feeding or drinking or some form of locomotor or exploratory activity (Iversen and Lattal, 
1991; van Haaren, 1993; Wellman and Hoebel, 1997). 
A critical element to many studies is the establishment of reliable and stable performance of 
the target behavior as a baseline against which to judge the drug effect. Especially when 
trained behaviors, such as lever pressing, are used, experimental sessions are conducted five 
to seven days per week. These may be brief (e.g., 30 minutes) or they may be long (e.g., three 
hours). In some experiments (e.g., those studying self-administration or drug dependence or 
the time-course of a drug effect), the experiment may run virtually continuously (24 
hours/day). 
In drug discrimination studies, animals are trained to make one response after receiving a 
dose of a drug and to make a different response after receiving saline (placebo). After repeated 
pairings, the internally perceived drug serves as a cue (technically termed a discriminative 
stimulus) that controls which response is made. Testing consists of sessions in which a novel 
drug is presented to the animal. Thus, the investigator can “ask” the animal to tell, by its 
differential response, whether or not it "feels” the drug. 
CONSIDERATIONS RELATED TO HOUSING AND SOCIAL GROUPING 
Exposure to drugs usually necessitates individual housing in order to permit repeated access 
to each animal for dosing and testing. Individual housing also may be preferred because, in a 
group situation, drug-altered behaviors may increase an animal's risk of abuse by cage mates, 
as well as impair its ability to compete for food. For animals in studies of intravenous drug 
self-administration or of constant intragastric infusion, the animal may be fitted with a vest 
and tether apparatus to protect the chronically indwelling cannula, as described in Chapter 5. 
Behavior may be measured in the animal's living cage, to which devices for presenting stimuli 
and recording responses have been attached (Ator, 1991; Evans, 1994). Such arrangements 
may preclude conventional group housing. 
Behavioral experiments in pharmacology often employ restricted access to food or water for 
two purposes: (1) to maintain a consistent motivation of behavioral performance (Ator, 1991) 
and (2) to standardize content of the digestive tract for uniform absorption and uptake of 
orally administered drugs. This involves scheduling the availability of food and water but not 
necessarily deprivation. In addition, for experiments that take place over many weeks, it may 
be important to keep the total amount of drug delivered relatively constant, even when drug 
doses are calculated on a per weight basis. 
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