Activation of corticotropin-releasing factor in the limbic system during cannabinoid withdrawal

'One-trial sensitization' to the anxiolytic-like effects of cannabinoid receptor antagonist SR141716A in the mouse elevated plus-maze

Significant variability in the effects of cannabinoid CB1 receptor ligands on emotional reactivity in animals and humans suggests that the endocannabinoid system may selectively modulate certain types of anxiety. In view of substantial evidence for qualitative differences in the nature of anxiety elicited on initial and subsequent exposures to the elevated plus-maze, the present studies contrasted the behavioural effects of the selective CB1 receptor antagonist SR141716A (0.1-10.0 mg/kg) and the reference benzodiazepine chlordiazepoxide (CDP, 15 mg/kg) both in maze-naive mice (trial 1) and in mice that had been given a single undrugged exposure to the maze 24 h prior to testing (trial 2). Results confirmed the anxioselective effect of CDP on trial 1 but a complete absence of such activity on trial 2 (i.e. one trial tolerance). In marked contrast, SR141716A had no behavioural effects in maze-naive mice but, at doses of 1.0-3.0 mg/kg (effect maximal at 1.0 mg/kg), significantly reduced anxiety-like responses in maze-experienced animals. Like the effect of CDP on trial 1, the antianxiety profile of SR141716A on plus-maze trial 2 was observed in the absence of any change in general activity levels. The apparent experientially induced 'sensitization' to the anxiolytic-like effects of SR141716A in the plus-maze contrasts markedly with the widely reported loss of benzodiazepine efficacy in test-experienced animals. Data are discussed in relation to the recently described phenotypes of CB1 receptor knockout mice and, in particular, to mounting evidence for the existence of a novel SR141716A-sensitive neuronal cannabinoid receptor.

Dopamine-dependent responses to cocaine depend on corticotropin-releasing factor receptor subtypes

The effects on locomotor response to cocaine challenge, acquisition of cocaine conditioned place preference and cocaine-induced dopamine (DA) release in nucleus accumbens and ventral tegmental area by the non-specific corticotropin-releasing factor (CRF) receptors antagonist alpha-helical CRF, the selective CRF receptor subtype 1 antagonist CP-154,526 and the selective CRF receptor subtype 2 antagonist anti-sauvagine-30 (AS-30) were investigated in rats. Both alpha-helical CRF (10 microg, i.c.v.) and CP-154,526 (3 microg, i.c.v.) decreased the cocaine-induced distance travelled, whereas AS-30 (3 microg, i.c.v.) did not show such an effect. The CRF receptor antagonists also have significant effects on stereotype counts induced by cocaine injection, in which the alpha-helical CRF or CP-154,526 but not AS-30 did significantly reduce the stereotype counts. alpha-Helical CRF (10 microg) prior to each injection of cocaine blocked cocaine conditioned place preference with no significant difference observed in the time spent in the drug-paired side between post- and pre-training and both 1 and 3 microg CP-154,526 also had significant inhibitory effects on cocaine-induced place preference. However, pre-treatment with an i.c.v. infusion of AS-30 (1 or 3 microg) prior to each injection of cocaine did not affect the acquisition of conditioned place preference. The alpha-helical CRF and CP-154,526 reduced extracellular DA levels of nucleus accumbens and ventral tegmental area in response to the injection of cocaine. However, both alpha-helical CRF and CP-154,526 did not modify extracellular DA levels under basal conditions. In contrast, the i.c.v. infusion of AS-30 had no effects on either the basal DA or the cocaine-induced increase in DA release in nucleus accumbens and ventral tegmental area. These findings demonstrate that activation of the CRF receptor is involved in behavioral and neurochemical effects of cocaine challenge and cocaine reward and that the role of CRF receptor subtypes 1 and 2 in cocaine-induced locomotion, reward and DA release is not identical. The CRF receptor subtype 1 is largely responsible for the action of the CRF system on cocaine locomotion and reward. These results suggest that the CRF receptor antagonist, particularly the CRF receptor subtype 1 antagonist, might be of some value in the treatment of cocaine addiction and cocaine-related behavioral disorders.

The pharmacology of CP-154,526, a non-peptide antagonist of the CRH1 receptor: a review

Since CRH has been shown to mediate stress-induced physiological and behavioral changes, it has been hypothesized that CRH receptor antagonists may have therapeutic potential in disorders that involve excessive CRH activity. CP-154,526 and its close analog antalarmin are potent, brain-penetrable, selective nonpeptide CRH1 receptor antagonists that were discovered in an effort to develop compounds with efficacy in CNS disorders precipitated by stress. Since its discovery many investigators have used CP-154,526 as a tool to study the pharmacology of CRH and its receptors and to evaluate its therapeutic potential in a variety of CNS and peripheral disorders. Systemically-administered CP-154,526 has been demonstrated to antagonize CRH- and stress-induced neuroendocrine, neurochemical, electrophysiological, and behavioral effects. These findings support the hypothesis that CRH1 receptor antagonists may have therapeutic utility in a number of neuropsychiatric disorders. CP-154,526, as well as other CRH1 receptor antagonists that have since been discovered, have also shown activity in several preclinical models of anxiety, depression, and substance abuse, while having little effect on locomotor activity and motor function. Although these effects are on occasion inconsistent among different laboratories, clinical evaluation of CRH1 antagonists appears justified on the basis of these and clinical data implicating the involvement of CRH in several CNS disorders. The effects of CRH1 antagonists on cognition, neurodegeneration, inflammation, and the gastrointestinal system have not been as extensively characterized and additional studies will be necessary to evaluate their therapeutic potential in these areas.

Functional consequences of the acute administration of the cannabinoid receptor antagonist, SR141716A, in cannabinoid-naive and -tolerant animals: a quantitative 2-[14C]deoxyglucose study

Cannabinoid systems have been shown to be involved in the regulation of ingestive behaviors. Administration of the cannabinoid antagonist, SR141716A, markedly reduces intake of sucrose solutions, food pellets, and ethanol. The purpose of the present studies was to identify the neural substrates that mediate these actions in rats using the quantitative autoradiographic 2-[14C]deoxyglucose (2-DG) method. In the first study, rats were trained to lever press in daily 15-min sessions for food pellets under a fixed-ratio schedule of food presentation. On the day of the experiment, rats received SR141716A (0, 1 or 3 mg/kg, i.p.) 15 min prior to behavioral testing, and the 2-DG procedure was initiated immediately after the operant test session. The acute administration of SR141716A dose-dependently decreased rates of responding and was accompanied by decreases in glucose utilization concentrated in the limbic system, particularly those areas mediating motivated behavior. Because the effects of SR141716A on behavior are intensified in animals tolerant to the effects of Delta(9)-THC, the purpose of the second study was to assess the effects of the SR141716A administration on food-maintained responding and rates of glucose utilization in tolerant animals. The suppression of responding was greater in tolerant than in drug-naive animals. Furthermore, decreases in cerebral metabolism were more intense and widespread. Although still concentrated in limbic regions, functional changes now included areas subserving the regulation of ingestive behavior including the hypothalamus. These data suggest that the effects of SR141716A administration shift in the tolerant animal and may involve different aspects of feeding behavior than in cannabinoid-naive animals.

Alcoholism: allostasis and beyond

Alcoholism is a chronic relapsing disorder characterized by compulsive drinking, loss of control over intake, and impaired social and occupational function. Animal models have been developed for various stages of the alcohol addiction cycle with a focus on the motivational effects of withdrawal, craving, and protracted abstinence. A conceptual framework focused on allostatic changes in reward function that lead to excessive drinking provides a heuristic framework with which to identify the neurobiologic mechanisms involved in the development of alcoholism. Neuropharmacologic studies in animal models have provided evidence for specific neurochemical mechanisms in specific brain reward and stress circuits that become dysregulated during the development of alcohol dependence. The brain reward system implicated in the development of alcoholism comprises key elements of a basal forebrain macrostructure termed the extended amygdala that includes the central nucleus of the amygdala, the bed nucleus of the stria terminalis, and a transition zone in the medial (shell) part of the nucleus accumbens. There are multiple neurotransmitter systems that converge on the extended amygdala that become dysregulated during the development of alcohol dependence, including gamma-aminobutyric acid, opioid peptides, glutamate, serotonin, and dopamine. In addition, the brain stress systems may contribute significantly to the allostatic state. During the development of alcohol dependence, corticotropin-releasing factor may be recruited, and the neuropeptide Y brain antistress system may be compromised. These changes in the reward and stress systems are hypothesized to maintain hedonic stability in an allostatic state, as opposed to a homeostatic state, and as such convey the vulnerability for relapse in recovering alcoholics. The allostatic model not only integrates molecular, cellular, and circuitry neuroadaptations in brain motivational systems produced by chronic alcohol ingestion with genetic vulnerability but also provides a key to translate advances in animal studies to the human condition.

Modulation of anxiety through blockade of anandamide hydrolysis

The psychoactive constituent of cannabis, Delta(9)-tetrahydrocannabinol, produces in humans subjective responses mediated by CB1 cannabinoid receptors, indicating that endogenous cannabinoids may contribute to the control of emotion. But the variable effects of Delta(9)-tetrahydrocannabinol obscure the interpretation of these results and limit the therapeutic potential of direct cannabinoid agonists. An alternative approach may be to develop drugs that amplify the effects of endogenous cannabinoids by preventing their inactivation. Here we describe a class of potent, selective and systemically active inhibitors of fatty acid amide hydrolase, the enzyme responsible for the degradation of the endogenous cannabinoid anandamide. Like clinically used anti-anxiety drugs, in rats the inhibitors exhibit benzodiazepine-like properties in the elevated zero-maze test and suppress isolation-induced vocalizations. These effects are accompanied by augmented brain levels of anandamide and are prevented by CB1 receptor blockade. Our results indicate that anandamide participates in the modulation of emotional states and point to fatty acid amide hydrolase inhibition as an innovative approach to anti-anxiety therapy.

Addictive potential of cannabinoids: the underlying neurobiology

Drugs that are addictive in humans have a number of commonalities in animal model systems-(1). they enhance electrical brain-stimulation reward in the core meso-accumbens reward circuitry of the brain, a circuit encompassing that portion of the medial forebrain bundle (MFB) which links the ventral tegmental area (VTA) of the mesencephalic midbrain with the nucleus accumbens (Acb) of the ventral limbic forebrain; (2). they enhance neural firing of a core dopamine (DA) component of this meso-accumbens reward circuit; (3). they enhance DA tone in this reward-relevant meso-accumbens DA circuit, with resultant enhancement of extracellular Acb DA; (4). they produce conditioned place preference (CPP), a behavioral model of incentive motivation; (5). they are self-administered; and (6). they trigger reinstatement of drug-seeking behavior in animals behaviorally extinguished from intravenous drug self-administration behavior and, perforce, pharmacologically detoxified from their self-administered drug. Cannabinoids were long considered 'anomalous', in that they were believed to not interact with these brain reward processes or support drug-seeking and drug-taking behavior in these animal model systems. However, it is now clear-from the published data of several research groups over the last 15 years-that this view of cannabinoid action on brain reward processes and reward-related behaviors is untenable. This paper reviews those data, and concludes that cannabinoids act on brain reward processes and reward-related behaviors in strikingly similar fashion to other addictive drugs.

The enzymatic inactivation of the fatty acid amide class of signaling lipids

The fatty acid amide (FAA) class of signaling lipids modulates a number of neurobehavioral processes in mammals, including pain, sleep, feeding, and locomotor activity. Representative FAAs include the endogenous cannabinoid anandamide and the sleep-inducing lipid oleamide. Despite activating several neuroreceptor systems in vitro, most FAAs produce only weak and transient behavioral effects in vivo, presumably due to their expeditious catabolism. This review focuses on one enzyme, fatty acid amide hydrolase (FAAH) that appears to play a major role in regulating the amplitude and duration of FAA signals in vivo. In particular, we will highlight a series of recent papers that have investigated the physiological functions of the mouse and human FAAH enzymes. Collectively, these studies promote FAAH as a central component of FAA signaling pathways, especially those mediated by the endocannabinoid anandamide, and suggest that this enzyme may represent an attractive pharmaceutical target for the treatment of pain and related neurophysiological disorders.

A peripheral mechanism for CB1 cannabinoid receptor-dependent modulation of feeding

Recent studies suggest that the endocannabinoid system modulates feeding. Despite the existence of central mechanisms for the regulation of food intake by endocannabinoids, evidence indicates that peripheral mechanisms may also exist. To test this hypothesis, we investigated (1) the effects of feeding on intestinal anandamide accumulation; (2) the effects of central (intracerebroventricular) and peripheral (intraperitoneal) administration of the endocannabinoid agonist anandamide, the synthetic cannabinoid agonist R-(+)-(2,3-dihydro-5-methyl-3-[(4-morpholinyl)methyl]pyrol[1,2,3-de]-1,4-benzoxazin-6-yl)(1-naphthalenyl) methanone monomethanesulfonate (WIN55,212-2), and the CB1-selective antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methylpyrazole-3-carboxamide (SR141716A) on food intake in rats; and (3) the effects of sensory deafferentation on the modulation of feeding by cannabinoids. Food deprivation produced a sevenfold increase in anandamide content in the small intestine but not in the brain or stomach. Refeeding normalized intestinal anandamide levels. Peripheral but not central administration of anandamide or WIN55,212-2 promoted hyperphagia in partially satiated rats. Similarly, peripheral but not central administration of SR141716A reduced food intake. Capsaicin deafferentation abolished the peripheral effects of both cannabinoid agonists and antagonists, suggesting that these agents modulate food intake by acting on CB1 receptors located on capsaicin-sensitive sensory terminals. Oleoylethanolamide, a noncannabinoid fatty ethanolamide that acts peripherally, prevented hyperphagia induced by the endogenous cannabinoid anandamide. Pretreatment with SR141716A enhanced the inhibition of feeding induced by intraperitoneal administration of oleoylethanolamide. The results reveal an unexpected role for peripheral CB1 receptors in the regulation of feeding.

Development and consequences of cannabis dependence

The past 10 to 15 years of clinical and basic research have produced strong evidence demonstrating that cannabis can and does produce dependence. Clinical and epidemiological studies indicate that cannabis dependence is a relatively common phenomenon associated with significant psychosocial impairment. Basic research has identified a neurobiological system specific to the actions of cannabinoids. Human and nonhuman studies have demonstrated a valid withdrawal syndrome that is relatively common among heavy marijuana users. Last, clinical trials evaluating treatments for cannabis dependence suggest that this disorder, like other substance dependence disorders, is responsive to intervention, yet the majority of patients have difficulty achieving and maintaining abstinence. Of concern, treatment seeking for marijuana dependence has increased almost twofold over the past 10 years. This report briefly reviews selected research literature relevant to our current understanding of cannabis dependence, its associated consequences, and treatment efficacy.

Marijuana withdrawal syndrome in the animal model

Although the proposition that repeated marijuana use can lead to marijuana dependence has long been accepted, only recently has evidence emerged suggesting that abstinence leads to clinically significant withdrawal symptoms. Converging evidence from human and animal studies has increased our understanding of cannabinoid dependence. One of the most powerful tools to advance this area of research is the CB1 cannabinoid receptor antagonist SR 141716A, which reliably precipitates withdrawal syndromes in mice, rats, and dogs that have been treated repeatedly with cannabinoids. In addition, the use of CB1 receptor knockout mice has revealed that not only cannabinoid dependence is mediated through a CB1 receptor mechanism of action, but CB1 receptors also modulate opioid dependence. Moreover, the results of other genetically altered mouse models suggest the existence of a reciprocal relationship between cannabinoid and opioid systems in drug dependence. Undoubtedly, these animal models will play pivotal roles in further characterizing cannabinoid dependence and elucidating the mechanisms of action, as well as developing potential pharmacotherapies for cannabinoid dependence.

Changes in endocannabinoid contents in the brain of rats chronically exposed to nicotine, ethanol or cocaine

Despite recent data suggesting that the endocannabinoid transmission is a component of the brain reward system and plays a role in dependence/withdrawal to different habit-forming drugs, only a few studies have examined changes in endocannabinoid ligands and/or receptors in brain regions related to reinforcement processes after a chronic exposure to these drugs. Recently, we carried out a comparative analysis of the changes in cannabinoid CB(1) receptor density in several rat brain regions caused by chronic exposure to some of the most powerful habit-forming drugs. In the present study, we have extended this objective by examining changes in the brain contents of arachidonoylethanolamide (AEA) and 2-arachidonoyl-glycerol (2-AG), the endogenous ligands for cannabinoid receptors, in animals chronically exposed to cocaine, nicotine or ethanol. Results were as follows. Cocaine was the drug exhibiting the minor number of effects, with only a small, but significant, decrease in the content of 2-AG in the limbic forebrain. In contrast, chronic alcohol exposure caused a decrease in the contents of both AEA and 2-AG in the midbrain, while it increased AEA content in the limbic forebrain. This latter effect was also observed after chronic nicotine exposure together with an increase in AEA and 2-AG contents in the brainstem. In contrast, the hippocampus, the striatum and the cerebral cortex exhibited a decrease in AEA and/or 2-AG contents after chronic nicotine exposure. We also tested the effect of chronic nicotine on brain CB(1) receptors, which had not been investigated before, and found an almost complete lack of changes in mRNA levels or binding capacity for these receptors. In summary, our results, in concordance with previous data on CB(1) receptors, indicate that the three drugs tested here produce different changes in endocannabinoid transmission. Only in the case of alcohol and nicotine, we observed a common increase in AEA contents in the limbic forebrain. This observation is important considering that this region is a key area for the reinforcing properties of habit-forming drugs, which might support the involvement of endocannabinoid transmission in some specific events of the reward system activated by these drugs.

Role of corticotropin-releasing hormone in the amygdala and bed nucleus of the stria terminalis in the behavioral, pain modulatory, and endocrine consequences of opiate withdrawal

The extra-hypothalamic actions of corticotropin-releasing hormone (CRH) have been accorded an important role in coordinating responses to stressors and contributing to the consequences of drug abuse. Recent proposals suggest that CRH actions in the bed nucleus of the stria terminalis coordinate responses to tonic/unpredictable stressors whereas these actions in the central nucleus of the amygdala coordinate responses to phasic/predictable stressors. We used in situ hybridization histochemistry and site-specific microinjections of a CRH receptor antagonist to study the role of CRH in opiate withdrawal. Rats undergoing opiate withdrawal displayed clear behavioral and autonomic changes accompanied by hyperalgesia and increased plasma corticosterone. In situ hybridization of CRH mRNA revealed significant increases in the central nucleus of the amygdala but not in the bed nucleus of the stria terminalis among rats either chronically pre-treated with morphine, given an injection of naloxone, or both (precipitated withdrawal). An increase of CRH mRNA in the paraventricular nucleus of the hypothalamus was specific to rats undergoing withdrawal. Intracerebroventricular microinjection of the CRH receptor antagonist, alpha(h)CRH(9-41), reduced the severity of opiate withdrawal. Microinjections of alpha(h)CRH(9-41) into the central nucleus of the amygdala also reduced the severity of withdrawal whereas bed nucleus of the stria terminalis microinjections of alpha(h)CRH(9-41) were without effect. These experiments provide evidence for a role of amygdala, but not bed nucleus of the stria terminalis, CRH in opiate dependence. We propose a specific role for down-regulation of opiate receptor signaling in increased expression of the CRH gene in the amygdala. Moreover, we suggest that the roles accorded to CRH in the bed nucleus of the stria terminalis versus amygdala in coordinating responses to stressors may need to be reconsidered to distinguish between external and internal/interoceptive stressors.

Ethanol, endocannabinoids, and the cannabinoidergic signaling system

This article represents the proceedings of a symposium at the 2001 annual meeting of the Research Society on Alcoholism in Montreal, Canada. The chairpersons were Appa Hungund and George Koob. The presentations were (1) Role of endocannabinoids in ethanol tolerance, by Appa Hungund; (2) Modulation of cannabinoid receptor and its signal transduction in chronic alcoholism, by B. S. Basavarajappa; (3) Endocannabinoid involvement in the control of appetitive behavior, by George Kunos; (4) Regulation of voluntary ethanol intake by cannabinoid receptor agonists and antagonists in alcohol-preferring sP rats, by Giancarlo Colombo; (5) Role of endogenous cannabinoid system in alcoholism, by Fernado Rodriguez de Fonseca; and (6) Endocannabinoids and dopamine interactions in vivo, by Loren Parsons and George Koob.

Study of cannabinoid dependence in animals

Different animal models have been used to clarify the consequences of chronic exposure to cannabinoid agonists and their abuse liability. Following the chronic administration of cannabinoids, tolerance develops to most of their pharmacological effects. The development of cannabinoid tolerance is particularly rapid, and seems to be due to pharmacodynamic events. A cross-tolerance among different exogenous cannabinoid agonists has been reported. Somatic signs of spontaneous withdrawal have not been reported after chronic Delta(9)-tetrahydrocannabinol (THC) treatment, but were observed after chronic treatment with the cannabinoid agonist WIN-55,212-2. The administration of the CB(1) cannabinoid antagonist SR141716A in animals chronically treated with THC and other cannabinoid agonists precipitated somatic manifestations of withdrawal. The potential ability of anandamide to induce physical dependence has not been clarified. Subjective drug effects of cannabinoids have been reported by drug discrimination studies, which show cross discrimination among different natural and synthetic agonists. The rewarding effects of cannabinoids have been revealed by using several paradigms: place conditioning, intracranial self-stimulation, and self-administration. Cannabinoids have been reported to lower intracranial self-stimulation thresholds in rats. However, particular experimental conditions are required to induce conditioned place preference with cannabinoids. Numerous studies have shown that THC is unable to induce a self-administration behaviour in animals. However, WIN-55,212-2 was intravenously self-administered in mice, and monkeys that had a previous history of cocaine self-administration also self-administered THC. The mesolimbic dopaminergic system seems to be the substrate for the rewarding properties of cannabinoids.

A missense mutation in human fatty acid amide hydrolase associated with problem drug use

Problem drug use and dependence are neurobehavioral disorders of complex origin. Although environmental factors contribute to drug abuse and addiction, genetic factors also play a significant role estimated at 40-60% of the total risk. Nonetheless, the precise identities of human genes that confer vulnerability to problem drug use remain mostly unknown. Here, we describe a natural single nucleotide polymorphism in the human gene that encodes the principal endocannabinoid-inactivating enzyme, fatty acid amide hydrolase (FAAH), that in homozygous form is strongly associated with both street drug use and problem drug/alcohol use. This single nucleotide polymorphism results in a missense mutation (385C-->A) that converts a conserved proline residue to threonine (Pro129-->Thr), producing a FAAH variant that displays normal catalytic properties but an enhanced sensitivity to proteolytic degradation. Collectively, these results suggest that genetic mutations in FAAH may constitute important risk factors for problem drug use and support a potential link between functional abnormalities in the endogenous cannabinoid system and drug abuse and dependence.

Inhibition of methamphetamine self-administration in rats by cannabinoid receptor antagonist AM 251

Cannabinoids are drugs that are frequently abused not only alone, but also in combination with other drugs. The present study investigated possible functional interactions between the psychostimulant methamphetamine and the cannabinoid receptor agonists anandamide, or R-(+)-methanandamide and cannabinoid antagonist AM 251 in the rat model of i.v. drug self-administration. In rats trained to self-administer methamphetamine, the intake was significantly decreased by the cannabinoid antagonist and tended to be dose-dependently increased by pre-treatment with cannabinoid receptor agonists. Possible mechanisms for these drug interactions are discussed and the use of the cannabinoid antagonist for the treatment of drug abuse is considered.

A review of the published literature into cannabis withdrawal symptoms in human users

Recent experimental papers have been published suggesting the appearance of withdrawal symptoms upon the cessation of cannabis use in human users and proposing the introduction of a diagnostic category for such symptoms. Research also continues to be published into the physiological effects of cannabis on animals via self-administration paradigms and the use of cannabinoid antagonists. Animal research does not provide a clear picture of a consistent withdrawal effect. The literature on withdrawal symptoms appearing in human users following the cessation of cannabis is investigated in this paper to clarify this issue further and enhance the scientific and lay debate on the status of the drug. Methodological weaknesses in the literature are highlighted. These include variable levels of drug-dose administered in laboratory conditions, lack of controlled studies and the absence of definitions of the withdrawal syndrome sought. It is suggested that the studies conducted to date do not provide a strong evidence base for the drawing of any conclusions as to the existence of a cannabis withdrawal syndrome in human users, or as to the cause of symptoms reported by those abstaining from the drug. On the basis of current research cannabis cannot be said to provide as clear a withdrawal pattern as other drugs of abuse, such as opiates. However, cannabis also highlights the need for a further defining of withdrawal, in particular the position that rebound effects occupy in this phenomenon. It is concluded that more controlled research might uncover a diagnosable withdrawal syndrome in human users and that there may be a precedent for the introduction of a cannabis withdrawal syndrome before the exact root of it is known.

Genetic factors involved in central nervous system/immune interactions

Analysis of several inbred rat strains has led us to hypothesize that HPA axis abnormalities may contribute, in part, to susceptibility to both autoimmune disease and addiction. In this article we review the evidence for this hypothesis and describe our ongoing efforts to genetically characterize these traits. We have mapped the locations of 23 loci that regulate autoimmune disease in rats, and are currently constructing QTL congenic lines in which a genomic region from the resistant strain is transferred to the susceptible strain or vice versa. These QTL congenic lines will be valuable to test whether genes encoding autoimmune regulation also control neuroendocrine traits. Further genetic dissection and identification of the underlying genes will be necessary to infer a mechanistic link between autoimmune and neuroendocrine traits.

Cannabinoid addiction: behavioral models and neural correlates

The use of cannabis sativa preparations as recreational drugs can be traced back to the earliest civilizations. However, animal models of cannabinoid addiction allowing the exploration of neural correlates of cannabinoid abuse have been developed only recently. We review these models and the role of the CB1 cannabinoid receptor, the main target of natural cannabinoids, and its interaction with opioid and dopamine transmission in reward circuits. Extensive reviews on the molecular basis of cannabinoid action are available elsewhere (Piomelli et al., 2000; Schlicker and Kathmann, 2001).

Elevated extracellular CRF levels in the bed nucleus of the stria terminalis during ethanol withdrawal and reduction by subsequent ethanol intake

Corticotropin-releasing factor (CRF) is widely distributed throughout the brain and has been shown to mediate numerous endocrine and behavioral responses to stressors. During acute ethanol withdrawal, CRF release is increased in the central nucleus of the amygdala (CeA), and there is evidence to suggest that this activation of amygdala CRF systems may mediate the anxiogenic properties of the ethanol withdrawal syndrome. The present study was conducted to determine if another CRF-containing limbic structure, the bed nucleus of the stria terminalis (BNST), we would exhibit similar increases in CRF neurotransmission during ethanol withdrawal. Rats were administered an ethanol-containing (6.7% v/v) or control liquid diet for 2 weeks and subsequently implanted with microdialysis probes into the lateral BNST. A 50-75% increase in dialysate CRF levels was observed following removal of the ethanol-containing diet, while no changes were observed in control animals. When ethanol-withdrawn animals were given subsequent access to the ethanol-containing diet, dialysate CRF levels returned to basal levels. However, when ethanol-withdrawn animals were given subsequent access to the control diet, dialysate CRF levels increased further to 101% above basal levels. These data demonstrate that extracellular CRF levels are increased in the BNST during ethanol withdrawal, and that these increases are reduced by subsequent ethanol intake.

Marijuana use among adolescents

More than half of US adolescents will experiment with marijuana. Of those who try marijuana more than once, approximately one third will subsequently use marijuana regularly, although most will have stopped by their late 20s. Although genetic predisposition plays the most important role in determining who will develop dependence, environmental factors influence who will initiate marijuana use. One of the challenges for prevention and treatment programs is that the immediate adverse effects of marijuana use are not extreme, and many adolescents have difficulty in making decisions based on future risks. Therefore, the consequences of leaving school early, having unprotected sex, and driving while intoxicated are often insufficient to deter adolescents from using marijuana. Thus, it is not surprising that current prevention and treatment programs have had limited success in decreasing the rates of initiation and regular use of marijuana among adolescents. However, the accumulation of data about marijuana use in adolescents has the potential to enable the development of more effective prevention and treatment programs.

Glucocorticoid feedback increases the sensitivity of the limbic system to stress

In the hypothalamus, corticotropin-releasing hormone (CRH) has a well-described role initiating the hypothalamic-pituitary-adrenal (HPA) axis response to stress. Cortisol, released from the adrenal gland, exerts negative feedback on this axis. The role of extrahypothalamic CRH in stress responses is less well known. The purpose of this study was to measure the response of CRH in the amygdala to acute and repeated stress and to examine if cortisol had any effect on this response. Immunosensor-based microdialysis probes were used to measure CRH and cortisol in the amygdala and cortisol systemically in sheep exposed to a predator stress (a dog). Upon presentation of a dog, CRH increased in the amygdala of the sheep and then fell off. Cortisol levels rose both systemically and in the amygdala, and as they peaked, a second CRH response was observed. Repeated stress changed this response, with the magnitude of the first CRH peak decreasing while the second peak increased. Repeated stress also produced an exaggeration in both of the CRH peaks to presentation of a subsequent novel stress (a forelimb electric shock). Animals that had an escape route from the repeated dog stress did not show this exaggeration when faced subsequently with the novel stress. Administration of mifepristone, a glucocorticoid receptor antagonist, prior to the delivery of the repeat stress prevented subsequent changes in the CRH response. The data suggest that the amygdala shows a CRH response to presentation of a stressor acutely and repeatedly and that repeated stress can alter subsequent amygdala responsiveness to the same or a different stressor. This alteration appears dependent on circulatory glucocorticoids.

Endocannabinoids in cognition and dependence

Cannabis use is associated with a wide range of pharmacological effects, some of which have potential therapeutic benefit while others result in negative outcomes. Acute cannabinoid intoxication has been well documented to produce deficits in cognitive functioning with concomitant changes in glutamatergic, GABAergic, and cholinergic neurochemical systems in the hippocampus, each of which has been implicated in memory. Additionally, cannabis-dependent individuals abstaining from this drug can undergo a constellation of mild withdrawal effects. The use of the CB(1) cannabinoid receptor antagonist SR141716A and transgenic mice lacking the CB(1) receptor are critical tools for investigating the role of the endocannabinoid system in cognition, drug dependence, and other physiological processes. Converging evidence in which performance in a variety of memory tasks is enhanced following either SR141716A treatment or in CB(1) receptor knockout mice indicates that this system may play an important role in modulating cognition. There are also indications that this system may function to modulate opioid dependence. The purpose of this review is to describe recent advances that have furthered our understanding of the roles that the endocannabinoid system play on both cognition and drug dependence.

Prevention of cannabinoid withdrawal syndrome by lithium: involvement of oxytocinergic neuronal activation

Cannabis (i.e., marijuana and cannabinoids) is the most commonly used illicit drug in developed countries, and the lifetime prevalence of marijuana dependence is the highest of all illicit drugs in the United States. To provide clues for finding effective pharmacological treatment for cannabis-dependent patients, we examined the effects and possible mechanism of lithium administration on the cannabinoid withdrawal syndrome in rats. A systemic injection of the mood stabilizer lithium, at serum levels that were clinically relevant, prevented the cannabinoid withdrawal syndrome. The effects of lithium were accompanied by expression of the cellular activation marker Fos proteins within most oxytocin-immunoreactive neurons and a significant increase in oxytocin mRNA expression in the hypothalamic paraventricular and supraoptic nuclei. Lithium also produced a significant elevation of oxytocin levels in the peripheral blood. We suggest that the effects of lithium against the cannabinoid withdrawal syndrome are mediated by oxytocinergic neuronal activation and subsequent release and action of oxytocin within the CNS. In support of our hypothesis, we found that the effects of lithium against the cannabinoid withdrawal syndrome were antagonized by systemic preapplication of an oxytocin antagonist and mimicked by systemic or intracerebroventricular injection of oxytocin. These results demonstrate that oxytocinergic neuronal activation plays a critical role in the action of lithium against the cannabinoid withdrawal syndrome in rats, thus providing a potentially novel strategy for the treatment of cannabis dependence in humans.

Absence of delta -9-tetrahydrocannabinol dysphoric effects in dynorphin-deficient mice

The involvement of dynorphin on Delta-9-tetrahydrocannabinol (THC) and morphine responses has been investigated by using mice with a targeted inactivation of the prodynorphin (Pdyn) gene. Dynorphin-deficient mice show specific changes in the behavioral effects of THC, including a reduction of spinal THC analgesia and the absence of THC-induced conditioned place aversion. In contrast, acute and chronic opioid effects were normal. The lack of negative motivational effects of THC in the absence of dynorphin demonstrates that this endogenous opioid peptide mediates the dysphoric effects of marijuana.

Distribution of CB1 cannabinoid receptors in the amygdala and their role in the control of GABAergic transmission

Cannabinoids are the most popular illicit drugs used for recreational purposes worldwide. However, the neurobiological substrate of their mood-altering capacity has not been elucidated so far. Here we report that CB1 cannabinoid receptors are expressed at high levels in certain amygdala nuclei, especially in the lateral and basal nuclei, but are absent in other nuclei (e.g., in the central nucleus and in the medial nucleus). Expression of the CB1 protein was restricted to a distinct subpopulation of GABAergic interneurons corresponding to large cholecystokinin-positive cells. Detailed electron microscopic investigation revealed that CB1 receptors are located presynaptically on cholecystokinin-positive axon terminals, which establish symmetrical GABAergic synapses with their postsynaptic targets. The physiological consequence of this particular anatomical localization was investigated by whole-cell patch-clamp recordings in principal cells of the lateral and basal nuclei. CB1 receptor agonists WIN 55,212-2 and CP 55,940 reduced the amplitude of GABA(A) receptor-mediated evoked and spontaneous IPSCs, whereas the action potential-independent miniature IPSCs were not significantly affected. In contrast, CB1 receptor agonists were ineffective in changing the amplitude of IPSCs in the rat central nucleus and in the basal nucleus of CB1 knock-out mice. These results suggest that cannabinoids target specific elements in neuronal networks of given amygdala nuclei, where they presynaptically modulate GABAergic synaptic transmission. We propose that these anatomical and physiological features, characteristic of CB1 receptors in several forebrain regions, represent the neuronal substrate for endocannabinoids involved in retrograde synaptic signaling and may explain some of the emotionally relevant behavioral effects of cannabinoid exposure.

Behavioural and biochemical evidence for interactions between Delta 9-tetrahydrocannabinol and nicotine

Behavioural and pharmacological effects of Delta9-tetrahydrocannabinol (THC) and nicotine are well known. However, the possible interactions between these two drugs of abuse remain unclear in spite of the current association of cannabis and tobacco in humans. The present study was designed to analyse the consequences of nicotine administration on THC-induced acute behavioural and biochemical responses, tolerance and physical dependence. Nicotine strongly facilitated hypothermia, antinociception and hypolocomotion induced by the acute administration of THC. Furthermore, the co-administration of sub-threshold doses of THC and nicotine produced an anxiolytic-like response in the light - dark box and in the open-field test as well as a significant conditioned place preference. Animals co-treated with nicotine and THC displayed an attenuation in THC tolerance and an enhancement in the somatic expression of cannabinoid antagonist-precipitated THC withdrawal. THC and nicotine administration induced c-Fos expression in several brain structures. Co-administration of both compounds enhanced c-Fos expression in the shell of the nucleus accumbens, central and basolateral nucleus of the amygdala, dorso-lateral bed nucleus of the stria terminalis, cingular and piriform cortex, and paraventricular nucleus of the hypothalamus. These results clearly demonstrate the existence of a functional interaction between THC and nicotine. The facilitation of THC-induced acute pharmacological and biochemical responses, tolerance and physical dependence by nicotine could play an important role in the development of addictive processes.

Temporal concordance of cocaine effects on mood states and neuroendocrine hormones

Cocaine stimulates the release of adrenocorticotropin hormone (ACTH) and cortisol in both clinical and preclinical studies, but the temporal sequence of cocaine-induced changes in other hormones and affective states is unclear. The purpose of this study was to analyze the pattern and temporal concordance of cocaine-induced changes in ACTH, cortisol, dihydroepiandrosterone (DHEA), epinephrine, heart rate and subjective reports of euphoria. Six healthy men who met Diagnostic and Statistical Manual-IV (DSM-IV) criteria for cocaine abuse provided informed consent for participation. Cocaine (0.4 mg/kg) or saline placebo was infused intravenously over 1 min under double-blind conditions. Euphoria, ACTH, epinephrine and heart rate increased significantly within 8 to 12 min after i.v. cocaine administration in all subjects (P<0.01-0.001). Moreover, the increases in euphoria, ACTH, epinephrine and heart rate each were significantly correlated with increases in plasma cocaine levels (P<0.001). Euphoria increased significantly within 2 min after i.v. cocaine injection, as plasma cocaine levels were increasing, and peak euphoria was reported at 10 min (P<0.001). Peak ACTH values were measured at 8.7 (+/-0.8) min after cocaine injection (P<0.01). Peak levels of epinephrine were measured at 10 (+/-1) min after cocaine injection (P<0.05). Peak increases in heart rate occurred at 11.7 (+/-1.1) min after cocaine injection (P<0.05). Peak levels of cortisol and DHEA were measured at 36 (+/-4.0) and 28.7 (+/-4.3) min after cocaine injection (P<0.01 and P<0.01). The temporal concordance between cocaine-induced stimulation of ACTH, epinephrine and subjective euphoria suggests that these hormonal changes are significant concomitants of the abuse-related effects of cocaine. The similarities between these hormonal profiles, the subjective effects of cocaine and the effects of "stress" are discussed.

The distribution of cannabinoid-induced Fos expression in rat brain: differences between the Lewis and Wistar strain

Previous studies have suggested that cannabis-like drugs produce mainly aversive and anxiogenic effects in Wistar strain rats, but rewarding effects in Lewis strain rats. In the present study we compared Fos expression, body temperature effects and behavioral effects elicited by the cannabinoid CB(1) receptor agonist CP 55,940 in Lewis and Wistar rats. Both a moderate (50 microg/kg) and a high (250 microg/kg) dose level were used. The 250 microg/kg dose caused locomotor suppression, hypothermia and catalepsy in both strains, but with a significantly greater effect in Wistar rats. The 50 microg/kg dose provoked moderate hypothermia and locomotor suppression but in Wistar rats only. CP 55,940 caused significant Fos immunoreactivity in 24 out of 33 brain regions examined. The most dense expression was seen in the paraventricular nucleus of the hypothalamus, the islands of Calleja, the lateral septum (ventral), the central nucleus of the amygdala, the bed nucleus of the stria terminalis (lateral division) and the ventrolateral periaqueductal gray. Despite having a similar distribution of CP 55,940-induced Fos expression, Lewis rats showed less overall Fos expression than Wistars in nearly every brain region counted. This held equally true for anxiety-related brain structures (e.g. central nucleus of the amygdala, periaqueductal gray and the paraventricular nucleus of the hypothalamus) and reward-related sites (nucleus accumbens and pedunculopontine tegmental nucleus). In a further experiment, Wistar rats and Lewis rats did not differ in the amount of Fos immunoreactivity produced by cocaine (15 mg/kg). These results indicate that Lewis rats are less sensitive to the behavioral, physiological and neural effects of cannabinoids. The exact mechanism underlying this subsensitivity requires further investigation.

Neurobiology of the nicotine withdrawal syndrome

The aversive aspects of withdrawal from chronic nicotine exposure are thought to be an important motivational factor contributing to the maintenance of the tobacco habit in human smokers. Much emphasis has been placed on delineating the underlying neurobiological mechanisms mediating different components of the nicotine withdrawal syndrome. Recent studies have shown that both central and peripheral populations of nicotinic acetylcholine receptors (nAChRs) are involved in mediating somatic signs of nicotine withdrawal as measured by the rodent nicotine abstinence scale. However, only central populations of nAChRs are involved in mediating affective aspects of nicotine withdrawal, as measured by elevations in brain-stimulation reward thresholds and conditioned place aversion. Nicotine interacts with several neurotransmitter systems, including acetylcholine, dopamine, opioid peptides, serotonin, and glutamate systems. Evidence so far suggests that these neurotransmitters play a role in nicotine dependence and withdrawal processes. The available evidence also suggests that different underlying neurochemical deficits mediate somatic and affective components of nicotine withdrawal. The aim of the present review is to discuss preclinical findings concerning the neuroanatomical and neurochemical substrates involved in these different aspects of nicotine withdrawal.

The decade 1989-1998 in Spanish psychology: an analysis of research in psychobiology

In this paper, we present an analysis of the research published during the 1989-1998 decade by tenured Spanish faculty members from the area of psychobiology. Database search and direct correspondence with the 110 faculty members rendered a list of 904 psychobiological papers. Classification and analysis of these papers led to the definition of at least 70 different research trends. Topics are grouped into several specific research areas: Learning and Memory; Development and Neural Plasticity; Emotion and Stress; Ethology; Neuropsychology; Sensory Processing; and Psychopharmacology. The international dissemination of this research, published in journals of high impact index, and the increasing number of papers are two noteworthy features.

Cannabinoid effects on anxiety-related behaviours and hypothalamic neurotransmitters

The aim of the present study was to examine the effects of the cannabinoid agonist CP 55,940 and the antagonist SR 141716A, alone and in combination, on rat exploratory and anxiety-like behaviour in the holeboard and elevated plus-maze tests. A further aim was to evaluate the effects of these treatments on hypothalamic neurotransmitters. Animals treated with CP 55,940 doses of 0.125 and 0.1 mg/kg exhibited less exploration and an increase in anxiety-like behaviour accompanied by great motor inhibition. No hypoactivity was seen at 0.075 mg/kg dosage, but anxiety and neophobic responses persisted, indicating independent and specific effects. Motor activity effects induced by CP 55,940 were reversed by pretreatment with SR 141716A (3 mg/kg). Surprisingly, when administered on its own, the antagonist also induced a reduction in exploratory parameters and an increase in anxiety-like responses. These apparently similar effects might be caused by different neural mechanisms. Finally, CP 55,940 increased hypothalamic dopamine and serotonin levels. These increases might be involved in the activation of the hypothalamic-pituitary-adrenal axis described for cannabinoids.

The psychoactive ingredient of marijuana induces behavioural sensitization

Here we describe, for the first time, the occurrence of behavioural sensitization after chronic exposure to Delta9-tetrahydrocannabinol. Rats were treated twice a day, for five days, with increasing doses (5, 10, 20, 40, 40 mg/kg i.p.) of Delta9-tetrahydrocannabinol or its vehicle and after 20 days of withdrawal, animals were challenged with 5 mg/kg (i.p.) of the drug and their behaviour was assessed. Contrary to the motor inhibition induced in control rats, challenge with Delta9-tetrahydrocannabinol in pre-exposed animals elicited a complex behavioural syndrome mainly characterized by oral stereotyped items. Due to the relevance of behavioural sensitization in drug-seeking behaviour that persists long after discontinuation of drug use, our findings suggest that cannabinoids could trigger neurobiological alteration not dissimilar from those observed with more harmful abused drugs.

Role of gonadal steroids in the corticotropin-releasing hormone and proopiomelanocortin gene expression response to Delta(9)-tetrahydrocannabinol in the hypothalamus of the rat

Chronic exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC) increases corticotropin-releasing hormone (CRH) and proopiomelanocortin (POMC) gene expression in the rat hypothalamus. The levels of circulating gonadal steroids concurrently modulate both neuropeptides in male and female rats. However, it remains unknown whether gonadal steroids regulate Delta(9)-THC effects on CRH and POMC gene expression in the hypothalamus of male and female rats. To explore this hypothesis, experiments were conducted on intact, 2-week-gonadectomized, 1-week-gonadectomized, 1-week-dihydrotestosterone (DHT)- or estradiol-replaced male and female rats. One week after hormonal replacement, animals were treated with vehicle or Delta(9)-THC (5 mg/kg/day, i.p. for 7 days). Administration of Delta(9)-THC to intact male rats increased CRH gene expression. Castration abolished Delta(9)-THC effects of CRH gene expression in males but not in females. On the other hand, POMC mRNA levels were reduced as a result of castration, and DHT treatment did not prevent this decrease. Delta(9)-THC treatment similarly increases POMC gene expression of intact, orchidectomized and DHT-replaced males. In females, ovariectomy decreased CRH gene expression. Delta(9)-THC administration increased CRH gene expression to the same extent in castrated and estradiol-replaced rats. On the other hand, POMC gene expression was increased by ovariectomy, and Delta(9)-THC administration did only increase POMC transcript levels in the estradiol-replaced group. These data show that gonadal steroids differentially regulate the effects of Delta(9)-THC on both CRH and POMC gene expression in the hypothalamus of male and female rats, suggesting gender differences in the reaction to cannabinoids.

Delta9-tetrahydrocannabinol releases and facilitates the effects of endogenous enkephalins: reduction in morphine withdrawal syndrome without change in rewarding effect

Recent studies have suggested that cannabinoids might initiate the consumption of other highly addictive substances, such as opiates. In this work, we show that acute administration of Delta9-tetrahydrocannabinol in mice facilitates the antinociceptive and antidepressant-like responses elicited by the endogenous enkephalins protected from their degradation by RB 101, a complete inhibitor of enkephalin catabolism. This emphasizes the existence of a physiological interaction between endogenous opioid and cannabinoid systems. Accordingly, Delta9-tetrahydrocannabinol increased the release of Met-enkephalin-like material in the nucleus accumbens of awake and freely moving rats measured by microdialysis. In addition, this cannabinoid agonist displaced the in vivo [3H]diprenorphine binding to opioid receptors in total mouse brain. The repetitive pretreatment during 3 weeks of Delta9-tetrahydrocannabinol in mice treated chronically with morphine significantly reduces the naloxone-induced withdrawal syndrome. However, this repetitive administration of Delta9-tetrahydrocannabinol did not modify or even decrease the rewarding responses produced by morphine in the place preference paradigm. Taken together, these behavioural and biochemical results demonstrate the existence of a direct link between endogenous opioid and cannabinoid systems. However, chronic use of high doses of cannabinoids does not seem to potentiate the psychic dependence to opioids.

Functional interaction between opioid and cannabinoid receptors in drug self-administration

The present study was designed to explore the relationship between the cannabinoid and opioid receptors in animal models of opioid-induced reinforcement. The acute administration of SR141716A, a selective central cannabinoid CB1 receptor antagonist, blocked heroin self-administration in rats, as well as morphine-induced place preference and morphine self-administration in mice. Morphine-dependent animals injected with SR141716A exhibited a partial opiate-like withdrawal syndrome that had limited consequences on operant responses for food and induced place aversion. These effects were associated with morphine-induced changes in the expression of CB1 receptor mRNA in specific nuclei of the reward circuit, including dorsal caudate putamen, nucleus accumbens, and septum. Additionally, the opioid antagonist naloxone precipitated a mild cannabinoid-like withdrawal syndrome in cannabinoid-dependent rats and blocked cannabinoid self-administration in mice. Neither SR141716A nor naloxone produced any intrinsic effect on these behavioral models. The present results show the existence of a cross-interaction between opioid and cannabinoid systems in behavioral responses related to addiction and open new strategies for the treatment of opiate dependence.

Chronic treatment with Delta(9)-tetrahydrocannabinol enhances the locomotor response to amphetamine and heroin. Implications for vulnerability to drug addiction

Cannabis sativa preparations are some of the most widely used illicit recreational drugs. In addition to their direct addictive potential, cannabinoids may influence the sensitivity to other drugs. The aim of the present study was to determine if a cross-sensitization between Delta(9)-tetrahydrocannabinol (Delta(9)-THC) and other drugs (amphetamine and heroin) could be demonstrated. We examined the effects of a chronic treatment with Delta(9)-THC (0.6, 3 and 15mg/kg, ip) on the locomotor response to amphetamine (1mg/kg, ip) and heroin (1mg/kg, ip). Chronic treatment with Delta(9)-THC resulted in tolerance to the initial hypothermic and anorexic effects. Pre-treatment with Delta(9)-THC increased the locomotor responses to amphetamine and heroin. This cross-sensitization was time-dependent as it was observed three days after the last injection of Delta(9)-THC for amphetamine, and a relatively long time after the end of chronic treatment (41 days) for heroin. Moreover, the enhanced response to amphetamine or heroin was noted in some individuals only: the high-responder rats (HR). These animals have previously been shown to be vulnerable to drug taking behaviors. It is hypothesised that repeated use of Cannabis derivates may facilitate progression to the consumption of other illicit drugs in vulnerable individuals.

Delta 9-tetrahydrocannabinol-induced MAPK/ERK and Elk-1 activation in vivo depends on dopaminergic transmission

It is now well established that central effects of Delta 9-tetrahydrocannabinol (THC), the main psychoactive component of marijuana, are mediated by CB1 cannabinoid receptors. However, intraneuronal signalling pathways activated in vivo by THC remain poorly understood. We show that acute administration of THC induces a progressive and transient activation (i.e. phosphorylation) of the mitogen activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) in the dorsal striatum and the nucleus accumbens (NA). This activation, corresponding to both neuronal cell bodies and the surrounding neuropil, is totally inhibited by the selective antagonist of CB1 cannabinoid receptors, SR 141716A. However, blockade of dopaminergic (DA) D1 receptors by administration of SCH 23390, prior to THC, totally prevents ERK activation in the striatum, thus demonstrating a critical involvement of DA systems in THC-induced ERK activation. DA-D2 and glutamate receptors of NMDA subtypes also participate, albeit to a lesser extent, to THC-induced ERK activation in the striatum, as shown after injection of selective antagonists (raclopride and MK801, respectively). Furthermore, THC-induced phosphorylation of the transcription factor Elk-1, and up-regulation of zif268 mRNA expression are blocked by SL327, a specific inhibitor of MAPK/ERK kinase (MEK), the upstream kinase of ERK, as well as SCH 23390. Finally, using the place-preference paradigm, we show that ERK inhibition blocks THC-induced rewarding properties. Altogether, our data strongly support that ERK activation in the striatum is critically involved in long-term neuronal adaptive responses underlying THC-induced long-term behaviours.

Lofexidine versus clonidine in rapid opiate detoxification

The aim of the present study is to evaluate lofexidine and clonidine, in an accelerated opiate detoxification procedure (3 days), without anaesthesia. Forty heroin-dependent individuals were detoxified, evaluating withdrawal symptoms, craving levels, mood changes, urine toxicologic screens, and dropout during therapy with either (1) clonidine, oxazepam, baclofen, and ketoprofene, with naloxone and naltrexone for 3 days (20 subjects) or (2) lofexidine, oxazepam, baclofen, and ketoprofene with naloxone and naltrexone for 3 days (20 subjects). Both clonidine and lofexidine rapid detoxifications were found effective. The subjects treated with lofexidine showed significantly lower levels of withdrawal symptoms, fewer mood problems, less sedation and hypotension. No significant differences in craving levels, morphine metabolites in urine, or dropout rate were evidenced between the two groups. The early use of naltrexone during detoxification in combination with either alpha-2-agonist facilitated the acceptance for long-term naltrexone treatment. Lofexidine appeared to be more useful than clonidine in a 3-day accelerated opiate detoxification, not only to counteract withdrawal symptoms, but also in the treatment of dysphoria and mood changes. Because lofexidine does not produce hypotension, safe outpatient treatment, without hospital support, could be possible.

Behavioral sensitization to heroin by cannabinoid pretreatment in the rat

The behavioral consequences of acute heroin challenge (0.5 mg/kg, s.c.) were measured in rats previously submitted to repeated administration of increasing doses of the synthetic cannabinoid receptor agonist, R(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl)methyl]pyrrolo-[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl) methanone mesylate (WIN55212.2) (first day 2 mg/kg, second day 4 mg/kg, third day 8 mg/kg) or vehicle. Heroin administration to rats pretreated with vehicle produced catalepsy. The same dose of heroin in WIN55212.2-pretreated rats was followed by a marked increase of locomotor activity with stereotyped and non-stereotyped behaviors. These effects were blocked by the opioid receptor antagonist, naloxone. These findings indicate that pretreatment with WIN55212.2 produces cross-sensitization to heroin in the rat. These changes might reflect long-lasting changes of receptor population or transcriptional mechanisms in the mesolimbic system.

Hu 210: a potent tool for investigations of the cannabinoid system

The synthetic compound HU 210 displays a multiplicity of biochemical, pharmacological, and behavioral effects, most of which have been demonstrated to be dependent on a selective agonistic activity at CB(1) and CB(2) cannabinoid receptors and to involve the main neurotransmitter systems. Results obtained in various studies suggest a potential clinical application of this highly potent drug (e.g., as antipyretic, antiinflammatory, analgesic, antiemetic, and antipsychotic agent) as well as its usefulness in research aimed to develop a better understanding of the involvement of the endogenous cannabinoid system in a number of physiopathological functions.

Compulsive drug-seeking behavior and relapse. Neuroadaptation, stress, and conditioning factors

The development of addiction and vulnerability to relapse following withdrawal is proposed to be the result of neuroadaptive processes within the central nervous system that oppose the acute reinforcing actions of drugs of abuse. These changes lead to impairment in the mechanisms that mediate positive reinforcement and the emergence of affective changes such as anxiety, dysphoria, and depression during withdrawal. Considerable evidence exists implicating perturbations in DA and 5-HT transmission in the nucleus accumbens--neurochemical systems that are activated by cocaine and ethanol self-administration and deficient during withdrawal--as potential substrates for these affective changes. In addition, growing evidence suggests that enhanced CRF release in the central nucleus of the amygdala represents a mechanism underlying the anxiogenic and stress-like consequences of withdrawal that are common to all drugs of abuse. A growing body of evidence also implicates dysregulation of the non-neuroendocrine CRF stress system within the central nucleus of the amygdala as a common factor in the anxiogenic and aversive consequences of withdrawal from drugs of abuse. Moreover, a possible link may exist between long-lasting abnormalities in CRF function in the CeA and vulnerability to relapse during protracted abstinence. Another presumably critical element contributing to the chronic relapsing nature of drug addiction is the learned responses to drug-related stimuli. The long-lasting efficacy of drug- and alcohol-associated contextual stimuli in eliciting drug-seeking behavior in animal models of relapse resembles the endurance of conditioned cue reactivity and cue-induced cocaine craving in humans and confirms a significant role of learning factors in the long-lasting addictive potential of cocaine. With cocaine, D1-dependent neural mechanisms within the medial prefrontal cortex and basolateral amygdala may be important substrates for the motivating effects of drug-related environmental stimuli. With ethanol, available data suggest a role for opioid receptors in the mediation of conditioned drug-seeking behavior. Finally, conditioning factors (i.e., exposure to drug-associated stimuli) and stress can interact to augment vulnerability to relapse. This finding emphasizes that it will be important to consider the simultaneous effects of multiple environmental triggers for relapse in the development of treatment and medication strategies.

Precipitated cannabinoid withdrawal is reversed by Delta(9)-tetrahydrocannabinol or clonidine

The availability of the cannabinoid antagonist, SR 141716A, to precipitate withdrawal following repeated cannabinoid administration provides a model to investigate the mechanisms underlying cannabinoid dependence as well as potential treatments to alleviate withdrawal symptoms. The goal of the present study was to determine whether SR 141716A-precipitated withdrawal symptoms in Delta(9)-tetrahydrocannabinol (Delta(9)-THC)-tolerant mice could be alleviated by either readministration of Delta(9)-THC or clonidine, an alpha(2)-receptor agonist. SR 141716A elicited paw tremors in Delta(9)-THC-tolerant mice, but produced a significant increase in head shakes independently of repeated Delta(9)-THC treatment. Readministration of Delta(9)-THC, following SR 141716A-precipitated withdrawal, reversed paw tremors (ED(50)=9.9 mg/kg), but failed to reduce head shaking behavior. Clonidine reversed SR 141716A-precipitated paw tremors (ED(50)=0.18 mg/kg) and blocked head shakes at all doses tested. The reversal effects did not appear to be the result of motor impairment because neither decreases in spontaneous locomotor activity nor motor incoordination, as assessed in the inverted screen test, could account for the effects. These findings suggest that SR 141716A precipitates paw tremors in mice by competing with Delta(9)-THC at the CB(1) receptor, though it also produced head shaking in nondependent animals. Finally, the observation that clonidine alleviated SR 141716A-precipitated paw tremors suggests its potential as a treatment for cannabinoid dependence.

Behavioral sensitization to WIN55212.2 in rats pretreated with heroin

There is evidence of similarities and interactions between central opioid and cannabinoid system with reference to drug reinforcement and abuse. Here we demonstrate that repeated injection of heroin produces behavioral sensitization towards administration of the synthetic cannabinoid receptor agonist WIN55212.2 in the rat. These effects were blocked by both the cannabinoid antagonist SR141716A and the opioid antagonist naloxone. These findings suggest that repeated exposure to heroin produces neuroadaptative changes in brain circuits that contribute to mediate the behavioral consequences of acute administration of WIN55212.2. The present results expand our knowledge on the interactions between central opioid and cannabinoid systems with respect to drug abuse.

The endocannabinoid nervous system: unique opportunities for therapeutic intervention

The active principle in marijuana, Delta(9)-tetrahydrocannabinol (THC), has been shown to have wide therapeutic application for a number of important medical conditions, including pain, anxiety, glaucoma, nausea, emesis, muscle spasms, and wasting diseases. Delta(9)-THC binds to and activates two known cannabinoid receptors found in mammalian tissue, CB1 and CB2. The development of cannabinoid-based therapeutics has focused predominantly on the CB1 receptor, based on its predominant and abundant localization in the CNS. Like most of the known cannabinoid agonists, Delta(9)-THC is lipophilic and relatively nonselective for both receptor subtypes. Clinical studies show that nonselective cannabinoid agonists are relatively safe and provide therapeutic efficacy, but that they also induce psychotropic side effects. Recent studies of the biosynthesis, release, transport, and disposition of anandamide are beginning to provide an understanding of the role of lipid transmitters in the CNS. This review attempts to link current understanding of the basic biology of the endocannabinoid nervous system to novel opportunities for therapeutic intervention. This new knowledge may facilitate the development of cannabinoid receptor-targeted therapeutics with improved safety and efficacy profiles.

Dark Agouti and Fischer 344 rats: differential behavioral responses to morphine and biochemical differences in the ventral tegmental area

We sought to identify behavioral and biochemical differences between Dark Agouti and Fischer 344 inbred rat strains to assess whether they could serve as a model of genetically determined differences in sensitivity to drugs of abuse. We compared the strains for the following traits: morphine-induced locomotor activity and sensitization; circadian variation in plasma levels of corticosterone, a hormone reported to affect sensitivity to drugs of abuse; and several biochemical parameters in the ventral tegmental area and nucleus accumbens, brain regions implicated in the locomotor activating and reinforcing actions of drugs of abuse. Fischer 344 rats exhibited greater initial locomotor responses to morphine but, unlike Dark Agouti rats, did not develop sensitization to a second morphine exposure. Fischer 344 rats displayed a marked rise in basal plasma corticosterone levels in the late light phase and early dark phase, whereas Dark Agouti rats showed no significant circadian variation in corticosterone levels. Relative to drug-naive Fischer 344 rats, drug-naive Dark Agouti rats showed higher levels of tyrosine hydroxylase and glial fibrillary acidic protein, and lower levels of neurofilament proteins, in the ventral tegmental area. In contrast, no strain differences were found in levels of tyrosine hydroxylase, specific G protein subunits or protein kinase A in the nucleus accumbens. Together, these results demonstrate that Dark Agouti rats and Fischer 344 rats exhibit differences in specific behavioral, endocrine and biochemical parameters related to sensitivity to drugs of abuse.

Regulation of corticotropin-releasing factor messenger RNA by nicotine in an immortalized amygdalar cell line

Preliminary data suggest that amygdalar corticotropin-releasing factor (CRF) is regulated by nicotinic agonists. We sought to confirm and extend these observations by determining the effects of various concentrations of nicotine on CRF messenger RNA expression in the AR-5 immortalized amygdalar cell line. Nicotine produced concentration- and time-dependent increases in CRF mRNA. This cell line thus confirms that nicotinic agonists stimulate amygdalar CRF and appears to be a useful model for studying molecular factors important in this interaction.