Abstract
The fimbria is a major route for afferent and efferent fibers of the hippocampal formation. However, little is known about the intrinsic organization of the fimbria-fornix complex. In this study, the anterograde tracer Phaseolus vulgaris-leucoagglutinin (PHAL) was used to analyze the ultrastructure and topography of identified fiber tracts within the fimbria-fornix. Septo-hippocampal fibers are loosely distributed throughout the fimbria-fornix. Commissural fibers cross the midline in the ventral hippocampal commissure and form a tight fiber bundle in the fimbria. Crossed entorhino-hippocampal fibers cross the midline in the ventral hippocampal commissure rostral to the commissural fiber bundle, and crossed entorhino-entorhinal fibers pass through the dorsal hippocampal commissure. This suggests a topographical organization of fiber tracts within the fimbria-fornix that reflects the laminar organization of the hippocampal target structure: fibers of the diffusely terminating septohippocampal projection are loosely distributed throughout the fimbria-fornix, while those projections that are known to terminate in specific laminae of the hippocampal formation (commissural projection, crossed entorhino-hippocampal projection) form fiber bundles within the fimbria and the ventral hippocampal commissure.
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Abbreviations
- A :
-
Astrocyte
- CA1, CA3 :
-
hippocampal subfields
- CC :
-
corpus callosum
- D :
-
dendrite
- DG :
-
dentate gyrus
- DHC :
-
dorsal hippocampal commissure
- Fi :
-
fimbria
- LS :
-
lateral septal area
- LV :
-
lateral ventricle
- O :
-
oligodendrocyte
- SFO :
-
subfornical organ
- VHC :
-
ventral hippocampal commissure
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Adelmann, G., Deller, T. & Frotscher, M. Organization of identified fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study. Anat Embryol 193, 481–493 (1996). https://doi.org/10.1007/BF00185879
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DOI: https://doi.org/10.1007/BF00185879