Effects of Δ9-THC and a water soluble ester of Δ9-THC on schedule-controlled behavior

Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) and one of its water soluble esters (SP-111) decreased the rates of responding by pigeons working under a variable interval 3-min schedule of food presentation, or a multiple fixed-ratio 30, fixed-interval 5-min schedule of food presentation. Δ⁹-THC was 3–6 times more potent than SP-111 and had a faster onsetof effects on behavior.     

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.     

GABAergic mediation in the inhibition of hippocampal acetylcholine turnover rate elicited by delta 9-tetrahydrocannabinol.

Both intravenous Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and intraseptal muscimol reduce the turnover rate of acetylcholine (TR_ACh) in the hippocampus by 50 and 58%, respectively, without affecting the hippocampal content of ACh. The ACh content and the TR_ACh, in other areas of rat brain examined are unchanged. Bicuculline fails to alter the hippocampal TR_ACh when administered intraseptally but prevents the decreased hippocampal TR_ACh induced by Δ⁹-THC or muscimol. The effect is specific to the septal-hippocampal cholinergic pathway since lesioning the fimbria (2 hr) abolishes the effect. Moreover, neither naltrexone nor destruction of septal dopaminergic nerve terminals with 6-hydroxy-dopamine injected into area A₁₀ prevents the decreased TR_ACh after Δ⁹-THC. This suggests that neither endophinergic nor dopaminergic neurons are involved in the reduction of the TR_ACh in the hippocampas following administration of Δ⁹-THC or muscimol. When the metabolism of γ-aminobutyric acid (TR_GABA) is measured, Δ⁹-THC produces a 2-fold increase in the TR_GABA which is specific for the septum. These results suggest that Δ⁹-THC inhibits TR_ACh in the cholinergic septal-hippocampal pathway by increasing the release of GABA from septal GABAergic interneurons.     

The effect of cannabinoids (Δ9-THC and Δ8-THC) on hepatic microsomal metabolism of testosterone in vitro

The effects of Δ⁹-THC and Δ⁸-THC on testosterone metabolism by rat liver microsomal enzymes were studied in vitro. Δ⁹-THC (25 μM) inhibit the 5α-reduction of testosterone while Δ⁸-THC has no effect at double the concentration. Both Δ⁹-THC and Δ⁸-THC inhibit the hydroxylation of testosterone. This inhibition is dose dependent over the dose range (25–100 μM) tested. At the same molar concentration, Δ⁸-THC inhibits testosterone hydroxylation to a greater extent than Δ⁹-THC. The kinetic data suggest that the observed inhibition on 5α-reduction and total hydroxylation by the tetrahydrocannabinoids is of the competitive type.     

Parameters influencing the effect of delta9-THC on activity wheel behavior

In 2 studies the effect of Δ⁹-THC on activity wheel behavior in rats was examined. The amount of laboratory acclimation prior to testing was manipulated and either 4 mg/kg or 8 mg/kg Δ⁹-THC was given intraperitoneally. Activity counts were taken 15 minutes, 1, 6, 24, 48 or 72 hr after the injection. Those animals that received 4 mg/kg Δ⁹-THC and had little laboratory acclimation were significantly more active than their controls during the first 15 min but, after 1 hr were, like the other 3 experimental groups, less active than the appropriate controls. The time course for the depressant action of the Δ⁹-THC at both dose levels was quite similar and lasted for approximately 24 hr.     

The effect of Δ-tetrahydrocannabinol on the uptake and release of C-dopamine from crude striatal synaptosomal preparations

Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) and a water soluble ester derivative (compound I) caused a concentration-related decrease in the uptake of ¹⁴C-dopamine into crude synaptosomal preparations derived from mouse striata. Both were less potent than amphetamine in this preparation. In the presence of 10^?7m amphetamine the IC₅₀ of Δ⁹-THC was unaffected. The IC₅₀ is the concentration of drug in the medium which will inhibit the uptake of ¹⁴C-dopamine into the synaptosomes by 50%. However in the presence of 3.0 × 10^?6m Δ⁹-THC, the dose response curve to amphetamine was shifted to the right and the IC₅₀ of amphetamine was increased. Δ⁹-Tetrahydrocannabinol and compound I increased the release of ¹⁴C-dopamine from preparations pre-incubated with ¹⁴C-dopamine. The effect was small but significant. The effects of amphetamine and Δ⁹THC combined were additive on this system. The mode of action of Δ⁹-THC with regard to the dopaminergic system of the striatum is discussed.     

Pharmacological potency of R- and S-3′-hydroxy-Δ9-tetrahydrocannabinol: additional structural requirement for cannabinoid activity

The pharmacological potency of R- and S-3′-hydroxy-Δ⁹-tetrahydrocannabinol (THC) was compared to that of Δ⁹-THC as well as R/S-3′-OH-Δ⁹-THC. The S-isomer was found to be considerably more potent than the R-isomer in producing hypoactivity in mice, static-ataxia in dogs, and in generalization testing in rats trained to discriminate Δ⁹-THC from vehicle. S-3′-OH-Δ⁹-THC was more active than Δ⁹-THC in these tests which means that Δ⁹-THC may be either activated or inactivated in vivo depending upon which metabolite is formed. The difference in potency of these isomers suggests that the conformation of the side chain is critical for behavioral activity. The R and S isomers were found to be equally active in producing hypothermia in mice which is in contrast to the behavioral effects.     

Influence of several anesthetic agents on the effects of Δ9-tetrahydrocannabinol on the heart rate and blood pressure of the mongrel dog

Δ⁹-Tetrahydrocannabinol (Δ⁹-THC) 1 mg/kg, i.v. produced a slight but significant reduction in the heart rate of conscious mongrel dogs, and these effects were greatly potentiated by pentobarbital and/or urethane anesthesia. However, significant increase in the heart rate was noted following Δ⁹-THC administration in the dogs anesthetized with a combination of morphine plus chloralose; further, neither morphine nor chloralose alone could reverse the bradycardic effects of Δ⁹-THC. Tachycardia induced by Δ⁹-THC in these dogs could be reversed by bilateral vagotomy or by pretreatment of the animals with methylatropine, or propranolol and/or practolol. The data indicated a complex interaction between Δ⁹-THC and morphine-chloralose combination and the tachycardia induced by Δ⁹-THC under this anesthesia may be due to release of epinephrine by a reflexogenic mechanism involving afferent vagi. Further, while the bradycardic effects of Δ⁹-THC were essentially identical under pentobarbital or urethane anesthesia, the hypotensive effects were similar in urethane or chloralose anesthetized dogs. The study emphasizes that anesthetic interaction should be taken into consideration while investigating mechanisms of actions of pharmacological agents.     

Exposure to a high-fat diet decreases sensitivity to Δ9-tetrahydrocannabinol-induced motor effects in female rats

Arachidonic acid, a fatty acid component of neuronal cell membranes, forms the backbone of endogenous ligands of the endocannabinoid system. The lipid nature of this system may make it particularly susceptible to changes in fat content of the diet, which may, in turn, affect endocannabinoid tone and subsequent changes in receptor expression or activity. The latter would also be expected to affect responses to exogenous cannabinoids. The purpose of the present study was to determine the effects of a high-fat diet on sensitivity to the pharmacological effects of Δ⁹-tetrahydrocannabinol (Δ⁹-THC). Male and female Long-Evans rats were fed either a diet of standard rodent chow or chow enhanced with corn oil. Subsequently, they were repeatedly assessed for Δ⁹-THC-induced hypomobility, catalepsy and hypothermia. Female rats that received the high-fat diet beginning in adolescence or in adulthood became significantly less sensitive to the effects of Δ⁹-THC on motor behavior, but not its hypothermic effects, with faster development of decreased sensitivity in female rats that began the high-fat diet as adults. In contrast, diet-induced differences either did not occur, or were less pronounced, in male rats of both ages. After acute injection, brain and blood levels of Δ⁹-THC and its two primary metabolites were similar regardless of diet. Combined with the fact that diet differentially affected only some of the measures, these results suggest that pharmacokinetic differences cannot fully account for the effects of the high-fat diet on response to Δ⁹-THC. Further, these results suggest that dietary fat content may represent an important consideration in predicting the effects of marijuana in females.     

The effect of (minus)-delta 9-trans-tetrahydrocannibinol on myocardial contractility and venous return in anesthetized dogs

Administration of (?)-Δ⁹-trans-tetrahydrocannabinol (Δ⁹-THC, 2.5 mg/kg i.v.) to pentobarbital-anesthetized dogs in which heart rate was maintained constant by electrical pacing, decreased aortic blood pressure, cardiac output, left ventricular peak pressure and left ventricular end diastolic pressure and dP/dt. However, the contractility index (max. dP/dt)/I.P. was not altered by the compound. Furthermore, it was shown that the decrease in cardiac output due to Δ⁹-THC could be restored to original levels by an infusion of saline-dextran in quantities sufficient to elevate the left ventricular end diastolic pressure to pre-Δ⁹-THC level.In dogs in which cardiac output was maintained constant by a right heart bypass procedure Δ⁹-THC decreased blood pressure and total peripheral resistance and augmented intravascular blood volume. This increase in intravascular blood volume was significantly less (74%) in animals in which the splanchnic (superior, inferior and celiac) arteries were ligated prior to the administration of Δ⁹-THC. On the other hand, in spinal dogs Δ⁹-THC was devoid of any measurable cardiovascular effects.These observations clearly support the hypothesis that the diminution of cardiac output induced by Δ⁹-THC in animals with constant cardiac rate is primarily due to diminished venous return to the heart and not to an impaired ability of the myocardium.     

Inhibition of naloxone-induced withdrawal in morphine dependent mice by l-trans-Δ9-tetrahydrocannabinol

The effects of various doses of l-trans-Δ⁹-tetrahydrocannabinol (Δ⁹-THC) on naloxone-induced withdrawal were studied in mice rendered dependent on morphine by the pellet implantation procedure. When administered i.p., 30 min prior to naloxone, Δ⁹-THC, inhibited the naloxone-induced withdrawal jumping response. Two other signs of morphine withdrawal (defecation and rearing behavior) were also suppressed by Δ⁹-THC. It is suggested that Δ⁹-THC or some of its derivatives may have potential use in narcotic detoxification.     

Role of the central autonomic nervous system in the hypotension and bradycardia induced by (-)-delta 9-trans-tetrahydrocannabinol

(-)-Δ⁹-trans-Tetrahydrocannabinol (Δ⁹-THC), when given intravenously (2 mg kg^?1) to cats, produced marked decreases in blood pressure and heart rate which developed gradually and were of prolonged duration. Cervical spinal transection (C₁-C₂) abolished these effects whereas surgical removal of neurogenic tone to the myocardium selectively eliminated the bradycardia. Bilateral vagotomy alone did not modify the action of Δ⁹-THC upon heart rate or blood pressure. Recordings of spontaneous sympathetic outflow in the inferior cardiac nerve indicated a rapid reduction in neural discharge rate after Δ⁹-THC administration. These observations support the hypothesis that Δ⁹-THC produces a cardiodecellerator and hypotensive effect by acting at some level within the sympathetic nervous system. Experiments conducted to investigate transmission in the superior cervical and stellate ganglia demonstrated that Δ⁹-THC did not alter ganglionic function. Also, responses to intravenous isoprenaline and noradrenaline were unchanged which suggested that Δ⁹-THC did not interact with α- or β- adrenoceptors. The possible action of Δ⁹-THC on central sympathetic structures was investigated by perfusion of Δ⁹-THC into the lateral cerebral ventricle. Δ⁹-THC so administered produced a significant reduction in heart rate without a substantial lowering of blood pressure. Tritiated or ¹⁴C-Δ⁹-THC perfused into the lateral ventricle demonstrated that the amount of radioactive compound passing into the peripheral circulation was insignificant and could not account for the decrease in heart rate. The current data are in agreement with the proposal that Δ⁹-THC produces cardiovascular alterations by an action on the central nervous system which results in a decrease in sympathetic tone.     

Factors inflencing tolerance to the effects of Δ9-THC on a conditioned avoidance response

Male, Fischer strain rats were resistant to the impairing effects of Δ⁹-THC (15–60 mg/kg, IG) on performance of a conditioned pole-climb avoidance response (CAR) after daily subacute pretreatment for 4 or 6 days. A single administration of 20 mg/kg Δ⁹-THC independent of the performance test did not attenuate the subsequent impairment caused by Δ⁹-THC when tested 1–6 days later; however, administration 2 hr before each test attenuated the effect on subsequent tests given at intervals of 1–5 weeks. Similarly, subacute treatment with 20 mg/kg Δ⁹-THC for 4 days independent of the performance test attenuated the impairment caused by Δ⁹-THC during tests given to separate groups of rats 1 or 6, but not 14 days later. However, when the tests for tolerance were conducted repeatedly in the same rats, the attenuation appeared to persist for intervals up to 5 weeks. The results are discussed in terms of metabolic, functional and compensatory (behavioral) tolerance.     

Delta 9-THC: selective impairment of corticosterone uptake by limbic structures of the rat

Δ⁹-Tetrahydrocannabinol (THC) has a marked influence on the selective uptake of ³H-corticosterone by the hippocampus and septum of the rat. Analysis of variance on blood/tissue ratios showed that a dose of 9 mg/kg of Δ⁹-THC significantly (P < 0.01) lowered ³H-corticosterone uptake in the hippocampus. Compared with uptake in frontal and hind cortices, Δ⁹-THC selectively depressed ³H-corticosterone uptake within the septum and hippocampus. The decrease in uptake across the 3 and 9 mg/kg doses for the limbic system components compared with the cortical samples is highly significant (P < 0.001) and suggests that Δ⁹-THC exerts differential actions on hormone uptake within the central nervous system.     

Antipyretic, analgesic and anti-inflammatory effects of delta 9-tetrahydrocannabinol in the rat

The effects on body temperature produced by graded doses of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and phenylbutazone were compared in both normal and pyretic rats. Dose related hypothermic responses were produced by the oral administration of Δ⁹-THC in normal animals. Moreover, Δ⁹-THC significantly reduced elevated temperatures in yeast-induced pyretic rats to near normal levels at doses which exhibited little hypothermic activity in normal rats. The oral antipyretic potency of Δ⁹-THC was approximately 2 times that of phenylbutazone. The comparative oral antinociceptive activity of Δ⁹-THC and selected narcotic and non-narcotic analgesics was determined by the increase in response latency to pressure applied to normal and yeast-inflamed paws. Δ⁹-THC administered orally was essentially inactive at dose levels below those producing pronounced central nervous system depression. The oral anti-inflammatory efficacy of Δ⁹-THC was compared to phenylbutazone and acetylsalicylic acid. Δ⁹-THC was ineffective in inhibiting carrageenin-induced edema of the rat paw following acute or chronic administration.     

Effects of long-term administration and withdrawal of tetrahydrocannabinols (delta 8-THC and delta 9-THC) on open-field behavior in rats

The behavior of female Wistar rats, injected daily with Δ⁸-THC (5.0 mg/kg), Δ⁹-THC (2.5 mg/kg) or vehicle was studied in an open-field test both during the two weeks' period of drug administration and after withdrawal. The behavior of rats allowed long-term acclimation to the laboratory (LTA), studied in Experiment 1, was compared with those of Experiment 2, which were subjected to short-term acclimation (STA). Throughout the injection period a depressant effect of both isomers of THC was seen on ambulation, rearing, grooming and latency. Length of acclimation period interacted with the effects of THC:s on ambulation, producing even an increased ambulation for Δ⁸-THC in the STA group. Minor indications of tolerance to Δ⁹-THC were observed in the LTA condition only. A kind of circling behavior was characteristic of both drug groups, its frequency declining with repeated injections. At drug withdrawal, most open-field measures slowly returned to control levels, whereas rate of grooming showed a manifold increase. Possible implications of the results for behavioral research with the THC:s are discussed.     

Enzymatic changes in the male reproductive organs by delta-9-tetrahydrocannabinol

Like most psychoactive agents, cannabis and its active component delta-9-tetrahydrocan-nabinol (Δ⁹-THC) have been reported to affect the neuroendocrine axis in animals. The effect of Δ⁹-THC on some of the functionally important enzymes of the male reproductive organs are reported. The study indicates that Δ⁹-THC reduces the activities of the enzymes, β-glucuronidase, α-glucosidase acid phosphatase and fructose-6-phosphatase in a dose related manner in the testis, prostate as well as in the epididymis. It may be concluded that Δ-THC may interfere with the normal functioning of the male reproductive organs.     

Influence of tetrahydrocannabinols (delta8-THC and delta9-THC) on body weight, food, and water intake in rats

Female Wistar rats, six to a group, were injected daily for a 23-day period with Δ⁸-THC (5.0 mg/kg), Δ⁹-THC (2.5 mg/kg) or vehicle. Body weight, food and water intake were recorded every second day. It was found that Δ⁸-THC caused a decrease of body weight, to a level maintained throughout the injection period, with only slight signs of recovery. Both drugs caused a marked decrease of water intake. Food intake was not significantly affected by the drugs. Factors in relation to the effects of THC on body weight, food and water intake are discussed.     

Cannabidiol interferes with the effects of delta 9 - tetrahydrocannabinol in man

Based on previous observations that cannabidiol (CBD) blocks some effects of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) in laboratory animals, the present work was carried out to study possible interaction between CBD and Δ⁹-THC in human beings. In a double blind procedure, 40 healthy male volunteers were assigned to 1 of 8 experimental groups, receiving per oral route, placebe, 30 mg Δ⁹-THC, 15 30 or 60 mg of CBD, and mixtures of 30 mg of Δ⁹-THC plus either 15, 30 or 60 mg of CBD respectively. Pulse rate, time production tasks and psychological logical reactions were measured at several time intervals after drug ingestion. 30 mg Δ⁹-THC alone increased pulse rate, disturbed time tasks and induced strong psychological reactions in the subjects. 15–60 mg of CBD alone provoked no effects. On the other hand, CBD was efficient in blocking most of the effects of Δ⁹-THC when both drugs were given together. CBD also decreased the anxiety component of Δ⁹-THC effects, in such a way that the subjects reported more pleasurable effects.     

Tetrahydrocannabinol and acetylcholinesterase

Recent evidence suggests that the psychoactive effect of delta-9-tetrahydrocannabinol (Δ⁹-THC), the major psychoactive constituent of marihuana, may be mediated through an alteration of cholinergic neurotransmission. One possible mechanism by which Δ⁹-THC could have its effect is by affecting acetylcholinesterase (AChE) and there is evidence that has suggested that this may be an important mechanism. The results reported in the present study have shown that there is no physiologically important interaction between AChE and Δ⁹-THC or its metabolites that could explain its psychoactive effects or the profound clinical depression observed when human marihuana users are administered the cholinesterase inhibitor physostigmine.