Tetrahydrocannabinol-attenuated abstinence and induced rotation in morphine-dependent rats: possible involvement of dopamine

Opioid withdrawal suppression efficacy of oral dronabinol in opioid dependent humans

BACKGROUND

The cannabinoid (CB) system is a rational novel target for treating opioid dependence, a significant public health problem around the world. This proof-of-concept study examined the potential efficacy of a CB1 receptor partial agonist, dronabinol, in relieving signs and symptoms of opioid withdrawal.

METHODS

Twelve opioid dependent adults participated in this 5-week, inpatient, double-blind, randomized, placebo-controlled study. Volunteers were maintained on double-blind oxycodone (30mg oral, four times/day) and participated in a training session followed by 7 experimental sessions, each testing a single oral test dose (placebo, oxycodone 30 and 60mg, dronabinol 5, 10, 20, and 30mg [decreased from 40mg]). Placebo was substituted for oxycodone maintenance doses for 21h before each session in order to produce measurable opioid withdrawal. Outcomes included observer- and participant-ratings of opioid agonist, opioid withdrawal and psychomotor/cognitive performance.

RESULTS

Oxycodone produced prototypic opioid agonist effects (i.e. suppressing withdrawal and increasing subjective effects indicative of abuse liability). Dronabinol 5 and 10mg produced effects most similar to placebo, while the 20 and 30mg doses produced modest signals of withdrawal suppression that were accompanied by dose-related increases in high, sedation, bad effects, feelings of heart racing, and tachycardia. Dronabinol was not liked more than placebo, showed some impairment in cognitive performance, and was identified as marijuana with increasing dose.

CONCLUSION

CB1 receptor activation is a reasonable strategy to pursue for the treatment of opioid withdrawal; however, dronabinol is not a likely candidate given its modest withdrawal suppression effects of limited duration and previously reported tachycardia during opioid withdrawal.

Effect of Pharmacological Modulation of the Endocannabinoid System on Opiate Withdrawal: A Review of the Preclinical Animal Literature

Over the years, animal studies have revealed a role for the endocannabinoid system in the regulation of multiple aspects of opiate addiction. The current review provides an overview of this literature in regards to opiate withdrawal. The opiate withdrawal syndrome, hypothesized to act as a negative reinforcer in mediating continued drug use, can be characterized by the emergence of spontaneous or precipitated aversive somatic and affective states following the termination of drug use. The behaviors measured to quantify somatic opiate withdrawal and the paradigms employed to assess affective opiate withdrawal (e.g., conditioned place aversion) in both acutely and chronically dependent animals are discussed in relation to the ability of the endocannabinoid system to modulate these behaviors. Additionally, the brain regions mediating somatic and affective opiate withdrawal are elucidated with respect to their modulation by the endocannabinoid system. Ultimately, a review of these findings reveals dissociations between the brain regions mediating somatic and affective opiate withdrawal, and the ability of cannabinoid type 1 (CB1) receptor agonism/antagonism to interfere with opiate withdrawal within different brain sub regions.

The neurobiology of addiction

Drug addiction includes complex neurobiological and behavioural processes. Acute reinforcing effects of drugs of abuse are responsible for the initiation of drug addiction, whereas the negative consequences of drug abstinence have a crucial motivational significance for relapse and maintenance of the addictive process. The mesocorticolimbic system represents a common neuronal substrate for the reinforcing properties of drugs of abuse. Both dopamine and opioid transmission play a crucial role in this reward pathway. Common neuronal changes have also been reported during the abstinence to different drugs of abuse that could underlie the negative motivational effects of withdrawal. These changes include decreased dopaminergic activity in the mesolimbic system and a recruitment of the brain stress pathways. All drugs of abuse interact with these brain circuits by acting on different molecular and neurochemical mechanisms. The existence of bidirectional interactions between different drugs of abuse, such as opioids and cannabinoids, provides further findings to support this common neurobiological substrate for drug addictive processes.

Study of cannabinoid dependence in animals

Different animal models have been used to clarify the consequences of chronic exposure to cannabinoid agonists and their abuse liability. Following the chronic administration of cannabinoids, tolerance develops to most of their pharmacological effects. The development of cannabinoid tolerance is particularly rapid, and seems to be due to pharmacodynamic events. A cross-tolerance among different exogenous cannabinoid agonists has been reported. Somatic signs of spontaneous withdrawal have not been reported after chronic Delta(9)-tetrahydrocannabinol (THC) treatment, but were observed after chronic treatment with the cannabinoid agonist WIN-55,212-2. The administration of the CB(1) cannabinoid antagonist SR141716A in animals chronically treated with THC and other cannabinoid agonists precipitated somatic manifestations of withdrawal. The potential ability of anandamide to induce physical dependence has not been clarified. Subjective drug effects of cannabinoids have been reported by drug discrimination studies, which show cross discrimination among different natural and synthetic agonists. The rewarding effects of cannabinoids have been revealed by using several paradigms: place conditioning, intracranial self-stimulation, and self-administration. Cannabinoids have been reported to lower intracranial self-stimulation thresholds in rats. However, particular experimental conditions are required to induce conditioned place preference with cannabinoids. Numerous studies have shown that THC is unable to induce a self-administration behaviour in animals. However, WIN-55,212-2 was intravenously self-administered in mice, and monkeys that had a previous history of cocaine self-administration also self-administered THC. The mesolimbic dopaminergic system seems to be the substrate for the rewarding properties of cannabinoids.

Overview of drugs used in treating drug-induced dependence: a treatise interrelating existing hypotheses in order to attain maximal therapeutic benefits

Despite the fact that we do not yet completely understand the physiology of physical dependence, many treatment modalities are available. In this overview, an attempt is made to discuss available treatments and mechanisms to possibly attain a better understanding of the complex interactions that occur between systems. An attempt is also made to understand interrelations between drug misuse and mental disorders as one aspect of the treatment process--the ultimate goal being more efficacious and safer therapy.

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.

Effectiveness of nantradol in blocking narcotic withdrawal signs through nonnarcotic mechanisms

Male rats were made narcotic dependent through continuous intravenous infusion of morphine. During withdrawal, nantradol, clonidine, and morphine were found to block withdrawal signs in a dose-dependent manner. Almost complete alleviation of withdrawal occurred with nantradol or clonidine at 0.16 mg/kg and with morphine at 40 mg/kg. The effectiveness of morphine, but not of nantradol or clonidine, was reversed by naloxone. Likewise, in naive rats given castor oil, naloxone did not block the antidiarrheal effect of nantradol or clonidine. In order to compare possible subjective effects of nantradol with other antiwithdrawal drugs, naive rats were trained to discriminate either morphine, cyclazocine, or clonidine from vehicle by selecting different levers for reinforcement. Nantradol failed to produce any generalization to morphine, cycloazocine, or clonidine, suggesting that this drug does not produce central subjective effects like those of the training drugs. In additional testing in behavioral experiments, nantradol failed to produce any sign of anxiogenic activity.

A comparison of THC, nantradol, nabilone, and morphine in the chronic spinal dog

Morphine and delta 9-tetrahydrocannabinol (THC) have been shown to have certain pharmacologic characteristics in common. Among these are antinociception, hypothermia, and the suppression of precipitated abstinence in morphine-dependent rats. In the present study the effects of morphine were compared with the effects of THC and two synthetic cannabinoids, nantradol and nabilone, in both nondependent and morphine-dependent chronic spinal dogs. Single doses of THC, nantradol, and nabilone depressed the flexor and skin twitch reflexes and had a calming effect after intravenous infusion. These effects are similar to those of morphine. Morphine, nantradol, and nabilone, but not THC, depressed rectal temperature. Unlike morphine, however, the cannabinoids produced mydriasis and an increased startle response, and these effects were not antagonized by naltrexone. THC, nantradol, and nabilone suppressed withdrawal abstinence in 40-hour and maximally abstinent morphine-dependent chronic spinal dogs. The results suggest that THC, nantradol, and nabilone share some properties with morphine since they increased the latency of the skin twitch reflex and suppressed withdrawal abstinence. It is doubtful, however, that these actions of the cannabinoids are mediated through opioid receptors since they were not antagonized by naltrexone.

Effect of delta 9-tetrahydrocannabinol on the morphine-induced hyperactivity of mice

The effect of delta 9-tetrahydrocannabinol (THC) on the locomotor activity-stimulating action of morphine has been investigated in mice. THC (10 mg/kg) has been found to potentiate morphine-induced hyperactivity. On the other hand, the stimulating action of morphine on motor activity strongly diminished in mice rendered tolerant by the implantation of a morphine pellet. The pretreatment of morphine-tolerant mice with the same dose of THC did not change the effect of morphine on the motor activity. These results suggest that tolerance also developed to the potentiating action of THC on morphine-induced hyperactivity during the development of tolerance to this action of morphine.

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

The present experiments dealt the effects of delta 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.

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.

Screening hallucinogenic drugs II. Systematic study of two behavioral tests

The effects of hallucinogenic and nonhallucinogenic drugs were studied on two behavioral tests: (1) discriminated Sidman avoidance, using modified Bovet-Gatti profiles, which have been proposed as specific in detecting hallucinogenic activity and (2) a drug discrimination experiment. By the first method, the "hallucinogenic profile" was obtained with both hallucinogenic and nonhallucinogenic drugs and, at least as used here, was not a suitable screening method. In the drug discrimination experiment, data from the present study along with other available evidence suggest the potential value of this method for drug screening procedures.

Stereospecific and nonstereospecific effects of (+)- and (-)-morphine: evidence for a new class of receptors?

The unnatural (+) enantiomer of morphine had minimal activity in three opiate assays in vitro: the rat brain homogenate binding assay, the electrically stimulated guinea pig ileum assay, and the inhibition of adenylate cyclase in neuroblastoma X glioma hybrid cell homogenates. When (+)-morphine was microinfected into the periaqueductal gray (a site known to mediate morphine analgesia) of drug-naive rats, there was only minimal analgesia, but the hyperresponsivity usually observed after microinfection of (-)-morphine occurred. Also, when (+)-morphine was microinfected into the midbrain reticular formation of drug-naive rats, rotation similar to that following microinjection of (-)-morphine occurred. These behaviors were not blocked by naloxone. Significantly, they typically occur in precipitated abstinence in morphine-dependent rats. These observations suggest that there are at least two classes of receptors, one stereospecific and blocked by naloxone and the other only weakly stereospecific and not blocked by naloxone, and that precipitated abstinence may be due, in part, to a selective blockade of receptors of the former class but not of the latter.

Cannabis, catecholamines, rapid eye movement sleep and aggressive behaviour

1. Previous work from our laboratory has shown that cannabis induces aggressive behaviour in rats that have been deprived of rapid eye movement (REM) sleep. It was suggested that this effect was related to brain catecholamines, with dopamine playing an agonist role and noradrenaline an inhibitory one. The present paper describes new experiments dealing with this subject. 2. Previous REM sleep-deprivation enhanced both delta9-tetrahydrocannabinol (THC)-induced hypothermia and nomifensine effects on aggressive behaviour. 3. A marihuana extract decreased brain dopamine turnover in REM sleep-deprived rats, an effect not observed in non-deprived rats. Noradrenaline metabolism was not altered. 4. Fighting behaviour was elicited in REM sleep-deprived rats treated with 4 different dopamine-beta-hydroxylase inhibitors. 5. Apomorphine, nomifensine and delta9-THC administered to non-deprived rats pretreated with bis(4-methyl-1-homopiperanzinyl-thiocarbonyl) disulphide (Fla-63), induced fighting behaviour. 6. Nomifensine and apomorphine induced fighting in non-deprived rats pretreated with delta9-THC. 7. Clonidine inhibited the fighting elicited in REM sleep-deprived rats by either delta9-THC or Fla-63 pretreatment. 8. The data are discussed in terms of the influence of REM sleep-deprivation (or the stress associated with deprivation) on the response to dopaminergic drugs and cannabis. Taken together they emphasize the participation of brain dopamine and noradrenaline systems in the aggressive behaviour studied.

Stimulus effects of delta(9)-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 delta(9)-tetrahydrocannabinol (delta(9)-THC, 4 mg/kg) and the effects of the vehicle were tested for antagonism and generalization to the delta(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 delta(9)-THC stimulus, nor were they found to generalize to delta(9)-THC.

Morphine-induced rotation in naive, nonlesioned rats

In rats injected with morphine in the midbrain reticular formation, pronounced ipsilateral rotation behavior was elicited by mild auditory and visual stimuli. The frequency of occurrence and rate of rotation were dose-dependent. This effect was site specific and drug specific; other drugs (except heroin) failed to induce this behavior. Naloxone potentiated the morphine rotation. Pretreatment with drugs that either potentiated or attenuated the morphine rotation indicated involvement of the noradrenergic and cholinergic systems and excluded a role for the dopaminergic system. No analgesia was observed after morphine microinjection in this site; thus, the hyperresponsivity to mild auditory and visual stimuli and concurrent analgesia previously seen in animals with morphine microinjections in the periaqueductal gray matter appear to be dissociable effects of morphine, and site specific.