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.     

Effect of cannabinoids on the turnover rate of acetylcholine in rat hippocampus,striatum and cortex

Summary The effects of ⁹-tetrahydrocannabinol, (⁹THC) the major psychoactive compound of marijuana, and cannabidiol (CBD), a non-psychoactive component, on the acetylcholine (ACh) concentration and the turnover rate of ACh (TR_ACh) have been studied in various regions of the rat brain. Neither ⁹THC doses from 0.2 to 10 mg/kg nor CBD (10 or 20 mg/kg) alter the ACh concentration in the brain areas examined 30 min, after the intravenous injection. However, ⁹-THC (doses from 0.2 to 10 mg/kg) causes a marked dose-related decrease in the TR_ACh in hippocampus whereas CBD is without effect in this brain region even when 20 mg/kg is given. Furthermore, high doses of ⁹-THC (5 mg/kg) and CBD (20 mg/kg) that produce a significant decrease in the TR_ACh of striatum fail to change the TR_ACh in parietal cortex. The low doses of ⁹-THC required to reduce hippocampal TR_ACh suggest that an action on these cholinergic mechanisms may play a role in the psychotomimetic activity of ⁹-THC.     

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.     

Comparative analgesic activity of various naturally occurring cannabinoids in mice and rats

The analgesic effectiveness of ⁹-tetrahydrocannabinol (THC), a crude marihuana extract (CME), cannabinol (CBN), cannabidiol (CBD), morphine SO⁴ and aspirin following oral administration was directly compared in mice using the acetic-induced writhing and hot plate tests and the Randall-Selitto paw pressure test in rats. THC and morphine were equipotent in all tests except that morphine was significantly more potent in elevating pain threshold in the uninflamed rat hind paw. In terms of THC content, CME was nearly equipotent in the hot plate and Randall-Selitto tests, but was 3 times more potent in the acetic acid writhing test. On the other hand, CBN, like aspirin, was only effective in reducing writhing frequency in mice (3 times more potent than aspirin) and raising pain threshold of the inflamed hind paw of the rat (equipotent with aspirin). CBD did not display a significantly analgesic effect in any of the test systems used. The results of this investigation seem to suggest that both THC and CME possess narcotic-like analgesic activity similar to morphine, while CBN appears to be a non-narcotic type analgesic like aspirin.     

Analysis of the respiratory effects of cannabinoids in rats

The objective of the present study was to evaluate the respiratory effects of cannabinoids and their influence on cardiovascular homeostasis.In spontaneously breathing urethane-anaesthetised rats, intravenous injection of the two synthetic cannabinoid receptor agonists WIN55212-2 and CP55940 strongly and dose-dependently lowered mean arterial pressure, heart rate and the plasma noradrenaline concentration. The cardiovascular depressive effects were associated with a large decrease in respiratory rate, hypoxia, hypercapnia and blood acidosis. All depressor effects of WIN55212-2 were abolished by the selective CB₁ cannabinoid receptor antagonist SR141716A. The bradycardia elicited by WIN55212-2 was inhibited by the muscarinic acetylcholine receptor antagonist methylatropine. The natural agonist ⁹-tetrahydrocannabinol also elicited cardiovascular and respiratory depression. In contrast, WIN55212-3, an enantiomer of WIN55212-2 lacking affinity for cannabinoid receptors, had no effect. The cannabinoid-evoked decreases in blood pressure and heart rate were much more pronounced in spontaneously breathing than in artificially ventilated urethane-anaesthetised rats. In contrast, the plasma noradrenaline concentration was lowered equally in both preparations.Our results show that activation of CB₁ cannabinoid receptors not only induces cardiovascular depression, but also markedly impairs ventilation. The second major finding of the present study is that the respiratory depression evoked by cannabinoids largely amplifies the cardiovascular depression.     

Effects of marihuana extract on the operant behavior of chimpanzees

Six chimpanzees were trained to panel push under a food reinforcement baseline in which three operant schedules, each associated with a different stimulus, were presented successively. The fixed ratio (FR) reinforcement schedule required the emission of 40 responses for reinforcement. Reinforcement under the differential reinforcement of low rate (DRL) schedule was delivered only when successive responses were spaced by at least 10 sec. During the extinction or time out from positive reinforcement schedule (TO), no responses were reinforced. In Experiment 1, amounts of marihuana extract containing from 0.2 to 4.0 mg/kg (?)-Δ ⁹-trans-tetrahydrocannabinol (Δ ⁹-THC) were orally administered 1 h prior to experimentation. In Experiment 2, 1.0 mg/kg Δ ⁹-THC was orally administered between 1 and 23 h prior to experimental sessions. No disruption of stimulus control or drug effects during TO were observed. Both DRL and FR response suppression occurred at the highest drug dose. Lower Δ ⁹-THC doses produced facilitation of DRL responding up to 12 h following drug administration. Although FR responding was less sensitive, Δ ⁹-THC stimulated FR behavior from 2 to 5 h following drug administration. It was concluded that marihuana has a biphasic effect on food reinforcement schedule controlled operant behavior.     

Effect of Δ9-THC on the open-field activity of the rat

Using the open-field activity of the hooded rat as a model of overall activity, the dose-response and time-action effects of doses of ⁹-THC which did not adversely affect spontaneous activity or behavior on appetitively motivated tasks were studied. Subjects received two exposures to an open field one week apart. Prior to the first exposure subjects were treated with small doses of Tween 80-water. At 30 min or 3 h prior to the second exposure subjects were treated with Tween or ⁹-THC in doses which ranged from 0.5–5 mg/kg. Results indicated that ⁹-THC affected various indices of open-field activity such as grooming, sniffing and ambulation differently depending on the time after injection. Rearing and defecation were affected similarly by THC independent of post-injection intervals.This research was supported by USPHS Grant No. R01-MH18392-01. The ⁹-THC was supplied by Dr. John A. Scigliano, NIMH, Chevy Chase, Maryland. The authors wish to thank Dr. Patrick Deluca for assistance in the solvent studies.     

The effect of Δ9, cannabidiol,and cannabinol on the anaesthesia induced by various anaesthetic agents in mice

⁹-Tetrahydrocannabinol (2.5–80.0 mg/kg) significantly prolonged the anaesthesia induced by ketamine, pentobarbitone, thiopentone, propanidid, and Alfathesin^® in a dose-dependent manner. Cannabinol and cannabidiol (both 5.0–80.0 mg/kg) were essentially inactive, except that cannabidiol prolonged pentobarbitone-induced anaesthesia. The interaction of ⁹-tetrahydrocannabinol with the anaesthetic agents was postulated to be due to a centrally mediated action, whereas the effect of cannabidiol on pentobarbitone-induced anaesthesia probably depended on a metabolic interaction. The interaction between the cannabinoids in influencing anaesthesia induced by the above agents was examined, and the interactions were found to be complex.     

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.     

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.     

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.     

Enhancement by α-fluoromethylhistidine of the thiopental sleep-prolonging action of Δ9-tetrahydrocannabinol

The effect of -fluoromethylhistidine (-FMH), a specific inhibitor of histidine decarboxylase, on the potentiation of thiopental-induced sleep by ⁹-tetrahydrocannabinol (THC), which inhibits the histamine turnover in the brain, was examined in mice and rats. The sleeping time after injection of thiopental sodium (40 mg/kg, IV) was prolonged by THC (10 mg/kg, IP, 1 h before) to approximately twice the control value. -FMH (50 mg/kg, IP) administered alone had no significant influence on the thiopental sleeping time. However, -FMH given 1 or 3 h before THC treatment markedly enhanced the THC potentiation of thiopental-induced sleep. Such an enhancement by -FMH was not observed when -FMH was administered 15 h before THC treatment. The brain histamine level decreased by 60% during the first 4 h after -FMH injection and remained low until 15 h after the treatment. The thiopental sleep-potentiating action of morphine, chlorpromazine and diazepam was not affected by pretreatment with -FMH. The transient enhancing effect of -FMH on the THC potentiation of thiopental-induced sleep suggests that the histaminergic system is one of the activating transmitter systems in the brain.     

Anandamide inhibits the DOI-induced head-twitch response in mice

Rationale Recently, ⁹-tetrahydrocannabinol (THC), the major psychoactive component of marijuana, and synthetic cannabinoid receptor agonists reportedly reduced the head-twitches induced by the 5-HT_2A/2C receptor agonist 1-(2,5-dimethoxy 4-iodophenyl)-2-amino propane (DOI) in mice, which is mediated via the activation of 5-HT_2A receptor. However, the effect of endogenous cannabinoid anandamide on the head-twitch response has not been studied.Objectives In this study, we investigated the effect of anandamide on the DOI-induced head-twitch response in mice.Methods Five minutes after the injection of DOI (5 mg/kg IP), the number of head-twitches was counted for a 5-min period. THC or anandamide was injected IP 60 min or 10 min before the number of head-twitches was counted, respectively.Results THC and anandamide each reduced the DOI-induced head-twitch response. The inhibition of the DOI-induced head-twitch response by THC was reversed by SR141716A (N-piperidino-5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-3-pyrazole-carboxamide), a CB₁ receptor antagonist, while the effect of anandamide was not blocked by SR141716A. Cyclooxygenase (COX) inhibitors such as aspirin and indomethacin reversed the inhibition of the DOI-induced head-twitch response by anandamide. On the other hand, COX inhibitors did not affect the inhibition of the DOI-induced head-twitch response by THC.Conclusions Taken together, these findings suggest that the endocannabinoid anandamide may inhibit 5-HT_2A receptor-mediated function via the arachidonic acid cascade, but not via a direct interaction with the CB₁ cannabinoid receptor, and that the mechanism of its action is clearly different from that of THC.     

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     

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.     

Interaction between Δ 9-tetrahydrocannabinol and morphine on the motor activity of mice

The present experiments dealt the effects of ⁹-tetrahydrocannabinol (THC) on the locomotor activity stimulating action of morphine in mice. In the first series of experiments, the pretreatments of mice by THC in doses up to 20 mg/kg have been found to potentiate the morphine-induced hyperactivity in dose-dependent manner, but higher doses of THC did not produce such an action. In the second series of experiments the dose-response curve of morphine for the motor activity has been found to shift to the left by the pretreatment of mice with 10 mg/kg of THC. These results show a synergism between morphine and THC and suggest that both drugs may share some common site of action.     

A comparison of some pharmacological actions of morphine and Δ9-tetrahydrocannabinol in the mouse

The effects of morphine and ⁹-tetrahydrocannabinol (THC) on the tail-flick reflex, body temperature, and catecholamine synthesis were examined in the mouse in order to compare their effects in a single species and strain under uniform conditions. Naloxone antagonism of THC and cross-tolerance between morphine and THC were also studied. Both morphine and THC produced antinociception, hypothermia, and increased catecholamine synthesis at 30 min after s.c. injection. Morphine produced greater increases in dopamine synthesis and was a more potent antinociceptive agent, while THC produced greater increases in norepinephrine synthesis and was a more potent hypothermic agent. Naloxone pretreatment (1 mg/kg) partially antagonized the hypothermia and increase in catecholamine synthesis produced by THC. There was also crosstolerance between morphine and THC, but it was asymmetric in that THC-tolerant animals were crosstolerant to only the hypothermic action of morphine and morphine-tolerant animals cross-tolerant to only the antinociceptive action of THC.     

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.     

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.     

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.