The validity and utility of geotaxis in young rodents.

Negative geotaxis, an automatic, reliable, stimulus-bound, orientation and movement directionally against gravitational cues, is often used for behavioral assessments of infant rodents. We summarize historical and contemporary analyses and conclude that negative geotaxis does not exist in infant rats. Infant rodents placed on inclined surfaces (ranging from 15 degrees to 70 degrees in most tests) are posturally unstable and their compensatory responses have been misinterpreted as negative geotaxis. In fact, recent findings suggest that if infant rats display a geotaxis, they show positive geotaxis on shallow angles of inclination (e.g., 4 degrees and 8 degrees ). There may be utility in assessing postures and motoric responses of infant rats on relatively robust angles of inclination, but these are not tests of negative geotaxis.