Tag Archives: Optogenetics

How to treat Alzheimer’s disease

Let’s say you’re an engineer whose wife has early Alzheimer’s disease.  Would you build the following noninvasive device to remove her plaques?  [ Cell vol. 177 pp. 256 – 271 ’19 ] showed that it worked in mice.

Addendum 18 April — A reader requested a better way to get to the paper — Here is the title — “Multisensory Gamma Stimulation Ameliorates Alzheimer’s Associated Pathology and Improves Cognition”.  It is from MIT — here is the person to correspond to  —Correspondence — lhtsai@mit.edu

The device emits sound and light 40 times a second.  Exposing mice  to this 1 hour a day for a week decreased the number of senile plaques all over the brain (not just in the auditory and visual cortex) and improved their cognition as well.

With apologies to Steinbeck, mice are not men (particularly these mice which carry 5 different mutations which cause Alzheimer’s disease in man).  Animal cognition is not human cognition.  How well do you think Einstein would have done running a maze looking for food?

I had written about the authors’ earlier work and a copy of that post will be found after the ****.

What makes this work exciting is that plaque reduction was seen not only  in the visual cortex (which is pretty much unaffected in Alzheimer’s) but in the hippocampus (which is devastated) and the frontal lobes (also severely affected).  Interestingly, to be effective, both sound and light had to be given simultaneously

Here are the details about the stimuli  —

“Animals were presented with 10 s stimulation blocks interleaved with 10 s baseline periods. Stimulation blocks rotated between auditory-only or auditory and visual stimulation at 20 Hz, 40 Hz, 80 Hz, or with random stimulation (pulses were delivered with randomized inter-pulse intervals determined from a uniform distribution with an average interval of 25 ms). Stimuli blocks were interleaved to ensure the results observed were not due to changes over time in the neuronal response. 10 s long stimulus blocks were used to reduce the influence of onset effects, and to examine neural responses to prolonged rhythmic stimulation. All auditory pulses were 1 ms-long 10 kHz tones. All visual pulses were 50% duty cycle of the stimulation frequency (25 ms, 12.5 ms, or 6.25 ms in length). For combined stimulation, auditory and visual pulses were aligned to the onset of each pulse.”

The device should not require approval by the FDA unless a therapeutic claim is made, and it’s about as noninvasive as it could be.

What could go wrong?  Well a flickering light could trigger seizures in people subject to photic epilepsy (under 1/1,000).

Certainly Claude Shannon who died of Alzheimer’s disease, would have had one built, as would Fields medal winner Daniel Quillen had he not passed away 8 years ago.

Here is the post of 12/16 which has more detail

 

*****

Will flickering light treat Alzheimer’s disease ?

Big pharma has spent zillions trying to rid the brain of senile plaques, to no avail. A recent paper shows that light flickering at 40 cycles/second (40 Hertz) can do it — this is not a misprint [ Nature vol. 540 pp. 207 – 208, 230 – 235 ’16 ]. As most know the main component of the senile plaque of Alzheimer’s disease is a fragment (called the aBeta peptide) of the amyloid precursor protein (APP).

The most interesting part of the paper showed that just an hour or so of light flickering at 40 Hertz temporarily reduced the amount of Abeta peptide in visual cortex of aged mice. Nothing invasive about that.

Should we try this in people? How harmful could it be? Unfortunately the visual cortex is relatively unaffected in Alzheimer’s disease — the disease starts deep inside the head in the medial temporal lobe, particularly the hippocampus — the link shows just how deep it is -https://en.wikipedia.org/wiki/Hippocampus#/media/File:MRI_Location_Hippocampus_up..png

You might be able to do this through the squamous portion of the temporal bone which is just in front of and above the ear. It’s very thin, and ultrasound probes placed here can ‘see’ blood flowing in arteries in this region. Another way to do it might be a light source placed in the mouth.

The technical aspects of the paper are fascinating and will be described later.

First, what could go wrong?

The work shows that the flickering light activates the scavenger cells of the brain (microglia) and then eat the extracellular plaques. However that may not be a good thing as microglia could attack normal cells. In particular they are important in the remodeling of the dendritic tree (notably dendritic spines) that occurs during experience and learning.

Second, why wouldn’t it work? So much has been spent on trying to remove abeta, that serious doubt exists as to whether excessive extracellular Abeta causes Alzheimer’s and even if it does, would removing it be helpful.

Now for some fascinating detail on the paper (for the cognoscenti)

They used a mouse model of Alzheimer’s disease (the 5XFAD mouse). This poor creature has 3 different mutations associated with Alzheimer’s disease in the amyloid precursor protein (APP) — these are the Swedish (K670B), Florida (I716V) and London (V717I). If that wasn’t enough there are two Alzheimer associated mutations in one of the enzymes that processes the APP into Abeta (M146L, L286V) — using the single letter amino acid code –http://www.biochem.ucl.ac.uk/bsm/dbbrowser/c32/aacode.html.hy1. Then the whole mess is put under control of a promoter particularly active in mice (the Thy1 promoter). This results in high expression of the two mutant proteins.

So the poor mice get lots of senile plaques (particularly in the hippocampus) at an early age.

The first experiment was even more complicated, as a way was found to put channelrhodopsin into a set of hippocampal interneurons (this is optogenetics and hardly simple). Exposing the channel to light causes it to open the membrane to depolarize and the neuron to fire. Then fiberoptics were used to stimulate these neurons at 40 Hertz and the effects on the plaques were noted. Clearly a lot of work and the authors (and grad students) deserve our thanks.

Light at 8 Hertz did nothing to the plaques. I couldn’t find what other stimulation frequencies were used (assuming they were tried).

It would be wonderful if something so simple could help these people.

For other ideas about Alzheimer’s using physics rather than chemistry please see — https://luysii.wordpress.com/2014/11/30/could-alzheimers-disease-be-a-problem-in-physics-rather-than-chemistry/

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Will flickering light treat Alzheimer’s disease ?

Big pharma has spent zillions trying to rid the brain of senile plaques, to no avail. A recent paper shows that light flickering at 40 cycles/second (40 Hertz) can do it — this is not a misprint [ Nature vol. 540 pp. 207 – 208, 230 – 235 ’16 ]. As most know the main component of the senile plaque of Alzheimer’s disease is a fragment (called the aBeta peptide) of the amyloid precursor protein (APP).

The most interesting part of the paper showed that just an hour or so of light flickering at 40 Hertz temporarily reduced the amount of Abeta peptide in visual cortex of aged mice. Nothing invasive about that.

Should we try this in people? How harmful could it be? Unfortunately the visual cortex is relatively unaffected in Alzheimer’s disease — the disease starts deep inside the head in the medial temporal lobe, particularly the hippocampus — the link shows just how deep it is -https://en.wikipedia.org/wiki/Hippocampus#/media/File:MRI_Location_Hippocampus_up..png

You might be able to do this through the squamous portion of the temporal bone which is just in front of and above the ear. It’s very thin, and ultrasound probes placed here can ‘see’ blood flowing in arteries in this region. Another way to do it might be a light source placed in the mouth.

The technical aspects of the paper are fascinating and will be described later.

First, what could go wrong?

The work shows that the flickering light activates the scavenger cells of the brain (microglia) and then eat the extracellular plaques. However that may not be a good thing as microglia could attack normal cells. In particular they are important in the remodeling of the dendritic tree (notably dendritic spines) that occurs during experience and learning.

Second, why wouldn’t it work? So much has been spent on trying to remove abeta, that serious doubt exists as to whether excessive extracellular Abeta causes Alzheimer’s and even if it does, would removing it be helpful.

Now for some fascinating detail on the paper (for the cognoscenti)

They used a mouse model of Alzheimer’s disease (the 5XFAD mouse). This poor creature has 3 different mutations associated with Alzheimer’s disease in the amyloid precursor protein (APP) — these are the Swedish (K670B), Florida (I716V) and London (V717I). If that wasn’t enough there are two Alzheimer associated mutations in one of the enzymes that processes the APP into Abeta (M146L, L286V) — using the single letter amino acid code –http://www.biochem.ucl.ac.uk/bsm/dbbrowser/c32/aacode.html.hy1. Then the whole mess is put under control of a promoter particularly active in mice (the Thy1 promoter). This results in high expression of the two mutant proteins.

So the poor mice get lots of senile plaques (particularly in the hippocampus) at an early age.

The first experiment was even more complicated, as a way was found to put channelrhodopsin into a set of hippocampal interneurons (this is optogenetics and hardly simple). Exposing the channel to light causes it to open the membrane to depolarize and the neuron to fire. Then fiberoptics were used to stimulate these neurons at 40 Hertz and the effects on the plaques were noted. Clearly a lot of work and the authors (and grad students) deserve our thanks.

Light at 8 Hertz did nothing to the plaques. I couldn’t find what other stimulation frequencies were used (assuming they were tried).

It would be wonderful if something so simple could help these people.

For other ideas about Alzheimer’s using physics rather than chemistry please see — https://luysii.wordpress.com/2014/11/30/could-alzheimers-disease-be-a-problem-in-physics-rather-than-chemistry/

We know how to make a mouse dream when we want

Everybody knows abut Rapid Eye Movement sleep (REM sleep) now. It wasn’t always that way. I found out about it in med school when my wife pointed me to a fascinating article in the New Yorker, concerning the work of Dement and Kleitman. Briefly, if you wake someone up during REM, they’ll tell you they’re dreaming. As a budding Neurologist, I actually got an afternoon off from my internship to hear Dement talk. I’d been up most of the previous night, and after a nice lunch they turned the lights off as Dement began showing slides and I promptly feel asleep. After it was over and the lights came back on, the guy next to me asked what I’d been dreaming.

There’s been a huge amount of progress on sleep in the past year.

1. At long last, we may actually have a clue as to why we spend a third of our lives asleep. The short answer is that it is to flush out the brain. For details please see https://luysii.wordpress.com/2013/10/21/is-sleep-deprivation-like-alzheimers-and-why-we-need-sleep-in-the-first-place/

2. A recent paper found an area in the brain, which, when stimulated, takes a sleeping mouse into REM sleep. The technique is yet another use of optogenetics (which is almost sure to win Karl Diesseroth a Nobel). For details please see https://luysii.wordpress.com/2013/05/19/a-certain-nobel-prize/.

Optogenetics gives you the ability (after a lot of molecular biological work) to turn specific sets of neurons on (or off). It was known that a very old area of the brain was involved in consciousness, wake and sleep. Just which areas were crucial for REM was controversial. Prior to optogenetics, lesions were made in various place and the animals studied. Neurologic diagnosis of what part of the brain did what was essentially done this way using the various natural disasters which befall the brain. A stroke here cause language problems, a tumor there, caused visual disturbance etc. etc. It worked well, but always contained an essential ambiguity. If you turn of a switch, a light bulb stops shining. But the switch doesn’t really produce the light although it is necessary.

However, stimulating a given nucleus and shifting an animal from regular sleep to REM sleep is far less ambiguous.

The details are quite technical and probably not comprehensible to most of the readership, but here they are for the neurophysiologists in the audience.

[ Proc. Natl. Acad. Sci. vol. 112 pp. 584 – 589 ’15 ] Cholinergic neurons in the mesopontine tegmentum have been implicated in REM sleep, but lesions of the area have had varying effects on REM. This work shows that selective optogenetic activation of cholinergic neurons in the pedunculopotine tegmentum (PPT) or the laterodorsal tegmentum (LDT) increases the number of REM sleep episodes without changing REM sleep duration. Activating them in either nucleus during NREM induces REM. The work was done in transgenic mice which have extra copies of the vesicular AcCh transporter with increased cholinergic tone.

Monamines (particularly norepinephrine) are alerting, and it has been shown that neurons in LDT are inhibited by seronin in rat and guinea pig.

A certain Nobel prize

Chemists will be green with envy to find out that a Nobel prize (possibly in Chemistry) is almost certain to be won by someone using using nothing fancier than formaldehyde, acrylamide and an ionic detergent (Sodium Dodecyl Sulfate — the SDS of electrophoresis fans everywhere)_. For details see Nature vol. 497 pp. 332 – 337 ’13 (16 May Issue). It’s by the same man (Karl Deisseroth) who already has a Nobel coming for the invention of optogenetics.

First — a bit of history. The tissue of the brain is so tightly packed that it is impossible to see the cells that make it up with the usual stains used by light microscopists. People saw nuclei all right but they thought the brain was a mass of tissue with nuclei embedded in it (like a slime mold). Muscle is like that — long fibers with hundreds of nuclei here and there. It wasn’t until that late 1800’s that Camillo Golgi developed a stain which would now and then outline a neuron with all its processes. Another anatomist (Ramon Santiago y Cajal) used Golgi’s technique and argued with Golgi that yes the brain was made of cells. Fascinating that Golgi, the man responsible for showing nerve cells, didn’t buy it. This was a very hot issue at the time, and the two received a joint Nobel prize in 1906 (only 5 years after the prizes began).

How tightly packed is the brain? The shortest wavelength of visible light is 4000 Angstroms. Cells in the brain are packed far more tightly. To see the space between the brain cell external membranes you need an electron microscope (EM). Just preparing a sample for EM really fries the tissue. Neurons are packed together with less than 1000 Angstroms between them. So how much of this is artifact of preparation for electron microscopy has never been clear to me. One study injected a series of quantum dots of known diameter into the cerebral spinal fluid (CSF) to see the smallest sized dot that could insinuate itself between neurons [ Proc. Natl. Acad. Sci. vol. 103 pp. 5567 – 5572 ’06 ]. The upper limit was around 350 Angstroms. No wonder the issue was contentious when all they had was the light microscopy.

Your brain (and mine) is mostly fat. Light doesn’t get through fat very well at all. Deisseroth figured out a way to remove the fat leaving the other brain structures intact. The technique even works on brains fixed in formaldehyde for years. First they infused formaldehyde and acrylamide into brain tissue at 4 degrees Centigrade. The formaldehyde hardens the tissue, but it also links the acrylamide to the proteins making up the tissue. Then they raised the temperature to 37 Centigrade causing the acrylamide to polymerize. Then they infused sodium dodecyl sulfate into the tissue using electrophoresis. When the SDS was pulled out of the tissue (again by electrophoresis) pulling the fat (lipids) of the brain with it, this left what they call a hydrogel (which light could go through).

Using the technique it is possible to look through slabs of brain tissue 500 microns thick (5 million Angstroms thick) with a light microscope and see cell bodies and nerve fibers in their natural habitat (e.g. whole populations of neurons along with their projections). Even better you can stain the hydrogel with your antibody of choice and see what protein is where. Then you can wash this out and look at something else.

It is an incredible advance and certain to revolutionize our understanding of the brain. Look at the paper. The pictures are amazing and more are sure to follow from other workers. Definitely Nobel caliber work.

It is extremely amusing to me that this work could have been done 50 years ago. It just took someone smarter than you and I to think of it.