This result seems to have nothing to do with Kant. The logical explanation for this has to do with the fact that rats have evolved in three dimensional Euclidean space. Any result that Kant had in this regard is a lucky coincidence.
Technically, almost Euclidean space.
I've often wished for a list of cases where philosophy has proven useful, or has at least anticipated science in drawing correct conclusions. Here's one for the list:
The June 18 2010 Science has two very similar articles on how rat brains represent space. Both conclude that the brain already represents space as a grid before rat pups take their first steps into the world. Both make the point that this validates Kant's claim that space is an innate concept prior to experience.
(The next task is to make a corresponding list of cases where philosophers made incorrect conclusions; and estimate whether the number of correct conclusions is greater than chance.)