Answer: A “vehicle” in behavioral neuroscience is the control substance that is injected into the animal.
In studying drug-induced behavior of an animal, a substance is injected into the animal. These types of behavioral tests are common in behavioral neuroscience, and they are often done in rodents such as mice or rats.
Often times, the substance that is to be injected arrives in a powdered form that has to be solubilized before injection. Many polar chemicals are easily dissolved in a saline solution, which can be injected into the body for easy absorption into the bloodstream. However, some substances are high in lipid content, and do not dissolved very easily in a polar solvent like water or physiological saline (0.9%). Instead, they must be dissolved in an equally lipid rich solvent. One that is used in the laboratory is cremophor. The nature of the substance determines which vehicle should be used.
Having a control substance is part of good experimental design in science. Consider the following example: A behavioral neuroscientist wants to measure rat activity in an open field test. According to one interpretation of the paradigm, increased activity in the middle area of the open field indicates that there is less anxiety of the rat. The experimenter could then deliver an injection of some drug that changes anxiety. That drug would be dissolved in some solution. A good scientist would inject the non-experimental animals with the vehicle before performing the behavioral test. This serves to control for several variables. It controls for handling the mouse necessary for injection, it controls for the pain or discomfort caused by the injection, and it controls for the physical change in volume that the subject experiences.