Everyone, at some point in our lives, has had to memorize in science class the parts of the brain stem: midbrain, bridge and medulla oblongata. They are terms that sound familiar to us, but surely they don’t tell us anything. Perhaps we would have paid more attention to them if someone had told us that this region of the nervous system hides fascinating secrets, and that for decades scientists have debated whether this is where something as mysterious as consciousness itself resides.
The brainstem is a basic structure that connects the peripheral nerves, the spinal cord, and the forebrain. It would be a kind of strategic communications hub, like the traffic points where several main highways converge. And the more we know about its operation, the more new questions arise about it.
Within the brain stem there is a region called the gigantic cellular reticular nucleus which, as its name suggests, contains neurons of enormous size. They are so large that they contain links to practically the entire nervous system, so they surely have a fairly important role.
This is how giant neurons activate the brain
A few weeks ago, the Rockefeller University Neurobiology and Behavior Laboratory published an article in PNAS in which they detailed a trial with mice that sheds a lot of light on the functioning of these giant neurons and their role in activating the brain. “It is enough to see the morphology of these cells to suspect that they are fundamental, ” stresses Donald Pfaff, director of the laboratory. But what are they important for? We believe that they are essential for the initiation of any behavior, what we call generalized activation. It is the mechanism that wakes us up in the morning and the one that keeps us conscious throughout the day ”.
What Pfaff and his colleagues did was find which genes the giant neurons expressed, and for this they used a technique called ‘retro-TRAP’ and developed by themselves. The results revealed that these brain cells express a gene that codes for the enzyme endothelial nitric oxide synthetase (eNOS), which in turn is responsible for the production of nitric oxide.
Although it sounds like a very harmful atmospheric pollutant, it turns out that nitric oxide plays a very important role as a regulator of different physiological functions in cells. As a curiosity: the glow that fireflies give off is due in part to the action of nitric oxide in their cells.
Another well-known function of nitric oxide is its action as a vasodilator: by relaxing the blood vessels, it increases the flow of oxygenated blood to the tissue. And one of the things the scientists in Pfaff’s team observed was that the giant neurons that express genes for eNOS are located near blood vessels.
In the researchers’ opinion, these neurons are so important to the normal development of central nervous system functions that they have the ability to control their own blood supply. ” We believe that if these neurons need more oxygen and glucose, they will release nitric oxide into nearby blood vessels in order to obtain them, ” says the scientist.
In successive experiments, the authors found that changes in the mice’s environment, for example the introduction of new odors, also stimulated the activity of eNOS and as a consequence more nitric oxide was released. “When the animal is in a family environment there is a low level of production,” explains Inna Tabansky, another of the researchers. But, when the animal has to adapt to a new scenario, the activity of the giant neurons increases , confirming their essential role in generalized activation.
Involvement in psychiatric disorders
Some genetic research has suggested that these neurons are linked to the development of conditions such as bipolar disorder or ADHD, although the process that would explain this connection is unclear.
One of the future lines of research for the Rockefeller University team will be precisely this. “At least in the rodent brain we already know that these genes and associated pathways have a fundamental function in the nervous system, so this is a first clue,” said Tabansky.
Reference: Inna Tabansky et al., 2018. Molecular profiling of reticular gigantocellularis neurons indicates that eNOS modulates environmentally dependent levels of arousal. PNAS. DOI: 10.1073 / pnas.1806123115
