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Organization of identified fiber tracts in the rat fimbria-fornix: an anterograde tracing and electron microscopic study

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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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Authors and Affiliations

  1. Institute of Anatomy, University of Freiburg, P.O. Box 111, D-79001, Freiburg, Germany

    G. Adelmann, T. Deller & M. Frotscher

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  1. G. Adelmann
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  2. T. Deller
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  3. M. Frotscher
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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

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