Showing papers by "Billy R. Martin published in 2007"

Nicotine dependence and reward differ between adolescent and adult male mice.

Abstract: The present study defined age differences in several aspects of nicotine dependence using male mice of two age groups [postnatal day (PND) 28 and PND 70]. Adolescent and adult mice displayed differences in acute sensitivity to nicotine, rewarding and withdrawal effects, development of tolerance to nicotine, and nicotinic receptor function. In the condition place preference model, adolescent mice displayed a higher sensitivity to nicotine than adults. In addition, in spontaneous and mecamylamine-precipitated withdrawal models, adolescent mice displayed fewer withdrawal signs than adults. In response to acute nicotine, it was found that adolescent mice displayed greater nicotine-induced antinociception compared with adult counterparts in the tail-flick test. Furthermore, differences in tolerance to nicotine were also noted in that adolescents developed a significantly higher degree of tolerance to nicotine in the hot-plate test compared with adults. Finally, using rubidium efflux assays, it was found that adolescent nicotinic receptors in different brain areas displayed significantly increased functionality compared with adult receptors. These data indicate that the underlying receptor mechanisms of nicotine dependence differ for adults and adolescents, suggesting that the effectiveness of smoking cessation therapies will differ for various age groups.

Evaluation of fatty acid amide hydrolase inhibition in murine models of emotionality.

Abstract: Rationale Manipulations of the endocannabinoid/fatty acid amide hydrolase (FAAH) signaling systems result in conflicting and paradoxical effects in rodent models of emotional reactivity.

Cannabinoid CB2 receptor activation decreases cerebral infarction in a mouse focal ischemia/reperfusion model

Abstract: Cannabinoid CB(2) Receptor (CB(2)) activation has been shown to have immunomodulatory properties without psychotropic effects. The hypothesis of this study is that selective CB(2) agonist treatment can attenuate cerebral ischemia/reperfusion injury. Selective CB(2) agonists (O-3853, O-1966) were administered intravenously 1 h before transient middle cerebral artery occlusion (MCAO) or 10 mins after reperfusion in male mice. Leukocyte/endothelial interactions were evaluated before MCAO, 1 h after MCAO, and 24 h after MCAO via a closed cranial window. Cerebral infarct volume and motor function were determined 24 h after MCAO. Administration of the selective CB(2) agonists significantly decreased cerebral infarction (30%) and improved motor function (P<0.05) after 1 h MCAO followed by 23 h reperfusion in mice. Transient ischemia in untreated animals was associated with a significant increase in leukocyte rolling and adhesion on both venules and arterioles (P<0.05), whereas the enhanced rolling and adhesion were attenuated by both selective CB(2) agonists administered either at 1 h before or after MCAO (P<0.05). CB(2) activation is associated with a reduction in white blood cell rolling and adhesion along cerebral vascular endothelial cells, a reduction in infarct size, and improved motor function after transient focal ischemia.

The psychoactive plant cannabinoid, Δ9-tetrahydrocannabinol, is antagonized by Δ8- and Δ9-tetrahydrocannabivarin in mice in vivo

Abstract: Background and purpose: To follow up in vitro evidence that Δ9-tetrahydrocannabivarin extracted from cannabis (eΔ9-THCV) is a CB1 receptor antagonist by establishing whether synthetic Δ9-tetrahydrocannabivarin (O-4394) and Δ8-tetrahydrocannabivarin (O-4395) behave as CB1 antagonists in vivo. Experimental approach: O-4394 and O-4395 were compared with eΔ9-THCV as displacers of [3H]-CP55940 from specific CB1 binding sites on mouse brain membranes and as antagonists of CP55940 in [35S]GTPγS binding assays performed with mouse brain membranes and of R-(+)-WIN55212 in mouse isolated vasa deferentia. Their ability to antagonize in vivo effects of 3 or 10 mg kg−1 (i.v.) Δ9-tetrahydrocannabinol in mice was then investigated. Key results: O-4394 and O-4395 exhibited similar potencies to eΔ9-THCV as displacers of [3H]-CP55940 (Ki=46.6 and 64.4 nM, respectively) and as antagonists of CP55940 in the [35S]GTPγS binding assay (apparent KB=82.1 and 125.9 nM, respectively) and R-(+)-WIN55212 in the vas deferens (apparent KB=4.8 and 3.9 nM respectively). At i.v. doses of 0.1, 0.3, 1.0 and/or 3 mg kg−1 O-4394 and O-4395 attenuated Δ9-tetrahydrocannabinol-induced anti-nociception (tail-flick test) and hypothermia (rectal temperature). O-4395 but not O-4394 also antagonized Δ9-tetrahydrocannabinol-induced ring immobility. By themselves, O-4395 and O-4394 induced ring immobility at 3 or 10 mg kg−1 (i.v.) and antinociception at doses above 10 mg kg−1 (i.v.). O-4395 also induced hypothermia at 3 mg kg−1 (i.v.) and above. Conclusions and implications: O-4394 and O-4395 exhibit similar in vitro potencies to eΔ9-THCV as CB1 receptor ligands and as antagonists of cannabinoid receptor agonists and can antagonize Δ9-tetrahydrocannabinol in vivo. British Journal of Pharmacology (2007) 150, 586–594. doi:10.1038/sj.bjp.0707124

Exposure to Marijuana Smoke Impairs Memory Retrieval in Mice

Abstract: Marijuana (Cannabis sativa) and its primary psychoactive component, delta-9-tetrahydrocannabinol (Delta(9)-THC), have long been known to disrupt cognition in humans. Although Delta(9)-THC and other cannabinoids disrupt performance in a wide range of animal models of learning and memory, few studies have investigated the effects of smoked marijuana in these paradigms. Moreover, in preclinical studies, cannabinoids are generally administered before acquisition, and because retention is generally evaluated soon afterward, it is difficult to distinguish between processes related to acquisition and retrieval. In the present study, we investigated the specific effects of marijuana smoke and injected Delta(9)-THC on acquisition versus memory retrieval in a mouse repeated acquisition Morris water-maze task. To distinguish between these processes, subjects were administered Delta(9)-THC or they were exposed to marijuana smoke either 30 min before acquisition or 30 min before the retention test. Inhalation of marijuana smoke or injected Delta(9)-THC impaired the ability of the mice to learn the location of the hidden platform and to recall the platform location once learning had already taken place. In contrast, neither drug impaired performance in a cued task in which the platform was made visible. Finally, the cannabinoid-1 (CB(1)) receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide HCl (rimonabant) blocked the memory disruptive effects of both Delta(9)-THC and marijuana. These data represent the first evidence demonstrating that marijuana impairs memory retrieval through a CB(1) receptor mechanism of action and independently of its effects on sensorimotor performance, motivation, and initial acquisition.

Genetic Approaches Identify Differential Roles for α4β2* Nicotinic Receptors in Acute Models of Antinociception in Mice

Abstract: The effects of nicotine on the tail-flick and hot-plate tests were determined to identify nicotinic receptor subtypes responsible for spinally and supraspinally mediated nicotine analgesia in knockin mice expressing hypersensitive 4 nicotinic receptors (L9S), in seven inbred mouse strains (C57BL/6, DBA/2, A/2, CBA/2, BALB/ cByJ, C3H/HeJ, and 129/SvEv), and in two F1 hybrids (B6CBAF1 and B6D2F1). L9S heterozygotes were 6-fold more sensitive to the antinociceptive effects of nicotine than the wild-type controls in the hot-plate test but not in the tail-flick assay. Large differences in the effects of nicotine were also observed with both tests for the seven mouse strains. A/J and 129 mice were 6- to 8-fold more sensitive than CBA and BALB mice. In addition, B6CBAF1 hybrid mice were even less sensitive than CBA mice. Nicotinic binding sites were measured in three spinal cord regions and the hindbrain of the inbred strains. Significant differences in cytisine-sensitive, high affinity [ 125 I]epibatidine binding site levels (42* subtypes), but not in 125 I--bungarotoxin binding (7* subtypes), were observed. Significant negative correlations between cytisine-sensitive [ 125 I]epibatidine binding and nicotine ED50 for both tests were noted. Our results indicate that 42* acetylcholine nicotinic receptors (nAChR) are important in mediating nicotine analgesia in supraspinal responses, while also showing that 42*-nAChR and at least one other nAChR subtype appear to modulate spinal actions.

WIN55,212-2-mediated inhibition of HIV-1 expression in microglial cells: involvement of cannabinoid receptors.

Abstract: Cannabinoid receptors CB1 and CB2 are primarily expressed in cells of the nervous and immune systems, respectively. Recently, the synthetic CB1/CB2 agonist WIN55,212-2 was found to suppress replication of HIV-1 in microglial cell cultures. The present study was undertaken to test the hypothesis that WIN55,212-2’s antiviral effect is mediated via CB2 receptors. By reverse transcription-polymerase chain reaction, microglia were found to express both CB1 and CB2 receptors. Using additional CB1/CB2 receptor agonists and selective antagonists, we found that CB2 receptors are involved in WIN55,212-2’s antiviral activity and surprisingly that the CB1 receptor-selective antagonist SR141716A behaved as an agonist in these brain macrophages.

Cannabimimetic Properties of Ajulemic Acid

Abstract: Side effects of marijuana-based drugs and synthetic analogs of Δ9-tetrahydrocannabinol (Δ9-THC), including sedation and dysphoria, have limited their therapeutic application. Ajulemic acid (AJA), a side-chain synthetic analog of Δ8-THC-11-oic acid, has been reported to have anti-inflammatory properties without producing undesired psychoactive effects. Moreover, it has been suggested that AJA does not interact with cannabinoid receptors to produce its pharmacological effects. The aim of the present study was to conduct a thorough evaluation of the pharmacological effects of AJA then to determine whether actions at cannabinoid receptor (CB)1 mediated these effects. This study evaluated the psychoactive and analgesic effects of AJA by examining its cannabimimetic properties in ICR mice (i.e., antinociception, catalepsy, hypothermia, and hypomobility), its discriminative stimulus effects in Long Evans rats trained in a two-lever Δ9-THC (3.0 mg/kg) versus vehicle drug discrimination procedure, and its antihyperalgesia effects in a rat model of inflammatory pain [complete Freund's adjuvant (CFA)-induced mechanical hyperalgesia]. Lastly, antagonism tests with SR 141716A [ N -(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1 H -pyrazole-3-carboximide hydrochloride], CB1 receptor antagonist, were conducted. These studies demonstrated that AJA shares a number of CB1-mediated pharmacological properties with Δ9-THC, including cannabimimetic, discriminative stimulus, and antihyperalgesic effects. Furthermore, a separation between doses that produced antinociception and those that produced the other pharmacological effects in mice was not observed. Moreover, AJA showed nearly equipotency for therapeutic efficacy in the CFA model and for substitution in Δ9-THC discrimination. In summary, this study shows that AJA, like Δ9-THC, exhibits psychoactive and therapeutic effects at nearly equal doses in preclinical models, suggesting similar limitations in their putative therapeutic profiles.

Inhibition of Nicotine Metabolism by Methoxysalen: Pharmacokinetic and Pharmacological Studies in Mice

Abstract: Studies were undertaken to examine whether methoxsalen (9-methoxyfuro\[3,2-g\]\[1\]benzopyran-7-one), a specific and relatively selective inhibitor of human CYP2A6, inhibited CYP2A5-mediated nicotine metabolism in vitro. Furthermore, studies were performed in vivo to determine whether methoxsalen would modulate acute nicotine pharmacokinetics and pharmacological effects (antinociception and hypothermia) in the ICR mouse. Our results demonstrated that methoxsalen competitively inhibits in vitro nicotine metabolism in mice. The inhibition was potent, as seen in human inhibition studies, with a K i of 0.32 μM. In addition, we found that administration of methoxsalen significantly increased the plasma half-life of nicotine (approximately doubled) and increased its area under the curve compared with saline treatment. There was a dose-dependent enhancement in the pharmacological effects of nicotine (body temperature and analgesia) after methoxsalen treatment. Methoxsalen prolonged the duration of nicotine-induced antinociception and hypothermia (2.5 mg/kg) for periods up to 180 min postnicotine administration. Furthermore, this prolongation in nicotine's effects after methoxsalen was associated with a parallel prolongation of nicotine plasma levels in mice. These data strongly suggest that variation in the rates of nicotine metabolic inactivation substantially alter nicotine's pharmacological effects. In conclusion, these results confirmed that methoxsalen did indeed inhibit the conversion of nicotine to cotinine both in vitro and in vivo. They also suggest that mice may represent a suitable model for studying variation in nicotine metabolism and its impact on mechanisms of nicotine dependence, including the use of inhibitors to reduce nicotine metabolism.

Lack of behavioral sensitization after repeated exposure to THC in mice and comparison to methamphetamine

Abstract: Rationale Recent evidence has provided support for the incentive-sensitization model of addiction, where repeated stimulation of neural reward circuits leads to a long-lasting sensitization of mesolimbic dopaminergic activity. This phenomenon has been demonstrated with many drugs of abuse, most often by measuring progressively increased activating effects of drugs on locomotor activity, thought to reflect an underlying neural sensitization. Whether cannabinoids, and in particular Δ9-tetrahydrocannabinol (THC), produce similar effects in this model is somewhat controversial, with mixed evidence in the literature.

RhoA, encoding a Rho GTPase, is associated with smoking initiation.

Abstract: We used microarray analysis of acute nicotine responses in mouse brain to choose rationale candidates for human association studies on tobacco smoking and nicotine dependence (ND). Microarray studies on the time–course of acute response to nicotine in mouse brain identified 95 genes regulated in ventral tegmental area. Among these, 30 genes were part of a gene network, with functions relevant to neural plasticity. On this basis and their known roles in drug abuse or synaptic plasticity, we chose the genes RhoA and Ywhag as candidates for human association studies. A synteny search identified human orthologs and we investigated their role in tobacco smoking and ND in a human case–control association study. We genotyped five and three single nucleotide polymorphisms from the RhoA and Ywhag genes, respectively. Both single marker and haplotype analyses were negative for the Ywhag gene. For the RhoA gene, rs2878298 showed highly significant genotypic association with both smoking initiation (SI) and ND (P = 0.00005 for SI and P = 0.0007 for ND). In the allelic analyses, rs2878298 was only significant for SI. In the multimarker haplotype analyses, significant association with SI was found for the RhoA gene (empirical global P values ranged from 9 × 10−5 to 10−5). In all multimarker combinations analyzed, with or without inclusion of the single most significant marker rs2878298, identical risk and protective haplotypes were identified. Our results indicated that the RhoA gene is likely involved in initiation of tobacco smoking and ND. Replication and future model system studies will be needed to validate the role of RhoA gene in SI and ND.

Short communication Assessment of anandamide's pharmacological effects in mice deficient of both fatty acid amide hydrolase and cannabinoid CB 1 receptors

Abstract: In the present study, we investigated whether anandamide produces its behavioral effects through a cannabinoid CB1 receptor mechanism of action The behavioral effects of anandamide were evaluated in mice that lacked both fatty acid amide hydrolase (FAAH) and cannabinoid CB1 receptors (DKO) as compared to FAAH (�/�), cannabinoid CB1 (�/�), and wild type mice Anandamide produced analgesia, catalepsy, and hypothermia in FAAH (�/�) mice, but failed to elicit any of these effects in the other three genotypes In contrast, anandamide decreased locomotor behavior regardless ofgenotype, suggesting the involvement of multiple mechanisms ofaction, including its productsof degradation These findings indicate that the cannabinoid CB1 receptor is the predominant target mediating anandamide's behavioral effects

The Endocannabinoid System and the Therapeutic Potential of Cannabinoids

Abstract: Much has been written about the history of the medical uses of cannabis (1). In the past two centuries, there have been numerous references to the use of cannabis extracts for a wide range of disorders (2). In the early part of the 20th century, a standardized cannabis elixir was marketed in the United States. Following the introduction of synthetic drugs such as barbiturates and opioids into medicine, interest in cannabis elixir declined. The discovery of the primary active constitutent in marijuana, Δ9-tetrahydrocannabinol (THC), in 1964 (3) rekindled interest in the area. However, the emphasis shifted to synthetic cannabinoids rather than the plant or plant extracts. For example, in the 1970s, clinical studies were conducted in an effort to determine the efficacy of THC as an analgesic (4), antiemetic (5), antidepressant (6,7), appetite stimulant (7), and for treatment of glaucoma (8). These efforts resulted in the approval of THC (dronabinol, Marinol™) for treatment of chemotherapy-induced nausea and vomiting in 1985 and for appetite stimulation in 1992.

Marijuana: Pharmacology and Interaction with the Endocannabinoid System

Abstract: Marijuana is one of the most widely used illicit psychoactive substances in the U.S. Recently, negative perceptions of marijuana as an abused substance have been tempered somewhat by the idea that it may also have medicinal properties. Regardless of perception of marijuana, however, investigation of its active substituents and their mechanism of action led to the discovery of an endocannabinoid system that is activated by marijuana as well as by several endogenous cannabinoids, including anandamide and 2-arachidonylglycerol. In this chapter, we review the pharmacology of marijuana and discuss how its interaction with the endocannabinoid system may have implications for understanding the physiology of this system. Keywords: anandamide; endocannabinoids; marijuana; pharmacology review