The three-dimensional morphology of afferent terminal fields in the rat dentate gyrus: periodic variation

The laminated afferent terminal fields in the rat dentate gyrus molecular layer exhibit differential histochemical staining properties. Dependent variables (e.g., field geometrics, stain intensity) based on this organization can allow evaluation of the effect of independent variables upon the integrity of each afferent, but anatomically justifiable procedures for matching measurement regions across animals are necessary. We describe such a procedure and a serendipitous observation on the normal organization of the terminal fields. From a 10 X 10 mediolateral X anteroposterior array of measurement points per animal, it was determined that each afferent field, and the total molecular layer, exhibits periodic variation in width relative to the granule cell layer. Thus, to reduce statistical variability, either a high dependent variable sampling rate, or sampling within a region of naturally low variability, is suggested. Evidence for such a region is presented, and possible consequences of this novel topology of afferentation are discussed.