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.     

Metabolism of n-hexyl-homologues of delta-8-tetrahydrocannabinol and delta-9-tetrahydrocannabinol in the mouse

n-Hexyl-delta-8-tetrahydrocannabinol (n-hexyl-delta-8-THC) and n-hexyl-delta-9-THC were synthesized by condensation of (1S)-cis-verbenol with 5-n-hexyl-1,3-dihydroxybenzene and administered intraperitoneally to male Charles-River CD-1 mice. Hepatic metabolites were isolated by solvent extraction and chromatography on Sephadex LH-20 and identified by GC/MS. Eleven metabolites were identified from n-hexyl-delta-8-THC and sixteen from n-hexyl-delta-9-THC. The pattern of metabolites was intermediate between that previously observed from the pentyl homologues and that from n-heptyl-delta-9-THC with the major biotransformation pathway being hydroxylation and oxidation at C-11. Other metabolites were mainly hydroxylated derivatives of these compounds. Metabolites containing two hydroxy groups in the side-chain were present in low concentration. These have not been observed from lower homologues but are major metabolites of n-heptyl-delta-9-THC. Compared with the metabolism of the n-pentyl homologue, there was a trend towards the production of more hydroxy metabolites at the expense of carboxylic acids, in keeping with the general reduction of oxidation observed with other homologous cannabinoids as the chain length increases.     

Shock-elicited fighting and delta-9-tetrahydrocannabinol

The frequency with which electric shock to the feet elicited fighting in five pairs of albino rats was not altered significantly by intraperitoneal injections of delta-9-tetrahydrocannabinol (THC) in doses ranging from 0.064–6.4 mg/kg, although chlordiazepoxide reduced the frequency of such fighting in a dose-related manner. This finding held true despite manipulations of THC vehicle, injection-test interval, and the previous drug experience of the subjects. In contrast, doses of 4.0 mg/kg produced a striking reduction in lever-pressing maintained by an FI 60 schedule of food reinforcement.     

Rectal bioavailability of delta-9-tetrahydrocannabinol from various esters.

The bioavailability of delta-9-tetrahydrocannabinol (delta 9-THC) from suppository formulations containing several polar esters was studied. The esters tested were the hemisuccinate, N-formyl alaninate, N-methyl carbamate, and methoxy acetate. These esters were administered to monkeys in both lipophilic and hydrophilic suppository bases, namely, Witepsol H15 and polyethylene glycol, respectively. Each suppository contained a dose equivalent to 10 mg delta 9-THC. Blood samples were analyzed for both delta 9-THC and its carboxylic acid metabolite (ll-nor-delta 9-THC-9-COOH) using gas chromatography/mass spectrometry. The data showed that, with the exception of the hemisuccinate, no delta 9-THC or its metabolite was detected in the blood samples using the Witepsol H15. Using polyethylene glycol, low levels of delta 9-THC and its metabolite were detected in blood for all esters tested. The levels, however, were lower than those observed with delta 9-THC hemisuccinate using Witepsol H15. Subsequent studies in the conscious dog using the hemisuccinate in Witepsol H15 showed 67% bioavailability of delta 9-THC with a linear response in the dose range equivalent to 5-20 mg of delta 9-THC. No significant bioavailability differences were found when delta 9-THC hemisuccinate ester was administered in various lipophilic bases (Hydrokote 25, Kaomel, Suppocire AIML, and Witepsol H15).     

Penetration of delta-9-tetrahydrocannabinol and 11-OH-delta-9-tetrahydrocannabinol through the Blood-brain Barrier

Abstract The relative brain uptake (extraction into brain) of delta-9-tetrahydro-cannabinol (delta-9-THC) and the primary metabolite 11-OH-delta-9-tetrahydrocannabinol (11-OH-delta-9-THC) was measured after close intracarotid injection in rats of radiolabelled moities using labelled antipyrine as reference. The extraction percentage was of the same magnitude when injections were given in saline, 66 ± 11 % and 70 ± 9 % respectively after 5 sec., 59 ± 4 and 67 ± 8 respectively after 15 sec. While the extraction of 11-OH-delta-9-THC was the same when injected into plasma, the extraction of delta-9-THC was only about half of the extraction from saline, and also half the extraction of the metabolite from plasma. The higher uptake quantity of the metabolite into the brain may account for the relatively greater effect on the central nervous system of the metabolite than of the parent compound at equal concentrations in plasma. Moreover our experiments demonstrate that 11-OH-delta-9-THC formed in the liver after cannabis (delta-9-THC) administration may exert significant brain effects.     

Anticonvulsant activity of delta-8- and delta-9-tetrahydrocannabinol in rats

Intraperitoneal injections of Δ⁸-tetrahydrocannabinol (THC) and Δ⁹-THC, two major psychoactive constituents of cannabis, produced dose-related protection against tonic extension induced by electroshock in rats. The cannabinoids provided protection against clonic convulsions induced by pentylenetetrazol (Metrazol) only at very high and sometimes lethal doses, and the protection was quantal rather than dose-related. The two isomers of the THC were equipotent in terms of behavioral toxicity and protection against tonic convulsions. However, the significance of the drugs' anticonvulsant activity must be qualified by the observatin that protection was provided by either drug only at doses producing marked toxic behavioral reactions.     

Cardiopulmonary toxicity of delta-9-tetrahydrocannabinol in the anesthetized dog.

Eighteen anesthetized dogs were treated with 0.5 mg/kg Δ⁹-tetrahydrocannabinol (THC) or control vehicle by iv injection, and cardio-pulmonary responses were determined in intact and vagotomized animals. Blood specimens were examined periodically for pO₂, pCO₂, pH, and lactate and pyruvate concentrations. In addition, cardiac output, heart rate, and lung compliance (C_L) and resistance (R_L) were measured. Δ⁹-Tetrahydrocannabinol markedly increased R_L in intact dogs but not in vagotomized dogs, while C_L remained essentially unchanged in both intact and vagotomized animals. The administration of THC had no effect on arterial blood gases in intact or vagotomized dogs as compared to controls. However, intact animals, unlike those vagotomized, exhibited a significant decrease in blood pH. Bradycardia developed in intact animals (28% decrease in heart rate), which could not be completely prevented by vagotomy (17% decrease in heart rate). Cardiac output also decreased in intact and, to a lesser extent, in vagotomized animals. Diminished cardiac output was associated with metabolic acidosis characterized by an increase in blood lactate and in the lactate-pyruvate ratio. The administration of THC in dogs resulted in an increase in R_L, which appears to be vagally mediated and is not accompanied by a decrease in C_L or blood gas changes.     

Oral delta-9-tetrahydrocannabinol suppresses cannabis withdrawal symptoms

BACKGROUND: This study assessed whether oral administration of delta-9-tetrahydrocannbinol (THC) effectively suppressed cannabis withdrawal in an outpatient environment. The primary aims were to establish the pharmacological specificity of the withdrawal syndrome and to obtain information relevant to determining the potential use of THC to assist in the treatment of cannabis dependence. METHOD: Eight adult, daily cannabis users who were not seeking treatment participated in a 40-day, within-subject ABACAD study. Participants administered daily doses of placebo, 30 mg (10 mg/tid), or 90 mg (30 mg/tid) oral THC during three, 5-day periods of abstinence from cannabis use separated by 7-9 periods of smoking cannabis as usual. RESULTS: Comparison of withdrawal symptoms across conditions indicated that (1) the lower dose of THC reduced withdrawal discomfort, and (2) the higher dose produced additional suppression in withdrawal symptoms such that symptom ratings did not differ from the smoking-as-usual conditions. Minimal adverse effects were associated with either active dose of THC. CONCLUSIONS: This demonstration of dose-responsivity replicates and extends prior findings of the pharmacological specificity of the cannabis withdrawal syndrome. The efficacy of these doses for suppressing cannabis withdrawal suggests oral THC might be used as an intervention to aid cannabis cessation attempts.     

Tissue glutathione levels in mice treated with delta-9-tetrahydrocannabinol.

Glutathione (GSH) is widely distributed among living cells and is involved in many biological functions. It provides the sulfhydryl groups for conjugation of toxic metabolites of several xenobiotica. Acetaminophen (Tylenol) toxicity is a classical example of this property. For this purpose, we studied the effects of delta-9-tetrahydrocannabinol (THC) on tissue levels of GSH in the mice. Groups of male Swiss Webster mice weighing 25 +/- 5 g were treated with 50 mg/kg, PO THC at 1300 h. Control mice were given equal volume of sesame oil (5 ml/kg, PO) which was the vehicle for THC. Ninety minutes following THC administration, mice were sacrificed, their plasma, brain, heart, liver, kidney and testis were collected. All tissues were homogenized in 5% TCA/EDTA solution and supernatant solutions of these homogenates were diluted. In these diluted samples, levels of GSH were determined by a modified spectrophotometric procedure and the GSH levels were expressed as micromoles of GSH/g tissue. In this study, THC caused no effects on GSH levels in brain, heart, testis and plasma. However, GSH levels in liver and kidney were decreased by 14% and 7% respectively. Although the decrease in kidney GSH levels were insignificant, these changes in liver and kidney could be indicative of a possible metabolic and/or dispositional interaction between THC and different commonly available drugs such as acetaminophen.     

The identification, isolation, and preservation of delta-9-tetrahydrocannabinol (delta-9-THC)

(—)-trans-Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) was isolated from marihuana plant extract, by adsorptive column and glc. The adsorptive column chromatography method consisted of chromatographing marihuana extract on a column packed with a mixture of silica gel (gas chromatography grade (100/120 mesh), silver nitrate and calcium sulphate (CaSO₄·H₂O) (3:1:0·5) with benzene as the eluting solvent. The glc method consisted of chromatographing the extract on a 3 ft silanized glass column (3/8 inch o.d.) packed with 1·5 ft of 2% QF-1 and 1·5 ft of 2% OV-17 on chromosorb W, AW 30–60 mesh, prep grade. A purity of 99% for the isolated Δ⁹-THC was confirmed by infrared spectroscopy, nuclear magnetic resonance, mass spectroscopy. The effects of storage conditions on Δ⁹-THC stability, monitored by glc, indicated the best method for preserving Δ⁹-THC was at 0°, protected from light, stored under nitrogen.     

Ethanol and delta-9-tetrahydrocannabinol: Mechanism for cross-tolerance in mice

The pharmacological interaction between equipotent doses of ethanol (1.35 g/kg) and delta-9-tetrahydrocannabinol (THC, 17 mg/kg) was evaluated in mice using rotarod performance as a measure of drug action. Tolerance to the effects of ethanol and THC as well as a symmetrical cross-tolerance between these two drugs was demonstrated. Ethanol elimination was not altered by previous treatment with either ethanol or THC as determined by measuring blood ethanol concentrations with an enzymatic assay. THC metabolite ratios in blood, brain and liver tissues determined after a dose of ³H-THC demonstrated that THC treatment had no effect upon THC metabolism or disposition. Ethanol treatment altered the distribution of THC and also altered hepatic THC metabolism as evidenced by the occurrence of increased proportions of polar THC metabolites. No treatment regimens produced lower whole brain levels of subsequent ethanol or THC suggesting that tolerance to ethanol or THC and cross-tolerance between these two drugs does not develop due to lower brain concentrations. A vehicle effect was shown when treatment with a mixture of propylene glycol and Tween-80 altered the metabolic and behavioral effects of subsequently administered THC.     

Chronic delta-9-tetrahydrocannabinol. Transient and lasting effects on avoidance behavior.

Delta-9-Tetrahydrocannabinol (THC) was administered to albino rats with extensive experience in free-operant (Sidman) lever-press shock avoidance. Dosing (30 mg/kg intragastrically) continued once daily, 3 hr before testing, for 1 to 6 weeks. Significant changes were noted in the response rates of several animals, but both the magnitude and direction of these were highly variable. However, shock rates were reliably elevated by THC, but complete tolerance was observed within 6 sessions. In several rats this was followed by sessions with significantly lower shock rates than the predrug baseline. These rats continued to perform at this level of proficiency until THC was discontinued, at which point the baseline was reacquired. These data emphasize that an important determinant of tolerance to a drug effect is the consequence of the effect for the organism.     

Effects of delta-9-tetrahydrocannabinol on evaluation of emotional images

There is growing evidence that drugs of abuse alter processing of emotional information in ways that could be attractive to users. Our recent report that Δ(9)-tetrahydrocannabinol (THC) diminishes amygdalar activation in response to threat-related faces suggests that THC may modify evaluation of emotionally-salient, particularly negative or threatening, stimuli. In this study, we examined the effects of acute THC on evaluation of emotional images. Healthy volunteers received two doses of THC (7.5 and 15 mg; p.o.) and placebo across separate sessions before performing tasks assessing facial emotion recognition and emotional responses to pictures of emotional scenes. THC significantly impaired recognition of facial fear and anger, but it only marginally impaired recognition of sadness and happiness. The drug did not consistently affect ratings of emotional scenes. THC's effects on emotional evaluation were not clearly related to its mood-altering effects. These results support our previous work, and show that THC reduces perception of facial threat. Nevertheless, THC does not appear to positively bias evaluation of emotional stimuli in general.     

The effect of delta-9-tetrahydrocannabinol and 11-hydroxy-delta-9-tetrahydrocannabinol on T-lymphocyte and B-lymphocyte mitogen responses

Previous studies have shown that delta-9-tetrahydrocannabinol (THC) suppresses T-lymphocyte proliferation when added to human cell cultures. We report that THC when added to mouse splenocyte cultures suppressed T-lymphocyte (Con A, PHA) and B-lymphocyte (LPS) mitogen-induced proliferation. Although the ED50 concentrations (5 micrograms/ml; 1.6 X 10(-5)M) of THC were similar for suppressing all three mitogen responses, higher threshold concentrations of drug were required to effect suppression of the T-lymphocyte mitogen responses. Complete suppression of T- and B-lymphocyte responses was achieved with THC concentrations (8 micrograms/ml or 2.6 X 10(-5)M) which were not directly toxic as judged by vital dye exclusion. The hydroxylated metabolite of THC, 11-hydroxy-THC, was observed to be much less potent in the inhibition of lymphocyte proliferation. However, as with the parent compound, B-lymphocyte responses appeared to be the most affected by the drug. Additional studies demonstrated that both T- and B-lymphocyte proliferation is rapidly suppressed following THC treatment, not affected by a 24 hr. pretreatment with THC, and not as readily suppressed by THC in cultures containing 20% serum. Thus, THC appears to inhibit both T- and B-lymphocyte proliferation with B-lymphocyte responses displaying greater inhibition at lower drug concentration. The 11-hydroxy metabolite is much less suppressive in this system than the parent compound.     

Tau protein after delta-9-tetrahydrocannabinol in a human neuroblastoma cell line

• 1.1. A human neuroblastoma cell line, SH-SY5Y, was used to determine the effects of delta-9-tetrahydrocannabinol (THC) on microtubule-associated tau protein.
• 2.2. After 48-hr treatment, THC (10⁻⁹ M) decreased 50 kD tau protein in the cytoplasmic (supernatant) fraction, and in the membrane (pellet) fraction the drug (10⁻⁷ M) also decreased 50 kD tau protein.
• 3.3. This reduction in tau protein was accompanied by a 27% reduction (P<0.05) in the membrane (pellet) total protein after (10⁻⁷ M) THC and a 28% increase (P<0.02) in cytoplasmic (supernatant) total protein after 10⁻⁹ M THC.

     

Plasma concentrations of delta-9-tetrahydrocannabinol and impaired motor function

Fifty-nine volunteer subjects were allowed to smoke marijuana cigarettes until a satisfactory level of 'high' was obtained. They then had blood samples taken 5, 30, 90 and 150 min following smoking after which they were tested with the roadside sobriety test. Attempts to correlate passing or failing on three coordination tests with plasma concentrations of delta-9-tetrahydrocannabinol (THC) showed that if concentrations measured at 5 min were ignored, failures were almost inevitably associated with plasma concentrations of THC above 25-30 ng/ml. Overall, 94% of subjects failed to pass the test 90 min after smoking and 60% after 150 min, despite the fact that by then plasma concentrations were rather low. It would seem that establishing a clear relation between THC plasma concentrations and clinical impairment will be much more difficult than it has been for alcohol.     

Rectal bioavailability of delta-9-tetrahydrocannabinol from the hemisuccinate ester in monkeys.

Oral administration of delta-9-tetrahydrocannabinal (delta 9-THC) was shown to result in low and erratic bioavailability, while the drug showed no bioavailability from various suppository formulations. delta 9-THC-Hemisuccinate was formulated as a prodrug for delta 9-THC in suppositories using Witepsol H15 base. The bioavailability of delta 9-THC from this formulation was evaluated in monkeys. The plasma levels of delta 9-THC and its metabolite 11-nor-delta 9-THC-9-COOH were determined using GC/MS analysis. The calculated bioavailability of delta 9-THC from this formulation was found to be 13.5%. Non-compartmental analysis of the plasma concentration data using statistical moments showed the mean residence time (MRT) for delta 9-THC in the body to be 3 h following iv administration of delta 9-THC or its hemisuccinate ester (3.4 and 2.7 h, respectively), as compared with 5.8 h following rectal administration of the delta 9-THC hemisuccinate. The observed rectal bioavailability of delta 9-THC from suppositories containing the hemisuccinate ester as a prodrug is of significant importance in developing an alternative approach to oral administration of the drug.     

Synergistic affective analgesic interaction between delta-9-tetrahydrocannabinol and morphine

Evidence for an analgesic interaction between delta-9-tetrahydrocannabinol (Delta(9)-THC) and morphine was sought using an experimental pain model applied to normal volunteers. The study incorporated a double blinded, four treatment, four period, four sequence, crossover design. Subjects received Delta(9)-THC 5 mg orally or placebo and 90 min later morphine 0.02 mg/kg intravenously or placebo. Fifteen minutes later subjects rated the pain associated with the application of thermal stimuli to skin using two visual analog scales, one for the sensory and one for the affective aspects of pain. Among sensory responses, neither morphine nor Delta(9)-THC had a significant effect at the doses used, and there was no significant interaction between the two. Among affective responses, although neither morphine nor Delta(9)-THC had a significant effect, there was a positive analgesic interaction between the two (p = 0.012), indicating that the combination had a synergistic affective analgesic effect. The surprisingly limited reported experimental experience in humans does not support a role for Delta(9)-THC as an analgesic or as an adjunct to cannabinoid analgesia, except for our finding of synergy limited to the affective component of pain. Comparison of our results with those of others suggests that extrapolation from experimental pain models to the clinic is not likely to be a straight-forward process. Future studies of Delta(9)-THC or other cannabinoids in combination with opiates should focus upon clinical rather than experimental pain.     

Effects of delta-9-tetrahydrocannabinol, 11-hydroxy-delta-9-tetrahydrocannabinol and cannabidiol on neuromuscular transmission in the frog

Intracellular recording techniques were used on neuromuscular junctions of the sartorius muscle of the frog, in vitro, to define the synaptic pharmacology of delta-9-tetrahydrocannabinol (THC), 11-hydroxy-THC and cannabidiol (CBD). The frequency of miniature endplate potentials was increased by THC, decreased by CBD and was unaffected by 11-hydroxy-THC, whereas the amplitude of the miniature endplate potentials was depressed by all three cannabinoids. In addition, the mean quantum content of the endplate potential (m) was first increased and then decreased by THC and 11-hydroxy-THC, but CBD produced only depression. Changes in m and the frequency of the miniature endplate potential indicated presynaptic sites of drug action and reduction of the amplitude of the miniature endplate potential suggested a postsynaptic site. The findings suggest possible mechanisms of action for the central excitatory and depressant properties of the cannabinoids.     

Prenatal delta-9-tetrahydrocannabinol in the rat: effects on postweaning growth.

Either 15 or 30 mg/kg of delta-9-tetrahydrocannabinol (delta-9-THC) was administered from Day 2 through Day 22 of gestation. Pair-fed and nontreated groups served as controls and all treated and control litters were fostered at birth to untreated dams. When weighed at 57-60 days of age, pair-fed controls were significantly heavier than the nontreated, whereas the treated animals were intermediate between the controls. These findings are discussed with respect to nutritional studies that have reported postnatal growth enhancement following prenatal maternal undernutrition and the possibility that prenatal delta-9-THC inhibits this effect.