Cerebellar CB(1) receptor mediation of Delta(9)-THC-induced motor incoordination and its potentiation by ethanol and modulation by the cerebellar adenosinergic A(1) receptor in the mouse

Adenosine Improves Mitochondrial Function and Biogenesis in Friedreich's Ataxia Fibroblasts Following L-Buthionine Sulfoximine-Induced Oxidative Stress

Adenosine is a nucleoside that is widely distributed in the central nervous system and acts as a central excitatory and inhibitory neurotransmitter in the brain. The protective role of adenosine in different pathological conditions and neurodegenerative diseases is mainly mediated by adenosine receptors. However, its potential role in mitigating the deleterious effects of oxidative stress in Friedreich's ataxia (FRDA) remains poorly understood. We aimed to investigate the protective effects of adenosine against mitochondrial dysfunction and impaired mitochondrial biogenesis in L-buthionine sulfoximine (BSO)-induced oxidative stress in dermal fibroblasts derived from an FRDA patient. The FRDA fibroblasts were pre-treated with adenosine for 2 h, followed by 12.50 mM BSO to induce oxidative stress. Cells in medium without any treatments or pre-treated with 5 µM idebenone served as the negative and positive controls, respectively. Cell viability, mitochondrial membrane potential (MMP), aconitase activity, adenosine triphosphate (ATP) level, mitochondrial biogenesis, and associated gene expressions were assessed. We observed disruption of mitochondrial function and biogenesis and alteration in gene expression patterns in BSO-treated FRDA fibroblasts. Pre-treatment with adenosine ranging from 0-600 µM restored MMP, promoted ATP production and mitochondrial biogenesis, and modulated the expression of key metabolic genes, namely nuclear respiratory factor 1 (NRF1), transcription factor A, mitochondrial (TFAM), and NFE2-like bZIP transcription factor 2 (NFE2L2). Our study demonstrated that adenosine targeted mitochondrial defects in FRDA, contributing to improved mitochondrial function and biogenesis, leading to cellular iron homeostasis. Therefore, we suggest a possible therapeutic role for adenosine in FRDA.

THC and CBD: Similarities and differences between siblings

Δ9-tetrahydrocannabinol (THC) and its sibling, cannabidiol (CBD), are produced by the same Cannabis plant and have similar chemical structures but differ dramatically in their mechanisms of action and effects on brain functions. Both THC and CBD exhibit promising therapeutic properties; however, impairments and increased incidence of mental health diseases are associated with acute and chronic THC use, respectively, and significant side effects are associated with chronic use of high-dose CBD. This review covers recent molecular and preclinical discoveries concerning the distinct mechanisms of action and bioactivities of THC and CBD and their impact on human behavior and diseases. These discoveries provide a foundation for the development of cannabinoid-based therapeutics for multiple devastating diseases and to assure their safe use in the growing legal market of Cannabis-based products.

Combined alcohol and cannabinoid exposure leads to synergistic toxicity by affecting cerebellar Purkinje cells

Combined use of cannabis and alcohol results in greater psychoactive toxicity than either substance alone, but the underlying central mechanisms behind this worsened outcome remain unclear. Here we show that the synergistic effect of Δ⁹-tetrahydrocannabinol (THC) and ethanol on motor incoordination in mice is achieved by activating presynaptic type 1 cannabinoid receptors (CB₁R) and potentiating extrasynaptic glycine receptors (GlyR) within cerebellar Purkinje cells (PCs). The combination of ethanol and THC significantly reduces miniature excitatory postsynaptic current frequency in a CB₁R-dependent manner, while increasing the extrasynaptic GlyR-mediated chronic chloride current, both leading to decreased PC activity. Ethanol enhances THC actions by boosting the blood-brain-barrier permeability of THC and enriching THC in the cell membrane. Di-desoxy-THC, a designed compound that specifically disrupts THC-GlyR interaction without affecting the basic functions of CB₁R and GlyR, is able to restore PC function and motor coordination in mice. Our findings provide potential therapeutic strategies for overcoming the synergistic toxicity caused by combining cannabis and alcohol use.

Synthetic cannabinoids enhanced ethanol-induced motor impairments through reduction of central glutamate neurotransmission

Marijuana or synthetic cannabinoids and alcohol are often used together, with these combinations causing motor impairments that can subsequently lead to motor vehicle accidents. This study investigated the combined use of both synthetic cannabinoids and ethanol and their effect on motor coordination in mice in addition to examining the neurochemical changes in the cerebellum. Ethanol (2 g/kg, i.p.) significantly induced motor impairment in the accelerating rotarod test in mice. Furthermore, ethanol-induced motor impairments were further accentuated when combined with the synthetic cannabinoid, JWH-018 or AB-CHMINACA. The enhancement effects of the synthetic cannabinoids were completely antagonized by pretreatment with the selective CB₁ receptor antagonist AM251, but not by the selective CB₂ receptor antagonist AM630. Neurochemical study results showed that ethanol caused a reduction in the extracellular glutamate levels in the cerebellum during periods of ethanol-induced motor impairment. In addition to the enhanced motor impairment seen when ethanol was combined with JWH-018, these combinations also enhanced the reduction of the extracellular glutamate levels in the cerebellum. We additionally used microelectrode array recordings to examine the effects of ethanol and/or JWH-018 on the spontaneous network activity in primary cultures from mouse cerebellum. Results showed that ethanol combined with JWH-018 significantly reduced spontaneous neuronal network activity in the primary cerebellar culture. Our findings demonstrate that ethanol-induced motor impairments are enhanced by synthetic cannabinoids, with these effects potentially mediated by CB₁ receptors. An accentuated reduction of neurotransmissions in the cerebellum may play an important role in motor impairments caused by ethanol combined with synthetic cannabinoids.

Assessment of Acute Motor Effects and Tolerance Following Self-Administration of Alcohol and Edible ∆9 -Tetrahydrocannabinol in Adolescent Male Mice

BACKGROUND

Cannabinoids and their principle psychoactive target, the cannabinoid type 1 receptor (CB1R), impact a number of alcohol-related properties, and although alcohol and cannabis are often co-used, particularly in adolescence, few animal models of this phenomenon exist. We modeled the co-use of alcohol and ∆⁹ -tetrahydrocannabinol (THC) in adolescent mice using ingestive methods popular during this developmental period in humans, namely binge-drinking and edible THC. With this model, we assessed levels of use, acute effects, and tolerance to each substance.

METHODS

Adolescent male C57BL/6J mice had daily, limited access to 1 of 2 edible doughs (THC or control), to 1 of 2 fluids (ethanol (EtOH) or water), and in 1 of 2 orders (dough-fluid or fluid-dough). Home cage locomotor activity was recorded both during access and after access. On the day following the final access session, a subset of mice were assessed for functional and metabolic tolerance to alcohol using accelerating rotarod and blood EtOH concentrations, respectively. The remaining mice were assessed for tolerance to THC-induced hypothermia, and whole-brain CB1R expression was assessed in all mice.

RESULTS

EtOH intake was on par with levels previously reported in adolescent mice. Edible THC was well-consumed, but consumption decreased at the highest dose provided. Locomotor activity increased following EtOH intake and decreased following edible THC consumption, and edible THC increased fluid intake in general. The use of alcohol produced neither functional nor metabolic tolerance to an alcohol challenge. However, the use of edible THC impaired subsequent drug-free rotarod performance and was associated with a reduction in THC's hypothermic effect.

CONCLUSIONS

Adolescent mice self-administered both alcohol and edible THC to a degree sufficient to acutely impact locomotor activity. However, only edible THC consumption had lasting effects during short-term abstinence. Thus, this adolescent co-use model could be used to explore sex differences in self-administration and the impact substance co-use might have on other domains such as mood and 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.

Acetate as an active metabolite of ethanol: studies of locomotion, loss of righting reflex, and anxiety in rodents

It has been postulated that a number of the central effects of ethanol are mediated via ethanol metabolites: acetaldehyde and acetate. Ethanol is known to produce a large variety of behavioral actions such anxiolysis, narcosis, and modulation of locomotion. Acetaldehyde contributes to some of those effects although the contribution of acetate is less known. In the present studies, rats and mice were used to assess the acute and chronic effects of acetate after central or peripheral administration. Male Sprague-Dawley rats were used for the comparison between central (intraventricular, ICV) and peripheral (intraperitoneal, IP) administration of acute doses of acetate on locomotion. CD1 male mice were used to study acute IP effects of acetate on locomotion, and also the effects of chronic oral consumption of acetate (0, 500, or 1000 mg/l, during 7, 15, 30, or 60 days) on ethanol- (1.0, 2.0, 4.0, or 4.5 g/kg, IP) induced locomotion, anxiolysis, and loss of righting reflex (LORR). In rats, ICV acetate (0.7–2.8 μmoles) reduced spontaneous locomotion at doses that, in the case of ethanol and acetaldehyde, had previously been shown to stimulate locomotion. Peripheral acute administration of acetate also suppressed locomotion in rats (25–100 mg/kg), but not in mice. In addition, although chronic administration of acetate during 15 days did not have an effect on spontaneous locomotion in an open field, it blocked ethanol-induced locomotion. However, ethanol-induced anxiolysis was not affected by chronic administration of acetate. Chronic consumption of acetate (up to 60 days) did not have an effect on latency to, or duration of LORR induced by ethanol, but significantly increased the number of mice that did not achieve LORR. The present work provides new evidence supporting the hypothesis that acetate should be considered a centrally-active metabolite of ethanol that contributes to some behavioral effects of this alcohol, such as motor suppression.

Gait and balance in treatment-naïve active alcoholics with and without a lifetime drug codependence

BACKGROUND

Disturbed gait and balance are among the most consistent sequelae of chronic alcoholism. However, although a majority of alcoholics have never sought treatment, most investigations showing ataxia in alcohol-dependent individuals have relied on samples drawn from treated populations. In addition, few studies have addressed the associations of codependence on other drugs with alcoholic gait and balance disturbance.

METHODS

This study employed the Walk-a-Line Ataxia Battery (Fregly et al. Alcohol Clin Exp Res 1972;43:395-399) to assess gait and balance in treatment-naïve, actively drinking alcohol-dependent men and women (TNA; n = 69) who were dependent on alcohol only (ALC; n = 43), or who also had a lifetime drug dependence (ALC + DRG; n = 26; i.e., methamphetamine, cocaine, opiates, and/or marijuana), compared with nonsubstance abusing controls (NSAC; n = 74).We also examined associations between lifetime alcohol use and age with gait and balance measures.

RESULTS

Our main findings were (i) no evidence of disturbed gait and balance in ALC versus NSAC and (ii) significantly disturbed gait and balance in ALC + DRG, relative to both NSAC and ALC, along with steeper age-associated decline in gait and balance performance in ALC versus ALC + DRG.

CONCLUSIONS

Our results provide evidence consistent with previous studies that TNA (without a lifetime drug codependence) may represent a population that is different and less impaired (including in gait and balance) than treated alcoholics. Additionally, we provide evidence that ALC + DRG, with greater alcohol use and family drinking density than ALC, have an accelerated effect of age on gait and balance disturbance compared with both NSAC and ALC. The ALC + DRG group likely represents a subset of TNA with different characteristics than ALC.

Regulation of hippocampal cannabinoid CB1 receptor actions by adenosine A1 receptors and chronic caffeine administration: implications for the effects of Δ9-tetrahydrocannabinol on spatial memory

The cannabinoid CB(1) receptor-mediated modulation of γ-aminobutyric acid (GABA) release from inhibitory interneurons is important for the integrity of hippocampal-dependent spatial memory. Although adenosine A(1) receptors have a central role in fine-tuning excitatory transmission in the hippocampus, A(1) receptors localized in GABAergic cells do not directly influence GABA release. CB(1) and A(1) receptors are the main targets for the effects of two of the most heavily consumed psychoactive substances worldwide: Δ(9)-tetrahydrocannabinol (THC, a CB(1) receptor agonist) and caffeine (an adenosine receptor antagonist). We first tested the hypothesis that an A(1)-CB(1) interaction influences GABA and glutamate release in the hippocampus. We found that A(1) receptor activation attenuated the CB(1)-mediated inhibition of GABA and glutamate release and this interaction was manifested at the level of G-protein activation. Using in vivo and in vitro approaches, we then investigated the functional implications of the adenosine-cannabinoid interplay that may arise following chronic caffeine consumption. Chronic administration of caffeine in mice (intraperitoneally, 3 mg/kg/day, for 15 days, >12 h before trials) led to an A(1)-mediated enhancement of the CB(1)-dependent acute disruptive effects of THC on a short-term spatial memory task, despite inducing a reduction in cortical and hippocampal CB(1) receptor number and an attenuation of CB(1) coupling with G protein. A(1) receptor levels were increased following chronic caffeine administration. This study shows that A(1) receptors exert a negative modulatory effect on CB(1)-mediated inhibition of GABA and glutamate release, and provides the first evidence of chronic caffeine-induced alterations on the cannabinoid system in the cortex and hippocampus, with functional implications in spatial memory.

Combined effects of acute, very-low-dose ethanol and delta(9)-tetrahydrocannabinol in healthy human volunteers

RATIONALE

Previous studies examining the combined effects of ethanol and cannabis, or its primary psychoactive ingredient, ∆⁹-tetrahydrocannabinol (THC), have provided mixed results. Data from an in vitro study suggests that combined, sub-threshold doses of these drugs may interact to produce synergistic effects. Very low doses of the two drugs in combination have not been tested in humans.

MATERIALS AND METHODS

This study assessed whether combinations of acute, very low doses of ethanol and THC produce synergistic effects on subjective, cognitive, and physiological measures. Healthy volunteers (n=11) received capsules containing placebo or THC (2.5 mg), and beverages containing placebo or ethanol (0.1 and 0.2 g/kg) alone, and in combination, across separate sessions, in a within-subjects, randomized, double-blind design. During each session, participants completed measures of working memory, psychomotor ability, and simple reaction time, and provided subjective mood and drug effect ratings. Cardiovascular measures were obtained at regular intervals.

RESULTS

As intended, when administered alone, these very low doses of ethanol and THC had only moderate effects on isolated measures. The combined effects of these drugs were not synergistic, and in some cases appeared to be less-than-additive.

CONCLUSIONS

Our data provide no evidence for synergistic effects of acute combinations of very-low-dose ethanol and THC on subjective or physiologic response, or on cognitive performance.

Cannabinoid receptor CB1 mediates baseline and activity-induced survival of new neurons in adult hippocampal neurogenesis

Background

Adult neurogenesis is a particular example of brain plasticity that is partially modulated by the endocannabinoid system. Whereas the impact of synthetic cannabinoids on the neuronal progenitor cells has been described, there has been lack of information about the action of plant-derived extracts on neurogenesis. Therefore we here focused on the effects of Δ9-tetrahydrocannabinol (THC) and Cannabidiol (CBD) fed to female C57Bl/6 and Nestin-GFP-reporter mice on proliferation and maturation of neuronal progenitor cells and spatial learning performance. In addition we used cannabinoid receptor 1 (CB1) deficient mice and treatment with CB1 antagonist AM251 in Nestin-GFP-reporter mice to investigate the role of the CB1 receptor in adult neurogenesis in detail.

Results

THC and CBD differed in their effects on spatial learning and adult neurogenesis. CBD did not impair learning but increased adult neurogenesis, whereas THC reduced learning without affecting adult neurogenesis. We found the neurogenic effect of CBD to be dependent on the CB1 receptor, which is expressed over the whole dentate gyrus. Similarly, the neurogenic effect of environmental enrichment and voluntary wheel running depends on the presence of the CB1 receptor. We found that in the absence of CB1 receptors, cell proliferation was increased and neuronal differentiation reduced, which could be related to CB1 receptor mediated signaling in Doublecortin (DCX)-expressing intermediate progenitor cells.

Conclusion

CB1 affected the stages of adult neurogenesis that involve intermediate highly proliferative progenitor cells and the survival and maturation of new neurons. The pro-neurogenic effects of CBD might explain some of the positive therapeutic features of CBD-based compounds.

Abnormal cerebellar morphometry in abstinent adolescent marijuana users

Functional neuroimaging data from adults have, in general, revealed frontocerebellar dysfunction associated with acute and chronic marijuana (MJ) use. The goal of this study was to characterize cerebellar volume in adolescent chronic MJ users following 1 month of monitored abstinence. Participants were MJ users (n=16) and controls (n=16) aged 16-18 years. Extensive exclusionary criteria included history of psychiatric or neurologic disorders. Drug use history, neuropsychological data, and structural brain scans were collected after 28 days of monitored abstinence. Trained research staff defined cerebellar volumes (including three cerebellar vermis lobes and both cerebellar hemispheres) on high-resolution T1-weighted magnetic resonance images. Adolescent MJ users demonstrated significantly larger inferior posterior (lobules VIII-X) vermis volume than controls, above and beyond effects of lifetime alcohol and other drug use, gender, and intracranial volume. Larger vermis volumes were associated with poorer executive functioning. Following 1 month of abstinence, adolescent MJ users had significantly larger posterior cerebellar vermis volumes than non-using controls. These greater volumes are suggested to be pathological based on linkage to poorer executive functioning. Longitudinal studies are needed to examine typical cerebellar development during adolescence and the influence of marijuana use.

[Neuropsychopharmacology of delta-9-tetrahydrocannabinol]

Today, the main route of introduction of tetrahydrocannabinol (THC), the main active substance of cannabis, into the human body is via the lungs, from smokes produced by combustion of a haschich-tobacco mixture. The use of a water pipe (nargileh-like) intensifies its fast supply to the body. THC reaches the brain easily where it stimulates CB1 receptors; their ubiquity underlies a wide variety of effects. THC disappears from extracellular spaces by dissolving in lipid rich membranes, and not by excretion from the body. This is followed by a slow release, leading to long lasting effects originating from brain areas containing a large proportion of spare receptors ("reserve receptors"). Far from mimicking the effects of endocannabinoids, THC caricatures and disturbs them. It induces both psychical and physical dependencies, but the perception of withdrawal is weak on account of its very slow elimination. THC disturbs cognition. Acutely, it develops anxiolytic- and antidepressant-like effects, which causes a lot of users to abuse THC, thus leading to a tolerance (desensitization of CB1 receptors) making anxiety and depression to reappear more intensely than originally. THC has close relationships with schizophrenia. It incites to tobacco, alcohol and heroine abuses.

The antinociceptive interaction of anandamide and adenosine at the spinal level

Both anandamide and adenosine have significant roles in pain mechanisms, but no data are available concerning their interaction at the spinal level. The goal of this study was to determine how adenosine and the adenosine receptor antagonist caffeine affect the antinociceptive effect of anandamide. The pain sensitivity was assessed by the acute tail-flick test and by paw withdrawal test after carrageenan-induced inflammation. The substances were administered intrathecally to male Wistar rats. Anandamide alone (1, 30 and 100 microg) dose-dependently decreased the hyperalgesia, however it had low potency in the tail-flick test. Neither adenosine (100 microg) nor caffeine (400 microg) alone changed the pain sensitivity markedly. Their combination caused a short-lasting antihyperalgesia, but it did not influence the tail-flick latency. Both adenosine and caffeine decreased the antihyperalgesic potential of 100 microg anandamide, while adenosine-caffeine pretreatment temporarily enhanced its effect. As regards acute heat pain sensitivity, no combination with anandamide influenced the effect of anandamide. These findings provide new data concerning the interaction between two endogenous ligands and caffeine. Since these substances may exert effects on several receptors and/or systems, their interaction in vivo must be very complex and the net outcome after their coadministration could not been predicted from the in vitro results.

Effects of prenatal exposure to the CB-1 receptor agonist WIN 55212-2 or CO on the GABAergic neuronal systems of rat cerebellar cortex

The aim of this study was to assess the effects of prenatal exposures to cannabinoids or carbon monoxide (CO) in an animal experimental model reproducing the environmental conditions in which a fetus develops whose mother, during pregnancy, ingests by smoking low doses of cannabinoids or CO. Particular attention was devoted to analyses of the long-term effects of the exposures at the level of the cerebellar cortex, where already during prenatal development the GABAergic neuronal systems may be modulated by both cannabinoids and CO. Three groups of rats were subjected to the following experimental conditions: exposure to cannabinoids by maternal treatment during pregnancy with the cannabinoid CB-1 receptor agonist WIN 55212-2 (WIN) (0.5 mg/kg/day, s.c.); exposure to CO by maternal exposure during pregnancy to CO (75 parts per million, by inhalation); and exposure to WIN+CO at the above doses and means of administration; a fourth group was used as control. The body weight of dams, length of pregnancy, litter size at birth, body weight and postnatal mortality of pups were monitored in order to evaluate possible effects of the exposures on reproduction and on prenatal and postnatal development. In the different groups, the long-term effects of the exposures were studied in adult rats (120-150 days) by light microscopy analyses of the structure of the cerebellar cortex and of the distribution in the cortex of markers of GABAergic neurons, such as GAD and GABA itself. Results. Exposures to WIN or CO did not affect reproduction or prenatal/postnatal development. Moreover, the exposed rats showed no structural alterations of the cerebellar cortex and displayed qualitative distribution patterns of GAD and GABA immunoreactivities similar to those of the controls. However, quantitative analyses indicated significant changes of both of these immunoreactivities: in comparison with the controls, they were significantly increased in WIN-exposed rats and reduced in CO-exposed rats, but not significantly different in WIN+CO-exposed rats. The changes were detected in the molecular and Purkinje neuron layers, but not in the granular layer. Prenatal exposures of rats to WIN or CO, at doses that do not affect reproduction, general processes of development and histomorphogenesis of the cerebellar cortex, cause significant changes of GAD and GABA immunoreactivities in some GABAergic neuronal systems of the adult rat cerebellar cortex, indicating selective up-regulation of GABA-mediated neurotransmission as a long-term consequence of chronic prenatal exposures to cannabinoids or CO. Because the changes consist of overexpression or, vice versa, underexpression of these immunoreactivities, functional alterations of opposite types in the GABAergic systems of the cerebellum following exposure to WIN or CO can be postulated, in agreement with the results of behavioral and clinical studies. No changes in immunoreactivities were detected after prenatal exposure to WIN and CO in association.

Cannabinoid modulation of neuronal function after oxygen/glucose deprivation in area CA1 of the rat hippocampus

Endocannabinoids released during cerebral ischemia have been implicated as neuroprotective agents. We assessed the role of cannabinoid receptors in modulating the response of neurons to oxygen/glucose deprivation (OGD), a model for in vitro ischemia, in rat hippocampal slices using extracellular recording techniques. Under control conditions, 15 min OGD resulted in only 50% recovery of CA1 field excitatory postsynaptic potentials (fEPSPs) 60 min post-insult. This post-OGD depression of function was primarily NMDA receptor-dependent as the NMDA receptor antagonist MK-801 (50 microM) promoted recovery of synaptic transmission to 76% of the baseline. Treatment with the CB1 receptor antagonist AM251 (1 microM), which prevented the depression of excitatory synaptic transmission caused by WIN55,212-2 (1 microM), also markedly enhanced recovery of function (71% of control). The enhanced recovery after OGD in the presence of AM251 was independent of both GABA(A) receptors and NMDA receptors since co-application of AM251 with either bicuculline (10 microM) or MK-801 (50 microM) did not alter recovery, or further improved recovery, respectively. These results suggest endocannabinoids released during OGD may modulate synaptic transmission and post-OGD neuronal outcome via activation of an AM251-sensitive cannabinoid receptor.

Motor effects of delta 9 THC in cerebellar Lurcher mutant mice

The present study evaluated the effects of the principal active component of marijuana (delta 9 THC) on motor abilities and motor learning in mice with cerebellar dysfunction. For this purpose, spontaneous locomotor activity, equilibrium abilities, muscular tone, motor coordination and motor learning were investigated in Lurcher mutant and non-mutant B6/CBA mice 20 min after i.p. administration of 4 or 8 mg kg(-1) of delta 9 tetra hydro cannabinol (delta 9 THC). The performances were compared to those obtained by Lurcher and non-mutant mice injected with vehicle (Tween 80). The results showed that at the dose of 4 mg kg(-1) but not at the dose of 8 mg kg(-1), the cannabinoid (CB) substance reduced deficits in motor coordination, equilibrium and muscular tone and facilitated motor learning in Lurcher mice. On the other hand, only a muscular strength decrease was observed in control B6/CBA mice injected with the dose of 8 mg kg(-1) of delta 9 THC. These results suggested that cannabinoid derivative could represent a new field of investigation concerning the treatment of cerebellar ataxic syndrome in humans.

Involvement of the alpha4beta2 nicotinic receptor subtype in nicotine-induced attenuation of delta9-THC cerebellar ataxia: role of cerebellar nitric oxide

We have recently reported that mediation of intracerebellar nicotine-induced attenuation of cerebellar delta9-THC ataxia was via the alpha4beta2 nAChR. The present study was meant to investigate the role of cerebellar nitric oxide (NO)-guanylyl cyclase (GC) signaling in the alpha4beta2-mediated attenuation in CD-1 male mice. Drugs were given via intracerebellar microinfusion using stereotaxically implanted guide cannulas, with ataxia evaluated by Rotorod. Intracerebellar microinfusion of SNP (sodium nitroprusside, NO donor; 15, 30, 60 pg) and SMT (S-methylisothiourea, inhibitor of inducible NO synthase; 70, 140, 280 fg) significantly enhanced and reduced, respectively, intracerebellar RJR-2403 (selective alpha4beta2 agonist)-induced attenuation of delta9-THC ataxia dose-dependently. Intracerebellar isoliquiritigenin (GC-activator; 1, 2, 4 pg) and ODQ (1H[1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, GC inhibitor; 200, 400, 800 fg), significantly enhanced and reduced, respectively, intracerebellar RJR-2403-induced attenuation of delta9-THC ataxia dose-dependently. Further support for the role of NO was evidenced via increases in cerebellar NO(x) (nitrate+nitrite) levels following microinfusion of nicotine or RJR-2403 as compared to control, whereas delta9-THC significantly decreased NO(x) levels. "Nicotine/RJR-2403+delta9-THC" treated mice had cerebellar NO(x) levels significantly increased as compared to mice infused with delta9-THC alone. Results of the present investigation support the role of cerebellar NO-GC signaling in alpha4beta2 nAChR subtype-mediated attenuation of delta9-THC ataxia.

Co-modulation of acute ethanol-induced motor impairment by mouse cerebellar adenosinergic A1 and GABAA receptor systems

We have previously demonstrated that cerebellar adenosine modulates ethanol ataxia. Using Rotorod method, we investigated the role of cerebellar GABA(A) receptors in the adenosinergic modulation of ethanol ataxia in mice. Direct cerebellar microinfusion of GABA(A) agonist, muscimol (2.5, 5 and 10 ng) and antagonist, bicuculline (50, 100 and 200 ng), via permanently implanted guide cannulas, produced a marked and dose-dependent accentuation and attenuation, respectively, of ethanol (2g/kg; IP) ataxia. The accentuation of ethanol ataxia by intracerebellar muscimol was through GABA(A) receptor because intracerebellar pretreatment with bicuculline virtually abolished muscimol effect. Intracerebellar microinfusion of adenosine A(1) agonist, N(6)-cyclohexyladenosine (CHA: 4 ng), and antagonist, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX: 100 ng) markedly accentuated and attenuated, respectively, ethanol ataxia consistent with our previously published data. Intracerebellar microinfusion of CHA (4 ng) or DPCPX (100 ng) markedly enhanced and reduced, respectively, muscimol (10 ng)-induced accentuation of ethanol ataxia suggesting co-modulation of ethanol ataxia by cerebellar adenosinergic A(1) and GABA(A) receptors. Similarly, intracerebellar bicuculline (200 ng) pretreatment not only prevented CHA-induced accentuation of ethanol ataxia, but caused further decrease in ethanol ataxia. No change in the normal coordination was observed when microinfusion of the highest dose of muscimol, bicuculline, DPCPX or CHA alone or in combination was followed by saline injection instead of ethanol. The results of the present study suggest a functional similarity between GABA(A) and adenosine A(1) receptors even though both receptor types are known to couple to different signaling system and their location is on the opposite ends of the cerebellar granule cells, axons and axonal terminals (i.e., GABA(A) at the granule cells and adenosine A(1) on axons and axonal terminals of the granule cells) and act as co-modulators of ethanol ataxia.

Behavioral interaction between nicotine and ethanol: possible modulation by mouse cerebellar glutamate

BACKGROUND

Epidemiological studies show that people who drink alcoholic beverages also smoke cigarettes and vice versa. Furthermore, animal studies provide circumstantial evidence for ethanol and nicotine interaction. Previously, we demonstrated that intracerebellar nicotine attenuates ethanol ataxia. This study investigated the possible role of glutamate in modulating the interaction of nicotine and ethanol.

METHODS

Glutamate drugs N-methyl-d-aspartate (NMDA) and (+)-alpha-amino-3-hydroxy-5-methylisoxazole-4-propionic acid hydrate (AMPA) as well as their antagonists were directly microinfused into the cerebellum of CD-1 male mice to evaluate their effect on ethanol (2 g/kg i.p.) ataxia. Drug microinfusions were made via stereotaxically implanted stainless-steel guide cannulas. Rotorod was used to evaluate the ataxic response of ethanol.

RESULTS

Microinfusion of nicotine (0.3125, 1.25, 5 ng) significantly attenuated ethanol ataxia dose-dependently, confirming the functional interaction between nicotine and ethanol as reported earlier. Intracerebellar pretreatment with hexamethonium, a nicotinic receptor (nAChR) antagonist, significantly blocked nicotine-induced attenuation of ethanol ataxia suggesting participation of nAChRs. When ethanol was injected before nicotine microinfusion, nicotine failed to attenuate ethanol ataxia, indicating the critical importance of initial activation of nAChRs by nicotine. Intracerebellar microinfusion of NMDA (30, 60, 125 ng) and its antagonist, (+)-MK-801 (50, 100, 200 ng), significantly increased and decreased, respectively, the nicotine-induced attenuation of ethanol ataxia in a dose-related manner, suggesting participation of the NMDA receptor. Similarly, intracerebellar microinfusion of AMPA (7.5, 15, 30 ng) and its antagonist, nitro -2, 3-dioxobenzoquinoxaline-sulfonamide (NBQX; 25, 50, 100 ng), significantly increased and decreased, respectively, the nicotine-induced attenuation of ethanol ataxia in a dose-dependent manner. This suggests participation of the AMPA receptor and further supports involvement of the glutamate system in the ethanol-nicotine interaction. Intracerebellar nicotine failed to attenuate sodium-pentobarbital (25 mg/kg i.p.) ataxia, suggesting the relative specificity of the nicotine-ethanol interaction.

CONCLUSIONS

The results suggested that glutamate modulates the functional interaction between nicotine and ethanol because NMDA and AMPA enhanced the nicotine-induced attenuation of ethanol ataxia, whereas (+)-MK-801 and NBQX reduced the attenuation.

Mouse cerebellar nicotinic–cholinergic receptor modulation of Δ9-THC ataxia: Role of the α4β2 subtype

In spite of widespread association of nicotine and cannabinoids in humans, very few studies in which nicotine and cannabinoids are co-administered have been reported. Previously, we have reported that intracerebellar (ICB) Delta(9)-tetrahydrocannabinol (Delta(9)-THC) produces dose-dependent cerebellar ataxia. The present study investigated the functional consequences of ICB microinfusion of nicotine on ICB Delta(9)-THC ataxia in CD-1 male mice. Nicotine (0.625, 1.25, 2.5, 5 ng; ICB) markedly attenuated Delta(9)-THC ataxia dose dependently, which was abolished by ICB hexamethonium (5 microg), thus suggesting that the attenuation by nicotine occurred via the nicotinic acetylcholine receptor (nAChR). To further investigate which specific nAChR subtype was involved, ICB microinfusion of RJR-2403 (250, 375, 500, 750 ng), a alpha(4)beta(2) selective nAChR agonist, markedly attenuated Delta(9)-THC ataxia. DHbetaE (500 ng), a alpha(4)beta(2) selective nAChR antagonist, virtually abolished RJR-2403-induced attenuation of Delta(9)-THC ataxia. ICB microinfusion of MLA, a alpha(7) selective nAChR antagonist (1, 5 microg) failed to antagonize nicotine or RJR-2403-induced attenuation of Delta(9)-THC ataxia. This suggested a lack of a role of the alpha(7) subtype and further reinforced the significance of alpha(4)beta(2). Additionally, ICB treatment with DHbetaE virtually abolished nicotine-induced attenuation of Delta(9)-THC ataxia that suggested alpha(4)beta(2) as the primary cerebellar nAChR subtype. Lack of effect of ICB DHbetaE or MLA alone on Delta(9)-THC ataxia ruled out a tonic effect of the alpha(4)beta(2) subtype. The results of the present investigation, therefore, strongly support involvement of the cerebellar alpha(4)beta(2), but not alpha(7), nicotinic receptor subtype in the mediation via nicotine and RJR-2403 on attenuation of Delta(9)-THC ataxia.

Cannabinoids modulate the P-type high-voltage-activated calcium currents in purkinje neurons

Endocannabinoids released by postsynaptic cells inhibit neurotransmitter release in many central synapses by activating presynaptic cannabinoid CB1 receptors. In particular, in the cerebellum, endocannabinoids inhibit synaptic transmission at granule cell to Purkinje cell synapses by modulating presynaptic calcium influx via N-, P/Q-, and R-type calcium channels. Using whole cell patch-clamp techniques, we show that in addition to this presynaptic action, both synthetic and endogenous cannabinoids inhibit P-type calcium currents in isolated rat Purkinje neurons independent of CB1 receptor activation. The IC50 for the anandamide (AEA)-induced inhibition of P-current peak amplitude was 1.04 +/- 0.04 microM. In addition, we demonstrate that all the tested cannabinoids in a physiologically relevant range of concentrations strongly accelerate inactivation of P currents. The effects of AEA cannot be attributed to the metabolism of AEA because a nonhydrolyzing analogue of AEA, methanandamide inhibited P-type currents with a similar efficacy. All effects of cannabinoids on P-type Ca2+ currents were insensitive to antagonists of CB1 cannabinoid or vanilloid TRPV1 receptors. In cerebellar slices, WIN 55,212-2 significantly affected spontaneous firing of Purkinje neurons in the presence of CB1 receptor antagonist, in a manner similar to that of a specific P-type channel antagonist, indicating a possible functional implication of the direct effects of cannabinoids on P current. Taken together these findings demonstrate a functionally important direct action of cannabinoids on P-type calcium currents.

Possible role of mouse cerebellar nitric oxide in the behavioral interaction between chronic intracerebellar nicotine and acute ethanol administration: Observation of cross-tolerance

Many studies have reported cross-tolerance between nicotine and ethanol. Previously we demonstrated that intracerebellar nicotine attenuates ethanol-induced motor impairment. In this study, intracerebellar nicotine (0.625, 2.5, 5 ng; once daily for five days) significantly attenuated ethanol-induced motor impairment in a dose-dependent fashion suggesting the development of cross-tolerance between nicotine and ethanol in male CD-1 mice. Using the same paradigm, intracerebellar nicotine (5 ng) microinfused for 1, 2, 3, 5, 7 days significantly attenuated ethanol-induced motor impairment in all groups except the 1-day treatment group. Cross-tolerance, which developed optimally in 5-day nicotine treatment group, was reversible and detectable up to 40 h post-nicotine microinfusion. Intracerebellar microinfusion of hexamethonium (1 mug once daily for 5 days): (i) did not alter ethanol-induced motor impairment indicating no tonic nicotine receptor involvement; (ii) 10 min prior to daily intracerebellar nicotine treatment virtually abolished the cross-tolerance between nicotine and ethanol indicating nicotinic acetylcholine receptor participation; (iii) when microinfused 10 min after daily intracerebellar nicotine treatment, failed to abolish the cross-tolerance which suggested possible participation of downstream second messenger mechanisms. Chronic intracerebellar microinfusion of nicotine: (i) failed to attenuate acute pentobarbital (25mg/kg i.p.)-induced motor impairment; and (ii) produced no change in normal motor coordination when followed by saline injection. Finally, the cerebellar concentration of total nitric oxide products (nitrite+nitrate; NO(x)); (i) was increased after 5-day intracerebellar nicotine; (ii) was decreased by acute ethanol administration; and (iii) decreased due to acute ethanol administration which was opposed by chronic intracerebellar nicotine treatment. These results support a functional correlation between the cerebellar nitric oxide production and ethanol-induced motor impairment and suggest possible participation of nitric oxide as a factor in the observed cross-tolerance between nicotine and ethanol.

Antagonism of ethanol ataxia by intracerebellar nicotine: possible modulation by mouse cerebellar nitric oxide and cGMP

We have reported previously that intracerebellar nicotine attenuates ethanol ataxia via nicotinic-cholinergic receptors. We report now that attenuation of ethanol ataxia by intracerebellar nicotine is modulated by cerebellar nitric oxide-guanylyl cyclase (GC) messenger system. Intracerebellar microinfusion of SNP (sodium nitroprusside, a nitric oxide donor; 15, 30, and 60 pg) and SMT (S-methylisothiourea; 70, 140, and 280 fg; an inhibitor of inducible nitric oxide synthase), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related manner. Similarly, intracerebellar isoliquiritigenin (an activator of GC; 1, 2, and 4 pg) and ODQ (1H [1,2,4]oxadiazolo-[4,3-a]quinoxalin-1-one, an inhibitor of GC; 375, 750, and 1500 fg), significantly enhanced and reduced, respectively, intracerebellar nicotine-induced attenuation of ethanol ataxia in a dose-related fashion. These results suggest that the functional interaction between nicotine and ethanol may involve modulation by cerebellar nitric oxide and cGMP. Intracerebellar microinfusion of isoliquiritigenin (4, 8, and 16 pg) in the absence of nicotine significantly attenuated ethanol ataxia dose-dependently indicating a tonic involvement of cGMP in ethanol ataxia. Finally, intracerebellar nicotine (5 ng) significantly increased and ethanol 2 g/kg i.p. decreased levels of total cerebellar nitrite+nitrate (NOx) which were functionally correlated with ethanol ataxia and its attenuation by intracerebellar nicotine. The ethanol-induced decrease in NOx was significantly antagonized by intracerebellar nicotine. The NOx data further supported an involvement of nitric oxide in the behavioral interaction between nicotine and ethanol. Overall, the results of the present investigation demonstrate a functional correlation between cerebellar nitric oxide messenger system and the behavioral interaction between nicotine and ethanol.

Long-term administration of Delta9-tetrahydrocannabinol desensitizes CB1-, adenosine A1-, and GABAB-mediated inhibition of adenylyl cyclase in mouse cerebellum

Cannabinoid CB(1) receptors in the cerebellum mediate the inhibitory effects of Delta(9)-tetrahydrocannabinol (THC) on motor coordination. Intracellular effects of CB(1) receptors include inhibition of adenylyl cyclase via activation of G(i/o) proteins. There is evidence for the convergence of other neuronal receptors, such as adenosine A(1) and GABA(B), with the cannabinoid system on this signaling pathway to influence motor function. Previous studies have shown that brain CB(1) receptors are desensitized and down-regulated by long-term THC treatment, but few studies have examined the effects of long-term THC treatment on downstream effector activity in brain. Therefore, these studies examined the relationship between CB(1), adenosine A(1), and GABA(B) receptors in cerebella of mice undergoing prolonged treatment with vehicle or THC at the level of G protein activation and adenylyl cyclase inhibition. In control cerebella, CB(1) receptors produced less than additive inhibition of adenylyl cyclase with GABA(B) and A(1) receptors, indicating that these receptors are localized on overlapping populations of cells. Long-term THC treatment produced CB(1) receptor down-regulation and desensitization of both cannabinoid agonist-stimulated G protein activation and inhibition of forskolin-stimulated adenylyl cyclase. However, G protein activation by GABA(B) or A(1) receptors was unaffected. It is noteworthy that heterologous attenuation of GABA(B) and A(1) receptor-mediated inhibition of adenylyl cyclase was observed, even though absolute levels of basal and forskolin- or G(s)-stimulated activity were unchanged. These results indicate that long-term THC administration produces a disruption of inhibitory receptor control of cerebellar adenylyl cyclase and suggest a potential mechanism of cross-tolerance to the motor incoordinating effects of cannabinoid, GABA(B), and A(1) agonists.

Analysis of the effects of cannabinoids on synaptic transmission between basket and Purkinje cells in the cerebellar cortex of the rat

The hypothesis of the present work was that activation of CB1 cannabinoid receptors inhibits GABAergic neurotransmission between basket and Purkinje cells in the cerebellar cortex. The aim was to test this hypothesis under near-physiological conditions. Action potentials of basket cells and spontaneous inhibitory postsynaptic currents (sIPSCs) in synaptically coupled Purkinje cells were recorded simultaneously in rat brain slices. The cannabinoid agonists (R)-(+)-[2,3-dihydro-5-methyl-3-[(morpholinyl) methyl] pyrrolo[1,2,3-de]-1,4-benzoxazinyl]-(1-naphthalenyl)methanone mesylate (WIN 55212-2) and (-)-cis-3-[2-hydroxy-4-(1,1-dimethylheptyl)-phenyl]-trans-4-(3-hydroxy-propyl)-cyclohexanol (CP55940) decreased the amplitude of sIPSCs occurring simultaneously with basket cell action potentials and lowered the success rate of synaptic transmission. These effects were prevented by the CB1 receptor antagonist N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichloro-phenyl)-4-methyl-3-pyrazole-carboxamide (SR141716). Depolarization of Purkinje cells also led to suppression of neurotransmission; prevention of this suppression by CP55940 and SR141716 indicates that endocannabinoids released from Purkinje cells were involved. WIN 55212-2 lowered the amplitude of autoreceptor currents recorded in basket cells (autoreceptor currents are due to the action of GABA released from axon terminals on GABAA autoreceptors of the same axon terminals); this is novel proof of the presynaptic action of cannabinoids. Autoreceptor current experiments also indicated that endogenous cannabinoids are not released by basket cell axon terminals. A presynaptic action is additionally supported by the observation that WIN 55212-2 lowered the frequency of miniature IPSCs recorded in the presence of tetrodotoxin and the calcium ionophore ionomycin. In conclusion, activation of CB1 receptors by exogenous cannabinoids and by endogenous cannabinoids released by Purkinje cells presynaptically inhibits GABAergic neurotransmission between basket and Purkinje cells. This was demonstrated under near-physiological conditions: transmitter release was elicited by action potentials generated by spontaneously firing intact presynaptic neurons.

Ten years of antisense inhibition of brain G-protein-coupled receptor function

Antisense oligonucleotides (AOs) are widely used as tools for inhibiting gene expression in the mammalian central nervous system. Successful gene suppression has been reported for different targets such as neurotransmitter receptors, neuropeptides, ion channels, trophic factors, cytokines, transporters, and others. This illustrates their potential for studying the expression and function of a wide range of proteins. AOs may even find therapeutic applications and provide an attractive strategy for intervention in diseases of the central nervous system (CNS). However, a lack of effectiveness and/or specificity could be a major drawback for research or clinical applications. Here we provide a critical overview of the literature from the past decade on AOs for the study of G-protein-coupled receptors (GPCRs). The following aspects will be considered: mechanisms by which AOs exert their effects, types of animal model system used, detection of antisense action, effects of AO design and delivery characteristics, non-antisense effects and toxicological properties, controls used in antisense studies to assess specificity, and our results (failures and successes). Although the start codon of the mRNA is the most popular region (46%) to target by AOs, targeting the coding region of GPCRs is almost as common (41%). Moreover, AOs directed to the coding region of the GPCR mRNA induce the highest reductions in receptor levels. To resist degradation by nucleases, the modified phosphorothioate AO (S-AO) is the most widely used and effective oligonucleotide. However, the end-capped phosphorothioate AOs (ECS-AOs) are increasingly used due to possible toxic and non-specific effects of the S-AO. Other parameters affecting the activity of a GPCR-targeting AO are the length (mostly an 18-, 20- or 21-mer) and the GC-content (mostly varying from 30 to 80%). Interestingly, one-third of the AOs successfully targeting GPCRs possess a GC/AT ratio of 61-70%. AO-induced reductions in GPCR expression levels and function range typically from 21 to 40% and 41 to 50%, respectively. In contrast to many antisense reviews, we therefore conclude that the functional activity of a GPCR after AO treatment correlates mostly with the density of the target receptors (maximum factor 2). However, AOs are no simple tools for experimental use in vivo. Despite successful results in GPCR research, no general guidelines exist for designing a GPCR-targeting AO or, in general, for setting up a GPCR antisense experiment. It seems that the correct choice of a GPCR targeting AO can only be ascertained empirically. This disadvantage of antisense approaches results mostly from incomplete knowledge about the internalisation and mechanism of action of AOs. Together with non-specific effects of AOs and the difficulties of assessing target specificity, this makes the use of AOs a complex approach from which conclusions must be drawn with caution. Further antisense research has to be carried out to ensure the adequate use of AOs for studying GPCR function and to develop antisense as a valuable therapeutic modality.

Acute ethanol/cannabinoid-induced ataxia and its antagonism by oral/systemic/intracerebellar A1 adenosine receptor antisense in mice

Previous reports from our laboratory have demonstrated that ethanol- and cannabinoid-induced ataxia is modulated by cerebellar adenosine A(1) receptor because intracerebellar (i.c.b.) adenosine A(1) agonists potentiated and A(1) antagonist attenuated ataxia by these psychoactive drugs. In this study, the novel approach involving pretreatment with adenosine A(1) antisense oligodeoxynucleotide via multiple routes provided further direct evidence of mouse cerebellar A(1) modulation of ethanol- and cannabinoid-induced ataxia. Animal groups were pretreated with A(1) antisense and its mismatch by oral (p.o.) (3.12, 6.25, 12.5, 50 microg/12 h; total three treatments/each dose), intraperitoneal (i.p.) (3.12, 5, 10, 50 microg/12 h; total three treatments/each dose), and i.c.b. (2 microg/12 h; total three treatments) routes. Based on our standard rotorod test, marked antagonism to ethanol (2 g/kg; i.p.) and delta(9)-THC (15 microg; i.c.b)-induced ataxia was observed 12 h after the last antisense treatment. Pretreatment with A(1) receptor mismatch was without an effect. The antagonism following systemic (p.o.; i.p.) antisense pretreatment was dose-dependent. No change in the normal motor coordination was observed when the animals were pretreated with antisense or its mismatch followed by vehicle. Results of Western blotting using commercially available antibodies and cerebellar membranes from various animal groups which received antisense and its mismatch via three routes confirmed a significant decrease in the A(1) adenosine receptor protein. These results, for the first time, demonstrated an oral and systemic effectiveness of A(1) antisense towards adenosine receptors in the central nervous system.

Modulation of the release of endogenous adenosine by cannabinoids in the myenteric plexus-longitudinal muscle preparation of the guinea-pig ileum

1. Interactions between the cannabinoid system and the adenosine system were investigated in the myenteric plexus-longitudinal muscle (MPLM) of the guinea-pig ileum. 2. Electrically-evoked contractions of the MPLM were inhibited in a concentration dependent manner by exogenous adenosine and the adenosine receptor agonist 2-chloroadenosine. These inhibitory effects were reversed by the selective A(1) receptor antagonist DPCPX (20 nM). 3. Preincubation of the MPLM with the cannabinoid receptor agonist CP55,940 (1 nM) or the endogenous cannabinoid ligand anandamide caused a significant leftward shift in the concentration-effect curves to adenosine and 2-chloroadenosine. 4. Electrically-evoked contractions of the MPLM were inhibited in a concentration dependent manner by the adenosine uptake inhibitor dipyridamole. This inhibition was reversed by DPCPX (20 nM). 5. Pretreatment with CP55,940 (1 nM) or anandamide (10 microM) significantly reduced the inhibition produced by dipyridamole, an effect which was completely reversed by the selective CB(1) receptor ligand SR141716 (100 nM). 6. Electrically evoked adenosine release, measured in real time by means of adenosine-specific biosensors, was inhibited by CP55,940 (10 nM). This inhibition was blocked when CP55,940 was applied in the presence of SR141716 (100 nM). 7. These results confirm the presence of presynaptic CB(1) and A(1) receptors in the guinea-pig MPLM, and suggest that CB(1) receptor stimulation reduces electrically-evoked adenosine release. Overall the data raise the possibility that the cannabinoid system plays a role in the modulation of adenosine transmission in the MPLM.

Involvement of the cerebellar adenosine A(1) receptor in cannabinoid-induced motor incoordination in the acute and tolerant state in mice

Cannabinoids are known to impair motor function in humans and laboratory animals. We have demonstrated an accentuation of cannabinoid (CP55,940)-induced motor incoordination in mice by the adenosine A(1) receptor-selective agonist N(6)-cyclohexyladenosine (CHA) (4 ng) using an intracerebellar (ICB) microinjection method. This effect was mediated by the A(1) receptor because pre-treatment with ICB 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) (100 ng), an adenosine A(1) receptor selective antagonist, completely abolished the accentuation. Furthermore, ICB pre-treatment with DPCPX (100 ng) before ICB CP55,940 (15 microg) attenuated the motor incoordination suggesting a modulation by an endogenous adenosine A(1) system. ICB microinjection of CHA or DPCPX prior to ICB vehicle had no effect on normal motor coordination. ICB microinjection of dipyridamole (25 microg), an adenosine transport inhibitor, significantly accentuated the motor incoordination by ICB CP55,940 (15 microg), providing further support for the involvement of endogenous adenosine in the action of CP55,940. Tolerance to the motor incoordinating effect of ICB CP55,940 was demonstrated following 3 days of i.p. CP55,940 (0.1, 1 or 2 mg/kg every 12 or 24 h; total of six or three injections, respectively). Interestingly, animals which exhibited tolerance to ICB CP55,940 also demonstrated tolerance to the accentuating effect of ICB CHA suggesting cross-tolerance between adenosine agonists and cannabinoids. Cross-tolerance was also demonstrated following 3 days of i.p. CHA (0.25 or 1 mg/kg every 24 h; total of three injections) as further evidence of the modulatory role of the cerebellar adenosine system in the acute manifestation of CP55,940-induced motor incoordination. The involvement of cerebellar adenosine and the A(1) receptor in cannabinoid actions is circumstantially supported by previous evidence that CB(1) receptors and A(1) receptors are both localized on cerebellar granule cell parallel fiber terminals and basket cell neurons where they serve to inhibit the release of neurotransmitters.

Cannabinoid-induced motor incoordination through the cerebellar CB(1) receptor in mice

Cannabinoids are known to impair motor function in humans and laboratory animals. We have observed dose-dependent motor incoordination in mice evaluated by rotorod following direct intracerebellar (i.c.b.) microinjection of synthetic cannabinoid agonists CP55,940 (5-25 microg) and HU-210 (1.56-6.25 microg), through permanently implanted stainless steel guide cannulas. The motor incoordination was marked at 15, 35 and 55 min post-microinjection. The motor incoordination elicited by HU-210 (6.25 microg) and CP55,940 (20 microg) was significantly blocked by the CB(1) receptor-selective antagonist SR141716A (25 microg i.c.b.), indicating mediation by a cerebellar CB(1) receptor. Further direct evidence of CB(1) mediation was obtained through a CB(1) receptor antisense/mismatch oligodeoxynucleotide approach (3 microg/12 h; total of six doses). Mice treated with intracerebellar antisense had a significantly diminished motor incoordination response to intracerebellar CP55,940 15 microg compared to mice that received intracerebellar mismatch or no prior treatment. Also, the response to intracerebellar CP55,940 in the CB(1) mismatch-treated mice did not differ from the mice that received only CP55,940. A separate study using a cerebellar tissue punching technique, following intracerebellar [3H]-CP55,940 microinjection, confirmed that cannabinoid drug dispersion following microinjections was exclusively confined to the cerebellum. Microinjection of CP55,940 (20 microg) into the hippocampus, an area with a large density of CB(1) receptors, did not impair motor coordination. Taken together, these results indicate that cannabinoid-induced motor impairment occurs by activation of a CB(1) receptor in the cerebellum. The participation of other brain motor areas in cannabinoid-induced motor incoordination will require future study.

Effects of SR141716A on ethanol and sucrose self-administration

BACKGROUND

Previous studies have demonstrated that administration of central cannabinoid receptor (CB1) ligands can produce marked effects on ingestive behaviors. However, the possible relationship to ethanol self-administration has not been fully examined. The present series of experiments was designed to characterize further the role of CB1 receptors in appetitive and consummatory behaviors related to sucrose and ethanol.

METHODS

To determine the relative contribution of CB1 receptors to ethanol seeking and consumption, a series of experiments was designed using the sipper-tube model. In this paradigm, the appetitive and consummatory phases of ethanol and sucrose self-administration are separated. In the appetitive phase, animals are required to complete a response requirement (16 lever presses) within 20 min. If the requirement is successfully completed, access to a sipper tube containing either sucrose or ethanol (consummatory phase) is made available for 20 min.

RESULTS

In the ethanol condition, the CB1 receptor antagonist SR141716A (0.3-3.0 mg/kg, ip) produced dose-related decreases in the probability of response requirement completion without significantly affecting latency to first lever press or overall lever press rate. In the sucrose condition, SR141716A (0.3-3.0 mg/kg, ip) increased first lever press latency without affecting lever press rate. In the consummatory phase, SR141716A (0.3-3.0 mg/kg, ip) administration markedly decreased total intake and the total number of licks for both ethanol and sucrose.

CONCLUSIONS

These data indicate that CB1 receptors are involved in mediating both appetitive and consummatory aspects of ingestive behaviors related to sucrose and ethanol.