Cannabis is a rewarding drug for most people. It activates the reward centers in the way that many other addicting drugs do, and most people find it a pleasurable experience to take cannabis. However, the rewarding properties of cannabis in literature remain ambiguous and the mechanisms poorly understood.
This study was designed to cast some light on the reward mechanism of cannabis in rat brains, which are believed to be suitably similar to human brains that the findings can be extrapolated to us. Cocaine, a cannabinoid antagonist (a drug that alters or inhibits a receptor’s function) called SR141716A, THC, and a very potent cannabinoid agonist (a drug that binds to cannabinoid receptors directly) called HU210 were administered to rats.
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As predicted, the cocaine and cannabinoid antagonist produced preferential behaviors in the rats and HU210 and THC did not, producing aversion effects. This means that cannabinoid antagonists produce reward signaling in the brain and agonists do not. Motivation in humans is thought to require this mechanism and the implications are significant for cannabis therapies and abuse treatment.
For this study, a variety of cannabinoid agonists and antagonists, as well as a known addictive chemical, cocaine, were administered to rats. Their responses were logged and assessed. Whether the rats chose to self administer the drugs offered and how much time they spent in areas designed to be neutral enough that their behaviors could be compared.
Place conditioning is a form of Pavlovian conditioning, where a human or other animal is conditioned to prefer a certain place through some form of input. In this case, it involved the drugs used in this study. Cocaine produced significant place conditioning effects, with the rats preferring the areas they were administered cocaine. They also chose to self administer cocaine.
However, THC and HU210, an agonist and an antagonist, respectively, were shown to produce aversive effects. This is consistent with other studies that show that synthetic and natural cannabinoids produce aversive motivational states.
Cannabinoids have similar effects on some parts of the brain that are involved with addiction and rewards from other drugs. However, the behavior of people who have cannabis abuse disorders are not the same as those for cocaine or heroin, for example.
Withdrawal symptoms are not as severe and it is possible that the demotivating effects of cannabinoids explored here are the reason that people who habitually or addictively use cannabis do not exhibit the drug seeking behaviors of heroin addicts or other heavy drug users.
Although these findings are helpful in exploring the differences between cannabis addiction and motivation, and the effects of other addictive drugs of abuse, there remains a lot to be explored. Rat models are only so useful for examining addiction because they lack the complex motivational, emotional, and cognitive reasoning that is involved in human behaviours. The reasons humans use cannabis are complex and are not addressed here.
This study reinforces the view that cannabinoids are in fact aversive modulators in behaviour. However, there remains a lot to be explored as to the mechanism of this induced change and whether it directly translates to humans or not.