Behavioral effects of hashish in mice. III. Social interactions between two residents and an intruder male

Biomarkers in aggression

Aggressive behavior exerts an enormous impact on society remaining among the main causes of worldwide premature death. Effective primary interventions, relying on predictive models of aggression that show adequate sensitivity and specificity are currently lacking. One strategy to increase the accuracy and precision of prediction would be to include biological data in the predictive models. Clearly, to be included in such models, biological markers should be reliably associated with the specific trait under study (i.e., diagnostic biomarkers). Aggression, however, is phenotypically highly heterogeneous, an element that has hindered the identification of reliable biomarkers. However, current research is trying to overcome these challenges by focusing on more homogenous aggression subtypes and/or by studying large sample size of aggressive individuals. Further advance is coming by bioinformatics approaches that are allowing the integration of inter-species biological data as well as the development of predictive algorithms able to discriminate subjects on the basis of the propensity toward aggressive behavior. In this review we first present a brief summary of the available evidence on neuroimaging of aggression. We will then treat extensively the data on genetic determinants, including those from hypothesis-free genome-wide association studies (GWAS) and candidate gene studies. Transcriptomic and neurochemical biomarkers will then be reviewed, and we will dedicate a section on the role of metabolomics in aggression. Finally, we will discuss how biomarkers can inform the development of new pharmacological tools as well as increase the efficacy of preventive strategies.

Drugs of abuse and the elicitation of human aggressive behavior

The drug-violence relationship exists for several reasons, some direct (drugs pharmacologically inducing violence) and some indirect (violence occurring in order to attain drugs). Moreover, the nature of that relationship is often complex, with intoxication, neurotoxic, and withdrawal effects often being confused and/or confounded. This paper reviews the existing literature regarding the extent to which various drugs of abuse may be directly associated with heightened interpersonal violence. Alcohol is clearly the drug with the most evidence to support a direct intoxication-violence relationship. The literatures concerning benzodiazepines, opiates, psychostimulants, and phencyclidine (PCP) are idiosyncratic but suggest that personality factors may be as (or more) important than pharmacological ones. Cannabis reduces likelihood of violence during intoxication, but mounting evidence associates withdrawal with aggressivity. The literature on the relationship between steroids and aggression is largely confounded, and between 3,4-methylenedioxymethamphetamine (MDMA) and aggression insufficient to draw any reasonable conclusions. Conclusions and policy implications are briefly discussed.

Marihuana: much ado about THC

The availability of delta 1-THC, the major psychoactive component of marihuana, in pure form offered an opportunity for better understanding of the mechanism of action of this drug. Two decades after the isolation of delta 1-THC its mode of action is still obscure despite the enormous amount of research invested in it. Studying cannabis content as a whole offers a different approach for better understanding of this ancient weed and its effects.

Cannabis and delta-9-tetrahydrocannabinol. Effects on elements of social behaviour in mice

Behavioural effects of cannabis and delta-9-tetrahydrocannabinol (THC) in male mice encountering solvent-treated males, and of cannabis in males encountering control females, were examined by ethological procedures. Effects on elements and element-groups within behavioural categories were investigated, and effects of cannabis on the response sequence to the behaviour of male partners examined. Effects were detected on elements that previously had been grouped within categories. Flight elements "flag, evade, retreat and flee" and immobility were increased both by cannabis (50 and 100 mg/kg in male-male encounters and 25 mg/kg in male-female encounters) and by THC (5 mg/kg), whereas "scan", "wash and self-groom" and some elements of social investigation were reduced. Bout length and duration of "explore" were increased by THC. In encounters with females, cannabis decreased sexual behaviour. Sequence analysis showed that cannabis, within the limitations of the comparatively small size of sample, to have no significant effect upon normal behavioural responses at 50 and 100 mg/kg, apart from enhancement of the flight response to aggression and some elements of social investigation by partners. These more detailed analyses revealed effects that would not be detectable by the conventional approach.

Influence of hashish extract on the social behaviour of encountering male baboons (Papio c. anubis)

The effects of hashish extract (2 mg delta 9-THC/kg)on the social behaviour of encountering male baboons were tested by ethological methods. In the "approaching" male the drug reduced "approach" and the aggressive elements "hit-ground", "brows-back" and "attack" but increased the frequency of "retreat". Social interactions were generally diminished. In the "retreating" male friendly social interactions as "lipsmack" and "touch-back/handle-genitals" were suppressed but the threatening elements "open-mouth" and "tooth-grind" were stimulated. "Retreat" was additionally more frequent. Non-social activities and locomotion were not affected in either of the males. Treating both subjects with hashish resulted in a reduction of "lipsmack", "approach", "fight" and "chase" in the approaching and "lipsmack", "touch-back/handle-genitals", "chase", "retreat" and "flee" in the retreating male. Social activities were generally reduced in both animals. Comparing the behavioural effects of hashish in male baboons to those described in other non-human primates, in rodents but also in man revealed analogous effects in all species. The drug generally impaired social interactions, induced social withdrawal and led to social isolation of the drugged subject.

Effects of multiple, chronic and early hashish exposure on mating behavior, nest-building and gestation in mice

1. The effects of hashish extract on social behavior were investigated in pairs of mice living together from mating to parturition. The drug was administered orally to both animals at a dose of 20 mg delta 9-tetrahydrocannabinol/kg three times a week, either (I) during the 3 weeks from mating to parturition, (II) during the 12 weeks from weaning to mating and parturition, or (III) only during the 3 weeks after weaning. 2. In the mating tests, an acute administration (I) caused a general sedation. Chronically treated animals (II) showed decreased sexual behavior and lower social investigations despite significantly more non-social activities. Early drug treatment (III) had no effect on mating behavior. In all three series of experiments the females had conceived by the next morning. 3. The nest-building behavior during pregnancy was suppressed after multiple (I) and chronic (II) drug administration. In early drug-treated animals (III) the transport of nesting material was only slowed down. Non-social activities were normal or increased in all three series. 4. Parturition was significantly delayed by one day after multiple (I) and chronic (II) drug administration. The birth weight was not affected, but the litter size was decreased after chronic drug treatment. Early drug administration (III) had no effects on these parameters. 5. In conclusion, whereas tolerance to the sedative effects of hashish developed very rapidly, the drug influences on social behavior were stable. Therefore, discussions on legalization of cannabis should pay attention to the drug effects on social behavior.

Behavioural effects of hashish in mice in comparison with other psychoactive drugs

1. The behavioural effects of hashish extract (10 mg delta 9-THC/kg) were compared to those of morphine (20 mg/kg), diazepam (10 mg/kg), imipramine (10/kg), amphetamine (10 mg/kg) and chlorpromazine (10 mg/kg) by testing male mice in a resident-intruder situation. 2. The drugs were given either to the resident or to the intruder male. 3. Hashish extract similar to diazepam and chlorpromazine reduced social activities in resident and intruder males. 4. Intruder males treated with hashish or diazepam were more frequently attacked and submission and light was increased. 5. Amphetamine and morphine stimulated locomotion and non-social activities but impaired social behaviour especially in residents. 6. Imipramine increased aggressive behaviour in resident and intruder males.

Behavioral effects of hashish in mice. IV. Social dominance, food dominance, and sexual behavior within a group of males

Within groups of three adult male mice the acute and subchronic effects of hashish extract (20 mg delta 9-THC/kg) on social dominance, food dominance, and sexual interactions with a female were investigated. An initial drug treatment of only the dominant male weakened his social position, but dominance was regained after treatment 2 or 3. In contrast, a persistent change in dominance was found when only the male which was dominant in the feeding test was treated with the extract. Simultaneous drug treatment of all three males did not affect the social dominance relationship but resulted in a reversible change in food dominance. The original feeding order was reestablished after drug treatment 3. Upon meeting an estrous female, no male of the group was distinctly dominant in mating. After treatment 1 was given to all members of the group, all types of behavior were impaired and total activity was significantly reduced. After treatment 2, animals showed tolerance to the sedative effects, and after treatment 3, sexual behavior was even more frequent in drugged animals than in controls. The results are discussed in relation to a possible dependence of behavioral drug effects and tolerance development on the experimental situation.