X-Message-Number: 18180
From: 
Date: Tue, 18 Dec 2001 18:54:00 EST
Subject: Im not Sheepish

David Shipman writes:

>I think these kinds of studies are very important and can teach us a
>lot. I've heard Mike Darwin say that sheep may be a better animal to use 
>since their brains are more similar to human brains than are those of other 
>animals.

It's funny how things get twisted around with good intentions. I've met David 
Shipman and he is a very smart and nice guy. However, I did not say that 
sheep were good animals to work with for ischemia research. Larry Niven once 
said it doesn't take much brains to sneak up on a leaf. With the exception of 
elephants, he seems to be right. Most herbivores are, by human criteria, 
stupid. This doesn't mean that they are really stupid, just that they don't 
process and learn in the way we do. Sheep have a very limited repertoire of 
taught behavior and do not interact with humans emotionally in the complex 
way that dogs and cats do (this tell you something about the psychology of 
lonely men on farms). 

Beyond this, it is possible to destroy half or more of the neurons in a 
sheep's brain without any easily discernible change in behavior. I've seen 
both sheep and calves with massive brain infarcts (from artificial hearts or 
valves) and no visible change in behavior. This makes evaluation of complex 
behavior difficult, if not impossible. Yes, if you test sheep and other 
herbivores in demanding ways you can detect a difference, but it is not 
anything like what you see with dogs. I mean, think about cows; these are 
animals who won't walk over a painted grid on the road...

Regrettably, dogs are one of the best animals for ischemia research. They 
show the same devastating and heart wrenching neuroinjury humans do, on the 
same time line of blood flow deprivation. They recognize and interact 
uniquely with individual humans and they have a complex repertoire of 
curiosity seeking and exploratory behavior that is similar to, and easily 
understood and objectively scored by humans. (See Stanley Coren's The 
Intelligence of Dogs.) Dogs and humans have co-evolved in a close mutual 
relationship for 10,000 years or more, and they "read" each other very well. 
Anatomically, dogs and humans share very large femoral blood vessels which 
allows them to be put on cardiopulmonary bypass easily (without opening the 
chest which neither they nor pigs tolerate well) thus facilitating 
resuscitation and instrumentation.

Pigs are arguably more intelligent than dogs. You can teach a dog to open 
your refrigerator door if you have a lot of patience. Speaking from 
experience, a pig may need to see you open the door only once and get food out
. Next time you come home you may find the entire contents of your 
refrigerator scattered over the household floor! I had this experience once 
with a juvenile pot belly pig I was trying to socialize as a companion 
animal. Pigs can relate to people socially in many of the ways dogs can, but 
the bond is more difficult and they are nasty, nasty animals when you try to 
do something to them they don't like. It takes three men and a large board 
with handles on and a hole in the middle it to maneuver a pig into a corner 
and give it an injection!

Pigs are also not runners. They have few surface vessels; your best shot for 
IV access is a vein running down the middle of the ear. They can break your 
arm easily with one bite. They have femoral vessels (if you can find them) 
about the half the size of a pencil making fem-fem bypass impossible. They 
are covered in fat which insulates them, makes surgery difficult, and makes 
finding surface anatomical features difficult. Because they are "smarter" 
than dogs and socially more independent they are much more like people than 
dogs. They quickly figure out what you are about and they don't like it! They 
violently shriek their non-consent to your experimental overtures. I have 
worked with them a fir bit and, apart from their anatomical unsuitability, 
they are difficult and morally challenging.

Monkeys are a nightmare. They hate humans as a rule. They are paranoid. They 
have a social structure like the Taliban. They are (from our perspective) 
vicious and unpredictable. They have extraordinary resistance to cerebral 
ischemia; monkeys have recovered from 15 to 22 minutes of cardiac arrest with 
little or no neurological deficit. They also carry a number of dangerous and 
loathsome diseases including Monkey B virus which is difficult to test for. 
Frequently animals get through quarantine carrying it. Baboons are included 
in this list of difficult animals. They also like to spit in your face 
without provocation.

I have had decent social relationships with some monkeys; it took time, 
patience and considerable risk. No researcher wants to handle his subjects 
with a noose on the end of a pole and full leather gear or Kevlar! But no 
monkey would ever let me experiment on it without a fight!

Cat's are also more resistant to ischemia than humans or dogs and get quite 
nasty when you make them do things they don't like. They especially dislike 
needles and baths and you have to put them in a bag or box to start and IV. 
The racket is horrible.

As to cryonics work, sheep may be an acceptable model to look for neuro 
cryoinjury. The problem is that no comparative studies have been done. One of 
the first things I did before working with cats and dogs was to look at the 
comparative data, and even generate some of my own. That's why I chose dogs. 

As far as monkeys go, once you've worked with them it is very hard to feel 
the kind of heart break you do when working with dogs. An animal that treats 
you as The Enemy as a default, slings feces at you, bites at every chance and 
generally behaves as Satan's spawn (from our perspective) does not build up 
compassion. Neither should it build up hatred or disrespect. But, it does 
make you want to keep your distance. I'm sure this why evolution put this 
kind of behavior there.

Some investigators have used sheep for brain blood flow studies because they 
have complete circles of Willis and nearly absent vertebral circulation; you 
can tie off a sheep's carotids and she'll walk have absent or nearly absent 
cerebral blood flows. They also do very well for heart valve testing since 
they tolerate thoracotomy well and are up on their feet in a few hours after 
open heart surgery. If the valve throws clots you can see the infarcts in the 
brain at necropsy even if you can see any change in behavior.

Mike Darwin

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