Involvement of brain histamine in Δ9-tetrahydrocannabinol tolerance and withdrawal

The involvement of brain histamine (HA) in Δ⁹-tetrahydrocannabinol (Δ⁹-THC) tolerance and dependence was studied in rats. Rats treated for 5 days with Δ⁹-THC (2–6 mg/kg, IV) developed tolerance to the hypothermic effects of the drug. Tolerance also developed over the 5 day period to the decrease in brain regional HA concentrations observed after an acute injection of Δ⁹-THC. Administration of the tricyclic antidepressant drug clomipramine hydrochloride to tolerant rats induced a withdrawal-like behavioural syndrome. Accompanying this behaviour was a fall in HA concentrations of the midbrain, cortex, medulla oblongata/pons and the cerebellum. Administration of Δ⁹-THC, but not of the Δ⁹-THC vehicle, prior to clomipramine challenge attenuated both the intensity of the withdrawal-like syndrome and the reductions in brain regional HA concentration.     

Endocrine effects of cannabis in male rats

Male Wistar rats were administered either synthetic Δ⁹-tetrahydrocannabinol (Δ⁹-THC) or Mexican cannabis extract at doses of 1, 5, 10, 25, and 50 mg of Δ⁹-THC/kg of body weight. Steroid concentrations in urine and blood were measured using glass capillary gas chromatography and individual metabolites were identified by gas chromatography/mass spectrometry. Plasma corticosterone and its metabolite were elevated in a dose-response fashion up to 25 mg/kg. While testosterone is unaltered by Δ⁹-THC, except at 50 mg/kg, ⊙ther metabolites with possible relation to androgen metabolism were elevated. Measurable amounts of estrogens were produced by male rats given the drugs. Additional alterations were seen in the concentrations of conjugated steroids.     

Interaction of cannabinoids with pentobarbital in rats

The effect of cannabidiol (CBD), cannabigerol (CBG), cannabinol (CBN), Δ⁸-tetrahydrocannabinol (Δ⁸-THC), and Δ⁹-tetrahydrocannabinol (Δ⁹-THC) on the in vivo metabolism of [¹⁴C]pentobarbital (¹⁴C-P) was investigated in rats. The cannabinoids were administered ip (20 mg/kg) 30 min prior to either oral or iv treatment with ¹⁴C-P. When ¹⁴C-P was given po, the ¹⁴C blood concentrations were initially depressed and later elevated by CBG and CBD, increased by Δ⁸-THC and Δ⁹-THC and unaffected by CBN. When ¹⁴C-P was injected iv, the blood ¹⁴C values were elevated by CBD and unchanged by CBG, Δ⁸-THC or Δ⁹-THC. Urinary excretion of total ¹⁴C and the metabolites of P was decreased by CBD, CBG and Δ⁸-THC during the first 6 hr following treatment. The effect of CBD on the blood concentration and urinary excretion of ¹⁴C was dose-related. In rats treated with CBD + P, the liver and serum concentrations of P metabolites were significantly lower and the liver, serum and brain concentrations of unmetabolized P were significantly higher than in P-treated rats. Pentobarbital induction and sleeping times were potentiated by CBD and Δ⁹-THC and antagonized by CBG. It was concluded that CBD delayed P metabolism, CBG decreased the rate of P absorption and excretion. Δ⁸-THC and Δ⁹-THC decreased elimination of P and CBN had little effect on P absorption, metabolism or excretion. The effect of CBD + P on sleeping time was correlated with brain P concentrations.     

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.     

Effects of prenatal Δ9-tetrahydrocannabinol on the development of rat offspring

Pregnant rats were injected SC with 10 mg/kg Δ⁹-tetrahydrocannabinol (Δ⁹-THC) or vehicle solution on Days 10–12 of gestation. The course of pregnancy and parturition was unaffected by this drug treatment. The litter size, sex ratio, average birth weight and external appearance of the progeny did not differ from normal. Twenty-four male pups were selected from each of 6 Δ⁹-THC litters and 7 control litters for observations of physical maturation and for testing of reflexive and exploratory behavior development from birth to weaning. Cross fostered controls were employed. Offspring of Δ⁹-THC treated females showed delayed incisor eruption and retarded development of cliff avoidance and visual placing reflexes. Delta⁹-THC progeny were significantly hyperactive in an open field arena at 9 days of age. Decrements in rearing and grooming behavior were found at 13 and 17 days of age. Differences in open field exploration had disappeared by weaning age. Although no differences in body weight were present at birth, Δ⁹-THC exposed pups showed retarded growth from the fourth day through weaning. The failure of cross fostering procedures to reduce any of these effects indicates a direct, prenatal drug action on the developing fetus.     

Comparison of acute oral toxicity of cannabinoids in rats, dogs and monkeys

For preclinical toxicologic evaluation, Δ⁹-tetrahydrocannabinol (Δ⁹-THC), Δ⁸-THC, and Cannabis extract were administered po to rats, dogs and monkeys as solutions in either absolute ethanol, sesame oil, or sesame oil with 2.5–9.0% ethanol. All three compounds were significantly more potent in female than in male Wistar-Lewis and Fischer rats. However, within the dosage range of 225–3600 mg/kg, Δ⁹-THC and Δ⁸-THC produced the same lethality, while both isomers were approximately twice as potent as the Cannabis extract. Death due to all three compounds consistently occurred between 36 and 72 hr after treatment regardless of the dose level or sex of the rats. Mortality in rats apparently resulted from severe hypothermia and other central effects. Toxicity was characterized by severe hypothermia, bradypnea, rapid weight loss, inactivity, wide stance, ataxia, muscle tremors, and prostration. Rats treated with equimolar amounts of tetrahydrocannabinol from the three compounds exhibited equivalent diversities and severities of clinical signs. In dogs and monkeys, single oral doses of Δ⁹-THC and Δ⁸-THC between 3000 and 9000/mg/kg were nonlethal. Predominant toxic signs in dogs included drowsiness, ataxia, prostration, anesthesia, tremors, mild hypothermia, salivation, emesis, and anorexia. Toxic signs in monkeys included hyperreactivity to stimuli, lethargy, drowsiness, characteristic huddled posture, slow movements, abnormal eating procedures and sedation. Histopathologic alterations did not occur in either dogs or monkeys.     

A study of teratological effects of intravenous, subcutaneous, and intragastric administration of delta9-tetrahydrocannabinol in mice.

Delta-9-tetrahydrocannabinol (Δ⁹-THC) has been recognized to be the principal psychoactive component of cannabis. Pregnant Swiss Webster mice were given single treatments of Δ⁹-THC at doses ranging from 3.0 to 400 mg/kg by the iv, sc, and po routes on gestational Days 7 to 11. Untreated and vehicle-injected controls were used for each series. All fetuses were examined on Day 18 of gestation. Significant fetal growth retardation was induced by several dose levels. No malformations were found after single iv doses of 10 and 20 mg/kg of Δ⁹-THC. Subcutaneous injections of 6.25 mg/kg of Δ⁹-THC produced few abnormal fetuses (3.9%). However, a high po dose of 400 mg/kg given on Day 9 was teratogenic; 12.1% of the live fetuses were malformed. Fetuses from DBA mice given single po doses of Δ⁹-THC on Days 8, 9, or 10 of pregnancy also had a significantly increased incidence of gross external abnormalities as compared to corresponding controls; 23% of the fetuses from dams given 200 mg/kg of Δ⁹-THC on gestational Day 10 were abnormal. Skeletal anomalies were also induced in fetuses from dams treated with 200 mg/kg of Δ⁹-THC on Day 10 by gastric intubation. These results are considered in relation to previous reports of a complete lack of teratogenic activity of multiple exposure to Δ⁹-THC and a highly significant teratogenicity of crude extracts of cannabis in experimental animals.     

Reproductive and teratologic studies with Δ9-tetrahydrocannabinol and crude marijuana extract

Synthetic Δ⁹-tetrahydrocannabinol (Δ⁹-THC) and crude marijuana extract (CME) containing 16% Δ⁹-THC were administered orally to albino rats at doses of 0.5, 1.5, and 5 mg of Δ⁹-THC from either source/kg body weight. In the general reproductive study, males were dosed from 60 days prior to mating until termination of mating and females were dosed from 14 days prior to mating until 21 days postpartum. Mating and fertility indices were similar for control and treatment groups. No differences between control and treatment groups were seen at an interim sacrifice on gestation Day 14 with respect to corpora lutea, implantation sites, resorption sites, and viable fetuses. The average numbers of pups delivered and viable at birth did not differ among control and treatment groups, and pup survival was unaffected by treatment. In a perinatal/lactation study, females were dosed from gestation Day 15 until lactation Day 21. No adverse effects of treatment were observed directly or in a cross-fostering study. No evidence of teratogenic activity was obtained for either Δ⁹-THC or CME at Δ⁹-THC equivalent doses of 5, 15, and 50 mg/kg on gestation Days 6–15 in rats and 0.5, 1.5, 5, and 15 mg/kg on gestation Days 6–18 in rabbits. Fetal survival and pup survival were reduced at the highest CME treatment level.     

Tolerance to the hypothermic and aggression-attenuating effect of delta 8 - and delta 9 - tetrahydrocannabinol in mice

The effects of repeated administration of Δ⁸-andΔ⁹-tetrahydrocannabinol (Δ⁹-and Δ⁹-THC) on both temperature aggression of isolated aggressive mice were investigated. In the first experiment, Δ⁹-THC, mg/kg, caused significant hypothermia and diminished aggression. Acute tolerance to the hypothermic effect developed, which significant hypothermia and diminished aggression. Acute tolerance to the hypothermic effect developed, which could be overcome by doubling the dose. In the same mice no tolerance to the aggression inhibiting effect was seen. In the second experiment Δ⁸- and Δ⁸-THC were compared. Both compounds caused a dose-dependent decrease of body temperature. The effect of Δ⁹-THC on body temperature was about 1.5 times as strong as that Δ⁸-THC. Tolerance to the hypothermic effect appeared in one day for the 10 mg/kg dose, and in about 3 days in the 25 mg/kg group; no tolerance was seen to the aggression-attenuating effect.     

Effects of mescaline, [delta9]-tetrahydrocannabinol and pentobarbital on the auditory evoked responses in the cat

Effects of mescaline, [Δ⁹]-tetrahydrocannabinol ([Δ⁹]-THC) and pentobarbital were studied on the peak latency, area and amplitude of the waves (positive P₁ and negative N₁) of the averaged auditory evoked potentials in restrained conscious cats. Mescaline (5–15 mg/kg i.p.) caused a significant increase in peak latency (8–13%), area (77–195%) and amplitude (38–128%) of these waves. The onset of these changes was within 10–40 min and their duration ranged between 90–180 min. [Δ⁹]-THC (0.5–2 mg/kg in 4% Tween 80 i.p.) also caused a marked increase in peak latency, area and amplitude (10–25%, 113–370% and 66–310% respectively), while Tween 80 caused slight and variable effects. The effects of [Δ⁹]-THC had its onset within 40–105 min and lasted for more than 120–180 min. Pentobarbital (20 mg/kg i.p.) also caused an increase in the peak latency (8–23%), area (94–121%) and amplitude (119–132%) of these waves within 5–7 min. The peak effect occurred within 10–15 min and lasted for more than 100–120 min. These effects of the hallucinogens, mescaline and [Δ⁹]-THC thus appear to resemble those of pentobarbital, a central nervous system depressant; however the mechanism of their actions differs.     

Tolerance to the effects of Δ9-THC on shuttle-box performance and body temperature

Two groups of rats were trained in a shuttle-box and received Δ⁹-tetrahydrocannabinol (Δ⁹-THC), either before of after being tested. The drug-before group showed tolerance — within 3–6 sessions — to the response-inhibiting effect of THC. The drug-after animals appeared also to be tolerant when they received Δ⁹-THC before being tested. It is concluded that the tolerance to this effect probably is not learned, but has a physiological base. This is corroborated by the finding that during the same study all the animals developed tolerance to the hypothermic effect of Δ⁹-THC.     

Central excitatory properties of Δ9-tetrahydrocannabinol and its metabolites in iron-induced epileptic rats

The effects of δ⁹-tetrahydrocannabinol (Δ⁹-THC), two of its metabolites, 8β-hydroxy-Δ⁹-THC and 11-hydroxy-Δ⁹-THC, and cannabidiol were comparatively studied by means of an iron-induced cortical focal epilepsy in conscious rats with chronically implanted electrodes. Δ⁹-Tetrahydrocannabinol produced depression of the spontaneously firing epileptic focus, excitatory behavior, generalized after-discharge-like bursts of epileptiform polyspikes and frank convulsions. The pharmacological profiles of the two metabolites differed from that of the parent compound: 11-Hydroxy-Δ⁹-THC did not precipitate convulsions, but it did elicit all the other effects of Δ⁹-THC; the 8β-hydroxy derivative, on the other hand, exerted only two Δ⁹-THC-like effects; that is, it evoked polyspike bursts and convulsions. In contrast, cannabidiol, even in large doses (100 mg/kg) was devoid of all the effects of Δ⁹-THC. Furthermore, pretreatment with cannabidiol markedly altered the responses to Δ⁹-THC in the following ways: focal depression was partially blocked, polyspike activity was enhanced and convulsions abolished. Phenytoin pretreatment elicited similar effects, but it failed to block the Δ⁹-THC-induced convulsions. In general, the cannabinoids exhibit a wide spectrum of CNS effects ranging from focal depression to convulsions; specifically, however, the pharmacological profile of each agent can differ markedly; for example, the convulsant properties of Δ⁹-THC are not a universal characteristic of this class of drugs.     

Effects of delta 9-tetrahydrocannabinol on the levels of cyclic adenosine 3',5'-monophosphate in mouse brain

The effects of intraperitoneal injections of various doses of Δ⁹-tetrahydrocannabinol (Δ⁹-THC) on brain levels of cyclic adenosine 3',5'-monophosphate (cyclic AMP) have been studied in mice. Doses of Δ⁹-THC in the range of 0.1 to 1.0 mg/kg cause a 50–160 per cent elevation of cyclic AMP levels compared to controls (P < 0.0005), while doses of Δ⁹-THC in the range of 2.0 to 10.0 mg/kg cause a 30–60 per cent depression of cyclic AMP levels (P = 0.025 to 0.0005). This pattern was obtained in whole brain, as well as in dissected samples of cortex, cerebellum and medulla. This over-all biphasic effect of THC on cyclic AMP levels correlates with known changes in biogenic amines, temperature regulation, and behavior caused by this drug.     

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.     

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.     

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.     

Chronic oral toxicity of cannabinoids in rats

The preclinical toxicity of Δ⁹-tetrahydrocannabinol (Δ⁹-THC), Δ⁸-THC and a crude marihuana extract (CME) was evaluated in Fischer rats. The compounds were dissolved in sesame oil and administered po for 119 consecutive days at doses of 50, 250, 400 or 500 mg/kg/day for Δ⁹- and Δ⁸-THC, or 150, 750, 1200 or 1500 mg/kg/day for CME. These high dose levels were 30–300 times the usual oral dose in man and were chosen specifically to induce toxicity in rats. A biphasic toxicity pattern was characterized by generalized depression to which tolerance developed during the first week. Thereafter, hyperactivity, irritability and aggressiveness progressed and convulsions occurred by day 50. Cumulative toxicity occurred during the first few days of depression as indicated by increased chronic vs acute mortality. The singledose LD1 and LD4 for Δ⁹-THC produced 23 and 70% mortality in male rats which were treated chronically. A consistently higher incidence of mortality occurred in females than in males, but essentially all deaths from all three compounds occurred during the interval 36 to 72 hr after initial treatment. Dose-related hypothermia and bradypnea were prevalent and coincided with the interval for mortality. Growth in all treated groups was persistently decreased in a dose-related manner (30–130%) despite an increased consumption of food and water after approximately day 50; abdominal fat stores were depleted for extended periods. Organ weights decreased for uterus, prostate, ovary and spleen, and increased for adrenals, but pathologic changes in these organs were limited to splenic hypocellularity and vacuolization of the adrenal. Hematologic and biochemical parameters were generally normal except for mild leukopenia, increased SGOT and decreased coagulation time. Toxicity was similar for the three compounds and suggested a prominent effect on endocrinologic systems.     

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.     

Interactions of Δ9-tetrahydrocannabinol with phenobarbital,ethanol and chlordiazepoxide

The acute, reciprocal dose-response interactions between Δ⁹-tetrahydrocannabinol (Δ⁹-THC; 2.5, 5.0 and 10.0 mg/kg; IG) and each of three depressants — phenobarbital (PB; 10, 20 and 40 mg/kg; IP), ethanol (ETOH; 0.5, 1.0 and 2.0 g/kg; IP), and chlordiazepoxide (CDP; 2.5, 5.0 and 10.0 mg/kg; IP) — were studied for their effects on performance of a conditioned avoidance response (CAR), photocell activity, heart rate, body temperature, and rotarod performance. Δ⁹-THC impaired CAR and rotarod performance, depressed photocell activity, and decreased heart rate and body temperature. None of the three depressants significantly influenced CAR performance but they all decreased photocell activity and impaired rotarod performance at one or more doses. PB and ETOH also decreased heart rate and body temperature at the highest doses. When combined with Δ⁹-THC each of the three drugs at some dose combinations caused greater depressant effects on most measures than caused by either drug alone. Only CDP did not augment the impairment of CAR performance caused by Δ⁹-THC. The highest dose combinations of Δ⁹-THC and each of the three drugs almost completely eliminated photocell activity and rotarod performance. The interactions were also studied after subacute treatment for six days with Δ⁹-THC and/or each of the three depressants. There was clear evidence for tolerance to the effects of Δ⁹-THC and each of the depressants. There was also evidence for tolerance to the effects of PB and ETOH on some measuresbut not CDP. The reduction of effects alone or combined with Δ⁹-THC could be accounted for by assuming a partial loss of potency after subacute treatment that decreased the pharmacologically effective doses of either or both interacting drugs.     

Effects of marihuana cannabinoids on seizure activity in cobalt-epileptic rats

Rats rendered chronically epileptic by bilateral implantation of cobalt into frontal cortices were simultaneously prepared with permanent electrodes for longitudinal recording of the electroencephalogram (EMG). Delta-8-tetrahydrocannabinol (Δ-8-THC; 10 mg/kg), delta-9-tetrahydrocannabinol (Δ-9-THC; 10 mg/kg), cannabidiol (CBD; 60 mg/kg), or polyvinylpyrrolidone (PVP) vehicle (2 ml/kg) was administered IP twice daily from day 7 through 10 after cobalt implantation, at which time generalized seizure activity in non-treated cobalt-epileptic rats was maximal. Relative to PVP-treated controls, CBD did not alter the frequency of appearance of seizures during the course of repeated administration. In contrast, both Δ-8-THC and Δ-9-THC markedly reduced the incidence of seizures on the first and second days of administration, Interactal spiking during this period, on the other hand, was actually enhanced. On the third and fourth days, tolerance to the effect on seizures was evident, with a return of seizure frequency of THC-treated rats to values not significantly different from those of controls. Unlike the effect on seizures, no tolerance developed to the marked suppression of rapid eye movement (REM) sleep induces by Δ-8-THC and Δ-9-THC. REM sleep remained reduced in the treated animals during the first 2 days after termination of THC administration. In contrast, REM sleep time was unaffected by repeated administration of CBD. These results suggest that Δ-8-THC and Δ-9-THC exert their initial anticonvulsant effect by limiting the spread of epileptogenic activity originating from the cobalt focus.