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interpreted. Also, animals cannot refuse good medical care during periods of experimentation, whereas humans are not bound to follow medical advice. Animals are in controlled and protected environments, whereas we have little control over humans’ choices of environments. In addition, animals can be given new treatments and medications, and indeed, the FDA requires that animals be used for proof of safety of new medications. Despite these advantages, the use of animals inresearch is not taken without care or caution. Each and every experimental procedure must be described in detail and approved by a learned committee before the experiments can be carried out. 2 Unexpected problems are studied by committees to learn how we can better care for our animal subjects. Scientists are sensitive to these issues and often have beloved pets at home.
Going Back for More
    Although animals were part of addiction research during the 1920s, this earlier research focused primarily on understanding how drugs affected the animal’s physiology. Typically, drugs were injected into animals that were held or immobilized; the animals were passive recipients. Then a variety of tests and measurements were made on the animals, and a great deal was learned that is the basis of much work today. But in a new procedure developed in the 60s and 70s, the animals were given control over their own drug injections. They actively and freely pressed a lever to get a drug injection. The rate of lever pressing reflected their desire for more of the drug and its effects. This control over drug taking is more like the situation with humans who have control over drug taking and provides a better animal model of human drug taking.
    This procedure or model was developed by several scientists including Drs. James Weeks, C.R. Schuster, and Tomoji Yanagita. When animals were allowed to administer drugs to themselves by pressing a lever, they did so, and with surprising gusto! In this drug self-administration model, a catheter is placed surgically under anesthesia in an animal’s jugular vein so that a measured quantity of a drug can be delivered (by a lever press) directly to the animal’s bloodstream where it rapidly circulates to the brain. The animals appear to quickly adapt to the presence of the catheter, going about their activities probably with no more notice than a dog pays to his or her leash while out on a walk.
    There are small variations on how to do this, but the idea is that an animal is placed in a sound-insulated chamber to avoid distraction and is then presented with two levers. One activates delivery of a saline solution, the other a saline solution containing a drug such as cocaine. Of course, the animal does not know it is receiving an injection, but it obviously learns that pressing the drug-related lever produces a different sensation than pressing the saline-related lever. Which lever it presses and how often it does so are clear, quantifiable measures of which sensation it prefers (see Figure 2-1 ).
    Figure 2-1. Animals will self-administer drugs. The figure shows a rat that has access to levers (only one is visible), and each lever is hooked to either saline (a saltwater solution) or a drug solution such as one with cocaine. The rat also has a catheter or drug delivery tube implanted in its blood vessels. The computer controls how often and how much of the drug is given when the lever is pressed. When the drug-related lever is pressed, the rat does not know it is getting an injection, but rather it has a sensation, and if it likes the sensation, it will press the lever again and again and again. Moreover, the rat learns to ignore the lever that results in an injection of a drug-free solution. This animal model of drug self-administration is vitally important for research and understanding the how and why of addiction. (Modified from www.pharmaco.umontreal.ca/apropos/LaboFilep/images/Self-administrationEN_000.jpg , as accessed on February 24,