Interactions of delta9-tetrahydrocannabinol with d-amphetamine, cocaine, and nicotine in rats

Chronic nicotine exposure attenuates the effects of Δ9 -tetrahydrocannabinol on anxiety-related behavior and social interaction in adult male and female rats

INTRODUCTION

Anxiogenic and anxiolytic effects of cannabinoids are mediated by different mechanisms, including neural signaling via cannabinoid receptors (CBRs) and nicotinic cholinergic receptors (nAChRs). This study examined the effects of prior nicotine (the psychoactive component in tobacco) exposure on behavioral sensitivity to delta-9-tetrahydrocannabinol (THC; the psychoactive component of cannabis) challenge in animals.

METHODS

Male and female adult Sprague-Dawley rats (N = 96) were injected daily with nicotine (1 mg/kg, i.p.) or vehicle for 14 days, followed by a 14-day drug-free period. On test day, rats were injected with THC (0.5, 2.0, or 5.0 mg/kg, i.p.) or vehicle and anxiety-related behavior was assessed in the emergence (EM), elevated plus maze (EPM), and social interaction (SI) tests.

RESULTS

Chronic nicotine pretreatment attenuated some of the anxiogenic effects induced by THC challenge which can be summarized as follows: (a) THC dose-dependently affected locomotor activity, exploratory behavior, and social interaction in the EM, EPM, and SI tests of unconditioned anxiety; (b) these effects of acute THC challenge were greater in females compared with males except for grooming a conspecific; (c) prior nicotine exposure attenuated the effects of acute THC challenge for locomotor activity in the EPM test; and (d) prior nicotine exposure attenuated the effects of THC challenge for direct but not indirect physical interaction in the SI tests.

CONCLUSIONS

The ability of nicotine prior exposure to produce long-lasting changes that alter the effects of acute THC administration suggests that chronic nicotine may induce neuroplastic changes that influence the subsequent response to novel THC exposure.

Effects of nicotine and THC vapor inhalation administered by an electronic nicotine delivery system (ENDS) in male rats

BACKGROUND

Electronic nicotine delivery systems (ENDS, e-cigarettes) are increasingly used for the self-administration of nicotine by various human populations, including previously nonsmoking adolescents. Studies in preclinical models are necessary to evaluate health impacts of ENDS including the development of nicotine addiction, effects of ENDS vehicles, flavorants and co-administered psychoactive substances such as Δ⁹-tetrahydrocannabinol (THC). This study was conducted to validate a rat model useful for the study of nicotine effects delivered by inhalation of vapor created by ENDS.

METHODS

Male Sprague-Dawley rats (N = 8) were prepared with radio telemetry devices for the reporting of temperature and activity. Experiments subjected rats to inhalation of vapor generated by an electronic nicotine delivery system (ENDS) adapted for rodents. Inhalation conditions included vapor generated by the propylene glycol (PG) vehicle, Nicotine (1, 10, 30 mg/mL in the PG) and THC (12.5, 25 mg/mL).

RESULTS

Nicotine inhalation increased spontaneous locomotion and decreased body temperature of rats. Pretreatment with the nicotinic cholinergic receptor antagonist mecamylamine (2 mg/kg, i.p.) prevented stimulant effects of nicotine vapor inhalation and attenuated the hypothermic response. Combined inhalation of nicotine and THC resulted in apparently independent effects which were either additive (hypothermia) or opposed (activity).

CONCLUSIONS

These studies provide evidence that ENDS delivery of nicotine via inhalation results in nicotine-typical effects on spontaneous locomotion and thermoregulation in male rats. Effects were blocked by a nicotinic antagonist, demonstrating mechanistic specificity. This system will therefore support additional studies of the contribution of atomizer/wick design, vehicle constituents and/or flavorants to the effects of nicotine administered by ENDS.

Adolescent THC exposure does not sensitize conditioned place preferences to subthreshold d-amphetamine in male and female rats

The acute effects of marijuana consumption on brain physiology and behaviour are well documented, but the long-term effects of its chronic use are less well known. Chronic marijuana use during adolescence is of increased interest, given that the majority of individuals first use marijuana during this developmental stage , and  adolescent marijuana use is thought to increase the susceptibility to abusing other drugs when exposed later in life. It is possible that marijuana use during critical periods in adolescence could lead to increased sensitivity to other drugs of abuse later on. To test this, we chronically administered ∆ 9-tetrahydrocannabinol (THC) to male and female Long-Evans (LER) and Wistar (WR) rats directly after puberty onset. Rats matured to postnatal day 90 before being exposed to a conditioned place preference task (CPP). A subthreshold dose of d-amphetamine, found not to induce place preference in drug naïve rats, was used as the unconditioned stimulus. The effect of d-amphetamine on neural activity was inferred by quantifying cfos expression in the nucleus accumbens and dorsal hippocampus following CPP training. Chronic exposure to THC post-puberty had no potentiating effect on a subthreshold dose of d-amphetamine to induce CPP. No differences in cfos expression were observed. These results show that chronic exposure to THC during puberty did not increase sensitivity to a sub-threshold dose of d-amphetamine in adult LER and WR rats. This supports the concept that THC may not sensitize the response to all drugs of abuse.

Adolescent THC exposure does not sensitize conditioned place preferences to subthreshold d-amphetamine in male and female rats

The acute effects of marijuana consumption on brain physiology and behaviour are well documented, but the long-term effects of its chronic use are less well known. Chronic marijuana use during adolescence is of increased interest, given that the majority of individuals first use marijuana during this developmental stage , and  adolescent marijuana use is thought to increase the susceptibility to abusing other drugs when exposed later in life. It is possible that marijuana use during critical periods in adolescence could lead to increased sensitivity to other drugs of abuse later on. To test this, we chronically administered ∆ 9-tetrahydrocannabinol (THC) to male and female Long-Evans (LER) and Wistar (WR) rats directly after puberty onset. Rats matured to postnatal day 90 before being exposed to a conditioned place preference task (CPP). A subthreshold dose of d-amphetamine, found not to induce place preference in drug naïve rats, was used as the unconditioned stimulus. The effect of d-amphetamine on neural activity was inferred by quantifying cfos expression in the nucleus accumbens and dorsal hippocampus following CPP training. Chronic exposure to THC post-puberty had no potentiating effect on a subthreshold dose of d-amphetamine to induce CPP. No differences in cfos expression were observed. These results show that chronic exposure to THC during puberty did not increase sensitivity to d-amphetamine in adult LER and WR rats. This supports the concept that THC may not sensitize the response to all drugs of abuse.

Cannabinoids Modulate Neuronal Activity and Cancer by CB1 and CB2 Receptor-Independent Mechanisms

Cannabinoids include the active constituents of Cannabis or are molecules that mimic the structure and/or function of these Cannabis-derived molecules. Cannabinoids produce many of their cellular and organ system effects by interacting with the well-characterized CB1 and CB2 receptors. However, it has become clear that not all effects of cannabinoid drugs are attributable to their interaction with CB1 and CB2 receptors. Evidence now demonstrates that cannabinoid agents produce effects by modulating activity of the entire array of cellular macromolecules targeted by other drug classes, including: other receptor types; ion channels; transporters; enzymes, and protein- and non-protein cellular structures. This review summarizes evidence for these interactions in the CNS and in cancer, and is organized according to the cellular targets involved. The CNS represents a well-studied area and cancer is emerging in terms of understanding mechanisms by which cannabinoids modulate their activity. Considering the CNS and cancer together allow identification of non-cannabinoid receptor targets that are shared and divergent in both systems. This comparative approach allows the identified targets to be compared and contrasted, suggesting potential new areas of investigation. It also provides insight into the diverse sources of efficacy employed by this interesting class of drugs. Obtaining a comprehensive understanding of the diverse mechanisms of cannabinoid action may lead to the design and development of therapeutic agents with greater efficacy and specificity for their cellular targets.

Ecological momentary assessment of working memory under conditions of simultaneous marijuana and tobacco use

BACKGROUND AND AIMS

The neuropsychological correlates of simultaneous marijuana and tobacco use are largely unknown, which is surprising as both substances have similar neural substrates and have opposing influences on working memory (WM). This study examined the effects of marijuana alone, tobacco alone and simultaneous marijuana and tobacco use on WM.

DESIGN

Primary aims were tested using a within-subject design, controlling for multiple subject- and momentary-level confounds via ecological momentary assessment (EMA).

SETTING

Data collection occurred in the Chicago, USA area in participants' natural environments.

PARTICIPANTS

Participants were 287 community young adults from a larger natural history study, oversampled for ever smoking, all of whom event-recorded at least one substance use occasion during the study week.

MEASUREMENTS

Momentary tobacco, marijuana and alcohol use were recorded during multiple EMA across 1 week of data capture. WM was assessed at the end of each EMA assessment. Contextual variables that may influence WM were recorded via EMA.

FINDINGS

There were main effects for marijuana and tobacco: WM was poorer with marijuana [odds ratio (OR) = 0.91, 95% confidence interval (CI) = 0.84-0.99] and better with tobacco (OR = 1.11, 95% CI = 1.04-1.18). These effects were not qualified by an interaction (OR = 1.03, 95% CI = 0.84-1.26). Alcohol also reduced WM (OR = 0.87, 95% CI = 0.79-0.95), and the tobacco × alcohol interaction was significant (OR = 0.81, 95% CI = 0.66-0.99), indicating that the facilitative effect of tobacco disappeared with concurrent alcohol use.

CONCLUSIONS

Relative to when individuals did not use these substances, working memory decreased with acute marijuana and alcohol use and increased with acute tobacco use. However, the putative effect of marijuana on working memory and the facilitative effect of tobacco on working memory were no longer present when used simultaneously with tobacco and alcohol, respectively. Data suggest that tobacco use may compensate for working memory decrements from marijuana among young adults and highlight the importance of investigating further the negative impact of alcohol use on cognition.

Behavioral Characterization of the Effects of Cannabis Smoke and Anandamide in Rats

Cannabis is the most widely used illicit drug in the world. Delta-9-tetrahydrocannabinol (Δ9-THC) is the main psychoactive component of cannabis and its effects have been well-studied. However, cannabis contains many other cannabinoids that affect brain function. Therefore, these studies investigated the effect of cannabis smoke exposure on locomotor activity, rearing, anxiety-like behavior, and the development of dependence in rats. It was also investigated if cannabis smoke exposure leads to tolerance to the locomotor-suppressant effects of the endogenous cannabinoid anandamide. Cannabis smoke was generated by burning 5.7% Δ9-THC cannabis cigarettes in a smoking machine. The effect of cannabis smoke on the behavior of rats in a small and large open field and an elevated plus maze was evaluated. Cannabis smoke exposure induced a brief increase in locomotor activity followed by a prolonged decrease in locomotor activity and rearing in the 30-min small open field test. The cannabinoid receptor type 1 (CB1) receptor antagonist rimonabant increased locomotor activity and prevented the smoke-induced decrease in rearing. Smoke exposure also increased locomotor activity in the 5-min large open field test and the elevated plus maze test. The smoke exposed rats spent more time in the center zone of the large open field, which is indicative of a decrease in anxiety-like behavior. A high dose of anandamide decreased locomotor activity and rearing in the small open field and this was not prevented by rimonabant or pre-exposure to cannabis smoke. Serum Δ9-THC levels were 225 ng/ml after smoke exposure, which is similar to levels in humans after smoking cannabis. Exposure to cannabis smoke led to dependence as indicated by more rimonabant-precipitated somatic withdrawal signs in the cannabis smoke exposed rats than in the air-control rats. In conclusion, chronic cannabis smoke exposure in rats leads to clinically relevant Δ9-THC levels, dependence, and has a biphasic effect on locomotor activity.

Part III: Principal component analysis: bridging the gap between strain, sex and drug effects

Previous work has identified the adolescent period as particularly sensitive to the short- and long-term effects of marijuana and its main psychoactive component Δ9-tetrahydrocannabinol (THC). However, other studies have identified certain backgrounds as more sensitive than others, including the sex of the individual or the strain of the rat used. Further, the effects of THC may be specific to certain behavioural tasks (e.g. measures of anxiety), and the consequences of THC are not seen equally across all behavioural measures. Here, data obtained from adolescent male and female Long-Evans and Wistar rats exposed to THC and tested as adults, which, using standard ANOVA testing, showed strain- and sex-specific effects of THC, was analyzed using principal component analysis (PCA). PCA allowed for the examination of the relative contribution of our variables of interest to the variance in the data obtained from multiple behavioural tasks, including the skilled reaching task, the Morris water task, the discriminative fear-conditioning to context task, the elevated plus maze task and the conditioned place preference task to a low dose of amphetamine, as well as volumetric estimates of brain volumes and cfos activation. We observed that early life experience accounted for a large proportion of variance across data sets, although its relative contribution varied across tasks. Additionally, THC accounted for a very small proportion of the variance across all behavioural tasks. We demonstrate here that by using PCA, we were able to describe the main variables of interest and demonstrate that THC exposure had a negligible effect on the variance in the data set.

Control of the nigrostriatal dopamine neuron activity and motor function by the tail of the ventral tegmental area

Midbrain dopamine neurons are implicated in various psychiatric and neurological disorders. The GABAergic tail of the ventral tegmental area (tVTA), also named the rostromedial tegmental nucleus (RMTg), displays dense projections to the midbrain and exerts electrophysiological control over dopamine cells of the VTA. However, the influence of the tVTA on the nigrostriatal pathway, from the substantia nigra pars compacta (SNc) to the dorsal striatum, and on related functions remains to be addressed. The present study highlights the role played by the tVTA as a GABA brake for the nigrostriatal system, demonstrating a critical influence over motor functions. Using neuroanatomical approaches with tract tracing and electron microscopy, we reveal the presence of a tVTA-SNc-dorsal striatum pathway. Using in vivo electrophysiology, we prove that the tVTA is a major inhibitory control center for SNc dopamine cells. Using behavioral approaches, we demonstrate that the tVTA controls rotation behavior, motor coordination, and motor skill learning. The motor enhancements observed after ablation of the tVTA are in this regard comparable with the performance-enhancing properties of amphetamine, a drug used in doping. These findings demonstrate that the tVTA is a major GABA brake for nigral dopamine systems and nigrostriatal functions, and they raise important questions about how the tVTA is integrated within the basal ganglia circuitry. They also warrant further research on the tVTA's role in motor and dopamine-related pathological contexts such as Parkinson's disease.

Care and feeding of the endocannabinoid system: a systematic review of potential clinical interventions that upregulate the endocannabinoid system

Background

The “classic” endocannabinoid (eCB) system includes the cannabinoid receptors CB₁ and CB₂, the eCB ligands anandamide (AEA) and 2-arachidonoylglycerol (2-AG), and their metabolic enzymes. An emerging literature documents the “eCB deficiency syndrome” as an etiology in migraine, fibromyalgia, irritable bowel syndrome, psychological disorders, and other conditions. We performed a systematic review of clinical interventions that enhance the eCB system—ways to upregulate cannabinoid receptors, increase ligand synthesis, or inhibit ligand degradation.

Methodology/Principal Findings

We searched PubMed for clinical trials, observational studies, and preclinical research. Data synthesis was qualitative. Exclusion criteria limited the results to 184 in vitro studies, 102 in vivo animal studies, and 36 human studies. Evidence indicates that several classes of pharmaceuticals upregulate the eCB system, including analgesics (acetaminophen, non-steroidal anti-inflammatory drugs, opioids, glucocorticoids), antidepressants, antipsychotics, anxiolytics, and anticonvulsants. Clinical interventions characterized as “complementary and alternative medicine” also upregulate the eCB system: massage and manipulation, acupuncture, dietary supplements, and herbal medicines. Lifestyle modification (diet, weight control, exercise, and the use of psychoactive substances—alcohol, tobacco, coffee, cannabis) also modulate the eCB system.

Conclusions/Significance

Few clinical trials have assessed interventions that upregulate the eCB system. Many preclinical studies point to other potential approaches; human trials are needed to explore these promising interventions.

The effect of cocaine on rotarod performance in male C57BL/6J mice

There is surprisingly little research examining the effect of cocaine on motor learning. Given that changes in motor activity can confound behavioral assays of learning and memory a direct assessment of cocaine on motor learning seems warranted. The present study was conducted to examine the effect of cocaine on motor learning using an accelerating rotarod test in adult male C57BL/6J mice. Mice were given an injection of either saline or cocaine (10mg/kg, i.p.) for 6 consecutive days prior to rotarod training (Pre-exposure). In the first phase of training (Phase I), mice were given an injection of either saline or cocaine 10min prior to the start of each day's training on the rotarod for 6 consecutive days. In the second phase (Phase II), half the animals continued to receive the same drug during training, while the other half were switched from saline to cocaine or from cocaine to saline. All mice exhibited motor learning as evidenced by an increased latency to fall across days. Animals that received cocaine injections exhibited significantly longer latencies to fall on days 3-6 compared to those mice receiving saline. This enhanced performance was lost when cocaine-injected animals were switched to saline on day 7. It is hypothesized that the performance enhancing effects of cocaine are due to the increased stamina and/or psychomotor stimulation and not the result of enhanced motor learning as the increment in performance was lost when the drug was discontinued.

Cannabinoid CB1 receptor activation mediates the opposing effects of amphetamine on impulsive action and impulsive choice

It is well known that acute challenges with psychostimulants such as amphetamine affect impulsive behavior. We here studied the pharmacology underlying the effects of amphetamine in two rat models of impulsivity, the 5-choice serial reaction time task (5-CSRTT) and the delayed reward task (DRT), providing measures of inhibitory control, an aspect of impulsive action, and impulsive choice, respectively. We focused on the role of cannabinoid CB1 receptor activation in amphetamine-induced impulsivity as there is evidence that acute challenges with psychostimulants activate the endogenous cannabinoid system, and CB1 receptor activity modulates impulsivity in both rodents and humans. Results showed that pretreatment with either the CB1 receptor antagonist/inverse agonist SR141716A or the neutral CB1 receptor antagonist O-2050 dose-dependently improved baseline inhibitory control in the 5-CSRTT. Moreover, both compounds similarly attenuated amphetamine-induced inhibitory control deficits, suggesting that CB1 receptor activation by endogenously released cannabinoids mediates this aspect of impulsive action. Direct CB1 receptor activation by Δ9-Tetrahydrocannabinol (Δ9-THC) did, however, not affect inhibitory control. Although neither SR141716A nor O-2050 affected baseline impulsive choice in the DRT, both ligands completely prevented amphetamine-induced reductions in impulsive decision making, indicating that CB1 receptor activity may decrease this form of impulsivity. Indeed, acute Δ9-THC was found to reduce impulsive choice in a CB1 receptor-dependent way. Together, these results indicate an important, though complex role for cannabinoid CB1 receptor activity in the regulation of impulsive action and impulsive choice as well as the opposite effects amphetamine has on both forms of impulsive behavior.

Chronic administration of THC prevents the behavioral effects of intermittent adolescent MDMA administration and attenuates MDMA-induced hyperthermia and neurotoxicity in rats

Most recreational users of 3, 4-methylenedioxymethamphetamine (MDMA or "ecstasy") also take cannabis, in part because cannabis can reduce the dysphoric symptoms of the ecstasy come-down such as agitation and insomnia. Although previous animal studies have examined the acute effects of co-administering MDMA and Δ(9)-tetrahydrocannabinol (THC), which is the major psychoactive ingredient in cannabis, research on chronic exposure to this drug combination is lacking. Therefore, the present study was conducted to investigate the effects of chronic adolescent administration of both THC and MDMA on behavior and on regional serotonin transporter (SERT) binding and serotonin (5-HT) concentrations as indices of serotonergic system integrity. Male Sprague-Dawley rats were divided into four drug administration groups: (1) MDMA alone, (2) THC alone, (3) MDMA plus THC, and (4) vehicle controls. MDMA (2 × 10 mg/kg × 4 h) was administered every fifth day from postnatal day (PD) 35 to 60 to simulate intermittent recreational ecstasy use, whereas THC (5mg/kg) was given once daily over the same time period to simulate heavy cannabis use. THC unexpectedly produced a modest hyperthermic effect when administered alone, but in animals co-treated with both THC and MDMA, there was an attenuation of MDMA-induced hyperthermia on dosing days. Subsequent testing conducted after a drug washout period revealed that THC reduced MDMA-related behavioral changes in the emergence and social interaction tests of anxiety-like behavior and also blunted the MDMA-induced decrease in exploratory behavior in the hole-board test. THC additionally attenuated MDMA -induced decreases in 5-HT levels and in SERT binding in the frontal cortex, parietal cortex, and striatum, but not in the hippocampus. These results suggest that chronic co-administration of THC during adolescence can provide some protection against various adverse physiological, behavioral, and neurochemical effects produced by MDMA.

Influence of central nicotinic receptors on arachidonylcyclopropylamide (ACPA)-induced antinociception in mice

The nicotinic cholinergic receptors have been reported to be involved in several actions of cannabinoids (e.g., bradycardia, hypothermia). However, the influence of central cholinergic system on cannabinoids antinociceptive effect has not been reported. This study investigated the possible part played by nicotinic cholinergic modulator drugs on the antinociceptive effect of central administration of arachidonylcyclopropylamide (ACPA) in mice. The antinociceptive effects of intracerebroventricular (i.c.v.) administration of ACPA using the formalin test have been studied in mice. The effects of nicotine or mecamylamine (a nicotinic cholinergic antagonist) on ACPA analgesia are also studied. i.c.v. administration of ACPA (0.004-1 microg/mice) induced antinociceptive effect in mice. i.c.v. administration of nicotine (0.1 or 0.5 microg/mice) or mecamylamine (2 microg/mice) potentiated or antagonized ACPA antinociceptive effects, respectively. It is concluded that ACPA-induced analgesia is influenced by central nicotinic cholinergic activity.

Influence of nicotinic receptor modulators on CB2 cannabinoid receptor agonist (JWH133)-induced antinociception in mice

Delta9-tetrahydrocannabinol is the active component in cannabis and has long been associated with pain relief. This effect is believed to be mediated through central and peripheral CB1 and peripheral CB2 receptors. We have explored the possible antinociceptive effect of a CB2 receptor agonist, JWH133, using the formalin test in mice. The drug was administered by the intracerebroventricular and intraperitoneal routes. Although no antinociceptive effect was observed after intracerebroventricular administration of JWH133, when the drug was administered by the intraperitoneal route, it produced an analgesic effect. The influence of nicotinic cholinergic receptor modulators, nicotine and mecamylamine, on antinociceptive effect of JWH133 was also studied. Nicotine increased and mecamylamine decreased the antinociceptive effect of JWH133. It is concluded that JWH133-induced analgesia is influenced by nicotinic cholinergic receptor activity.

Modulation of the endocannabinoid system: therapeutic potential against cocaine dependence

Dependence on cocaine is still a main unresolved medical and social concern, and in spite of research efforts, no pharmacological therapy against cocaine dependence is yet available. Recent studies have shown that the endocannabinoid system participates in specific stages and aspects of drug dependence in general, and some of this evidence suggests an involvement of the cannabinoid system in cocaine effects. For example, cocaine administration has been shown to alter brain endocannabinoid levels, and the endocannabinoid system has been involved in long-term modifications of brain processes that might play a role in neuro/behavioral effects of psychostimulant drugs like cocaine. Human studies show that marijuana dependence is frequently associated with cocaine dependence, and that the cannabinoid receptor CNR1 gene polymorphism might be related to cocaine addiction. This article will review the main papers in the field showing how a modulation of different components of the cannabinoid system might interact with some of the neurobiological/behavioral effects of cocaine related to its reinforcing effects, evaluated in preclinical models or in clinical settings. The goal of this review will be to provide insights into the complex picture of cocaine abuse and addiction, and to extrapolate from such endocannabinoid-cocaine interactions useful information to test the therapeutic potential of cannabinoid ligands and endocannabinoid-level enhancers against cocaine dependence for future preclinical/clinical trials.

Subchronic nicotine exposure in adolescence induces long-term effects on hippocampal and striatal cannabinoid-CB1 and mu-opioid receptors in rats

There is evidence for the existence of functional interactions between nicotine and cannabinoids and opioid compounds in adult experimental animals. However, there is scarce information about these relationships in young animals. In the present study we evaluated short and long-term effects of a subchronic nicotine treatment [0.4 mg/kg daily i.p. injections from postnatal day (PND) 34 to PND 43], upon hippocampal and striatal cannabinoid-CB(1) and mu-opioid receptors in Wistar rats of both genders. Rats were sacrificed 2 h after the last nicotine injection (short-term effects, PND 43) or one month later (long-term effects, PND 75). Hippocampal and striatal cannabinoid CB(1) and mu-opioid receptors were quantified by Western blotting. The subchronic nicotine treatment induced a region-dependent long-lasting effect in cannabinoid CB(1) receptor: a significant increase in hippocampal cannabinoid CB(1) receptors and a significant decrease in striatal cannabinoid CB(1) receptors, with these effects being similar in males and females. With respect to mu-opioid receptors, subchronic nicotine induced a significant down-regulation in hippocampal and striatal mu-opioid receptors in the long-term, and within the striatum the effects were more marked in adult males than in females. The present results indicate that juvenile nicotine taking may have implications for the endocannabinoid and endogenous opioid function and for the behaviors served by those systems, this includes possible modification of the response of adults to different psychotropic drugs, i.e. cannabis and morphine/heroin when taken later in life.

Nicotine pre-exposure does not potentiate the locomotor or rewarding effects of Delta-9-tetrahydrocannabinol in rats

This study assessed the effects of nicotine pre-exposure on subsequent locomotor and rewarding effects of repeated Delta-9-tetrahydrocannabinol administration in Sprague-Dawley rats. Repeated administration of the same dose of Delta-9-tetrahydrocannabinol (0.01-2 mg/kg) did not produce significant tolerance or behavioral sensitization to Delta-9-tetrahydrocannabinol's locomotor effects. An unbiased place conditioning paradigm was then used to obtain a measure of the rewarding effects of Delta-9-tetrahydrocannabinol. Rats received an injection of either Delta-9-tetrahydrocannabinol (0.01-2 mg/kg) before being placed in one compartment (three trials) or saline before being placed in the other compartment (three trials) of a two-compartment apparatus. Control rats received saline injections associated with both compartments. Significant conditioned place preferences developed with 0.1 mg/kg Delta-9-tetrahydrocannabinol in control rats, but not in nicotine pre-exposed rats. Surprisingly, significant place aversions developed at higher 1 and 2 mg/kg doses of Delta-9-tetrahydrocannabinol in nicotine pre-exposed rats. To the extent that behavioral sensitization may reflect reward processes in drug dependence, the lack of behavioral sensitization on repeated Delta-9-tetrahydrocannabinol administration is consistent with the difficulties usually encountered in demonstrating rewarding or reinforcing effects of Delta-9-tetrahydrocannabinol in rats. The present findings suggest, moreover, that nicotine pre-exposure alters the qualitative nature of rewarding effects and accentuates aversive effects of Delta-9-tetrahydrocannabinol.

Adolescent exposure to nicotine modifies acute functional responses to cannabinoid agonists in rats

We have studied functional interactions between nicotine and the cannabinoid receptor agonist CP 55,940 (CP) in the modulation of behavioural and corticosterone responses of male and female adolescent Wistar rats. The animals underwent a subchronic nicotine treatment (0.4 mg/kg i.p., once daily) during the periadolescent period (postnatal days 34-43). Twenty-four hours after the last injection of nicotine an acute dose of CP (1 or 100 microg/kg i.p.) was administered. Thirty minutes after the cannabinoid injection, the animals were tested individually in the holeboard immediately followed by the elevated plus-maze. We also measured corticosterone levels by radioimmunoassay. In males, neither CP (1 microg/kg) nor nicotine induced any modification in anxiety when administered alone. However, the combination of the two drugs resulted in a significant anxiogenic-like effect. In females, the lower dose of CP was anxiogenic and nicotine, which did not induce any effect per se, prevented this response. In the holeboard, subchronic nicotine and the acute cannabinoid treatment interacted in the modulation of horizontal activity and the nature of this interaction also showed a clear sexual dimorphism. Both, the cannabinoid agonist and nicotine increased corticosterone concentrations and the animals receiving the two drugs showed higher levels than the animals receiving the cannabinoid alone. The data provide evidence for the existence of functional interactions between nicotine and cannabinoids in the modulation of behavioural responses and adrenocortical activity in adolescent rats.

Tardive dyskinesia and essential fatty acids

Tardive dyskinesia (TD) is a movement disorder described in individuals who have been treated with anti-dopaminergic agents. The pathophysiology of this condition remains to be fully elucidated. Several mechanisms like dopaminergic supersensitivity, dysfunction of striatonigral, GABAergic neurons and disturbed balance between dopaminergic and cholinergic systems have been described. Essential fatty acids (EFAs) are important components of neuronal membrane and the EFA content of these membranes can significantly influence neuronal functioning. Lower levels of EFAs have been reported in red blood cells (RBC) and plasma of individuals with moderate to severe TD. Supplementation with EFAs (omega-3 and omega-6 and ethyl-EPA) have been tried to alleviate TD in open and double-blind clinical trials and in some animal models of TD. In addition, antioxidants (Vitamin E) and melatonin have been tried. However, smaller numbers of patients and shortened length of clinical studies make it difficult to draw any definitive conclusions. Large multi-centre studies with sound methodology of both EFAs and antioxidants are needed.

Role of the cannabinoid system in the effects induced by nicotine on anxiety-like behaviour in mice

RATIONALE

Acute behavioural effects and motivational responses induced by nicotine can be modulated by the endocannabinoid system supporting the existence of a physiological interaction between these two systems.

OBJECTIVES

The present study was designed to examine the possible involvement of the cannabinoid system in the anxiolytic- and anxiogenic-like responses induced by nicotine in mice.

METHODS

Animals were only exposed once to nicotine. The acute administration of low (0.05) or high (0.8 mg/kg, s.c.) doses of nicotine produced opposite effects in the elevated plus-maze, i.e. anxiolytic- and anxiogenic-like responses, respectively. The effects of the pretreatment with the CB1 cannabinoid receptor antagonist, rimonabant (0.25, 0.5 and 1 mg/kg, i.p.), and the cannabinoid agonist, delta9-tetrahydrocannabinol (delta9-THC, 0.1 mg/kg, ip), were evaluated on the anxiolytic- and anxiogenic-like responses induced by nicotine.

RESULTS

Rimonabant completely abolished nicotine-induced anxiolytic-like effects and increased the anxiogenic-like responses of nicotine, suggesting an involvement of CB1 receptors in these behavioural responses. On the other hand, delta9-THC failed to modify nicotine anxiolytic-like responses but attenuated its anxiogenic-like effects. In addition, the association of non-effective doses of delta9-THC and nicotine produced clear anxiolytic-like responses.

CONCLUSIONS

These results demonstrate that the endogenous cannabinoid system is involved in the regulation of nicotine anxiety-like behaviour in mice and provide new findings to support the use of cannabinoid antagonists in the treatment of tobacco addiction.

Transdermal nicotine alters some of marihuana's effects in male and female volunteers

Despite the fact that tobacco and marihuana are often used together, relatively little is known about the effects of this combination. In order to investigate the effects of the principal psychoactive component in tobacco smoke, nicotine, on marihuana-induced intoxication, we conducted a double blind, cross-over experiment using nicotine transdermal patches. Ten male and 10 female participants received either placebo or a 21 mg transdermal nicotine patch 4 h before smoking one of two marihuana cigarettes (1.99 or 3.51% delta-9-tetrahydrocannabinol (Delta(9) THC) content). Measurements of physiological activity (heart rate, blood pressure, and skin temperature) and subjective effects (self-reports of drug effects on visual analog scales (VAS) and the Addiction Research Center Inventory (ARCI)) were made periodically before and for 3h after smoking. Nicotine pre-treatment enhanced several responses to marihuana, in particular, heart rate, reports of "stimulated" on the visual analog scales, and scores on the Amphetamine scale of the ARCI. Male participants reported a more pronounced effect of marihuana that persisted longer than that of the female participants. Compared to the male participants, female participants experienced an attenuated response to marihuana and were less affected by the drug combination. The results of this study show that nicotine can have an important influence on the subjective and physiological effects of smoked marihuana. These effects have implications for the safety and efficacy of marihuana smokers who are self-medicating with the nicotine transdermal patch to manage their tobacco dependence.

Delta9-tetrahydrocannabinol decreases somatic and motivational manifestations of nicotine withdrawal in mice

The possible interactions between Delta9-tetrahydrocannabinol (Delta9-THC) and nicotine remain unclear in spite of the current association of cannabis and tobacco in humans. The aim of the present study was to explore the interactions between these two drugs of abuse by evaluating the consequences of Delta9-THC administration on the somatic manifestations and the aversive motivational state associated with nicotine withdrawal in mice. Acute Delta9-THC administration significantly decreased the incidence of several nicotine withdrawal signs precipitated by mecamylamine or naloxone, such as wet-dog-shakes, paw tremor and scratches. In both experimental conditions, the global withdrawal score was also significantly attenuated by acute Delta9-THC administration. This effect of Delta9-THC was not due to possible adaptive changes induced by chronic nicotine on CB1 cannabinoid receptors, as the density and functional activity of these receptors were not modified by chronic nicotine administration in the different brain structures investigated. We also evaluated the consequences of Delta9-THC administration on c-Fos expression in several brain structures after chronic nicotine administration and withdrawal. c-Fos was decreased in the caudate putamen and the dentate gyrus after mecamylamine precipitated nicotine withdrawal. However, acute Delta9-THC administration did not modify c-Fos expression under these experimental conditions. Finally, Delta9-THC also reversed conditioned place aversion associated to naloxone precipitated nicotine withdrawal. Taken together, these results indicate that Delta9-THC administration attenuated somatic signs of nicotine withdrawal and this effect was not associated with compensatory changes on CB1 cannabinoid receptors during chronic nicotine administration. In addition, Delta9-THC also ameliorated the aversive motivational consequences of nicotine withdrawal.

Cannabinoids prevent the acute hyperthermia and partially protect against the 5-HT depleting effects of MDMA (“Ecstasy”) in rats

Cannabinoid-MDMA interactions were examined in male Wistar rats. MDMA (4 x 5 mg/kg or 2 x 10 mg/kg over 4 h on each of 2 days) was administered with or without Delta 9-tetrahydrocannabinol (THC) (4 x 2.5 mg/kg), the synthetic cannabinoid receptor agonist CP 55,940 (2 x 0.1 or 0.2 mg/kg) or the cannabinoid receptor antagonist SR 141716 (2 x 5 mg/kg). Co-administered Delta 9-THC and CP 55,940 but not SR 141716 prevented MDMA-induced hyperthermia, causing a powerful hypothermia. Co-administered Delta 9-THC, CP 55,940 and SR 141716 all tended to decrease MDMA-induced hyperactivity. Co-administered Delta 9-THC provided protection against the long-term increases in anxiety seen in the emergence test, but not the social interaction test, 6 weeks after MDMA treatment. Co-administered Delta 9-THC and CP 55,940, but not SR 141716, partly prevented the long-term 5-HT and 5-HIAA depletion caused by MDMA in various brain regions. SR 141716 administered with CP 55,940 and MDMA prevented the hypothermic response to the CP 55,940/MDMA combination but did not alter the CP 55,940 attenuation of MDMA-induced 5-HT depletion. These results suggest a partial protective effect of co-administered cannabinoid receptor agonists on MDMA-induced 5-HT depletion and long-term anxiety. This action appears to operate independently of cannabinoid CB1 receptors.

Differential Effects of Endogenous and Synthetic Cannabinoids on α7-Nicotinic Acetylcholine Receptor-Mediated Responses in Xenopus Oocytes

The effects of endogenous and synthetic cannabinoid receptor agonists, including 2-arachidonoylglycerol (2-AG), R-methanandamide, WIN55,212-2 [4,5-dihydro-2-methyl-4(4-morpholinylmethyl)-1-(1-naphthalenylcarbonyl)-6H-pyrrolo[3,2,1ij]quinolin-6-one], and CP 55,940 [1alpha,2beta-(R)-5alpha]-(-)-5-(1,1-dimethyl)-2-[5-hydroxy-2-(3-hydroxypropyl) cyclohexyl-phenol], and the psychoactive constituent of marijuana, Delta9-tetrahydrocannabinol (Delta9-THC), on the function of homomeric alpha7-nicotinic acetylcholine (nACh) receptors expressed in Xenopus oocytes was investigated using the two-electrode voltage-clamp technique. The endogenous cannabinoid receptor ligands 2-AG and the metabolically stable analog of anandamide (arachidonylethanolamide), R-methanandamide, reversibly inhibited currents evoked with ACh (100 microM) in a concentration-dependent manner (IC50 values of 168 and 183 nM, respectively). In contrast, the synthetic cannabinoid receptor agonists CP 55,940, WIN55,212-2, and the phytochemical Delta9-THC did not alter alpha7-nACh receptor function. The inhibition of alpha7-mediated currents by 2-AG was found to be non-competitive and voltage-independent. Additional experiments using endocannabinoid metabolites suggested that arachidonic acid, but not ethanolamine or glycerol, could also inhibit the alpha7-nACh receptor function. Whereas the effects of arachidonic acid were also noncompetitive and voltage-independent, its potency was much lower than 2-AG and anandamide. Results of studies with chimeric alpha7-nACh-5-hydroxytryptamine (5-HT)3 receptors comprised of the amino-terminal domain of the alpha7-nACh receptor and the transmembrane and carboxyl-terminal domains of 5-HT3 receptors indicated that the site of interaction of the endocannabinoids with the alpha7-nAChR was not located on the N-terminal region of the receptor. These data indicate that cannabinoid receptor ligands that are produced in situ potently inhibit alpha7-nACh receptor function, whereas the synthetic cannabinoid ligands, and Delta9-THC, are without effect, or are relatively ineffective at inhibiting these receptors.

Differential regulation of the endocannabinoids anandamide and 2-arachidonylglycerol within the limbic forebrain by dopamine receptor activity

Glutamatergic synaptic transmission within the striatum and prefrontal cortex regulates the neuronal synthesis of endocannabinoids. Because a primary role of dopamine is to modulate this excitatory transmission, we tested the hypothesis that dopaminergic transmission modulates endocannabinoid content in the limbic forebrain. Liquid chromatography/mass spectrometry was used to determine endogenous anandamide and 2-arachidonylglycerol (2-AG) contents within the limbic forebrain of mice after pharmacological manipulation of dopaminergic transmission. Increasing synaptic dopamine concentrations with methylphenidate significantly and dose dependently decreased both anandamide and 2-AG content. The selective dopamine reuptake inhibitor 1-[2-[bis(4-fluorophenyl)methoxy]ethyl]-4-(3-phenylpropyl)piperazine (GBR 12909) also significantly decreased anandamide and tended to decrease 2-AG content. The D1 receptor antagonist R-(+)-7-chloro-8-hydroxy-3-methyl-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine (SCH 23390) increased and the D1 receptor agonist 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-benzazepine (SKF 33939) decreased anandamide content. 2-AG content was unaffected by SCH 23390 but was significantly increased by the D2 receptor antagonist eticlopride, which had no effect on anandamide content. The D2 agonist quinpirole had a biphasic effect on anandamide content with low, autoreceptor-preferring doses increasing anandamide and higher doses decreasing it back toward control. Quinpirole did not significantly affect 2-AG content. Together, these data indicate that endogenous dopamine exerts a differential, net suppressive effect upon anandamide and 2-AG content via activation of D1 and D2 receptors, respectively. These data are consistent with the hypothesis that modulation of endocannabinoid content by dopamine is secondary to changes in glutamatergic transmission, and they provide a pharmacological framework for the rational development of endocannabinoid-based therapeutic interventions for dopamine-related neuropsychiatric disorders.

The endogenous cannabinoid anandamide inhibits alpha7 nicotinic acetylcholine receptor-mediated responses in Xenopus oocytes

The effect of the endogenous cannabinoid ligand anandamide on the function of the cloned alpha7 subunit of the nicotinic acetylcholine (ACh) receptor expressed in Xenopus oocytes was investigated by using the two-electrode voltage-clamp technique. Anandamide reversibly inhibited nicotine (10 microM) induced-currents in a concentration-dependent manner (10 nM to 30 microM), with an IC50 value of 229.7 +/- 20.4 nM. The effect of anandamide was neither dependent on the membrane potential nor meditated by endogenous Ca2+ dependent Cl- channels since it was unaffected by intracellularly injected BAPTA and perfusion with Ca2+-free bathing solution containing 2 mM Ba2+. Anandamide decreased the maximal nicotine-induced responses without significantly affecting its potency, indicating that it acts as a noncompetitive antagonist on nicotinic acetylcholine (nACh) alpha7 receptors. This effect was not mediated by CB1 or CB2 receptors, as neither the selective CB1 receptor antagonist N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboximide hydrochloride (SR 141716A) nor CB2 receptor antagonist N-((1S)-endo-1,3,3-trimethyl-bicyclo-heptan-2-yl]-5-(4-chloro-3-methylphenyl)-1-(4-methylbenzyl)-pyrazole-3-carboxamide (SR 144528) reduced the inhibition by anandamide. In addition, inhibition of nicotinic responses by anandamide was not sensitive to either pertussis toxin treatment or to the membrane permeable cAMP analog 8-Br-cAMP (0.2 mM). Inhibitors of enzymes involved in anandamide metabolism including phenylmethylsulfonyl fluoride, superoxide dismutase, and indomethacin, or the anandamide transport inhibitor AM404 did not prevent anandamide inhibition of nicotinic responses, suggesting that anandamide itself acted on nicotinic receptors. In conclusion, these results demonstrate that the endogenous cannabinoid anandamide inhibits the function of nACh alpha7 receptors expressed in Xenopus oocytes in a cannabinoid receptor-independent and noncompetitive manner.

WIN 55,212-2 decreases the reinforcing actions of cocaine through CB1 cannabinoid receptor stimulation

CB(1) cannabinoid receptor agonists show a different profile compared to other drugs of abuse on the basis of experimental data that reveal their reinforcing properties. Thus, there are controversial data in the literature concerning the ability of CB(1) receptor agonists to reinforce behavioral responses in experimental animals, i.e. to lower self-stimulation thresholds, and to support self-administration or conditioned place preference. The aim of the present study was to examine the effects of WIN 55,212-2, a potent CB(1) receptor agonist (graded doses 0.1, 0.3, 1 mg/kg, i.p.), on the rewarding efficacy of lateral hypothalamic self-stimulation and on the systemic cocaine-induced potentiation of brain-stimulation reward. WIN 55,212-2 did not affect lateral hypothalamic self-stimulation thresholds both in drug nai;ve rats and in rats pretreated with the drug, whereas it produced a significant, dose-dependent decrease in the maximal rate of responding, i.e. in the performance of the animals. Cocaine (5.0 mg/kg, i.p.) produced a significant reduction in self-stimulation threshold, without altering maximal rates of responding. Importantly, WIN 55,212-2 attenuated the effect of cocaine at the two higher doses tested. The effects of the CB(1) receptor agonist were reversed by pretreatment with the selective CB(1) receptor antagonist SR 141716A (0.02 mg/kg, i.p.) that did not by itself affect cocaine's action. These results indicate that acute stimulation of CB(1) receptors per se does not affect baseline self-stimulation, but reduces the reinforcing effects induced by cocaine. Taken together these findings suggest that cannabinoids may interfere with brain-reward systems responsible for the expression of acute reinforcing properties of drugs of abuse, such as cocaine, and provide evidence that the cannabinoid system could be an interesting drug discovery and development target for the treatment of drug addiction.

Pre-exposure to the cannabinoid receptor agonist CP 55940 enhances morphine behavioral sensitization and alters morphine self-administration in Lewis rats

Three experiments examined the influence of pre-exposure to the cannabinoid receptor agonist CP 55940 ((-)-cis-3-(2-hydroxy-4-(1,1-dimethylheptyl)phenyl)-trans-4-(3-hydroxypropyl)cyclohexanol) on the sensitization of morphine-induced locomotor hyperactivity and self-administration in Lewis rats. In Experiment 1, rats received daily injections of vehicle or CP 55940 (0.1 mg/kg for 7 days then 0.2 mg/kg for a further 7 days). Four weeks later, the locomotor response to morphine (10 mg/kg s.c.) was tested once per day over a 3-h period for 14 consecutive days. Rats given morphine showed hypoactivity during the first hour following morphine but hyperactivity during the second and third hours. A progressive increase in hyperactivity to morphine was seen over the 14 days of administration, which was significantly greater in rats pre-treated with CP 55940. In Experiment 2, rats were given morphine (10 mg/kg) once a day for 14 days in combination with either vehicle, CP 55940 (0.1 mg/kg) or the cannabinoid CB(1) receptor antagonist SR 141716 (N-(piperidin-1-yl)-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-1H-pyrazole-3-carboxamide hydrochloride) (3 mg/kg). Both CP 55940 and SR 141716 initially inhibited the hyperactive response to morphine, but these effects gradually wore off and by the end of 14 days, hyperactivity was similar in all morphine-treated groups. When tested 3 weeks later for their response to morphine (10 mg/kg) given alone, rats previously given the morphine/CP 55940 combination, but not the SR 141716/morphine combination, showed a greater locomotor stimulation than those previously exposed to morphine only. In Experiment 3, rats were pre-exposed to CP 55940 or vehicle for 14 days and were subsequently trained to self-administer morphine intravenously (1 mg/kg per lever press) for 14 days. Rats pre-exposed to CP 55940 self-administered a significantly greater number of morphine infusions than vehicle pre-exposed rats. However, both active and inactive ('dummy') lever presses were increased by cannabinoid pre-treatment. Overall, these results suggest that cannabinoid pre-exposure can lead to an exaggeration of morphine-induced hyperactivity and may alter the reinforcing effects of morphine in Lewis rats. The implications for 'gateway' theories of cannabinoid effects in humans are discussed.

Prenatal elevation of endocannabinoids corrects the unbalance between dopamine systems and reduces activity in the Naples High Excitability rats

Several evidences suggest that endocannabinoids exert a neurotrophic effect on developing mesencephalic dopamine neurons. Since an altered mesocorticolimbic system seems to underlie hyperactivity and attention deficit in clinical and animal studies of attention deficit hyperactivity disorder (ADHD), prenatal elevation of anandamide has been induced in Naples high excitability (NHE) rats by inhibition of its reuptake. To this aim, pregnant NHE and random-bred females received a subcutaneous injection of AM-404 (1 mg/kg) or vehicle daily from E11 until E20. Young adult male offsprings were exposed to a spatial novelty (Làt-maze) for 30 min and the behavior was videotaped and analysed for indices of activity (travelled distance, rearing frequency) and attention (rearing duration). Moreover, morphological analysis of the brains was carried out that pertained to cytochrome oxydase as marker of metabolic activity and thyrosine hydroxylase as marker of the dopamine systems. The results indicate that prenatal AM-404 treatment significantly reduces activity by about 20% during the entire testing period and modifies the distribution of scanning times towards short duration episodes in the first part of the test only in NHE-treated rats. In addition, image analysis revealed a significant increase in relative optical density of TH+terminals in the dorsal striatum and substantia nigra of AM-404 treated NHE rats and minor changes in the dorsal cortex of AM-404 treated NRB rats. The data suggest a corrected unbalance between the two dopamine systems that apparently leads to reduced hyperactivity and modified scanning times in this animal model of ADHD. This, in turn, might open new strategies in the treatment of a subset of ADHD cases.

Lack of CB1 cannabinoid receptors modifies nicotine behavioural responses, but not nicotine abstinence

Cannabis is the most widely consumed illicit drug and its consumption is currently associated with tobacco, which contains another psychoactive compound, namely nicotine. Interactions between cannabinoids and other drugs of abuse, such as opioids, have been previously reported. The aim of the present study was to evaluate the possible role of CB1 cannabinoid receptor in responses induced by acute and repeated nicotine administration by using knockout mice lacking the CB1 cannabinoid receptor and their wild-type littermates. Acute nicotine (0.5, 1, 3 and 6 mg/kg, sc) administration decreased locomotor activity and induced antinociceptive responses in the tail-immersion and the hot-plate test, in wild-type animals. The antinociceptive effects in the tail-immersion test were significantly enhanced in CB1 knockout mice. In wild-type mice nicotine (0.5 mg/kg, sc) produced a significant rewarding effect, as measured by a conditioned place preference paradigm. This response was absent in CB1 knockout mice. Finally, a model of mecamylamine-induced abstinence in chronic nicotine-treated mice (10 mg/kg/day, sc) was developed. Mecamylamine (1 and 2 mg/kg, sc) precipitated several somatic signs of nicotine withdrawal in wild-type dependent mice. However, no difference in the severity of nicotine withdrawal was observed in CB1 knockout mice. These results demonstrate that some acute effects and motivational responses elicited by nicotine can be modulated by the endogenous cannabinoid system and support the existence of a physiological interaction between these two systems.

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.

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.

Cocaine, but not morphine, induces conditioned place preference and sensitization to locomotor responses in CB1 knockout mice

The involvement of cannabinoid CB1 receptors in morphine and cocaine motivational effects was investigated using CB1 knockout mice. For this purpose, we evaluated the rewarding effects in the place conditioning paradigm and the sensitization to the locomotor responses induced by these drugs. The hyperlocomotion induced by acute morphine administration (15 mg/kg, s.c.) was preserved, but the sensitization to this locomotor response induced by chronic morphine treatment was abolished in CB1 mutant mice. Morphine (5 mg/kg, s.c.) induced conditioned place preference in wild-type mice but failed to produce any response in knockout mice, indicating the inability of morphine to induce rewarding effects in the absence of CB1 cannabinoid receptors. When the aversive effects of morphine withdrawal were investigated using the place aversion paradigm, no differences between genotypes were observed. Acute cocaine (10 mg/kg, i.p.) induced hyperlocomotor responses in wild-type and knockout mice and a chronic cocaine treatment produced a similar sensitization to this response in both genotypes. In the conditioning place preference paradigm, cocaine (20 mg/kg, i.p.) produced rewarding responses in both wild-type and knockout mice. These results demonstrate that CB1 receptors are essential for adaptive responses produced by chronic morphine but not by chronic cocaine treatment.

The endocannabinoid system: a physiological perspective on its role in psychomotor control

The discovery of cannabinoid receptors has led to the identification of two natural activators for these receptors, anandamide and 2-arachidonoylglycerol, and to the elucidation of their biochemical pathways of formation and inactivation. Although the physiological significance of the endogenous cannabinoid system is still poorly understood, important information is becoming available on the possible functional roles of this system in the basal ganglia, a forebrain region that is involved in the control of sensorimotor and motivational aspects of behavior. These discoveries - which are going to enrich the way in which we look at basal ganglia functions - are summarized in this mini-review. The role of the endocannabinoids as modulators of psychomotor behaviors and the potential therapeutic perspectives deriving from the pharmacological manipulation of the endogenous cannabinoid system are also discussed.

Reversal of dopamine D(2) receptor responses by an anandamide transport inhibitor

We characterized the pharmacological properties of the anandamide transport inhibitor N-(4-hydroxyphenyl)-arachidonamide (AM404) in rats and investigated the effects of this drug on behavioral responses associated with activation of dopamine D(2) family receptors. Rat brain slices accumulated [(3)H]anandamide via a high-affinity transport mechanism that was blocked by AM404. When administered alone in vivo, AM404 caused a mild and slow-developing hypokinesia that was significant 60 min after intracerebroventricular injection of the drug and was reversed by the CB1 cannabinoid receptor antagonist SR141716A. AM404 produced no significant catalepsy or analgesia, two typical effects of direct-acting cannabinoid agonists. However, AM404 prevented the stereotypic yawning produced by systemic administration of a low dose of apomorphine, an effect that was dose-dependent and blocked by SR141716A. Furthermore, AM404 reduced the stimulation of motor behaviors elicited by the selective D(2) family receptor agonist quinpirole. Finally, AM404 reduced hyperactivity in juvenile spontaneously hypertensive rats, a putative model of attention deficit hyperactivity disorder. The results support a primary role of the endocannabinoid system in the regulation of psychomotor activity and point to anandamide transport as a potential target for neuropsychiatric medicines.

Endogenous cannabinoid signaling and psychomotor disorders

The effects of cannabinoids on motor behaviors and cognitive functions are well documented. The discovery of the CB1 cannabinoid receptor and the mapping of its distribution in the central nervous system have provided a rationale to elucidate the molecular and cellular mechanisms of cannabinoid actions. The identification of naturally occurring ligands for these receptors, anandamide and 2-arachidonylglycerol, has prompted a large research effort aimed at investigating the physiological role of the endogenous cannabinoid system, as well as its potential use as a target for novel therapeutic interventions. This mini-review discusses the participation of the endogenous cannabinoid system in the regulation of motor behaviors, pointing out its possible involvement in the pathophysiology of psychomotor disorders.

Dopamine activation of endogenous cannabinoid signaling in dorsal striatum

We measured endogenous cannabinoid release in dorsal striatum of freely moving rats by microdialysis and gas chromatography/mass spectrometry. Neural activity stimulated the release of anandamide, but not of other endogenous cannabinoids such as 2-arachidonylglycerol. Moreover, anandamide release was increased eightfold over baseline after local administration of the D2-like (D2, D3, D4) dopamine receptor agonist quinpirole, a response that was prevented by the D2-like receptor antagonist raclopride. Administration of the D1-like (D1, D5) receptor agonist SKF38393 had no such effect. These results suggest that functional interactions between endocannabinoid and dopaminergic systems may contribute to striatal signaling. In agreement with this hypothesis, pretreatment with the cannabinoid antagonist SR141716A enhanced the stimulation of motor behavior elicited by systemic administration of quinpirole. The endocannabinoid system therefore may act as an inhibitory feedback mechanism countering dopamine-induced facilitation of motor activity.

Chronic (-)-delta9-tetrahydrocannabinol treatment induces sensitization to the psychomotor effects of amphetamine in rats

Clinical and basic research studies have linked cannabinoid consumption to the onset of psychosis, specially schizophrenia. In the present study we have evaluated the effects of the natural psychoactive constituent of Cannabis (-)-delta9-tetrahydrocannabinol on the acute actions of the psychostimulant, D-amphetamine, on behaviour displayed by male rats on a hole-board, a proposed animal model of amphetamine-induced psychosis. Cannabinoid-amphetamine interactions were studied (1) 30 min after acute injection of (-)-delta9-tetrahydrocannabinol (0.1 or 6.4 mg/kg, i.p.); (2) 30 min after the last injection of 14-daily treatment with (-)-delta9-tetrahydrocannabinol (0.1 or 6.4 mg/kg) and 3) 24 h after the last injection of 14-daily treatment with (-)-delta9-tetrahydrocannabinol (6.4 mg/kg). Acute cannabinoid exposure antagonized the amphetamine-induced dose-dependent increase in locomotion, exploration and the decrease in inactivity. Chronic treatment with (-)-delta9-tetrahydrocannabinol resulted in tolerance to this antagonistic effect on locomotion and inactivity but not on exploration, and potentiated amphetamine-induced stereotypies. Lastly, 24 h of withdrawal after 14 days of cannabinoid treatment resulted in sensitization to the effects of D-amphetamine on locomotion, exploration and stereotypies. Since (-)-delta9-tetrahydrocannabinol is a cannabinoid CB1 receptor agonist, densely present in limbic and basal ganglia circuits, and since amphetamine enhances monoaminergic inputs (i.e., dopamine, serotonin) in these brain areas, the present data support the hypothesis of a role for the cannabinoid CB1 receptor as a regulatory mechanism of monoaminergic neuron-mediated psychomotor activation. These findings may be relevant for the understanding of both cannabinoid-monoamines interactions and Cannabis-associated psychosis.

Role of the endogenous cannabinoid system in the regulation of motor activity

One of the prominent pharmacological features of drugs acting at the brain cannabinoid receptor (CB1) is the induction of alterations in motor behavior. Catalepsy, immobility, ataxia, or the impairment of complex behavioral acts are observed after acute administration of either natural and synthetic cannabinoid receptor agonists or the endogenous CB1 ligand anandamide. The dense presence of CB1 receptors in the cerebellum and in the basal ganglia, especially at the outflow nuclei (substantia nigra and the internal segment of the globus pallidus), supports the existence of an endogenous cannabinoid system regulating motor activity. In the basal ganglia, the functionality of the anandamide-CB1 system is poorly understood. Dual effects are often observed after the administration of CB1 ligands in animal models of pharmacological manipulation of basal ganglia transmitter systems, indicating that the activity of the anandamide-CB1 system depends on the ongoing activation of the different elements of the basal ganglia. This finding is in agreement with the proposed activity-dependent release of anandamide from a plasmalemma precursor. Additionally, a potential state-dependent bidirectional coupling of the CB1 receptor to the adenylate cyclase transduction system has also been described. From this perspective, the endogenous cannabinoid system can be proposed as a local regulator of neurotransmission processes within the basal ganglia. This system may serve as a counterregulatory homeostatic mechanism preserving the functional role of basal ganglia circuits in coding the serial order of events that constitute movement.

Characteristics of cocaine interaction with delta-9-tetrahydrocannabinol on glucose metabolism in the rat testis

In this study, the characteristics of cocaine (COC) interaction with delta-9-tetrahydrocannabinol (THC) on glucose metabolism in the rat testis were investigated at different time points. Rats receiving 20 mg/kg IP COC at 0830 h and sacrificed at 15 min, 30 min and 60 min posttreatment showed no change in glucose metabolism. Moreover, 5 mg/kg, IV, COC treatment at 0900 h to rats and sacrificed 60 min postexposure, also produced no change in glucose metabolism. However, at 1300 h, the same protocol with IV COC treatment resulted in a significant increase in glucose utilization by the testis. Furthermore, a THC dose of 10 mg/kg, PO to the rats at 0830 or at 1130 h, followed by sacrifice 90 min later caused a significant decrease in glucose utilization at both time points. Similarly, when rats were given both THC and COC (THC at 0830 h, COC 90 min later) and sacrificed 60 min post-COC, it resulted in a further decrease in testicular glucose metabolism as compared to the rats treated by THC alone. On the other hand, concurrent exposure of rats to these drugs at 1300 h with same protocol, ended up with no change in glucose utilization in the testis. These data suggest that not only the route of administration but also the time of exposure plays an important role in defining the nature of the effects of COC/THC interaction on rat testicular glucose metabolism.

The effects of cocaine in combination with other drugs of abuse on schedule-controlled behavior in the pigeon

The present experiment sought to provide information regarding the consequences of combining cocaine with other drugs of abuse. The effects of cocaine alone and in combination with d-amphetamine, caffeine, morphine or delta-9-tetrahydrocannabinol were determined in five male white Carneaux pigeons responding under a multiple fixed-ratio 30, fixed-interval 600 schedule (mult FR FI). Drug interactions were studied by redetermining the cocaine dose-response curve in the presence of various fixed doses of the other drugs. Under the mult FR FI schedule, when cocaine (1 to 10 mg/kg) was combined with inactive doses of d-amphetamine (0.1, 0.3, 1.0, and 1.8 mg/kg), caffeine (10, 30, and 100 mg/kg), morphine (0.3, and 1.0 mg/kg), and delta-9-tetrahydrocannabinol (0.1 mg/kg), the FR and FI response rate dose-response curves were not shifted relative to the cocaine-alone curves. When cocaine was combined with an active dose of a drug which decreased response rate when given alone (0.3 mg/kg delta-9-tetrahydrocannabinol and 3 mg/kg morphine), the position of the response rate dose-response curves shifted compared to the cocaine-alone curves. The most frequent and consistent outcome of these interactions can be described as less than or approximately equal to an effect-additive interaction. Thus, these data indicate that the potential consequences of coabusing cocaine with the drugs tested in the present experiment can most often be predicted from the effects of each drug when taken alone.

Differential sensitivity to cocaine in spontaneously hypertensive and Wistar-Kyoto rats

Physiological, pharmacological and toxicological responses to two regimens of cocaine administration were compared between spontaneously hypertensive (SHR) and Wistar-Kyoto (WKY) rats. An initial experiment examined renal excretory and hemodynamic function in response to an acute volume load in anesthetized SHR and WKY following subacute cocaine treatment (20 mg/kg, s.c., twice a day for 9 days). Anticipated renal responses to volume loading were obtained but the responses of cocaine-treated SHR and WKY did not differ from vehicle-treated rats. A second group of experiments compared responses to continuous i.v. infusions of cocaine (1.25 mg/kg.min). In freely moving animals, no differences were noted between SHR and WKY in the increases in mean blood pressure (MBP) and heart rate (HR) produced during cocaine infusion. The elapsed time-to-onset of convulsions (Tc) elicited by cocaine was similar in both strains. However, when rats were subjected to restraint during the infusion period, pressor and tachycardic responses were observed to be significantly less in WKY than in SHR or in freely moving rats of either strain. Restraint also differentially affected rectal temperature (RT) responses to cocaine. Hypothermic responses to cocaine were observed in all WKY. Both hypothermic and hyperthermic responses were observed in SHR. A significant correlation was demonstrated between the Tc and the maximal change in RT produced during cocaine infusion. Division of SHR into two arbitrary groups was made, based on the direction of cocaine-induced change in RT. A significant (p less than 0.01) shortening of the Tc was obvious in SHR (8 of 15) in whom cocaine produced a hyperthermia. These animals were designated SHRH. The mean value for Tc in those SHR which demonstrated a lowering in RT (SHRL; 7 of 15) in response to cocaine was similar to that for WKY. Moreover, the SHRH evidenced significantly greater increases in HR, but not MBP, to cocaine infusion than did SHRL. The results indicate that restraint stress causes expression of a significant heterogeneity in the RT response of SHR to cocaine. The magnitude and direction of the RT responses are negatively correlated with sensitivity to the convulsive effects of cocaine in SHR. Stress may modify toxic responses to cocaine by interactions with body temperature homeostasis.

Comparative effects of tetrahydrocannabinol on psychostimulant-induced behaviors

The behavioral effects of delta-9-tetrahydrocannabinol (THC), one of the major psychoactive cannabinoids in marijuana, were tested in two models of psychostimulant-induced behaviors in rats (locomotor behavior and stereotyped gnawing) induced by amphetamine (AMPH) and methylphenidate (MEPH). Pretreatment with THC (10 mg/kg gavage) almost doubled the amount of AMPH-induced gnawing but produced no effect on AMPH-induced locomotor behavior. In contrast to AMPH, THC produced no direct effect on MEPH-induced gnawing but caused a strong suppression of MEPH-induced locomotor activity. In addition, there was no additional interaction between THC and reserpine as measured by suppression of MEPH-induced gnawing. This result was unexpected in view of the powerful interaction between THC and reserpine reported previously. Because of the clear THC-induced dissociation of the behavioral effects of these two psychostimulants (AMPH and MEPH), our working hypothesis is that THC affects motor behaviors by some non-dopaminergic mechanism.

Effects of the administration of coca alkaloids on the primary immune responses of mice: interaction with delta 9-tetrahydrocannabinol and ethanol

The effects of cocaine, its metabolites, and other alkaloids from Erythroxylon coca on the primary immune responses of ICR mice to sheep red blood cells (sRBC) and dinitrofluorobenzene (DNFB) were studied. The Jerne hemolytic plaque assay (PFC) was used to evaluate the humoral immune response to sheep red blood cells, and the delayed type hypersensitivity (DTH) response to DNFB was used to study cellular immune responsiveness. Drugs were given in single daily po doses for 5 consecutive days beginning on the day of immunization or 3 days prior to and on Days 3 and 4 after immunization. Inhibition of both PFC and DTH responses occurred at doses of 15 to 60 mg/kg of cocaine and was greatest when fed during immunization. Five other alkaloids also suppressed the PFC and/or DTH response. Cocaine was more suppressive than the six other alkaloids tested. Ethanol (5 g/kg) did not suppress the DTH response and only marginally suppressed the PFC response. delta 9-THC inhibited the PFC response at doses of 10 mg/kg and marginally suppressed the DTH response at doses of 30 mg/kg, but not at other doses ranging from 10 to 90 mg/kg. Coadministration of 5 g/kg ethanol and 15 mg/kg cocaine resulted in 50% antagonism of effects of cocaine on the PFC response and complete antagonism of the suppression of the DTH response, but only if these substances were given during the period of immunization. Like ethanol, delta 9-THC also abolished the inhibitory effects of cocaine on the PFC and DTH response but only if coadministered during the period of immunization. Coadministration of ethanol and delta 9-THC resulted in synergistic inhibition of both DTH and PFC responses.

Changes in body temperature after administration of antipyretics, LSD, delta 9-THC, CNS depressants and stimulants, hormones, inorganic ions, gases, 2,4-DNP and miscellaneous agents

This survey concludes a series of complications of data from the literature, primarily published since 1965, on thermoregulatory effects of antipyretics in afebrile as well as in febrile subjects, LSD and other hallucinogens, cannabinoids, general CNS depressants, CNS stimulants including xanthines, hormones, inorganic ions, gases and fumes, 2,4-dinitrophenol and miscellaneous agents including capsaicin, cardiac glycosides, chemotherapeutic agents, cinchona alkaloids, cyclic nucleotides, cycloheximide, 2-deoxy-D-glucose, dimethylsulfoxide, insecticides, local anesthetics, poly I:poly C, spermidine and spermine, sugars, toxins and transport inhibitors. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary agents.

Changes in body temperature after administration of adrenergic and serotonergic agents and related drugs including antidepressants

This survey, the third in a series, presents extensive tabulations of literature, primarily since 1965, on thermoregulatory effects of adrenergic and serotonergic agonists and their antagonists including ergot alkaloids, amphetamines, tryptamines, monoamine oxidase inhibitors, tricyclic and other antidepressants, a variety of other agents which alter presynaptic aminergic mechanisms including reserpine, 6-hydroxydopamine, p-chlorophenylalanine, alpha-methyltyrosines, cocaine, guanethidine and bretylium. The information listed includes the species used, route of administration and dose of drug, the environmental temperature at which the experiments were performed, the number of tests, the direction and magnitude of body temperature change and remarks on the presence of special conditions, such as age or lesions, or on the influence of other drugs, such as antagonists, on the response to the primary drug.