Abstract
The locomotor activity of rats in the open field is an essential index of the standardized animal test for several neurotoxicity studies. To investigate the influences on activity of learning, memory and emotion, we studied the effect of repetitive measurement at a 1- or 24-h interval and tested the application of footshock (below 0.3 mA, reportedly insufficient to condition fear) at the first measurement. In an open-field cage (45 cm square) equipped with shock grids, the non-shocked control group gradually decreased their activity to 30% during the first measurement for 1 h. During the second measurement with a 1-h interval, the activity curve was consistently lower than the initial version, whereas the curve partially recovered in the 24-h interval group. Footshock presentation at the first measurement amplified this curve-lowering effect at the second measurement, and changes in applied timing varied the amplified magnitude. These observed dependencies on interval length and timing suggest that learning and memory, respectively, underlie the first gradual decrease and the second curve lowering. We report our analysis of locomotor activity as influenced by emotion and the effect of hippocampal and prefrontal lesions caused by ibotenic acid. This work has been supported as LRI by JCIA. [Jpn J Physiol 54 Suppl:S190 (2004)]
