Differences in localization of substantia nigra vs interaural line in Wistar and Sprague Dawley rats

The position of substantia nigra anterior to the interaural line has been correlated with body weight in Wistar rats. A regression line y=0.0050x+1.36 makes it possible to locate the substantia nigra in different sized rats ranging between 140 g and 460 g. This equation is not valid for Sprague Dawley rats. The position of bregma anterior to the interaural line has also been examined. A fairly good correlation was found for Sprague Dawley rats while the position of bregma in Wistar rats was much more variable.