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Cigarette smoking is the most preventable cause of death in industrialised countries. 30% of all deaths in smokers in the 35 to 69 years age range are attributed to chronic cigarette smoking; smokers dying in this age cohort lose an average of 23 years of life. Public health campaigns have attempted to reduce initiation of smoking in adolescents and to foster quitting in dependent smokers. The prevalence of smoking has declined in the US to 25% of the population, but this figure has held constant for the last decade. Vaccines against nicotine are a novel concept in the field of smoking cessation research and have not yet reached the stage of clinical testing. Vaccines could reduce smoking behaviour in 3 groups of smokers: (i) current smokers attempting to quit; (ii) former smokers wanting to avoid the possibility of relapse; and (iii) adolescent smokers before they become confirmed smokers. The rationale behind the approach is that nicotine is the pharmacological agent controlling the rate of cigarette smoking, and reducing its rate and extent of uptake into the brain may have therapeutic benefits.

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New technologies utilized for monitoring brain function can be more sensitive in the assessment of desired or undesired pharmacological effects than can clinical examination. Nonetheless, careful case-by-case analysis is required to determine to what extent a change detected with a sensitive imaging modality will have clinical significance. Whereas in some instances the technology may suggest a subclinical condition years before clinical signs develop, in other instances changes seen may be compensated for through system reserves, redundancy, or plasticity. Furthermore, simultaneous application of several assay instruments, including behavioral, electrophysiological, and nuclear medicine approaches, may be appropriate and useful for establishing correlations between changes in specific aspects of brain function and amelioration of a disease (drug abuse disorder) or its sequelae. In the example of ibogaine, a testing strategy was developed to assess human subjects for possible changes in cerebellar function (that were suggested by preclinical findings indicating subtle damage). Thus, subjects may be tested for subclinical alterations during and immediately following a clinical trial. This "harbinger of toxicity" approach would provide clinicians the critical data necessary for appropriate follow-up of subjects as well as the propriety of continuance of the clinical trials within the ibogaine project.

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This article is an exploration of the National Institute on Drug Abuse (NIDA) Technical Review on the role of glutamatergic systems in the development of opiate addiction. The effects of "glutamate antagonist" medications on opioid tolerance and withdrawal are examined. In rodents, mu opioid tolerance can be inhibited by noncompetitive N-methyl D-aspartate (NMDA) receptor antagonists [MK801, dextromethorphan (DM), ketamine, phencyclidine (PCP)], competitive NMDA receptor antagonists (LY274614, NPC17742, LY235959), partial glycine agonists (ACPC), glycine antagonists (ACEA-1328), and nitric oxide synthase (NOS) inhibitors [L-NNA, L-NMMA, methylene blue (MB)]. Similarly, some of the symptoms of opioid withdrawal observed in opioid-dependent rodents also can be inhibited by noncompetitive NMDA receptor antagonists (MK801, DM, ketamine), competitive NMDA receptor antagonists (LY274614), glycine antagonists (felbamate), and NOS inhibitors (L-NNA, L-NMMA, L-NAME, L-NIO, 7-NI, MB). There are some serious toxicological effects associated with the administration of some of the noncompetitive NMDA receptor antagonists in rodent but not in squirrel monkey brain, and some medications induce PCP-like behavioral effects. The medications with the most immediate clinical appeal are those that could be coadministered with methadone to decrease mu opioid tolerance and dependence; they include DM, MB, 7-NI, ACPC, and ACEA-1328.

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Fifty cocaine-dependent patients completed a 2-week double-blind, double-dummy, parallel-group comparison of four dosage levels of diethylpropion and placebo. This clinical trial was designed to evaluate both diethylpropion's ability to attenuate cocaine cue-induced craving and its potential for development as a medication with cocaine-agonist properties. The results indicated that diethylpropion was not superior to placebo and confirmed earlier reports that craving for cocaine diminishes over the course of an inpatient hospitalization. Moreover, the results showed that the cocaine cue-induced craving paradigm employed is effective in stimulating craving for cocaine. Medications that are effective in attenuating this type of "conditioned" craving may have relevance to the breaking of the cycle of relapse and long-term treatment of cocaine dependence. Diethylpropion may not be an appropriate candidate for future medication development because of its lack of obvious therapeutic efficacy and the emergence of a significant number of side effects. However, a cocaine-agonist medication strategy may be appropriate for a subgroup of cocaine-dependent patients with coexisting attention deficit-hyperactivity disorder.

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Drug abuse is of great public concern, and effective treatment strategies for opiate and cocaine dependence are urgently needed for the general addict population as well as for pregnant women and their infants. NIDA's effort to develop new pharmacotherapies as an adjunct to the treatment of opiate addiction has already led to the approval of LAAM and an NDA development program for buprenorphine. The momentum achieved by the new Medications Development Program's success with opiate addiction treatment must now be applied to the development of new treatments for cocaine addiction. With recent advances in neuroscience, imaging techniques, and pharmaceutical technology, the development of medications for significantly improving drug abuse treatment in a variety of directions holds real promise.

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Recent preclinical studies suggest utility for voltage-sensitive calcium channel blockers (VSCCBs) in the treatment of cocaine addiction. The following double-blind placebo-controlled study examined the role of the VSCCB nimodipine in attenuating cocaine craving in 66 recently abstinent cocaine-dependent patients on an inpatient substance abuse treatment unit utilizing an intensive 12-step milieu-oriented psychosocial therapy. While the medication was well tolerated, the dose of nimodipine used in this study (90 mg q.d.) was not superior to placebo in reducing background or cue-induced cocaine craving over the 3 weeks of the study. There was the suggestion that nimodipine might attenuate the severity of some cocaine-induced brain deficits, as detected by evaluation of smooth pursuit eye movement function. A rationale for evaluating higher doses of nimodipine for the treatment of cocaine addiction is presented. As nimodipine might have anticraving and mood-stabilizing properties and cardio- and neuroprotective properties in the face of cocaine intoxication and might possibly even reverse some cocaine-induced brain deficits, further investigation of the role of nimodipine (and other VSCCBs) in cocaine addiction appears an attractive avenue of future medication development.

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NIDA's MDD is faced with the formidable task of identifying, characterizing, and developing new chemical entities to combat substance abuse. The primary challenge is to find one or more medications that will be useful in treating cocaine addiction, withdrawal, and abstinence. In addition, a treatment for cocaine overdose is in progress. Methodological approaches include testing compounds that alter endogenous neurotransmitters and compounds that suppress conditioned cues and stimuli. Compounds that appear efficacious in these tasks and that have a satisfactory safety profile will be studied in humans.

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Assessments of the abuse potential of psychoactive drugs in preclinical and clinical studies are used in regulatory decision making process in the United States under the Controlled Substance Act (CSA) and the Federal Food, Drug, and Cosmetic Act (FD & C Act). Two types of drugs are evaluated in abuse potential studies, those being developed for a therapeutic indication by the pharmaceutical industry and illicitly manufactured 'street drugs' of abuse. Only the former will be considered here. In the case of drugs being pursued for marketing or are amendable to study in human subjects and are of scientific, medical, or regulatory interest, preclinical data may be inadequate for drug scheduling and marketing decisions. Preclinical data assessment can suggest hypotheses which must be validated in clinical studies. Moreover, there are limitations to the feasibility of evaluating certain drugs/dosage forms in preclinical studies. Thus, clinical studies are needed for the following scientific reasons: to validate preclinical hypotheses; to assess the time-course of subjective effects as a function of dose and route of administration; to evaluate the generalizability of drug liking in different human subject populations; and to evaluate the effects of drugs on cognitive and affective processes. Clinical studies are also needed if a claim is made regarding reduced or no abuse potential; and lack of additive or potentiative effects with alcohol.

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The effect of a single or repeated swim stress on in vivo benzodiazepine receptor binding to various brain regions in adrenalectomized and sham-operated (control) mice was assessed using the benzodiazepine receptor antagonist, [3H]Ro15-1788. In sham-operated mice the binding of [3H]Ro15-1788 to benzodiazepine receptors was reduced in the hippocampus and hypothalamus (single or repeated stress) and cerebral cortex (repeated swim stress) compared to non-stressed mice. In contrast, no alterations in [3H]Ro15-1788 binding were observed in any brain region in adrenalectomized mice after either single or repeated swim stress. These data suggest that an intact hypothalamic-pituitary-adrenal axis is required for the stress-induced decrease in benzodiazepine receptor occupancy measured using the in vivo binding method.

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The effects of repeated swim stress on brain benzodiazepine receptors were examined in the mouse using both an in vivo and in vitro binding method. Specific in vivo binding of [3H]Ro15-1788 to benzodiazepine receptors was decreased in the hippocampus, cerebral cortex, hypothalamus, midbrain and striatum after repeated swim stress (7 consecutive days of daily swim stress) when compared to nonstressed mice. In vivo benzodiazepine receptor binding was unaltered after repeated swim stress in the cerebellum and pons medulla. The stress-induced reduction in in vivo benzodiazepine receptor binding did not appear to be due to altered cerebral blood flow or to an alteration in benzodiazepine metabolism or biodistribution because there was no difference in [14C]iodoantipyrine distribution or whole brain concentrations of clonazepam after repeated swim stress. Saturation binding experiments revealed a change in both apparent maximal binding capacity and affinity after repeated swim stress. Moreover, a reduction in clonazepam's anticonvulsant potency was also observed after repeated swim stress [an increase in the ED50 dose for protection against pentylenetetrazol-induced seizures], although there was no difference in pentylenetetrazol-induced seizure threshold between the two groups. In contrast to the results obtained in vivo, no change in benzodiazepine receptor binding kinetics was observed using the in vitro binding method. These data suggest that environmental stress can alter the binding parameters of the benzodiazepine receptor and that the in vivo and in vitro binding methods can yield substantially different results.

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Laboratory animals are used as models for humans in toxicity studies. This use is based on the assumption that extrapolation of biological data from animals to humans is valid. Three methods of extrapolation are considered: the use of body mass equivalence, caloric scaling across species, and the use of the surface area equivalence. Allometry, defined as the study of size and its consequences, is considered. There is still controversy whether there is an allometric relationship for energy metabolism. Allometry offers, among others, the concept that not all of the mass of the animal is equally involved in metabolism. In recent years the principles of pharmacokinetics have been applied to interspecies scaling; pharmacokinetic short-term studies can be used to determine whether allometric scaling is justified. Considerations, however, should be given to (pharmacokinetic) differences in the same species and to species variability. It would be useful to develop a set of criteria for deciding when the pharmacokinetic model is needed and when simpler models will suffice.

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The specific binding of [3H]GBR-12935 to membranes prepared from human caudate nucleus is saturable (Bmax 1.36 +/- 0.18 pmol/mg protein), sodium dependent and of high affinity (KD 2.34 +/- 0.18 nM). Freezing of tissue from rat brain, or refrigeration followed by freezing, results in a small but significant (less than or equal to 20%) decrease in specific [3H]GBR-12935 binding when compared to the binding observed in fresh (nonfrozen) tissue, and this decrease may account, in part, for the differences in specific binding between rat and human brain membranes. Despite small differences in binding site density between fresh and frozen tissue there is a good correlation (r = 0.98; p less than 0.01) between the potencies of a series of drugs in displacing specific [3H]GBR-12935 binding to human caudate membranes and rat striatum as well as in inhibiting dopamine uptake in rat striatal synaptosomes (r = 0.96; p less than 0.01). The specific binding of [3H]GBR-12935 to membranes prepared from the caudate nuclei of patients with Parkinson's disease is decreased compared to membranes prepared from age- and sex-matched controls. These data suggest that [3H]GBR-12935 binds in a sodium-dependent fashion to the dopamine transport complex in human brain and that specific binding is decreased by a pathological degeneration of dopaminergic neurons to the caudate nucleus.

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The psychoactive cannabinoids, delta 9-tetrahydrocannabinol (delta 9-THC), delta 8-tetrahydrocannabinol (delta 8-THC), 11-hydroxy-delta 9-tetrahydrocannabinol (11-OH-delta 9-THC) and 9-nor-9 beta-hydroxyhexahydrocannabinol (beta-HHC), as well as the nonpsychoactive cannabinoids, cannabinol (CBN), cannabidiol (CBD), abnormal CBD, delta 8-THC methyl ether (1-OCH3-delta 8-THC) and 9-nor-9 alpha-hydroxyhexahydrocannabinol (alpha-HHC), were used to assess the role of cholinergic mechanisms in the different behavioral actions of these cannabinoids. Their effects on mouse brain choline and acetylcholine (ACh) levels and on ACh turnover were determined in cortex, hippocampus, striatum, midbrain and medulla-pons. delta 9-THC (30 mg/kg) caused a significant elevation of ACh in all five brain areas. 11-OH-delta 9-THC (30 mg/kg) increased ACh in hippocampus, striatum and midbrain. delta 8-THC (30 mg/kg) increased ACh in cortex and hippocampus. delta 9-THC and 11-OH-delta 9-THC increased choline in midbrain and cortex, whereas beta-HHC increased choline in all areas, except hippocampus, at a dose of 30 mg/kg. Also at this dose, delta 9-THC, 11-OH-delta 9-THC, delta 8-THC and beta-HHC decreased ACh turnover in the hippocampus, as did CBN (10-30 mg/kg), 1-OCH3-delta 8-THC (100 mg/kg) and alpha-HHC (100 mg/kg). ACh turnover was also decreased in midbrain by 1-OCH3-delta 8-THC and in the striatum by alpha-HHC. Thus, the most consistent effects of cannabinoids, both psychotomimetic and nonpsychotomimetic, were to increase ACh and decrease ACh turnover in the hippocampus.(ABSTRACT TRUNCATED AT 250 WORDS)

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High-affinity and saturable binding sites for the diphenyl-substituted piperazine derivative [3H]GBR-12935 have been characterized in crude synaptosomal membranes prepared from rat brain. The specific binding of [3H]GBR-12935 is sodium-dependent and is unevenly distributed among various brain regions, with the highest concentration of binding sites being found in the corpus striatum and nucleus accumbens. Sodium-dependent [3H]GBR-12935 binding in all other brain areas was 10% or less of the binding found in the striatum. The affinity of [3H]GBR-12935 for binding sites in the striatum is increased in the presence of Na+ but other cations, including K+, Ca2+, or Mg2+, inhibit specific binding. There is an excellent correlation (r = 0.96, p less than 0.01) between the potencies of a series of drugs in inhibiting [3H]GBR-12935 binding to striatal membranes and their potencies in inhibiting [3H]3,4-dihydroxyphenylethylamine ([3H]dopamine) uptake in synaptosomes. Agonists and antagonists of other neurotransmitter receptor or drug recognition sites have little or no effect on specific [3H]GBR-12935 binding to striatal membranes. In addition, prior intracerebroventricular administration of 6-hydroxydopamine results in a decrease in the number of specific [3H]GBR-12935 binding sites in the striatum. These data indicate that [3H]GBR-12935 is a selective radioligand of the presynaptic dopamine transport complex in brain.

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The intracerebroventricular injection of Ba++ and Sr++ produced naloxone and atropine reversible antinociception as measured by the mouse tail-flick test. Naloxone antagonized the antinociception produced by Ba++ more effectively than atropine (pA2 5.9 vs. 7.0, respectively). Naloxone was less efficient than atropine in blocking lethality. Together these results suggest different mechanisms involved in the production of antinociception and lethality by these ions.

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