Nikes and Neurons Flashcards
ITS BETTER FOR YOUR BRAIN to Walk or bike to class
In town, it usually faster to get somewhere by bike if you are traveling
PHYSICAL ACTIVITY
at least 30MIN / DAY
Decreases risk of Cancer, Diabetes, Heart disease
DOES PHYSICAL ACTIVITY AFFECT THE CNS?
YES
Enhances cognition
Counteracts age-relate memory decline
Delays neurodegenerative disease onset
Reduces depression & anxiety
PHYSICAL ACTIVITY AFFECTS THE CNS
Enhances cognition
Farmers in Indiana, Percept Mot Skills. 1986 Feb;62(1):71-7.
It was hypothesized that increased physical fitness would lead to improved information processing, decision making, and psycho-motor performance.
Two groups with a pre and post test with 8 months in between to allow an improvement in physical fitness
• Control = no exercise • Experimental = participated in physical fitness program of 3 1h sessions each week • 25min of jogging • 35min of stretching/calisthenics
Recorded measures of physical fitness:
O2, CO2, blood pressure, heart rate, body weight, skin fold measurement of fat vs muscle
Examined performance on a variety of cognitive tests
RESULTS:
Control groups fitness did not change.
Experimental group increased fitness by ~17%.
Cognitive performance increased.
Hypothesis testing: correct responses increased by 68%.
PHYSICAL ACTIVITY AFFECTS THE CNS
Counteracts age-relate memory decline
Longitudinal study of Cardio Fitness & Cognitive Function in Healthy Elderly Adults
Prior to this study, results were mixed; some studies found exercise improved cognitive function in older adults, maintained, or found no effect.
They were short-term studies (12 weeks to a year)
The authors hypothesized that baseline cardio-respiratory fitness would be positively associated with maintenance of cognitive function
Rationale:
Cardiorespiratory fitness is largely determined by habitual physical activity.
Wanted to specifically test if a person with sustained increased cardiorespiratory health had better cognitive function.
2092 OLDER ADULTS IN SONOMA, CALIFORNIA
• Longitudinal study
• gathered info approx. every 2 years
• in-home interviews to obtain data on subjects medical, physical, social, mental, emotional health
• Treadmill tests to obtain data on cardiorespiratory health (N=998)
• After 6 years, subjects underwent a detailed cognitive battery
• Random, sex-stratified subsample
Participants with lower VO2 max had:
• 4.6 fewer connections on the Trails B
• Named 8.4 fewer ink colors in 1 min
• Filled in 6.3 fewer squares per minute on the Digit Symbol
• Remembered 1.6 fewer words in immediate recall tests
• Produced 1.7 fewer words beginning with the letter ‘s’
• Named 1.8 fewer animals
VO2 max
aka, maximal oxygen uptake, maximal oxygen consumption, maxial oxygen uptake, peak oxygen uptake or maximal aerobic capacity
VO2 max is the maximum rate of oxygen consumption as measured during incremental exercise, most typically on a motorized treadmill.
VO2max is ultimately a measure of cardiorespiratory fitness.
PHYSICAL ACTIVITY AFFECTS THE CNS
Delays neurodegenerative disease onset
The Oldest Old and the 90+ Study
*Watch the video on this
Evaluated a short physical performance battery
• 4min walk
• 5 timed chair stands
• Standing balance
• Feet side-by-side
• One foot in front of the other in a stride
• One foot in front of the other in tandem
Evaluated dementia with Mini-Mental State Examine (MMSE)
Published in 2008
Correlated the incidence of dementia to many variables:
• Physical performance
• Vitamins
• Estrogen therapy
• BMI
• Alcohol consumption
• Physical activity
• Nonphysical activity (playing cards, reading the paper, etc…)
• Presynaptic marker expression & brain weight
Lower odds of dementia was associated with:
- High blood oxygen.
- Distance walked in in 4 minutes.
- Number of chair stands.
- Good balance.
- Strong grip
Cognitive function correlates strongly with presynaptic protein expression and brain weight
OR
Odds Ratio is strength of association between the risk factor and outcome
(odds of disease in exposed individuals)
÷
(odds of disease in unexposed individuals)
OR=1 Exposure does not affect odds of outcome
OR>1 Exposure associated with higher odds of outcome
OR
Lower odds of dementia was associated with
- High blood oxygen.
- Distance walked in in 4 minutes.
- Number of chair stands.
- Good balance.
- Strong grip
Cognitive function correlates strongly with….
presynaptic protein expression and brain weight
PHYSICAL ACTIVITY AFFECTS THE CNS
Reduces depression & anxiety
EFFECTS OF EXERCISE ON THE OLD & DEPRESSED:
156 men & women aged 50 and older
Randomly assigned to one of 3 groups:
• Medicated
• Exercise
(3x’s per week: 5 min warm up, 30 minutes of walk/jog to reach a target heart rate, 70-80% of heart rate reserve (max-resting).
• Combination of exercise (as above) + medication
VO2 Max & Treadmill test were given to evaluate cardiorespiratory
improvements
HAM-D and BDI tests were given to evaluate depression
Mean aerobic capacity and exercise tolerance for each treatment group, adjusting for pretreatment levels of depression.
I.E., VO2Max and length of time walking/running near max.
–> Compared with patients in the medication group, those in the exercise & combination groups showed significantly higher aerobic capacity (V̇O2) and longer treadmill test duration after 16 weeks of treatment.
Observed mean depression scores before and after treatment. All changes from pretreatment to posttreatment were statistically significant (P18 = moderately to severely depressed
Evaluated by two physicians
Self report questionnaire
Scale: 0 – 63
Higher the score = more depressed
Fitted values for HAM-D & BDI across 16 weeks of treatment.
–> Values represent the fitted scores in each treatment group for 2 selected values of baseline depression treatment (22 for moderate-severe, 16 for mild). Week 0 values represent the baseline starting points selected for this illustration and were not generated by the model. Depression ratings of mild and moderate-severe are at baseline.

Medicine improved depression symptoms more rapidly, but exercise was as effective as medication by 16 weeks
HAM-D indicates Hamilton Rating Scale for Depression;
BDI, Beck Depression Inventory.
HAM-D score and BDI Score are usually highly correlated
PHYSICAL ACTIVITY AFFECTS THE CNS
Improves recovery after CNS injury
Exercise helps cognition, aging, and depression in people.
This is supported by experiments in animal models.
The mechanism?
EXERCISE INDUCED IGF1 CAN CROSS THE BBB AND AFFECT NEURONAL FUNCTION
INSULIN GROWTH FACTOR-1
IGF-1 • Hormone • Peripherally derived from the liver • Stimulated by growth hormone • Can cross the BBB • Linked to exercise induced effects in the brain
Its effects are nonsuppressible insulin-like activity
Factors that are known to cause variation in the levels of growth hormone (GH) and IGF-1 in the circulation include: insulin levels, genetic make-up, time of day, age, sex, exercise status, stress levels, nutrition levels, body mass index (BMI), disease state, race, estrogen status, and xenobiotic intake.
IGF-1 binds to IGF receptors within the cells, which ultimately causes a stimulation of cell growth (both causing new tissue formation and existing tissue growth) and an inhibition of cell death. It is a highly anabolic and anti-catabolic compound. For the athlete or bodybuilder, this had many positive effects: increased nitrogen retention and protein synthesis because it is highly anabolic. IGF-1 (in the presence of sufficient protein) actually promotes growth of new muscle cells, which increases the overall number of cells in the muscle.
3 CNS NEURODEGENERATION MODELS
Domic acid = kills hippocampal neurons
Neurotoxin-3-acetylpyridine = damages inferior olive (IO) neurons
PCD mouse = degeneration of Purkinje cells in the cerebellum
Examined outcomes in mice
antibody
a large, Y-shape protein produced by plasma cells that is used by the immune system to identify and neutralize pathogens, such as bacteria & viruses.
The antibody recognizes a unique molecule of the harmful agent, called an antigen, via the variable region.
Using its binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or it can neutralize its target directly (for example, by blocking a part of a microbe that is essential for its invasion & survival).
EXERCISE INDUCED IGF1 CAN CROSS THE BBB AND AFFECT NEURONAL FUNCTION
Striatum
Cerebral cortex
Red nucleus (midbrain, involved in motor coordination)
HOW DO THEY KNOW IGF1 CROSSES THE BBB?
Digoxigenin (DIG)-labeled IGF1
Digoxigenin (DIG)
Digoxigenin is thus an all-purpose immuno-tag, and in particular a standard immunohistochemical marker for in situ hybridization.
IGF1 IS TAKEN UP BY NEURONS
Purkinje neurons
ANTI-IGF1 ANTIBODY INFUSION INTO THE CSF BLOCKS IGF1 PERMEABILITY INTO THE BRAIN
EXERCISED ANIMALS PERFORM BETTER ON BEHAVIORAL ASSAYS THAN SEDENTARY ANIMALS REGARDLESS OF BRAIN LESION
EXERCISE RESCUES NEURONAL DEATH!!!
WHAT DOES EXERCISE DO TO THE CNS?
Changes neurotransmitters, neurotrophins, and vasculature
Induces neurogenesis.
EXERCISE INCREASES THE AVAILABILITY OF TROPHIC SUPPORT
In situ hybridization to measure brain derived neurotrophic factor messenger RNA expression
What is in situ hybridization?
a type of hybridization that uses a labeled complementary DNA, RNA, or modified nucleic acids strand (i.e., probe) to localize a specific DNA or RNA sequence in a portion of tissue (in situ), or, if the tissue is small enough (e.g., plant seeds, Drosophila embryos), in the entire tissue (whole mount ISH), in cells, and in circulating tumor cells (CTCs).
This is distinct from immunohistochemistry, which usually localizes proteins in tissue sections.
In situ hybridization is a powerful technique for identifying specific mRNA species within individual cells in tissue sections, providing insights into physiological processes and disease pathogenesis.
However, in situ hybridization requires that many steps be taken with precise optimization for each tissue examined and for each probe used.
In order to preserve the target mRNA within tissues, it is often required that crosslinking fixatives (such as formaldehyde) be used.
In situ hybridization is used to reveal the location of specific nucleic acid sequences on chromosomes or in tissues, a crucial step for understanding the organization, regulation, and function of genes.
The key techniques currently in use include: in situ hybridization to mRNA with oligonucleotide and RNA probes (both radio-labelled and hapten-labelled); analysis with light and electron microscopes; whole mount in situ hybridization; double detection of RNAs and RNA plus protein; and fluorescent in situ hybridization to detect chromosomal sequences. DNA ISH can be used to determine the structure of chromosomes. Fluorescent DNA ISH (FISH) can, for example, be used in medical diagnostics to assess chromosomal integrity. RNA ISH (RNA in situ hybridization) is used to measure and localize RNAs (mRNAs, lncRNAs, and miRNAs) within tissue sections, cells, whole mounts, and circulating tumor cells (CTCs).
TROPHIC
(of a hormone or its effect) stimulating the activity of another endocrine gland.
IN SITU HYBRIDIZATION
Summary
…..
IN SITU HYBRIDIZATION TO MEASURE BRAIN DERIVED NEUROTROPHIC FACTOR MESSENGER RNA EXPRESSION
control rat brain
vs.
rats that exercised for 7 days
CA1, DG
EXERCISE Induces neurogenesis
The process of generating functional neurons from progenitor cells
Progenitor cells proliferate and mature into functional neurons – integrate into neural circuits
HOW DO WE STUDY NEUROGENESIS?
Mark proliferating cells
Bromodeoxyuridine (BrdU)
• Synthetic thymidine analogue
STUDY:
Running increases cell proliferation & neurogenesis in the adult mouse dentate gyrys.
Exposure to a rich environment induces structural & functional changes in the rodent brain and significantly increases hippocampal neurogenesis
THEY TESTED
the contribution of learning (via water maze) and physical activity (running wheel) on the generation of new dentate granule cells
WHAT THEY DID:
Divided the mice into 4 living conditions:
1. Enriched-environment (aka: enriched)
2. Hidden-platform water-maze learning (aka: swimmer &
forced exercise)
3. Voluntary exercise (aka: runners)
4. Standard living (aka: control)
Injected with BrdU for the first 12 days & examined the number of BrdU+ cells in the dentate gyrus
ASSESSMENT OF SUBGRANULAR PROGENITOR CELL PROLIFERATION
‘Enrichment’ is a combination of inanimate and social
stimulation
Larger housing area
More friends to interact with
Greater opportunity for physical activity
Greater opportunity for learning
MORRIS WATER MAZE:
THE MICE ARE LEARNING
IS LEARNING IN THE MORRIS WATER MAZE ASSOCIATED WITH CELL PROLIFERATION?
ASSESSED PROLIFERATION BY MEASURING BRDU INCORPORATION
12 days of BrdU injections followed by immunohistochemistry 1 day after the last injection
Runners were the only ones to be significantly better
12 days of BrdU injections followed by immunohistochemistry 4 weeks after the last injection
Runners were significantly the best.
Enriched Environment mice were also significantly affected.
Everybody else was not much different than the controls.
THERE ARE MORE NEURONS, SO WHAT
Are they functional?
YES!
Running enhances neurogenesis, learning, and long-term potentiation
Physical activity:
Facilitates recovery from injury
Improves cognitive function
Increases trophic factors associated with increased (Progenitor cell differentiation & survival, Long-term potentiation, Memory)
….This was known… but
Does physical activity affect synaptic plasticity & learning?
Does physical activity affect synaptic plasticity & learning?
THEY TESTED
If exercise will increase synaptic plasticity, learning, and neurogenesis
WHAT THEY DID:
Running wheel vs. controls with no wheel for excursive
ENTERTAINING ASIDE
Remember how I said reviewers can be Pains?
• “Scientists, researchers and animal rights advocates have argued over the years about the nature of mice running
on wheels in their cages. Rights activists claim the running is a form or neurotic behavior brought about by living in the confines of a small cage. Some researchers, on the other hand, have suggested that the mice seemed to like, or enjoy running on the wheel, and even exhibited unhappy behavior if a wheel was removed.”
“To learn more, Meijer & Robbers decided to carry out a very simple experiment—they set up a running wheel in their backyard, then used an infrared camera to capture on tape how animals in the wild would respond.”
WHEEL RUNNING IS REALLY ENRICHMENT
And, to personify mice, maybe even enjoyed by mice
MORRIS WATER MAZE
PROTOCOL
Training • 2 or 4 trails / day • 6 days • Subject placed in pool near edge • Entry point varied • Each trial last 40s or until the mouse found the platform
Testing was done between day 30 and 49
Length of swim path (path) & time to reach the platform
(latency) were recorded
TWO TRIAL/DAY
Slight, but significant improvements in
• Path length (runner
RUNNING INCREASED LTP IN THE DENTATE GYRUS
Running does not affect
initial EPSP amplitude
BUT
Running increased EPSP amplitude at a greater rate
RUNNING DID NOT CHANGE LTP INDUCTION IN THE CA1 SCHAFFER COLLATERAL PATHWAY
LTP IN THE DG AND THE CA1 SCHAFFER COLLATERAL IS USUALLY MEDIATED BY NMDA RECEPTORS
To test NMDA receptor dependence of enhanced LTP with running, they
blocked NMDA receptors by apply AP1 (NMDA receptor
antagonist) to the slices
LTP induction was completely blocked.
Suggests that NMDA receptors mediate running induced
increases in LTP
SUMMARY #2
BDNF is an exercise-induced trophic factor
Wheel running increased LTP in the dentate gyrus
Even slugs will use a running wheel
Motor skill learning requires active central myelination
THIS PAPER IS NOT LOOKING
AT THE EFFECT OF EXERCISE FOR THE SAKE OF EXERCISE…
its not neurons, its about oligodendrocytes…
OLIGODENDROCYTES
WRAP NEURONAL
PROCESSES IN MYELIN
a glial cell concerned with the production of myelin in the central nervous system.
WHAT IS MYELIN ?
protein and phospholipids that form an insulating sheath
around axons
increases the speed of electrical communication between
neurons
white matter (myelin tracts) vs grey matter (neurons)
in the CNS, myelin is made by oligodendrocytes
WHAT ABOUT
OLIGODENDROCYTES?
majority are born and develop in the first 6 weeks (in rodents)
there is some oligo proliferation in the adult mice
oligo precursor cells are called NG2+ glia
• NG2 is marker (a protein that can be immunostained and observed)
NG2+ glia are found in the adult brain
DOES MYELIN CHANGE
IN THE ADULT?
YES
MRI studies on piano players (or other people who learn complex motor tasks) show structural changes in white matter
If you train rodents in new
motor learning tasks, you can find changes to the structure of their white matter
UR: unskilled reaching
SR: skilled reaching
PRIMARY RESEARCH
QUESTION?
What is the role of adult
oligodendrogenesis?
HOW DO THEY ANSWER
THIS QUESTION?
Use Cre-LoxP conditional deletion techniques, they target a gene (myelin regulatory factor, Myrf) that when lost, blocks the maturation of oligodendrocytes and thus myelinating capability of new oligos
- Majority of oligos are already formed
- This approach only inhibiting the ability of new oligos to myelinate
- Use the Pdfra promoter (active in NG2+ oligo precursor cells) to drive Cre-ERt2 expression
- ER-T2 = estrogen receptor – treat with tamoxifen and Cre translocates from membrane to the nucleus where it can act on LoxP sites
- Spatial control conferred by the Pdfra promoter
- Temporal control conferred by ER-T2 (no deletion until tamoxifen treatment)
Does deleting oligo precursors cause major deficits in myelin or function?
- Deleted Myrf
- Waited 5 weeks
- Then asked: does loss of
oligo precursor cells cause demyelination? - Stained for myelin (dark
blue/purple) - Found no difference in
gross myelin characteristics - Looked a myelin wrapping by EM and found no difference
LOSS OF MYELINATION FROM
NEWLY DIFFERENTIATED/FORMED
OLIGOS DOES NOT CHANGE MOTOR FUNCTION
…rotarod
LOSS OF MYELINATION FROM
MATURE OLIGOS IMPAIRS
FUNCTION
Deletes Myrf from both
oligo and oligo precursors
Sox10 – drives Cre expression in oligo precursor & mature
oligodendrocytes
–> lose myelinating ability in
both
ESTABLISHED THE ANIMAL MODEL TO BLOCK THE MYELINATION ABILITY IN NEWLY FORMED OLIGOS
Now, what about the motor learning task?
Complex Wheel Running (CW)
• This running wheel has missing rungs
• Mice love running, so missing rungs will not stop them, they will ‘learn’ to deal with the missing rungs
THE EXPERIMENT... Cre active = Myrf loss of function in oligo precursor cells 3 weeks after Myrf Loss-Of-Function in OPs introduced to complex wheel
MYRF-/- MICE RUN
SLOWER
REMEMBER THOSE REVIEWER
QUESTIONS I SAID TO LOOK
OUT FOR?
Someone was not convinced…
Repeated the experiment a total of 5Xs
N=36 Myrf+/-
N=32 Myrf-/-
So do mice need active remyelination to remember how to use the complex wheel?
No!!
CW RUNNING STIMULATES OLIGO PRECURSOR PROLIFERATION & OLIGO PRODUCTION
CC1 = marks mature
oligos
EdU = marks proliferating cells
• similar to BrdU but
easier to use
Bromodeoxyuridine (BrdU)
a synthetic nucleoside that is an analog of thymidine.
BrdU is commonly used in the detection of proliferating cells in living tissues.
BrdU can be incorporated into the newly synthesized DNA of replicating cells (during the cell cycle in which DNA is replicated), substituting for thymidine during DNA replication.
Antibodies specific for BrdU can then be used to detect the incorporated chemical (see immunohistochemistry), thus indicating cells that were actively replicating their DNA.
Binding of the antibody requires denaturation of the DNA, usually by exposing the cells to acid or heat.
BrdU can be passed to daughter cells upon replication.
BrdU has been demonstrated to be detectable over two years post-infusion.
CW RUNNING STIMULATES OLIGO PRECURSOR PROLIFERATION & OLIGO PRODUCTION
Spike in precursors
2 days later spike in oligos
OLIGO PRECURSOR CELLS DO NOT PROLIFERATE WHEN MICE ‘REMEMBER’ HOW TO RUN ON THE COMPLEX WHEEL
Novelty of learning how to run on the CW is what triggered oligogenesis and myelination
OLIGO DIFFERENTIATION OCCURS AROUND THE SAME TIME THEIR RUNNING IMPROVES
Suggests new oligos are important for motor skill
learning/acquisition of new tasks
• How?
• New connections are formed and/or existing connections are strengthened which stimulates
myelination or myelin remodeling
Is there other evidence for this?
• Learn a new language = new myelination
TAKE HOME POINTS
New myelination / new oligos are necessary for motor learning
Existing myelination is sufficient to maintain previously learned motor tasks
Myelin-forming oligodendrocytes (OLs) are formed continuously in the healthy adult brain.
Learning a new motor skill (such as juggling) alters the structure of the brain’s white
matter, which contains many OLs, suggesting that late-born OLs might contribute to motor
learning.
Consistent with this idea, we show that production of newly formed OLs is briefly
accelerated in mice that learn a new skill (running on a “complex wheel” with irregularly spaced rungs).
By genetically manipulating the transcription factor myelin regulatory factor in OL precursors, they blocked production of new OLs during adulthood without affecting preexisting OLs or myelin.
This prevented the mice from mastering the complex
wheel.
Thus, generation of new OLs and myelin is important for learning motor skills.
Myelin greatly increases the speed of electrical communication among neurons and, hence, the brain’s computational power
….
What is the function of adult-born OLs and myelin?
(MRI) has detected changes in the structure of white matter in people trained in complex sensorimotor tasks such as playing the piano, juggling, or abacus use.
Active myelination during adulthood is required for motor skill learning and that motor learning increases OL production.
….
Preventing adult myelination by conditional deletion of myelin regulatory factor
Preventing new OL production does not trigger demyelination
Myelin regulatory factor (MyRF)
a transcription factor required in OLs to initiate & maintain their myelination program
It is not expressed in OL precursors, in other CNS cells, or in Schwann cells, which myelinate PNS axons
Administering tamoxifen induces Cre-mediated
recombination, inactivating one or both alleles of Myrf in Pdgfra-expressing precursors while simultaneously labeling the precursors with yellow fluorescent protein (YFP)
We refer to the tamoxifen-treated mice as P-Myrf (+/−) and P-Myrf (−/−).
Recombination at the Myrf locus was confirmed by reverse transcription polymerase chain reaction.
We inactivated Myrf in OPs by tamoxifen administration
on postnatal day 60 (P60) or P90.
our strategy prevents the formation of new OLs without affecting preexisting OLs
Consistent with the myelin histology, P-Myrf (–/–) mice showed no outward signs of demyelination (e.g., tremors) and were indistinguishable from their P-Myrf (+/−) littermates on an accelerating rotarod, a test for motor coordination & balance.
In contrast, S10-Myrf (−/−) mice
developed severe tremors around 1 month posttamoxifen, and their performance on the rotarod was seriously impaired, similar to when Myrf deletion was targeted to mature OLs using Plp-CreER.
Active myelination is required for motor skill learning.
Active myelination is not required to recall a prelearned skill
