Effects of delta1-tetrahydrocannabinol on schedule-induced aggression in pigeons

"Weeding out" violence? Translational perspectives on the neuropsychobiological links between cannabis and aggression

Recent shifts in societal attitudes towards cannabis have led to a dramatic increase in consumption rates in many Western countries, particularly among young people. This trend has shed light on a significant link between cannabis use disorder (CUD) and pathological reactive aggression, a condition involving disproportionate aggressive and violent reactions to minor provocations. The discourse on the connection between cannabis use and aggression is frequently enmeshed in political and legal discussions, leading to a polarized understanding of the causative relationship between cannabis use and aggression. However, integrative analyses from both human and animal research indicate a complex, bidirectional interplay between cannabis misuse and pathological aggression. On the one hand, emerging research reveals a shared genetic and environmental predisposition for both cannabis use and aggression, suggesting a common underlying biological mechanism. On the other hand, there is evidence that cannabis consumption can lead to violent behaviors while also being used as a self-medication strategy to mitigate the negative emotions associated with pathological reactive aggression. This suggests that the coexistence of pathological aggression and CUD may result from overlapping vulnerabilities, potentially creating a self-perpetuating cycle where each condition exacerbates the other, escalating into externalizing and violent behaviors. This article aims to synthesize existing research on the intricate connections between these issues and propose a theoretical model to explain the neurobiological mechanisms underpinning this complex relationship.

Marijuana withdrawal and aggression among a representative sample of U.S. marijuana users

BACKGROUND

Previous laboratory-based research suggests that withdrawal from marijuana may cause increased aggression. It is unclear whether this finding extends beyond the laboratory setting to the general population of marijuana users. The purpose of this study was to test a cross-sectional association between marijuana withdrawal symptoms and aggression among a representative sample of U.S. adult marijuana users, and to test whether this association was moderated by previous history of aggression.

METHODS

Data were analyzed from the National Epidemiologic Survey on Alcohol and Related Conditions. Wave Two data (2004-2005) were used for all variables except for history of aggression, which was assessed during the Wave One interview (2001-2002). Two outcomes were examined: self-report general aggression and relationship aggression. Odds ratios for aggression based on withdrawal symptoms and the interaction between withdrawal symptoms and history of aggression were calculated using logistic regression, adjusting for covariates and accounting for the complex survey design.

RESULTS

Among marijuana users with a history of aggression, marijuana withdrawal was associated with approximately 60% higher odds of past year relationship aggression (p<0.05). There was no association between withdrawal symptoms and relationship aggression among those without a history of aggression, and no association with general aggression regardless of history of aggression.

CONCLUSIONS

The findings from this study support the notion that laboratory-based increases in aggression due to marijuana withdrawal extend to the general population of marijuana users who have a previous history of aggression.

Acute effects of marijuana smoking on aggressive, escape and point-maintained responding of male drug users

Aggressive, escape and point-maintained operant responding of male marijuana smokers were measured during six 25-min sessions conducted over an 8-h experimental day. Aggressive responding ostensibly subtracted points exchangeable for money from another subject. Escape responding protected the subject's counter from point subtractions initiated by the other subject for some period of time. Aggressive and escape responding were engendered by subtracting points from the subjects and maintained by initiation of intervals free of point subtractions. Point subtractions presented to the subjects were attributed to other persons. Subjects earned points exchangeable for money on a third response option. Subjects participated in one session prior to smoking and five sessions after smoking. Subjects smoked placebo or three different potencies of active marijuana cigarettes. Marijuana smoking effects on escape responding were not significant and depended upon the frequency of provocation. Point-maintained responding was decreased after marijuana smoking. Aggressive responding was increased for the first hour after smoking and returned to placebo levels later in the day. These effects of marijuana smoking on aggressive responding are discussed in terms of subject characteristics, particularly drug use history.

Regular or decaffeinated coffee and subsequent human aggressive behavior

A new methodology was used to study the effects of coffee on human aggressive behavior in a laboratory situation. Aggressive responding was elicited by subtracting money from the research subjects, an action which was attributed to a fictitious person. Regular coffee compared to decaffeinated coffee produced decreases in aggressive responses, but increased nonaggressive monetary reinforced responding. Thus, the suppressing effect of regular coffee on aggressive responding was not due to a nonspecific depressant action.

Effects of caffeine on human aggressive behavior

A new methodology was employed to study the effects of caffeine on human aggressive behavior in a laboratory situation. Aggressive responding was elicited by subtracting money from the research subjects, which was attributed to a fictitious person. Caffeine compared to placebo produced decreases in two types of aggressive responses, but increased nonaggressive monetary reinforced responding. Thus, the suppressing effect of caffeine on aggressive responding was not due to a nonspecific depressant action.

Aggression induced by intermittent positive reinforcement

Mammalian and non-mammalian species engage in aggressive behavior toward animate and inanimate targets when exposed to intermittent access to a positive reinforcer. This behavior, called extinction- or schedule-induced aggression, typically includes a biting or striking topography that inflicts damage on a target. This paper critically reviews research and theoretical issues concerning such aggression and suggests directions for future investigation.

Effects of smoking different doses of nicotine on human aggressive behavior

A new methodology was employed to study the effects of drugs on human aggressive behavior in a laboratory situation. The effects of not smoking, smoking a low nicotine dose (0.42 mg/cigarette), and smoking a high nicotine dose (2.19 mg/cigarette) on human nonaggressive and aggressive responding was determined. A nonaggressive response, which resulted in the accumulation of money, was continuously available to the subject. Two different aggressive responses were also available: the ostensible subtraction of money from, and the ostensible presentation of a 1-s blast of white noise to a (fictitious) person. Aggressive responding was elicited by subtracting money from the research subjects, which was attributed to a fictitious person paired with the research subject randomly each day. Nicotine, administered with experimental cigarettes, produced dose-dependent decrease in both types of aggressive responding elicited by low or high frequency subtractions of money attributed to another person. Generally, the more aggressive response option, i.e., subtraction of money from another person, decreased more following nicotine administration. Smoking the same doses of nicotine increased nonaggressive monetary reinforced responding. This indicates that the suppressant effects of nicotine on aggressive responding was not due to a non-specific depressant action.

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.

Acute and chronic effects of cocaine on extinction-induced aggression

Pigeons worked individually in a chamber containing a response key and a mirror. Pecking on the key was controlled by a multiple schedule in which a brief period of continuous food reinforcement alternated with a 5-minute period of extinction. Under baseline conditions, aggressive behavior (responding on the mirror) occurred at the onset of each extinction period. In Experiment I (acute drug administration), the aggressive behavior was decreased by doses of cocaine that had little or no effect on key pecking. Such food-reinforced responding was disrupted, however, by higher doses of cocaine. An attempt to mimic the disruptive drugs effects by a prefeeding manipulation was unsuccessful. In Experiment II (chronic drug administration), some tolerance developed to the disruptive effects of cocaine on the food-reinforced responding, except at the highest dose tested. There was no clear-cut indication of tolerance to the initial effect of cocaine on the aggressive behavior at any dose.

Effect of chlordiazepoxide on schedule-controlled responding and schedule-induced drinking

Lever pressing of four rats was maintained under a multiple fixed ratio 80, fixed interval 2-min schedule of food presentation. Water was concurrently available from a drinking tube. Overall rates of lever pressing were highest under the fixed ratio schedule and, for three rats, most drinking occurred during the pause preceding responding under the fixed interval schedule. Chlordiazepoxide increased the lower rates of lever pressing maintained under the fixed interval schedule but generally decreased the higher response rates under the fixed ratio schedule. The effects of chlordiazepoxide on schedule-induced licking also depended on the extent to which this response occurred in each schedule component. Typically chlordiazepoxide produced relatively greater increases in the lower levels of licking and either increased less or decreased licking in that component where, under control conditions, this response was more extensive. Chlordiazepoxide also produced overall increases in the total amount of water consumed during the session. When the number of food pellets obtained during the experimental session was given all at one time in the home cage, the amount of water ingested over a period of time equivalent to the session duration was substantially less than that consumed during the experimental session. Chlordiazepoxide did not increase home cage water consumption under this condition.

Extinction-induced mirror responding as a baseline for studying drug effects on aggression

Pigeons worked individually in a chamber containing a response key and a mirror. Responding on the key was controlled by a multiple schedule in which a brief period of continuous food reinforcement alternated with a 5 min period of extinction. Under baseline conditions, aggressive behavior (responding on the mirror) occurred at the onset of each extinction period. After 10 saline control sessions, 5 mg/kg of chlordiazepoxide was injected IM 30 min presession for 60 daily sessions. The drug initially produced a marked decrease in aggressive behavior but had little or no effect on key pecking. The aggressive behavior generally remained suppressed during the chronic drug regimen and returned to control levels when the drug was withdrawn. It was concluded that the technique of extinction-induced mirror responding in pigeons provides a stable, sensitive and recoverable baseline for objectively assessing selective drug effects on aggression.

Delta 9-tetrahydrocannabinol produced discrimination in pigeons

In an operant situation pigeons learned to peck one response key 90 min after an injection of 0.25mg/kg delta9-tetrahydrocannabinol (delta9-THC) and another key when trained nondrugged. When tested with doses of delta9-THC lwer than the training dose the birds disciminated 0.20 mg/kg of the drug from the nondrugged state but not 0.15 mg/kg or lower doses. The animals were able to discriminate the drug state from the nondrugged 180 min but not 360 min after the injection At a shorter interval (45 min) both drug and nondrug responding appeared. Cannabinol and cannabidiol (4.0 - 8.0 mg/kg) did not elicit any drug responses, nor did pentobarbital, ditran or amphetamine. Tests with LSD resulted in both drug and nondrug responding. When administering noncannabinoid drugs in combination with delta9-THC 0.15 mg/kg the birds responded at the key associated with the drug state, suggesting interactional effects.