Only Controls: Effect of Handling, Sham Injection, and Intraperitoneal Injection of Saline on Behavior of Mice in an Elevated Plus-maze

In male NIH-Swiss mice intraperitoneal injection of physiological saline significantly diminished (vs. naive mice) the ratio of the number of entries into open arms over the sum of entries into open and closed arms, and significantly prolonged time spent in closed arms. These two effects are considered to be typical for anxiety-inducing drugs (anxiogens). The time spent in open arms and at the intersection was unaffected. An equal number of entries into closed and also open arms was observed among fast- and slow-moving individuals. This is an argument against using the number of entries into arms as a measure of locomotor activity of mice. Additional measurement of locomotor activity in actometers is needed to check whether drugs used in experiments with elevated plus-maze alter locomotor activity. Injection of saline significantly shortened the latency of reaching one of the closed arms from the free end of an open arm. Handling, sham injection, and injection significantly diminished the shortening of latency in a second experiment (vs the latency in the first one), a parameter used as a criterion of memory and learning. Thus, saline-treated groups taken as controls in pharmacological experiments possess the behavioral profile of stressed and anxious animals in an elevated plus-maze, a device used as a model of anxiety and a model for studying memory and learning in mice and rats.