Medication Development Program, NIDA/IRP

The endocannabinoid system has been implicated in the development of synaptic plasticity induced by several drugs abused by humans, including cocaine. However, there remains some debate about the involvement of cannabinoid receptors/ligands in cocaine-induced plasticity and corresponding behavioral actions. Here, we show that a single cocaine injection in Swiss-Webster mice produces behavioral and neurochemical alterations that are under the control of the endocannabinoid system. This plasticity may be the initial basis for changes in brain processes leading from recreational use of cocaine to its abuse and ultimately to dependence. Locomotor activity was monitored with photobeam cell detectors, and accumbens shell/core microdialysate dopamine levels were monitored by highperformance liquid chromatography with electrochemical detection. Development of single-trial cocaine-induced behavioral sensitization, measured as increased distance traveled in sensitized mice compared to control mice, was paralleled by a larger stimulation of extracellular dopamine levels in the core but not the shell of the nucleus accumbens. Both the behavioral and neurochemical effects were reversed by CB1 receptor blockade produced by rimonabant pre-treatments. Further, both behavioral and neurochemical cocaine sensitization were facilitated by pharmacological blockade of endocannabinoid metabolism, achieved by inhibiting the fatty acid amide hydrolase enzyme. In conclusion, our results suggest that a single unconditioned exposure to cocaine produces sensitization through neuronal alterations that require regionally specific release of endocannabinoids. Further, the present results suggest that endocannabinoids play a primary role from the earliest stage of cocaine use, mediating the inception of long-term brain-adaptive responses, shaping central pathways and likely increasing vulnerability to stimulant abuse disorders.

The dopamine-opioid link. ALCOHOL 13(1) 13-17, 1996.-Various lines of evidence support the view that ethanol is a neurochemical surrogate of conventional reinforcers, such as food and sex. In fact, ethanol activates central neuronal systems that utilize dopamine, opioids, and 7-aminobutyric acid (GABA) as neurotransmitters and also are activated by conventional reinforcers. These neurotransmitter systems are likely to mediate specific aspects of ethanol's reinforcing properties. Activation of the mesolimbic dopamine and endogenous opioid systems might be the substrate of the incentive and rewarding (ergotropic) properties of ethanol (arousal, euphoria, motor stimulation) and of the process of acquiring ethanol-related secondary reinforcers (incentive learning) and ethanol self-administration habits. Stimulation of the endogenous GABAergic system might mediate the sedative and drive-reducing (trophotropic) properties of ethanol. The dopamine and opioid systems are largely interconnected. Thus, pharmacological blockade of the endogenous opioid system by mu-or delta-opioid receptor antagonists prevents ethanol's activation of the dopamine system and reduces ethanol consumption. This interaction might contribute to naltrexone's effectiveness in reducing alcohol craving in humans.

Previous studies demonstrated the effectiveness of selective r-receptor (rR) agonists [1,3-di-o-tolylguanidine (DTG), PRE-084] as reinforcers in rats trained to selfadminister cocaine. Similar to cocaine, these drugs increased nucleus accumbens shell dopamine levels, and effects of DTG, but not PRE-084, on dopamine seemed to be mediated by rRs. In addition, rR antagonists blocked self-administration of rR agonists, but were inactive against reinforcing and neurochemical effects of cocaine. Thus, pharmacologically distinct mechanisms likely underlie the reinforcing and neurochemical effects of rR agonists and cocaine. This study further examined the cocaine-like effects of rR agonists in rats trained to discriminate injections of cocaine from saline to assess the similarity of their subjective effects. Standard dopamineuptake inhibitors (WIN 35 428, methylphenidate), but neither rR agonist (PRE-084, DTG), produced full cocainelike discriminative-stimulus effects. The lack of effects of rR agonists was obtained regardless of route of administration (intraperitoneal, subcutaneous, or intravenous) or pretreatment time (5 or 30 min before sessions). The present results demonstrate differences in the discriminative-stimulus effects of cocaine and selective rR agonists, indicating that an overlap of subjective effects is not necessary for rR agonist self-administration. The previously found differences in neurochemical effects of cocaine and rR agonists may contribute to their different subjective effects. Behavioural Pharmacology 22:525-530

Background: Subtypes of sigma () receptors, 1 and 2 , can be pharmacologically distinguished, and each may be involved in substanceabuse disorders. -Receptor antagonists block cocaine place conditioning and -receptor agonists are self-administered in rats that previously self-administered cocaine. Self-administration of abused drugs has been related to increased dopamine (DA) neurotransmission, however, -receptor agonist effects on mesolimbic DA are not fully characterized.

Background: Subjective effects of cocaine are mediated primarily by dopamine (DA) transporter (DAT) blockade. The present study assessed the hypothesis that different DAT conformational equilibria regulate differences in cocaine-like subjective effects and extracellular DA induced by diverse DA-uptake inhibitors (DUIs).

Although endogenous cannabinoid systems have been implicated in the modulation of the rewarding effects of abused drugs and food, little is known about the direct effects of endogenous ligands for cannabinoid receptors on brain reward processes. Here we show for the first time that the intravenous administration of anandamide, an endogenous ligand for cannabinoid receptors, and its longer-lasting synthetic analog methanandamide, increase the extracellular dopamine levels in the nucleus accumbens shell of awake, freely moving rats, an effect characteristic of most drugs abused by humans. Anandamide produced two distinctly different effects on dopamine levels: (1) a rapid, transient increase that was blocked by the cannabinoid CB 1 receptor antagonist rimonabant, but not by the vanilloid VR 1 receptor antagonist capsazepine, and was magnified and prolonged by the fatty acid amide hydrolase (FAAH) enzyme inhibitor, URB597; (2) a smaller delayed and long-lasting increase, not sensitive to CB 1 , VR 1 or FAAH blockade. Both effects were blocked by infusing either tetrodotoxin (TTX, 1 lM) or calciumfree Ringer's solution through the microdialysis probe, demonstrating that they were dependent on the physiologic activation of dopaminergic neurotransmission. Thus, these results indicate that anandamide, through the activation of the mesolimbic dopaminergic system, participates in the signaling of brain reward processes.

l-Deprenyl [selegiline, (R)-(Ϫ)-deprenyl] is a selective inhibitor of monoamine oxidase B (MAO-B) used in the treatment of Parkinson's disease and proposed as an antidepressant and an aid for cigarette-smoking cessation and treatment of psychostimulant abuse. Beneficial therapeutic effects of (R)-(Ϫ)-deprenyl may also result from indirect actions. Brain levels of dopamine and ␤-phenylethylamine (␤-PEA), a behaviorally active endogenous trace amine, increase after (R)-(Ϫ)-deprenyl treatment due to MAO-B blockade and (R)-(Ϫ)-deprenyl is metabolized to (R)-(Ϫ)-methamphetamine and (R)-(Ϫ)-amphetamine, suggesting that (R)-(Ϫ)-deprenyl may have psychostimulant-like behavioral effects. Indeed, (R)-(Ϫ)-deprenyl produces psychostimulant-like discriminative-stimulus effects in experimental animals.

antagonists have been reported to block certain effects of psychostimulant drugs. The present study examined the effects of R ligands in rats trained to self-administer cocaine (0.032-1.0 mg/kg/inj i.v.) under fixed-ratio 5-response schedules of reinforcement. Maximal rates of responding were maintained by 0.32 mg/kg/inj cocaine, or by the R agonists, 1,3-di-(2tolyl)guanidine (DTG; 1.0 mg/kg/inj) or 2-(4-morpholinethyl) 1-phenylcyclohexane-1-carboxylate hydrochloride (PRE-084; 0.32 mg/ kg/inj), when substituted for cocaine. Lower response rates were maintained at higher and lower doses of the compounds. No dose of the R antagonists [N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(1-pyrrolidinyl)ethylamine (BD 1008), N-[2-(3,4-dichlorophenyl)ethyl]-N-methyl-2-(dimethylamino)ethylamine (BD 1047), N-[2-(3,4-dichlorophenyl)ethyl]-4-methylpiperazine (BD 1063)] maintained responding appreciably above levels obtained when responding had no consequences. Presession treatment with R agonists dose-dependently shifted the cocaine self-administration dose-effect curve leftward. The dopamine-uptake inhibitor, (Ϫ)-2␤-carbomethoxy-3␤-(4-fluorophenyl)tropane (WIN 35,428), 524 Hiranita et al.

Emerging evidence suggests that the rewarding, abuse-related effects of nicotine are modulated by the endocannabinoid system of the brain. For example, pharmacological blockade or genetic deletion of cannabinoid CB 1 receptors can reduce or eliminate many abuse-related behavioral and neurochemical effects of nicotine. Furthermore, doses of ⌬ 9 -tetrahydrocannabinol and nicotine that are ineffective when given alone can induce conditioned place preference when given together. These previous studies have used systemically administered CB 1 receptor agonists and antagonists and gene deletion techniques, which affect cannabinoid CB 1 receptors throughout the brain. A more functionally selective way to alter endocannabinoid activity is to inhibit fatty acid amide hydrolase (FAAH), thereby magnifying and prolonging the effects of the endocannabinoid anandamide only when and where it is synthesized and released on demand. Here, we com-Recent findings suggest that behavioral and motivational

Sigma receptor (R) antagonists attenuate many behavioral effects of cocaine but typically not its reinforcing effects in selfadministration procedures. However, the R antagonist rimcazole and its N-propylphenyl analogs, [3-(cis-3,5-dimethyl-4-[3phenylpropyl]-1-piperazinyl)-propyl]diphenylamine hydrochloride (SH 3-24) and 9-[3-(cis-3,5-dimethyl-4-[3-phenylpropyl]-1piperazinyl)-propyl]carbazole hydrobromide (SH 3-28), dosedependently decreased the maximal rates of cocaine selfadministration without affecting comparable responding maintained by food reinforcement. In contrast, a variety of R (BD 1063), and N,N-dipropyl-2-[4-methoxy-3-(2-phenylethoxy)phenyl]-ethylamine monohydrochloride (NE-100)] had no effect on cocaine self-administration across the range of doses that decreased rates of food-maintained responding. Rimcazole analogs differed from selective R antagonists in their dual affinities for Rs and the dopamine transporter (DAT) assessed with radioligand binding. Selective DAT inhibitors and R antagonists were studied alone and in combination on cocaine self-administration to determine whether actions at both Rs and the DAT were sufficient to reproduce the effects of rimcazole analogs. Typical DAT inhibitors [2␤-carbomethoxy-3␤-(4-fluorophenyl)tropane (WIN 35,428), methylphenidate, and nomifensine] dose-dependently shifted the cocaine dose-effect curve leftward. Combinations of DAT inhibitor and R antagonist doses that were behaviorally inactive alone decreased cocaine self-administration without effects on food-maintained responding. In addition, whereas the DAT inhibitors were self-administered at rates similar to those of cocaine, neither rimcazole analogs nor typical R antagonists (NE-100 and AC927) maintained responding above control levels across a wide range of doses. These findings suggest that the unique effects of rimcazole analogs are due to dual actions at the DAT and Rs and that a combined target approach may have utility in development of medical treatments for cocaine abuse.

Inhibitors of fatty acid amide hydrolase (FAAH) increase endogenous levels of anandamide (a cannabinoid CB 1 -receptor ligand) and oleoylethanolamide and palmitoylethanolamide (OEA and PEA, ligands for a-type peroxisome proliferatoractivated nuclear receptors, PPAR-a) when and where they are naturally released in the brain. Using a passive-avoidance task in rats, we found that memory acquisition was enhanced by the FAAH inhibitor URB597 or by the PPAR-a agonist WY14643, and these enhancements were blocked by the PPAR-a antagonist MK886. These findings demonstrate novel mechanisms for memory enhancement by activation of PPAR-a, either directly by administering a PPAR-a agonist or indirectly by administering a FAAH inhibitor.