How the brain has grown over three billion years

3 billion years. That’s the amount of time it has taken for neurons to develop to the size they are today.

A research team led by Professor Antonio Estigara of the University of Manchester has used this interesting timeline to estimate that our brain has grown by a factor of 3.5 over the past three billion years, which is about the same time as the universe has expanded by 1.1 billion years.

The researchers used two types of cat scans — MRI and fMRI — to study a series of animal brain cells, called glial cells, and measured their activity across the lifespan of a mouse’s brain tissue. They saw that glial cells behave quite differently over the entire lifespan of the rodent brain. However, as cells in glial cell clusters live longer, their ability to aid the function of other cells declines as well.

One of the key ingredients in brain functioning is GABA. A type of chemical messenger, GABA is crucial for the normal development of nervous tissue and its ability to protect brain cells from damage. Glial cells have a special structural feature that protects their neurons from damage. According to the University of Manchester scientists, when this protection is reduced or not present, the brain can be damaged.

So, GABA receptors need to be present and can be found in a series of cells known as glial pro-gnano-phage complexes. The presence of these receptors, or mechanisms, may explain the rapid growth of the mammalian brain. However, it can’t explain why it shrinks in space between nuclear transfers. A second key component in the processing of the nervous system is Wnt signaling, which is partly responsible for the cells’ rapid maturation.

This decay in the function of Wnt signals was the focus of the second phase of the Manchester University experiments. The researchers used a brain scanning tool called the MRI imager to study brain activation in the three-billion-year-old brain tissue of a mouse. Based on the number of peaks found in the imaging regime, the researchers estimated the presence of GABA receptors.

“This shows that Wnt signaling is essential to the development of neurons, and GABA receptors are critically important for protecting against the degradation of brain cell survival,” explains Estigara.

The MRI technique also revealed a series of nucleotide polymorphisms which are genetic variations in sequence of nucleotide bases. These changes in sequence of base pairs, known as variations, often influence the volume of the brain.

In the second part of the experiments, the researchers used a different type of nerve cell scanning method known as fMRI. This method typically measures the amount of connectivity between brain cells, the ability of cells to communicate, and the neurotransmitters that are released across cells.

The researchers determined that this process of neuronal growth helps to drive synaptic plasticity, or the ability of cells to pass messages between each other. Neurotransmitters, the chemicals that cause the transmission of messages, are released by inhibitory cell membrane receptors. Increasing inhibition results in decreased release of neurotransmitters, creating a weakened communication system and leading to the “wasting” of brain tissue.

The researchers used another technique called positron emission tomography, or PET scan, to look at signal strength of certain types of nerve cells. Increased signal levels also result in decreased release of neurotransmitters. This technique also found that GABA receptors are present in tissue with increased activity, indicating that the environment needs to suppress the depletion of neurotransmitters to help with an increase in brain growth.

“Now that we have evidence that GABA is a critical component of brain growth, it opens the door to the possibility of regaining a certain amount of neurocognitive control, after injury or aging. There is now a desperate need to develop new drugs which target GABA receptors to give patients the aid they require,” says Estigara.

In terms of humans, Alzheimer’s disease is caused by beta amyloid, a protein in the neurons, which is made by the production of inflammatory molecules, such as C-reactive protein. Estigara suspects that the fact that GABA receptors are present in neurons may help support cell survival.

These receptors are well suited to boost the recovery and repair of nerve cells damaged by neurodegenerative diseases. There is still much that needs to be determined in terms of the causes of Alzheimer’s disease, but early exploration of the mechanism is an important step toward finding a cure.

Watch the video for more about the discovery.

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