Neuroscientist Rogier Min from the Amsterdam UMC has collaborated with Christiaan Levelt's lab from the Netherlands Institute for Neuroscience and discovered how brain cells may react to cannabis, along its potential impact on our brain's flexibility.
Cannabis binds to the so-called Cannabinoid receptor 1 (CB1-receptor), one of the most common receptors in our brain. CB1-receptors serve as switches that can turn various biological processes on or off. Under normal circumstances, the CB1-receptors are activated by cannabis-like substances that are produced in the brain. For a long time, CB1-receptors were believed to be situated only on nerve cells (neurons), but the team has shown that another player is involved as well: astrocytes.
Astrocytes are a type of glia cell in the brain and spinal cord. These cells play an important supportive role in the nervous system. The team discovered that the CB1-receptors located on these cells play an important role in how the brain develops, especially in one's earlier years. The researchers specifically looked at a process known as plasticity – which is how the brain adjusts and changes. At younger ages, there are certain periods when the brain has heightened plasticity, meaning that it can adapt and change more easily. This is known as the critical period.
What was investigated?
Christiaan Levelt: 'In earlier studies from the 80s, researchers injected astrocytes from a kitten into the visual cortex of an older cat, the brain area involved in vision. As a result, the critical period was opened once more, meaning that the brain could adjust more easily again. We also know that the CB1-receptor in astrocytes is expressed less and less as we age. Could there be a link here? And could this mean that the CB1-receptor on astrocytes play a role in this critical period plasticity?'
To investigate this, the team used a special mouse model in which the CB1-receptors of specific cells were turned off: either only on the nerve cells, or only on the astrocytes. They examined whether the absence of the receptor influenced the development of the inhibitory system in the brain. Our brain consists of both stimulating and inhibitory nerve cells. We need the inhibitory cells, also known as interneurons, to keep our brain activity balanced. This study focused on the visual cortex, the part of the brain that helps us process what we see.
What were the findings?
The researchers discovered that removing the CB1-receptors from astrocytes meant that the brain could less easily adjust to changes during development. Rogier Min: 'we found this by temporarily covering the eye of a young mouse during the critical period for vision. In normal mice, their brain is capable of adapting to this by strengthening the connection to the 'good eye'. Mice without CB1-receptors on the interneurons seemed
