influence on performance as well as a determination of any effects of the drug administration 
procedure itself. Where animals serve as their own controls, they typically become habituated 
to the dosing procedure, and behavior is not different from that in sessions not preceded by 
dosing. The exception to this may be if a vehicle or vehicle/drug combination irritates the 
tissue into which it is injected (e.g., due to high or low pH). Lesions can be eliminated or 
minimized by using less concentrated solutions or alternating injection sites. If less 
concentrated solutions require volumes that are too large for single injection sites, delivery 
may be made by small volume injections at different sites. In some cases, one can adjust the 
pH by adding another chemical after the drug is dissolved (although the solubility limitations 
of some drugs preclude much adjustment). 
ROUTE OF ADMINISTRATION 
In many cases, the rationale for choosing a route of administration will be dictated by goals of 
the study (including comparability of results with previous studies); in other studies, it may be 
dictated by constraints on the solubility of the drug. In many studies, more than one route is 
compatible with the goals of the research; the route may be chosen according to factors such 
as the route used with humans, the animal species, and/or information about the metabolism 
of the compound. 
The routes of drug administration used in studies with animals have included oral (per os, 
p.o.), subcutaneous (s.c.), intramuscular (i.m.), intraperitoneal (i.p.), intragastric (i.g.), 
intravenous (i.v.), inhalational, or intracranial (e.g., into the ventricles or to a specific brain 
region). Some routes are more practical for some species than others, and an important 
variable is precision of the amount of drug the animal receives. Drugs can be given orally by 
gavage needle (e.g., rats, pigeons) or nasogastric tube (monkeys). Injection by hypodermic 
needle is the most frequently used technique for administering drugs and chemicals in 
behavioral research (Iversen and Iversen, 1981; van Haaren, 1993). The site of injection may 
be determined by the characteristics of a particular drug's absorption or the solvent in which it 
is given. The most likely problems are incorrect site of injection during i.p. injection. These 
problems can be minimized by careful training of personnel and by prior adaptation of 
animals to the handling and restraint that normally accompany injection. The frequent 
handling of animals in behavioral studies by the same individual usually results in an animal 
that is quite well habituated to regular injection procedures. 
Direct insertion of a cannula, temporarily or chronically, into a blood vessel, a body cavity 
(e.g., the stomach), the spinal cord, or the brain is another route of drug administration. A 
permanently implanted cannula ensures that repeated injections can be given at precisely the 
same site and permits the study of drug effects without peripheral effects (e.g., pain at 
injection site). Implantable pumps for slow delivery of a drug also are used for chronic drug 
exposure studies, such as studies of the effects of drug tolerance or physical dependence on 
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