Interaction of cannabis and general anaesthetic agents in mice.

1 A cannabis extract (I) (in a concentration equivalent to 10 mg Delta(9)-tetrahydro-cannabinol(THC)/kg) prolonged pentobarbitone anaesthesia in mice maximally 20 min to 2 h after medication. The effect was still significant after 8 h, but less than at 2 hours.2 The cannabis extract (I) (equivalent to 10 mg Delta(9)-THC/kg) prolonged both pentobarbitone and ether anaesthesia in mice when administered 20 min before the anaesthetic. After eight consecutive daily doses of cannabis, the pentobarbitone anaesthesia was still significantly longer than a control group, while ether anaesthesia was not significantly prolonged.3 A second cannabis extract (II) with a different ratio of cannabinoids (also administered in dosage equivalent to 10 mg Delta(9)-THC/kg) failed to affect pentobarbitone anaesthesia in mice. This extract presented about 4% the dose of cannabidiol as extract I.4 Delta(8)-THC, Delta(9)-THC and cannabidiol prolonged pentobarbitone anaesthesia with cannabidiol being generally more active than Delta(9)-THC. Cannabinol (10 mg/kg) was inactive.5 The effects of cannabidiol and Delta(9)-THC were found to be additive, and there was a consistent trend for cannabinol to reduce the effectiveness of Delta(9)-THC and cannabidiol when given in combination.6 Premedication with phenoxybenzamine, phentolamine, propranolol, iproniazid, protriptyline, desipramine, reserpine, alpha-methyl tyrosine or parachlorophenylalanine did not affect the extract I-induced prolongation of pentobarbitone anaesthesia.7 It is concluded that cannabis may affect pentobarbitone and ether anaesthesia in mice at least partially by a direct depressant effect, and that the cannabis-induced prolongation of anaesthesia is probably unrelated to any effect on central 5-hydroxytryptamine or catecholamine neurones.

The effect of cannabinoids on intestinal motility and their antinociceptive effect in mice.

1. After oral administration to mice, pethidine, Delta(8)-tetrahydrocannabinol (THC), Delta(9)-THC, a cannabis extract and cannabinol had a dose-dependent antinociceptive effect when measured by the hot-plate method. Cannabidiol was inactive at 30 mg/kg. Delta(8)-THC, Delta(9)-THC and pethidine did not differ significantly in potency, but Delta(9)-THC was 6.5 times more active than cannabinol.2. After oral administration, three different cannabis extracts, Delta(8)-THC, Delta(9)-THC and morphine produced dose-dependent depressions of the passage of a charcoal meal in mice. Delta(8)-THC and Delta(9)-THC were equipotent and were about five times less potent than morphine. Cannabidiol was inactive up to 30 mg/kg. The effect of the three cannabis extracts on intestinal motility could be accounted for by their Delta(9)-THC content.3. The antinociceptive effect of pethidine and the effect of morphine on intestinal motility were antagonized by nalorphine whilst the effects of the cannabis extracts and the pure cannabinoids were not.4. From these results it is concluded that although cannabis and the narcotics share several common pharmacological properties, the mode of action of each is pharmacologically distinct.

An analysis of some effects of ethanol on performance in a passive avoidance task.

In a one-trial step-through passive avoidance task, pretraining administration of ethanol was shown to decrease the latencies to step through at both training (day 1) and testing (day 2) for both rats and mice. A detailed analysis of these effects showed that they differed from those reported previously by others. The mechanisms underlying these effects of ethanol were also examined. The decreased day 1 latency to step through seen in rats may have been caused by an ethanol-induced hypermotility. However, ethanol did not increase the locomotor activity of mice, although it also reduced the day 1 latency to step through of this species. In addition, it was found that the ethanol-induced impairment of passive avoidance responding (i.e. the decreased day 2 latency to step through) was not state-dependent and that it was unlikely that it could be explained by a drug-induced impairment of task acquisition, long-term memory formation or memory recall. It also seemed unlikely that the impairment could be explained by an ethanol-induced decrease in shock sensitivity. Other mechanisms which may be involved are discussed.

The attenuation of delta 9-tetrahydrocannabinol and morphine of the quasi-morphine withdrawal syndrome in rats.

The effect of delta 9-tetrahydrocannabinol (THC), morphine, haloperidol and chlordiazepoxide on the exhibition of the signs of the quasi-morphine withdrawal syndrome was studied in rats. In preliminary studies approximately equi-sedative doses of these drugs were chosen. Morphine and THC produced a very similar degree of suppression of the signs of the quasi-morphine withdrawal, but unlike morphine, the effects of THC were not reversed by the narcotic antagonist, naloxone. The dopamine receptor antagonist, haloperidol, produced a moderate suppression of the withdrawal syndrome and chlordiazepoxide was without significant effect. It is concluded that THC is of very similar potency to morphine in suppressing the quasi-morphine withdrawal syndrome, but its activity in this regard does not appear to be dependent upon the availability of opiate or dopamine receptors, nor is it due to sedation alone.

Naloxone has no effect on ethanol-induced impairment of psychomotor performance in man.

In a study designed to investigate the effect of naloxone on ethanol-induced performance deficits in man, ethanol (0.75 g/kg) and naloxone (0.4 mg) or saline were administered to 39 volunteers in a double-blind fashion. Psychomotor performance was assessed on a battery of tests (standing steadiness, pursuit rotor, simple and complex reaction times, a speeded number test and the Vienna Determination Apparatus) and blood and breath ethanol concentrations were monitored. Two experiments were performed: in Experiment 1 ethanol was given before naloxone and in Experiment 2 naloxone was administered before ethanol. There were no significant differences in either blood or breath ethanol concentrations at any time between the ethanol + naloxone and ethanol + saline groups in either Experiment 1 or 2. Although ethanol produced a significant decrement on most of the performance measures, naloxone was without effect. There was no suggestion of ethanol impairment being moderated by naloxone, whether it was given before or after ethanol.

No evidence for a protracted change in endogenous opioid activity following chronic opiate treatment in mice: parallel recovery of cross tolerance to stress and morphine antinociception.

The involvement of central endogenous opioids in swim-induced antinociception in mice is well documented. The response is attenuated by central or systemic naloxone, displays two-way cross tolerance with morphine and is correlated with apparent occupation of central opiate receptors by endogenous ligands. Swim-induced antinociception was utilised as an in vivo model of endogenous opioid function to investigate a possible protracted functional change in endogenous opioid release or inactivation following chronic opiate treatment. Antinociceptive responses (tail-flick latency) to morphine (4.4 mg/kg, SC) and swimming were determined at various times following chronic methadone (24 days treatment, 102 mg/kg day in drinking water for the last 20 days) and chronic morphine (1 g/kg sustained release) treatment. In both experiments, parallel recovery from cross tolerance was observed for morphine-and swim-induced antinociception. These results were consistent with the view that no protracted functional change in the release or inactivation of endogenous opioids had occurred following chronic opiate treatment.

The effect of delta 9-tetrahydrocannabinol, cannabidiol, and cannabinol on the anaesthesia induced by various anaesthetic agents in mice.

delta 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 delta 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 effect of cannabidiol, alone and in combination with ethanol, on human performance.

Fifteen volunteers received cannabidiol (CBD) (320 microgram/kg) or placebo (both orally, T0), and 60 min later they consumed an ethanolic beverage (0.54 g/kg) or placebo. The effects were measured at T1 (100 min after CBD ingestion), T2 (160 min) and T3 (220 min) using cognitive, perceptual and motor function tests. Factorial analysis indicated that test procedures could be adequately expressed by three rotated factors: A reaction speed factor (I), a standing steadiness factor (II) and a psychomotor coordination/cognitive factor (III). Ethanol produced a significant decrement in factor III. There was no demonstrable effect of CBD, either alone or in combination with ethanol. Neither CBD nor ethanol produced any significant effect on pulse rate. Prior administration of CBD did not significantly affect the blood ethanol levels. Whilst the subjects were able to identify correctly when they were given ethanol, they did not report any subjective effects of CBD.

The effect of (-) trans-delta9-tetrahydrocannabinol, alone and in combination with ethanol, on human performance.

Twenty five volunteers received (-) trans-delta9-tetrahydrocannabinol (THC) (320 microgram/kg) or placebo (both orally, T0), and, 60 min later, they consumed an ethanolic beverage (0.54 g/kg) or placebo. The effects of this medication were measured at T1 (100 min after THC ingestion), T2 (160 min), T3 (220 min) and T4 (280 min) using a battery of cognitive, perceptual and motor function tests. Factorial analysis indicated that the test procedures could be adequately expressed by four rotated factors: a reaction speed factor (I'), a cognitive factor (II'), a standing steadiness factor (III') and a psychomotor coordination factor (IV'). The first principal component (I) was used as a measure of general performance across the whole test battery. Both THC and ethanol produced significant decrements in the general performance factor. Ethanol produced significant decrements in standing steadiness and psychomotor coordination, while THC caused a significant deterioration in performance on all the four rotated factors. In all cases the peak effect of ethanol occurred at T1 and by T4 the effect had worn off. The performance decrements induced by THC were slower in onset and lasted longer than those induced by ethanol. In general, the peak effect of THC occurred at T1 and T2. There was no evidence of any interaction between THC and ethanol, and the effects of a combination of THC and ethanol were no more than additive. THC (but not ethanol) produced a significant rise in pulse rate. Prior administration of THC did not significantly affect the blood ethanol levels obtained. The subjects were able to identify correctly which of the treatments they had received.

Naloxone-induced contracture of ileum from stressed guinea pigs.

The in vitro preparation of guinea-pig ileum taken from animals which had been stressed by swimming for 5 min in water at 20 degrees C responded by a dose-dependent contracture to the narcotic antagonist naloxone. This response was antagonised by atropine (8 X 10(-8) g/ml). Ileum preparation from non-stressed guinea pigs did not respond to naloxone in concentrations up to 1 X 10(-5) g/ml. The possibility that this response is a consequence of the stress-induced release of endogenous opiate peptides is discussed.

Alpha-noradrenergic modulation of hypothalamic self-stimulation: studies employing clonidine, 1-phenylephrine and alpha-methyl-p-tyrosine.

An alpha-noradrenergic substrate of rewarding intracranial stimulation (ICS) has been hypothesized based on the observation that the alpha-antagonist phentolamine produced an inhibition of self-stimulation. The present experiment investigated the effects on hypothalamic self-stimulation of the alpha agonist clonidine in normal and in catecholamine-depleted rats. Using a shuttle-box technique that provides a rate-independent index of the rewarding and aversive components of ICS, it was demonstrated that clonidine produces a dose-dependent inhibition of reward that is clearly dissociable from any non-specific effects of the drug. The ineffectiveness of the peripheral alpha-agonist 1-phenylephrine indicates that the inhibition of reward produced by clonidine is mediated centrally. Clonidine and the catecholamine synthesis inhibitor alpha-methyl-p-tyrosine act together in a synergistic manner to greatly increase the magnitude and prolong the duration of the inhibition of reward while leaving the aversive component unaffected. These data are interpreted as supporting an alpha-noradrenergic basis of ICS reward while indicating that the aversive component of ICS is essentially independent of noradrenergic transmission.

[3H]Leu-enkephalin binding following chronic swim-stress in mice.

Warm water swimming produces in mice an opiate-like antinociceptive response. Chronic swimming produces tolerance to the antinociceptive response and, depending on the schedule, cross-tolerance with morphine and naloxone intensified withdrawal signs. Low affinity [3H]Leu-enkephalin binding to brain homogenates at low temperature was significantly reduced in acutely swum mice and chronically swum mice whether or not they were swum. Preincubation at 37 degrees C abolished all between-group differences. Results following chronic swimming were similar whether or not the schedule produced morphine cross-tolerance. These results were discussed in terms of the interpretation that reduced binding reflects increase in vivo occupation of opioid binding sites.

Physical dependence on physiologically released endogenous opiates.

Mice which had been submitted to a chronic schedule of warm water swimming exhibited a naloxone precipitated withdrawal behaviour which was remarkably similar to that produced in mice following chronic morphine treatment. These results are consistent with the activation of endogenous opiates during swim stress in mice and present the possibility that opiate receptors are activated in a manner analogous to the repeated application of exogenous opiates, producing both tolerance and withdrawal-like behaviour.

Tolerance and cross tolerance with morphine resulting from physiological release of endogenous opiates.

Mice which had been exposed to a chronic schedule of warm water swimming showed the development of a significant tolerance to the antinociceptive response (tail-flick latency) and a significant, two-fold increase in the ED50 of morphine (tail-flick latency and abdominal constriction response). These results suggest the involvement of endogenous opiates during swim stress in mice and are consistent with the hypothesis that during chronic stress the opiate receptors are activated in a manner analogous to the repeated application of exogenous opiates producing tolerance, morphine cross tolerance and (as previously reported) withdrawal-like behaviour.

Post-swim grooming in mice inhibited by dopamine receptor antagonists and by cannabinoids.

After a period of swimming, mice engaged in vigorous grooming activity. This behaviour was inhibited in a dose dependent manner by dopamine receptor antagonists and by the cannabinoids, delta 9-tetrahydrocannabinol and cannabinol. Cannabidiol was inactive. It is suggested that the post-swin grooming behaviour involves a dopaminergic mechanism. The mechanism of action of the cannabinoids on this behaviour is unknown.

The quasi-morphine withdrawal syndrome: effect of cannabinol, cannabidiol and tetrahydrocannabinol.

Delta-9-tetrahydrocannabinol (THC), the main psychoactive principle of cannabis, has been shown to attenuate the exhibition of signs of the quasi-morphine withdrawal syndrome in rats. Cannabinol (CBN) showed the same activity but required a dosage of approximately eight times that of THC to produce an equivalent effect. Cannabidiol was without effect at the dosage levels used. The efficacy of these cannabinoids and the potency differences recorded in this study are in accord with their effects on other behaviours, both in experimental animals and in man. The activity of THC and CBN was not affected by the narcotic antagonist, naloxone.

Method of sacrifice influences leucine enkephalin binding to mouse brain.

The methods used for sacrifice of animals and the time taken for any dissection procedures of the brain tissue at room temperature have been shown to influence the number of available binding sites for [3H] leucine enkephalin (10 nM) to mouse brain homogenates. These factors should be considered when utilizing receptor binding techniques as an indirect method for evaluating the in vitro functional state of opiate receptor populations.

The correlation between swim-stress induced antinociception and [3H] leu-enkephalin binding to brain homogenates in mice.

Mice which had been made to swim for 3 minutes showed a tail flick latency which was significantly longer than that of unswum controls. The [3H] leu-enkephalin [LE] binding to brain homogenates from swum mice was significantly reduced when compared with that form unswum controls. Scatchard analysis revealed that the reduction in binding occurred at the LE low affinity site. However, when homogenates were allowed a preincubation period of 20 min at 37 degree C, the difference in LE binding between swum and unswum mice was no longer apparent. These data are interpreted to suggest that the reduced LE binding may be due to the occupation of a proportion of the opiate receptor population by an endogenous ligand. A correlation between the duration of the swim induced antinociceptive response and the changes in LE binding is described which although non-significant, is consistent with the interpretation for the involvement of endogenous opiates in the observed increases in tail flick latency.

The effects of orally administered delta 9-tetrahydrocannabinol in man on mood and performance measures: a dose-response study.

A dose-response study of the effect of orally administered delta 9-tetrahydrocannabinol (THC) on human mood and skills performance was conducted. Using five dose levels of THC (0, 5, 10, 15, 20 mg) with 16 volunteers per dosage group, mood and performance measures were recorded at five testing occasions, one before and four after drug administration. The slope of the linear regression of performance on the test battery was significant for up to 200 minutes after dosage. That is to say, oral THC, at the doses used, produced significant dose-dependent impairment of performance for a period in excess of three hours. A similar time course for the effect of THC on the subjective assessment of intoxication ('stone') suggested a correlation between drug-induced impairment skills and the effects on mood.

The influence of analgesic drugs in road crashes.

The involvement in road crashes of two classes of drug referred to as analgesics is discussed. Evidence for the effect on traffic safety of each drug group is examined in terms of their behavioural pharmacology and of the available epidemiological data. In the case of the antipyretic analgesics, such as aspirin, there is no evidence to suggest any causative involvement in road crashes. In view of the striking differences in the supply and manner of use of the legal and illegal narcotic analgesics, these are examined separately. The behavioural pharmacology of intravenously administered heroin suggests that any drug induced deficit in driving performance is not due to any effect on psychomotor function, but might be expected from the effect of the drug on mood states. Methadone, as used in treatment schedules for narcotic dependence produces no significant effect on measures of human skills performance. Epidemiological data are contradictory though the suggestion is that the involvement of the narcotic analgesic drugs in road crashes is unlikely to be a source of significant concern. A suggestion is made that a closer examination be undertaken of the involvement in road crashes of the more widely available narcotic drugs codeine and propoxyphene when they are taken together with alcohol.