Effects of chronic Δ9-tetrahyrocannabinol administration on schedule-controlled behavior of pigeons: Cross-tolerance to pentobarbital and barbital

Pigeons responding under a variable-interval (VI) 75-s schedule of food presentation were used to study cross-tolerance from ⁹-tetrahyrocannabinol (⁹-THC) to pentobarbital and barbital. After initial dose-effect functions for pentobarbital and barbital were determined, the birds received ⁹-THC injections for 6 weeks. This chronic administration regimen resulted in a greater than 100-fold tolerance to ⁹-THC. Redetermination of the pentobarbital and barbital dose-effect functions during the chronic ⁹-THC regimen revealed statistically significant shifts to the right for the pentobarbital (0.191 log unit) and barbital (0.078 log unit) dose-effect curves. All six birds showed tolerance to pentobarbital, while four of the six showed tolerance to barbital. Blood barbital levels before and after chronic ⁹-THC administration did not differ significantly. Tolerance to ⁹-THC was more prolonged and of much greater magnitude than the cross-tolerance to pentobarbital or barbital. The results demonstrate that cross-tolerance can develop from ⁹-THC to a barbiturate that normally undergoes little metabolism.     

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.     

Δ9-THC as a discriminative stimulus in rats and pigeons: Generalization to THC metabolites and SP-111

In a drug discrimination paradigm pigeons and rats were trained with an operant procedure to discriminate between the presence and absence of the effects of ⁹-THC (1.0 and 3.0 mg/kg, injected IM 90 min and I.P. 30 min before the start of the session). Once trained, various THC metabolites as well as a water-soluble derivative of THC (SP-111), were substituted for ⁹-THC to test for generalization to the training drug. Generalization to ⁹-THC occurred with the 11-hydroxy metabolites and the potency order was 11-OH-⁹-THC >11-OH-⁸-THC ⁹-THC. Among the other metabolites tested (8-OH-⁹-THC, 8, 11-di-OH-⁹-THC, 8-OH-⁹-THC, 8, 11-di-OH-⁹-THC), it was only 11-di-OH-⁹-THC that completely substituted for ⁹-THC in pigeons, albeit at very high dose levels (rats were not tested with these metabolites). SP-111 generalized to ⁹-THC in both species. However, the onset of action of SP-111 was slower than that for ⁹-THC, especially in pigeons. These studies show the importance of obtaining complete dose-effect determinations over time when assessing structure-activity relationships with drug-discrimination procedures.A brief account of the results, which are summarized in Neuropharmacology 18:1023–1024, 1979), was presented at the British Association for Psychopharmacology Summer Conference, July 15–17, Birmingham, England, 1979     

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.     

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     

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.     

Δ9-Tetrahydrocannabinol and the extrapyramidal system

The behavioural effects of stereotypy and catalepsy by ⁹-Tetrahydrocannabinol (⁹-THC) in the rat were estimated and the possible involvement of the basal ganglia in these behaviours was studied using brain lesion techniques. In addition, the interactions of ⁹-THC with a dopaminergic (amphetamine) and a cholinergic stimulant (RS-86) were evaluated using the above methods.The excitatory effects of ⁹-THC alone, i.e., circling, sniffing, and head movements, were of low intensity and short duration and they were not significantly affected by lesions in the basal ganglia. On the other hand, ⁹-THC was found to depress behaviour, including catalepsy and atonic muscular prostration, the former being markedly potentiated, while prostration was unaffected by such lesions.⁹-THC was also found to potentiate cholinergic-induced catalepsy, extrapyramidal lesions causing further potentiation.Amphetamine-induced circling, sniffing, and gnawing emerged as a triad of related behaviour fragments. This was altermated by pallidal lesions and ⁹-THC treatment, the combination of the two being additive. The potentiation by ⁹-THC of amphetamine-induced rhythmic head and body movements was unaffected by pallidal lesions and so could be mediated by another brain area.The hypothesis is proposed that ⁹-THC exerts its cataleptogenic and some of its amphetamine interaction effects by reducing dopaminergic transmission in the basal ganglia.     

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.     

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.     

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.     

Further studies of the aggressive behavior induced by Δ 9-Tetrahydrocannabinol in REM sleep-deprived rats

The aggressive behavior induced by ⁹-tetrahydrocannabinol in pairs of REM sleep-deprived rats was studied in five experiments by measuring dominant and submissive behavioral patterns. When 2 REM-deprived rats received ⁹-THC, one of the animals displayed very aggressive postures, while its partner assumed incomplete defensive postures. The intensity of these behavioral postures was dosedependent. In pairs composed of one REM-deprived rat injected with ⁹-THC and one normal or one REM-deprived partner injected with control solution the deprived/drugged rat showed an aggressive posture and catatonia, or a strikingly bizarre behavior, while the control partner displayed typical defensive postures. The behavioral alterations induced in REM-deprived rats by amphetamine, LSD-25, and pentobarbital failed to provoke defensive postures in the normal rats paired with them; however, apomorphine partially mimicked the ⁹-THC effects.It is concluded that in REM-deprived rats ⁹-THC not only provokes aggressive behavior but also impairs the defensive-submissive behavioral patterns.     

Δ 1-tetrahydrocannabinol-induced circling behavior in rats: A possible measure of psychotomimetic activity?

Relatively high dosages of ¹-tetrahydrocannabinol ( ¹-THC) markedly suppressed almost all normally occurring behavioral elements in rats as observed in both a small and a large open field. This effect persisted following repeated treatment and testing for 3 consecutive days. The psychotropically inert but related compound cannabidiol (CBD) did not suppress behavior, but in contrast had a mild activating effect. Both compounds decreased defecation during the test procedure. In addition, ¹-THC, but not CBD, induced a bizarre circling and turning response, that was evident over all 3 test days and occurred even when the rats were deeply sedated. It is suggested that an analysis of this phenomenon may be useful in measuring the psychotominetic action of ¹-THC and similar compounds in rats.     

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.     

Clinical effects and plasma levels of Δ9-Tetrahydrocannabinol (Δ9-THC) in heavy and light users of cannabis

⁹-Tetrahydrocannabinol (⁹-THC) was administered in a crossover design by smoking and IV injection to groups of heavy and light users of marihuana. Plasma concentrations of ⁹-THC were similar for the groups after IV injection of 5.0 mg ⁹-THC, but the AUC_{0–240 min} showed a trend towards lower values for the heavy user group. To achieve a maximum desired high, both groups smoked similar amounts (about 13 mg) of ⁹-THC. Heavy users tended to have higher plasma levels than light users. The systemic availability of smoked ⁹-THC was significantly higher for the heavy users (heavy users 23±16% vs 10±7% for light users). These results also indicate that heavy cannabis users smoke more efficiently than casual smokers.Both light and heavy users showed more clinical effect following IV administration than after smoking. The response of the heavy users, both with respect to effect on heart and high, was quite comparable to that of light users.The present study does not suggest that tolerance readily develops in heavy users.     

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.     

Δ9-tetrahydrocannabinol induced inhibition of predatory aggression in the rat

⁹-tetrahydrocannabinol inhibits predatory aggression in rats. Increases in the degree of inhibition are obtained with increasing dosages of the drug. Although sex and strain of the subjects varied nonsystematically, inhibition of predatory aggression uniformly was found to be dose related. Readministration of ⁹-tetrahydrocannabinol did not effect motor activity measures at dose levels which inhibit aggression. Administration of ⁹-tetrahydrocannabinol increases whole brain serotonin, while norepinepherine is largely unaffected, indicating that the anti-aggressive effect may be mediated, in part, by serotonergic mechanisms.Preliminary report of this research was presented at the meeting of the South-western Psychological Association, Spring, 1971. ⁹-THC was provided by NIMH.     

Withdrawal-like behaviour induced by inhibitors of biogenic amine reuptake in rats treated chronically with Δ 9-tetrahydrocannabinol

The effects of the biogenic amine reuptake inhibitors fluoxetine, clomipramine and imipramine on the behaviour of rats after chronic treatment with ⁹ tetrahydrocannabinol ( ⁹-THC) for 5 and 10 days were examined. Rats with permanently in-dwelling IV cannulae were injected twice daily with doses of ⁹-THC (2–6 mg/kg). ⁹-THC treatment reduced the rate of body weight gain and induced the typical biphasic modifications of behaviour. Tolerance developed to both of these effects. On days 6 and 11 of the experiment, rats were injected IP with 15 mg/kg imipramine HCl, clomipramine HCl or fluoxetine HCl, and behaviour, consisting of writhes, backward kicks, jumps and wet shakes, was observed for the next 30 min. Each of the amine reuptake inhibitors induced changes in behaviour, the severity of which appeared to correlate with their ability to inhibit the reuptake of 5-hydroxytryptamine (5-HT). It is suggested that tryptaminergic mechanisms are involved in the production of a withdrawal-like behaviour after chronic ⁹-THC treatment.     

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.     

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.     

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.