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I was just wondering what exactly happens to your Mouse/Rat when you freeze and thaw it

It kind of "pre-digests" and makes the rat all mushy
I was just wondering what causes this "mushyness"

Thanks,
Dave
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Girlfriend: Your room smells like reptiles!
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Freezing once living cells causes them to degrade. When you thaw out the rodent it is "mushy" because the cells are no longer firm. Heating a frozen rodent also adds to this!
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*Amy*
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The "mushiness" is caused by cell membranes rupturing when freezing causes the water in the mouses body to expand. when you thaw the mouse, the normal turger (pressure) of the cells is gone, or at least greatly reduced, hence the "mushiness."

This has been your science minute for Wednesday, January 21, 2004. : )

K

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Rob

I do not buy this one bit. It stinks like an exploded rat. Cells make up only a fraction of an animals mass. Most of an animal (most of the bone, skin, organs) is made up of collagen, a non cellular matrix. The collagen gives the animal its firmness as does muscle tension. Leave a dead rodent in the firdge for a few days and it will become mushy.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

>>I do not buy this one bit. It stinks like an exploded rat. Cells make up only a fraction of an animals mass. Most of an animal (most of the bone, skin, organs) is made up of collagen, a non cellular matrix. The collagen gives the animal its firmness as does muscle tension. Leave a dead rodent in the firdge for a few days and it will become mushy.
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>>Derek Affonce
>>DeKeAff Exotics
>>dekeaffexotics.com

or at too high of a temp it will also become mushy whereas it you feed it soon after it is thawed it feels much more firm.
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Rob

I don't think it matters that much it is just muscle relaxation nothing to do with cells. if you heat it up to hot you cook the collagen and it breaks down. that is why they pop when hot.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

In reply to "Cells make up only a fraction of an animals mass." I would say, yes, a major fraction. But it is the fraction that accounts for structure. You know, little things like bones, muscles, tendons, ligaments, organs; i.e. the animal's physical form.

Most of us carbon based life forms are made up mostly of water ( 70%). When water freezes, it expands within the various cells that make up our bodies. Viola, ruptured cellular walls and tissue "breakdown" (otherwise known as "mushiness".

When you put the little critter in the fridge, you get another kind of cellular breakdown. Bacteria (natural fauna and flora) begin to feed on the tissues of the critter and that process breaks down the critters body mass. Similar outcomes, different causes.

When the critter is in the freezer, the bacterial action is halted or at least greatly inhibited. In the fridge, it can grow. That's why your leftovers get funky in the fridge, but can be saved for months in the freezer.

Ah, science.

Looking to make sense, not trouble. Peace out,

K

Bones are made up of a collagen matrix with very few cells in mature animals. Same for tendons and ligaments. Skin is also the same thing, collagen and very few cells. Fibroblasts of different types lay down different types of collagen. Collagen is not a cell. The liver is primarily collagen. The only tissue that I can think of that is not primarly collagen with a few cells in it is muscle tissue which is made up of cells. I don't have any pictures of what skin looks like under a scope at work. If you don't believe me I will post a picture of it. Cells do not make up the majority of tissue besides muscle tissue. You ever examined it under a scope? I have, have a paper in route to publication about human scar tissue.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

Can you post the paper? I think you're overstating. I'd like to see some citations.

Thanks.

In press can't post it. Will post a few figures tonight pointing out what I am talking about. Trust me the skin and other tissues are made up of a lot of connective tissue (collagen) and not cells.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

That is human skin viewed under 100X magnification. The blatent purple dots are cells (fibroblasts and maybe blood cells). The pink is collagen. I say the majority of the picture is nothing more than pink connective tissue. Most of the dells are in the epidermis which is a cell laden layer of the skin. The dermis (the primarly pink area) is what give skin it integrity, which is from the collagen and not the few cells that are present. Liver, bone, and ligaments/tendons are the same thing. I have more at home just found this quickly.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

Here is human skin viewed at 100X stained with Masson's Trichrome. Blue is collagen, purple is cells. Again note the epidermis is made up of large amounts of cells. The thicker dermis is made up of mostly collagen. You can also see a few blood vessels (round purple areas) they are lined with epithileal cells and smooth muscle hence the purple color.

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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

If I remember right aren't you working on your doctorate in biomedical engineering?

I'm just curious because I'd like to know what the correct answer here is and if the above is true I'd be inclined to lean towards yours.
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Rob

Rob when I was working on my master's I worked a lot with human skin. Hypertrophic scaring and laser treatment of these scars is what my thesis was based on. At time I felt like a pathologist not an engineer. I have plenty of time looking through a scope and know what liver, bone, muscle, ligaments, and skin look like under a scope. They are not made up of cells for the most part. There are cells there that break down the extracellular matrix (collagen) and cells that make new collagen. It is the way it works. Collagen does not break down because you freeze it, cells do or at least their membranes rupture. they will reseal after thawing. What give something its firmness is the colagen matrix it is virtually made up of. the matrix is broken down and remade continously. The reason why a live animal has a firmness is due to muscle tension. After death the muscle still have a tension in them. Then rigamortous sets in (all muscles stiffen in the posistion they are in), then after about 12 hours rigamortous disappears and all muscles cross bridges are unbound. At this point the animal is pretty flexible and floppy. This is why a rat after it has been frozen is floppy it has no muscle tone. Muscle are what keeps up from flopping all over the place. It is cellular wall integrity. And yes I am working on my doctorate in biomedical engineering.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

I don't buy that explanation either. Cell membranes should be elastic enough that they wouldn't rupture due to the extremely small volume change from the expansion of water freezing.

However, I don't think the collagen argument is very good either. Bones and connective tissues certainly retain a lot of structural integrity after being frozen and thawed. Ever cut up a frozen thawed chicken vs. a fresh one? Not any difference in the bones/cartilage that I can tell. If bones and cartilage are mostly collagen, why doesn't freezing affect them more than it does soft tissues? Especially when they contain higher percentages of collagen than muscle and skin?

However, ice crystals being formed could rupture both cells and damage collagen.--Ice crystals will damage pretty much anything that contains water.

Ever notice how pure water freezes very clear and tap water or mineral water freezes very foggy. Impurities (both minerals and gasses) cause ice crystals to form in "irregular" ways. How many impurities do you think there are in a rat? When these ice crystals melt, the damage they caused remains.

Rodney

Freezing certainly does rupture cell membranes. It is why cryopreservation does not work perfectly. Why you can't freeze blood and then use it. My point was that rupturing cells was not the cause of a rat feeling mushy because there are very few cells. It is more a function of pure muscle relaxation. A live animal has active muscles, an animal that has just died still has tension in the muscles then comes rigormortise then that relaxes and it goes all floppy. Nothing to do with freezing but rather with time.
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Derek Affonce
DeKeAff Exotics
dekeaffexotics.com

That I couldn't argue with. (but what's the fun in agreeing with you?)-LOL

Rodney

...freezing and thawing causes breakdown of cell MEMBRANES (not walls; walls only in plants) allowing release of proteolytic and lipolytic (protein and fat) enzymes with lead to putrefaction (rotting). The smell is from sulfur-containing (mercapto-) compounds in protein. Couple this with bacterial breakdown and maggots...you get mush!!! Scott J. MichaelsDVM