Why does the rapid delivery of drugs to the brain promote addiction?

Particle size distribution of nicotine in mainstream smoke from 2R4F, Marlboro Medium, and Quest1 cigarettes under different puffing regimens

Nicotine's dose and rate of delivery to the brain play an important role in its addiction and cardiovascular effects. Nicotine is mainly present in the particulate phase of cigarette smoke, and since particle size distribution controls the deposition behavior of particles in the respiratory tract, changes in the particle size distribution can produce variations in its regional and total dose to the lung. These variations can change its absorption rate and delivery to the brain. The particle size distribution of mainstream smoke (MS) varies with changes in puffing regimen and cigarette design and composition. This study examined nicotine in different particle size fractions of MS generated from 2R4F, Marlboro Medium, and Quest1 cigarettes using 3 puffing regimens: (1) FTC-like puff, 35 ml over 2 s; (2) short puff, 50 ml over 2 s; and (3) long puff, 100 ml over 10 s. MS was generated in a chamber at 37 degrees C and >95% relative humidity (RH), and size-segregated particles were collected using RJR cascade impactors. Particle size distribution was determined by spectrophotometry. Nicotine was analyzed using gas chromatography and mass spectrometry. Results showed that nicotine speciates in larger particles (1.1-1.9 microm diameter) under the long puffing regimen and in smaller particles (0.4-1.1 microm diameter) under the short puffing regimen, while mass median aerodynamic diameter of mainstream smoke particles was found to be approximately constant (0.9-1.0 microm) for the three puffing regimens. Overall, changes in puffing regimen have a significant effect on particle size distribution of nicotine and its deposited dose.

Smoking produces rapid rise of [11C]nicotine in human brain

RATIONALE

Variation in the rate at which drugs reach the brain influences many different drug effects and is also thought to influence liability to addiction. For example, rapid intravenous delivery of cocaine and nicotine is more effective in producing hedonic effects, tolerance, psychomotor sensitization, and in inducing gene expression. Smoking is thought to result in an especially rapid rate of rise of nicotine in the brain, but whether this is true has never been adequately addressed. Thus, in this study, we sought to determine the true rate of rise of smoked nicotine in human brain and compare this with previous intravenous nicotine delivery.

METHODS

Positron emission tomography scans of lung and brain regions and arterial and venous blood curves were obtained in human subjects after single puffs from cigarettes formulated with [(11)C]nicotine.

RESULTS

The rise of nicotine concentration following a single puff was rapid, reaching more than 50% of maximum brain levels within 15 s of bolus arrival in the brain in most subjects. This rate of rise was considerably faster than that seen in previous studies using intravenous administration.

CONCLUSIONS

Uptake in human brain from a single inhalation was sufficiently rapid that it is plausible that fast rate-of-rise contributes to nicotine dependence in smokers.

Kicking the habit: the neural basis of ingrained behaviors in cocaine addiction

Cocaine addiction is a complex and multifaceted process encompassing a number of forms of behavioral plasticity. The process of acquiring and consuming drugs can be sufficiently risky and complicated that the casual drug user may choose not to act on every motivation to use drugs. The repetition of drug seeking and taking, however, often results in the gradual development of drug craving and compulsive drug seeking associated with addiction. Moreover, the complex sets of behaviors associated with drug addiction can become ingrained to such an extent that, when activated by drug-associated stimuli or exposure to the drug itself, the processes underlying drug seeking and taking are automatically engaged and very difficult to suppress. Here, we examine the hypothesis that aspects of cocaine seeking and taking become ingrained with repetition, thereby contributing to continued drug use despite a conscious desire to abstain. We also review emerging evidence indicating that neuronal circuits including the dorsolateral striatum play a particularly important role in the habitual aspects of drug seeking and taking.

Smoking, nicotine and neuropsychiatric disorders

Tobacco smoking is an extremely addictive and harmful form of nicotine (NIC) consumption, but unfortunately also the most prevalent. Although disproportionately high frequencies of smoking and its health consequences among psychiatric patients are widely known, the neurobiological background of this epidemiological association is still obscure. The diverse neuroactive effects of NIC and some other major tobacco smoke constituents in the central nervous system may underlie this association. This present paper summarizes the pharmacology of NIC and its receptors (nAChR) based on a systematic review of the literature. The role of the brain's reward system(s) in NIC addiction and the results of functional and structural neuroimaging studies on smoking-related states and behaviors (i.e. dependence, craving, withdrawal) are also discussed. In addition, the epidemiological, neurobiological, and genetic aspects of smoking in several specific neuropsychiatric disorders are reviewed and the clinical relevance of smoking in these disease states addressed.

Effect of rate of delivery of intravenous cocaine on self-administration in rats

Many studies of drug self-administration in primates have shown that faster infusions of a drug are more reinforcing than slower infusions. Similar effects have not been shown in rats. We assessed the influence of delivery rate by allowing rats to choose between the same doses of intravenous cocaine delivered over two different infusion speeds. Rats were trained in chambers containing two nose-poke response devices. In Experiment 1, responses in one nose-poke delivered 0.3 mg/kg/injection of cocaine over 10 s, and responses in the other delivered the same dose over 100 s. In Experiment 2, the same procedure was used, but with 1.0 mg/kg/injection dose delivered over 1.7 versus 100 s. During acquisition, most rats preferred the faster infusion. When the delivery rates associated with the nose pokes were reversed, rats trained with 0.3 mg/kg/injection failed to switch nose-poke preference, but half the rats trained with 1.0 mg/kg/injection did switch. In Experiment 3, the choice was between 1 mg/kg cocaine delivered over 1.7 s and no reinforcement. Here, rats quickly learned to respond in the nose-poke associated with cocaine and quickly switched their choice during reversal. In Experiment 4, two groups of rats were allowed to choose between food delivered with a delay of 1 versus 5 s or 1 versus 10 s, respectively. Rats preferred the shorter delay during initial training. In reversal, some rats in the 1 vs 5 s group failed to reverse, while all the rats in the 1 vs 10 s group reversed. These results show that faster infusions of cocaine are clearly more reinforcing during acquisition, but delivery rate may not be as important to the maintenance of self-administration once it has been established. The results with food suggest that these findings represent general principles of behavior and are not unique to drug self-administration.

Pattern of intake and drug craving predict the development of cocaine addiction-like behavior in rats

BACKGROUND

Clinical observations suggest that cocaine addiction often emerges with new patterns of use. Whether these changes are a cause of addiction or its consequence is unknown. We investigated whether the development of an addiction-like behavior in the rat is associated with the pattern of cocaine intake and with cocaine craving, a major feature of cocaine addiction.

METHODS

To determine whether changes in the pattern of cocaine use and enhanced craving precede or parallel the onset of addiction, we used a rat addiction model that incorporates core features of human addiction. For this purpose, the pattern of inter-infusion intervals (a measure of pattern of cocaine intake), sensitivity to cocaine-induced reinstatement (a measure of cocaine craving), and addiction-like behaviour were assessed over several months of intravenous cocaine self-administration.

RESULTS

We found that, even at early stages of cocaine self-administration, both the pattern of cocaine intake and the intensity of drug-induced reinstatement predict the severity of cocaine use, measured after 75 days of self-administration.

CONCLUSIONS

Our results identify key predictors of cocaine addiction-intensified pattern of drug use and high drug-induced craving-that may help in the identification of subjects at risk for subsequent development of severe cocaine addiction.

Maturation of coordinated immediate early gene expression by cocaine during adolescence

Adolescence may be a critical period for drug addiction. Young adolescent male rats have greater locomotor responses than adults after acute low dose cocaine administration. Further, repeated cocaine administration produces as much or more conditioned place preference but reduced locomotor sensitization in adolescents compared to adults. Acute activation of neurons by cocaine induces long-term changes in behavior by activating transcriptional complexes. The purpose of the present study was to correlate cocaine-induced locomotor activity with neuronal activation in subregions of the striatum and cortex by acute cocaine in young adolescent (postnatal (PN) 28) and adult (PN 65) male rats by measuring the induction of the plasticity-associated immediate early genes (IEGs) c-fos and zif268 using in situ hybridization. Animals were treated with saline, low (10 mg/kg), or high (40 mg/kg) dose cocaine in locomotor activity chambers and killed 30 min later. Low dose cocaine induced more locomotor activity and striatal c-fos expression in adolescents than adults whereas high dose cocaine induced more locomotor activity, striatal c-fos, and striatal zif268 expression in adults. Locomotor activity correlated with the expression of both genes in adults but correlated with striatal c-fos only in adolescents. Finally, there was a significant correlation between the expression of c-fos and zif268 in the adult striatum but not in adolescents. Our results suggest that the coordinated expression of transcription factors by cocaine continues to develop during adolescence. The immature regulation of transcription factors by cocaine could explain why adolescents show unique sensitivity to specific long-term behavioral alterations following cocaine treatment.

Nicotine and Parkinson's disease: implications for therapy

Accumulating evidence suggests that nicotine, a drug that stimulates nicotinic acetylcholine receptors, may be of therapeutic value in Parkinson's disease. Beneficial effects may be several-fold. One of these is a protective action against nigrostriatal damage. This possibility stems from the results of epidemiological studies that consistently demonstrate an inverse correlation between tobacco use and Parkinson's disease. This reduced incidence of Parkinson's disease has been attributed to the nicotine in tobacco products, at least in part, based on experimental work showing a protective effect of nicotine against toxic insults. Second, several studies suggest a symptomatic effect of nicotine in Parkinson's disease, although effects are small and somewhat variable. Third, recent data in nonhuman primates show that nicotine attenuates levodopa-induced dyskinesias, a debilitating side effect that develops in the majority of patients on levodopa therapy. Collectively, these observations suggest that nicotine or CNS selective nicotinic receptor ligands hold promise for Parkinson's disease therapy to reduce disease progression, improve symptoms, and/or decrease levodopa-induced dyskinesias.

Subtype-selective GABAA receptor mimetics--novel antihyperalgesic agents?

Agonists at the benzodiazepine-binding site of ionotropic gamma-aminobutyric acid (GABA(A)) receptors are in clinical use as hypnotics, anxiolytics, and anticonvulsants since the early 1960. Analgesic effects of classical benzodiazepines have occasionally been reported in certain subgroups of patients suffering from chronic pain or after spinal delivery through intrathecal catheters. However, these drugs are generally not considered as analgesics but should in fact be avoided in patients with chronic pain. Recent evidence from genetically modified mice now indicates that agents targeting only a subset of benzodiazepine (GABA(A)) receptors should provide pronounced antihyperalgesic activity against inflammatory and neuropathic pain. Several such compounds have been developed recently, which exhibit significant antihyperalgesia in mice and rats and appear to be devoid of the typical side-effects of classical benzodiazepines.

Dual- and triple-acting agents for treating core and co-morbid symptoms of major depression: novel concepts, new drugs

The past decade of efforts to find improved treatment for major depression has been dominated by genome-driven programs of rational drug discovery directed toward highly selective ligands for nonmonoaminergic agents. Selective drugs may prove beneficial for specific symptoms, for certain patient subpopulations, or both. However, network analyses of the brain and its dysfunction suggest that agents with multiple and complementary modes of action are more likely to show broad-based efficacy against core and comorbid symptoms of depression. Strategies for improved multitarget exploitation of monoaminergic mechanisms include triple inhibitors of dopamine, serotonin (5-HT) and noradrenaline reuptake, and drugs interfering with feedback actions of monoamines at inhibitory 5-HT(1A), 5-HT(1B) and possibly 5-HT(5A) and 5-HT(7) receptors. Specific subsets of postsynaptic 5-HT receptors mediating antidepressant actions are under study (e.g., 5-HT(4) and 5-HT(6)). Association of a clinically characterized antidepressant mechanism with a nonmonoaminergic component of activity is an attractive strategy. For example, agomelatine (a melatonin agonist/5-HT(2C) antagonist) has clinically proven activity in major depression. Dual neurokinin(1) antagonists/5-HT reuptake inhibitors (SRIs) and melanocortin(4) antagonists/SRIs should display advantages over their selective counterparts, and histamine H(3) antagonists/SRIs, GABA(B) antagonists/SRIs, glutamatergic/SRIs, and cholinergic agents/SRIs may counter the compromised cognitive function of depression. Finally, drugs that suppress 5-HT reuptake and blunt hypothalamo-pituitary-adrenocorticotrophic axis overdrive, or that act at intracellular proteins such as GSK-3beta, may abrogate the negative effects of chronic stress on mood and neuronal integrity. This review discusses the discovery and development of dual- and triple-acting antidepressants, focusing on novel concepts and new drugs disclosed over the last 2 to 3 years.

[Differential therapeutic aspects of analgesia with oral sustained-release strong opioids: application intervals, metabolism and immunosuppression]

The oral "around-the clock" administration of sustained-release strong opioids has been recommended for the long-term treatment of patients suffering from chronic severe pain. At present a plethora of products are available in Germany. Modern galenics even allow for only once-daily oral application without clinically relevant negative chronobiological interference. This application scheme has been shown to improve compliance and sleep quality, factors that influence treatment outcome. Randomized controlled studies revealed no relevant differences between the different strong opioids with respect to efficacy and tolerability. However, hydromorphone and oxycodone appear to be advantageous over morphine due to a lack of immunosuppression. Hydromorphone has the additional benefit of a lower risk of intoxication by accumulation of active metabolites in patients with decreased renal function. As a result, although morphine has been regarded as the standard for the treatment of chronic severe pain, hydromorphone and oxycodone may be better and safer alternatives for certain patient groups (e.g. older age, multimorbidity, cancer).

The rate of intravenous cocaine or amphetamine delivery does not influence drug-taking and drug-seeking behavior in rats

We studied the influence of rate of intravenous infusion of cocaine or amphetamine on drug-taking and seeking behavior. First, drug-naive rats were tested for acquisition of self-administration of increasing doses of amphetamine or cocaine infused over 5 or 100 s. Second, self-administration of cocaine or amphetamine infused over 5-100 s was assessed on fixed or progressive-ratio (PR) reinforcement schedules. Finally, the ability of a single 5 or 100 s amphetamine or cocaine infusion to reinstate extinguished drug seeking was assessed. Although slower infusion rates produced a small effect on drug taking under continuous-reinforcement conditions, infusion rate did not alter drug taking on intermittent or PR reinforcement schedules, or the ability of cocaine or amphetamine to reinstate drug seeking. Taken together, our results suggest that variation in drug delivery rate over a range that we previously found alters the induction of behavioral sensitization, gene-expression and striatal dopamine activity, does not markedly alter drug-taking or seeking behavior.

Effect of opium addiction on new and traditional cardiovascular risk factors: do duration of addiction and route of administration matter?

Background

There is a belief among some society that opium has a number of beneficial effects on cardiovascular disease. The aim of the present investigation as a cross-sectional study was to assess this hypothesis. Several biochemical factors (Fasting blood sugar, Cholesterol, Triglyceride, LDL-Cholesterol, HDL-Cholesterol, HbA1C, CRP, Fibrinogen, Factor VII, SGOT, SGPT, Lpa, apo A and apo B were evaluated in opium-addicted men (case) against non opium-addicted men(control). Three hundred and sixty opium-addicted men were divided into three groups according to the route of administration (Orally, Vafour and Sikh-Sang) and each group was divided into four subgroups according to the duration of addiction (5 months, 1 year, 2 years and 5 years). Blood morphine concentration was measured by ELISA method.

Results

The results show that morphine concentration was significantly higher in orally administration. In all routes, there was a direct correlation between blood morphine concentration and period of addiction. Regardless to the period and route of administration, the level of HbA1C, CRP, factor VII, Fibrinogen, apo B, Lpa, SGOT, and SGPT were significantly higher in the case subjects as compared with controls and HDL-Cholesterol and apo a were significantly lower in the case subjects.

Conclusion

This study demonstrated the deleterious effects of opium on some traditional and new cardiovascular disease risk factors. These deleterious effects are related to the period of addiction and their levels are significantly increased after 2 years of addiction. Route of administration impresses cardiovascular risk factors and "Sikh-Sang" showed the worst effect.

Repeated intravenous amphetamine exposure: rapid and persistent sensitization of 50-kHz ultrasonic trill calls in rats

Short 50-kilohertz (kHz) range frequency-modulated ultrasonic vocalizations (USVs) produced by rats and mice are unconditionally elicited by drugs of abuse or electrical stimulation that increase dopamine activity in the nucleus accumbens, and it has been suggested that they reflect "positive affect" or incentive motivational states associated with appetitive behavior. The repeated administration of amphetamine is known to not only produce "psychomotor" sensitization, but also to facilitate a number of appetitive behaviors, including conditioned drug pursuit behavior. We were interested, therefore, in whether amphetamine-induced 50-kHz USVs would also increase with repeated drug exposure. USV recordings were made during 5-min sessions immediately after a saline infusion, and again 4-5h later after 1.0mg/kg intravenous amphetamine exposure. These sessions took place every other day over a 5-day period. A challenge dose of 1.0mg/kg amphetamine was administered 2 weeks later to determine whether sensitization would persist. The initial amphetamine infusion increased 50-kHz USVs relative to the saline infusion. This effect was enhanced over trials and during the amphetamine challenge 2 weeks later. Classification of 50-kHz range call types revealed that complex frequency-modulated trill calls were sensitized by amphetamine, but not flat 50-kHz calls. It is possible that 50-kHz USV recordings could provide a potentially valuable behavioral measure of sensitization linked to enhanced incentive salience and increased tendency to self-administer drugs of abuse.

Nicotine sensitization in adult male and female rats quinpirole-primed as neonates

RATIONALE

Increases in dopamine D2-like receptor function are common in several psychological disorders that demonstrate a four to five fold increase in nicotine abuse compared to the general population.

OBJECTIVE

The objective of this study was to analyze the interaction of sex differences and sensitization to nicotine in rats D2 receptor primed as neonates.

MATERIALS AND METHODS

A total of 32 male and 32 female Sprague-Dawley rats derived from eight litters were ontogenetically treated with quinpirole (1 mg/kg) or saline from postnatal days (P) 1-21 and raised to adulthood. At P60, all animals were given an acute injection of quinpirole HCl (100 microg/kg) and yawns were counted for 1 h. Yawning has been shown to be a behavioral event mediated by D2-like receptors. Beginning on P61-65, animals were habituated to a locomotor arena and subsequently administered either nicotine (0.5 mg/kg free base) or saline (intraperitoneal) every second day for 3 weeks. Approximately 15 min after each injection, animals were placed into the arena and horizontal activity and vertical rears were recorded.

RESULTS

A robust increase of yawning was observed at P60 in D2 primed as compared to saline controls. Priming of D2-like receptors increased the locomotor response to nicotine in horizontal activity in both males and females, but females demonstrated a more robust hypoactive locomotor response to initial nicotine treatment when compared to saline-treated females. Nicotine also produced a significant decrease of vertical rearing in both males and females.

CONCLUSIONS

It appears that D2 receptor priming enhances sensitization to nicotine in adult rats, and females may be more behaviorally sensitive to nicotine than males.

Methamphetamine suppression and route of administration: precursor regulation impacts on snorting, smoking, swallowing and injecting

AIMS

The route of drug administration affects risk for dependence and medical harm. This study examines whether routes used by methamphetamine treatment participants were impacted by a major drug suppression policy-federal regulation of the methamphetamine precursor chemicals ephedrine and pseudoephedrine.

DESIGN

Autoregressive-integrated moving average (ARIMA) intervention time-series analysis.

SETTING

California (1992-2004).

INTERVENTIONS

Ephedrine single-ingredient products regulation, implemented August 1995; ephedrine with other active medicinal ingredients regulation, implemented October 1996; pseudoephedrine products regulation, implemented October 1997.

MEASUREMENTS

Monthly counts of non-coerced methamphetamine treatment admissions reporting snorting, smoking, swallowing or injecting. Findings After rising sharply, snorting, smoking, swallowing and injecting admissions dropped 50%, 43%, 26% and 26%, respectively, when the 1995 regulation was implemented. Snorting also dropped 38% at the time of the 1997 regulation. Snorting, swallowing and injecting remained at lower levels to the end of the study period. Smoking resurged (40%) at the time of the 1996 regulation and continued rising.

CONCLUSIONS

Precursor regulation was associated with changes in the administration of methamphetamine. Injecting, the route with the greatest health risk, entered a long-term reduction. So, too, did snorting and swallowing, two routes with lower risk for dependence. In contrast, smoking, which has a relatively high risk for dependence, dropped, then rebounded and entered a long-term rise. A possible explanation is that injecting, snorting and swallowing were largely linked with US domestic methamphetamine production, which has yet to recover from the regulations. While Mexican production, which was impacted only temporarily by the regulations and has supplanted domestic production, may have helped to diffuse smoking, a route with which it is historically correlated.

Bioavailability of (+)-methamphetamine in the pigeon following an intramuscular dose

Pigeons are used frequently as subjects in behavioral pharmacology research. An advantage of the pigeon is an exceedingly vascular breast muscle, which is easily accessible for injections. The purpose of these studies was to provide a profile of the pharmacokinetics of (+)-methamphetamine (METH) and (+)-amphetamine (AMP), a pharmacologically active metabolite, in pigeons (n=6) after intramuscular (i.m.) and intravenous (i.v.) dosing (0.8 mg/kg). LC-MS/MS analysis was used to determine serum concentrations of METH and AMP. A modified crossover design was used to determine the bioavailability, time to maximum concentration, total clearance, the volume of distribution, the maximal concentration, the area under the concentration-time curve (AUC), and terminal elimination half-life for METH. The route of administration did not significantly affect these pharmacokinetic parameters. The time to maximum concentration for METH and AMP following i.m. administration was 0.3 h. Maximum AMP serum concentrations were achieved in 2 h, irrespective of the route of administration, and these concentrations remained essentially constant for an additional 6 h. The metabolism of METH to AMP was not affected by the route of administration, and the molar ratio AMP to METH AUC values were the same (i.v.=0.57; i.m.=0.41). These results show that METH pharmacokinetics after i.m. administration in the pigeon are similar to i.v. administration. Thus i.m. is a reasonable route of administration for METH behavioral assays in the pigeon if sufficient time for absorption is given following the dose, and the behavioral endpoint is not dependent on the rapid input of METH following an i.v. dose.

The rate of intravenous cocaine administration alters c-fos mRNA expression and the temporal dynamics of dopamine, but not glutamate, overflow in the striatum

The rapid entry of drugs into the brain is thought to increase the propensity for addiction. The mechanisms that underlie this effect are not known, but variation in the rate of intravenous cocaine delivery does influence its ability to induce immediate early gene expression (IEG) in the striatum, and to produce psychomotor sensitization. Both IEG induction and psychomotor sensitization are dependent upon dopamine and glutamate neurotransmission within the striatum. We hypothesized, therefore, that varying the rate of intravenous cocaine delivery might influence dopamine and/or glutamate overflow in the striatum. To test this we used microdialysis coupled to on-line capillary electrophoresis and laser-induced fluorescence, which allows for very rapid sampling, to compare the effects of a rapid (5 s) versus a slow (100 s) intravenous cocaine infusion on extracellular dopamine and glutamate levels in the striatum of freely moving rats. An acute injection of cocaine had no effect on extracellular glutamate, at either rate tested. In contrast, although peak levels of dopamine were unaffected by infusion rate, dopamine levels increased more rapidly when cocaine was administered over 5 versus 100 s. Moreover, c-fos mRNA expression in the region of the striatum sampled was greater when cocaine was administered rapidly than when given slowly. These data suggest that small differences in the temporal dynamics of dopamine neurotransmission may have a large effect on the subsequent induction of intracellular signalling cascades that lead to immediate early gene expression, and in this way influence the ability of cocaine to produce long-lasting changes in brain and behavior.

Cannabinoids in the management of difficult to treat pain

This article reviews recent research on cannabinoid analgesia via the endocannabinoid system and non-receptor mechanisms, as well as randomized clinical trials employing cannabinoids in pain treatment. Tetrahydrocannabinol (THC, Marinol((R))) and nabilone (Cesamet((R))) are currently approved in the United States and other countries, but not for pain indications. Other synthetic cannabinoids, such as ajulemic acid, are in development. Crude herbal cannabis remains illegal in most jurisdictions but is also under investigation. Sativex((R)), a cannabis derived oromucosal spray containing equal proportions of THC (partial CB(1) receptor agonist ) and cannabidiol (CBD, a non-euphoriant, anti-inflammatory analgesic with CB(1) receptor antagonist and endocannabinoid modulating effects) was approved in Canada in 2005 for treatment of central neuropathic pain in multiple sclerosis, and in 2007 for intractable cancer pain. Numerous randomized clinical trials have demonstrated safety and efficacy for Sativex in central and peripheral neuropathic pain, rheumatoid arthritis and cancer pain. An Investigational New Drug application to conduct advanced clinical trials for cancer pain was approved by the US FDA in January 2006. Cannabinoid analgesics have generally been well tolerated in clinical trials with acceptable adverse event profiles. Their adjunctive addition to the pharmacological armamentarium for treatment of pain shows great promise.

Bis-azaaromatic quaternary ammonium salts as antagonists at nicotinic receptors mediating nicotine-evoked dopamine release: An investigation of binding conformation

A series of conformationally restricted bis-azaaromatic quaternary ammonium salts (3 and 4) have been designed and synthesized in order to investigate the possible binding conformations of N,N'-dodecane-1,12-diyl-bis-3-picolinium dibromide (bPiDDB; 2), a compound which potently inhibits neuronal nicotinic acetylcholine receptors (nAChRs) mediating nicotine-evoked dopamine release. The preliminary structure-activity relationships of these new analogues suggest that bPiDDB binds in an extended conformation at the nAChR binding site, and that flexibility of the linker may be important for its high potency in inhibiting nAChRs mediating nicotine-evoked dopamine release.

How to make a rat addicted to cocaine

Procedures have been developed which provide extremely stable patterns of cocaine self-administration in rats and these have been useful in lesion and drug pretreatment studies aimed at understanding the neurobiology of cocaine reinforcement. The issue now is whether studying the neurobiology of reinforcement is the same as studying the neurobiology of addiction. If the goal is to understand a progressive and deteriorating disorder, then the self-administration procedures should model specific aspects of the progressive stages of the addiction process. Here we review theoretical strategies for modeling the addiction process and present data from a series of experiments from our laboratory showing conditions which produce a progressive change in the motivation to self-administer cocaine in rats. This phenomenon is revealed by an escalation in breakpoints on a progressive ratio schedule. The effect, which is robust and persistent, depends on dose and speed of injection. Interestingly, high drug intake can retard the development of this effect, which we argue indicates that the addiction process has a developmental sequence. Finally, we suggest that specific parameters (dose, price and availability) can be used to examine the transition from recreational use to binge-like intake.

Do formulation differences alter abuse liability of methylphenidate? A placebo-controlled, randomized, double-blind, crossover study in recreational drug users

The primary objective of this study was to determine if the abuse liability of methylphenidate is governed by formulation differences that affect rates of drug delivery. In this double-blind, placebo-controlled, randomized, crossover study, subjects with a history of recreational drug use received single oral doses of placebo, 60 mg of immediate-release methylphenidate (IR) and 108 mg of extended-release methylphenidate (osmotic release oral system [OROS]). Over 24 hours after dosing, blood was collected to determine plasma concentrations of methylphenidate, and subjects completed subjective assessments of abuse liability (Addiction Research Center Inventory, Drug Rating Questionnaire-Subject, and Subjective Drug Value). The abuse-related subjective effects of IR and OROS methylphenidate were statistically significantly different from placebo, confirming the overall validity of the study. Although a higher dose of OROS methylphenidate was used compared with IR methylphenidate (108 mg vs 60 mg), subjective effects were consistently lower for OROS compared with IR methylphenidate (statistically significant for 3 of 6 measures of positive effects), particularly at early time points. In general, pharmacokinetic-pharmacodynamic parameters were correlated from a poor to modest degree, with greater correlations observed for IR methylphenidate. In addition, a post hoc "qualification" method was developed, which demonstrated that pharmacological qualification might improve the assessment of subjective effects. Although requiring epidemiological confirmation, the results suggest that OROS methylphenidate, with its characteristic slow ascending plasma concentration profile, may have lower abuse potential. This conclusion is reflected by lower subjective responses during early hours as compared with the IR formulation with its rapid drug delivery and accompanying greater subjective effects.

Long-term effects of prior cocaine exposure on Morris water maze performance

Cocaine addiction is associated with long-term cognitive alterations including deficits on tests of declarative/spatial learning and memory. To determine the extent to which cocaine exposure plays a causative role in these deficits, adult male Long-Evans rats were given daily injections of cocaine (30 mg/kg/day x 14 days) or saline vehicle. Three months later, rats were trained for 6 sessions on a Morris water maze protocol adapted from Gallagher, Burwell, and Burchinal [Gallagher, M., Burwell, R., & Burchinal, M. (1993). Severity of spatial learning impairment in aging: development of a learning index for performance in the Morris water maze. Behavioral Neuroscience, 107, 618-626]. Rats given prior cocaine exposure performed similarly to controls on training trials, but searched farther from the platform location on probe trials interpolated throughout the training sessions and showed increased thigmotaxis. The results demonstrate that a regimen of cocaine exposure can impair Morris water maze performance as long as 3 months after exposure. Although the impairments were not consistent with major deficits in spatial learning and memory, they may have resulted from cocaine-induced increases in stress responsiveness and/or anxiety. Increased stress and anxiety would be expected to increase thigmotaxis as well as cause impairments in searching for the platform location, possibly through actions on ventral striatal dopamine signaling.

Interest for delivery of cocaethylene in a sustained release emulsion vs saline evaluated on behavioral sensitization in naive and cocaine-sensitized mice

RATIONALE

Repeated administration of psychostimulant elicits behavioral sensitization, characterized by an augmented locomotor response to a subsequent challenge injection. This sensitization is paralleled by neural adaptations. Evidences suggest that the rate at which drugs of abuse are delivered to the brain play a key role in this plasticity. Cocaethylene is a pharmacologically active homolog of cocaine, known to have a pharmacokinetic profile different to that of cocaine.

OBJECTIVES

Utilizing locomotor sensitization, we evaluated the consequences of the administration of cocaethylene in a rapid- and slow-onset formulation, in naïve and cocaine-sensitized mice.

MATERIALS AND METHODS

We investigated the development of sensitization after repeated administration of cocaine and cocaethylene and the effects of cocaethylene in animals previously exposed to cocaine. Cocaethylene was dissolved in two vehicles (saline and emulsion).

RESULTS

As observed with cocaine, chronic cocaethylene treatment in saline induced a behavioral sensitization, while in a sustained release emulsion, no behavioral sensitization was observed. Moreover, the expression of the sensitized behavior observed in cocaine-treated mice was reduced or totally abolished after cocaethylene administration in saline and emulsion, respectively. Interestingly, administration of cocaine in mice chronically treated with cocaethylene in saline induced an increase in locomotor activity as compared to control animals. In contrast, no difference was observed after the administration of cocaine in animals chronically treated with cocaethylene in emulsion or control group.

CONCLUSIONS

Cocaethylene in a sustained release emulsion blocked locomotor sensitization. These results suggest that cocaethylene, in a specific galenic preparation, such as gum, may be an efficacious harm-reduction alternative to cocaine users.

Pharmacokinetic profile of cocaine following intravenous administration in the female rabbit

Prenatal cocaine exposure in a rabbit intravenous model has revealed selective disruption of brain development and pharmacological responsiveness. We therefore examined the pharmacokinetic properties of cocaine in this model. Dutch-belted rabbits were surgically implanted with a catheter in the carotid artery, allowed to recover, and then injected intravenously with a cocaine bolus. Cocaine and benzoylecgonine concentrations were measured in arterial blood plasma and analyzed by nonlinear regression and noncompartmental analyses. Peak cocaine concentration occurred by 30s, was transient, and distribution was rapid. The profile of cocaine in the rabbit is similar to that observed in humans using cocaine at recreational doses.

A qualitative and quantitative review of cocaine-induced craving: the phenomenon of priming

Drug-induced craving is thought to play an important role in relapse occasioned by a "slip", or an isolated use of a previously abused drug after a period of abstinence. Clinical experience suggests that acute exposure to cocaine elicits craving (hereafter referred to as "priming"); however, this has received surprisingly little attention in the clinical literature.

AIMS

The intentions of this review are to provide a qualitative review of the literature as well as a more stringent quantitative review of the existence and presence of cocaine-induced priming effects.

METHODS

In order to determine whether priming effects occur following cocaine administration, we conducted qualitative and quantitative reviews of studies in which participants received cocaine under experimentally controlled conditions in the laboratory.

RESULTS

The results of the qualitative review were equivocal, while the quantitative review revealed that cocaine administration was associated with a significant increase in craving for cocaine, and the effect size of this relationship was large.

CONCLUSION

A review of the individual studies revealed marked variability, suggesting that priming effects did not occur consistently and that there may be factors that mediate or moderate the intensity of the priming effects induced by cocaine. The implications of these findings are discussed.

Evidence for elevated nicotine-induced structural plasticity in nucleus accumbens of adolescent rats

Male Long-Evans rats were administered nicotine bitartrate or sodium tartrate either during adolescence (p29-43) or adulthood (p80-94). Route of administration was via subcutaneously implanted osmotic pump (initial dose 2.0 mg/kg/day, free base). Five weeks following nicotine administration, brains were processed for Golgi-Cox staining. Medium spiny neurons from nucleus accumbens (NAc) shell were digitally reconstructed for morphometric analysis. Total dendritic length and branch number were greater in medium spiny neurons from animals pretreated with nicotine during adolescence. A branch order analysis indicated that increased branch number was specific to higher order branches. Mean branch lengths did not differ with respect to treatment as a function of branch order. Thus, nicotine-induced increases in total dendritic length were a function of greater numbers of branches, not increased segment length. In contrast, adult nicotine exposure did not significantly alter total dendritic length or branch number of medium spiny neurons. Total dendritic length and branch number of a second morphological type, the large aspiny neuron, did not differ following either adolescent or adult pretreatment. The age-dependent alteration of accumbal structure was associated with qualitatively different behavioral responses to drug challenge. These data provide evidence that drug-induced structural plasticity in nucleus accumbens is considerably more pronounced during adolescence.

High reinforcing efficacy of nicotine in non-human primates

Although tobacco appears highly addictive in humans, there has been persistent controversy about the ability of its psychoactive ingredient nicotine to induce self-administration behavior in laboratory animals, bringing into question nicotine's role in reinforcing tobacco smoking. Because of ethical difficulties in inducing nicotine dependence in naïve human subjects, we explored reinforcing effects of nicotine in experimentally-naive non-human primates given access to nicotine for periods of time up to two years. Five squirrel monkeys with no experimental history were allowed to intravenously self-administer nicotine by pressing one of two levers. The number of presses on the active lever needed to obtain each injection was fixed (fixed-ratio schedule) or increased progressively with successive injections during the session (progressive-ratio schedule), allowing evaluation of both reinforcing and motivational effects of nicotine under conditions of increasing response cost. Over time, a progressive shift toward high rates of responding on the active lever, but not the inactive lever, developed. The monkeys' behavior was clearly directed toward nicotine self-administration, rather than presentation of environmental stimuli associated with nicotine injection. Both schedules of reinforcement revealed a high motivation to self-administer nicotine, with monkeys continuing to press the lever when up to 600 lever-presses were needed for each injection of nicotine. Thus, nicotine, by itself, in the absence of behavioral or drug-exposure history, is a robust and highly effective reinforcer of drug-taking behavior in a non-human primate model predictive of human behavior. This supports the use of nicotinic ligands for the treatment of smokers, and this novel preclinical model offers opportunities to test future medications for the treatment of nicotine dependence.

Guidelines on nicotine dose selection for in vivo research

RATIONALE

This review provides insight for the judicious selection of nicotine dose ranges and routes of administration for in vivo studies. The literature is replete with reports in which a dosaging regimen chosen for a specific nicotine-mediated response was suboptimal for the species used. In many cases, such discrepancies could be attributed to the complex variables comprising species-specific in vivo responses to acute or chronic nicotine exposure.

OBJECTIVES

This review capitalizes on the authors' collective decades of in vivo nicotine experimentation to clarify the issues and to identify the variables to be considered in choosing a dosaging regimen. Nicotine dose ranges tolerated by humans and their animal models provide guidelines for experiments intended to extrapolate to human tobacco exposure through cigarette smoking or nicotine replacement therapies. Just as important are the nicotine dosaging regimens used to provide a mechanistic framework for acquisition of drug-taking behavior, dependence, tolerance, or withdrawal in animal models.

RESULTS

Seven species are addressed: humans, nonhuman primates, rats, mice, Drosophila, Caenorhabditis elegans, and zebrafish. After an overview on nicotine metabolism, each section focuses on an individual species, addressing issues related to genetic background, age, acute vs chronic exposure, route of administration, and behavioral responses.

CONCLUSIONS

The selected examples of successful dosaging ranges are provided, while emphasizing the necessity of empirically determined dose-response relationships based on the precise parameters and conditions inherent to a specific hypothesis. This review provides a new, experimentally based compilation of species-specific dose selection for studies on the in vivo effects of nicotine.

Relevance of rodent models of intravenous MDMA self-administration to human MDMA consumption patterns

RATIONALE

Despite decades of research specifying harmful effects produced by 3,4-methylenedioxymethamphetamine (MDMA; a principal component of 'ecstasy' pills), young people (and adults) continue to use it. In an attempt to model human MDMA consumption patterns, preclinical investigators have sought to establish reliable patterns of intravenous MDMA self-administration in rodents.

OBJECTIVE

The objective of this report is to offer a critical review of published data (including our own novel findings) that reveal MDMA self-administration in rodents.

RESULTS

The data indicate that MDMA serves as a reinforcer in rodents, though the responses are not similar to those previously reported for psychostimulants (i.e., cocaine). Important differences between rodent models and human use patterns include frequency of dosing and dosage exposure, routes of administration, tolerance that develops to MDMA after repeated exposure, polydrug use in humans but not by rodents, limits on the repertoire of behaviors that can be exhibited by rodents undergoing IV self-administration procedures, and the question of neurotoxicity as it relates to models of self-administration.

CONCLUSIONS

While MDMA is not as potent a reinforcer as other drugs of abuse, the fact remains that young people and adults continue to use the drug, and therefore, additional research is needed to determine why drugs with low reinforcing effects continue to be abused.

The relationship between crystalline methamphetamine use and methamphetamine dependence

BACKGROUND

The aim of the current study was to determine whether crystalline methamphetamine users are more dependent on methamphetamine than people who use other forms of the drug, and if so, whether this could be accounted for by their methamphetamine use history.

METHOD

A structured face-to-face interview was used to assess drug use patterns and demographics among a convenience sample of 309 regular methamphetamine users from Sydney, Australia. Dependence on methamphetamine in the past year was measured using the Severity of Dependence Scale. The use of crystalline methamphetamine in the past year was confirmed using a photographic identification sheet.

RESULTS

Participants who had used crystalline methamphetamine in the past year were significantly more likely to be dependent on methamphetamine than participants who took only other forms of methamphetamine during this time (61% versus 39%). Methamphetamine dependence was also associated with injecting or smoking methamphetamine (67% and 58%, respectively versus 30% for intranasal or oral use), using methamphetamine more than weekly (68% versus 34%), having used the drug for more than 5 years (61% versus 36%), and having used 'base' methamphetamine in the past year (59% versus 39%). Crystalline methamphetamine use remained significantly associated with methamphetamine dependence after adjusting for these patterns of methamphetamine use.

CONCLUSIONS

Methamphetamine users who took crystalline methamphetamine in the past year were more likely to be dependent than methamphetamine users who had not taken the crystalline form of the drug during this time.

Knockout of ERK1 enhances cocaine-evoked immediate early gene expression and behavioral plasticity

The ability of cocaine to produce lasting neural adaptations in mesocorticolimbic brain regions is thought to promote drug seeking and facilitate addiction in humans. The Ras-controlled Raf-MEK-ERK protein kinase signaling cascade has been implicated in the behavioral and neurobiological actions of cocaine in animals. However, these pharmacological studies have not been able to determine the specific role of the two predominant isoforms of ERK (ERK1 and ERK2) in these processes. We report here that deletion of the ERK1 isoform, which leads to increased ERK2 stimulus-dependent signaling, facilitates the development of cocaine-induced psychomotor sensitization and the acquisition of a cocaine conditioned place preference. Conversely, pharmacological blockade of ERK signaling attenuates the development of psychomotor sensitization to cocaine. Finally, cocaine-evoked gene expression in mesocorticolimbic brain regions is potentiated in ERK1-deficient mice. Thus, alterations in ERK signaling influence both the neurobiological impact of cocaine and its ability to produce enduring forms of drug experience-dependent behavioral plasticity. Our results suggest that enhanced ERK2 signaling following repeated drug exposure may facilitate the development of forms of cocaine-induced plasticity that contribute to addiction.

Medicinal smokes

All through time, humans have used smoke of medicinal plants to cure illness. To the best of our knowledge, the ethnopharmacological aspects of natural products' smoke for therapy and health care have not been studied. Mono- and multi-ingredient herbal and non-herbal remedies administered as smoke from 50 countries across the 5 continents are reviewed. Most of the 265 plant species of mono-ingredient remedies studied belong to Asteraceae (10.6%), followed by Solanaceae (10.2%), Fabaceae (9.8%) and Apiaceae (5.3%). The most frequent medical indications for medicinal smoke are pulmonary (23.5%), neurological (21.8%) and dermatological (8.1%). Other uses of smoke are not exactly medical but beneficial to health, and include smoke as a preservative or a repellent and the social use of smoke. The three main methods for administering smoke are inhalation, which accounts for 71.5% of the indications; smoke directed at a specific organ or body part, which accounts for 24.5%; ambient smoke (passive smoking), which makes up the remaining 4.0%. Whereas inhalation is typically used in the treatment of pulmonary and neurological disorders and directed smoke in localized situations, such as dermatological and genito-urinary disorders, ambient smoke is not directed at the body at all but used as an air purifier. The advantages of smoke-based remedies are rapid delivery to the brain, more efficient absorption by the body and lower costs of production. This review highlights the fact that not enough is known about medicinal smoke and that a lot of natural products have potential for use as medicine in the smoke form. Furthermore, this review argues in favor of medicinal smoke extended use in modern medicine as a form of drug delivery and as a promising source of new active natural ingredients.

Effects of dopamine transporter selective 3-phenyltropane analogs on locomotor activity, drug discrimination, and cocaine self-administration after oral administration

Several studies suggest that a dopamine transporter uptake inhibitor that has a slower onset and longer duration of action than cocaine in animal behavioral measures and decreases cocaine self-administration would be useful as an indirect dopamine agonist pharmacotherapy to treat cocaine addiction. In the present study, we compared five 3-phenyltropane analogs administered orally in locomotor activity in mice and drug discrimination in rats to gain information concerning relative potency, onset, and duration of action. The compounds were also evaluated for reduction of cocaine self-administration in rats after oral administration. In general, the compounds had a slower onset of action than cocaine and reduced cocaine self-administration. 3beta-(4-Chlorophenyl)-2beta-(3-(4'-methylphenyl)-isoxazol-5-yl)tropane (RTI-336) was the most potent in locomotor activity and drug discrimination; it was less stimulatory than cocaine in the first hour and had the slowest onset and longest duration of action. It also reduced self-administration of two infusion doses of cocaine in the rat.

Nicotinic receptor agonists as neuroprotective/neurotrophic drugs. Progress in molecular mechanisms

In the present work we reviewed recent advances concerning neuroprotective/neurotrophic effects of acute or chronic nicotine exposure, and the signalling pathways mediating these effects, including mechanisms implicated in nicotine addiction and nAChR desensitization. Experimental and clinical data largely indicate long-lasting effects of nicotine and nicotinic agonists that imply a neuroprotective/neurotrophic role of nAChR activation, involving mainly alpha7 and alpha4beta2 nAChR subtypes, as evidenced using selective nAChR agonists. Compounds interacting with neuronal nAChRs have the potential to be neuroprotective and treatment with nAChR agonists elicits long-lasting neurotrophic effects, e.g. improvement of cognitive performance in a variety of behavioural tests in rats, monkeys and humans. Nicotine addiction, which is mediated by interaction with nACh receptors, is believed to involve the modification of signalling cascades that modulate synaptic plasticity and gene expression. Desensitization, in addition to protecting cells from uncontrolled excitation, is recently considered as a form of signal plasticity. nAChR can generate these longe-lasting effects by elaboration of complex intracellular signals that mediate medium to long-term events crucial for neuronal maintenance, survival and regeneration. Although a comprehensive survey of the gene-based molecular mechanisms that underlie nicotine effects has yet not been performed a growing amount of data is beginning to improve our understanding of signalling mechanisms that lead to neurotrophic/neuroprotective responses. Evidence for an involvement of the fibroblast growth factor-2 gene in nAChR mechanisms mediating neuronal survival, trophism and plasticity has been obtained. However, more work is needed to establish the mechanisms involved in the effects of nicotinic receptor subtype activation from cognition-enhancing and neurotrophic effects to smoking behaviour and to determine more precisely the therapeutic objectives in potential nicotinic drug treatments of neurodegenerative diseases.

Vaccination against nicotine does not prevent nicotine-induced changes in fetal nicotinic receptor binding and c-fos mRNA expression in rats

Gestational exposure of rats to nicotine produces long-lasting alterations in brain development. Vaccination of adult female rats against nicotine reduces the distribution of maternally administered nicotine to fetal brain, suggesting that vaccination might protect against these effects. In the current study, the effects of vaccination on nicotine-induced changes in fetal (3)H-epibatidine binding and c-fos mRNA expression were evaluated using tissue from a previous pharmacokinetic study of vaccination. An intermittent nicotine dosing regimen designed to resemble nicotine intake in a smoker was administered from GD1-20. Peak nicotine levels in fetal brain were reduced by vaccination, whereas the chronic accumulation of nicotine in fetal brain was not. Gestational nicotine exposure produced significant increases in (125)I-epibatidine binding to brain and spinal cord on GD20, and decreased c-fos mRNA expression in fetal striatum, adrenal and lung. Vaccination did not significantly alter these effects. These data suggest that nicotine dosing, using a clinically relevant intermittent bolus dose regimen, produces substantial changes in fetal nicotinic receptor and c-fos mRNA expression. The decrease in c-fos mRNA expression contrasts with previously reported increases, and suggests that the nicotine dosing regimen used may influence its effects. The lack of effect of vaccination suggests that the cumulative exposure of fetal tissues to nicotine may influence the measured parameters to a greater extent than peak exposure levels.

Cocaine self-administration reduces excitatory responses in the mouse nucleus accumbens shell

Drugs of abuse affect behavior by altering neuronal communication within the brain. Previous research examining the effects of intraperitoneally administered cocaine has revealed that cocaine alters excitatory glutamatergic signaling, both directly through regulation of synaptic function, and indirectly through regulation of cellular excitability in areas of the drug reward circuitry such as the nucleus accumbens (NAcc) and ventral tegmental area. We have now extended these findings by testing the hypothesis that self-administration of cocaine might elicit similar alterations in excitatory signaling in the NAcc shell. We observed that cocaine self-administration reduces synaptically evoked excitatory responses recorded extracellularly in the NAcc shell compared to saline self-administration. This alteration was not accompanied by alterations in paired pulse ratio of synaptically evoked responses or in potentiation of these responses by application of the adenylyl cyclase activator forskolin. This reduction in glutamatergic signaling may be one mechanism by which cocaine exerts its long-term behavioral effects.

Research design strategies to evaluate the impact of formulations on abuse liability

Scheduling of a chemical drug substance under the Controlled Substances Act (CSA) includes an evaluation of preclinical and clinical safety, and experimental abuse liability studies, as well as information on diversion and overdose. Formulations that mitigate abuse liability, dependence potential and public health risks (e.g., altered absorption rate and tamperability, long half-life, pro-drugs and combination products) are amenable to preclinical and clinical studies to compare their abuse potential to reference compounds. For new formulations (NF) as marketed agents, direct comparison to the immediate release (IR) formulation of the reference compound is typically needed across the full range of potential studies. While the public health advantage of formulation changes in the marketplace can be conceptualized in behavioral economic terms, generating persuasive data is challenging. Study complexity increases because of additional conditions (e.g., placebo, 2-3 doses of the IR formulation, 2-3 doses of the new formulation, and 2-3 doses of the unscheduled or negative control drug), larger sample sizes (study power driven by the comparison of the new formulation versus the IR or placebo), and associated increases in study duration. However, the use of single maximal doses of well-characterized controls can reduce the number of study arms, and using incomplete block designs can reduce study duration. Less typical experimental approaches may also be useful, such as human choice or discrimination procedures, or pre-marketing consumer studies among experienced drug tamperers. New formulations that demonstrate a substantial difference from marketed or reference products have a potential marketing advantage and should require less onerous risk management. Post-marketing epidemiological data demonstrating the lack of abuse will carry the most weight from a public health and physician perspective.

Multi-target strategies for the improved treatment of depressive states: Conceptual foundations and neuronal substrates, drug discovery and therapeutic application

Major depression is a debilitating and recurrent disorder with a substantial lifetime risk and a high social cost. Depressed patients generally display co-morbid symptoms, and depression frequently accompanies other serious disorders. Currently available drugs display limited efficacy and a pronounced delay to onset of action, and all provoke distressing side effects. Cloning of the human genome has fuelled expectations that symptomatic treatment may soon become more rapid and effective, and that depressive states may ultimately be "prevented" or "cured". In pursuing these objectives, in particular for genome-derived, non-monoaminergic targets, "specificity" of drug actions is often emphasized. That is, priority is afforded to agents that interact exclusively with a single site hypothesized as critically involved in the pathogenesis and/or control of depression. Certain highly selective drugs may prove effective, and they remain indispensable in the experimental (and clinical) evaluation of the significance of novel mechanisms. However, by analogy to other multifactorial disorders, "multi-target" agents may be better adapted to the improved treatment of depressive states. Support for this contention is garnered from a broad palette of observations, ranging from mechanisms of action of adjunctive drug combinations and electroconvulsive therapy to "network theory" analysis of the etiology and management of depressive states. The review also outlines opportunities to be exploited, and challenges to be addressed, in the discovery and characterization of drugs recognizing multiple targets. Finally, a diversity of multi-target strategies is proposed for the more efficacious and rapid control of core and co-morbid symptoms of depression, together with improved tolerance relative to currently available agents.

Differential regulation of mesolimbic alpha 3/alpha 6 beta 2 and alpha 4 beta 2 nicotinic acetylcholine receptor sites and function after long-term oral nicotine to monkeys

Because the mesolimbic dopamine system plays a critical role in nicotine addiction/reinforcement and because nicotinic receptors regulate dopamine release, we initiated a study to evaluate the long-term effects of nicotine (>6 months at the final dose) on nicotinic acetylcholine receptor (nAChR) sites and function in the nucleus accumbens of nonhuman primates. Nicotine was given in the drinking water as this mode of administration is long-term but intermittent, thus resembling smoking in this aspect. We determined the effects of nicotine treatment on function and binding of the alpha3/alpha6beta2* and alpha4beta2* nAChRs subtypes in nucleus accumbens, a region directly implicated in the addictive effects of nicotine. To evaluate function, we measured nicotine and K+-evoked [3H]dopamine release from nucleus accumbens synaptosomes. Changes in alpha4beta2* and alpha3/alpha6beta2* nAChRs were measured using 125I-epibatidine, [125I]A85380 [5-[125I]iodo-3(2(S)-azetidinylmethoxy) pyridine] and 125I-alpha-conotoxin MII autoradiography. Chronic nicotine treatment, which led to plasma nicotine levels in the range of smokers, significantly increased nucleus accumbens alpha4beta2* nAChR sites and function compared with control. By contrast, this treatment did not significantly change alpha3/alpha6beta2* nAChR sites or evoked dopamine release in this region compared with control. Thus, these data are distinct from previous results in striatum in which the same nicotine treatment paradigm decreased striatal alpha3/alpha6beta2* nAChR sites and function. The finding that long-term nicotine treatment selectively modulates alpha4beta2* and not alpha3/alpha6beta2* nAChR expression in primate nucleus accumbens is consistent with the results of studies in nicotinic receptor mutant mice implicating the alpha4beta2* nAChR subtype in nicotine-mediated addiction.

Development of the dopamine transporter selective RTI-336 as a pharmacotherapy for cocaine abuse

The discovery and preclinical development of selective dopamine reuptake inhibitors as potential pharmacotherapies for treating cocaine addiction are presented. The studies are based on the hypothesis that a dopamine reuptake inhibitor is expected to partially substitute for cocaine, thus decreasing cocaine self-administration and minimizing the craving for cocaine. This type of indirect agonist therapy has been highly effective for treating smoking addiction (nicotine replacement therapy) and heroin addiction (methadone). To be an effective pharmacotherapy for cocaine addiction, the potential drug must be safe, long-acting, and have minimal abuse potential. We have developed several 3-phenyltropane analogs that are potent dopamine uptake inhibitors, and some are selective for the dopamine transporter relative to the serotonin and norepinephrine transporters. In animal studies, these compounds substitute for cocaine, reduce the intake of cocaine in rats and rhesus monkeys trained to self-administer cocaine, and have demonstrated a slow onset and long duration of action and lack of sensitization. The 3-phenyltropane analogs were also tested in a rhesus monkey self-administration model to define their abuse potential relative to cocaine. Based on these studies, 3beta-(4-chlorophenyl)-2beta-[3-(4'-methylphenyl)isoxazol-5-yl]tropane (RTI-336) has been selected for preclinical development.

Self-reported paranoia during laboratory "binge" cocaine self-administration in humans

Cocaine-induced paranoia (CIP) has been extensively studied by retrospective interviews; however, only limited efforts have been made to further characterize CIP by human laboratory methods. We examined CIP in 28 healthy cocaine-dependent volunteers, who participated in 2-h, intravenous cocaine self-administration sessions at 8, 16, and 32 mg/70 kg doses, including 18 in a placebo-controlled design. Self-reports of paranoia showed significant main effects of cocaine dose (p=0.0002) and time (p=0.0003), and were statistically distinguishable from placebo at the two highest doses (16 and 32 mg). These effects were accounted for by a subgroup of vulnerable subjects in whom self-reports were consistent across dose and test-retest sessions. Subjects with CIP did not differ from those without CIP with respect to demographic, cocaine use, or cocaine self-administration variables. In conclusion, self-reports of CIP in the human lab are frequently endorsed, dose-dependent, and though variable between subjects, reproducible within subjects. Such methods may facilitate our understanding of the vulnerability to CIP in humans.

Behavioural assessment of drug reinforcement and addictive features in rodents: an overview

Some psychoactive drugs are abused because of their ability to act as reinforcers. As a consequence behavioural patterns (such as drug-seeking/drug-taking behaviours) are promoted that ensure further drug consumption. After prolonged drug self-administration, some individuals lose control over their behaviour so that these drug-seeking/taking behaviours become compulsive, pervading almost all life activities and precipitating the loss of social compatibility. Thus, the syndrome of addictive behaviour is qualitatively different from controlled drug consumption. Drug-induced reinforcement can be assessed directly in laboratory animals by either operant or non-operant self-administration methods, by classical conditioning-based paradigms such as conditioned place preference or sign tracking, by facilitation of intracranial electric self-stimulation, or, alternatively by drug-induced memory enhancement. In contrast, addiction cannot be modelled in animals, at least as a whole, within the constraints of the laboratory. However, various procedures have been proposed as possible rodent analogues of addiction's major elements including compulsive drug seeking, relapse, loss of control/impulsivity, and continued drug consumption despite negative consequences. This review provides an extensive overview and a critical evaluation of the methods currently used for studying drug-induced reinforcement as well as specific features of addictive behaviour. In addition, comic strips that illustrate behavioural methods used in the drug abuse field are provided given for free download under http://www.zi-mannheim/psychopharmacology.de.

Nicotine as a typical drug of abuse in experimental animals and humans

RATIONALE AND BACKGROUND

Tobacco use through cigarette smoking is the leading preventable cause of death in the developed world. Nicotine, a psychoactive component of tobacco, appears to play a major role in tobacco dependence, but reinforcing effects of nicotine often are difficult to demonstrate directly in controlled laboratory studies with animal or human subjects.

OBJECTIVE

To review the major findings obtained with various procedures developed to study dependence-related behavioral effects of nicotine in experimental animals and humans, i.e., drug self-administration, conditioned place preference, subjective reports of nicotine effects and nicotine discrimination, withdrawal signs, and ratings of drug withdrawal.

RESULTS

Nicotine can function as an effective reinforcer of drug-seeking and drug-taking behavior both in experimental animals and humans under appropriate conditions. Interruption of chronic nicotine exposure produces withdrawal symptoms that may contribute to relapse. Difficulties encountered in demonstrating reinforcing effects of nicotine under some conditions, relative to other drugs of abuse, may be due to weaker primary reinforcing effects of nicotine or to a more critical contribution of environmental stimuli to the maintenance of drug-seeking and drug-taking behavior with nicotine than with other drugs of abuse. Further experiments are also needed to delineate the role other chemical substances inhaled along with nicotine in tobacco smoke play in sustaining smoking behavior.

CONCLUSION

Nicotine acts as a typical drug of abuse in experimental animals and humans.

Pharmacological determinants of the reinforcing effects of psychostimulants: relation to agonist substitution treatment

Illicit use of psychostimulants, such as cocaine and methamphetamine, continues to pose a significant public health concern. On the basis of the relative success at treating opiate and tobacco users with agonist substitution treatments, this strategy has been pursued in the search for a pharmacotherapy for psychostimulant addiction. The reinforcing effects of drugs are central to their abuse liability; therefore, gaining a better understanding of the factors that determine the reinforcing effects of psychostimulants should inform the development of an effective treatment. Although the reinforcing effects of drugs are known to be multiply determined, the author's dissertation research focused on pharmacological factors. This review presents results from that research as well as findings reported in the extant literature, suggesting that the reinforcing effects of psychostimulant drugs are determined both by their pharmacodynamic and pharmacokinetic profiles. There is evidence to support the conclusion that affinity for dopamine transporters appears to be of critical importance, whereas serotonin transporters seem to serve a modulatory function. A more rapid rate of onset may enhance a drug's reinforcing effects, but a drug with a slow onset can still maintain self-administration. A drug's duration of action may only influence the rate but not the strength of responding that is maintained. Slow-onset, long-acting monoamine transporter ligands can be expected to have reinforcing effects and therefore abuse liability, which has implications for the use of these drugs as pharmacotherapies. Nonetheless, on the basis of promising preclinical and clinical findings, this appears to represent a viable treatment strategy.

Rapid and persistent sensitization to the reinforcing effects of cocaine

The development of drug addiction involves a transition from recreational use to compulsive drug seeking and taking, and this progression can occur rapidly with cocaine use. These data highlight the importance of early drug exposure and the development of drug dependence; however, little experimental attention has been paid to this phenomenon in animal models of drug abuse. The present experiments demonstrate a progressive and rapid sensitization to the reinforcing strength of cocaine assessed using a progressive ratio (PR) schedule in rats. The first experiment found that rats show increased breakpoints over a 2-week period following acquisition. Subsequent experiments examined the role of total cocaine intake during the initial exposure period and found that low intakes (20 mg/kg/day x 5 days) resulted in sensitization, whereas relatively higher intake (60 or 100 mg/kg/day x 5 days) suppressed the development of sensitization. In contrast, this higher level of intake (60 mg/kg/day x 5 days) only transiently suppressed the expression of sensitization. Examination of breakpoints maintained by various doses of cocaine revealed an upward and leftward displacement of the cocaine dose-effect curve, relative to nonsensitized animals. These studies describe a form of sensitization that occurs rapidly to the reinforcing effects of cocaine, and provide a model to study the potential impact of initial experience on the development of drug dependence.

A tale of two cannabinoids: the therapeutic rationale for combining tetrahydrocannabinol and cannabidiol

This study examines the current knowledge of physiological and clinical effects of tetrahydrocannabinol (THC) and cannabidiol (CBD) and presents a rationale for their combination in pharmaceutical preparations. Cannabinoid and vanilloid receptor effects as well as non-receptor mechanisms are explored, such as the capability of THC and CBD to act as anti-inflammatory substances independent of cyclo-oxygenase (COX) inhibition. CBD is demonstrated to antagonise some undesirable effects of THC including intoxication, sedation and tachycardia, while contributing analgesic, anti-emetic, and anti-carcinogenic properties in its own right. In modern clinical trials, this has permitted the administration of higher doses of THC, providing evidence for clinical efficacy and safety for cannabis based extracts in treatment of spasticity, central pain and lower urinary tract symptoms in multiple sclerosis, as well as sleep disturbances, peripheral neuropathic pain, brachial plexus avulsion symptoms, rheumatoid arthritis and intractable cancer pain. Prospects for future application of whole cannabis extracts in neuroprotection, drug dependency, and neoplastic disorders are further examined. The hypothesis that the combination of THC and CBD increases clinical efficacy while reducing adverse events is supported.