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Depression, Exercise, & Neurogenesis

Twenty years ago, most physicians, scientists, and probably all science textbooks believed that brain cells that die, cannot be replaced or get fixed.

This “fact” at that time meant several scientific consequences; like for instance believing that the entire Central Nervous System (CNS) cannot regenerate or heal after a certain injury or excessive release of stress hormones.

Our brains are marvelous, sensitive, and powerful tools. They contain more than 100 billion neurons, each of which have thousands of connections with each other. As every other delicate tool on the face of this planet, it gets affected by the smallest of things, the food you consume, the air you breathe and the stress that pressures you.

Any of these factors can affect the brain in different ways till the lethal point that it can kill the neurons or at least block their functions. Healthy brain cells and cell membranes lead to happy mood, clear focus, and sharp memory. On the other hand, damaged brain cells and cell membranes lead to depression, loss of focus, and deprived memory.

Depression & Stress Effects on Brain Cells

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One of the most dangerous factors that affect the brain is depression…. Depression is a state of low mood and aversion to activity that can affect a person’s thoughts, behavior, feelings and sense of well-being. Depressed people may feel sad, anxious, empty, hopeless, worried, helpless, worthless, guilty, irritable, hurt, or restless.

They may lose interest in activities that once were pleasurable, experience loss of appetite or overeating, have problems concentrating, remembering details, or making decisions, and may contemplate or attempt suicide.

For many psychological or physiological or genetic causes, depression is translated in our bodies by some kind of imbalance of the neurotransmitters that are responsible for happy mood, motor function, memory, and reward system, like Serotonin, Dopamine, Nnorepinephrine, Gaba, and Acetylcholine.

These neurotransmitters are the messengers that transmit the neural signals and messages from one neuron to the other. The imbalance could be in the amount of the neurotransmitters themselves or in the ability of the neurons to release, accept, or getting triggered by them.

We will not get into depression as a disease, but we’ll get to know the relation between depression and brain cells impairment and the effect of exercise to protect us against brain cell impairment or death.

Some studies has shown using fMRI (Functional Magnetic Resonance Imaging) that severe clinical depression can affect the functions of the brain in an unhealthy way, and the longer the time depressed people are stuck in the dark abyss of depression the harsher their brain cells can lose their flexibility and functions.

The method in which a normal cell can be impaired under the effect of depression is complicated and still not entirely known, but in a way, the continuous release of stress hormones like Cortisol can gradually stops the Immune System and reduced serotonin and other neurotransmitters in the brain.

A study was conducted by the National Institute of Neuroscience, Tokyo, showed that stress induces neuronal death in the Hippocampus of castrated rats. When rats were stressed by restraint and immersion in water for 15 min/day for 30 days, significant loss of Hippocampal CA3 and CA4 neurons was observed.

Exercise & Neurogenesis

What is Neurogenesis? Neurogenesis is the birth of neurons and it is described as the process by which neurons are generated from neural stem and progenitor cells.

It is most active during pre-natal development, neurogenesis is responsible for populating the growing brain with neurons and it has been thought that it stops at a certain age.

However recently, neurogenesis was shown to continue in several small parts of the brain of mammals like the hippocampus and the Subventricular Zone.

Exercise leads to the release of certain neurotransmitters in the brain that alleviate pain, both physical and mental. Additionally, it is one of the few ways scientists have found to generate new neurons.

Much of the research developed in this area has focused on running, but all types of aerobic exercise and sports provide real health benefits. Although the exact nature of these benefits is still being determined, enough research has been accomplished to provide even skeptics with a motivation to take up exercise.

Exercise exerts its effects on the brain through several mechanisms, including neurogenesis, mood enhancement, and endorphin release.

One of the most exciting changes that exercise causes is neurogenesis.


Mice lacking a protein called DKK1 develop more new Neurons (right) compared with controls (left).

New neurons are created in the hippocampus, the center of learning and memory in the brain, however the exact mechanism behind this neurogenesis is still being explored. At a cellular level, it is possible that the mild physical stress generated by exercise stimulates an influx of calcium, which activates transcription factors in existing hippocampus neurons.

The transcription factors initiate the excretion of the BDNF (Brain-Derived Neurotrophic Factor) gene on Chromosome 11 in humans, creating BDNF proteins that act to promote neurogenesis.

Thus the generation of BDNF is a protective response to physical stress, and BDNF acts not only to generate new neurons, but also to protect existing neurons and to promote synaptic plasticity.

Thus, physical exercise can surely relieve depression by leading to neurogenesis which can counter the harmful effect of stress and depression in harming neurons, by stimulating the BDNF which stimulate neurons’ birth and protect the existing neurons from the harmful effects of stress & depression.

This article is from Science’s archive and we’ve originally published it on an earlier date.