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Eur J Neurosci. 2020 Feb 6. doi: 10.1111/ejn.14696. [Epub ahead of print]

Development and Topographic Organization of Subicular Projections to Lateral Septum in the Rat Brain.

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Neurosurgical Institute, Medical School, University of Ioannina, Ioannina, Greece.
Kavli institute for Systems Neuroscience, Centre for Computational Neuroscience, Egil and Pauline Braathen, Fred Kavli Centre for Cortical Microcircuits, NTNU Norwegian University of Science and Technology, Trondheim, Norway.
Department of Clinical Molecular Biology, University of Oslo, Akershus University Hospital, 1478, Lørenskog, Norway.
Department of Psychiatry, Columbia University, New York State Psychiatric Institute, New York.


One of the main subcortical targets of hippocampal formation efferents is the lateral septum. Previous studies on the subicular projections, as a main output structure of the hippocampus, have shown a clear topographic organization of septal innervation, related to the origin of the fibers along the dorsoventral axis of the subiculum in the adult brain. In contrast, studies on the developing brain depict an extensive rearrangement of subicular projections during the prenatal period, shifting from the medial to the lateral septum. Our study aimed to describe the postnatal development of subicular projections to the septum. We injected anterograde tracers into the subiculum of 57 pups of different postnatal age. Injections covered the proximo-distal and dorso-ventral axis of the subiculum. The age of the pups at day of tracer injection ranged from the day of birth to postnatal day 30. Analyses revealed that from the first postnatal day projections from subiculum preferentially target the lateral septum. Sparse innervation in the lateral septum was already present in the first few postnatal days and during the following 3 weeks the axonal distribution gradually expanded. Subicular projections to the lateral septum are topographically organized depending on the origin along the dorso-ventral axis of the subiculum, in line with the adult innervation pattern. Different origins along the proximo-distal axis of the subiculum are reflected in changes in the strength of septal innervation. The findings demonstrate that in case of the development of subicular projections, axonal expansion is more prominent than axonal pruning.


Axonal development; Hippocampus; Neural circuits; Postnatal development; Tracing


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