Δ9-Tetrahydrocannabinol impairs spatial memory through a cannabinoid receptor mechanism

The purpose of the present study was to investigate whether the cannabinoid and cholinergic systems impair working memory through a common mechanism. This hypothesis was tested by examining whether the cannabinoid antagonist SR141716A would ameliorate radial-arm performance deficits caused by either the naturally occurring cannabinoid, ⁹-THC, or scopolamine, a muscarinic antagonist. In addition, we evaluated whether the cholinesterase inhibitor, physostigmine, would prevent ⁹-THC-induced impairment of spatial memory. Finally, because the locomotor suppressive effects of cannabinoids may decrease radial arm choice accuracy independent of a direct effect on memory, we examined the impact of increasing the intertrial error on radial arm choice accuracy. As previously reported, ⁹-THC impaired maze performance (ED₅₀=3.0 mg/kg). Increasing the intertrial interval from 5 s to 30 s resulted in a three-fold increase in the amount of time required to complete the maze without affecting choice accuracy. Importantly, SR141716A prevented ⁹-THC-induced deficits in radial-arm choice accuracy in a dose-dependent manner (AD₅₀=2.4 mg/kg); however, the cannabinoid antagonist failed to improve the disruptive effects of scopolamine. Conversely, physostigmine failed to improve performance deficits produced by ⁹-THC. These data provide strong evidence that ⁹-THC impairs working memory through direct action at cannabinoid receptors. Moreover, these results suggest that scopolamine and ⁹-THC do not impair spatial memory in a common serial pathway, though they may converge on a third neurochemical system.     

Generalization of the discriminative stimulus properties of x0394; 9 in rats

Rats were trained in a water maze to discriminate between IP injections of 3 mg/kg ⁹- (⁹⁽¹¹⁾-THC) and its vehicle. Both ⁸- and ⁹⁽¹¹⁾ were generalized to the training drug. In contrast to our observations in rhesus monkeys, where ⁹-THC is at least 100 times less potent than ⁹-THC, ⁹⁽¹¹⁾ was found to be only seven times less potent in the rat. Relative potencies, expressed as the dosage at which 50% of the animals gave drug responses (ED₅₀) were 1.8 mg/kg and 12.2 mg/kg for ⁹-THC and ⁹⁽¹¹⁾ respectively. Twenty-four hours after receiving 7×ED₅₀=12 mg/kg ⁹ the tests showed intermediate results when conducted with the training dosage; 4×ED₅₀=50 mg/kg ⁹-THC 48 h prior to the training dosage of 3 mg/kg ⁹-THC completely blocked drug-appropriate responses. Coinjection of ED₅₀ dosages of ⁹- and ⁹⁽¹¹⁾-THC led to 90% drug responses, demonstrating the additivity of the cannabis-like effect of both cannabinoids. Differences in the individual sensitivity of the rats to the tested cannabinoids were observed. Findings are interpreted in terms of the receptor mechanism for cannabis-like activity.This paper is dedicated to the memory of Dr. M. Binder who died on February 15, 1984     

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.     

Evidence for separate neuronal mechanisms for the discriminative stimulus and catalepsy induced by Δ9-THC in the rat

The cataleptogenic effect of ⁹-THC was compared to its discriminative stimulus effects in rats. The ED₅₀s for the discriminative stimulus and catalepsy were 0.8 and 4.0 mg/kg, respectively, while their time courses were very similar. The ED₅₀ of ⁹-THC for catalepsy in experimentally naive rats was not different from that in rats trained with the drug discrimination procedure, indicating that the cataleptogenic effect was not appreciably attenuated by long-term exposure to low doses of ⁹-THC. Pharmacologically, the catalepsy produced by ⁹-THC more closely resembled that of haloperidol than of morphine, since anticholinergic pretreatment eliminated the ⁹-THC-induced catalepsy while pre-treatment with naloxone had no effect. Although the cataleptogenic effect of ⁹-THC could be pharmacologically manipulated by anticholinergic pre-treatment, its discriminative stimulus effects were not changed in the same animals. These results demonstrate that distinctive mechanisms of action exist for these cannabinoid-induced behaviors.     

Stimulus effects of Δ9-THC and its interaction with naltrexone and catecholamine blockers in rats

Rats trained in a T-shaped maze to discriminate the effects of i.p. injections of ⁹-tetrahydrocannabinol (⁹-THC, 4mg/kg) and the effects of the vehicle were tested for antagonism and generalization to the ⁹-THC stimulus by naltrexone (4 mg/kg), haloperidol (0.32 mg/kg), propranolol (20 mg/kg), and phenoxybenzamine (10 mg/kg). None of these drugs blocked the ⁹-THC stimulus, nor were they found to generalize to ⁹-THC.     

Effect of some cannabinoids on naloxone-precipitated abstinence in morphine-dependent mice

Mice were rendered morphine-dependent by the subcutaneous implantation of a pellet containing 75 mg of morphine base; 72 h after the implantation, the animals were injected intraperitoneally either with vehicle or with various doses of ₉-tetrahydrocannabinol, ₈-tetrahydrocannabinol, cannabidiol, cannabinol, or 11-hydroxy-₈-tetrahydrocannabinol. Thirty minutes after injection of the cannabinoids, the antagonist, naloxone HCl, was administered to induce the stereotyped withdrawal jumping syndrome. The dose of naloxone needed to induce withdrawal jumping in 50% of the animals (ED₅₀) was determined for each dose of the cannabinoids. All of the cannabinoids inhibited the naloxone-precipitated morphine abstinence as evidenced by an increase in the naloxone ED₅₀. Two additional signs of morphine abstinence, defecation and rearing behavior, were also suppressed by the cannabinoids. The relative effectiveness of the cannabinoids in inhibiting morphine abstinence appeared to be in the following order: ₉-tetrahydrocannabinol > ₈-tetrahydrocannabinol > 11-hydroxy-₈-tetrahydrocannabinol > cannabidiol > cannabinol.These data suggest that cannabinoids may be useful in facilitating narcotic detoxification.     

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.     

Effect of low doses of Δ<Superscript>9</Superscript>-tetrahydrocannabinol and cannabidiol on the extinction of cocaine-induced and amphetamine-induced conditioned place preference learning in rats

Rationale Using the place-preference conditioning paradigm, we evaluated the potential of the two most prominent cannabinoids found in marijuana, the psychoactive component ⁹-tetrahydrocannabinol (⁹-THC) and the nonpsychoactive component cannabidiol (CBD), to potentiate extinction of a cocaine-induced and an amphetamine-induced conditioned place preference in rats.Methods To determine the effects of pretreatment with ⁹-THC or CBD on extinction, a cocaine-induced and amphetamine-induced place preference was first established. Rats were then given an extinction trial, during which they were confined to the treatment-paired floor for 15 min. Thirty minutes prior to the extinction trial, they were injected with a low dose of ⁹-THC (0.5 mg/kg), CBD (5 mg/kg) or vehicle. The potential of the CB₁ receptor antagonist, SR141716, to reverse the effects of ⁹-THC or CBD was also evaluated. To determine the hedonic effects of CBD, one distinctive floor was paired with CBD (5 mg/kg) and another with saline. Finally, to determine the effect of ⁹-THC or CBD on the establishment and/or the expression of a place preference during four cycles of conditioning trials, rats were injected with ⁹-THC (0.25–1 mg/kg), CBD (5 mg/kg) or vehicle 25 min prior to receiving an injection of amphetamine followed by placement on the treatment floor; on alternate days, they received injections of vehicle followed by saline and placement on the nontreatment floor. The rats then received two test trials; on one trial they were pretreated with the cannabinoid and on the other trial with vehicle.Results ⁹-THC and CBD potentiated the extinction of both cocaine-induced and amphetamine-induced conditioned place preference learning, and this effect was not reversed by SR141716. The cannabinoids did not affect learning or retrieval, and CBD was not hedonic on its own.Conclusions These results are the first to show that both ⁹-THC, which acts on both CB1 and CB2 receptors, and CBD, which does not bind to CB₁ or CB₂ receptors, potentiate the extinction of conditioned incentive learning.     

Cannabis interferes with nest-building behavior in mice

Nest-building, a behavioral model shown to be disrupted by hallucinogens, has never been used to answer questions concerning the psychotomimetic effects of ⁹-THC. Several fractions of cannabis and tobacco pyrolysis products were tested consecutively in the same procedure. The following drugs were injected i.p. under a saline-drug-saline schedule: d-amphetamine (6 mg/kg), pentobarbital (25 mg/kg), ⁹-THC (10 mg/kg, 5 mg/kg, 2.5 mg/kg), the cannabis fractions designated I_s (water soluble products), II_s (nonsoluble, nonvolatile products), III_s (it comprises what is inhaled by a common hashish smoker), and analogous fractions of tobacco pyrolysis products designated III_B (what is inhaled by a common tobacco smoker), II_B and I_B.The effects of ⁹-THC (10 mg/kg), II_s, and III_s were quite similar as far as the disruption of the normal behavioral pattern is concerned. d-Amphetamine, ⁹-THC (5 mg/kg), and II_B disrupted the normal behavioral pattern as well. The similarity of the effects of II_s and III_s was unexpected in view of the different contents of cannabinoids in these fractions. Also unexpected was the similarity of the effects of ⁹-THC (10 mg/kg) and III_s (40 mg/kg containing 7% ⁹-THC) as well as the activity of fraction III_B.     

A repeated tests procedure to assess onset and duration of the cue properties of (−)Δ 9-THC, (−)Δ 8-THC-DMH and (+)Δ 8-THC

Rats were trained in a two-lever operant box in a drug discrimination procedure to respond differentially to the effects induced by 3 mg/kg of (-) ⁹-tetrahydrocannabinol and the drug vehicle. Tests with (-) ⁸-THC and the dimethyl-heptyl (DMH) homologue of (-) ⁸-THC indicated that (-) ⁸-THC-DMH was more potent but had a slower onset of action than (-) ⁸-THC. Two ways of testing the onset and duration of action were compared. In one procedure (separate tests) the time course of the drug action was established by testing each time interval on separate days with a new injection each test day, whereas in the other procedure (repeated tests) all intervals were evaluated after a single injection. The results were similar for both procedures. The median time intervals for the decay of the (-) ⁸-THC stimulus were 122 and 127 min for the separate and repeated tests procedures respectively. The median time intervals for the onset of action of the (-) ⁹-THC effects of (-) ⁸-THC were 65 and 62 min for the separate and repeated tests procedures respectively. The median time intervals for the decay of (-) ⁸-THC-DMH (0.30 and 0.56 mg/kg) was between 8 and 24 h after injection. Furthermore, a stereoselective action is indicated, as (+) ⁸-THC (5.6 and 10 mg/kg) did not substitute for (-) ⁹-THC.     

Δ9-Tetrahydrocannabinol produces naloxone-blockable enhancement of presynaptic basal dopamine efflux in nucleus accumbens of conscious,freely-moving rats as measured by intracerebral microdialysis

This study examined the effects of acute administration of delta-9-tetrahydrocannabinol (⁹-THC), the psychoactive ingredient in marijuana, on extracellular efflux of dopamine (DA) and its metabolites as measured by in vivo microdialysis in nucleus accumbens of conscious, freely-moving rats. ⁹-THC, at low doses (0.5–1.0 mg/kg), which significantly enhance brain stimulation reward (intracranial self-stimulation), significantly increased DA efflux in nucleus accumbens. Augmentation of DA efflux by ⁹-THC was abolished by removal of calcium (Ca⁺⁺) ions from the perfusion fluid, indicating a Ca⁺⁺-dependence of ⁹-THC's action. Augmentation of DA efflux by ⁹-THC was either totally blocked or significantly attenuated by doses of naloxone as low as 0.1 mg/kg. Given the postulated role of mesocorticolimbic DA circuits in mediating and/or modulating brain stimulation reward, the present data raise the possibility that marijuana's rewarding effects, and hence its euphorigenic effects and abuse potential, may be related to pharmacological augmentation of presynaptic DA mechanisms. Additionally, the DA mechanisms enhanced by marijuana appear to be modulated by an endogenous opioid peptide system.     

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.     

Pre-exposure effects of morphine,diazepam and Δ9-THC on the formation of conditioned taste aversions

Prior to taste aversion conditioning with morphine, diazepam or ⁹-tetrahydrocannabinnol (⁹-THC), rats received pre-exposures to the vehicle or one of the three drugs. Morphine pre-exposures blocked the aversion normally induced by morphine, but not by ⁹-THC or diazepam. Diazepam pre-exposures attenuated both the morphine- and diazepam-induced taste aversions to a significantly greater degree than the taste aversion induced by ⁹-THC. As a result of ⁹-THC pre-exposures, the aversions induced by diazepam and ⁹-THC were attenuated as well as the morphine-induced aversion, which was the most greatly attenuated. These results demonstrate that pre-exposure effects are not necessarily bi-directional and, moreover, they are inconsistent with current hypotheses which attempt to account for the attenuating effect of drug pre-exposures on taste-aversion conditioning.     

Acute effects of two tetrahydrocannabinols (Δ9-THC and Δ8-THC) on water intake in water deprived rats: Implications for behavioral studies on marijuana compounds

Water intake was studied in water deprived albino rats at various time intervals after injections of two tetrahydrocannabinols ( ⁹-THC and ⁸-THC) and solvents. The dose levels used were: 1.25, 2.5, and 5.0 mg/kg of ⁹-THC and 2.5, 5.0, and 10.0 mg/kg of ⁸-THC. The results show a clear, dose dependent inhibitory effect on water intake as compared to the controls.Reduced intake of food was seen at 1 day post injection. This effect was, however, significant only for the groups treated with 5.0 and 10.0 mg/kg of ⁸-THC. A decreased body weight was also recorded after the drug treatment, especially with ⁸-THC. With respect to cannabis-induced vocalization the data suggest an increased possibility of its appearance with increasing dosages of THC.     

Relationship between body temperature and brain monoamines during the development of tolerance to Δ9-tetrahydrocannabinol in the rat

The development of tolerance to ⁹-tetrahydrocannabinol (⁹-THC) was examined. Rats with permanently indwelling intravenous catheters were injected daily with ⁹-THC, 2 mg/kg, for up to 10 days and on each day subjective behaviour and body weight of each rat were noted. Tolerance appeared to develop to both the exciatory and depressant behavioural effects of ⁹-THC, whereas the rate of gain, in body weight of ⁹-THC treated rats, was retarded and tolerance to this phenomenon did not develop over the experimental period. On days 1, 2, 3, 5, 6 and 10 body temperature was recorded continuously for at least 2 h after ⁹-THC and in other groups of rats the brain levels of noradrenaline (NA), dopamine (DA), 5-hydroxytryptamine (5-HT), and 5-hydroxyindoleacetic acid (5-HIAA) were measured spectrophotofluorimetrically 1 h after ⁹-THC. Tolerance developed to the ⁹-THC-induced hypothermia by day 3, and on days 6 and 10 hyperthermia, was observed. ⁹-THC did not markedly affect the brain levels of NA or DA over the experimental period. The brain levels of 5-HT were unchanged, on days 1–5 but there was a decrease on days 6 and 10. On days 1, 2, and 3 brain levels of 5-HIAA were raised, whereas on day 6 there was a decrease. These results show that ⁹-THC induces tolerance to the hypothermia and elevation of brain 5-HIAA levels in a linear manner. An inverse relationship appears to exist between these two parameters.     

A comparative analysis of the potential of cannabinoids and ondansetron to suppress cisplatin-induced emesis in the<Emphasis Type="Italic"> Suncus murinus</Emphasis> (house musk shrew)

Rationale The 5-HT₃ antagonist, ondansetron (OND), and the cannabinoid, ⁹-tetrahydrocannabinol (⁹-THC), have been shown to interfere with emesis; however, their relative and/or combined effectiveness in suppressing vomiting produced by the chemotherapeutic agent, cisplatin, is unknown.Objectives To evaluate the potential of: 1) a broad range of doses of ⁹-THC and OND to prevent cisplatin-induced vomiting and retching in the Suncus murinus (house musk shrew), 2) combined treatment with ineffective individual doses of ⁹-THC and OND to prevent cisplatin-induced vomiting and retching, 3) the CB₁ receptor antagonist, SR141716, to reverse the antiemetic effects of OND, and 4) cannabidiol (CBD), the principal non-psychoactive component of marijuana, to reverse cisplatin-induced vomiting in the shrew.Methods Shrews were injected with various doses of OND (0.02–6.0 mg/kg), ⁹-THC (1.25–10 mg/kg) and a combination of ineffective doses of each (0.02 mg/kg OND+1.25 mg/kg ⁹-THC) prior to being injected with cisplatin (20 mg/kg) which induces vomiting. Shrews were also injected with CBD (5 mg/kg and 40 mg/kg) prior to an injection of cisplatin.Results OND and ⁹-THC both dose-dependently suppressed cisplatin-induced vomiting and retching. Furthermore, a combined pretreatment of doses of the two drugs that were ineffective alone completely suppressed vomiting and retching. CBD produced a biphasic effect, suppressing vomiting at 5 mg/kg and potentiating it at 40 mg/kg.Conclusions A low dose of the non-intoxicating cannabinoid CBD may be an effective anti-emetic treatment and combined doses of OND and ⁹-THC that are ineffective alone suppresses cisplatin-induced emetic reactions in shrews.     

Effects of Δ8-THC,and Δ9-THC on the acquisition of a discriminative positional habit in rats

Using a reversal learning paradigm the dissociative effects of two tetrahydrocannabinols (THC) on the acquisition and reversal of a discriminative positional habit in rats were studied. A T-shaped water maze was used. From these experiments it is concluded that learning under the influence of ⁸-THC (10 and 20 mg/kg), and ⁹-THC (5 mg/kg) is state-dependent (StD) in the rat.Numbering system according to IUPAC rules.Parts of the results were presented at the Symposium on the chemistry and biological activity of cannabis, Stockholm, October 26–28, 1971 and at the Symposium on medical plants of Brazil, Sao Paulo, April 17–20, 1972.     

The mechanism of action of Δ 9 -tetrahydrocannabinol on body temperature in mice

The effect of ⁹-tetrahydrocannabinol ( ⁹-THC) on body temperature of the mouse was studied. A dose-response relationship (5–100 mg/kg) for the hypothermic effect of ⁹-THC was seen. The investigation as to the mechanism underlying the hypothermic action of ⁹-THC was also investigated. The relatively specific dopamine antagonist haloperidol potentiated ⁹-THC-induced hypothermia as did the -adrenoceptor antagonist phenoxybenzamine. However, depletion of serotonin with P-chlorophenylalanine reduced the hypothermic response to ⁹-THC as did pretreatment with the serotonin antagonist methysergide. Inhibition of re-uptake of serotonin with clomipramine potentiated the hypothermia following ⁹-THC. It is suggested that the hypothermic effect of ⁹-THC in the mouse is mediated to a large extent via serotonergic mechanisms.     

The effects of Δ9-tetrahydrocannabinol on the metabolism of norepinephrine in rat brain

⁹-THC (approximately 80 mg/kg) was administered to rats by intraperitoneal injection. This dose was found to cause an accelerated rate of disappearance of intracisternally administered norepinephrine-H³ from the brain and a small increase in the uptake of norepinephrine-H³ in the brain. In contrast to most stimulants, euphoriants, or antidepressants (e.g., cocaine or amphetamine, monoamine oxidase inhibitors and tricyclic antidepressants), ⁹-THC appeared to cause no decrease in the deamination of norepinephrine-H³ in brain. Levels of endogenous norepinephrine in brain tended to be slightly lower, whereas levels of endogenous serotonin were slightly higher in animals treated with ⁹-THC than in matched control animals. Behavioral effects were observed and are described in the text.     

Cannabinols and feeding in sheep

Marijuana, long used for the euphoria which results, recently has been found to stimulate hunger in humans but in several laboratory animals cannabinoids decrease food intake. Sheep, relatively more sensitive to chemicals that affect food intake, were injected IV with the d-and l-isomers of tetrahydrocannabinol and with a 9-aza-cannabinol) 9-AC) (8-(1,2-dimethylheptyl)-5,5-dimethyl-5H-[1]benzopyranol[3,4]pyridin-10-01, HCl) and feeding behavior was monitored. In the first 30 min, food intake was increased by the l-isomer and by 9-AC but not affected by d- ⁹-THC. After 24h, feed intake was decreased by at least one dose of d-and l- ⁹-THC and 9-AC. The l- but not d-isomer was active at very low doses compared with doses used in many laboratory animals.