Interaction between Δ9-Tetrahydrocannabinol and d-amphetamine

d-Amphetamine increases the motor activity at a dose range of 0.5–4 mg/kg. ⁹-Tetrahydrocannabinol (THC) diminishes this effect dose-dependently. Also, the hyperthermia caused by 5 mg/kg d-amphetamine is antagonized by THC, whereas the d-amphetamine induced sterotype movements (above 4 mg/kg) are prolonged by the cannabinoid.THC and d-amphetamine both reduce the food and water intake and the normal development of body weight of rats. In combination the two substances have an additive effect.Rats treated with 5 mg/kg d-amphetamine show a significant enhancement of the dopamine (DA) concentration (26%) in the brain stem 2 h p.i. Pretreatment with 10 mg/kg THC, which also causes an increase of DA by 15%, raises the DA content by 50%. Norepinephrine (NE) in the brain stem and hypothalamus is reduced by d-amphetamine but THC has no effect on the concentration of this monoamine.After subchronical treatment with THC tolerance is demonstrable to all THC effects tested. But there is no cross tolerance between ⁹-THC and d-amphetamine since the pharmacological as well as the biochemical effects of d-amphetamine occur despite the subchronical treatment with THC.     

Metabolism and autoradiographic distribution of Δ8- and Δ9 tetrahydrocannabinol in some organs of the monkey callithrix jacchus

Summary Metabolism and autoradiographic distribution of the two isomeric tetrahydrocannabinols, (2,4-¹⁴C)-⁸-THC and (2,4-¹⁴C)-⁹-THC), were studied in the marmoset Callithrix jacchus. Of the two cannabinoids, ⁸-THC had a slower initial rate of biotransformation to the psychopharmacologically more potent 11-hydroxylated metabolite. This may explain the minor psychopharmacological activity of the ⁸-isomer. In glandular tissues an accumulation of unchanged ⁹-THC was observed.Autoradiography revealed characteristic label distributions in some organs 30 min after the administration of the drugs. This labelling pattern was found to be changed after a 6-hr incorporation period. The autoradiographic distribution of ⁸- and ⁹-THC appeared to be identical.     

Pharmacological specificity of Δ9-tetrahydrocannabinol discrimination in rats

While many previous studies have shown that a variety of cannabinoids substitute and cross-substitute for ⁹-tetrahydrocannabinol (THC) in drug discrimination procedures, few have systematically examined potential THC-like effects of non-cannabinoid compounds. The purpose of the present study was to delineate further the pharmacological specificity of THC discrimination. Rats were trained to discriminate THC (3.0 mg/kg) from vehicle. Following determination of a dose-effect curve with THC, substitution tests with selected compounds from a variety of pharmacological classes, includingl-phenylisopropyl adenosine, dizocilpine, dextromethorphan, clozapine, buspirone, MDL 72222, muscimol, midazolam and chlordiazepoxide, were performed. Whereas THC produced full dose-dependent substitution, substitution tests with non-cannabinoid drugs resulted in less than chance (50%) levels of responding on the THC-appropriate lever, with the exception of (+)-MDMA (2.5 mg/kg, 50%) and diazepam (3.0 mg/kg, 67%). These results are consistent with those of previous studies and suggest that the discriminative stimulus effects of THC exhibit pharmacological specificity.     

Metabolomics of Δ9-tetrahydrocannabinol: implications in toxicity

Cannabis sativa is the most commonly used recreational drug, Δ⁹-tetrahydrocannabinol (Δ⁹-THC) being the main addictive compound. Biotransformation of cannabinoids is an important field of xenobiochemistry and toxicology and the study of the metabolism can lead to the discovery of new compounds, unknown metabolites with unique structures and new therapeutic effects. The pharmacokinetics of Δ⁹-THC is dependent on multiple factors such as physical/chemical form, route of administration, genetics, and concurrent consumption of alcohol. This review aims to discuss metabolomics of Δ⁹-THC, namely by presenting all known metabolites of Δ⁹-THC described both in vitro and in vivo, and their roles in the Δ⁹-THC-mediated toxic effects. Since medicinal use is increasing, metabolomics of Δ⁹-THC will also be discussed in order to uncover potential active metabolites that can be made available for this purpose.     

Facilitory effect of Δ9-tetrahydrocannabinol on hypothalamically induced feeding

Six male Lewis rats were tested for the effect of ⁹-tetrahydrocannabinol (⁹-THC) on feeding evoked by electrical stimulation of the lateral hypothalamus. Treatment with ⁹-THC (0.4 mg/kg IP) decreased frequency threshold for feeding by 20.5% (±4.3), causing a leftward shift in the function relating stimulation frequency to the latency to begin eating 45-mg food pellets upon stimulation onset; there was no change in the asymptotic performance that was approached with sufficiently high stimulation frequencies. Naloxone (1 and 2 mg/kg) reduced the facilitory effect of ⁹-THC, but did so at doses that can inhibit feeding in the no-drug condition. These data are consistent with evidence implicating endogenous opioids in feeding, and suggest (but do not confirm) that the facilitation of feeding by ⁹-THC may be mediated by endogenous opioids. The facilitation of stimulation-induced feeding by doses of ⁹-THC that have been found to facilitate brain stimulation reward is consistent with evidence suggesting common elements in the brain mechanisms of these two behavioral effects of medial forebrain bundle stimulation.     

Naloxone-induced or postwithdrawal abstinence signs in Δ9-Tetrahydrocannabinol-Tolerant rats

Acute stressing procedures cause a shortlasting increase in the levels of guanosie 3,5-monophosphate (cGMP) in mouse brain without significantly influencing the concentrations of adenosine 3,5-monophosphate (cAMP). Animals were pretreated with various centrally acting drugs before being stressed in order to study the involvement of specific neurotransmitters in the stress-induced rise of cGMP levels. Centrally depressant drugs affecting different synaptic mechanisms, such as chlorpromazine, reserpine, haloperidol, diazepam, and pentobarbital, inhibited the cGMP increase elicited by stress. Pretreatment with atropine, diphenhydramine, antazoline, cyproheptadine, phentolamine, bunitrolol, and indomethacin had no significant effect. Clonidine and both the (-)-and (+)-isomers of propranolol inhibited the stress-induced cGMP increase in a doserelated manner. Our results suggest that norepinephrine, serotonin, acetylcholine, or prostaglandins are not involved in the elevation of cGMP levels elicited by acute stress. Participation of other neurotransmitter(s), such as dopamine or GABA, cannot be excluded.     

Modulation of Δ9-tetrahydrocannabinol-induced hypothermia by fluoxetine in the rat

1. It has been suggested that the dose of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) that induces hypothermia in the rat increases the release of brain 5-hydroxytryptamine (5-HT). In light of this, we investigated the hypothermia produced by Δ⁹-THC, and the effect the selective serotonin reuptake inhibitor fluoxetine has on this response.
2. A significant dose-dependent decrease in body temperature occurred after i.v. administration of 0.5 to 5 mg kg⁻¹ Δ⁹-THC; maximum decreases being 0.8±0.2°C to 2.9±0.3°C. This hypothermic response was attenuated by the cannabinoid CB₁ receptor antagonist SR 141716.
3. Fluoxetine (10 mg kg⁻¹ i.p.) alone caused a decrease in body temperature of 0.6±0.1°C (n=32, P<0.05) after 40 min. However, pretreatment with fluoxetine (10 mg kg⁻¹ i.p.) 40 min before Δ⁹-THC significantly reduced the Δ⁹-THC-induced hypothermia (n=7–8, P<0.05). Contrary to this antagonist-like effect, fluoxetine administered 40 min after Δ⁹-THC significantly potentiated the Δ⁹-THC-induced hypothermia, producing a maximum decrease of 3.2±0.3°C.
4. It is suggested that the effect of fluoxetine on the Δ⁹-THC-induced hypothermic response is dependent on the time of its administration relative to that of Δ⁹-THC. Pretreatment with fluoxetine increases extracellular 5-HT due to reuptake inhibition. Increased extracellular 5-HT can activate autoreceptors which may decrease serotonergic activity, thereby reducing the Δ⁹-THC-induced hypothermia. Conversely, when fluoxetine is adminstered after Δ⁹-THC, the reuptake block is thought to potentiate the already activated serotonegic system, hence potentiating the Δ⁹-THC-induced hypothermia.

     

Influence of Δ9 and cannabidiol on photically evoked after-discharge potentials

Two cannabinoids, ⁹ and cannabidiol, and several reference drugs were compared relative to their effects in a recently developed anticonvulsant test system, the after-discharge potentials of the visually evoked response; the potentials were recorded electrophysiologically from electrodes permanently mounted over the visual cortices of conscious rats. In anticonvulsant doses, trimethadione and ethosuximide produced an extensive depression of after-discharge activity, whereas diphenylhydantoin and cannabidiol exerted no such effect. In contrast, anticonvulsant doses of ⁹ and subconvulsant doses of pentylenetetrazol markedly increased after-discharge activity, which may represent a manifestation of their central nervous system excitatory properties. The data from the present study support our previously published observations from several other anticonvulsant tests that indicate the anticonvulsant characteristics of cannabidiol resemble those of diphenylhydantoin rather than those of trimethadione and that the central excitatory properties of ⁹ distinguish it from cannabidiol. The results consistently suggest that the cannabinoids will be effective against grand mal but not absence seizures.     

Epoxide-diol pathway of Δ1 -THC in the rat in vitro

1. 1α,2α-Epoxyhexahydrocannabinol was identified as a metabolite of Δ₁-tetrahydrocannabinol.

2. The two trans-1,2-dihydroxyhexahydrocannabinol isomers, 1α,2β-dihydroxy-hexahydrocannabinol and 1β,2α-dihydroxyhexahydrocannabinol (as their acetates) were tentatively identified as metabolites from incubation of 1α,2α-epoxyhexahydrocannabinol with rat hepatic microsomes in vitro.

3. The 1α,2α-epoxyhexahydrocannabinol acetate was found to be a good substrate for epoxide hydratase as compared to styrene oxide.

4. The synthesis of metabolites of 1α,2α-epoxyhexahydrocannabinol is described.     

Acute Δ9-tetrahydrocannabinol exposure: Effects of hypothalamic-pituitary-testicular activity in mice

The endocrine functions of the median eminence, pituitary and testes were examined in the male mice after exposure to Δ⁹-tetrahydrocannabinol (THC) either in vivo or in vitro. The secretion of luteinizing hormone-releasing hormone (LHRH) under basal conditions, and in the presence of norepinephrine (NE; 60μM), was significantly enhanced in median eminence fragments obtained 1 hr post-treatment with THC (50 mg/kg), while addition of THC (250 ng/ml) to the incubation media enhanced clonidine, as well as NE-stimulated LHRH release, but did not affect basal LHRH release. In vitro exposure to THC also enhanced LHRH-stimulated LH release by pituitaries, but did not affect basal secretion rates. In vivo THC exposure tended to enhance pituitary responsiveness to LHRH, although this effect was not statistically significant. In testicular perifusions, addition of THC at a concentration of 250 ng/ml completely blocked hCG-stimulated T secretion within 30 min. The suppressive effects of a lower dose of THC, 25 ng/ml, required 60 min to inhibit T production, an affect which persisted for 60–80 min post-THC. These findings indicate that THC exposure enhances responsivity at neuroendocrine target sites, but attenuates gonadotropin-stimulated testicular steroidogenesis.     

Cannabidiol attenuates deficits of visuospatial associative memory induced by Δ9tetrahydrocannabinol

BACKGROUND AND PURPOSE

Recent human studies suggest that recreational cannabis strains that are relatively high in cannabidiol (CBD) content produce less cognitive impairment than do strains with negligible CBD and similar Δ⁹tetrahydrocannabinol (THC) content. Self-selection in such studies means it is impossible to rule out additional variables which may determine both cannabis strain selection and basal cognitive performance level. Controlled laboratory studies can better determine a direct relationship.

EXPERIMENTAL APPROACH

In this study, adult male rhesus monkeys were assessed on visuospatial Paired Associates Learning and Self-Ordered Spatial Search memory tasks, as well as additional tests of motivation and manual dexterity. Subjects were challenged with THC (0.2, 0.5 mg·kg⁻¹, i.m.) in randomized order and evaluated in the presence or absence of 0.5 mg·kg⁻¹ CBD.

KEY RESULTS

CBD attenuated the effects of THC on paired associates learning and a bimanual motor task without affecting the detrimental effects of THC on a Self-Ordered Spatial Search task of working memory. CBD did not significantly reverse THC-induced impairment of a progressive ratio or a rotating turntable task.

CONCLUSIONS AND IMPLICATIONS

This study provides direct evidence that CBD can oppose the cognitive-impairing effects of THC and that it does so in a task-selective manner when administered simultaneously in a 1:1 ratio with THC. The addition of CBD to THC-containing therapeutic products may therefore help to ameliorate unwanted cognitive side-effects.

LINKED ARTICLE

This article is commented on by Mechoulam and Parker, pp 1363–1364 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.12400     

Discriminative effects of combinations of Δ9-Tetrahydrocannabinol and pentobarbital in pigeons

The purpose of the present study is to examine potentially additive effects of pentobarbital and ⁹-Tetrahydrocannabinol ⁹-THC using a drug discrimination paradigm. Three groups of pigeons were trained to discriminate between the effects induced by i.m. administrations of either (a) 0.25 mg/kg ⁹-THC and vehicle, (b) 4 mg/kg pentobarbital and saline, and (c) ⁹-THC and pentobarbital. Test probes under extinction conditions produced orderly dose generalization gradients among the drug-vs nondrug-trained animals. ED₅₀ for pentobarbital was 1.60 mg/kg and ED₅₀ for ⁹-THC was 0.10 mg/kg. Tests in birds discriminating between pentobarbital and ⁹-THC suggested a sharpening of the drug cue effects; tests with the vehicles resulted in approximately a random key selection (33%–66%) while tests with combinations of the two training drugs suggested that ⁹-THC was the more salient cue in this group. Tests with combinations of various doses of pentobarbital and ⁹-THC in the drug-vs nondrug-trained birds did not increase responding on the respective drug-training associated key. Thus the cue effects of pentobarbital and ⁹-THC were not summational under these experimental conditions. In conclusion, rather low doses of pentobarbital and ⁹-THC are effective as discriminative cues in pigeons and the cues thus induced are different. Combinations of the two drugs are not necessarily summational, and the pentobarbital vs the ⁹-THC discriminations augmented the discriminable effects of the two drugs. In addition, the analeptic drug, bemegride, antagonizes the pentobarbital (4 mg/kg) stimulus in the group trained to discriminate between this barbiturate and saline, which agrees with earlier drug antagonism data obtained among mammals (gerbils and rats), required to discriminate between barbiturates and the nondrug condition.     

Detection of Δ9-tetrahydrocannabinol in exhaled breath collected from cannabis users

Exhaled breath has recently been proposed as a new possible matrix for drugs of abuse testing. A key drug is cannabis, and the present study was aimed at investigating the possibility of detecting tetrahydrocannabinol and tetrahydrocannabinol carboxylic acid in exhaled breath after cannabis smoking. Exhaled breath was sampled from 10 regular cannabis users and 8 controls by directing the exhaled breath by suction through an Empore C(18) disk. The disk was extracted with hexane/ethyl acetate, and the resulting extract was evaporated to dryness and redissolved in 100 μL hexane/ethyl acetate. A 3-μL aliquot was injected onto the LC-MS-MS system and analyzed using positive electrospray ionization and selected reaction monitoring. In samples collected 1-12 h after cannabis smoking, tetrahydrocannabinol was detected in all 10 subjects. The rate of excretion was between 9.0 and 77.3 pg/min. Identification of tetrahydrocannabinol was based on correct retention time relative to tetrahydrocannabinol-d(3) and correct product ion ratio. In three samples, peaks were observed for tetrahydrocannabinol carboxylic acid, but these did not fulfill identification criteria. Neither tetrahydrocannabinol or tetrahydrocannabinol carboxylic acid was detected in the controls. These results confirm older reports that tetrahydrocannabinol is present in exhaled breath following cannabis smoking and extend the detection time from minutes to hours. The results further support the idea that exhaled breath is a promising matrix for drugs-of-abuse testing.     

Chronic Δ9-tetrahydrocannabinol administration affects serotonin levels in the rat frontal cortex

Adult rats were subjected to chronic treatment with the cannabinoid agonist, Δ⁹-tetrahydrocannabinol, or with vehicle, and their brains used to analyze the contents of serotonin (5HT) and of its intraneuronal metabolite, 5-hydroxyindolacetic acid (5HIAA). 5HT and 5HIAA contents were not affected by chronic cannabinoid administration in most of the brain regions analyzed. We found a marked increase in 5HT contents in the frontal cortex that was accompanied by no changes in 5HIAA contents. This originated a decrease in 5HIAA/5HT ratio, which suggests a possible reduction in the activity of serotoninergic terminals reaching this cortical area. This effect was not seen after an acute injection of this cannabinoid. The relevance of these observations was that they occurred in a region where changes in serotoninergic transmission have been implicated in the development of depression; therefore, our data support the theory that the cannabinoid system might be a potential target for the treatment of this neuropsychiatric disease.     

A behavioural model to reveal place preference to Δ9-tetrahydrocannabinol in mice

Rationale: The rewarding properties of Δ9- tetrahydrocannabinol (THC) are difficult to demonstrate in rodents using standard procedures. Objective: To evaluate the motivational responses of THC in the place conditioning paradigm in mice after minimizing the dysphoric effects of the first drug exposure and/or the consequences of its pharmacokinetic properties. Methods: Mice were conditioned to THC (1 or 5 mg/kg) using an unbiased procedure with an elevated number of pairings and long conditioning time. Results: A place aversion was observed with 5 mg/kg THC using a standard protocol. Similar results were obtained when the CB-1 receptor antagonist SR 141716A (1 mg/kg) was administered immediately after each THC conditioning period. However, mice receiving a priming THC injection and conditioned 24 h later showed a place preference with 1 mg/kg THC and no effect with 5 mg/kg THC. Conclusion: THC produces a clear place preference in mice by using a long period of conditioning and avoiding the possible dysphoric consequences of the first drug exposure. Received: 12 August 1999 / Final version: 28 September 1999     

Behavioural sensitization after repeated exposure to Δ9-tetrahydrocannabinol and cross-sensitization with morphine

RATIONALE: Repeated exposure to several drugs of abuse has been reported to induce behavioural sensitization. So far no evidence has been provided that such a phenomenon also applies to cannabinoids. OBJECTIVES: In this study we investigated if repeated exposure to Delta(9)-tetrahydrocannabinol (Delta(9)-THC) induces behavioural sensitization. In addition we tested the possibility of cross-sensitization between Delta(9)-THC and morphine. METHODS: Male Sprague-Dawley rats were administered for 3 days, twice daily, with increasing doses of Delta(9)-tetrahydrocannabinol (2, 4 and 8 mg/kg i.p.) or increasing doses of morphine (10, 20 and 40 mg/kg s.c.) or vehicle. After a washout of 14 days the animals were challenged with Delta(9)-THC (75 and 150 microg/kg i.v.), with a synthetic cannabinoid agonist WIN55212-2 (75 and 150 microg/kg i.v.) or with morphine (0.5 mg/kg i.v.), through a catheter inserted into the left femoral vein 24 h before, and the behaviour recorded. RESULTS: Rats previously administered with Delta(9)-THC showed a greater behavioural activation compared to controls in response to challenge with Delta(9)-THC (150 microg/kg i.v.) and to challenge with morphine (0.5 mg/kg i.v.). Similar to that observed after repeated opiates, this behavioural sensitization was characterized by stereotyped activity. Animals administered with a schedule of morphine that induces behavioural sensitization to morphine also showed a behavioural sensitization to challenge with cannabinoids (Delta(9)-HC and WIN55212-2, 75 and 150 microg/kg i.v.). The effect of the challenge with Delta(9)-THC was prevented by the administration of the CB1 antagonist SR141716A (1 mg/kg i.p.), 40 min beforehand. CONCLUSIONS: The results of the present study demonstrate that repeated exposure to Delta(9)-THC induces behavioural sensitization not only to cannabinoids but also to opiates. This cross-sensitization was symmetrical since rats behaviourally sensitized to morphine were also sensitized to cannabinoids. These observations further support the evidence of an interaction between the opioid and the cannabinoid system and might provide a neurobiological basis for a relationship between cannabis use and opiate abuse.     

Effects of Δ9-tetrahydrocannabinol in individuals with a familial vulnerability to alcoholism

Background and aims

A family history (FH) of alcoholism accounts for approximately 50 % of the risk of developing alcohol problems. Several lines of preclinical evidence suggest that brain cannabinoid receptor (CB₁R) function may mediate the effects of alcohol and risk for developing alcoholism including the observations that reduced CB₁R function decreases alcohol-related behaviors and enhanced CB₁R function increases them. In this first human study, we probed CB₁R function in individuals vulnerable to alcoholism with the exogenous cannabinoid Δ⁹-tetrahydrocannabinol (Δ⁹-THC).

Design, setting, and participants

Healthy volunteers (n?=?30) participated in a three test day study during which they received 0.018 and 0.036 mg/kg of Δ⁹-THC, or placebo intravenously in a randomized, counterbalanced order under double-blind conditions.

Measurements

Primary outcome measures were subjective “high,” perceptual alterations, and memory impairment. Secondary outcome measures consisted of stimulatory and depressant subjective effects, attention, spatial memory, executive function, Δ⁹-THC and 11-hydroxy-THC blood levels, and other subjective effects. FH was calculated using the Family Pattern Density method and was used as a continuous variable.

Findings

Greater FH was correlated with greater “high” and perceptual alterations induced by Δ⁹-THC. This enhanced sensitivity with increasing FH was specific to Δ⁹-THC’s rewarding effects and persisted even when FH was calculated using an alternate method.

Conclusions

Enhanced sensitivity to the rewarding effects of Δ⁹-THC in high-FH volunteers suggests that alterations in CB₁R function might contribute to alcohol misuse vulnerability.