Relative aversion thresholds for shock in infant mice

Using a spatial-preference technique, we tested separate groups of mice, 5, 7, 9, 11, 13, and 15 days of age, for escape and avoidance of a range of shock intensities administered from AC contant current and fixed impedance shock sources. With intensities ranging from 0 to .2 mA and 0 to 70 V for the respective sources, near asymptotic escape and avoidance were obtained at .1 mA and at 50 V for ages tested. Although few differences in the relative aversiveness of particular shock intensities were noted across ages with each source, the fixed impedance source produced more consistent avoidance than did the constant source. The findings suggest that the motivational properties of shock remain relatively constant throughout the early development of the mouse and that the technique employed in this study should prove useful in assessing possible age-related alterations in sensitivity to shock as a result of physiological or pharmacological manipulations.