Animal Model of Drug Self-Adminstration, Part 2

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The Addicted Brain

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The Addicted Brain

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This is a course about addiction to drugs and other behaviors. It will describe what happens in the brain and how this information helps us deal with and overcome addiction. It will also discuss other topics such as government policy and our vulnerability to take drugs.

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Classes of Drugs with Animal Models

In this fourth week, we'll take a look at the drug self-administration model in animals and the implications of these results.

Animals in Drug Addiction Research4:51

Animal Model of Drug Self-Administration, Part 19:15

Animal Model of Drug Self-Adminstration, Part 24:45

Conditioned Place Preference5:17

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Michael Kuhar, Ph.D.
Professor
Yerkes/Emory Pharmacology and Neuroscience

In this video, we're going to continue

to talk about the drug self-administration model.

We're going to describe yet another use of this procedure that

allows us to explore the value of a substance to an animal.

To quantitatively determine how much the animal wants

the drug, we're going to talk about the break-point.

The break-point is used to measure how much

work the animal will do to get the drug.

Let me review some of the basic things needed to understand this.

In the drug self-administration paradigm, the animal has undergone surgery

such that a catheter is placed inside a jugular vein.

The animal's presented with two levers and they both

result in the delivery of a substance through the catheter.

One lever results in the delivery of drugs such

as cocaine, while the other delivers saline or water.

The animal quickly learns which is the

cocaine-related lever and presses that lever relentlessly.

If the experimenter switches levers, so the cocaine is now delivered by pressing

the other lever, the animal quickly learns that this change has been made.

The animal switches his preference for the other lever, which delivers cocaine.

The computer and investigator control the frequency of the injections and the dose.

Now, we haven't discussed this detail before, but the animal does not

have to get the drug for each and every individual lever press.

It can be set up so that more than

one lever press is required to get an injection.

Now we can define the ratio.

When a drug injection is given every time

that there's a lever press, the ratio is one.

If five lever presses are required to get one drug injection, the ratio is five.

As you increase the ratio, a point

is reached where the animal gives up pressing.

That ratio is called the break-point.

We can relate this to our own experience.

If we have to press a lever to get a very nice, desirable dessert, we would do so.

But if the number of lever presses required to get the tasty dessert

were increased steadily, then we'd reach a point at which we would lose interest.

The number of lever presses, the work required, the time required would

be just more than we're interesting in giving to get that particular dessert.

But if to the, the dessert were more

desirable, then you might be willing to press more.

So as I mentioned, the break-point is a measure of

how much the animal will work to get the drug.

It's a measure of the drug's value to the animal.

We can talk about a real experiment.

A brain chemical called CART Peptide is known to reduce the behavioral

effects of cocaine when it is injected into a specific region of the brain.

The question is, is CART affecting how the animal values the

drug or is it having some other nonspecific effect on behavior?

When the drug was employed in the break-point

study, the result showed that injection of CART

peptide lowered the break-point, suggesting that CART somehow

lowered the value of the drug to the animal.

This implies that a substance with actions similar to CART peptide might be a

good medication for cocaine users because it

will reduce the interest of users in cocaine.

These few comments allow us to see yet another use of drug self-administration.

It helps us consider new ideas for treatment.

Before we end, it's important that I mention one caveat.

Throughout these experiments, I have often interpreted

the animal's behavior in terms of human experience.

I've used words that the animal chooses or that

the animal values, which we usually apply to humans.

Some investigators feel that we should be very

cautious about that kind of description of animal behavior.

We should be cautious in applying human motivations to animal behaviors.

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