorphine (n=21), oral clonidine (n=16), or oral methadone (n=18). Observer- and subject-rated opiate withdrawal scores decreased significantly following the first dose of medication and overall during treatment. Among all 55 subjects, self-reported and observer-reported pain decreased after treatment (on average OOWS scores declined 5.6 units and SOWS declined 4.77 units p<0.001 for both) with no indication of increased pain during medication taper. There were no significant differences of pain decline and other measures of withdrawal between the 3 treatment groups. Supplemental morphine was administered as medically indicated for pain to 45% of the patients; only 34% of men versus 62% of women received morphine (p< .05). These findings suggest buprenorphine, clonidine, and methadone regimens each decrease opioid withdrawal in medically ill HIV-infected patients. No differences between effectiveness of these treatment regimens were detected. Umbricht, A., Leslie, J.M., Tucker, M.J., Hoover, D.R., Chaisson, R.E. and Preston, K.L. Drug and Alcohol Dependence, 69, pp. 263-272, 2003.

Abstinence Reinforcement Maintenance and One-Year Follow-Up in Methadone Maintenance Patients Relapse to drug use is often seen when contingencies designed to reduce drug use are discontinued. IRP scientists tested a stepdown maintenance contingency and 1-year follow-up in 110 patients who had completed the contingency management trial targeted to decreasing their opiate use. In this study participants were rerandomized to receive vouchers and take-home methadone doses contingent on providing opiate-negative urine specimens (N=55) or noncontingently (N=55) for 12 weeks. Follow-up interviews were conducted at 3, 6, and 12 months after study participation. Patients who received the maintenance contingency following an 8-week induction contingency had better outcomes than those who received noncontingent incentives in either the maintenance or induction phases of the trial. Good outcome at follow-up was predicted by enrollment in methadone maintenance after the study. Significantly more participants in the maintenance contingency group transferred directly to another methadone program. These findings support the therapeutic value of extending the duration of contingency management and long-term methadone maintenance. Preston, K.L., Umbricht, A. and Epstein, D. Drug and Alcohol Dependence, 67, pp. 125-137, 2002.

Cognitive-Behavioral Therapy Plus Contingency Management for Cocaine Use in Methadone-Maintenance Patients: Emergent Effects One Year Later? This project assessed methods for decreasing HIV-risk behaviors in substance abusers, and assessed the safety and efficacy of pharmacological and behavioral treatments for opioid dependence in those already infected with HIV. Contingency management (CM) rapidly reduces cocaine use, but its effects subside after treatment. Cognitive-behavioral therapy (CBT) produces reductions that emerge 6-12 months after treatment ends. Combined, the 2 treatments might be complementary. In a 2x2 design, 193 cocaine-using methadone-maintained outpatients were randomly assigned to 12 weeks of group therapy (CBT or a control condition) and voucher availability (CM contingent on cocaine-negative urines, or noncontingent vouchers). As part of the CBT treatment, patients were taught 1) to identify and seek out sources of reinforcement that do not carry risks of HIV; and 2) to develop adaptive problem-focused and emotion-focused coping responses to general and drug-specific stressors that might otherwise trigger HIV-risk behaviors. Follow-up visits occurred 3, 6, and 12 months after study exit. The primary outcome measure was cocaine-negative urines. During treatment, the initial effect of CM was apparently dampened by CBT. Posttreatment, there were signs of additive benefits, significant in 3 vs. 12-month contrasts. Former CBT participants were also more likely to acknowledge cocaine use and its effects, and to report more employment. The treatment outcome data have been published. Data on HIV risk behaviors are currently being analyzed. Epstein, D., Hawkins, W., Covi, L., Umbricht, A. and Preston, K.L. Psychology of Addictive Behaviors, 17, pp. 73-82, 2003.

Urinary Elimination of Cocaine Metabolite in Chronic Cocaine Users During Cessation In an earlier study, IRP investigators showed that chronic cocaine use by active illicit users produced a longer plasma half-life than expected based on acute low-dose cocaine studies. In this study urinary excretion patterns of cocaine metabolites such as benzoylecgonine (BE) equivalents from 18 of the same individuals, housed for up to 14 days on a closed research unit, were evaluated. In addition, the investigators evaluated whether creatinine normalization of BE equivalents increased mean detection time and reduced mean within-subject variability. All urine voids (N=953) were individually assayed; BE equivalents were determined semi-quantitatively by immunoassay. Compared to the concentration found in first void after admission, BE equivalents decreased to approximately 33%, 8%, and 4% at 24, 48, and 72 hours, respectively. Mean + SD (range) time to first negative specimen (BE equivalents <300 ng/mL) was 43.6 + 17.1 (16-66) hours. BE equivalents fluctuated considerably across successive specimens; 69% of participants tested positive at least once after testing negative, and the mean time to last positive specimen was 57.5 + 31.6 (11-147) hours after the first specimen. Thus, mean cocaine metabolite detection times were consistent with prolonged elimination, with 63% of participants testing positive longer than the expected 48-hour window of detection after admission to the unit. Mean time to last positive after last use of cocaine, known by self-report only, was approximately 81 + 34 [range 34 - 162] hours. Creatinine normalization, with the cutoff of 300 ng BE equivalents/mg creatinine, increased detection time: mean time to first negative specimen was 54.8 + 20.7 (20-100) hours, and mean time to last positive specimen was 88.4 + 51.0 (35.6-235) hours. Compared to the concentration found in the first void after admission, BE equivalents/creatinine decreased to approximately 56%, 6%, and 5% at 24, 48, and 72 hours. However, creatinine normalization did not reduce the fluctuation of BE equivalents across successive specimens. Thus, creatinine normalized values may be useful when the goal is to maximize the probability or duration of cocaine metabolite detection, but may be less useful in determining whether an individual has used cocaine since a previous specimen collection. Preston, K.L., Epstein, D.H., Cone, E.J., Wtsadik, A.T., Huestis, M.A. and Moolchan, E.T. Journal of Analytical Toxicology, 26, pp. 393-400, 2002.

A Dose-response Study of Cognitive Behavioral Therapy in Cocaine Abusers In order to evaluate the effect of frequency of counseling sessions, IRP scientists studied retention, cocaine use and craving, and psychiatric symptoms of 68 cocaine-dependent outpatients randomly assigned to twice weekly, once weekly, or biweekly sessions in a 12-week treatment program that utilized manual-based, individual cognitive behavioral psychotherapy. All participants were tested and monitored twice a week. Retention was comparable among treatment groups, and improvement was found regardless of counseling frequency. Cocaine use (urine toxicology and self-report), cocaine craving (VAS), and total psychiatric symptoms (SCL-90) decreased by modest but statistically significant (p<0.05) amounts in all treatment groups. Findings suggest that cognitive behavioral therapy is effective in reducing cocaine use even if a less intensive schedule is used. Covi, L., Hess, J.M., Schroeder, J.R. and Preston, K.L. Journal of Substance Abuse Treatment, 23, pp. 191-197, 2002.

Does Cannabis Use Predict Treatment Failure in Methadone-maintenance Patients? It is unclear whether cannabinoid-positive urine specimens in heroin-dependent outpatients predict other drug use or impairments in psychosocial functioning, and whether such outcomes are better predicted by cannabis-use disorders than by cannabis use itself. IRP scientists have completed retrospective analyses of three clinical trials conducted in an urban outpatient methadone clinic. Each trial included a behavioral intervention (contingency management) for cocaine or heroin use during methadone maintenance, lasted 25-29 weeks, and had follow-up evaluations at 3, 6, and 12 months posttreatment. Data were pooled across trials where appropriate. Four hundred and eight polydrug abusers meeting methadone-maintenance criteria were categorized as nonusers, occasional users, or frequent users of cannabis based on thrice-weekly qualitative urinalyses. Cannabis-use disorders were assessed with the Diagnostic Interview Schedule III-R. Outcome measures included proportion of cocaine- and opiate-positive urines and the Addiction Severity Index (at intake and follow-ups). Cannabis use was not associated with retention, use of cocaine or heroin, or any other outcome measure during or after treatment. The analyses employed had a power of .95 to detect an r2 of .11 between cannabis use and heroin or cocaine use; the r2 we detected was less than .03 and nonsignificant. A previous finding that cannabis use predicted lapse to heroin use in heroin-abstinent patients did not replicate in the current sample. However, cannabis-use disorders were weakly associated with psychosocial problems at posttreatment follow-up. Cannabinoid-positive urines need not be a major focus of clinical attention during treatment for opiate dependence, unless patients report symptoms of cannabis-use disorders. Epstein, D.H. and Preston, K.L. Addiction, 98, pp. 269-279, 2003.