How exercise works to slow memory loss

Becoming more brain fit and following a
lifestyle that is rich in mental and physical activity, has been shown to aid
in protecting us from Alzheimer’s disease.

Keeping active is one of the mainstays for
maintaining health, both physically and mentally. The benefits of regular
exercise for improved mood and cognition have been known for a while.

It has also been known that exercise
stimulates the production of BDNF (brain derived neurotrophic factor) which
assists in maintaining existing neurons as well as stimulating neurogenesis;
the production of new neurons.

But what hasn’t been known is the mechanism by which exercise protects the
brain. In particular how exercise works in relation to memory changes associated
with Alzheimer’s disease. Researchers from the University of Nottingham, using
mice models, have discovered that the stress hormone CRF (corticotrophic-
releasing factor) works as a neuroprotector.

Now stress as you know, is not all bad. We
need some stress in order to simply get out of bed in the morning and it helps
to keep us mentally sharp and cognitively on our toes. Our stress response results
in the release of stress hormones, which is normal.

However, being exposed to severe stress,
especially if it is long lasting has been shown to be highly detrimental to the
brain resulting in loss of memory and poorer function especially of the
prefrontal cortex, (the area of the brain associated with planning, decision
making, our working memory and paying attention) and the hippocampus (the area
associated with learning and long term memory).

Severe chronic stress, which may manifest
itself as anxiety or depression is considered a risk factor for cognitive
decline and dementia. But what is actually going on here in the brain?

What the researchers noticed firstly was that
people with Alzheimer’s disease have been shown to have lower levels of the CRF
hormone.

Using cognitively intact mice, they used an
experimental drug to block the effect of CRF from being able to bind to its
specific receptors (called CRF1) in the brain. The mice were then placed in a
stressful situation, which here meant being placed in a new environment, not
dissimilar to ourselves when we find ourselves fronting up to a new job. Except
here the new environment was devoid of any stimulus. What happened was that the
mice then exhibited what was noted as an abnormal stress response.

In other words the mice’s brains showed less
anxiety, but increased loss of behavioural function. Hence stress, if human
brains work in the same way, results in poorer cognitive capability and
potentially increases our risk of developing Alzheimer’s. Keeping ourselves
stimulated cognitively with mental challenges (something novel, with variety
and ongoing stretch) helps to promote an active and useful stress response by
triggering the CRF1 receptors.

Maintaining normal levels of CRF appears to
be key here to helping the brain resist the potential adverse effects of
stress.

In the same way the researchers also
discovered that interrupting CRF from binding to its receptors leads to a block
in how exercise normally stimulates memory. Using mice with Alzheimer’s disease,
they were able to show how moderate exercise then restored the levels of CRF to
normal, thus providing the CRF system the ability to allow its memory enhancing
effects to work.

The implication of this is that even in the
presence of symptoms of Alzheimer’s peoples are likely to gain significant
benefit from undertaking a regular exercise program because it helps to
modulates the negative effects of stress on the brain, and stimulates an individual’s
ability to cope better not only with life stresses themselves but also to help
maintain their memory for longer.

Switching on the CRF1 receptor was shown to
be crucial to build an increased number of synapses in response to the stimulus
of exercise. Building more and strengthening existing synaptic connections in
our brain, is the key to building cognitive reserve and maintaining healthy
brain function for longer.

So there you have it. Living a life that is
full and varied keeps our brains fit by stimulating a normal stress response.

Bottom line?

Your choice of lifestyle matters: Keeping
active, engaged and curious can help delay the onset of Alzheimer type
symptoms.
In addition it appears that our stress
response and levels of CRF are what matters to maintain synaptic plasticity and
genesis which is necessary for learning and memory

Ref:   

Gillian A. Scullion, Katherine N. Hewitt and Marie-Christine
Pardon (2013) Corticotropin-Releasing Factor Receptor 1 Activation During
Exposure to Novelty Stress Protects Against Alzheimer’s Disease-Like Cognitive
Decline in AβPP/PS1 Mice
Journal of Alzheimer’s Disease  DOI 
10.3233/JAD-122164

 

If you liked this post, click to share