January 28, 2016
Now presenting for you a beautiful three-dimensional model of two mouse brain neurons, created by labmate Julian Bartram. For those who are interested in this sphere, available explanations of the benefits of such reconstructions (other than that they are beautiful) and how to get such images in the lab.
Researchers often photograph neural membranes to track reactions to different effects, such as specific stimulants or narcotic substances. An example of this is how the brain responds to picrotoxin, a substance that causes epileptic seizures in mammals. Such observations will help to better understand the effects of epilepsy on the human brain.
In order to do this kind of research, it would be necessary to record the membranes of various neurons that have been exposed to picrotoxin for weeks or months. And after each of these entries, you have to check which cell the information came from.
Could it be a cell that produces dopamine? Or a neuron that sends a signal using GABA, the cellular inhibitor? Is this neuron only connected to the nearest cells, or can it transmit signals to distant areas of the brain? It’s really important to get answers to these questions, because there are a lot of neurons in the brain with different forms and structures, so each cell type can execute different functions. The picture below is a demonstration of the vast variety of brain cells in mammalian brains.In some cases, neuron imaging uses electrodes injected into the brain.
This form of research is actually done “blindly” because it is not clear what kind of cell a picture is taken from. Moreover, when analyzing the brain under the microscope, discovering the right neuron is very difficult, as all neurons are really similar to droplets (as can be seen in the image below). So making an X-ray of a neuron’s membrane is really important, because it allows us to study the structure of the cell, and therefore identify it. So how to do that?
Before injecting a micropipet into the brain for recording, is filling up with a liquid with a certain protein — usually biocytin. When the pipet reaches the right neuron and penetrates the membrane to record activity, the biocytin enters the cell and fills all of its connections in minutes. At the end of the recording, the cut of the brain is washed in a liquid with a second protein that captures the biocytin inside the nerve cell. This second protein contains a fluorophore, a chemical that emits colored light when light with a different spectrum hits it.
In results is obtained a neuron that’s labeled with a chemical compound that can emit light — all you have to do is activate that radiation and take pictures of the light to get an image of the cell. This is most often performed using a two-photon microscope. By taking pictures together of light emitted from the inside of a neuron of different depths, we can create a detailed three-dimensional model, as my colleague did!
Before going any further, you can to assess one of the most beautiful and complex neurons, the Purkinje cerebellar cell (the area in the human brain that is responsible for the coordination of movements).