Development of aggressive behavior in rats by chronic administration of Cannabis sativa (marihuana)

Endocannabinoid system and aggression across animal species

This narrative review article summarizes the current state of knowledge regarding the relationship between the endocannabinoid system (ECS) and aggression across multiple vertebrate species. Experimental evidence indicates that acute administration of phytocannabinoids, synthetic cannabinoids, and the pharmacological enhancement of endocannabinoid signaling decreases aggressive behavior in several animal models. However, research on the chronic effects of cannabinoids on animal aggression has yielded inconsistent findings, indicating a need for further investigation. Cannabinoid receptors, particularly cannabinoid receptor type 1, appear to be an important part of the endogenous mechanism involved in the dampening of aggressive behavior. Overall, this review underscores the importance of the ECS in regulating aggressive behavior and provides a foundation for future research in this area.

Illicit drug use and violence

This chapter reviews evidence on the relationship between illicit drug use and violence, specifically cannabis, stimulant drugs, and opioids. It summarizes findings of systematic reviews of evidence on cannabis, stimulant drugs, and opioids. It also examines evidence from epidemiological studies of drug use among violent offenders and of violence among persons who use drugs, intervention studies, animal studies, human laboratory studies, and human neuroimaging studies. More studies have examined cannabis because of its higher prevalence of use. There is an association between cannabis use and violence, suggestive evidence of a dose-response relationship between the frequency of cannabis use and violence, and a stronger association in persons with psychoses. There is similar emerging evidence on stimulant use and violence, but evidence on opioids is very limited. There is limited and mixed evidence from intervention studies that reducing drug use reduces violence. Animal and human studies provide potential biological explanations for these associations. The association between cannabis use and violence is most consistent but limited by study heterogeneity and lack of control for potential confounders. It is unclear whether these associations are causal or reflect reverse causation or the effects of confounding.

Measurement of the three phases of muricidal behavior induced by delta9-tetrahydrocannabinol in isolated, fasting rats

Delta9-Tetrahydrocannabinol (THC) has long been recognized as inducing mouse-killing behavior (muricidal behavior) in starving, isolated rats after a single injection. We showed that when the killing tendency was increased by THC, a preliminary contact with a mouse decreased the probability of muricidal behavior. By quantifying the three phases of the muricidal behavior in either nonkiller or naive THC-treated rats, we showed that the duration of each step was notably increased as compared to untreated natural killer rats, mainly the attack on the dead mouse, indicating increased aggressiveness. Finally, no significant changes were observed in the duration of the three phases in natural killer rats when the muricide assays were repeated every hour. In contrast, in THC-treated rats--either naive or nonkiller--all three phases decreased with the assay repetition to levels comparable to those of natural killer rats, suggesting that the killer behavior was progressively acquired for the six assays. These changes could be a useful model to study the central effects of THC and either its agonists or antagonists.

Antianxiety effect of cannabis: involvement of central benzodiazepine receptors

The present work, involving clinical, behavioral, and biochemical studies, was undertaken to elucidate the probable mechanism of the observed antianxiety effects of cannabis. The population for the clinical study consisted of 50 male chronic cannabis users who were otherwise healthy and 50 matched controls. When evaluated on Taylor's Manifest Anxiety Scale (TMA), these subjects had low anxiety scores as compared with the controls. To explore the possible interaction of cannabis with the benzodiazepine receptors, behavioral and biochemical studies in mice were devised, involving acute and chronic cannabis administration. Behavioral study revealed that mice under chronic cannabis treatment scored significantly higher on foot shock-induced aggression, but this was significantly blocked by benzodiazepine receptor antagonist. Furthermore, chronic cannabis treatment significantly (p less than 0.001) increased the frequency of licking response periodically punished by shocks. This confirms the antianxiety effect of cannabis, which also appears to be mediated through a benzodiazepine receptor, as it was reduced significantly (p less than 0.001) by a benzodiazepine receptor blocker. Specific 3H-diazepam binding was carried out in frontal cortex to assess both the population and affinity of benzodiazepine receptors. Our results indicate that acute cannabis treatment has no significant effect, whereas chronic cannabis treatment significantly increased 3H-diazepam binding as compared with controls. Scatchard analysis further reveals that increased affinity is responsible for increased binding to these receptors. It is therefore our contention that the antianxiety effect of cannabis is mediated through central benzodiazepine receptors.

Irritable aggression induced by delta 9-tetrahydrocannabinol in rats pretreated with 6-hydroxydopamine

Administration of delta 9-tetrahydrocannabinol (THC) to grouped rats injected intraventricularly with 6-hydroxydopamine (6-OHDA) produced violent fighting accompanied by remarkable hyperirritability. This behavior was induced reproducibly from the 10th to 100th postoperative days. It was shown that this irritable aggression could be measured continuously and quantitatively in terms of degree of activity and/or vocalization using a newly designed analyzer. The effect of THC differed markedly from the action of apomorphine and methamphetamine in 6-OHDA pretreated rats. Apomorphine induced irritable aggression but not vigorous vocalization. On the other hand, methamphetamine induced much less irritable aggression than apomorphine-induced aggression. It is assumed that a THC-invoked imbalance in catecholamine agonistic and serotonin antagonistic action brought about by activation of supersensitized catecholaminergic receptor was operating to produce the aggression. Specifically, hypoactivity of serotonergic neurons might play a key role in the occurrence of THC-induced irritable aggression.

Chronic delta 9-tetrahydrocannabinol administration and schedule-induced aggression

The effects of 0.5 mg/kg and 1.0 mg/kg of delta 9-tetrahydrocannabinol (delta 9-THC) on key-pecking maintained by a response-initiated fixed interval (FI) schedule of food presentation and schedule-induced aggression in the pigeon were studied. Initially, following the administration of delta 9-THC both the rate of key-pecking and attack responding were markedly reduced. Over sessions, tolerance developed to the suppressant effect on key-pecking, with the rate returning to the predrug level. The suppressing effect of delta 9-THC on the rate of attack remained at or near zero throughout the series of delta 9-THC injections.

Chronic administration of delta-9-tetrahydrocannabinol to pregnant rats: studies of pup behavior and placental transfer

Tritiated delta-9-tetrahydrocannabinol was administered orally to female rats throughout pregnancy at a dose level of 2 mg/kg/day. Chemical analysis of rat pup tissues indicated an average drug level near 20 ng/gm was attained via placental transfer. Although there was no teratogenicity, the pups showed both transient and relatively permanent behavioral effects. A deficit in acquisition of a passive avoidance response at 21 days of age was observed. This effect was not apparent during retraining and testing at 90 days of age. Rats whose dams had received the drug forced control animals to back out of a push tube in 67% of the tests at 21 days of age and 94% of the tests at 90 days of age.

Effects of delta-9-tetrahydrocannabinol on social behaviour in the laboratory mouse and rat

The behavioural effects of delta-9-tetrahydrocannabinol in mice and rats have been studied by an ethological analysis of encounters between animals injected with the drug and partners injected with the solvent (Tween-saline). In both species, Immobility was increased and Non-Social Activity reduced after injections of 5 mg/kg of delta-9-tetrahydrocannabinol. Flight was increased in treated mice but not in treated rats. Aggression was not significantly altered in either species. Thus, in the mouse, the qualitative behavioural effects of delta-9-tetrahydrocannabinol were similar to those previously reported for crude cannabis resin. Comparison of the dose-response data indicated that some other constituents of cannabis may reduce the Flight reaction from delta-9-tetrahydrocannabinol although not interfering with Immobility.

The effects of chronic cannabis treatment upon brain 5-hydroxytryptamine, plasma corticosterone and aggressive behavior in female rats with different hormonal status

Ovariectomized rats, chronically treated with cannabis extract or control solution, were given different hormonal treatments. Results indicated that both cannabis-treated and estrogen-treated animals were more aggressive than controls. Furthermore, aggressiveness was virtually abolished when cannabis-treated females were made sexually receptive by estrogen and progesterone treatments. After 25 days of cannabis or control solution treatment, all subjects were sacrificed. The levels and turnover rate of brain 5-HT and peripheral plasma corticosterone were then assayed. Data indicated both a significant inverse relationship between plasma corticosterone and whole brain levels of 5-HT(r = -0.742 to -0.985) for all groups and a significant positive relationship between aggressive behavior and plasma corticosterone (r = +0.675 to +0.946) in all groups that were fighting prior to decapitation. Results are tentatively explained, suggesting that the variability of the female response to stress during the different phases of the estrus cycle, permitted them to perform differently after chronic cannabis treatment. 5-HT is apparently involved, either directly in its effects on aggressive behavior or indirectly through the pituitary-adrenocortical axis activation.

Pharmacologic interaction between cannabinol and delta9-tetrahydrocannabinol

The pharmacological activities of delta9-THC [(minus)-delta9-trans-tetrahydrocannabinol], CBN (Cannabinol) and mixtures of delta9-THC + CBN were studied in rabbits, rats and mice. CBN, although in general less active, mimicked the effects of delta9-THC in several pharmacological tests: corneal arreflexia in rabbits; climbing rope, open-field, irritability and aggressiveness after REM sleep deprivation in rats; catatonia, analgesia and sleeping time in mice. When the mixture delta9-THC + CBN was used, a synergistic effect occurred on most of the depressant effects. On the other hand CBN did not interfere with or slightly inhibited the excitatory effects of delta9-THC. In the one peripheral test used, CBN did not alter the delta9-THC effect.

Factors influencing the aggressiveness elicited by marihuana in food-deprived rats

1. Aggressive behaviour was elicited in rats that had been deprived of food for 20 h daily (starved), by chronic administration of Cannabis sativa extract or (-)-Delta(9)-trans-tetrahydrocannabinol.2. The influence of intraperitoneal (i.p.) or oral glucose administration, cold environment, acidosis, and corn, and protein-free diets on this aggressiveness was studied.3. Intraperitoneal injections of glucose (100-1,600 mg/kg) did not alter the aggressiveness induced by marihuana in starved rats; glucose given orally, however, blocked this behaviour.4. Low temperature (14 degrees C) strongly potentiated the aggressive behaviour induced by marihuana in the starved rats.5. Lactic acid in doses capable of potentiating thiopental anaesthesia, failed to alter the marihuana-aggressiveness of starved rats or to facilitate this effect of marihuana in rats fed ad libitum. The same negative results were obtained with ammonium chloride.6. In rats fed ad libitum with protein-free or corn diets, marihuana administered chronically did not elicit aggressive behaviour. However, aggressiveness appeared when rats were fed for only 2 h daily on those diets.7. The results suggest that the stress of hunger (and not hypoglycaemia, acidosis or lack of specific nutrients due to starvation) is the factor that facilitates the development of aggressive behaviour by chronic administration of marihuana.