Summary
Fragments of the dentate gyrus containing portions of the stratum granulosum and the overlying stratum moleculare were isolated from their commissural, associational and hypothalamic inputs in 11 and 28-day-old rats. Six weeks later the distribution of the entorhinal afferents to the isolated portion of the stratum moleculare was determined autoradiographically by the injection of 3H-proline into the medial entorhinal area, and the appearance of the molecular layer was examined in Timm's sulfide silver preparations. It is evident from our material that under these circumstances the entorhinal afferents to the dentate gyrus can extend right up to the stratum granulosum and that the normal staining pattern that characterizes the “hippocampal zone” of the molecular layer in Timm's preparations may disappear and be replaced, in part, by a narrow zone of dense, mossy fiber-like staining.
The simplest interpretation of these findings is that fibers from the medial entorhinal area are capable of sprouting into the deafferented “hippocampal zone” of the dentate gyrus. However, the observation that entorhinal afferents may occupy the entire thickness of the molecular layer does not, by itself, establish this point because in every case examined the whole molecular layer was shrunken. While this calls for some caution in the interpretation of the findings, our results suggest that there is no special barrier to the growth of entorhinal fibers and that the inner part of molecular layer of the dentate gyrus is capable of receiving afferents other than those normally present.
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This work was supported in part by grants NS-10943 and EY-01255 from the National Institutes of Health
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Stanfield, B., Cowan, W.M. Evidence for the sprouting of entorhinal afferents into the “hippocampal zone” of the molecular layer of the dentate gyrus. Anat Embryol 156, 37–52 (1979). https://doi.org/10.1007/BF00315714
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DOI: https://doi.org/10.1007/BF00315714