Ziegler, D., Keith, J. R., Pitts, R. C., & Galizio, M. (2002).
Navigation in the Morris swim task as a baseline for drug discrimination: A demonstration with morphine.
Journal of the Experimental Analysis of Behavior,
78, 215-223.
A morphine versus saline discrimination was demonstrated using
the Morris swim task as the behavioral baseline. The apparatus
was a large circular pool filled with water made opaque by
floating polypropylene pellets. Rats were placed in the tank in
randomly selected locations (12 trials per session) and could
escape by swimming to a platform submerged 2 cm below the
surface. Morphine (5.6 mg/kg) or saline was injected prior to
training sessions. The position of the platform in a given
session depended on the drug condition, thus forming the basis
for discriminative responding. Three of the 4 rats acquired the
discrimination, as evidenced by direct swims to the
condition-appropriate platform. Generalization probe sessions
were conducted following acquisition. Probe sessions were
preceded by injections of morphine (0, 1.0, 3.0, 5.6, or 10.0
mg/kg) and involved placing the rat in the pool for 1 min without
a platform. Swim patterns revealed a gradient, with probe
swimming more concentrated in the area of the morphine platform
position after higher morphine doses. In addition, dose-dependent
increases in the likelihood of swimming first to the
morphine-associated platform location were obtained. These
results illustrate the generality of drug discrimination across
different behavioral procedures, and of particular interest with
respect to spatial learning, demonstrate interoceptive stimulus
control of navigation.
Key words: drug discrimination, Morris water maze, spatial
learning, morphine, rat