Interview conducted by April Cashin-Garbutt, BA Hons (Cantab)
Please could you describe what effects cannabis has on the body?
Cannabis has both physical and behavioural effects. People using cannabis can experience feelings of euphoria (well-being), hunger, sleepiness, problems with motor coordination, and sometimes feelings of anxiety and paranoia.
How does cannabis act on the brain?
Chemicals in the cannabis plant attach to proteins in the brain called CB1 receptors. CB1 receptors are located on cells in the brain called neurons. Normal brain functions, like memory and decision-making, rely on these neurons communicating with each other, and CB1 receptors help to ‘fine tune’ this communication. So if cannabis compounds attach to these CB1 receptors, they can disrupt the normal regulation of communication in the brain.
Could you please give a brief introduction to the endocannabinoid system?
The body makes its own cannabis-like chemicals, called endocannabinoids. These endocannabinoids act like messengers between the cells of the body. In the brain, endocannabinoids attach to CB1 receptors located on neurons to modify the way that the neurons communicate with each other.
Specialised proteins called enzymes help to make the endocannabinoid messengers when they are needed, and other enzymes break down the endocannabinoids when they are no longer required. Together, the endocannabinoid messengers, the receptors they attach to, and these specialised enzymes make up the endocannabinoid system.
How does the endocannabinoid system change during adolescence?
We have looked at how the endocannabinoid system develops in the brain across the human lifespan from newborns to adults. We have found that some of the most dramatic change happens in adolescence. We see that the brain’s capacity to make CB1 receptors is declining, compared with very early life when this capacity is very high. On the other hand, one of the enzymes that helps to make the endocannabinoid messengers is higher at adolescence than it is in toddlerhood or adulthood, suggesting that there is still a great need for these messengers to help with communication in the brain.
Can using cannabis during adolescence disrupt these changes?
During adolescence, the brain is trying to ‘settle’ itself, to achieve the right balance in communication between neurons. This is crucial for the transition from adolescent to adult behaviour. For example, the risky behaviour common in teenagers is less prominent by the time a person is in their mid-twenties. Since the endocannabinoid system is a part of the process by which the brain balances its communication, and since it seems to be working very hard to sculpt these connections during adolescence, exposure to cannabis at this time could have a higher impact than in adulthood, when the brain's connections are more stable.
Please could you explain how your research showed that using cannabis during adolescence can have consequences for the development of healthy brains in adults?
Well, we haven’t investigated the impact of cannabis use on the molecules we studied in the brain samples, since the samples came from people who had not been exposed to cannabis. However, knowing what is happening in these healthy brain samples is very helpful, since it gives us a comparison for future experiments looking at how the endocannabinoid system is changed in the brains of people with illnesses like schizophrenia, for example.
What impact do you think your research will have?
We know that people who use cannabis, particularly earlier in life, are at greater risk of developing illnesses like schizophrenia, and of an earlier onset of these illnesses. We also see that in the brains of people with schizophrenia, there are changes in the molecules of the endocannabinoid system. So, if we can understand what goes wrong in the normal developmental patterns that we have identified, we can look towards developing treatment strategies that prevent or modify the changes in schizophrenia, which may help to alleviate the symptoms of the illness.
How does the damage that cannabis causes compare to the damage caused by alcohol and other drugs?
Alcohol, cannabis and other drugs all exert their effects in different ways, since they attach to different molecules in the body. The extent of detrimental effects of any drug depends on the individual and how long and how much drug use has occurred. We still don’t know the full mechanisms by which cannabis causes its detrimental effects, but studies so far show that negative effects of cannabis exposure, such as problems with social interaction and memory, may be due to changes in certain proteins in the brain.
Where can readers find more information?
My latest paper in BMC Neuroscience: http://www.biomedcentral.com/content/pdf/1471-2202-13-87.pdf
Our research group page at http://www.neura.edu.au
The NeuRA blog: http://blog.neura.edu.au
About Dr Leonora Long
Leonora is a research officer with the Shannon Weickert group at Neuroscience Research Australia. Her work combines developmental neurobiology and endocannabinoid pharmacology to determine the role of genetic and environmental factors in causing schizophrenia. Leonora began professional life as a pharmacist, practicing in hospital and community pharmacy and specialising in psychiatry and addiction pharmacotherapy. Building on these interests, her PhD (Monash University 2006) investigated the effects of cannabinoid ligands on sensorimotor gating and its molecular correlates in rodents. Her postdoctoral work focused on the neurobehavioural effects of THC and cannabidiol, two cannabis compounds, in a genetic mouse model of schizophrenia symptoms. She is currently investigating how the endocannabinoid system develops in the normal human brain, and how mutation in a schizophrenia risk gene, neuregulin 1, impacts on development of genes, proteins and behaviours associated with schizophrenia.